Microbiology ASCP MLT medialab exams

Sheep's blood agar is least suitable for the growth of which of the following organisms? - Haemophilus influenzae - Staphylococcus aureus - Streptococcus species - Neisseria meningitidis

Haemophilus influenzae

The cryptococcal antigen test used to diagnosis Cryptococcus neoformans meningitis is based on what type of rapid methodology?

Latex agglutination

When three tubes of cerebrospinal fluid are received in the laboratory they should be distributed to the various laboratory sections as follows: - #1 Hematology, #2 Chemistry, #3 Microbiology - #1 Chemistry, #2 Microbiology, #3 Hematology - #1 Microbiology, #2 Hematology, #3 Chemistry - #1 Chemistry, #2 Hematology, #3 Microbiology

- #1 Chemistry, #2 Microbiology, #3 Hematology When three tubes of CSF are collected, the first tube is used for chemical and/or serological analysis. The second tube is used in microbiology in order to prevent any contamination of the bacterial culture by skin microbiological flora that may have occurred during the insertion of the spinal needle during the collection process. The last tube (#3) should always be used for hematology studies in order to minimize the effect of any peripheral blood (traumatic tap) contamination that may have occurred during the insertion of the spinal needle.

Which of the following would be the most appropriate temperature for long term storage of specimens for viral culture? - 4° C - -20° C - -70° C - Room temperature

- -70° C Storage of specimens for viral culture (>4 days) should be at -70° C for best preservation of the viruses. Freeze-thaw cycles should be avoided as this can cause the loss of viral viability. 4° C is an appropriate temperature for short term storage of specimens for viral culture, but specimens should always be set up as soon as possible for optimal recovery of the organisms. -20° C is not an appropriate temperature for storage of specimens for viral culture. At this temperature, ice crystals can form which can disrupt the host cells and result in loss of viability of the viruses. Room temperature is not an appropriate temperature for storage of specimens for viral culture. If there is any processing delay, the specimens should be stored at 4° C.

With regard to blood cultures, which blood to broth ratio is most conducive to growth? - 1 : 1 - 1 : 2 - 1 : 10 - 10 : 1

- 1 : 10 Blood is generally inoculated into broth in a ratio of 1 part blood to 5 to 10 parts broth, to dilute antibacterial activity of serum. However, at least 10 mL up to 30 mL of blood per draw should be obtained. Generally, the greater the volume, the greater the yield of bacterial organisms. This is particularly important in febrile patients with suspected endocarditis, and immunocompromised patients. A 1:1 ratio (one part blood to one part broth) does not dilute the serum sufficiently to dilute or inactivate the antibacterial components of the blood. A 1:2 ratio (one part blood to two parts broth) does not dilute the serum sufficiently to dilute or inactivate the antibacterial components of the blood. A 10:1 ratio (ten parts blood to one part broth) provides a sufficient amount of blood but not enough broth to dilute or inactivate the antibacterial components of the blood.

The minimum time of retention for microbiology test reports is? - 5 years - 1 year - 2 years - 7 years

- 2 years 2 years is the correct answer. Test reports include all preliminary reports. Typically, test reports are placed in the patient's hospital record and retained permanently; however, any identical legally reproduced copy will be retained by the laboratory. 5 years is incorrect. Personnel and safety records are required to be kept for a minimum of 5 years. 1 year and 7 years are incorrect answers as they do not represent a minimum retention time for microbiology records.

Pseudomonas aeruginosa is often used as a bacterial species for the quality control of Kligler Iron Agar (KIA). The expected reaction is: - Acid slant/acid deep - Alkaline slant/acid deep - Alkaline slant/acid deep/H2S - Alkaline slant/alkaline deep

- Alkaline slant/alkaline deep Alkaline slant/alkaline deep is the correct answer because Pseudomonas aeruginosa is a nonfermenter; therefore, it cannot produce acid from glucose (deep) or lactose (slant) in a fermentative medium. As such, there is no change in the KIA tube and both the slant and the deep remain alkaline (red). Acid slant/acid deep is incorrect because this reaction pattern indicates the organism can ferment both glucose and lactose. Escherichia coli, a lactose fermenter, is used as the control organism to visualize the acid slant/acid deep reaction. Alkaline slant/acid deep is incorrect because this reaction pattern indicates the organism can ferment glucose only. Shigella flexneri, a non-lactose fermenter, is used to visualize the alkaline slant/acid deep reaction. Alkaline slant/acid deep/H2S is incorrect because this reaction pattern indicates the organism can ferment glucose only and produce H2S. Salmonella typhimurium is used to detect the alkaline slant/black deep (production of H2S) reaction.

This suspicious form, that measures 25 µm, was recovered in an eye sample. It is associated with which of the following diseases? - None; this image represents a nonpathogen - Amebic keratitis - African eye worm infection - River blindness

- Amebic keratitis The organism depicted in the image is an Acanthamoeba species cyst. In addition to infecting the eye causing amebic keratitis, this organism is also known to invade the central nervous system and cause granulomatous amebic encephalitis (GAE). GAE is generally subacute or chronic and is most often associated with trauma or an underlying disease, and not as a result of swimming in contaminated water. Patients with GAE may experience nausea, vomiting, stiff neck, dizziness, headaches and seizures. This organism is a pathogen and should not be present in an eye specimen. Thus, this response is not correct. African eye worm infection is caused by the filarial nematode, Loa loa, which circulates in the blood and lives in the subcutaneous tissue of the host. It is generally identified within the subconjunctiva of the eye of the host. The image is not of a filarial worm. River blindness or onchocerciasis occurs because of subcutaneous infection with Onchocerca volvulus, a filarial nematode. The infection usually localizes in the skin, lymph nodes and eye. The image is not of a filarial worm.

The laboratory diagnosis of this nematode is most commonly made by observing the characteristic eggs in stool specimens. On occasion, adult worms may be observed in the intestine, anchored to the mucosal lining in specimens that have been surgically resected or at autopsy. Illustrated in the photograph is the mouth part as observed in one of these adult worms. From the list below, select the most likely presumptive identification. - Necator americanus - Ancylostoma duodenale - Strongyloides stercoralis - Trichostrongylus

- Ancylostoma duodenale Ancylostoma duodenalealso known as "Old World hookworm" is the correct answer because Ancylostoma duodenale has a pair of teeth as shown in the photograph, in contrast to Necator americanus that has a pair of cutting plates rather than teeth. Ancylostoma infections are indigenous in Western Africa and in many European countries. Necator americanus, the New World species of hookworm, is an incorrect response. The mouth part of N. americanus has a pair of cutting plates rather than the double pair of teeth as seen in the photograph. Strongyloides stercoralisis an incorrect response. Strongyloides adult worms are very small, colorless and semi-transparent and would be rarely seen within the intestine. The species identification is made by observing rhabditiform larvae in stool specimens. Trichostrongylus species is an incorrect response. Although small, Trichostrongylus adults are similar to the hookworms by burying their heads in the intestinal epithelium, the mouth parts are smooth and devoid of the biting teeth or cutting plates. Trichostrongylus is endemic in animals such as sheep, goats, and cattle, and rarely seen in human infections.

Illustrated in the top image is a 3.5-day-old brown/black, smooth yeast colony that is usually considered a contaminant when recovered in laboratory cultures. Reports of verrucose skin and visceral infections with this black yeast have been reported. The bottom image illustrates the microscopic view as prepared in a mount prepared from the surface of the colony. Note the background dark-staining hyphae from which are produced small, elliptical conidia. Select from the choices below the correct presumptive identification of this isolate. - Phaeoannellomyces werneckii - Cladophialophora carrionii - Aureobasidium pullulans - Exophiala jeanselmei

- Aureobasidium pullulans Aureobasidium pullulans is the correct response. The relatively rapidly-growing, brown pigmented colony is not species specific. The identification can be made by the microscopic view of a touch preparation from the surface of the colony in which dark dematiaceous hyphae are observed in the background. Myriads of elliptical, single cell conidia are also present, being produced from the hyphae. Although most commonly a contaminant when recovered in laboratory cultures, reports of infections have been published (Bolignano, G., and Crisco G. J. Clin Microbiol 41: 4483, 2003).Exophiala jeanselmei colonies are often yeast-like upon initial isolation, later becoming a velvety yellow brown to black mold on maturity. In microscopic mounts, darkly pigmented hyphae are also observed, from which loose clusters of dark-staining elliptical conidia are produced from distinctive long narrow conidiophores with a sharply pointed tip.Phaeoannellomyces werneckii is another of the "black yeasts", distinguished by the microscopic production of elongated yeast cells that are divided into segments when a daughter cell is produced from an extension from the mother cell that then contracts to form a scar (annelide).Cladophialophora carrionii colonies are more in the form of a slow growing smooth mold distinguished by distinctive cladosporium type sporulation in which long, un-branched chains of elliptical conidia are produced, with each pair separated by a scar-like dysjunctor.

Cultures from a post-abdominal cellulitis specimen grew Gram negative pleomorphic rods with the following characteristics: Grows on KV agar but does not show fluorescence Produces black colonies BBE agar Resistant to penicillin Which of the following is the MOST likely identification? - Bacteroides fragilis - Fusobacterium nucleatum - Prevotella species - Veillonella species

- Bacteroides fragilis Bacteroides fragilis is the correct answer because Bacteroides fragilis is able to grow on KV agar and does not show fluorescence, while producing black colonies BBE agar. BBE agar is selective and differential for B. fragilis. B. fragilis is resistant to penicillin and the most frequently recovered anaerobe in the clinical laboratory. Fusobacterium nucleatum is incorrect because Fusobacterium nucleatum are slender gram negative rods with pointed ends that will not grow on KV agar, but will fluoresce chartreuse in color on anaerobic blood agar. Prevotella species is incorrect because Prevotella species will grow on KV agar, but the colonies can fluoresce brick red on anaerobic blood agar and black pigment on KV agar. Veillonella species is incorrect because Veillonella species are gram negative, tiny diplococci in clusters that can fluoresce red on anaerobic blood agar.

The following is the vector for the transmission of Onchocerca volvulus: - Mosquitos - Sandflies - Reduviid - Black Flies

- Black Flies The black fly (Simulium spp.) is the vector that transmits Onchocerca volvulus, a blood nematode, that causes onchocerciasis or 'river blindness'. This parasite is transmitted during the blood meal by the female fly. The mosquito transmits Plasmodium species that cause malaria but it is not the vector for Onchocerca volvulus. The sandfly transmits Leishmania species that cause leishmaniasis but it is not the vector for Onchocerca volvulus. The reduviid (or the assassin bug) transmits Trypanosoma cruzi that causes Chagas disease. It is not the vector for Onchocerca volvulus.

From the list of fungal species below, select the one for which optimum recovery in a laboratory culture requires the use of an enriched agar base such as inhibitory mold agar, SABHI (Sabouraud's dextrose agar + heart infusion agar), or brain-heart infusion with cycloheximide and chloramphenicol. - Aspergillus terreus - Cryptococcus neoformans - Blastomyces dermatitidis - Fusarium species

- Blastomyces dermatitidis Blastomyces dermatitidis is the correct answer because as one of the dimorphic fungi, this species would require one of the selective media necessary for their recovery in culture. The addition of cycloheximide and or chloramphenicol to the media is recommended for the culture of certain specimens to inhibit the growth of rapidly growing fungi that may prevent the recovery of the slower growing dimorphic species. Aspergillus terreusis would not grow well on media containing cycloheximide or chloramphenicol. Aspergillus terreusis can best be recovered from Sabouraud Dextrose Agar (SDA). Cryptococcus neoformans would not grow well on media containing cycloheximide or chloramphenicol. Media that is esculin based with chloramphenicol and gentamicin or birdseed agar are best for the recovery of Cryptococcus neoformans. Fusarium species would not grow well on fungal isolation culture media containing cycloheximide or chloramphenicol. Fusarium species can best be recovered from Sabouraud Dextrose Agar (SDA).

Each of the following bacterial species are commonly associated with wound infections following a dog bite except? - Staphylococcus intermedius - Bordetella bronchiseptica - Pasteurella multicida - Capnocytophaga cynodegmi

- Bordetella bronchiseptica Bordetella bronchiseptica is an agent causing respiratory tract infections in animals (tracheobronchitis or "kennel cough" in dogs, atrophic rhinitis in pigs, pneumonia and otitis media in rabbits and guinea pigs). Although humans, particularly those who are immunosurppressed, may acquire B. bronchiseptica respiratory infections by contact with dogs, wound infections following dog bites is not part of the clinical spectrum of this organism. In contrast, Staphylococcus intermedius, Pasteurella multicida and Capnocytophaga cynodegmi are all known to be associated with dog bites, to the point that when one of these species is recovered, either from a wound or a blood culture, an animal source must be presumed.

The best clinical specimen for the recovery of Legionella pneumophilia is: - Nasopharyngeal swab - Wound aspirate - Stool - Bronchial washings

- Bronchial washings The best clinical specimen for the recovery of Legionella pneumophilia is bronchial washings. Legionella pneumophilia causes Legionnaire's disease, which is a respiratory illness that typically leads to pneumonia. Bronchial washings are ideal since infections occur in the respiratory tract and many patients infected with L. pneumophilia, do not produce enough productive sputum to culture. Nasopharyngeal swabs, wound aspirates, and stool are not appropriate sources for culture as the organisms infects the lower respiratory tract and thus a lower respiratory tract specimen, such as sputum, broncholaveolar lavage, or bronchial washings are the only appropriate specimens for culture.

Which is the most commonly reported organism in cases of laboratory-acquired bacterial infection? - Francisella tularensis - Brucella species - Burkholderia species - Yersinia pestis

- Brucella species Although all of these organisms have the potential to cause laboratory-acquired infections, Brucella is the MOST commonly reported laboratory-associated bacterial infection. Approximately 2% of all Brucella cases are acquired in the laboratory. The chance of acquiring an infection from laboratory exposure is 30-100% depending on different factors. Typically, laboratory personal will perform testing on the organism prior to identification, which can create an aerosol, which is then inhaled, and can lead to infection. The laboratory is not always aware of the potential for Brucella in the culture, which can lead to increased exposure levels. F. tularensis carries a high risk of laboratory-acquired infection and documented cases of infection have occurred. Most cases of tularemia are reported in the southern and south-central United States. Typically the lab is alerted that the physician is suspecting Franciscella and can take appropriate precautions and handle the specimen under the appropriate biological safety hood. Burkholderia species can also cause laboratory-acquired infections. Specifically B. mallei and B. pseudomallei can cause aerosols that lead to inhalation of the organism in the laboratory. These organisms are much less common to encounter and the laboratory is typically alerted that one of these organisms is suspected so that proper safety precautions can be used. Yersinia pestis causes plague and can cause aerosols and laboratory acquired infections. This organism is less common to encounter and clinical manifestations typically alert the physician to the infection. The physician typically alerts the laboratory so that proper safety precautions can be used.

The stage of viral replication where the envelope is being acquired and the HIV is leaving the host cell is known as: - Budding - Reverse transcription - Penetration - Uncoating

- Budding The correct answer is budding. Budding is defined as the stage of viral replication where the envelope is being acquired and the HIV is leaving the host cell. Reverse transcription is the stage at which viral RNA is transcribed into DNA. Penetration is the stage at which the virus enters the host cell. Uncoating is the stage at which the viral genome is released. RNA viruses generally release their genome in the cytoplasm, where DNA viruses release their genome into the host nucleus.

Of the Gram-negative bacilli listed below, which is motile with polar tufts of flagella and can produce yellow pigment? - Alcaligenes faecalis - Bordetella bronchiseptica - Burkholderia cepacia - Acinetobacter baumannii

- Burkholderia cepacia Motility via a polar flagellum is characteristic of the bacterial cells of Pseudomonas species, including the rRNA group II Pseudomallei group, reclassified within the genus Burkholderia. Burkholderia species, including Burkholderia cepacia, have tufts of multitrichous polar flagellae, as shown in the photomicrograph. Colonies of B. cepacia are non-wrinkled and may produce yellow pigment, aiding in identification. Both Alcaligenes faecalis and Bordetella bronchiseptica are motile, but via peritrichous and not polar flagella.Acinetobacter baumannii is non motile and lacks flagellae. Pigment production is not an identifying feature of these species.

Which of the following images shows a Gram stain that is consistent with Nocardia species? - A - B - C - D

- C Image C is the correct answer. The bacterial cells of Nocardia species are described as Gram positive filamentous bacilli that branch. Image A shows the bacterial cells of Corynebacterium species, which are short Gram positive bacilli that tend to arrange irregularly in Oriental letter patterns. Image B shows the bacterial cells of lactobacilli, which are rectangular-shaped, Gram positive bacilli that often form short chains. Image D shows the bacterial cells of Bacillus species. These microorganisms may produce either short or long Gram positive bacilli; however, the presence of spores is a key identifying feature of the genus.

An organism grew at 37° C and 42° C from a stool culture that was oxidase, catalase, and hippurate positive. This organism will be identified as: - Campylobacter coli - Campylobacter jejuni - Streptococcus pneumoniae - Aeromonas hydrophila

- Campylobacter jejuni Campylobacter jejuni is the correct answer. The spreading growth into the streak line as seen in the image is characteristic of many strains of Campylobacter species, including Campylobacter jejuni. C. jejuni will grow at 37° C and 42° C and is oxidase, catalase, and hippurate positive. Campylobacter jejuni is the most common isolate of all the Campylobacter species that causes diarrhea. Campylobacter coli is isolated from stool, produces spreading growth as seen in the image, grows at 37° C and 42° C, is oxidase and catalase positive, and hippurate negative. The hippurate negative test separates this species from Campylobacter jejuni. Streptococcus pneumoniae may produce mucoid appearing colonies, but they do not run along the streak line as seen here, will not grow at 42° C, and is not isolated from stool specimens. Most commonly isolated from respiratory specimens. Aeromonas hydrophila can be isolated from stool, but does not produce mucoid colonies and it does not grow at 42° C.

What organism (represented in the photomicrograph--showing a pear-shaped organism with a spiral groove across the ventral surface) is recovered from a stool sample and measures 15 µm by 8 µm? - Trichomonas tenax trophozoite - Enteromonas hominis trophozoite - Giardia duodenalis trophozoite - Chilomastix mesnili trophozoite

- Chilomastix mesnili trophozoite This organism is difficult to distinguish from stool pseudoparasites and artifacts. Fine focusing reveals an irregular oblong organism that comes to a narrow, rounded posterior end (pear-shaped). Keys to the identification of Chilomastix mesnili trophozoites include a spiral groove, when seen; a single nucleus; and a fibril cytostome, which is often difficult to see. The usual size range is 10-15 µm by 4-8 µm. Trichomonas tenax trophozoites are only found in preparations from the mouth. Enteromonas hominis trophozoites are oval measuring 8 µm by 6 µm. They will have one side of body flattened and the posterior flagellum extends free posteriorly or laterally. Giardia duodenalis trophozoites are pear shaped, but the size is up to 20 µm by 15 µm. They will have a sucking disc that occupies one-half to three-fourths of the ventral surface.

Which of these parasites are hermaphroditic in their adult phase? - Clonorchis sinensis - Schistosoma haematobium - Wuchereria bancrofti - Trichuris trichiura

- Clonorchis sinensis Organisms that are hermaphroditic are capable of self-fertilization. Of the organisms listed, only Clonorchis sinensis has this ability. Schistosoma haematobium (fluke), Wuchereria bancrofti (filariae), and Trichuris trichiura (nematode) have separate male and female adults for reproduction.

Protozoal parasites that typically do not produce disease in humans are referred to as being: - Pathogenic - Parthenogenic - Commensal - Facultative

- Commensal Commensal is the correct answer because a commensal relationship is defined as an association between two organisms; one benefits (the parasite) and the other is unaffected (the human host). Persons infected with such organisms typically remain asymptomatic. By definition pathogenic is the ability of an organism to cause a disease. Parthenogenic is asexual reproduction where embryos develop without fertilization. Facultative refers to the growth characteristics of an organism. For instance, Escherichia coli is considered a facultative anaerobe because it can grow aerobically and anaerobically.

Cystine-tellurite blood agar is recommended for the isolation of which organism? - Yersinia enterocolitica - Legionella pneumophilia - Corynebacterium diphtheriae - Francisella tularensis

- Corynebacterium diphtheriae The correct answer is Corynebacterium diphtheriae. Cystine-tellurite blood agar is a differential and selective medium recommended for the isolation of C. diphtheriae. On this media, C.diphtheriae produces black/gray colonies since the tellurite is reduced intracellularly to tellurium. The cystine-tellurite culture plates should be observed after 18 to 24 hours of incubation at 37°C in a 5% carbon dioxide-enriched atmosphere. Yersinia enterocolitica does not require special media in order to be isolated, but is more biochemically reactive at room temperature than at 37°C. Media is often inoculated in duplicate, with one set being incubated at each temperature. When Legionella pneumophilia is suspected, samples are often inoculated onto BYCE agar or BYCE-based selective agar (with added antibiotics to inhibit other flora). Francisella tularensis does require cysteine for growth, but is able to grow on chocolate agar due to its enrichment with heme-containing growth enrichment.

The colonies illustrated in the photograph on the surface of an anaerobic blood agar plate are relatively small, measuring 1 - 2 mm in diameter, round, smooth with a shiny surface, and are non-hemolytic. The Gram stain photomicrograph reveals small Gram positive bacilli in short chains and loose diphtheroidal-like clusters. The indole reaction was found to be strongly positive. This isolate is part of the normal flora of the skin, nasopharynx, oral cavity, and the gastrointestinal and urinary tracts. It is commonly recovered as a contaminant from blood cultures, but on occasion may be the cause of skin and shunt infections. From these observations, select the presumptive identification of this isolate. - Bifidobacterium species - Clostridium septicum - Actinomyces israelii - Cutibacterium (Propionibacterium) acnes

- Cutibacterium (Propionibacterium) acnes Cutibacterium (Propionibacterium) acnes is the correct response. Colonies after anaerobic incubation on blood agar are small, enamel white, circular and opaque. Hemolysis is not observed. Observed in Gram stains are Gram positive coccobacilli that are arranged singly, in short chains, and more distinctly in diphtheroidal clusters. Indole and catalase reactions are positive. Except for fermentation of glucose, carbohydrate fermentation is negative (asaccharolytic). P. acnes most often may be a culture contaminant, but on occasion serve as the cause of skin wound and shunt infections. Bifidobacterium species is incorrect. Colonies growing on blood agar are irregular in size, smooth, entire, convex, and non-hemolytic, ranging from gray-white to light yellow. Distinctive is the Gram stain appearance of the slender Gram positive bacilli with extensive branching and terminal protuberances that simulate "dog bones" that do not arrange in diphtheroidal clusters. Most species are biochemically inactive except for the fermentation of glucose and lactose. Clostridium septicum is incorrect. Colonies on anaerobic blood agar are flat, semi-translucent and spreading, with an outer zone of beta hemolysis. Gram positive bacilli may be long and slender without branching or terminal protuberances, distinctive for the production of sub-terminal spores. Indole and catalase reactions are negative. Both glucose and lactose are fermented. Actinomyces israelii is incorrect. Colonies on anaerobic blood agar are entire, gray-white and distinctly sunken centrally when mature, resembling a "molar tooth". The Gram stain observation is that of thin, Gram positive slender filaments with extensive branching that do not arrange in diphtheroidal clusters. Catalase and indole reactions are negative. Glucose is fermented as are a variety of other carbohydrates by other Actinomyces strains.

The Echinococcus granulosus life cycle requires both an intermediate host (sheep) and definitive host (dogs), as humans are an accidental intermediate. While the eggs are ingested by humans and sheep, what structures need to be ingested by the definitive host, dogs, in order to complete the life cycle of Echnicoccus? - Eggs - Cysts - Proglottids - Adult worms

- Cysts The life cycle of Echinococcus granulosus is incomplete when humans become involved as the intermediate host, whereas when sheep serve in this role, the life cycle is completed. This organism also requires a definitive host which is typically a canine. The life cycle starts with mature adult worms that release eggs and proglottids in canine feces that are ingested by sheep (intermediate host). Eggs released in sheep feces are then ingested by humans (accidental host) and form hydatid cysts in liver, lungs and brain. If the eggs are able to hatch in the sheep, they are carried in the blood stream to other locations and mature into hydatid cysts. Once these cysts are ingested by canines, the life cycle is complete as the cysts can mature into adult worms, starting the process over again.

What is the BEST method for detection of Chlamydia trachomatis in cases of sexually transmitted disease (STD)? - Non-culture EIA methods - Cervical tissue culture - Culture of Thayer-Martin agar - DNA amplification techniques

- DNA amplification techniques The correct answer is DNA amplification techniques. DNA amplification techniques, such as nucleic acid amplification tests (NAAT), probe for the DNA of Chlamydia trachomatis. These tests are the most sensitive tests available and PCR is one of the most common forms of this method. Non-culture EIA methods are not recommended for urine or vaginal swab specimens. Until the development of PCR assays, cell cultures were the gold standard for Chlamydia trachomatis identification, Cervical tissue culture is now not the method of choice due to the inherent technical complexity, time, specimen handling requirements, and expense. Chlamydia trachomatis is an obligate intracellular organism, so it would not grow on Thayer-Martin agar.

Which of the following groups correctly matches the parasite with its infective stage? - Entamoeba hartmanni : sporozoite - Plasmodium malariae : oocyst - Cryptosporidium species: cyst - Dientamoeba fragilis : trophozoite

- Dientamoeba fragilis : trophozoite Dientamoeba fragilis is an intestinal flagellate and the trophozoite is its infective stage, there is no known no cyst stage. The life cycle and mode of transmission are unknown. Entamoeba hartmanni is an intestinal ameba and cysts serve as its infective stage. Transmission occurs through the digestion of mature cysts from contaminated food or water. Plasmodium malariae causes quartan malaria and the infective stage of the organism is the sporozoite stage. The sporozoite is contained in the salivary glands of the Anopheles mosquito and is discharged into the puncture wound when the mosquito takes a blood meal. Cryptosporidium species are members of the sporozoa and the infective stage is the oocyst. Humans can acquire infection through direct contact with infected people or animals or by consuming contaminated water or food.

In order to obtain an appropriate specimen before preparing a smear for acid-fast bacilli staining in a sputum sample, what must be done to the original sample? - Mincing or grinding - Concentration and centrifugation - Digestion and decontamination - Nothing needs to be done to the original specimen

- Digestion and decontamination The correct answer is digestion and decontamination. Digestion is necessary to liquefy the sample by removing proteinaceous material from samples that contain excess mucus, such as respiratory samples. Decontamination is necessary to kill all non-mycobacterial organisms in samples that contain abundant normal flora, such as respiratory samples. Mincing or grinding is necessary when examining tissue samples for the presence of acid-fast bacilli. Concentration and centrifugation may be necessary when attempting to identify acid-fast bacillus in large amounts of a sterile body fluid.

Bacitracin susceptibility testing is useful for: - Distinguishing staphylococci from micrococci - Presumptive identification of Group B streptococci - Identification of Haemophilus spp. - Identification of Neisseria spp.

- Distinguishing staphylococci from micrococci Staphylococci and micrococci are both Gram positive cocci that are catalase positive. Testing for bacitracin susceptibility is one way to differentiate between the two. Staphylococci are usually resistant to bacitracin while micrococci are susceptible. Group A beta-hemolytic streptococci are susceptible to bacitracin, while most other groups are resistant, therefore bacitracin susceptibility is not helpful when identifying group B streptococci. Bacitracin is a polypeptide antibiotic that works by inhibiting cell wall synthesis. It is active against Gram positive organisms. Since Haemophilus and Neisseria are both Gram negative, susceptibility testing of bacitracin would provide no additional information in the identification of these organisms.

Which phrase describes enrichment media? - Contains certain factors that allow colonies of specific organisms to appear different than other colonies. - Contains pigments to differentiate lactose fermenters from non-lactose fermenters. - Encourages the growth of specific types of organisms. - Contains agents that inhibit all but one specific organism.

- Encourages the growth of specific types of organisms. Enrichment media contain specific nutrients required for the growth of particular bacterial pathogens. Differential media contain certain factors that allow colonies of specific organisms to appear different than other colonies such as MacConkey agar differentiating Gram negative bacteria that can and cannot ferment the sugar lactose. Selective media that contains agents that inhibit all but one specific organism.

The amoeba that lives in the gumline of the mouth is known as: - Entamoeba polecki - Trichomonas tenax - Entamoeba gingivalis - Acanthamoeba species

- Entamoeba gingivalis Entamoeba gingivalis is the correct answer because the species name "gingivalis," which is related to the term gingivitis, aids in determining that this organism is a mouth-dweller. All of the organisms that begin with the word Entamoeba are classified as amoebae. Entamoeba polecki is incorrect because this species is an intestinal amoeba. Trichomonas tenax is incorrect. Trichomonas tenax is a mouth-dweller, but it is a member of the flagellates. Acanthamoeba species is incorrect because this species is an atrial amoeba that affects the central nervous system (CNS).

What is the only nematode egg that is characteristically flattened on one side? - Enterobius vermicularis - Paragonimus westermani - Schistosoma japonicum - Trichuris trichiura

- Enterobius vermicularis The eggs of Enterobius vermicularis (pinworm) are flattened on one side and are usually gathered by cellophane tape preparation collected from the perianal region. Paragonimus westermani is a trematode and the eggs are oblong and possesses an obvious terminal operculum. Schistosoma japonicum is a trematode and the eggs are roundish and contains a discrete terminal spine. Trichuris trichiura (whipworm) eggs are football-shaped and have prominent polar plugs at each end.

A 6-year-old female presented to the local clinic complaining of intense perianal itching and diarrhea. The doctor ordered a cellophane tape prep and stool for routine culture and parasitic examination. The cellophane tape prep revealed suspicious form on the left. The stool culture was negative. The form on the right was seen upon examination of the stool for parasites, which measures 10 µm. What are the two forms present in the image, from left to right? - Giardia intestinalis and Dientamoeba fragilis - Enterobius vermicularis and Dientamoeba fragilis - Dientamoeba fragilis and Giardia intestinalis - Enterobius vermicularis and Giardia intestinalis

- Enterobius vermicularis and Dientamoeba fragilis In the image, the figure on the left is Enterobius vermicularis and the figure on the right is Dientamoeba fragilis. Enterobius vermicularisis also known as pinworm and the most common symptom is intense itching in the anal area. The specimen of choice for recovery is the cellophane tape prep collected from the perianal region. The collection can show the worm, which is shown in the image, or the egg. The worm has a clear, pointed tail that resembles a pinhead. The other end of the worm shows the mouth. Internal organs including the intestines may be visible. Dientamoeba fragilis has a life cycle that is poorly understood. The exact mode of transmission is also not understood, but one theory suggests that D. fragilis is transmitted via the eggs of Enterobius vermicularis. Many times these organisms are seen co-infecting with one another. D. fragilis is identified in the image by the irregular round shape and an average size of 8-12 µm. The trophozoite seen here has two nuclei, each consisting of 4-8 centrally located massed chromatin granules, arranged in a symmetrical fashion. Peripheral chromatin is absent. Giardia intestinalis is not either form seen in the image. Giardia intestinalis is a flagellate and has a cyst and trophozoite form, not any form that resembles a worm. The trophozoite stage is typically leaf or pear shaped, not round. There are typically two nuclei present, but each has a large karyosome that is centrally located. Peripheral chromatin is absent. Axonemes and median bodies are also present.

This photograph shows a positive reaction in each of the tubes with the tube on the left containing esculin medium and the tube on the right containing heart infusion broth with 6.5% sodium chloride. The bacterial species that characteristically produces these reactions is: - Staphylococcus aureus - Streptococcus bovis - Enterococcus faecalis - Listeria monocytogenes

- Enterococcus faecalis The correct answer is Enterococcus faecalis. Of the bacterial species listed, only Enterococcus faecalis hydrolyzes esculin (black color in the medium) and can grow in culture medium containing 6.5% sodium chloride (turbid broth and yellow color). Staphylococcus aureus can grow in 6.5% sodium chloride, but does not hydrolyze esculin. Both Streptococcus bovis and Listeria monocytogenes hydrolyze esculin, but neither will grow in a 6.5% sodium chloride.

An alpha-hemolytic streptococcus isolated from a urine culture is resistant to optochin and bactracin, grows in 6.5% NaCI broth, and is PYR positive. The organism is MOST likely: - Streptococcus pyogenes - Streptococcus agalactiae - Streptococcus pneumonia - Enterococcus speciese

- Enterococcus speciese Growth in 6.5% NaCl broth and PYR positive indicates the most likely identification is an Enterococcus species. This organism may be described as alpha-hemolytic but has also been described as gamma-hemolytic and occasionally beta-hemolytic. The organism may be optochin negative but this test is not typically performed on alpha-hemolytic organisms from a urine sample. Bacitracin is usually performed on beta-hemolytic organisms. Streptococcus pyogenes is PYR positive but it is strongly beta-hemolytic, bacitracin sensitive, does not grow in high salt concentration. It is not typically associated with urinary tract infections. Streptococcus agalactiae may be isolated from urine cultures but it is beta-hemolytic and occasionally gamma-hemolytic. It is bacitracin resistant, PYR negative, and will not grow in high salt concentration. Streptococcus pneumoniae is not associated with urinary tract infections. This organism is alpha hemolytic but it is optochin sensitive, PYR negative, and it does not grow in high salt concentrations.

Which of the following is a common cause of urinary tract infections? - Shigella spp. - Escherichia coli - Mycobacterium tuberculosis - Lactobacillus spp.

- Escherichia coli Escherichia coli is a common cause of urinary tract infections (UTI). The urinary tract is the most common site of E. coli infection, and up to 90% or more of all UTIs are caused by E. coli infection. Shigella spp. cause gastrointestinal infections. Mycobacterium tuberculosis is primarily isolated from the respiratory tract. Lactobacillus spp. is part of the microbiota of several sites, namely the vagina.

Which of the following specimen processing techniques is based on the principle that parasites are heavier than sample debris and will be present in the sediment after being processed? - Ethyl acetate concentration - Zinc sulfate flotation - Cellophane tape preparation - Entero-test

- Ethyl acetate concentration Formalin-ethyl acetate sediment concentration is commonly used for concentration techniques. An easy way to remember the terms is that in ethyl acetate concentration procedures, the parasites typically end up in the concentrate (sediment) whereas in flotation, the parasites "float" and may be found in a supernatant layer. Zinc sulfate flotation may not detect operculated or heavy eggs. Cellophane tape preparations and the entero-test are not associated with such debris-removal processes. The cellophane tape preparation is for detecting pinworm eggs by collecting from the skin across the anal opening. The entero-test uses a nylon cord inside a gelatin capsule that is swallowed. The cord is weighted and passes out of the stool where the mucus that is collected on the cord is examined for parasites.

From the four specimens listed for Gram stain and culture, which one should be rejected? - Synovial fluid in a sterile heparinized syringe for aerobic culture - Peritoneal fluid in sterile sodium polyanethol sulfonate (SPS) tube for aerobic culture - Expectorated sputum in sterile container for anaerobic culture - Vaginal secretions on polyester swab in sterile saline for aerobic culture

- Expectorated sputum in sterile container for anaerobic culture Expectorated sputum is likely to contain many different endogenous anaerobic bacteria, making it impossible to determine if infection is present. All of the other specimens are acceptable for aerobic culture.

This rapidly growing hyaline fungus is the most common cause of Keratomycosis (an infectious disease of the cornea). The colonies can range in color from rose to mauve to orange. This organism is commonly recovered from blood and grows on sabourauds dextrose agar with brain heart infusion. The microscopic appearance shows abundant banana or canoe shaped macroconidia. What fungus causes this disease? - Beauveria species - Fusarium species - Chrysosporium species - Geotrichum species

- Fusarium species Fusarium macroconidia are banana or canoe shaped and are formed singly, on small clusters or clustered together in mats termed sporodochia. The macroconidia are typically multicelled. Fusarium colonies can range in color from rose to mauve to orange. This colony has the distinctive rose-red to purple pigmentation which is characteristic. Beauveria is an insect pathogen. They have abundant, single celled tear shaped sympodulconidia are formed on sympodulae. (Blastic conidia formed on condigenous cell by growth of a succession of apices, each originating below and to one side of the last.) Chrysosporium wide-based, single-celled conidia are produced on nonspecialized cells. Geotrichum microscopically abundant arthroconida are seen.

The staining reaction for yeast is: - Gram negative - Gram positive - Kinyoun positive - Ziehl-Neelsen positive

- Gram positive Yeast stain gram positive and are easily detectable in gram stains. They may decolorize easily and appear gram variable. Yeast do not have an increased cell wall lipid content including mycolic acids and therefore do not stain positive with the Kinyoun stain or Ziehl-Neelsen stain. Both the Kinyoun and Ziehl-Neelsen stains are used to identify acid fast organisms. Acid fast organisms have cell walls with a high lipid content including mycolic acids that resist decolorization with acids.

Illustrated in the photograph is a large trematode fluke averaging 3.0 - 7.0 cm. This fluke resides primarily in the small intestine. Characteristic is the rounded cephalic end, the convoluted uterus in the anterior half of the fluke, and a delicate branching testes in the posterior half. Humans become infected by ingesting metacercaria contaminated water vegetables. Select the presumptive identification. - Clonorchis sinensis - Schistosoma mansoni - Fasciolopsis/Fasciola species - Paragonimus westermani

- Fasciolopsis/Fasciola species Fasciolopsis/Fasciola species is the correct response. Key to identification is the large size, measuring 2.0 - 8.0 cm x 0.8 - 2.0 cm, and the smooth, rounded curved cephalic end without a protrusion. The distinct anterior convoluted uterus and the delicate branching testes to the posterior are observed. Fasciolopsis/Fasciola species are indistinguishable from one another. Clonorchis sinensis is an incorrect response. C. sinensis flukes are distinctly small (0.7 - 1.5 cm) and are bottle-shaped with a long protruding cephalic head. Characteristic is a highly visible, broad-branched testes that occupy the posterior part of the fluke, from which the genus name clonorchis ("branched testes") is derived. Humans contract this parasite by ingesting raw, smoked, or poorly cooked fish. Schistosoma mansoni is an incorrect response. S. mansoni flukes measure 0.6 - 2.2 cm and have a flattened, leaf shape appearance. The flukes are not typically found in stool as they tend to remain in the small veins that supply the intestines. Human contract this parasite by being exposed to water containing cercariae that penetrate the skin. Paragonimus westermani is an incorrect response. P. westermani flukes are relatively small (1.0 - 1.6 cm) with a flattened oval spoon shape. One end appears contracted and the other is in the form of a broad smooth curve. Irregularly lobed testes lie oblique to one another in the posterior third of the worm, with a lobed ovary anterior and to the right of the testes opposite a closely coiled uterus. Human contract this parasite by ingested infected crustaceans.

How would you classify the organism on this gram stain? - Gram positive cocci - Gram negative cocci - Yeast - Gram positive rods

- Gram positive cocci Bacteria with thick cell walls containing teichoic acid retain the crystal violet-iodine complex dye after decolorization and appear deep blue; they are gram positive bacteria as suggested in this photo. Organisms with round, spherical shapes are considered cocci, whereas organisms that are rod shaped are considered bacilli. Other bacteria with thinner walls containing lipopolysaccharides do not retain the dye complex; they are gram negative bacteria, and subsequently stained red using the counterstain safranin dye. Gram negative organisms show pink under microscopic light. Yeast cells will also stain a deep blue-purple color using Gram stain, however, they are typically much larger than gram positive cocci and have a distinct shape.

How long after hospitalization would stool samples be rejected for testing for parasitic infections? - No set time - Greater than 24 hours - Greater than 48 hours - Greater than 72 hours

- Greater than 72 hours Stools for parasitic exam may be rejected from inpatients who have been in-house for longer than 3 days. Data suggest that patients who begin to have diarrhea after they have been inpatients for a few days are not symptomatic from parasitic infections, but generally from other causes. The chance (although rare) always exists that the problem is related to a health care associated (nosocomial) parasitic infection. Cryptosporidium spp. and microsporidia may be possible considerations.

From the fungi listed below, which is considered to be a true pathogen that also infects immunocompromised patients? - Scopulariopsis species - Penicillium species - Histoplasma capsulatum - Fusarium species

- Histoplasma capsulatum When Histoplasma capsulatum is recovered in culture, regardless of the body source or type of the specimen, it must be considered as a true pathogen that can innately cause a variety of infections and must be aggressively treated. In immunocompromised patients it can be fatal. In healthy hosts symptoms can be mild, but the organism can stay dormant and re-emerge as immunity drops. The other species listed in the multiple choices are most commonly considered to be non-pathogens, except in cases where they may be recovered from a patient who has an underlying infection or is immune-suppressed, then serving as an opportunistic pathogen for which therapy may be required. Scopulariopsis spp. are found in immunocompromised patients and causes pulmonary disease. Penicillium spp. rarely causes infection, but when it does it causes chronic sinusitis. Fusarium spp. has been found to infect soft contact lenses and bone transplants. These are rare occurrences, but it can be fatal since antifungal therapy is not successful.

In the image to the right, small, minute, colonies are growing around a colony of Staphylococcus aureus on sheep blood agar. Which of the following organisms is this a characteristic? - Haemophilus influenzae - Abiotrophia species - Moraxella catarrhalis - Haemophilus ducreyi

- Haemophilus influenzae Haemophilus influenzae is the correct answer. Haemophilus influenzae requires both X (hemin) and V (NAD) factors to grow. The X factor is provided by the blood agar, but since sheep blood agar has NADase, the V factor is broken down; therefore, the Staphylococcus aureus provides the Haemophilus influenzae organism the V factor needed. Hence, the tiny growth around the Staphylococcus aureus colonies. Abiotrophia species is incorrect. Abiotrophia species will not grow on sheep blood agar unless vitamin B6 is provided. Vitamin B6 can be provided either by using blood agar supplemented with vitamin B6 or by placing a pyridoxal disk on sheep blood agar. In addition, this species does not need X or V factors in order to grow. Moraxella catarrhalis is incorrect because Moraxella catarrhalis does not need X or V factors to grow and does not have any fastidious growth requirements. Moraxella catarrhalis can grow on sheep blood agar. Haemophilus ducreyi is incorrect because Haemophilus ducreyi will grow on sheep blood agar as this species only needs X factor to grow.

This organism has been placed in trypticase soy broth and then streaked on a nutrient agar plate. Strips containing X, V, and XV were place on the plate and it was incubated 24 hours in CO2 conditions. With this information and the picture to the right, what is the identification of this organism? - Brucella abortus - Haemophilus influenzae - Haemophilus parainfluenzae - Pasteurella multocida

- Haemophilus influenzae The correct answer is Haemophilus influenzae . Haemophilus influenzae requires both X (hemin) and V factors (nicotinomide adenine dinucleotide-NAD) to grow. H.influenzae typically causes infections of the lower respiratory tract in patients with chronic respiratory ailments and meningitis in children less than two years of age. Brucella abortus does not require X or V factor. It is a slow-growing, faintly staining, tiny coccobacillus. Haemophilus parainfluenzae does require V factor, but not X factor. Colonies look similar to those of H.influenzae, but they appear smaller and have a matte appearance. Pasteurella multocida does not require X or V factor and will grow on both sheep blood agar (SBA) and chocolate agar.

From the multiple choices below, select the most appropriate culture medium for optimum recovery and differentiation of Salmonella and/or Shigella. - Columbia colistin-nalidixic acid (CNA) agar - Thiosulfate citrate bile salts sucrose (TCBS) agar - Hektoen enteric (HE) agar - Sabouraud dextrose agar

- Hektoen enteric (HE) agar Hektoen enteric agar is used for recovery of Salmonella and Shigella. It contains bile salts that inhibit Gram positive organisms and most Gram negative enteric flora. Fermentation of lactose, sucrose, or salicin results in an acidic pH, and color change to orange or pink. Salmonella and Shigella appear blue to blue-green from lack of fermentation. Colonies of Salmonella species that produce hydrogen sulfide will contain black centers from sodium thiosulfate and ferric ammonium citrate present in the medium. Columbia CNA agar is a blood agar base containing colistin and nalidixic acid, allowing for selectivity of Gram positive organisms in mixed specimens. Thiosulfate citrate bile salts sucrose agar selects for Vibrio species in mixed stool specimens. TCBS contains sucrose and a blue indicator for detection and differentiation of fermentation. TCBS also has a high pH for suppression of other intestinal bacteria, bile salts to inhibit Gram positive bacteria, sodium citrate and sodium thiosulfate to support halophilic Vibrio species and to detect hydrogen sulfide. Sabouraud dextrose agar is used for the cultivation of fungi. Selectivity is based on the antimicrobial content (chloramphenicol, gentamicin, and tetracycline).

The 70 µm ovum illustrated in the high power microscopic view of a saline preparation is uncommonly found in human feces. The cestode represented by this ovum is more commonly found in rats and mice, but infections may be uncommonly transmitted to humans. Water or food contaminated with arthropod related insects within which the cysticercoid larval forms develop may be inadvertently ingested. Once in the human intestine, these larvae develop into adults that attach to the lining cells, and excrete ova that may be observed in fecal specimens. From the multiple choices listed below, select the name of the cestode represented by this ovum. - Taenia solium - Hymenolepis nana - Hymenolepis diminuta - Diphyllobothrium latum

- Hymenolepis diminuta Hymenolepis diminuta is the correct response. Characteristic of this ovum is its larger size (average 70 µm), spherical shape, a smooth, thin outer shell, and an inner membrane within which are contained three pairs of hooklets. Absent are the pair of polar filaments that extend from either side of the inner hexacanth membrane. Hymenolepis nana is an incorrect response. Although also having the thin, smooth outer shell and inner hexacanth membrane containing pairs of hooklets, H. nana ova can be distinguished from those of H. diminuta by its smaller size (30 - 40 µm) and the presence of polar filaments that extend from either side of the inner membrane. Taenia solium is an incorrect response. Although T. solium ova also contain pairs of hooklets, an internal membrane is absent. The outer shell is also distinctive by being thick with distinctive radial striations. Diphyllobothrium latum is an incorrect response. D. latum ova are also large, measuring up to 70 µm; however, they are distinctively oval to almond-shaped, and have a thin outer shell with a non-shouldered operculum at one end. The internal cleavage extends to the inner shell membrane.

Which one of the following combinations of organisms would be appropriate positive and negative controls to verify the specific test functions listed? - Beta hemolysis - Escherichia coli and Streptococcus pyogenes - Catalase - Staphylococcus aureus and Staphylococcus epidermidis - Hydrogen sulfide production - Proteus mirabilis and Salmonella typhi - Indole - Escherichia coli and Klebsiella pneumonia

- Indole - Escherichia coli and Klebsiella pneumonia Escherichia coli and Klebsiella pneumoniae are two good quality control choices for the indole test. E. coli is indole positive, while K. pneumoniae is indole negative. A positive reaction is noted when there is a red layer at the top of the tube after the addition of Kovács reagent, while the negative result is a lack of color change in the top of the tube after the addition of Kovács reagent. Neither E. coli nor S. pyogenes would not be considered acceptable controls for beta hemolysis. Both microorganisms produce some strains that demonstrate beta hemolysis and some strains that do not demonstrate beta hemolysis. An appropriate positive control for beta hemolysis is Staphylococcus aureus and a negative control is Streptococcus pneumoniae. Staphylococcus aureus is the preferred positive control for catalase; however, Staphylococcus epidermidis also produces oxygen bubbles so it is not an acceptable negative control. The negative control of choice is Streptococcus pyogenes. Both P. mirabilis and S. typhi produce hydrogen sulfide and are considered acceptable positive controls for hydrogen sulfide production. E. coli is considered and acceptable negative control for hydrogen sulfide production.

The anaerobe producing the double zone of hemolysis, seen in this photograph, can be presumptively identified as Clostridium perfringens. The enzyme producing the outer zone of hemolysis is: - Cytotoxin A - Beta hemolysin - Lecithinase - Endotoxin

- Lecithinase Lecithinase is the correct answer because the outer zone of hemolysis is due to an alpha toxin that hydrolyzes lecithin and sphingomyelin found in the cell membranes of red blood cells, platelets, and white blood cells. The alpha toxin acts on the erythrocytes in blood agar and breaks down the cells releasing lecithins into the medium. Egg yolk agar is often included in the battery of differential tests for the identification of anaerobes. Egg yolk is rich in lecithin, a phospholipid found in animal tissues. Clostridium perfringens actively produces lecithinase, which will break down lecithin to produce diglycerides resulting in an opaque, white halo around the colony. Cytotoxin A is incorrect because this toxin is produced by Clostridium difficile, resulting in superficial necrosis of the bowel mucosa and pseudomembrane formation. Beta hemolysin is incorrect because a beta hemolysin has the ability to cause complete lysis of red blood cells. Streptococcus pyogenes is a common organism that produces a beta hemolysin resulting in the complete destruction of red blood cells, which results in the production of a clear zone of hemolysis around the colony growth. Endotoxin is incorrect because endotoxins are typically found in Gram negative bacteria such as Enterobacteriaceae. This group of organisms has a lipopolysaccharide that makes up their structure and serves as an endotoxin. The lipopolysaccharide plays a role in the organism's pathogenesis, but the degree of toxicity will vary from one organism to another.

A 34-year-old female was seen in the dermatology clinic for some lesions on her fingers that had not responded to topical antimicrobial therapy. A tissue biopsy was sent for histological examination, routine culture, acid-fast bacilli (AFB) culture, and fungal culture. There was no growth on any culture, but AFB were seen in the histological preparations. The tissue culture for AFB had been incubated at both 35oC and 32oC, in liquid media and on media with hemoglobin added for several weeks. What is the most likely diagnosis of her skin lesions? - Buruli's ulcer - Swimming pool granuloma - Leprosy - AIDS

- Leprosy The correct answer is Leprosy. Leprosy is the common name for Mycobacterium leprae, which will not grow on artificial media. It is known to infect the skin, mucous membranes, and peripheral nerves. Contrary to historical assumptions, it is not considered highly contagious. Buruli's ulcer is caused by Mycobacterium ulcerans, which would exhibit growth at 32oC. Swimming pool granuloma is caused by Mycobacterium marinum, which would exhibit growth at 32oC. AIDS patients with skin lesions may present with Mycobacterium haemophilum, which requires medium that contains hemoglobin and exhibits growth at 32oC.

A gram positive bacillus grew as a diffusely beta-hemolytic colony from a newborn. It was catalase positive and had tumbling motility on a hanging drop preparation. The image shows how the organism grew in the motility medium. What is the most likely diagnosis? - Listeria monocytogenes - Streptococcus agalactiae - Erysipelothrix rhusiopathiae - Escherichia coli

- Listeria monocytogenes Listeria monocytogenes is the correct answer. There are many key characteristics of Listeria monocytogenes given in the question; gram positive bacilli, beta hemolytic, catalase positive, and tumbling motility in a hanging drop preparation. In addition, the picture shows a motility medium showing motility at the top of the tube, but not deeper, and overall looking like an umbrella. The umbrella shaped motility is another key characteristic of Listeria monocytogenes. Listeria monocytogenes has colony morphology almost identical to Streptococcus agalactiae. They are both beta hemolytic and can share many other reactions as well including CAMP test positive and hippurate hydrolysis positive. However, Streptococcus agalactiae is a gram positive cocci, catalase negative, and non-motile at room temperature, which differentiates the organism from Listeria monocytogenes. Erysipelothrix rhusiopathiae is also a gram positive bacilli. Typically colonies are non-hemolytic on sheep's blood agar. The catalase reaction is also negative. Erysipelothrix rhusiopathiae also shows a test tube brush-like appearance in a gelatin stab culture and is H2S positive. Escherichia coli is a gram negative bacillus, which eliminates it as the correct answer, since the question asks for a gram positive bacilli. E. coli can sometimes appear beta hemolytic on sheep's blood agar.

Performing quantitative cultures on bronchoalveolar lavage and protected brush specimens are better than performing routine semi-quantitative cultures because in quantitative cultures there should be which of the following? - Low numbers of contaminating normal respiratory flora and colonizing organisms and higher numbers of potential pathogens. - Low numbers of contaminating normal respiratory flora and colonizing organisms and low numbers of potential pathogens. - High numbers of contaminating normal respiratory flora and colonizing organisms and higher numbers of potential pathogens. - High numbers of contaminating normal respiratory flora and colonizing organisms and lower numbers of potential pathogens.

- Low numbers of contaminating normal respiratory flora and colonizing organisms and higher numbers of potential pathogens. Low numbers of contaminating normal respiratory flora and colonizing organisms and higher numbers of potential pathogens is correct because when obtaining these specimens, the respiratory tract is bypassed by using a bronchoscope, which will allow recovery of a larger number of pathogens and prevent contamination from the upper respiratory tract. In a BAL procedure, a large amount of saline is infused into a lung segment through a bronchoscope, which will allow the collection of cells and protein from the pulmonary interstitium and alveolar spaces from the area in question. A protected brush is a small brush that is inserted through a bronchoscope to the area of interest. Both processes allows for the bypass of contamination from upper respiratory flora. Low numbers of contaminating normal respiratory flora and colonizing organisms and low numbers of potential pathogens is incorrect because the goal is to recover a higher number of pathogens to diagnosis a true bacterial infection instead of low numbers of pathogens. High numbers of contaminating normal respiratory flora and colonizing organisms and higher numbers of potential pathogens is incorrect because the goal of using these procedures is to prevent contamination of the specimen with normal respiratory flora and colonizing organisms. High numbers of contaminating normal respiratory flora and colonizing organisms and lower numbers of potential pathogens is incorrect because these procedures are used to reduce contamination of specimens with normal respiratory flora and colonizing organisms while collecting a higher yield of potential pathogens.

Which of the following instruments is used for continuous monitoring of mycobacterial growth? - MALDI-TOF - DNA microarray - MGIT 960 - BacT/ALERT

- MGIT 960 MGIT 960 is the correct answer because this is a fully automated system used to detect growth of mycobacteria. This instrument uses a MGIT (modified Middlebrook 7H9 broth) that incorporates a fluorescence quenching based oxygen sensor for detection. If a mycobacterium organism is growing, the oxygen will be utilized, and the concentration will decrease allowing the sensor to fluoresce. The MGIT broth tube will be pulled and an acid-fast stain will be performed for confirmation of mycobacterial growth. Identification will follow based on institution procedures. MALDI-TOF is incorrect answer because this instrument is used for organism identification. The name describes its methodology (Matrix-Assisted Laser Desorption Ionization Time of Flight mass spectrometry). With this methodology, an organism will be placed directly onto a plate and a chemical matrix will be applied. Afterwards, a laser will be applied to the sample and the matrix will absorb the energy creating an ion cloud. These ions will travel through a tube called a flight tube. The lighter ions will travel faster through the tube to the detector while the heavier ions will travel slower. The detector will measure the time of flight and report out a mass spectrum. This spectrum will be compared to other spectrums within the data library for identification. DNA microarray is incorrect because this instrumentation is used for rapid identification of mycobacterial species. This method exams large numbers of DNA sequences by a single hybridization step. BacT/ALERT is the incorrect answer because this instrument uses colorimetric sensor methodology located at the bottom of the blood culture bottle to identify the growth of bacterial organisms. As CO2 is produced, the CO2 will dissolve in the water within the sensor and free hydrogen ions will be generated. As a result of hydrogen ion production, a color change will occur from blue to light green to yellow as the pH decreases. The instrument will read this color change and alert the microbiologist that a blood culture is positive.

The bacterial species illustrated in these photographs was recovered from septic peritoneal fluid of a patient undergoing continuous peritoneal dialysis. The most likely identification is: - Micrococcus luteus - Staphylococcus aureus - Staphylococcus cohnii - Staphylococcus epidermidis

- Micrococcus luteus The photographs illustrate a gram positive coccus that is susceptible to 0.04 µg bacitracin ("A" disk) and resistant to furazolidone along with a gram stain morphology of tetrads (an arrangement of four bacterial cells). This presentation characteristically represents a Micrococcus species. Micrococcus luteus can be also be recognized by its bright yellow pigmentation on culture media. Micrococcus species can also be isolated from immunocompromised patients and this isolate was obtained from a patient undergoing continuous peritoneal dialysis. Staphylococcus aureus, Staphyloccus cohnii, and Staphylococcus epidermidis are incorrect as they are resistant to bacitracin and susceptible to furazolidone. In addition, the gram stain morphology of Staphylococcus species is gram positive cocci in clusters. In addition, lysostaphin can be used to differentiate Micrococcus species from Staphylococcus species as Micrococcus species is resistant and Staphylcoccus species is sensitive to lysostaphin.

A culture was taken of a conjunctival exudate. The bacterial species, represented by the tiny colonies seen on this chocolate agar plate were recovered after 48 hours incubation at 35°C. The isolate was cytochrome oxidase positive and highly susceptible to penicillin. What is the most likely identification of this organism? - Moraxella lacunata - Moraxella catarrhalis - Neisseria subflava - Haemophilus aphrophilus

- Moraxella lacunata Moraxella lacunata has been known since the turn of the century as an agent of acute conjunctivitis. The colonies on chocolate agar are typically pinpoint, as illustrated here, and are highly susceptible to low concentrations of penicillin. As the species name indicates, M. lacunata may pit the agar; however, this property is best seen in a serum medium such as Loeffler's and is usually not seen on chocolate agar. Moraxella catarrhalis produces colonies considerably larger than the pinpoint colonies seen here after 48 hours incubation, and most strains are penicillin resistant from the production of beta lactamases. The colonies of Neisseria subflava are also larger than those seen here, have a yellow pigmentation, and many strains are penicillin resistant. Haemophilus aphrophilus produces tiny colonies similar to those seen here; however, this species is cytochrome oxidase negative.

All of the following are characteristic of Burkholderia pseudomallei EXCEPT? - Has been reported as the cause of laboratory-acquired infection - Oxidase positive - Non-motile - Catalase positive

- Non-motile The correct answer is non-motile. B. pseudomallei is motile, a characteristic that differentiates it from the non-motile B. mallei. Burkholderia species is a dangerous and highly virulent organism that can cause laboratory-acquired infections. It should NOT be manipulated on an open bench. B. pseudomallei is oxidase positive, while B. mallei is oxidase variable. Both organisms are catalase positive and testing MUST be performed with extreme caution in a biosafety cabinet (BSC) due to the creation of aerosols. B. pseudomallei causes melioidosis, which is a glandular disease in animals and humans. It is found in the soil and stagnant water of primarily in Thailand, Vietnam, and parts of northern Australia.

The colonies illustrated in the upper photograph, recovered from a cat bite skin lesion of a child, reveal good growth of entire, convex, gray-white, smooth colonies on blood and chocolate agars. The colonies on blood agar are non-hemolytic and growth was not observed on MacConkey agar. Coccoid to rod-shaped Gram-negative bacilli are observed in the Gram stain. Positive tube reactions for indole, Voges Proskauer, ornithine, arginine, and strong production of esculin are observed in the lower photograph. The cytochrome oxidase reaction is also positive. With these observations, select the best choice for the identification of this isolate. - Capnocytophaga canimorsus - Pasteurella multocida - Cardiobacterium hominis - Eikenella corrodens

- Pasteurella multocida Pasteurella multocida is the correct response. Colonies on blood agar are smooth, convex, spreading, gray white and non-hemolytic with a musty odor. Growth is not observed on MacConkey agar. With these colony observations and knowing that a specimen had been obtained from a cat bite infection, observing a strong spot indole reaction would provide for a presumptive identification of Pasteurella species. Positive biochemical reactions include oxidase, catalase, Voges Proskauer, and strong esculin. The decarboxylation of ornithine and arginine would provide for a definitive identification. Coccoid to rod-shaped Gram-negative bacilli are observed in Gram stains. P. multocida is endogenous in the respiratory tract of cats and other domestic and wild animals. Most human infections involve wounds and cellulitis associated with cat bites and scratches. Capnocytophaga canimorsus colonies are slow-growing, often requiring 4 - 7 days of incubation, with better growth on blood agar or other primary recovery media supplemented with cystine (such as IsoVitalex). Early colonies are pin-point, developing into slightly larger smooth convex, non-hemolytic colonies on supplemented blood agar. Growth on MacConkey agar is absent. Thin, fusiform Gram negative bacilli are seen in the Gram stain. In contrast to P. multocida, biochemical reactions for oxidase, catalase, indole, Voges Proskauer and Arginine decarboxylation are negative. Many infections are also associated with dog bites and scratches. Eikenella corrodens colonies on blood and chocolate agars are relatively small and smooth, but distinctive for pitting of the adjacent agar ("corrodens"). Light yellow pigment may be detected with a cotton swab. The colonies give a sharp odor of bleach. Gram stains reveal slender Gram-negative bacilli or coccobacilli with rounded ends. Identifying reactions include positive reactions for oxidase, nitrate reduction, and lysine and ornithine decarboxylases. Catalase, esculin, and carbohydrate utilization of most carbohydrates are negative (asaccharolytic). Cardiobacterium hominis colonies are slow-growing, small, smooth and entire on all blood culture media. Gram stains reveal Gram variable staining short bacilli that often line up in rosette-like clusters. Oxidase is positive and catalase, nitrate, urease, and esculin reactions are negative. Indole is weakly positive with spot tests often being negative. C. hominis is normal flora in the upper respiratory tract but has been recovered from blood cultures in cases of endocarditis of individuals with damaged heart valves from rheumatoid arthritis or following heart valve replacement.

The trophozoite is the only morphologic form in the life cycle of: - Trypanosoma cruzi - Pentatrichomonas hominis - Chilomastix mesnili - Retortamonas intestinalis

- Pentatrichomonas hominis Pentatrichomonas hominis is the correct answer because of those listed, Pentatrichomonas hominis is the only known parasite that exists in the trophozoite form. This nonpathogenic parasite resides in the large intestines and feeds on intestinal bacteria. Trypanosoma cruzi is incorrect because trophozoites do not exist in this life cycle. This hemoflagellate consists of trypomastigotes and amastigotes in the human host and epimastigotes in the triatomid bug vector. Chilomastix mesnili is incorrect because this parasite has both trophozoites and cysts in its life cycle. Retortamonas intestinalis is incorrect as this parasite has both trophozoites and cysts in its life cycle. Retortamonas intestinalis resembles Chilomastix mesnili cysts by its lemon shaped morphology.

All of the following may cause systemic mycoses EXCEPT: - Actinomyces israeli - Nocardia brasiliensis - Coccidioides immitis - Piedraia hortae

- Piedraia hortae Piedraia hortae does not cause systemic mycosis, but instead causes a condition known as black piedra. This disease is characterized by the formation of brown or black nodules which are attached to the hair shaft. Scalp hair is the most frequently infected area. Black piedra does not become systemic. The remaining organisms may cause systemic mycoses Actinomycosis is caused by infection with Actinomyces israeli. Actinomyces infections are most often found in the head, neck or jaw area but may also involve the thorax, pelvic area and central nervous system. Nocardia brasiliensis causes mycetoma, lymphocutaneous infections and cellulitis; in immunosuppressed individuals, Nocardia can cause invasive pulmonary infections and disseminated infections that can affect the brain, skin and central nervous system. Disseminated nocardiosis has a poor prognosis. Coccidioidomycosis is caused by infection with Coccidioides immitis, which generally begins as a respiratory infection but may disseminate in a small percentage of patients to the bones, joins, brain or meninges.

All of the following are statements concerning the gram stain. Which of the following is a TRUE statement? - Can diagnose most parasites. - Identification of organism is definitive. - Mycobacteria can be diagnosed. - Presumptive evidence is provided.

- Presumptive evidence is provided. Presumptive evidence is provided is the correct answer because the purpose of doing gram stains is to provide a grouping of bacteria into categories based on cell wall physical and chemical properties. The bacteria cell will either be gram positive (blue) or gram negative (red) cocci or bacilli. Can diagnose most parasites is incorrect because parasites are not diagnosed through the use of a gram stain. Parasites are diagnosed through of a combination of stains (Trichrome, Giemsa, and Wright) and immunological testing methods. Identification of organism is definitive is incorrect because the gram stain only provides presumptive interpretation of the specimen submitted and the type of bacteria that is present. Mycobacteria can be diagnosed is incorrect because Mycobacteria species do not stain very well with gram staining. Mycobacteria species are acid-fast due to waxes and mycolic acids in their cell wall, which requires the use of staining methods such as Ziehl-Neelsen and Kinyoun.

Which Pseudomonas species produces pyocyanin (bright bluish pigment on Mueller-Hinton agar)? - Pseudomonas fluorescens - Pseudomonas putida - Pseudomonas veronii - Pseudomonas aeruginosa

- Pseudomonas aeruginosa Pseudomonas aeruginosa strains produce a pigment called pyocyanin. Pyocyanin means "blue pus", which is a characteristic of certain infections caused by Pseudomonas aeruginosa. The pigment produces by this bacterium diffuses into the medium surrounding its growth. P. aeruginosa, P. fluorescens, P. putida, P. veronii, P. monteilii, and P. mosselii comprise the group known as fluorescent pseudomonads. These species all produce pyoverdin, a water-soluble, yellow-green or yellow-brown pigment that fluoresces blue-green under ultraviolet light. Pseudomonas aeruginosa can be distinguished from the others in this group by its ability to grow at 42° C and production of pyocyanin.

The formula for oxidative/fermentative (OF) culture media, for the determination of glucose oxidizers, differs from carbohydrate fermentation media by each of the following properties except: - Relative decrease in the protein concentration - Relative increase in the carbohydrate concentration - Relative decrease in the agar concentration - Relative increase in the salt concentration

- Relative increase in the salt concentration The concentration of protein is reduced in OF medium, and the relative amount of carbohydrate is increased. This is done to maximize the production of acid from the increased amounts of carbohydrate and to reduce the amount of alkaline amines produced from the oxidation of the amino acids. The agar concentration is decreased so that any acid produced from the carbohydrate will have free access to the color indicator. The concentration of sodium chloride is equal both in fermentative and OF media.

On a plate growing Streptococcus pneumoniae, the zone of inhibition around the disk shown in the image has been measured at 23 mm. Based on this result, you should: - Report oxacillin-susceptible - Repeat the test - Check the potency of the disk - Perform a minimum inhibitory concentration (MIC) test on the isolate

- Report oxacillin-susceptible According to the current Clinical and Laboratory Standards Institute(CLSI) guidelines, an isolate of Streptococcus pneumoniae is considered to be susceptible if the zone of inhibition around the 1ug oxacillin disk is > 20 mm. Thus, in this case, the isolate is oxacillin susceptible and penicillin can be administered. A follow-up MIC should be performed only if the zone of inhibition measures <19 mm as the degree of resistance cannot be determined.

The photomicrograph on the right illustrates single conidia in succession both laterally and around the tip of a straight phialide. This type of sporulation, characteristic of certain species of dematiaceous mold, is called: - Acrotheca - Acropetal - Rhinocladiella - The image does not illustrate sporulation

- Rhinocladiella The production of single conidia in succession both laterally and around the tip of a straight phialide is called the rhinocladiella type of sporulation, characteristic of Fonsecaea pedrosoi. Acrotheca type sporulation is also produced by F. pedrosoi; however, is characterized by the production of short chains of elliptical conidia in a circular arrangement from the tips of branching phialides. Acropetal is the term referring to a type of sporulation where chains of conidia are formed with each new daughter cell produced from the previous one, leaving the oldest cell at the base of the chain. This type of sporulation is characteristic of Aspergillus species and Penicillium species.

Examine the KIA tube on the right in the image provided and determine which of the following organisms produces the biochemical reaction seen. - Shigella sonnei - Pseudomonas aeruginosa - Shewanella putrifaciens - Salmonella typhi

- Salmonella typhi Salmonella typhi is the correct answer because the patch of black seen in the KIA (Kligler Iron Agar) tube to the right in the photograph represents a small amount of H2S production confined to the angle between the slant and the deep. This small amount of H2S gas production is characteristic of Salmonella typhi. Shigella sonnei is incorrect because the organism does not produce H2S. Pseudomonas aeruginosa is incorrect because this organism is a nonfermenter; therefore, the glucose will not be fermented resulting in an alkaline (red) deep. Pseudomonas aeruginosa also lacks the ability to produce H2S. Shewanella putrifaciens is incorrect because this organism is a nonfermenter; however, it does have the capability to produce H2S. Shewanella putrifaciens will produce an alkaline (red) deep, due to it being a nonfermenter.

The ovum as illustrated in the high-power photomicrograph, averages 140 µm. These ova are most commonly observed in a urine sediment from a patient complaining of frequent urination, dysuria, hematuria and recurrent urinary tract infections. Note the characteristic delicate, sharply pointed terminal spine (blue arrow) extruding from the anterior margin of the shell. From the multiple choices listed below, select the presumptive identification of this ovum. - Schistosoma haematobium - Schistosoma mansoni - Fasciola hepatica - Schistosoma japonicum

- Schistosoma haematobium The ova of Schistosoma haematobium is large and oval with a terminal spike. The adult is found in the veins surrounding the bladder with the ova commonly observed in the urine and only rarely found in the feces. Schistosoma mansoni ova, although of the same large size as S. hematobium, are characterized by the extension of a large, pointed lateral spike. The adult is located in the venules of the large intestine. The ova would be observed in the feces, not in urine specimens. Fasciola hepatica ova are large with a smooth, thin outer shell, but with an indistinct non-shouldered operculum at one of its narrow margins, rather than having the pointed spikes as seen with certain Schistosoma species. Schistosoma japonicum ova are comparatively small, averaging 80 µm. In contrast to other Schistosoma species, S. japonicum are broadly oval to semi-spherical in shape with a knob-like extension from one margin of the shell rather than the pointed spikes observed in the ova of other Schistosoma species.

The first intermediate host in all of the fluke life cycles are the: - Copepods - Snails - Fish - Water plants

- Snails Once the miracidium emerges from a fluke egg (in fresh water), it searches for the appropriate species of snail to penetrate. The next stage, known as a sporocyst, develops inside the snail. Copepods are the second intermediate host, which houses the infective stage of Paragonimus westermani, the oriental lung fluke. After emerging from the snail, cercariae of Heterophyes hterophyes (heterophytid) and Clonochis sinensis (oriental liver fluke) enter fish (second intermediate host) and encyst in tissue. Water plants are the second intermidate host and home to the infective stage of Faciolopsis buski (large intestinal fluke) and F. hepatica (sheep liver fluke).

The colonies shown in the upper image, obtained from a biopsy of an ulcerating skin lesion of the arm, are growing on agar slants of Sabouraud's dextrose agar. The lower image is a photomicrograph of a lactophenol blue mount made from a portion of the colony growing in the left slant. The diagnosis is: - Coccidioidomycosis - Blastomycosis - Histoplasmosis - Sporotrichosis

- Sporotrichosis Sporothrix schenckii (causative agent of sporotrichosis) causes chronic subcutaneous infections related to trauma (thorns, splinters, or scratches) with contaminated dead or living vegetation. The colonies seen growing in the upper image has a gray-green, delicate, cottony consistency. The lactophenol blue mount reveals tiny, ovoid microconidia, arranged in a daisy-head pattern at the tip of a straight conidiophore. This appearance is characteristic of the mold form of Sporothrix schenckii. By moving the focus up and down in a microscopic preparation, delicate hair-like attachments may be observed for each conidium. The mold form of Coccidioides immitis (causative agent of coccidioidomycosis) produces delicate hyphae that break up into arthroconidia separated by empty cells, giving an alternatively staining appearance. It causes a self-limiting respiratory infection but may disseminated to the skin and other sites. The mold form of Blastomyces dermatitidis (causative agent of blastomycosis) is characterized by the production of single, smooth microconidia, each borne on a single, thin conidiophore ("lollipops"). It causes granulomatous infections typically beginning in the lungs but able to disseminate to the soft tissue and other sites. The mold form of Histoplasma capsulatum (causative agent of histoplasmosis) is recognized by the production of large, tuberculated macroconidia, appearing as a prickly surface. It causes chronic granulomatous infections typically beginning in the lungs.

What parasite resides in the human intestines and is identified in the picture? - Taenia solium scolex - Hymenolepis nana scolex - Dipylidium caninum scolex - Diphyllobothrium latum scolex

- Taenia solium scolex The Taenia solium scolex is identified by the presence of four suction-cuplike suckers and the presence of a fleshy rostellum with hooklets. When raw or undercooked meat is ingested, the scolex attaches to the intestinal wall and matures into an adult worm in about 10 weeks. Hymenolepis nana scolex is small with four suckers and a rostellum with spines. Infection can occur with direct fecal-oral transmission. The scolex develops into an adult worm in the intestinal tissues. Dipylidium caninum scolex is a conical-shape with a retractable rostellum. Children are usually infected from dog fleas. Diphyllobothrium latum scolex has two sucking grooves instead of suckers and is elongated. Eating raw fish will cause infection, and the scolex develops in the intestines into an adult worm.

A tech is reviewing a Gram stain from a positive blood culture bottle. The background on the stain shows pink debris and the tech thinks that there is also Gram negative bacilli but is having difficulty differentiating the artifact and possible organisms. What could the tech do next to help determine if bacteria are present in the blood culture bottle? - Stain with Wright-Giemsa - Stain with Acridine Orange - Use Calcofluor White - Stain with Periodic Acid-Schiff

- Stain with Acridine Orange Acridine orange is a fluorescent stain used in microbiology to determine bacteria in direct smears of biological fluids. It is very helpful in cases of fluids with low bacterial numbers suspected (such as CSF) and to differentiate bacteria from debris on slides. The stains detects both living and dead bacteria. A Gram stain will still have to be performed in order to differentiate Gram-positive and Gram-negative organisms. Wright-Giemsa stain is used in Microbiology for direct blood smears, typically to stain blood cells, in the instance of direct blood smears for detection of malaria. Bacteria can stain with Wright-Giemsa, but debris will also, not allowing for differentiation of the bacteria. Calcofluor White is a dye used to detect yeast cells and hyphae in skin and mucous membrane scrapings. This dye can help to differentiate between background material and fungus but does not assist with bacterial determinations. Periodic Acid-Schiff is used to stain tissues to identify fungal elements in the tissue. It is not used to differentiate bacteria from debris.

Illustrated in the photograph are smooth, non-hemolytic, white 48 hour old colonies incubated at 37oC growing on the surface of blood agar. This isolate was recovered from a urine culture. Microscopic examination of a gram stain reveals gram positive cocci. The catalase reaction was positive and the coagulase test was negative. This isolate is a common agent of urinary tract infections. What is the name of this isolate? - Staphylococcus aureus - Staphylococcus epidermidis - Staphylococcus saprophyticus - Micrococcus spp.

- Staphylococcus saprophyticus Staphylococcus saprophyticus is the correct response. Staphylococcus saprophyticus colonies are smooth but not pigmented and the gram-positive cocci in slide preparations. The catalase test is positive and coagulase test is negative. Demonstrating resistance to novobiocin is an additional identifying characteristic. S. saprophyticus is an agent of urinary tract infections. Staphylococcus aureus colonies are smooth and yellow-pigmented with gram-positive cocci on the slide preparation and having both tests positive for catalase and coagulase. Most strains are novobiocin susceptible. Species confirmation can be made by demonstrating a positive coagulase reaction. Staphylococcus epidermidis colonies are smooth but with a light gray pigmentation. Microscopic observation of gram stains reveals gram-positive positive cocci and catalase is positive. The coagulase test is negative. S. epidermidis is susceptible to novobiocin. Differentiation from S. saprophyticus may require carbohydrate utilization reactions utilizing kit systems or more advanced molecular assays. It is considered normal flora and is associated with nosocomial infections. Micrococcus spp. are usually considered contaminants of clinical specimens and are rarely implicated as cause of infections in humans.

All of the following pose a significant risk of transmitting bloodborne pathogens, EXCEPT? - Bloody urine - Semen - Pleural fluids - Sweat

- Sweat The correct answer is sweat. Sweat is a body fluid that does not pose a high risk of blood borne pathogen transmission. Blood and all body fluids, including secretions and excretions, except sweat, regardless of whether visible blood is present, are considered infectious based on the CDC safety guidelines called standard precautions.

What are the two general categories of nucleic acid amplification (NAA) techniques? - Polymerase chain reaction (PCR) and branched chain DNA (bDNA) - Fluorescence in situ hybridization (FISH) and strand displacement amplification (SDA) - Target amplification and signal amplification - PCR and reverse transcriptase PCR (RT-PCR)

- Target amplification and signal amplification The correct answer is target amplification and signal amplification. Target amplification and signal amplification are two general categories of amplification techniques. Target amplification involves making copies of a target sequence to such a level that they can be detected in vitro. Signal amplification does not increase the number of target or probe sequences, but does increase the amount of signal bound to target sequences. Polymerase chain reaction (PCR), RT-PCR, and strand displacement amplification (SDA) are specific examples of target amplification, while branched chain DNA (bDNA) is an example of signal amplification. FISH assays do not involve amplification.

Which Plasmodium morphologic form is considered most immature? - Trophozoite - Schizont - Microgametocyte - Macrogametocyte

- Trophozoite The trophozoite (ring form) is the most immature for the Plasmodium species maturation in the red blood cells. The stages of maturation are: early trophozoite, late trophozoite, schizont, microgametocyte, and macrogametocyte.

Which of the following statements about hepatitis C virus (HCV) is true? - There is vaccination against infection with HCV. - The primary route of infection with HCV is airborne transmission. - Patients infected with HCV will always have observable symptoms. - The majority of individuals who are infected with HCV and develop antibodies in their serum (seroconvert) will develop a chronic infection and active liver disease.

- The majority of individuals who are infected with HCV and develop antibodies in their serum (seroconvert) will develop a chronic infection and active liver disease. The correct answer is that the majority of patients with antibodies will develop chronic infection and active liver disease. Approximately 75 to 85% of individuals who are infected with Hepatitis C and seroconvert develop a chronic form of the disease and about 70% of the chronically-infected individuals will develop active liver disease. There is currently no vaccine that will protect against HCV infection. HCV is primarily transmitted through blood and body fluids. Individuals who are chronically infected with hepatitis C may have no symptoms for many years.

An iodine prep is LEAST helpful in the identification of which parasitic stage? - Larvae - Eggs - Cysts - Trophozoites

- Trophozoites The correct answer is trophozoites. Iodine kills trophozoites, so when iodine is added to wet preps, trophozoites no longer appear motile. In larvae, eggs, and cysts, iodine emphasizes nuclear material and glycogen masses, which often makes identifying distinguishing characteristics easier.

Which of the following statements about Gram-positive bacteria is TRUE? - They resist acetone-alcohol decolorization - They are always decolorized by acetone-alcohol - They resist staining by crystal violet - They readily stain with safranin in the Gram stain

- They resist acetone-alcohol decolorization Bacteria with thick cell walls containing teichoic acid retain the crystal violet-iodine complex after decolorization, appearing purple/deep blue, and are called gram-positive bacteria. Other bacteria with thinner walls containing lipopolysaccharides do not retain the dye complex when the alcohol-acetone decolorizer is applied. This is due to the thin lipid walls being damaged by the decolorizer, which allows the crystal violet stain to wash out. When the safranin counter stain is applied, the bacteria appear pink, and are called gram-negative.

Illustrated in the photomicrograph is a Giemsa-stained impression smear prepared from an aspirate of an enlarged cervical lymph node. Human infections are acquired through the ingestion of poorly cooked meat. Pregnant women in particular are advised to avoid handling of cats and the ingestion of under-cooked meat. Based on the morphology of the 8 µm long tachyzoites observed in the photomicrograph, select the name of the protozoan parasite as listed for making a presumptive identification. - Leishmania species - Trypanosoma cruzi - Toxoplasma gondii - Onchocerca volvulus

- Toxoplasma gondii Toxoplasma gondii is the correct selection. The tachyzoites as illustrated are distinctly bow shaped and have a light to dark staining central nucleus. Leishmania species is an incorrect response. Leishmania tachyzoites of are small (3 - 4 µm), oval in shape with a distinctive bar-like kinetoplast positioned adjacent to the nucleus. Trypanosoma cruzi is an incorrect response. T. cruzi developing trypanosomes have a distinctive "C" shape, and possess a posterior deep-staining dot-like kinetoplast with the anterior extension of a flagellum. Onchocerca volvulus is an incorrect response. O. volvulus has microfilaria that are long and thread-like, often arranged in spiral circles. The microfilaria may wander through the skin to other organs, particularly the eye where distortion of vision called "river blindness" may occur. Microfilariaare are rarely observed in the peripheral blood.

The colony illustrated in the top image developed after 4 days of growth on Sabouraud's dextrose agar. Note the extension of the outer margin to the rim of the Petri dish. The bottom image 2 is a methylene-blue stained image of an inoculum obtained from the surface of the colony. From these characteristics, select the fungus genus from the multiple choices. - Trichoderma - Fusarium - Acremonium - Gliocladium

- Trichoderma Trichoderma is the intended selection. The border to border extensions of the colony is similar to those of Gliocladium except the surface pigmentation is light yellow green rather than deep green. Microscopically observed are small rather than large dense clusters of spherical conidia, here located at the tips of short conidiophores that are projected laterally from the hyphae. Acremonium colonies are gray to light shades of yellow with a smooth surface. Conidia are arranged in loose clusters, each borne at the tip of a long, slender conidiophore ending in a blunt tip. A septum is observed at the base of each conidiophore. Fusarium colonies are cottony or woolly with a distinctive lavender, pink, deep red or magenta coloration. Microscopic Identification is usually made by observing macro-conidia that are long, sickle-shaped, and multi-celled, with transverse septa separating the cells from one another. Exact focusing on the hilar cell reveals a hair-like "foot cell" extension. Gliocladium colonies also have a border to border "lawn-like" extension along the Petri dish but with a green pigmentation. Illustrated in the photomicrograph are large clusters of densely packed spherical conidia borne from the tips of fingerlike conidiophores, simulating a penicillus in structure.

This microscopic field is representative of other fields that were observed on a Gram-stained smear. Which of the following describes the quality of the smear? - Under-decolorized; Poor Quality - Over-decolorized; Good Quality - Sufficiently decolorized; Poor Quality - Under-decolorized; Good Quality

- Under-decolorized; Poor Quality Under-decolorized; Poor Quality is the correct answer because this gram stain is of poor quality, due to under-decolorization. Too little use of decolorizer will result in the retention of the crystal violet- iodine mordant complex in gram negative organisms making them appear gram positive. The image provided represents a slide that is under-decolorized due to the overabundance of crystal-violet in white blood cell nuclei, resulting in a slide with poor quality. Over-decolozired; Good Quality is incorrect. Too much alcohol or acetone will cause all organisms to lose the crystal violet-iodine mordant complex and cause gram positive organisms to appear as gram negative organisms, which can result in misidentification. The image provided exhibits an under-decolorized specimen, due to the increase amount of crystal-violet stain within the nucleus of the white blood cells resulting in a slide with poor quality. Sufficiently decolorized; Poor Quality is incorrect. The image represents a slide with poor quality due to under-decolorization that can result in erroneous results. If this smear was sufficiently decolorized, the nucleus of the white blood cells would be redder from the safarnin instead of blue from the crystal-violet giving rise to a good quality smear resulting in the reporting of accurate organism gram stain morphology. Under-decolorized; Good Quality is incorrect even though this image is under-colorized. As a result of having an under-decolorized smear, the smear is of poor quality that can result in erroneous results.

Which one of the following tests would be positive in the presence of Klebsiella spp.? - Methyl-red test - Coagulase test - CAMP test - Voges-Proskauer test

- Voges-Proskauer test The correct answer is the Voges-Proskauer test. A positive Voges-Proskauer test indicates the production of acetoin. It is converted to diacetyl, which is subsequently converted to a red complex in the presence of creatine and naphthol. An organism which is Voges-Proskauer positive is usually methyl-red negative and vice versa. Enterobacter, Klebsiella, Serratia, and Hafnia are usually Voges-Proskauer positive. The coagulase test is used to differentiate Staphylococcus aureus from coagulase negative Staphylococcus (CNS) species. The CAMP test is used to identify Group B Streptococcus (GBS).

A woman came to see her physician as she was having vaginal/vulvar itching and some pain upon urination. To obtain a diagnosis of a yeast infection, which of the following is the test of choice? - Fungal culture - Wet preparation - Routine vaginal culture - Nucleic acid base test

- Wet preparation Wet preparation is the correct answer as budding yeast cells and pseudohyphae can be identified from wet preparations of vaginal specimens; therefore, making it a rapid, inexpensive, test for a quick diagnosis. Fungal culture is incorrect as growth in culture can take several days to grow. This method is not a rapid method to provide a quick diagnosis. Routine vaginal culture is incorrect as this method looks for all vaginal pathogens besides Candida and does not provide a rapid diagnosis. Nucleic acid base test is incorrect as Candida is not routinely performed directly from vaginal specimens. The cost of performing a nucleic acid test versus a wet preparation is more expensive and the treatment option does not change when Candida presence is detected.

The photograph on the right illustrates the Rosco Diagnostica IMI/EDTA disk test and the bioMerieux MBL E test. Both tests are used to detect metallo beta-lactamse production. After viewing the results of these tests, does this organism produce metallo-beta-lactamase? - Yes - No - Indeterminate - Further testing is required

- Yes The correct answer is yes. This organism is positive for metallo beta-lactamase production. The IMI/EDTA disks contain imipenem (IMI 0) alone and imipenem + an inhibitor (IMI 0E) - that inhibitor is EDTA. If the zone increases by 5 mm between the imipenem and the imipenem + EDTA, the test is positive for metallo-betalactamse production. With the organism shown in this image, the zone size increased by 8 mm indicating a positive EDTA inhibition test. The BioMerieux MBL E test strip has meropenem alone at the bottom half of the strip and meropenem plus an inhibitor (EDTA) at the top half of the strip. If there is a 3 dilution difference in the MIC between the meropenem and meropenem + EDTA then the test is positive. In this image, the organism is resistant to meropenem alone but EDTA inhibited the enzyme and restored susceptibility as seen in the top half of the strip. This test is also positive for metallo beta-lactamase production.

The organisms Klebsiella pneumonia, Enterobacter cloacae, and Escherichia coli can produce carbapenemases due to which of the following genes? - mec A - van A - blaKPC - erm

- blaKPC blaKPC is the correct answer. The Klebsiella pneumoniae carbapenemase enzymes are encoded by the blaKPC gene and are produced by Klebsiella pneumonia, Enterobacter cloacae, and Escherichia coli. mec A is incorrect. This gene codes for methicillin resistance found in Staphylcoccus aureus organisms. van A is incorrect. This gene codes for vancomycin resistance in Enterococcus faecium and Enterococcus faecalis. erm is incorrect. This gene codes for inducible clindamycin resistance in Staphylococcus and Streptococcus species.

The 48-hour growth of small pinpoint gray-white, smooth colonies on chocolate agar (right plate) are most commonly recovered as normal upper respiratory flora but may cause otitis media and sinusitis. There was no growth on Thayer Martin media (left plate). Growth on MacConkey agar is also absent. Short, plump, Gram negative cocci lying singly and in loose clusters are seen in Gram stain, as illustrated in the lower photomicrograph. This non-fermenter is non-motile, oxidase positive, and does not utilize carbohydrates (assacharolytic). Nitrates are reduced and DNAse is positive. From these observations, select from the multiple choices the presumptive identification of this isolate. - Burkholderia cepacia - Alcaligenes faecalis - Moraxella catarrhalis - Acinetobacter baumannii

Moraxella catarrhalis Moraxella catarrhalis is the correct response. The big clues in the question were the Gram negative cocci (diplococci) and no growth on MacConkey that ruled out the other organisms in this list. All of the other organisms are Gram negative bacilli or cocobacilli but do grow on MacConkey agar. The colonies growing on chocolate agar are small, initially pinpoint in size after 24 hours incubation, and non-pigmented. Growth on Thayer Martin media is scant or absent, ruling out pathogenic Neisseria species. Small, Gram negative cocci are observed in Gram stains. Cytochrome oxidase, nitrate reduction, and catalase reactions are positive. Acid is not produced from carbohydrates (asaccharolytic). M. catarrhalis is commonly recovered from upper respiratory and ear specimens obtained from patients with otitis media and sinusitis. To confirm the identification, butyrate esterase testing can be performed, which is positive for M. catarrhalis. Burkholderia cepacia colonies are relatively small, entire, convex and smooth, with gray yellow pigmentation. Colonies grow on MacConkey agar and are without pigment characteristic of a non-fermenter. The oxidase and catalase reactions are positive; however, nitrate reduction is negative. Acid is produced oxidatively from most carbohydrates. B. cepacia is often recovered from sputum samples of patients with cystic fibrosis. Alcaligenes faecalis colonies on blood agar are grey pigmented and spreading, with light pigment extending into the adjacent agar. Small, plump, Gram negative coccobacilli are seen on Gram stain. A. faecalis does grow well on MacConkey agar. Acid is not produced from carbohydrates and cytochrome oxidase and catalase reactions are positive. Distinctive is the denitrification of nitrates with the production of gas. Acinetobacter baumannii colonies growing on blood agar are relatively large, white, entire, convex and opaque. Entire, smooth, slightly wrinkled colonies with light pink pigmentation are produced on MacConkey agar. Gram negative coccobacilli are also observed in Gram stains. Oxidase and catalase reactions are negative. A. baumannii is saccharolytic while A. lwoffii is asaccharolytic.

Which cell is targeted by the AIDS virus? - B lymphocyte - Erythrocyte - Neutrophil - T lymphocyte

- T lymphocyte IV (the virus causing AIDS) infects the T lymphocytes (T helper cells) since these cells have the marker CD4 on their surface. The HIV virus utilizes this marker to attach itself to the cell. Hence, the T helper cells can be called CD4+ lymphocytes. As the number of CD4+ T lymphocytes decreases, the risk and severity of opportunistic infections increases. Since the CD4 marker is found on T lymphocytes, the AIDS virus would not infect B lymphocytes, erythrocytes, and neutrophils.

Acridine orange is used for: - Visualization of fungal structures with fluorescent microscopy - Separation of bacteria into two categories based on cell wall composition - Visualization of protozoa in direct wet mounts or smears - Visualization of bacteria in specimens where debris may be present

- Visualization of bacteria in specimens where debris may be present Acridine orange is a fluorochrome dye that binds to nucleic acids in bacterial specimens to aid in visualization. Calcofluor white allows visualization of fungal structures with fluorescent microscopy. Gram stain is used to separate bacteria into two categories based on cell wall composition. Trichome stain is used to visualize protozoa in direct wet mounts or smears.

What is the MOST likely identification of a pink yeast isolate, recovered from respiratory secretions of a patient with AIDS, that gave the following results? Germ tube - negative Urease - positive Blastospores - positive Arthrospores - negative - Rhodotorula spp. - Cryptococcus spp. - Candida albicans - Trichosporon spp.

Rhodotorula spp. Rhodotorula spp. are normal flora of the skin and are often found growing in the corners and creases of the shower with their characteristic pink pigment. They are occasional isolated as causative agents of opportunistic mycoses in immunocompromised patients. Rhodotorula spp. show typical budding (blastoconidia), but do not have pseudohyphae and therefore do not produce arthroconidia or germ tubes. Cryptococcus spp. are common sources of mycoses in immunocompromised individuals. They grow with a normal cream pigment and are traditionally identified by seeing the characteristic polysaccharide capsule using india ink. Candida albicans is the most commonly isolated yeast in the clinical laboratory. Colonies growth with a characteristic cream pigment, produce normal buds (blastoconidia), pseudohyphae (arthroconida), and germ tubes. Trichosporon spp. produce hyaline hyphae, numerous round to rectangular arthroconidia, and occasionally a few blastoconidia.

A parasitic egg was found in stool and measured 170 µm by 63 µm (see image to the right). Identify the parasitic egg.

Schistosoma mansoni egg Schistosoma mansoni egg is the correct answer. Schistosoma mansoni eggs measure 115-180 µm x 40-75 µm and are found in stool specimens. The parasitic egg of this species has a large lateral spine (as seen in the image), is embryonated, and unoperculated. Schistosoma japonicum egg is incorrect. Schistosoma japonicum eggs measure 70-100 µm x 50-85 µm and are found in the small intestines. The eggs have a small lateral spine, are unoperculated, and embryonated. Fasciola hepatica egg is incorrect. Fasciola hepatica eggs measures 130-150 µm x 70-90 µm, are operculated, unembryonated, and have a brownish-yellow color. In addition, this species is known as a liver fluke and can cause bile duct obstructions. Ascaris lumbricoides egg is incorrect. Ascaris lumbricoides eggs measure 45-95 µm x 35-40 µm, have a very thick shell, and may have a mammilated outer albuminoid coat.

The subsurface umbrella-shaped zone of motility seen in this SIM tube (arrow) is characteristic of Listeria monocytogenes. The optimum temperature of incubation to best illustrate this property is: - 25°C - 30°C - 35°C - 42°C

- 25°C It is common practice in clinical laboratories to incubate the SIM motility tube at room temperature (25°C) when confirming the identification of an unknown species as Listeria monocytogenes. Although motility will be observed at 30°C, this is not the optimum temperature to demonstrate this property. The flagella are inactive at temperatures above 30°C and therefore motility will not be detected at the normal incubator temperatures of 35°C or 37°C or higher (such as 42°C ).

Which of the following is the correct order when performing a permanent stained smear of a stool specimen? - 100% ethanol; 70% ethanol/D'Antoni's iodine; 70% ethanol; Trichrome stain; 90% ethanol; Xylene - 90% ethanol; 70% ethanol/D'Antoni's iodine; 70% ethanol; Trichrome stain; 100% ethanol; Xylene - 70% ethanol/D'Antoni's iodine; 70% ethanol; Trichrome stain; 90% ethanol;100% ethanol; Xylene - 70% ethanol/D'Antoni's iodine; 100% ethanol; 90% ethanol; Trichrome stain; 70% ethanol; Xylene

- 70% ethanol/D'Antoni's iodine; 70% ethanol; Trichrome stain; 90% ethanol;100% ethanol; Xylene The trichrome stain is used to distinguish the internal elements among cysts and trophozoites and enhances their morphologic features. It also serves as a permanent record of the results. The specimen must first be rid of mercuric chloride, which is accomplished by the addition of 70% ethanol/D'Antoni's iodine and then the 70% ethanol steps. Immersion in trichrome stain is the next major step in the process. The 100% alcohol followed by the 90% ethanol steps are next. Xylene is the final step listed and serves as the final debris removal stage prior to microscopic examination.

When performing quantitative cultures from bronchoalveolar lavage specimens, which of the following colony forming units per milliliter indicates a true bacterial pneumonia? - >10 4 colony forming units/mL - >10 3colony forming units/mL - >10 2 colony forming units/mL - >10 1 colony forming units/mL

- >10 4 colony forming units/mL >104 colony forming units/mL is the correct answer. Quantitative cultures in bronchoalveolar lavage (BAL) specimens increase the sensitivity of a diagnosis; however, the sensitivity is dependent on the amount of growth that is present. Colony growth >/=104 CFU/mL is consistent with bacterial pneumonia. Counts <104 CFU/mL are most likely an indication of normal flora. >103colony forming units/mL is incorrect. Counts at this level in BAL specimens are considered as normal bacteria flora. However, in protected brush specimens, a colony count at this level is consistent with bacterial pneumonia. >102 colony forming units/mL and >101 colony forming units/mL are incorrect answers. A count <104 CFU/mL in BAL specimens is considered as normal bacterial flora and not consistent with bacterial pneumonia.

All of the following are included in a standard ova and parasites examination, EXCEPT: - Visual examination - Direct wet mount examination - Permanent stained smear examination - A parasite culture

- A parasite culture The correct answer is a parasite culture. There is no culture for parasites. A visual examination is performed to locate any materials that may make the specimen unacceptable for examination and to determine if there are any specific area of the sample that should be used for further testing, such as blood, mucin, or pus. The direct wet mount gives a rapid detection of intestinal parasites, especially helping to identify protozoan trophozoites, cysts, oocysts, helminth eggs and larvae. A permanent stained smear examination allows a technologist to better visualize the internal morphology of cysts and trophozoites of intestinal protozoa.

The pathogenicity of Staphylococcus aureus, as well as the frequency with which this organism produces infections, can be attributed to all of the following EXCEPT: - Exfoliative toxin and enterotoxins - A porous cell wall - Natural colonization/reservoir for infection - Hyaluronidase

- A porous cell wall Staphylococcus aureus colonizes approximately 25 - 30 % of the general population, providing significant reservoirs of organism for transmission. In addition, it produces a number of different enzymes and toxins, including (but not limited to) exfoliative toxin, enterotoxins, hyaluronidase and lipase, and beta lactamases. The cell wall of S. aureus is not porous. Structural components of its cell wall function as a protective barrier, aid in adherence to mucous membranes, and allow the organism to resist phagocytosis.

Which two of the following tests are helpful for documenting previous streptococcal throat and skin infections? - ASO titer & anti-DNase B - CAMP & PYR - Coagulase & catalase - Bacitracin & SXT

- ASO titer & anti-DNase B Individuals with disease caused by Streptococcus pyogenes produce antibodies against various antigens. The most common are antistreptolysin O (ASO), anti-DNAse B, antistreptokinase, and antihyaluronidase. Use of serodiagnostic tests is most useful to demonstrate prior streptococcal infection in patients. CAMP & PYR are used to identify group B or group A streptococci. The CAMP test will be positive for group B (S. agalactiae) streptococci and the PYR will be positive for group A (S. pyogenes) streptococci. Once an isolate is identified as, or strongly suspected to be, a species of staphylococci, a test for coagulase production is performed to separate Staphylococcus aureus from other species. The Staphylococcus spp. are distinguishable from the related family Streptococcaceae by the catalase test. For isolating group A streptococci from throat swabs, the most common medium is 5% sheep blood agar supplemented with trimethoprimsulfamethoxazole (SXT), to suppress the growth of normal microbiota. A bacitracin disc is placed on the initial inoculum streak to aid in identification (S. pyogenes will show sensitivity).

All of the following are collected from sterile sites, EXCEPT: - Urine - Pleural Fluid - Abscess fluid - Cerebrospinal fluid (CSF)

- Abscess fluid The correct answer is abscess fluid. An abscess is the accumulation of pus exuding from a sinus tract or from a mucocutaneous surface. This is indicative of a suppurative infection, meaning that the body is mounting a response to something foreign, likely a microorganism. Essentially, an abscess is not a sterile site. Urine is collected directly from the urethra, which is connected to the bladder, both of which are sterile sites. Pleural fluid is the fluid that lines he pleural cavity, which is a sterile site. CSF is found in the subarachnoid space that lines the central nervous system, which is a sterile site.

The border to border extension of the mycelium as illustrated in the top photograph is characteristic of one of the Zygomycetes. Although a light yellow green pigmentation of the mycelium is observed, the identification of the isolate depends on the presentation of the fruiting body observed in the bottom photomicrograph. From these observations, select the name of this isolate from the list of multiple choices. - Rhizopus species - Syncephalastrum species - Mucor species - Absidia species

- Absidia species Absidia species is the correct response. Of interest is the recent taxonomic reclassification of Absidia species into the genus Lichtheimia. However, the more familiar genus name Absidia is still used in laboratory practice to prevent confusion in the medical community. Although rhizoids are not observed in this photomicrograph, they are produced by Absidia. The conidiophores originate from the main hyphae between the rhizoids ("intermodal"). The conidiophores terminate in a saclike sporangium, that in early development has a distinctive funnel-like expansion, an apophysis, as seen in the image insert. Rhizopus species produce root-like rhizoids in a"nodal" placement directly below the base of the sporangiophore. At the tip of the sporangiophore is produced a saclike sporangium. Syncephalastrum species produce spherical sporangia at the tips of narrow sporangiphores. Distinctive is the cylindrical arrangement of elongated merosporangia from the surface of the sporangium simulating "daisy petal". Tiny sporangiospores are aligned one after another in tandem within each merosporangium. Rhizoids are not produced. Mucor species microscopic mounts also reveal a spherical, smooth-walled sporangium at the end of a conidiophore with a bulbous end rather than a funnel like expansion. Sporangiospores are contained within the sporangium and develop a yellow-brown pigmentation that is observed within the mycelium of the colony. Rhizoids are not produced.

The bacterial species growing on the surface of the MacConkey agar plate shown in this photograph, a coccobacillary non-fermenter and a common cause of nosocomial hospital-acquired pneumonia, can be presumptively identified as: - Acinetobacter baumannii - Burkholderia cepacia - Moraxella catarrhalis - Neisseria lactamica

- Acinetobacter baumannii Acinetobacter baumannii is a non-lactose fermenting gram-negative coccobacillus that produces a pigment causing colonies on MacConkey agar to have a purplish hue. This organism has emerged as one of the most frequent causes of hospital-acquired pneumonia. Burkholderia cepacia can cause pulmonary infections, particularly in patients with cystic fibrosis; however, the organism is a bacillus and not a coccobacillus and does not produce a purplish hue when grown on MacConkey agar. Moraxella catarrhalis is a diplococcus that resembles Acinetobacter baumannii on gram stain. It has been the cause of respiratory infections in patients with chronic obstructive pulmonary disease or chronic bronchitis. However, the organism does not grow on MacConkey agar and the infections are usually not considered to be hospital-acquired. Neisseria lactamica is a gram-negative diplococcus that does not grow on MacConkey agar. It is not associated with respiratory infections and it is not associated with hospital-acquired infections.

The growth on a blood agar plate as illustrated in the photograph was prepared from the surface drainage of a subcutaneous abscess of a 50-year-old man following a deep penetrating splinter wound. The colonies on this young culture are small, rough, gray-white, and non-hemolytic. Older larger colonies became sunken centrally having a "molar tooth" appearance. The Gram stain reveals gram-positive branching filaments. Key biochemical reactions include hydrolysis of Esculin, nitrate reduction, and negative catalase. From these observations, select from the multiple choices the identification of this isolate: - Bifidobacterium species - Cutibacterium (Propionibacterium) species - Actinomyces israeli - Clostridium septicum

- Actinomyces israeli Actinomyces israeli is the correct response. Colonies on anaerobic blood agar are entire, gray-white and sunken centrally when mature, resembling a "molar tooth". The Gram stain observation of thin, gram-positive slender filaments with extensive branching provides for a presumptive identification of Actinomyces israeli. Additional biochemical reactions including the demonstration of the hydrolysis of esculin and reduction of nitrates provide for a more definitive identification. Bifidobacterium species colonies growing on blood agar, although not species specific, differ from those of Actinomyces israeli by being smooth and convex without central "molar tooth" depression and with a gray-white to light yellow pigmentation. Distinctive is the gram stain appearance of slender but not filamentous gram positive bacilli with extensive branching and distinctive terminal protuberances that simulate "dog bones". Most species are biochemically inactive including negative reactions for esculin hydrolysis and nitrate reduction. Cutibacterium (Propionibacterium) species colonies on anaerobic blood agar are relatively small, circular, convex, gray-white and smooth without central "molar tooth" depressions. Short coccobacilli arranged singly, in short chains and more distinctly in diphtheroidal clusters differing from the long, branching slender bacilli of Actinomyces Israeli. Reactions for esculin hydrolysis and nitrate reduction are negative. Clostridium septicum colonies on anaerobic blood agar are flat, semi-translucent and spreading, with an outer zone of beta hemolysis. Short gram positive bacilli with sub-terminal spores rather than long, branching filaments are observed on gram stain. The nitrate reaction is negative; esculin hydrolysis activity varies with different strains. As C. septicum has high association with cancer of colon and leukemia, colonoscopy and bone marrow examination are recommended when recovered in positive blood cultures.

The organism depicted in the image to the right is found as normal flora of the mouth, GI, and genital tracts; it is known to cause a chronic disease that exhibits abscesses, tissue fibrosis, and draining sinuses. What is the name of this chronic disease? - Nocardiosis - Sporotrichosis - Borreliosis - Actinomycosis

- Actinomycosis The correct answer is actinomycosis. Actinomyces spp. is a Gram positive non-spore forming bacilli. It is found as normal flora in the mouth, GI, and genital tracts. Actinomycosis is the term for chronic diseases caused by Actinomyces spp. There are thoracic, abdominopelvic, and central nervous system forms of the disease, but the most common type involves the face and neck. Nocardiosis is caused by Nocardia spp. which are ubiquitous in the environment with over 30 species characterized as causing human disease. The Gram stain observed would be similar, but the site and type of infection is not typical of Nocardia spp. Sporotrichosis is the most common cause of nodular lymphangitis and is caused by Sporothrix spp. In the image to the right, branching Gram positive rods are observed, not fungal elements. Borreliosis does not exhibit the chronic disease discussed above and does not exhibit branching Gram positive rods, instead it is a spirochete.

The clinical Gram stain taken from an endocervix revealed many WBC's with both intracellular and extracellular gram-negative diplococci. The specimen was plated onto a Modified Thayer-Martin plate and incubated. Following incubation, colonies resembling Neisseria gonorrhoeae were inoculated into separate CTA tubes containing glucose, lactose, sucrose and maltose. The fluorescent monoclonal antibody test was positive as well as the CTA maltose and glucose tubes. What is the most appropriate next step? - Issue a final report of Neisseria meningitidis - Issue a final report of Neisseria gonorrhoeae - Analyze another maltose tube using a known strain of Neisseria gonorrhoeae - Request a new specimen

- Analyze another maltose tube using a known strain of Neisseria gonorrhoeae Typically, Neisseria gonorrhoeae will oxidize glucose, but not maltose. In this case, another maltose tube should be checked by running a "control" of a known Neisseria gonorrhoeae to ensure that the test process is functioning accurately. This is a great example of analyzing the entire situation, and using your Medical Laboratory Science training to make sure the results make sense.

The colonies illustrated in the upper photograph were recovered from the aspiration of nasal secretion from a patient with acute sinusitis. The 48 hour colonies on blood agar are relatively small, entire, white, and non-hemolytic. Colonies growing on chocolate agar are also small, smooth and entire with a light yellow pigmentation. On Gram stain, pale-staining, Gram negative coccobacilli are observed, with a tendency to form long, narrow filaments. The lower photograph reveals tube reactions with a KIA: Acid/Acid and the oxidative utilization of several carbohydrates except xylose and mannose. Nitrate reduction is positive and ornithine and arginine decarboxylases are negative. From the observations, select from the multiple choices the genus/species name of this isolate. - Moraxella catarrhalis - Kingella kingae - Aggregatibacter aphrophilus - Eikenella corrodens

- Aggregatibacter aphrophilus Aggregatibacter aphrophilus is the correct response. Colonies growing on blood agar are small, entire, smooth, gray-white and non-hemolytic. Colonies growing on chocolate agar are also small, smooth, and entire with a light yellow pigmentation. On Gram stain, pale-staining, Gram negative cocco-bacilli are observed, with a tendency to sometimes form long, narrow filaments. A. aphrophilus is saccharolytic and acid is produced from many commonly tested carbohydrates, except xylose. Nitrates are reduced. Moraxella catarrhalis colonies are smooth and gray to white on blood and chocolate agars. The colony remains intact when pushed across the agar plate so is described as being like a "hockey puck." Short, more plump than filamentous, Gram negative bacilli and coccobacilli are observed on Gram stain. This organism does not utilize carbohydrates (asaccharolytic) but reduces nitrates. Kingella kingae forms large white to beige beta-hemolytic colonies on blood agar and may produce a yellow-brown pigment. Short, plump, Gram negative rods with square ends and in chains are observed on Gram stains, without the formation of filaments. K. kingae is asaccharolytic with the exception of the oxidative utilization of dextrose and maltose. Eikenella corrodens colonies grow more slowly and are nonhemolytic on blood agar and 45% of the colonies may distinctively pit or corrode the surface of the agar. A chlorine bleach like odor may be obvious. This organism does not utilize carbohydrates (asaccharolytic).

With regards to identifying resistance in Enterococcus species, all of the statements below are true, EXCEPT: - Both disk diffusion and broth microdilution tests should be incubated a full 24 hours to detect vancomycin resistance. - BHI agar with 6 µg/mL vancomycin can be employed as a screening methodology for vancomycin resistance. - All antibiotics on a gram-positive panel should be reported. - Methodologies employed should also address the detection of high level resistance to gentamicin and streptomycin.

- All antibiotics on a gram-positive panel should be reported. The correct answer is all antibiotics on a gram-positive panel should be reported. CLSI criteria for reporting antibiotics should be strictly adhered to. Since the enterococci possess many intrinsic resistance factors, there are many antibiotics that should not be included in the final report. CLSI provides the definitive guidelines for detection of resistance in Enterococci. BHI with 6 µg/mL vancomycin can be employed as a screening methodology for vancomycin resistance; the presence of >1 colony indicates the need for further testing to confirm potential resistance. All screening and susceptibility tests require a full 24 hours incubation. Since the standard approach for treating systemic infections with enterococci is a combination of a cell wall drug with an aminoglycoside, testing protocols should also address the detection of high level resistance to gentamicin and streptomycin.

The microscopic illustration demonstrates the golden-brown pigmented conidia and macroconidia of the following mold: - Cladophialophora - Alternaria - Bipolaris - Curvularia

- Alternaria Alternaria species are microscopically characterized by the muriform, elongated, and "drumstick' shaped macroconidia with longitudinal and horizontal septa. The macroconidia are connected together in chains with the blunt end of one conidium attached to the narrow end of another. Cladophialophora species are microscopically characterized by branching chains of blastoconidia at the end of long conidiophores. The connection between the blastoconidia exhibits prominent scars. The cell that produces the chains of conidia is referred to as a 'shield' cell due to their shape. The branching conidia are not readily visible on wet mount as they are easily dislodged during the preparation of the mount. Bipolaris species produce smooth-walled, oblong-shaped, multi-celled conidia with the individual cells surrounded and separated by a sac-like wall called a distosepta that is not part of the cell wall. The macroconidia are borne sympodially from bent, geniculate conidiophores. The macroconidia of Curvularia species have cells separated by true septa extending from the cell wall. The multi-celled, dark brown, macroconidia are slightly curved (bow- or boomerang-shaped) due to overgrowth of the central cells.

Illustrated in the upper image is a stained histological section of a bowel showing a heavy inflammatory reaction within which 10 - 12 µm spherical cysts are observed. The lower image is a close up view of one of the trophozoites from a smear preparation of the exudates. There is a distinctive central karyosome, even distribution of the ring of chromatin, and the finely granular cytoplasm. What disease can be presumptively reported? - Giardiasis - Balantidiasis - Amebiasis - Cysticercosis

- Amebiasis Amebiasis is the correct selection. In the upper image, the size of the spherical shaped parasitic forms can be estimated to be 10 - 12 µm in comparison with the 2 - 3 µm size of the background inflammatory cells. A close view of one of these forms is observed in the lower image. This can be recognized as a trophozoite of Entamoeba histolytica by the distinctive central karyosome, even distribution of the ring of chromatin, and the finely granular cytoplasm providing for a diagnosis of "amebiasis". Giardiasis - the invasive Giardia trophozoites are distinctly oval in shape and have a pair of nuclei on either side of a vertical axostyle, fitted with a central para-basal body. These features resemble a "monkey face". Balantidiasis - the trophozoites of Balantidium coli are kidney shaped and large, approaching 100 µm in diameter, and have a large central dumbbell-shaped nucleus. Cysticercosis - is an infection in which cysts are commonly found in the brain and lungs. Humans become infected after ingesting the ova of Taenia solium contained in contaminated food. Once in the intestine, the ova hatch into larvae that enter the circulation. Although the larvae then permeate fibrous tissue, they do not cause an inflammatory response. Once the larvae lodge in the brain, lungs, or other tissue, they develop into a cyst that transforms into an adult Taenia tapeworm as part of its life cycle.

A mucoid alpha hemolytic translucent colony suspected of being Streptococcus pneumoniae was isolated from a blood culture. All of the of the following are appropriate tests to make a presumptive or definitive identification of this organism EXCEPT? - Bile solubility test - Specific co-agglutination assay - Optochin susceptibiity - Bacitracin susceptibility

- Bacitracin susceptibility Bacitracin susceptibility testing is used for the presumptive identification of Streptococcus pyogenes, not for Streptococcus pneumoniae. The bile solubility test can be used in the presumptive identification of S. pneumoniae. It is positive while other alpha-hemolytic Streptococcus spp. are negative. This test detects the lysis of S. pneumoniae in the presence of bile salts. A Phadebact pneumococcus test is available for the identification of S. pneumoniae. It is a co-agglutination assay. Streptococcus pneumoniae is susceptible to optochin while other alpha hemolytic Streptococcus spp. are not.

The eggs of Necator americanus are basically indistinguishable from the eggs of: - Ancylostoma duodenale - Ascaris lumbricoides - Trichinella spiralis - Trichuris trichura

- Ancylostoma duodenale Necator and Ancylostoma are both commonly known as hookworms. The eggs are oval and thin-shelled with the developing embryo inside. Recovery of the adult worms, particularly the examination of the buccal capsules, is necessary to speciate these two organisms. Ascaris lumbricoides eggs are brown from bile, large, broadly oval, and mammillated. The mammilated layer causes the egg to appear 'lumpy'. Some eggs appear decorticated (lack the mammilated layer). Infertile eggs are typically more elongated and oval with a thinner cell wall and containing internal granules. Trichinella spiraliseggs are typically not observed in the stool sample. The egg is usually visible in an encysted form in the tissue. A tissue biopsy demonstrates the larvae inside giving a spiral appearance due to the histological cut of the cyst. Trichuris trichuraeggsare brown and barrel-shaped with hyaline polar plugs at each end. The infection is associated with poor hygiene. The severity of the disease is dependent on the worm load.

A tech receives a request for MRSA/MSSA colonization testing on a patient in the hospital. Which of the following is an appropriate area of the body for culture for screening? - Anterior nares - Stool - Urine - Sputum

- Anterior nares Most patients that are colonized with Staphylococcus aureus (MRSA or MSSA) carry this organism is the anterior nares. Treatment of this organism to remove the carrier state has been shown to greatly reduce nosocomial infections. Other sites that can be screened for colonization include groin, axilla, and external auditory canal. Stool is not an appropriate specimen for colonization of MRSA or MSSA. Stool is used for screening of other multiple drug resistant organisms such as VRE (vancomycin resistant Enterococci) or CRE (carbapenemase resistant Enterobacteriaceae). Urine and sputum are not typically used for colonization of organisms as the resistant organisms typically do not harbor in these areas.

In patients who present with a classic "strep throat", the beta-hemolytic, catalase negative, Gram positive bacillus that must be included in the differential diagnosis is: - Actinomyces species - Arcanobacterium haemolyticum - Listeria monocytogenes - Gardnerella vaginalis

- Arcanobacterium haemolyticum Several species of beta-hemolytic gram-positive bacilli, formerly included within the genus Corynebacterium, have been moved to other genera based on nucleic acid and other phenotypic studies. One of these, Arcanobacterium haemolyticum, can be confused with group A beta-hemolytic streptococci because it is beta hemolytic, catalase negative and can cause acute pharyngitis. This species should be considered when the colonial morphology, hemolytic reaction, biochemical and serological studies do not confirm an oropharyngeal isolate as a group A streptococcus. Actinomyces species is culturally and biochemically closely related to Arcanobacterium haemolyticum, however the former is not an agent of acute pharyngitis. Listeria monocytogenes is beta hemolytic; however, it is catalase positive. It is associated with meningitis and septicemia but it is not associated with pharyngitis. Gardnerella vaginalis is beta-hemolytic; however, it is hemolytic only on media containing human blood. It is associated with bacterial vaginosis but is not associated with pharyngitis.

What is this form, measuring 45 µm and found in stool? - Balantidium coli cyst - Ascaris lumbricoides egg - Schistosoma mansoni egg - Hymenolepis diminuta egg

- Ascaris lumbricoides egg This image shows a round egg with a distinct corticated outer shell, which is definitive for Ascaris lumbricoides. Balantidium coli cysts are round, but have a distinctive large, kidney-bean shaped macronucleus present in the cytoplasm. There can also be a visible micronucleus located adjacent to the macronucleus. Vacuoles can also be present. This image does not show a nucleus, so cysts and trophozoite forms can be ruled out. Schistosoma mansoni eggs can be distinguished by a large lateral spine present on the egg. They are also a much larger egg, ranging from 112 to 182 µm in size. Hymenolepis diminuta eggs do have a capsule around the embryo which can look similar to the Ascaris lumbricoides corticated shell, but Hymenolepis diminuta contains three pairs of hooks in the embryo that are distinguishable. Hymenolepis is also larger, typically 55 by 85 µm in size.

What is the phenotypic property of Saccharomyces yeast species that is helpful in establishing its species identification? - Polysaccharide capsule - Ascospore production - Trehalose assimilation - Slow growing yeast

- Ascospore production The identification of Saccharomyces species can be confirmed by looking for the formation of ascospores after incubation of a subculture on nutritionally poor ascospore agar. Torulopsis (Candida) glabrata has the unique characteristic of assimilating only glucose and trehalose. Cryptococcus species is characterized by the production of a thick, polysaccharide capsule. Saccharomyces species is a rapid growing yeast.

Which Aspergillus species show biseriate with phialides covering the entire surface of a spherical vesicle with black conidia as microscopic morphological features? - Aspergillus flavus - Aspergillus niger - Aspergillus fumigatus - Aspergillus terreus

- Aspergillus niger Aspergillus niger has these microscopic morphologic features: biseriate with phialides covering the entire surface of a spherical vesicle; conidia are black. Aspergillus flavus has these microscopic morphologic features: uniseriate or biseriate or both with phialides covering the entire surface of a spherical vesicle. Aspergillus fumigatus has these microscopic morphologic features: uniseriate heads with phialides covering the upper half to two thirds of the vesicle. Aspergillus terreus has these microscopic morphologic features: biseriate with phialides covering the entire surface of a hemispherical vesicle; aleurioconidia are formed on submerged hyphae.

What is the most likely identification of a rapidly growing hyaline mold that began as a white colony and later develops a black "pepper" effect on the agar surface? As the colony aged it produced jet black, powdery colonies which then caused it to resemble a dematiaceous mold. - Penicillium notatum - Aspergillus niger - Paecilomyces spp. - Scopulariopsis spp.

- Aspergillus niger Aspergillus niger is a rapidly growing hyaline mold that begins as a white colony and later develops a black "pepper" effect on the agar surface. Aspergillus species are opportunistic saprobes and may be fungal contaminants and are isolated from a variety of clinical specimens. A. niger may be pathogenic in the immunosuppressed populations, causing respiratory, skin and disseminated infections.Penicillium notatum is a rapidly growing hyaline mold that produces blue-green, velvety, powdery growth.Paecilomyces spp. grows rapidly within 3 days and produce colonies that are first white and later become yellow, yellow-green, tan, olive brown or pink to violet depending on the species.Scopulariopsis spp. grows at a moderate rate producing white, granular colonies that later become light brown or gray in color with a powdery texture.

Illustrated in the composite image on the left is a 72-hour growth on Sabouraud's dextrose agar of a finely granular, black pigmented colony obtained from a subcutaneous abscess at the site of an intravenous transfusion. The image to the right illustrates the microscopic appearance of a small inoculum taken from the surface of the center portion of the colony. A small spherical vesicle is surrounded by a row of phialides producing small, black-staining conidia. With these observations, select from the multiple choices the name of the fungus species as presented. - Aspergillus fumigatus - Aspergillus flavus - Aspergillus niger - Aspergillus terreus

- Aspergillus niger Aspergillus niger is the correct response, as indicated by the species name. Characteristic is the black, peppered portion of the central mature colony. The reverse of the colony is not pigmented ruling out one of the dematiaceous fungi. Microscopically, the conidiophore is long and narrow (arrow), terminating in a globose vesicle surrounded by a single row of phialides that give rise to aggregates of small, spherical black-staining conidia. Conidia may become roughened when colonies mature. Aspergillus fumigatus is characterized by blue-green pigmented colonies and a fruiting head consisting of a single row of bottle-shaped phialides over the top half of a dome-shaped vesicle, giving rise to chains of small, spherical conidia. Aspergillus flavus colonies are yellow-green and microscopically a single or double row of phialides cover the entire surface of a spherical vesicle, giving rise to short chains of spherical, yellow-orange elliptical or round conidia. Aspergillus terreus colonies are tan colonies that resemble cinnamon. Microscopically, the phialides cover the top half of a club-shaped to spherical vesicle, similarly to that of A. fumigatus, except they form a double row of shorter phialides that are arranged atop a club-shaped spherical vesicle from which straight chains of small, spherical conidia are produced.

The image on the right of a mold colony on an agar plate is most representative of which of the following molds? - Acremonium species - Microsporum canis - Scopulariopsis species - Aspergillus niger

- Aspergillus niger The colony that is represented in this image is Aspergillus niger. A mature colony has a "peppered "effect, due to the thick black conidia covering the surface. Acremonium species typically produce a smooth, pastel rose pigmented colony. The colony of Microsporum canis is usually cottony white with a lemon-yellow apron. Scopulariopsis species produce a buff-brown colony with distinctive radial rugae.

A farmer is diagnosed with a fungal respiratory infection. A fungal culture demonstrates rapid growth of a blue-green colony on fungal media. Microscopically, the organism demonstrated septate hyphae with long conidiophore ending in a dome-shaped vesicle. Long chains of conidia protrude from the vesicle as demonstrated in the illustration. The most likely identification is: - Penicillium species - Fusarium species - Aspergillus species - Geotrichum species

- Aspergillus species Aspergillus species are opportunistic molds that may be found as contaminates or may cause serious respiratory infections. One serious respiratory infection is called 'Farmers Lung' which is associated with inhaling spores from moldy hay. Aspergillus species grow rapidly on fungal media and demonstrate colonies of tan, black, yellow-green, or blue-green pigmentation. The conidiophores end in a swollen vesicle with chains of conidia extending from the vesicle. Penicillium species grow rapidly and produce a blue-green colony. The conidiophore ends in a branching structure called a penicillus that resembles a broom. Fusarium species grow rapidly producing pink, purple, or yellow fluffy colonies. The conidia are multi-celled and typically sickle-shaped. Geotrichum species produce white to cream colored yeast-like colonies or powdery molds. Microscopically, it produces barrel-shaped arthroconidia.

Illustrated in the upper left image of the composite photograph is a 3 day old colony with a central, granular yellow surface (resembling cinnamon) surrounded by a broad white apron. This colony was recovered from a fungus ball infection of the lung. The microscopic presentation of a methylene-blue stained mount of a sample from the surface of the colony is observed in the upper right and lower left images. In the lower right image taken of a direct mount of the colony showing vegetative hyphae. With these observations, select from the list of multiple choice responses the correct fungal species as presented. - Penicillium species - Aspergillus fumigatus - Paecilomyces species - Aspergillus terreus

- Aspergillus terreus Aspergillus terreus is the correct response. Distinctive is the yellow pigmentation of colonies with a granular surface. Observed microscopically is the arrangement of a double rather than a single row of phialides, derived from the surface of a club-shaped vesicle from which straight chains of small, spherical conidia are being produced. Also characteristic of A. terreus is the observation in a direct mount prepared from the colony showing vegetative hyphae with distinctive spherical micro-conidia produced along the outer margins. Aspergillus fumigatus colonies are blue-green, with the microscopic observation of a fruiting head that has only a single row of phialides placed over the top half of a club-shaped vesicle. Penicillium species colonies are also rapidly growing, and have a green granular surface. The conidia also are produced in chains but from an inner row of short branching metulae giving rise to the spore bearing finger like phialides that end in a flat surface. Paecilomyces species colonies have a light yellow-brown pastel pigmentation and microscopically are observed chains of irregular sized, uneven staining conidia that are produced from distinctly pointed phialides.

Which of the following organisms display the characteristic "Medusa head" on 5% sheep blood agar (SBA) after 18 hours of incubation at 35°C? - Yersinia pestis - Bacillus anthracis - Francisella tularensis - Brucella abortus

- Bacillus anthracis After 18 hours of incubation on SBA at 35°C, the slightly undulate margin of B. anthracis may show curling, displaying a so-called "Medusa head" appearance. This characteristic is also described as comma-shaped protrusions. Colonies have a ground glass appearance and are non-hemolytic, two characteristics that may also be used to differentiate B. anthracis from other Bacillus species. A distinguishing characteristic of Yersinia pestis is its preference and faster growth that occurs at 25°C. At 24 hours of incubation on SBA at 35°C, colonies are only pinpoint and translucent with a gray-white color. Colonies begin to demonstrate a "fried egg" morphology at 48 hours of incubation on SBA. F. tularensis can grow poorly or not at all on SBA, producing only tiny, pin-point, translucent colonies at best after 18-24 hours. This organism prefers cysteine-enriched media such as chocolate (CHOC), Thayer-Martin (TM), and buffered charcoal-yeast extract (BCYE). It would be difficult to see individual colonies on SBA growth that is less than 24 hours old. Although most isolates of Brucella abortus may grow on 5% sheep blood agar and chocolate agar, enriched agars and special incubation conditions are often required to achieve optimal growth. Colonies appear small and translucent after at least 48 hours of incubation.

Which of the following is MOST often determined to be the cause of sepsis? - Parasites - Bacteria - Fungal organisms - Viruses

- Bacteria The correct answer is bacteria. Bacteria are the most common cause of sepsis, but fungal organisms, viruses and parasites can also cause sepsis. Infection by any microorganism could potentially result in sepsis, if the immune system overreacts to the invader. However, bacterial organisms account for the majority of sepsis cases. Septicemia is the clinical syndrome characterized by fever, chills, malaise, tachycardia, and hyperventilation.

It is important to make a presumptive identification of the large, flat, spreading, gray-white, non-hemolytic colonies, with comma-like extensions growing on blood agar, as illustrated in the upper photograph. When mucoid colonies are observed, peak-like extensions may be observed when the colony is lifted with an inoculating loop (lower left image in the composite). Long, spore-bearing, Gram positive bacilli, often in straight and branching chains, are observed on Gram stain. Based on the results given, select the presumptive identification of this isolate. - Corynebacterium jeikeium - Bacillus anthracis - Lactobacillus species - Listeria monocytogenes

- Bacillus anthracis Bacillus anthracis is the correct response. It is important to immediately recognize the large, flat, spreading, non-hemolytic gray-yellow colonies on blood agar with a ground-glass surface and irregular margins with comma-shaped extensions. The presumptive identification of Bacillus anthracis is supported by the peak like extension from the tip of an inoculating wire and the long chains of elongated, spore-bearing gram positive bacilli arranged in long branching chains. With these observations, the culture should be immediately referred to the local state laboratory to confirm this anthrax-producing agent of bio-terrorism. Corynebacterium jeikeium colonies are small, 0.5 - 1.0 mm, gray white, without peripheral extensions and are non-hemolytic. Microscopically are observed short Gram-positive bacilli arranged in V-forms or palisades, never in chains. Spores are not produced. Lactobacillus species colonies on sheep blood agar after 24 hours incubation are small, gray white, convex, and smooth without peripheral extensions. Light alpha hemolysis may be observed. Microscopic examination of Gram stained mounts reveal long, slender, non-spore forming positive bacilli also arranged in chains. Listeria monocytogenes colonies growing on blood agar are small, smooth, gray-white, and surrounded by narrow zones of soft beta hemolysis. Microscopically are observed small non-spore forming gram-positive bacilli with rounded ends lying singly in loose diphtheroidal-like clusters. The CAMP test is positive but with rectangular external rather than inverse zones of hemolysis.

The well circumscribed, ulcerating pustule illustrated in the upper photograph evolved over 8 days following direct contact with raw animal hides that had been shipped from Central Asia. The lesion began as a small papule, which progressively enlarged, ultimately ulcerated and became covered centrally with a black eschar. The lower photomicrograph is a gram stain prepared from a colony that grew within 48 hours on blood agar. The most likely agent of this infection is: - Bacillus anthracis ("malignant pustule") - Erysipelothrix rhusiopathiae (erysipeloid) - Francisella tularensis - Streptococcus pyogenes (pyoderma)

- Bacillus anthracis ("malignant pustule") The photograph illustrates a "malignant pustule" characteristic of cutaneous anthrax infection. Such papules and pustules develop at the site of skin penetration of bacterial spores, most commonly found in wool, hair, hides and animal bones that are shipped from countries where the disease is endemic. The lower photograph demonstrates spore-forming, "boxcar-shaped" gram positive bacilli characteristic of Bacillus anthracis. Although a similar appearing pustule may be produced in some stage of evolution by each of the other bacterial species listed in this exercise, only B. anthracis produces bacterial cells with spores. F. tularensis, which causes tularemia (ulceroglandular in this instance) is a short, gram negative coccobacillus, E. rhusiopathiae, which causes erysipeloid, is a non-spore forming gram positive bacillus and Streptococcus pyogenes, which can be responsible for a number of skin infections, is a gram positive coccus in chains.

Which bacterial species is most likely represented by the spreading, gray-white, beta-hemolytic colonies with a "frosted glass" appearance as illustrated in the photograph? - Burkholderia pseudomallei - Listeria monocytogenes - Bacillus cereus - Streptomyces anulatus

- Bacillus cereus Bacillus cereus colonies are characteristically spreading, gray-white, and beta hemolytic, with a "frosted glass" appearance. Burkholderia pseudomallei also produces spreading colonies, but they are more wrinkled in appearance and without beta hemolysis. Listeria monocytogenes produces small, round, translucent colonies that characteristically have a narrow zone of beta hemolysis, noted if colonies are removed. The nocardioform bacteria, Streptomyces (formerly greseus) anulatus, produces opaque, chalky, white colonies. This species can also be suspected if the colonies have a pungent, musty basement odor.

The colonies seen growing on the surface of the blood agar plate shown in the upper photograph were recovered from a blood culture after 36 hours of aerobic incubation at 35° C. A Gram stain prepared from one of the colonies is shown in the lower photomicrograph. The most likely identification is: - Clostridium species - Listeria monocytogenes - Corynebacterium striatum - Bacillus circulans

- Bacillus circulans Bacillus circulans is the correct answer. The colonies shown on the blood agar plate are gray, semitransparent, spreading and have a distinctly mucoid appearance. Without the Gram stain, Gram negative species such as Klebsiella pneumoniae or Pseudomonas aeruginosa might be suspected. However, the Gram stain reveals short, Gram positive bacilli, many cells of which include a subterminal spherical spore that expands the cell wall (examples shown by blue arrows). Bacillus circulans has the ability to grow both aerobically and anaerobically. Clostridium species is incorrect. As a genus, Clostridium species are Gram positive rods that characteristically produces spores; however, only on anaerobic incubation. Listeria monocytogenes is incorrect. Listeria monocytogenes is a Gram positive, non-spore forming coccobacillus. This species can be beta-hemolytic and can be easily misidentified as Group B streptococci (Streptococcus agalactiae) upon visual inspection; however, Listeria is catalase positive whereas Group B streptococcus is catalase negative. Listeria can grow at room temperature and produce tumbling motility in motility agar. Corynebacterium striatum is incorrect. Corynebacterium striatum is a Gram positive diptheroidal rod that presents a palisading arrangement on a Gram stain preparation. This species does not produce spores, which separates it from Clostridium and Bacillus species and is esculin negative, which separates this species from Listeria.

Which of the following is considered a normal skin flora organism? - Bacillus subtilis - Salmonella typhi - Bacillus anthracis - Pseudomonas aeruginosa

- Bacillus subtilis Bacillus subtilis is the correct answer because this organism can be found on the skin and is commonly considered a skin contaminant in blood cultures. Salmonella typhi is incorrect because this organism is a gastrointestinal pathogen and is not found as part of the normal skin flora. However, sometimes this organism has been found in blood cultures when a patient has an extraintestinal infection. Bacillus anthracis is incorrect because this organism is always considered a pathogen and has been used as a bioterrorist agent. This organism can cause cutaneous, pulmonary, or gastrointestinal anthrax. Pseudomonas aeruginosa is incorrect because this organism is an environmental organism and is typically found in wet or damp environments. This organism commonly causes respiratory, ear, and eye infections.

An abdominal wound culture grows E. coli on the aerobic culture. The anaerobic culture has growth of two, gram- negative rods, one of which is aerobic. The other gram negative rod has 2+ growth on BBE plate and is resistant to kanamycin, colistin, and vancomycin disc. What is this organism's identification? - Veillonella - Prevotella intermedia - Bacteroides fragilis group - Fusobacterium necrophorum

- Bacteroides fragilis group Bacteroides Bile Esculin Agar (BBE) is an enriched selective and differential medium for the isolation and presumptive identification of obligate anaerobic, gram-negative bacilli of the Bacteroides fragilis group. BBE contains gentamicin at a concentration which inhibits most facultative anaerobes. Bacteroides fragilis group are resistant to kanamycin and vancomycin and colistin. Veillonella is susceptible to kanamycin and colistin, but resistant to vancomycin. Prevotella intermedia is resistant to kanamycin and vancomycin, but susceptible to colistin. Fusobacterium necrophorum is susceptible to kanamycin and colistin, but resistant to vancomycin.

Aspiration material recovered from a ruptured appendix abscess was inoculated to anaerobic culture media per laboratory protocol. Gray colonies (> 1 mm) grew anaerobically in 24 hours on BBE agar, blackening the media. The photograph illustrates the gram stain features of the organism. The bacterial species most likely associated with the abscess is: - Bacteroides fragilis group - Fusobacterium nucleatum - Porphyromonas species - Prevotella species

- Bacteroides fragilis group Bacteroides fragilis group are anaerobes most commonly recovered from human infections, and commonly associated with parappendiceal abscesses. This organism group grows readily on Bacteroides Bile Esculin (BBE) agar in an anaerobic atmosphere and produces gram negative bacilli with rounded ends, as seen in the photograph. Fusobacterium nucleatum can also be associated with intra-abdominal cavity abscesses; however, the bacterial cells are slender and tapered and growth is inhibited by 20% bile, and esculin is not produced. Characteristic of the Bacteroides fragilis group is the ability to grow in 20% bile and to hydrolyze esculin, two key characteristics that separate the B. fragilis group from Prevotella species and Porphyromonas species, which are negative for both.

Which microscopic, intestinal parasite is the only ciliate that is pathogenic for humans? - Giardia duodenalis - Balantidium coli - Blastocystis hominis - Cystoisosospora belli

- Balantidium coli Of all the parasites listed, Balantidium coli is a ciliate transmitted through the fecal-oral route, with pigs as a host. Balantidium coli has two life stages, the infective cyst, and the trophozoite. Many cases of infection with Balantidium coli are asymptomatic. Giardia duodenalis is the most common intestinal protozoan reported in the U.S. It causes traveler's diarrhea, or "beaver fever." Cysts are the infective form, and transmission occurs most often through contaminated water. The classification and life cycle of Blastocystis hominis is currently unresolved, although it has been associated with cases of diarrhea. Cysts are the infective stage, with transmission occurring as cysts are ingested. Cystoisospora belli is considered a coccidian intestinal opportunistic pathogen, as many cases are asymptomatic. Transmission occurs through ingestion of oocysts.

Which of the following protozoa is the largest? - Entamoeba histolytica trophozoite - Endolimax nana trophozoite - Iodamoeba butschlii trophozoite - Balantidium coli trophozoite

- Balantidium coli trophozoite The correct answer is Balantidium coli trophozoite. Balantidium coli trophozoites can be up to 100 µm. It is the only member of the ciliates known to cause disease in humans. It is found worldwide, but most reports of infection come from Latin America, the Far East and New Guinea.Entamoeba histolytica trophozoites range from 12 - 40 µm. It is known to cause amebic dysentery and is transmitted via fecal-oral route. Iodamoeba butschlii trophozoites range from 6-25 µm. These protozoa are not considered pathogenic by the CDC, but are necessary to identify in order to differentiate from protozoa that are pathogenic.Endolimax nana trophozoites range from 5-8 µm. These protozoa are also not considered to be pathogenic by the CDC.

The following is the term used to describe the total clearing of the agar surrounding colonies on a blood agar plate as seen in this illustration: - Alpha Hemolysis - Beta Hemolysis - Gamma hemolysis - Satellite formation

- Beta Hemolysis The blood agar plate in the illustration is showing beta-hemolytic bacterial growth. Beta hemolysis is the clear zone that surrounds the bacterial colonies in which the red blood cells have been lysed. This phenomenon is associated with some forms of Streptococcus that produce streptolysin; an enzyme produced by the bacteria which causes the complete lysis of red blood cells. Alpha hemolysis is the partial lysis of red blood cells in blood agar that results in a greenish discoloration around the colony. Streptococcus pneumoniae and the viridans streptococci are examples of two organisms that produce alpha hemolysis. No change to the agar surrounding a colony on blood agar is referred to as gamma hemolysis. The coagulase-negative staphylococci are an example of gamma hemolytic organisms. Haemophilus species require X and V factors for growth.Haemophilus species will form tiny colonies when grow in close proximity to organisms that produce NAD (or V factor) such as Staphylococcus aureus. This phenomenon is referred to as satellitism.

Which culture medium is specifically formulated to recover Salmonella typhi from stool specimens? - Selenite broth - Bismuth sulfite agar - Salmonella/Shigella (SS) agar - Deoxycholate citrate agar

- Bismuth sulfite agar The correct answer is bismuth sulfite agar. Bismuth sulfite agar is a peptone enriched agar that contains bismuth sulfite and brilliant green which serve as inhibitors of most enteric bacteria except Salmonella typhi, and other salmonellae. Selenite broth is used to inhibit the growth of E.coli and other coliform bacilli, but it must be subcultured to another media, commonly bismuth sulfite agar. SS agar is selective for Salmonella and Shigella. Deoxycholate citrate agar is selective for Salmonella paratyphi.

The black colonies growing on the surface of this cystine-tellurite agar plate, with dark brown halos surrounding the colonies, is one of the characteristics of: - Bordetella pertussis - Bordetella parapertussis - Legionella pneumophila - Corynebacterium diphtheriae

- Corynebacterium diphtheriae Cystine-tellurite or Tinsdale agar is used for the isolation of Corynebacterium diphtheriae. Corynebacteria colonies are black due to reduction of tellurite. Further differentiation may be made from observation of brown halos surrounding the black colonies, a result of cystinase activity. In addition to Corynebacterium diphtheriae, cystinase activity is also characteristic of C. ulcerans and C. pseudotuberculosis. Isolation of Bordetella pertussis and Bordetella parapertussis may be achieved with selective enrichment medium such as Bordet-Gengou or Regan-Lowe. Isolation of Legionella pneumophila may be achieved using buffered charcoal yeast extract (BCYE) with L-cysteine.

Yeast colonies, as illustrated in the top image, can be cultured in the mycology laboratory either by transferring samples from growing colonies to enriched agar incubated at 35o - 37o C, or by setting up a second culture for incubation at the elevated temperature. The yeast colonies appear smooth and pasty, off-white pigmentation. The species identification is made by observing the morphology of a yeast cell as observed in lactophenol blue-stained mounts as shown in the bottom image. With these observations, select the correct presumptive identification of this isolate from the choices listed below. - Coccidioides immitis - Histoplasma capsulatum - Blastomyces dermatitidis - Paracoccidioides brasiliensis

- Blastomyces dermatitidis Blastomyces dermatitidis is the correct response. The yeast colonies are not distinctive and microscopic evaluation is required. Illustrated in the image is a high power view of large spherical yeast cell (10 - 15 µm), one with a budding daughter cell that demonstrates the distinctive broad-base attachment. These broad-based budding yeast forms may also be observed in tissue sections often associated with either an acute or chronic granulomatous inflammatory response. Coccidioides immitis is excluded as a yeast form in culture is never produced. Histoplasma capsulatum produces small 2- 4 µm in diameter yeast cells, often in loose clusters. Distinctive cells that individually produce a bud connected by a narrow filament are noted. When seen in tissue sections, small spherical yeast cells appear as a small capsule with a central nucleus surrounded by a clear halo. Paracoccidioides brasiliensis yeast forms are distinctive for the production of multiple small, spherical, narrow-neck buds encircling a central spherical yeast cell, in contrast to the single broad-based buds of the yeast cells of Blastomyces dermatitidis.

Identify the species of dimorphic fungi in its yeast form as observed under the microscope in this image. - Blastomyces dermatitidis - Paracoccidioides brasiliensis - Sporothrix schenckii - Coccidioides immitis

- Blastomyces dermatitidis The yeast form of Blastomyces dermatitidis is a thick-walled yeast cell, measuring 8-15 µm in diameter, that characteristically produces a single bud attached by a broad base. Paracoccidioides brasiliensis produces large yeast cells, approximately 15-30 µm in diameter, with multiple buds attached by narrow necks, giving the appearance of a "mariner's wheel." The yeast forms of Sporothrix schenckii are elongated cells that have been called "cigar bodies." Coccidioides immitis does not produce a yeast form in laboratory culture; rather, is identified in stained tissue sections by the production of varying sized spherules, ranging from 30-60 µm in diameter at maturity. The larger, more mature spherules may contain spherical endospores, making identification from direct examination difficult, as Coccidioides species may resemble other dimorphic fungi.

Which of these methods are used to identify prior exposure to Mycobacterium tuberculosis? - Gram stain - White blood cell count - Blood tests known as interferon-gamma release assays. - Any of the above tests can be used to identify prior exposure to Mycobacterium tuberculosis.

- Blood tests known as interferon-gamma release assays. The tuberculin skin test (TST) is traditionally used for the identification of prior exposure to Mycobacterium tuberculosis. Blood tests, collectively known as interferon-gamma release assays (IGRA), may also be used to identify prior exposure, or latent tuberculosis infection (LTBI). This test is also known as the QuantiFERON-TB Gold (QFT-G). A Gram stain is not effective for detecting M. tuberculosis in specimens. A white blood cell count would not provide specific information related to prior M. tuberculosis exposure.

The parasite Endolimax nana trophozoite shows what type of nuclear appearance? - Blot-like karyosome, no peripheral chromatin - Central karyosome, even peripheral chromatin - Large karyosome, no peripheral chromatin - Eccentric karyosome, uneven peripheral chromatin

- Blot-like karyosome, no peripheral chromatin The nuclear appearance of Endolimax nana trophozoite has a blot-like karyosome but lacks peripheral chromatin. As examples, an Entamoeba hartmanii cyst has a central karyosome with even peripheral chromatin; an Endolimax nana cyst posses a large karyosome with no peripheral chromatin and Entamoeba coli trophozoites, is a parasite with eccentric karyosome and uneven peripheral chromatin.

Which of the following growth factor(s) is necessary for the proper culture of Haemophilus influenzae? - X factor - V factor - Hemoglobin - Both X and V factors

- Both X and V factors Haemophilus species are small, nonmotile, gram-negative bacilli that are facultative anaerobes requiring a 5-7% CO2 enriched environment for growth. They typically grow on chocolate agar as smooth flat or convex, buff or slightly yellow colonies. Both X factor (hemin), and V factor (nicotinamide adenine nucleotide), are usually required for the in vitro growth of Haemophilus influenzae.

A cancer patient was admitted to the hospital with fever, tachycardia, and a drop in blood pressure. Due to the patient being treated for cancer, her chemotherapy had been administrated through an intravenous catheter. To rule out a catheter-related infection, the physician ordered two sets of blood cultures with one set being collected from the catheter site and the second set being collected by venipuncture. After 48 hours, the patient had positive blood cultures that grew Staphylococcus epidermidis. How will the physician know if the Staphylococcus epidermidis present is due to an infected catheter or is a contaminant? - Both blood culture sets (catheter and venipuncture) must have no growth - The blood culture collected via venipuncture will be positive while the blood culture collected via catheter will be negative - The blood culture collected via venipuncture must always be negative - Both blood culture sets (catheter and venipuncture) will be positive

- Both blood culture sets (catheter and venipuncture) will be positive Both blood culture sets (catheter and venipuncture) will be positive is the correct answer. There are two ways that catheter-related infections can be determined. One way is that more bacterial organisms can be seen in the intravenous catheter blood culture when compared to the venous blood culture specimen. A second way is the time of positivity. For instance, if the time between a positive catheter blood culture and a positive venous blood culture is greater than 2 hours, this indicates a probable catheter-related infection. Staphylococcus epidermidis is a normal skin flora organism; however, in immunocompromised patients, this organism can cause a bacteremia associated with indwelling vascular catheters. Both blood culture sets (catheter and venipuncture) must have no growth is incorrect because if no organisms grew out of the blood cultures then how could a Staphylococcus epidermidis be isolated. This does not support the scenario described. In addition, one would expect based on the patient's symptoms, an organism would grow. The blood culture collected via venipuncture will be positive while the blood culture collected via catheter will be negative is incorrect because this would indicate that the Staphylococcus epidermidis that grew was skin contamination resulting from inadequate cleansing of the skin prior to blood culture collection. The blood culture collected via venipuncture must always be negative is incorrect because in some instances the blood culture collected by venipuncture will grow an organism, especially if the patient has an overwhelming bacteremia.

Smears that are appropriately stained using acridine orange should be examined using which of the following? - Bright field microscopy - Polarizing microscopy - Ultraviolet microscopy - Phase contrast microscopy

- Ultraviolet microscopy The correct answer is ultraviolet microscopy. Once stained slides are dried, they are examined with a microscope that is equipped with an ultraviolet light source. Due to the nature of the stain, organisms would not be visible with the other options listed.

All of the following are commercial methodologies that Chlamydia and Neisseria identification have been based on, EXCEPT? - Ligase chain reaction - Hybrid capture - Branched chain DNA technology - Strand displacement amplification

- Branched chain DNA technology Branched chain DNA technology was utilized by Bayer Versant for their human immunodeficiency virus (HIV), hepatitis B virus (HBV), and hepatitis C virus (HCV) viral load assays. The assay is a signal amplification technique used for viruses. Target probes attach to preamplifier probes and target nucleic acids. The probes then bind to label probes with an alkaline phosphatase. A substrate is added that amplifies a signal. Ligase chain reaction (Abbott LCX®), hybrid capture (Digene), and strand displacement amplification (Becton Dickenson Probe Tec™) are all examples of commercial assays that were introduced for the detection of Chlamydia and Neisseria. Ligase chain reaction uses a thermostable ligase that binds probes together which are amplified for detection. Hybrid capture uses RNA probes that attach to target DNA. This complex is then fixed to a solid capture antibody and a substrate is added for detection. Strand displacement amplification is an isothermal nucleic acid amplification technique.

This parasite is found in blood, is sheathed, and measures 200 µm. From the parasites listed, what is the correct identification? - Brugia malayi microfilaria - Loa loa microfilaria - Wuchereria bancrofti microfilaria - Onchocerca volvulus microfilaria

- Brugia malayi microfilaria The correct answer is Brugia malayi. B. malayi ranges in length from 200-280 µm and is typically found in blood. They possess a sheath, rounded anterior end, and numerous nuclei. The two distinct nuclei present in the tip of the tail, distinguishes this organism from other microfilariae. These two nuclei are separated and distinct from the other nuclei present in the body of the organism. Loa loa is also sheathed but typically 248-300 µm in length. Loa loa can also be found in the blood but not until years after initial infection. The organism resides in the subcutaneous tissue after initial infection by the bite of an infected Chrysops fly. The differentiating characteristic is the nuclei in the tip of the tail. Loa loa have nuclei that are continuous and fill the tip of the tail. Wuchereria bancrofti is also sheathed but typically measures 240-300 µm in length. W. bancrofti has an anterior end is blunt and round. The tip of the tail is free of nuclei, which differentiates it from the other microfilariae. Onchocerca volvulus ranges in length from 150-355 µm. The main characteristic that differentiates this organism is that it does not contain a sheath. The body contains numerous nuclei that extend almost down to the entire tip. This organism is also only found in subcutaneous tissue, it is not found in blood smears.

The following statement is true regarding hospital-associated methicillin-resistant Staphylococcus aureus (HA-MRSA) and community-associated MRSA (CA-MRSA)? - Resistance is conferred by the mecA gene for only the HA strains. - CA strains tend to demonstrate resistance to more drug classes than HA strains. - CA strains tend to be associated with the PVL gene and skin and soft tissue infections. - HA Strains are typically more susceptible to the non-beta-lactam antibiotics.

- CA strains tend to be associated with the PVL gene and skin and soft tissue infections. PBP2a, which has a reduced binding affinity for beta-lactams, and remains active in cell wall synthesis even in the presence of beta-lactam antibiotics, is coded by the mecA gene. Both HA and CA strains of MRSA possess the mecA gene, although CA strains typically possess a smaller variant of that gene. CA strains are also associated with the PVL gene, which codes for enzymes that produce tissue necrosis and leukocyte destruction. The mecA gene confers resistance to both the HA and CA strains of MRSA. HA strains of MRSA are typically more resistant to a wide range of antibiotics compared to the CA strains. CA Strains are typically more susceptible to the non-beta-lactam antibiotics.

Any media that supports the growth of Staphylococcus aureus can be used to recover Methicillin-Resistant Staphylococcus aureus (MRSA). However, to improve the recovery of MRSA, selective media for MRSA will provide the best sensitivity. Which of the following media is most helpful in recovering MRSA from surveillance cultures? - Columbia-Colistin Nalidixic Acid (CNA) media - Sheep Blood Agar - Mannitol-salt agar - CHROMagar MRSA agar

- CHROMagar MRSA agar CHROMagar MRSA agar is the correct answer as this media can be used to distinguish Methicillin-Sensitive Staphylococcus aureus and coagulase negative staphylococci from Methicillin-Resistant Staphylococcus aureus by the addition of oxacillin or cephamycins. In addition, each organism will produce a different color. MRSA will be detected by a mauve coloration of the bacterial colonies. Columbia-Colistin Nalidixic Acid (CNA) media is incorrect because this media is a selective agar used to isolate Gram positive cocci from Gram negative rods. This media is not a differential media and cannot be used to identify Gram positive organisms to the species level. Sheep Blood Agar is incorrect because this media is not selective or differential because it supports the growth of both Gram positive and Gram negative organisms. This media supports the growth of both methicillin-sensitive and methicillin-resistant Staphylococcus aureus, but does not differentiate. Mannitol-salt agar is incorrect. Mannitol-salt agar can support the growth of Methicillin-Sensitive and Methicillin- Resistant Staphylococcus aureus; however, the only way that this media can differentiate between the two is if oxacillin or cefoxitin is added to the media for MRSA selectivity.

The recovery of this bacterial species from diarrhea stool specimens requires the use of selective culture media such as Butzler selective media or Skirrow blood agar incubated at 42° C in an atmosphere of 5% oxygen, 10% CO2, and 85% nitrogen. Growth on Skirrow blood agar as illustrated in the upper image are confluent smooth non-hemolytic colonies growing along the streak line with lateral extensions (arrows). Slender, long branching, S-shaped Gram negative rods are observed on Gram stain, as observed in the lower image. Positive reactions for oxidase, indoxyl, and hippurate provide for a more definitive identification. With these observations, select the name of this isolate. - Campylobacter coli - Campylobacter jejuni - Helicobacter cinaedi - Cardiobacterium hominis

- Campylobacter jejuni Campylobacter jejuni is the correct response. Obviously, in order to set up stool cultures on selective Campy culture media, the laboratory needs to be alerted that the specimen had been collected from a person with bloody diarrhea, particularly from those patients associated with house pets or involved in raising turkeys or chickens in which C. jejuni is endemic. Campylobacter species can be suspected by observing the smooth, non-hemolytic spreading colonies along the streak lines. Curved, spiral, or S-shaped, Gram negative bacilli microscopically observed in Gram stains support this presumptive identification. Positive indoxyl and hippurate reactions provide for a more definitive identification. Campylobacter coli colonies on blood agar are also large and spreading. The curved, spiral and S-shaped Gram negative bacilli characteristic of the genus are also observed. Distinctive for C. coli is the negative reactions for indoxyl and hippurate. Helicobacter cinaedi colonies are small, gray and translucent, and slowly growing. Small spiral and curved Gram negative bacilli may also be observed in Gram stains. Oxidase and, catalase, reactions are positive; indoxyl and hippurate reactions are negative. Cardiobacterium hominis on blood agar are small, clear, smooth and non-spreading. Slender, Gram variable bacilli are observed on Gram stains, with a distinctive tendency to form rosette clusters. Acid is produced from most carbohydrates, indole is strongly positive; reactions for indoxyl and hippurate are negative.

The following statements regarding automated identification systems are correct EXCEPT: - May misidentify the biological threat agents - Designed to identify rapidly growing microorganisms - Likely to produce aerosols during set-up - Can reliably identify Francisella tularensis

- Can reliably identify Francisella tularensis Francisella tularensis is often incorrectly identified on commercial identification systems. These systems may key out as Pasturella multocida. Automated systems should not be relied upon to identify this organism. Manufacturers of automated identification systems have included biothreat level A organisms in the system databases, however, the identification of these rarely identified organisms can be inaccurate and should not be relied upon. This is in part due to the limited number of strains in the databases. Also, the systems are designed to identify rapidly growing microorganisms. The systems work well on those organisms that grow rapidly. Many of the bioterrorism related organisms are slower growing therefore the systems do not accurately identify them. It is important to note that automated systems can create aerosols during the inoculation and reading phases adding to the possibility of laboratory exposure. All potential biothreat level A organisms should be worked within biological safety cabinets.

This photomicrograph was prepared from tease mounts of 3 day-old smooth, white yeast colonies obtained from an aspirate of nasal fluid of a middle aged patient with sinusitis. Note the clusters of small blastoconidia along the pseudohyphae and also the larger spherical chlamydospores (arrow), as observed in the right lower corner. From the multiple choices below, select the identification of this yeast isolate. - Candida glabrata - Candida tropicalis - Candida albicans - Candida parapsilosis

- Candida albicans Candida albicans is the correct response. Distinctive for Candida albicans is production of blastoconidia that are arranged in evenly distributed clusters along the pseudo-hyphae and the distinctive relatively large, spherical chlamydospores also arranged in clusters. When obtained from clinical specimens, accurate identification of this yeast is indicated as specific therapy will be required. Candida glabrata also produces pseudohyhae; however, uniform, small, regular sized cells arranged in relatively tight clusters are observed microscopically. The large, spherical chlamydospores and clusters of blastoconidia arranged in small clusters evenly distributed along the pseudohyphae, characteristic of C. albicans, are not produced by C. glabrata. Candida tropicalis produces delicate pseudohyphae from which blastoconidia are borne either singly or in small irregular sized clusters at points of constriction. Large spherical chlamydospores are not produced. Candida parapsilosis produces a radial arrangement of delicate conidiophores from which tiny dispersed conidia are produced, colloquially referred to as "sagebrush" or "cross matchstick" patterns. Large spherical chlamydospores are not produced.

A fusiform-shaped, Gram negative, oxidase negative bacillus that produces colonies with marginal finger-like projections was recovered from the oral cavity of a patient with periodontal disease. The most likely identification is: - Capnocytophaga canimorsus - Capnocytophaga ochracea - Actinobacillus actinomycetemcomitans - Eikenella corrodens

- Capnocytophaga ochracea Capnocytophaga ochracea, a commensal organism within the oral cavity of humans, may produce a variety of aminopeptidases, neuraminidases, and products that have direct toxic effects on neutrophils resulting in degradation of subgingival and periodontal tissue leading to periodontal disease. The fingerlike projections emanating from the colonies is known as "gliding motility", an additional factor that permits the organism to penetrate deeply into gingival fissures. Capnocytophaga canimorsus has a similar appearance to C. ochracea to culture; however, is indigenous in the oral cavity of dogs and causes human dog bite infections but not oral disease. Actinobacillus actinomycetemcomitans can also cause periodontal disease; however, the bacterial cells are not fusiform and the colonies do not produce gliding motility. Eikenella corrodens also inhabits the oral cavity of humans, but has none of the characteristics for C. ochracea as previously described.

Which Gram negative organism can produce "gliding motility" on agar plates and is a primary cause of juvenile periodontitis? - Eikenella corrodens - Aggregatibacter actinomycetemcomitans - Capnocytophaga ochracea - Fusobacterium nucleatum

- Capnocytophaga ochracea The association of children, teeth and "gliding" (referring to the unique motility seen on agar plates) all point to Capnocytophaga ochracea, one of the primary causes of localized juvenile periodontitis, an aggressive dental disease that leads to destruction of teeth and the underlying alveolar bone. A variety of factors lead to this progressive disease, including the production of substances that inhibit neutrophil function, proteolytic enzymes and penetration of the deeper tissues through its unique gliding motility. Aggregatibacter actinomycetemcomitans, formerly Actinobacillus actinomycetemcomitans, is also associated with periodontal disease; however, in the context of this exercise is ruled out because it does not demonstrate gliding motility. Eikenella corrodens is also an inhabitant of the oral cavity and produces colonies that pit the agar; however, has not been incriminated in dental disease and is not motile. Fusobacterium nucleatum is an anaerobe with Gram stain features similar to Capnocytophaga, but in contrast as the propensity, along with species of spirochetes, to cause gingivitis (trench mouth), but not periodontitis.

The isolate is represented by the slow growing small, gray-white, opaque and non-hemolytic colonies on blood agar. Short, gram-negative bacilli are, lying singly but also in the form of characteristic "rosette-like" clusters (arrows) are observed in the lower photomicrograph. As additional biochemical reactions necessary to confirm a presumptive identification, oxidase and indole reactions are positive; catalase, nitrate and urease reactions are negative. Based on these observations, select from the multiple choices the presumptive identification of this isolate. - Capnocytophaga canimorsus - Cardiobacterium hominis - Eikenella corrodens - Kingella kingae

- Cardiobacterium hominis Cardiobacterium hominis is the correct response. Growth is slow, and colonies are small and non-hemolytic on sheep blood culture media. A presumptive identification can be made based on the observation of variable staining cocco-bacilli that often line up in rosette-like clusters. More definitive identification can be made by demonstrating positive oxidase and indole reactions, and negative reactions for catalase, nitrate and urease. Acid is produced from most carbohydrates. Endogenous as normal flora in the upper respiratory tract uniquely causing secondary endocarditis in individuals with previously diseased or damaged heart valves secondary to previous heart valve replacement or from rheumatoid arthritis. Capnocytophaga canimorsus colonies grow poorly on sheep blood agar and are best observed on chocolate or trypticase soy agars. The colonies are indistinctively small, circular and smooth. Long, slender fusiform gram-negative bacilli are observed in gram stains and rosette formations are not observed. Most carbohydrates are fermented, and biochemical reactions are not distinctive. Important reactions include negative oxidase, negative indole and positive catalase. This isolate is typically recovered from a skin abscess at the site of a dog bite; or may be recovered from blood cultures in cases where the infection may spread. Eikenella corrodens colonies are distinctive for being rapidly growing and relatively large on both blood and chocolate agars. Unique is the pitting of the agar surrounding the colonies ("corrodens"), particularly on chocolate agar, with a light gray-white pigmentation of the adjacent agar. Gram stains reveal slender, straight gram negative bacilli with rounded ends. Rosette formations are not observed. Nitrate reduction reaction is positive. Acids are not produced from most carbohydrates; thus the organism is asaccharolytic. Kingella kingae colonies are also small and entire on blood agar, but are distinctive for soft beta hemolysis. Short, plump gram negative coccobacilli are observed in gram stains, without the formation of rosette clusters. K. kingae is non-saccharolytic with the exception of the oxidative utilization of dextrose and maltose. The positive oxidase and negative catalase reactions are non discriminatory from C. hominis. Found as normal flora in the upper respiratory tract, particularly of children, causing a variety of infections in the pediatric population.

Adult intestinal roundworms are equipped with this structure that serves as a protective outer layer: - Chitin - Cuticle - Cortication - Copulatory bursa

- Cuticle Adult roundworms are in the nematode class and have a protective outer cuticle, which is a surface covering on the adult nematodes. Chitin is also known as a shell and is in between the embryo and the cortication in a nematode egg. This structure is used to protect against the environment, but only seen in the eggs and not in the adult worm. Cortication refers to an outer mammillated, albuminous coating that can be seen on some roundworm eggs, especially Ascaris lumbricoides. Although the cortication is a protection from the outside environment as well, it is seen only in the egg and not in the adult worm. Copulary bursa are found in male worms to assist with copulation with female worms. The structure has no protective features and is purely used for reproduction.

Beta hemolytic colonies grew from the blood culture bottle after 18 hours incubation (see image). If the gram stain shows gram positive cocci, which of following tests would be helpful with making a preliminary identification? - Catalase - Regrow on CNA plate - Serological testing - Vancomycin susceptibility

- Catalase Streptococci are catalase negative while the Staphylococci are catalase positive, which is helpful in establishing a genus identification. CNA agar will inhibit gram negative organism, staphylococci, Bacillus spp., and coryneforms, making it useful for specimens with mixed flora. Therefore, it is a selective type of agar and not an identification agar. The specific group antigen can be demonstrated by follow-up serological tests. Detection of antigens is possible using latex agglutination or enzyme-linked immunosorbent assay (ELISA) technologies. These commercial kits have been reported to be very specific, but false-negative results may occur if specimens contain low numbers of S. pyogenes. A screening test for vancomycin susceptibility is often useful for differentiating among many alpha-hemolytic cocci. Since the hemolysis pattern is beta-hemolytic, this would not be a useful test.

A tech receives a call from the floor regarding antimicrobial therapy. The patient culture yielded an aerobic Gram-negative bacillus and the physician would like to use an antibiotic that inhibits cell wall synthesis. Which of the following antibiotics would be the best choice? - Gentamycin - Tetracycline - Ciprofloxacin - Cefazolin

- Cefazolin Cefazolin is part of the Cephalosporin family and part of the beta-lactam antibiotics with the Penicillins. Cephalosporins have a species range of both aerobic and anaerobic Gram-positive and Gram-negative species. The main target for these antibiotics are penicillin binding proteins, which inhibits the crosslinking in peptidoglycan in the cell wall of the organism. This inhibition results in cell lysis and cell death. Gentamycin is part of the aminoglycosides. These are effective against aerobic Gram-positive and Gram-negative species, but the target for the antibiotic is inhibition of protein synthesis by interfering with the translation of protein in the 30S ribosome. Tetracycline is also effective against aerobic Gram-positive and Gram-negative species. The target is protein translation in the 30S ribosome, not cell wall synthesis. Ciprofloxacin is part of the fluoroquinolones. These are effective against aerobic Gram-positive and Gram-negative species, but the target for the antibiotic is inhibition is DNA replication in the cell.

Methicillin resistant Staphylococcus aureus (MRSA) is a serious health concern in the hospital environment and also in the community for patients who have had no contact with the healthcare setting. In order to control the spread of MRSA and prevent infection with the organism, it is recommended to screen patients for MRSA prior to being admitted to a healthcare setting. Which of the following antimicrobials is best to use when testing for methicillin resistance? - Methicillin - Cefoxitin - Penicillin - Oxacillin

- Cefoxitin Cefoxitin is the recommended antimicrobial to use for detection of methicillin resistance in Staphylococcus aureus isolates. Since methicillin is no longer used in the US, resistance has routinely been tested by using oxacillin. However, it is now known that cefoxitin is a better inducer of resistance mediated by the mecA gene - the gene responsible methicillin resistance in S. aureus. The majority of Staphylococcus (approximately 90% or more) isolates are resistant to penicillin due to their production of the beta-lactamase enzyme. Penicillin will not indicate resistance to penicillinase-resistant penicillins like methicillin, oxacillin, or nafcillin. Methicillin-resistant Staphylococcus aureus (MRSA) has been present in hospital settings (HA-MRSA) for several decades. However, MRSA strains have emerged outside the hospital in community settings among otherwise healthy individuals. These strains are referred to as community-associated MRSA (CA-MRSA), and they now account for the majority of staphylococcal infections seen in the hospital emergency department or in clinics.

Which of the culture media listed is selective for the isolation of Yersinia enterocolitica in stool samples? - Cycloserine Cefoxitin Fructose Agar (CCFA) - MacConkey Sorbitol Agar - Bordet-Gengou Blood Agar - Cefsulodin-Irgasan-Novobiocin (CIN)

- Cefsulodin-Irgasan-Novobiocin (CIN) Cefsulodin-Irgasan-Novobiocin (CIN) is a selective agar for Yersinia entercolitica. CIN inhibits growth of other enteric bacteria found in stool. Growth of Y. entercolitica produces clear colonies with a red "bulls-eye" center due to mannitol fermentation, with neutral red as the pH indicator. Cycloserine Cefoxitin Fructose Agar (CCFA)is a selective medium used to isolateClostridium difficilefrom stool specimens. Unlike other intestinal bacterial flora,Clostridium difficileis not inhibited by CCFA. MacConkey Sorbitol Agar substitutes sorbitol for lactose. It is used to screen for E. coli O157:H7 which may be differentiated from other E. coli isolates by slow or non-fermentation on MacConkey Sorbitol, appearing as colorless colonies. Bordet-Gengou Blood Agaris a selective medium used for the isolation ofBordetellaspecies. The medium contains penicillin, methicillin, or cephalexin.

In the image to the right, letter B represents what type of endospore placement? - Terminal - Subterminal - No endospore is seen - Central

- Central Central is the correct answer. Central endospores are centrally located within the organism. Bacillus and Clostridium species can form endospores that are resistant to heat. The formation of endospores occurs when adverse conditions are encountered and provides protection for the organism until more favorable conditions are met. Clostridium perfringens can have either central or subterminal endospores. Terminal spores are located at the end of the organism and resembles a tennis racket or chicken drumstick. Clostridium tetani has terminal endospore location. Subterminal spores are located just below the surface at the end of the organism and resembles a candlestick. Clostridium perfringens has subterminal endospore location. No endospore is incorrect because all three images represents a type of endospore placement.

The following morphologic structure identifies Candida albicans and distinguishes it from most of the other Candida species. - Hypha - Blastoconidia - Mycelium - Chlamydospore

- Chlamydospore The morphologic structure that identifies Candida albicans and distinguishes it from other Candida species (other than C. dublinensis) is the chlamydospore. Candida albicans causes a disease called Candidiasis, which ranges from a mild to severe skin, nail, and mucous membrane infections. Hyphae are tubular structures that are part of the vegetative mycelium of molds. A similar structure called pseudohypha may be produced by yeast but they are not true hyphae. Pseudohyphae are elongated buds that fail to dissociate from subsequent buds. Blastoconidia are buds or daughter cells that form from a larger cell. It is the yeast's method of asexual reproduction and is produced by most yeast. It does not identify Candida albicans from other yeast. Mycelium is a mass of vegetative hyphae that is produce by molds. Yeast produce bacteria-like colonies but not mycelium that gives mold colonies texture such as woolly, granular, fluffy, cottony, and more.

The laboratory receives a synovial fluid for acid-fast culture. How should the tech proceed with this culture? - Digest the sample for culture - Centrifuge the specimen and directly inoculate the culture - Perform a direct smear only - Reject the specimen

- Centrifuge the specimen and directly inoculate the culture Body fluids, such as synovial fluid and spinal fluid, do not have normal flora like respiratory specimens. Thus, these samples do not need to be digested before setting up the culture. The specimen should be centrifuged, unless the volume is very low, then the sediment is used to inoculate the smears and culture media. The specimen should not be digested as synovial fluid is a sterile body fluid. The digestion process removes normal flora organisms to select for acid fast organisms. Since there is no normal flora in the fluid, digestion is not needed. Performing a direct smear only on the body fluid is not appropriate. With low numbers in the sample, acid fast bacilli could be overlooked on the smear, but grown via culture. Also, the smear does not provide information on the species present or the opportunity for sensitivity if needed. The specimen should not be rejected. Samples outside of the respiratory tract are appropriate for certain patient populations, such as patients with AIDS or that are immunocompromised. These patients can have disseminated infections outside of the respiratory tract.

All of the following life stages of schistosome worms are appropriately matched with the host they are found in, EXCEPT: - Cercaria - cow - Sporocysts - snail - Adult worm - human - Egg - human

- Cercaria - cow The correct answer is cercaria - cow. Adult schistosome worms reside in the human where they produce numerous eggs that are excreted in the feces or urine. The eggs consist of a developed miracidium that emerges upon contact with fresh water. Select snail species serve as the intermediate host, where the miracidium matures into sporocysts. Sporocysts divide into hundreds of cercariae which serve as the infective stage for humans. Once inside the body (accomplished by penetration through the skin) schistosomules emerge from the cercariae. Further maturation results in the development of adult worms and subsequent eggs.

Which of the following specimen types should be centrifuged prior to performing the Gram stain and culture? - Cerebrospinal fluid (CSF) - Clean catch urine - Wound swab - Blood

- Cerebrospinal fluid (CSF) The correct answer is cerebrospinal fluid (CSF). CSF should be centrifuged to concentrate any bacteria that may be present. When determining treatment, physicians need to exclude bacterial meningitis to hasten the treatment process, so a Gram stain and culture are essential. Clean catch urine, wound swabs, and blood are not normally centrifuged prior to performing a Gram stain or culture. A Gram stain is not routinely performed on clean catch urine samples. The cultures performed are quantitative, based on an uncentrifuged urine sample. Wound swabs are either used directly to inoculate media and slides or placed into saline before using the saline to perform the Gram stain and culture. Blood is generally directly inoculated into blood culture bottles; no centrifugation is used.

Which of the following conditions is caused by Trypanosoma cruzi? - Malaria - Chagas' Disease - Tapeworms - Sleeping Sickness

- Chagas' Disease Trypanosoma cruzi causes Chagas' disease. T. cruzi is transmitted via the bite of a reduviid bug. Chagas' disease presents with an erythematous nodule (chagoma) at the site of infection, typically the face. Edema follows with a rash around the eyes and face. The disease may occur after this initial acute stage, or after the patient has asymptomatic for years. Chagas' disease can attack many tissues in the body and lead to enlargement of the colon, esophagus, liver, and heart. Malaria is caused by Plasmodium species. These species infect humans by the bite of the Anopheles mosquito. The parasites infect red blood cells and cause them to rupture. This can lead to an insufficient blood supply to body tissues and also blockages of capillaries and blood sinuses. Tapeworm infections are caused by tapeworms, which are part of the cestodes. The most common tapeworms areTaenia saginata(beef tape worm) and Taenia solium (pork tapeworm). Tapeworms are transmitted by consuming the egg or worm in undercooked or contaminated meat. Symptoms of the disease include gastrointestinal discomfort, abdominal pain, and can lead to weight loss, vitamin deficiencies, and anemia. Sleeping sickness is caused by Trypanosoma brucei gambiense (West African sleeping sickness) or Trypanosoma brucei rhodesiense (East African sleeping sickness). The diseases are found in different areas and have a tsetse fly vector, but different species of that vector are responsible for the different diseases. Typically, West African sleeping sickness is a milder form of the disease. Both diseases typically have fever, malaise, headache, and generalized weakness.

Trypanosoma cruzi is the etiologic agent of: - African sleeping sickness - Relapsing fever - Filariasis - Chagas' disease

- Chagas' disease Trypanosoma cruzi is the etiologic agent of Chagas' disease. The disease can also be called American trypnaosomiasis as the disease is distributed in the southern United States, Mexico, and Central and South America. The organism is transmitted to humans via a bite of the reduviid bug. African sleeping sickness is caused by either Trypanosoma brucei gambiense (West African) or Trypanosoma brucei rhodesiense (East African) based on the geographical location. The vectors for both are different species of the tsetse fly. Relapsing fever is seen with malaria caused by Plasmodium species. Malaria is transmitted through the bite of the anopheles mosquito. The infection causes a period of chills followed by fever due to the release of organisms in the blood. Filariasis is caused by any of the filariae organisms such as Brugia or Wuchereria bancrofti. Microfilaria are seen in the bloodstream but will also migrate to the lymphatic system, block a lymph duct, and cause elephantitis in the area beneath the blockage.

Which age group has been most affected by the H1N1 virus? - Children - MIddle-aged men - Elderly - Women of child bearing age

- Children The correct answer is children. Confirmed cases of H1N1 virus have been reported more often in children and younger adults than in any other age group. This strain was highly contagious, but no more virulent than seasonal influenza A strains. This strain did quickly develop a resistance to the anti-viral medication osteltamivir. It was first identified in Mexico, but quickly spread to the United States. Unlike previous pandemics, this strain did not disappear, but rather became an endemic strain seen along with the seasonal influenza infections.

Which of the following has been compared to a hockey puck when discussing its morphology on chocolate agar? - Neisseria subflava - Moraxella catarrhalis - Neisseria lactamica - Neisseria sicca

- Moraxella catarrhalis Moraxella catarrhalis are large, pinkish to brown opaque colonies that can be moved over the agar intact with a loop, similar to a hockey puck on ice. Neisseria subflava are medium greenish yellow to yellow smooth colonies. Neisseria lactamica are small, nonpigmented to yellowish, smooth, and transparent colonies. Neisseria sicca are large, nonpigmented, wrinkled, coarse, dry, adherent colonies.

Illustrated in the image to the right is a tube of tryptophane agar with a positive indole reaction, as seen by the red ring at the top of the medium. It is necessary to use xylene extraction and Ehrlich's reagent rather than the conventional Kovac's reagent when detecting indole production by which of the following organisms: - Pasteurella multocida - Chryseobacterium (Flavobacterium) meningosepticum - Shigella sonnei - Klebsiella oxytoca

- Chryseobacterium (Flavobacterium) meningosepticum The correct answer is Chryseobacterium (Flavobacterium) meningosepticum. Ehrlich's reagent is formulated in ethyl alcohol rather than the isoamyl alcohol contained in Kovac's reagent. For bacterial species that are extremely weak producers of indole, such as Chryseobacterium (Flavobacterium) meningosepticum, the indole in the medium must first be extracted with xylene or a comparable organic compound and then reacted with the more sensitive Ehrlich's reagent. The isoamyl alcohol in Kovac's reagent is sufficient to extract indole produced in larger quantities. Therefore, Pasteurella multocida and Klebsiella oxytoca, both of which produce large quantities of indole, can be easily detected with Kovac's reagent.Although some Shigella species produce indole, all strains of S. sonnei are negative.

Based on the reactions observed in the tubes shown in the photograph (including open and closed OF dextrose and a positive nitrate reaction only after addition of zinc dust, as shown in the right tube of the pair labeled "Nit"), the most likely identification is: - Bordetella bronchiseptica - Chryseobacterium spp. - Moraxella osloensis - Oligella ureolytica

- Chryseobacterium spp. The OF dextrose reactions indicate that the bacterial species is a non-oxidizer. The positive urease reaction would lead one immediately to select either Bordetella bronchiseptica or Oligella ureolytica; however, both of these species reduce nitrates to nitrites. The left tube of the nitrate pair shows no red pigment, indicating that nitrates were not reduced to nitrites. The red pigment only appears in the tube after the addition of zinc dust. The zinc reduces nitrates to nitrites, confirming that nitrates were still unchanged in the original tube. None of the Moraxella species hydrolyze urea. In fact, all of the reactions shown here, including the positive urease, can be produced by Chryseobacterium spp., which is the correct response.

The images to the right show a 4-day-old colony grown on Sabouraud's Dextrose agar (left image). It was recovered from what was considered a "contaminant" from a bacterial culture. The image on the right is a high power photomicrograph of a methylene-blue stained mount prepared from the surfaces of the colony. With these observations, select the fungus genus from the choices below. - Scedosporium - Chrysosporium - Sepedonium - Beauveria

- Chrysosporium Chrysosporium is the correct answer. The colony as illustrated, is non-specific, with a fine silky surface and a light gray-pink pigmentation with shallow radiating rugae extending peripherally. Distinctive for the identification is the microscopic observation of spherical to pyriform conidia that are borne singly at the tips of long, slender conidiophores. These resemble the conidia of the dimorphic fungus, Blastomyces dermatitidis, except that growth is much longer. Chrysosporium cannot be converted to a yeast form upon incubation at 35 - 37°C. Scedosporium colonies are also rapidly growing with a low cottony surface mycelium, with the centers of older colonies having a distinct "house mouse gray" pigmentation. Clavate, smooth walled microconidia produced at the tips of long, delicate conidiophores are similar to those seen with Chrysosporium, with the distinction that the spores of Scedosporidium have a dark brown pigmentation that is responsible for the "house mouse" gray appearance on the surface of the colonies. Sepedonium colonies are gray white with a cottony surface that is non-specific. Microscopically, large spherical, bluntly spiked macroconidia are borne singly and not in clusters from long, delicate conidiophores. Beauveria colonies have a non-distinctive delicate silky, light gray-white surface mycelium. Key to the identification is the observation of small, spherical micro-conidia produced in loose clusters from delicate conidiophores with a zig-zag ("geniculate") bent knee effect.

Illustrated in the photograph is a citrate tube. Sodium citrate is converted into alkaline products by bacteria that can utilize citrate as the sole source of carbon, giving a blue color from the conversion of the bromothymol blue indicator. Select the species of Enterobacteriaceae that produces this reaction. - Escherichia coli - Yersinia enterocolitica - Citrobacter freundii - Shigella sonnei

- Citrobacter freundii Citrobacter freundii is the correct answer, as the genus name indicates. It should be mentioned that laboratory isolates of occasional strains of Citrobacter freundii, as well as other Citrobacter species, may initially produce a negative citrate reaction. More prolonged incubation may result in a positive color reaction indicating the assimilation of citrate and an alkaline blue color reaction of the bromothymol blue indicator. Escherichia coli, Yersinia enterocolitica, and Shigella sonnei are incorrect answers because all three species are citrate negative because they are unable to utilize citrate as a carbon source.

Illustrated in the top image is a slow-growing, 8-day-old colony growing on Sabouraud Dextrose with Brain Heart Infusion (SabHI) agar obtained from a darkened superficial skin infection. Although the colony is not specific for one of the fungal species causing chromomycosis, the black outer border that extends into the reverse of the colony is consistent. The identification is made by observing the distinctive conidiation illustrated in the bottom image. Which of the following organisms is represented by the description and images shown? - Exophiala jeanselmei - Fonsecaea pedrosoi - Cladophialophora carronii - Phialophora verrucosa

- Cladophialophora carronii Cladophialophora carronii is the correct response. Colonies are slow growing and are not specific. Distinctive for making the identification of cladosporium-type sporulation, as seen in microscopic mounts, are hyphae giving rise to long chains of dark-staining, elliptical conidia each separated by a scar called a dysjunctor. Its colony is gray-green to black with a black reverse. Exophiala jeanselmei is incorrect. Exophiala jeanselmei sporulation is in the form of darkly stained conidiophores that branch from the pigmented hyphae. The conidiophores terminate in sharply pointed tips, from which loose clusters of small, elliptical pigmented conidia are produced. Fonsecaea pedrosoiis incorrect.Fonsecaea pedrosoisporulation is of the acrotheca-type that is characterized by the sympodial branching of conidiophores produced from the ends of septate hyphae, simulating the prongs of a coat rack. Short chains of elliptical conidia are produced from the tips of these conidiophores. This species is the most common cause of chromoblastomycosis and produces a mixed type of sporulation that is characteristic of theCladosporium,Phialophora, andRhinocladiellaspecies.Phialophora verrucosais incorrect.Phialophora verrucosasporulation is characterized by the production of short urn-shaped phialides with a narrow bottle-like opening derived laterally from the sides of the hyphae. Spherical of oval-shaped, yellow pigmented conidia are produced from within each phialide, forming loose aggregates at the terminal opening.

A Gram stain of drainage from an open wound revealed gram-positive bacilli with spores. This description would commonly rule out which one of the following organisms? (Choose the BEST response.) - Clostridium perfringens - Bacillus cereus - Clostridium septicum - Bacillus anthracis

- Clostridium perfringens The presence of spores virtually rules out Clostridium perfringens. While the organism does produce spores, they are rarely seen in clinical infections. Bacillus cereus produce spores, but it does so only under aerobic and not under anaerobic conditions. Clostridium septicum produces spores as does B. anthracis. By elimination, Clostridium perfringens is the best answer.

Illustrated in the image is the fruiting head of one of the fungal agents of chromomycosis. Note the long chains of elliptical conidia each separated by a distinct scar, called a "dysjunctor". Which of the following choices represents the type of sporulation illustrated in this image? - Acremonium sporulation - Cladosporium sporulation - Curvularia sporulation - Phialophora sporulation

- Cladosporium sporulation Cladosporium sporulation is the correct response. Characteristic are the elliptical, dark-staining conidia that are produced in long, branching chains, each separated by a delicate scar known as a dysjunctor. Acremonium sporulation is characterized by simple, unbranched, erect conidiophores, single-celled conidia that cluster at the tip of the conidiophore. It also produces intercalary and terminal chlamydoconidia. Curvularia sporulation is characterized by dematiaceous septate hyphae with bent conidiophores where curved multicellular conidia attach. The conidia have a swollen central cell that gives the conidia a curved appearance. Phialophora sporulation is in the form of short urn-shaped phialides each with a narrow bottle-like opening. Spherical or oval-shaped, yellow pigmented conidia are produced from within each phialide, forming loose aggregates at the terminal opening.

This form, which measures 30 µm by 15 µm was found in stool. What is the identification? - Diphyllobothrium latum egg - Paragonimus westermani egg - Clonorchis sinensis egg - Fasciola hepatica egg

- Clonorchis sinensis egg Clonorchis sinensis eggs are characterized by an operculum on one end of the egg, and a small knob on the other end of the egg. Also, there is a distinct rim around the operculum, which is referred to as shoulders. The size of the eggs is approximately 30 µm by 15 µm. Diphyllobthrium latum eggs also have an operculum and terminal knob, but no shoulders. The egg is also much larger with an average size of 65 µm by 48 µm. Paragonimus westermani eggs also have an operculum and shoulders, but do not have a terminal knob. They do show a terminal shell thickening. The eggs are also much larger, ranging from 78-120 µm by 45-60 µm. Fasciola hepatica eggs also have an operculum, but they do not have a terminal knob or shoulders. The eggs are also much larger, about 128-150 µm by 60-90 µm.

What organism is responsible for a potentially lethal type of food poisoning caused by improperly canned food? - Bacillus cereus - Clostridium botulinum - Clostridium perfringens - Staphylococcus aureus

- Clostridium botulinum The correct answer is Clostridium botulinum. Clostridium botulinum causes a potentially lethal type of food poisoning when canned food is improperly canned. According to the Centers for Disease Control and Prevention (CDC), "C. botulinum is an anaerobic, gram-positive, spore-forming rod that produces a potent neurotoxin. The spores are heat-resistant and can survive in foods that are incorrectly or minimally processed." It takes only a small amount of neurotoxin to produce paralysis and death. Bacillus cereus, Clostridium perfringens, and Staphylococcus aureus are all capable of causing food poisoning, but not related to improperly canned food.

From the choices listed below, which organism is classified as an obligate anaerobe? - Mycobacteria - Staphylococcus aureus - Neisseria species - Clostridium novyi

- Clostridium novyi Clostridium novyi is one of the most oxygen-susceptible anaerobes, with cells being killed within 10 minutes of exposure to atmospheric air. This species is often used as a quality control strain to indicate an adequate anaerobic environment in anaerobe tents and jars. On the other side of the spectrum, Mycobacteria are obligate aerobes, requiring 15-21% O2, although increased CO2 many enhance growth of some species. Staphylococcus aureus is classified as a facultative anaerobe, preferentially using oxygen for growth, but able to grow in the absence of oxygen. Most Neisseria species are aerobic, but some are capnophilic, requiring 5-10% CO2.

A 25-year-old motorcyclist incurred superficial and deep penetrating lacerations of his right shoulder when thrown off his speeding vehicle into the ditch. The shoulder became painful and continued to swell over the next 24 hours. The bacterial species shown in the upper image was recovered after 36 hours under anaerobic incubation and the lower image illustrates the microscopic features. What is the most likely identification? - Clostridium septicum - Clostridium perfringens - Lactobacillus acidophilus - Eubacterium nodatum

- Clostridium perfringens The correct answer is Clostridium perfringens. The infectious disease resulting in this case was post trauma gas gangrene. The bacterial species most commonly associated with gas gangrene is Clostridium perfringens. Clostridium septicumis second most likely bacterial species known to cause post trauma gas gangrene. The double zone of hemolysis seen in the upper image (the blue arrow indicates the inner zone of beta hemolysis, the green arrow the outer faint zone of lecithinase activity) is characteristic of C. perfringens, helping to differentiate this species from C. septicum. C. perfringens does not produce spores in culture (the gram-positive bacilli seen in the lower image are devoid of spores), another helpful feature separating it from C. septicum. Lactobacilli and

Which of the following organisms is responsible for myonecrosis with gas gangrene, food poisoning as well as necrotizing enteritis, a life threatening that causes ischemic necrosis of the jejunum? - Clostridium perfringens - Prevotella melanogenica - Cutibacterium (Propionibacterium) spp. - Fusobacterium necrophorum

- Clostridium perfringens The correct answer is Clostridium perfringens. Myonecrosis, accompanied by gas gangrene, is the classic clinical manifestation of Clostridium perfringens infections of the skin. C. perfringens has also been implicated in self-limiting, toxin-mediated food poisoning and NEC, necrotizing enteritis, which is often found in immunocompromised patients. C. perfringens is a Gram positive, spore forming anaerobic bacillus. Cutibacterium (Propionibacterium) spp. are associated with inflammatory acne and opportunistic infections such as endocarditis and osteomyelitis. Cutibacterium (Propionibacterium) acnes is a Gram positive, anaerobic cocci that is part of the commensal flora of the skin. Prevotella melaningoseptica and Fusobacterium necrophorum are common anaerobes in the oropharynx. Both are associated with mixed anaerobic infections (abscesses) throughout the body that produce a foul odor, but are mainly isolated in head, neck and pleuropulmonary infections. P. melaningoseptica is a Gram negative, anaerobic bacillus that can produce a red fluorescence. Fusobacterium necrophorum is a pleomorphic, anaerobic bacilli that will fluoresce chartreuse.

Which Plasmodium species tends to infect any red blood cell, regardless of the age of the cell? - Plasmodium ovale - Plasmodium falciparum - Plasmodium vivax - Plasmodium malariae

- Plasmodium falciparum Plasmodium falciparum and Plasmodium knowlesi will infect any red cell, at any age. Because of this, heavy infections may result. Plasmodium ovale and Plasmodium vivax tend to infect young red blood cells. Plasmodium malariae tends to infect old red blood cells.

The following is a spore-forming anaerobe that is associated with neutropenic enterocolitis: - Clostridium septicum - Porphyromonas spp. - Bacteroides fragilis - Fusobacterium nucleatum

- Clostridium septicum Clostridium septicum is an anaerobic, spore-forming, Gram positive organism bacillus that has been associated with neutropenic enterocolitis. This organism is characterized as producing subterminal spores, gelatin positive, lecithinase and lipase negative, indole negative, and esculin positive. Porphyromonas spp. are anaerobic non-spore forming Gram negative bacilli that have been associated with endogenous infections associated with the intestinal tract. They characteristically produce pigmented colonies. Bacteroides fragilis are anaerobic non-spore forming Gram negative bacilli that have been associated with endogenous infections associated with the oral and gastrointestinal tract. It is the most commonly isolated anaerobic organism from clinical specimens. Fusobacterium nucleatum is anaerobic non-spore forming Gram negative bacillus that has been associated with endogenous infections of the head and neck region in relation to dental biofilms.

The flat, spreading gray-white colonies with an outer zone of beta hemolysis as observed on the surface of an anaerobic blood agar plate shown in the upper image were recovered from a blood culture of an elderly man leading to a potential diagnosis of cancer of the colon. Observed in the gram stain are short gram-positive bacilli, some with distinctive central and sub-terminal spores. From these observations, select the most likely isolate. - Cutibacterium (Propionibacterium) acnes - Clostridium septicum - Actinomyces israeli - Clostridium difficile

- Clostridium septicum Clostridium septicum is the correct response. Distinctive are the flat, spreading gray-white colonies with surrounding beta hemolysis. A presumptive identification can be made by observing in gram stains short varying sized rectangular gram positive coccobacilli, some of which have distinctive central and sub-terminal spores. The definitive laboratory identification of C. septicum, using additional biochemical assays, is important because of its association with cancer of the colon. Key characteristics are fermentation of glucose and lactose, hydrolysis of gelatin and production of DNA'se. Cutibacterium (Propionibacterium) acnes colonies are small, enamel white, and entire without spreading. Beta-hemolysis is not observed. Gram stains reveal gram positive coccobacilli that are arranged singly, in short chains and more distinctly in diphtheroidal cluster. Spores are not produced. Cutibacterium (Propionibacterium) acnes is most commonly considered as a contaminant when recovered in culture; on occasion it may serve as the cause of skin wound and shunt infections. Actinomyces israeli colonies on anaerobic blood agar are entire, gray-white and distinctly sunken centrally when mature, resembling a "molar tooth". Colonies are non-spreading and beta hemolysis is not observed. The Gram stain observation is that of thin, gram-positive slender branching filaments within which spores are not produced. Glucose and several additional carbohydrates are fermented. Gelatin hydrolysis is negative. Cases of lymphadenitis are more commonly encountered and an association with cancer of the colon has not been reported. Clostridium difficile colonies are entire, flat, and gray-white with less spreading than those of C. perfringens, and are not beta hemolytic. This presumptive identification is further supported by the observation of long, slender gram-positive bacilli with production of distinct sub-terminal spores. Negative gelatin hydrolysis is a differential characteristic. Antibiotic associated colitis with complication of pseudo-membranous colitis is also distinctive for C. difficile.

A CSF shunt tip specimen was sent to the microbiology laboratory for culture. The shunt specimen was inoculated to sheep blood agar, chocolate agar, and a thioglycollate broth. After 24 hours of CO2 and non CO2 incubation at 37°C, the sheep blood agar, chocolate agar, and the thioglycollate broth had growth. The microbiology tech evaluated the media and observed the following: Growth: Sheep blood grew small, white non-hemolytic colonies. Chocolate grew small, white colonies. Gram Stain: Gram positive cocci in clusters Biochemical: Catalase positive; coagulase negative Which of the following organisms is most likely the cause of the CSF shunt tip infection? - Staphylococcus aureus - Cutibacterium (Propionibacterium) acnes - Coagulase negative staphylococci - Viridans group streptococci

- Coagulase negative staphylococci Coagulase negative staphylococci is the correct answer. Coagulase negative staphylococci will grow on blood and chocolate agars with and without CO2 incubation. In addition, colonies can grow as white to cream in color and be non-hemolytic on blood agar media. Gram stain morphology will appear as Gram positive cocci in clusters. Coagulase negative staphylcocci are catalase positive and coagulase negative. This separates this species from Staphylococcus aureus, which is catalase positive and coagulase positive. Staphylococcus aureus is incorrect because this organism will typically grow as large, yellow beta-hemolytic colonies on blood agar media. This organism can grow with or without CO2 incubation and is catalase and coagulase positive. This separates this species from coagulase negative staphylcocci. Cutibacterium (Propionibacterium) acnes is the incorrect answer. Cutibacterium (Propionibacterium) species is part of normal skin flora and is often considered a skin contaminant in blood cultures, but it has been identified as causing systemic opportunistic infections within the central nervous system and a source of infection in endocarditis, osteomyelitis, and arthritis. However, this organism is an ananerobic organism and is catalase positive, nitrate reduction positive, and sensitive to vancomycin and kanamycin. Viridans Group Streptococci is incorrect because the viridans group streptococci are catalase negative and have a Gram stain morphology of Gram positive cocci in chains. This separates this group from coagulase negative staphylococcus species. In addition, this organism can grow at aerobic conditions or with or without CO2. All four organisms listed have been reported as common causes of shunt infections, in addition to Klebsiella species, Escherichia coli, and Serratia marcescens.

Parasites that belong to the category Sporozoa are also known as: - Flukes - Digenea - Hemoflagellates - Coccidia

- Coccidia Coccidial parasites do not possess specific organelles for locomotion and thus belong to the Sporozoa. Coccidia are a group of protozoal parasites where asexual replication occurs outside of the human host and sexual reproduction occurs inside the human host. Digenea is a class of parasites that includes the flukes. Hemoflagellates belong to the Mastigophora and are flagellates found in blood and tissue.

The following is a systemic, dimorphic genus that characteristically produces barrel-shaped arthroconidia separated by dysjunctor cells: - Coccidiodes immitus - Geotrichum species - Trichosporon species - Microsporum species

- Coccidiodes immitus The mold form of Coccidioides immitus produces barrel-shaped arthroconidia with alternate staining due to the presence of dysjunctor cells which are non-viable cells. This organism is the causative agent of coccidioidomycosis which is found primarily in the desert region of southwestern United States as well as the arid region of Mexico and Central and South America. The Geotrichum species produce rectangular-shaped arthroconidia; however, they are regularly rather than alternately staining. Additionally, the arthroconidia of Geotrichum may produce germ tubes from one corner Trichosporon species produce rectangular-shaped arthroconidia; however, they are regularly rather than alternately staining. Additionally, the arthroconidia of Trichosporon species may produce blastoconidia from adjacent corners, features not shared by either Malbranchia species or s. The Microsporum species may produce arthroconidia; however, they are much narrower in dimension and do not share the alternate staining characteristics. This genus is more noted for producing multicelled macroconidia that are spindle-shaped.

The most common eye complication in patients with candidiasis is: - Endophthalmitis - Keratoconjunctivitis - Extraocular muscle palsy - Scotoma (focus of depressed vision)

- Endophthalmitis Endophthalmitis is the correct answer because it is considered an emerging infection due to its increase of cases in addition to blood stream infections, osteomyelitis, endocarditis, meningitis, peritonitis, myositis, and pancreatitis. Keratoconjunctivitis is incorrect because it is a less likely agent than a number of filamentous molds. Candida species can cause keratoconjunctivitis following corneal trauma or ulceration. Extraocular muscle palsy and scotoma (focused of depressed vision) are both incorrect answers because they are complications most likely to occur in patients with cryptococcosis than candidiasis.

The image shows an antimicrobial susceptibility result for a Corynebacterium species on a 5% sheep blood agar plate. The zone around the 10 µg penicillin disk rules out: - Corynebacterium minitissmum - Corynebacterium ureolyticum - Corynebacterium xerosis - Corynebacterium aquaticum

- Corynebacterium ureolyticum Corynebacterium ureolyticum is one of a few species of Corynebacterium, including C. amycolatum, C. jeikeium, and C. resistens, that are resistant to penicillin and most other antibiotics.The 10 µg penicillin disk is often used in the initial identification of Corynebacterium species to screen for C. jeikeium. For this question, C. ureolyticum is the only available answer that is resistant to penicillin. Corynebacterium minitissmum is one of many Corynebacterium species that are naturally penicillin susceptible and show the large zone of growth inhibition as seen in the photograph. Corynebacterium xerosis is one of many Corynebacterium species that are naturally penicillin susceptible and show the large zone of growth inhibition as seen in the photograph. Corynebacterium aquaticum is one of many Corynebacterium species that are naturally penicillin susceptible and show the large zone of growth inhibition as seen in the photograph.

The colonies shown in this photograph were grown on Guizotia abyssinica (bird seed) agar at 30°C for 72 hours. The most likely identification is: - Cryptococcus laurentii - Cryptococcus neoformans - Candida parapsilosis - Saccharomyces cerevisiae

- Cryptococcus neoformans The colonies seen growing on the bird seed agar appear smooth and have a distinct reddish-brown pigmentation. The active ingredient in bird seed (Guizotia abyssinica) agar is caffeic acid, which is extracted and placed in an agar containing 1% glucose. Of the cryptococci, and other species of yeasts, Cryptococcus neoformans selectively produces the enzyme phenoloxidase, which oxidizes the caffeic acid in the medium to melanin, producing the red-brown pigmentation. The other yeast species included in this exercise remain cream colored (non-pigmented), when grown on bird seed agar as they do not possess phenoloxidase activity.

The story might be told that a pathologist, when first viewing an H & E - stained section of an endoscopic biopsy of duodenum (upper left image), may seek a consultation. The specimen was obtained from a patient with a mal-absorption syndrome. After observing tiny acid-fast globules along the intestinal epithelial lining cell (arrows, upper right image), one of the laboratory microbiologists was consulted for an answer. Having a presumptive identification in mind (lower left image), the microbiologist prepared an acid-fast stained smear of intestinal fluid (lower right image) and observed tiny 5 µm in diameter oocysts. From the multiple choices listed, select the presumptive identification, select what parasite the microbiologist might have reported. - Cryptosporidium parvum - Cyclospora cayetanensis - Microsporidium species - Cystoisospora belli

- Cryptosporidium parvum Cryptosporidium parvum is the correct response. Characteristic of C. parvum are the tiny 4 - 6 µm in diameter acid-fast oocysts that typically adhere to intestinal lining cells, resulting in mal-absorption and other symptoms including cholera-like watery diarrhea. The oocysts are even staining and devoid of sporocysts. Cyclospora cayetanensis is an incorrect response. C. cayetanensis oocysts are spherical with an appearance similar to those of Cryptosporidium. The distinguishing characteristics are acid-fast oocysts that are twice the size of Cryptosporidium oocysts, ranging from 8 - 12 µm, and a slightly wrinkled cytoplasm with two sporozoites within each oocyst. Microsporidium species is an incorrect response. Microsporidium also produces tiny spores measuring no more than 2 µm in diameter. They are located within the cytoplasm of the epithelial cells instead of on the surface. These spores are non-acid fast, and best observed in trichrome or Weber stained preparations. Cystoisospora belli is an incorrect response. Isospora belli produces oocysts of that are large, measuring up to 30 µm, with a long oval shape. These oocysts have a thin, smooth outer wall and possess two intra-cytoplasmic sporocysts.

Which statement about bacterial culture for Clostridioides (Clostridium) difficile is TRUE? - Routine bacteriological media will provide adequate recovery. - The culture is specific for toxigenic strains. - Culture on appropriate media provides an effective means of recovering the organism. - Culture for C. difficile provides desirable turnaround times.

- Culture on appropriate media provides an effective means of recovering the organism. Culture can be an effective means of recovering Clostridioides (Clostridium) difficile, if the appropriate selective and differential medium is used. If attempting to recover C. difficile from stool, cycloserine-cefoxitin-fructose agar (CCFA) should be inoculated. Routine agars, such as blood agar or Brucella blood agar, are NOT adequate for recovering this organism, especially from stool. Assays for detection of toxin production and nucleic acid amplification tests have largely replaced culture as a means to determine the presence of the organism. The drawbacks of culture are the length of time required (up to four days) and the fact that it does NOT differentiate between toxigenic and non-toxigenic strains.

Which of the following molds is classified as a zygomycete? - Microsporum nanum - Cunninghamella species - Trichophyton schoenleinii - Epidermophyton floccosum

- Cunninghamella species Cunninghamella species are zygomycetes. Members of this order are rapidly growing organisms normally found in the soil. They are often opportunistic pathogens in immunocompromised hosts. Zygomycetes generally produce profuse, gray to white, aerial mycelium characterized by the presence of hyaline, sparsely septate hyphae. Microsporum nanum, Trichophyton schoenleinii, and Epidermophyton floccosum are all species of dermatophytes. Dermatophytes contain the largest number of organisms that are causative agents of mycoses, including cutaneous, subcutaneous, and systemic disease. Organisms are placed into this group when no mode of sexual reproduction has been identified.

Which anaerobic bacteria incidence is increasing in CSF shunt infections? - Bacterioides fragilis - Cutibacterium (Propionibacterium) acnes - Fusobacterium nucleatum - Candida albicans

- Cutibacterium (Propionibacterium) acnes The correct answer is Cutibacterium (Propionibacterium) acnes. Cutibacterium (Propionibacterium) acnes is increasing in incidence in CSF shunt infections. Since this bacterium is considered normal skin flora, the source of infection (skin) is the same as the most common cause of CSF shunt infections: coagulase negative staphylococci. Bacterioides fragilis and Fusobacterium nucleatum are both anaerobic bacteria, but are not increasing in incidence as a cause of CSF shunt infections. Candida albicans is not an anaerobic bacterium, it is a yeast, but it is a cause of CSF shunt infections, especially in immunosuppressed patients.

Critical values not reported or not reported in a timely manner is an example of a laboratory error made during which phase of laboratory testing? - Centrifugation - Analytic - Postanalytic - Preanalytic

- Postanalytic Critical values not reported or not reported in a timely manner is an example of a postanalytic error. A centrifugation error is an error that occurs during centrifugation of a specimen such as spinning the sample for the wrong amount of time. An analytic error is an error associated with tasks that occur during testing, an example would be using the wrong testing method. A preanalytical error is an error associated with tasks that occur before testing beginnings. An example of a preanalytical error is improperly labeling a specimen.

The ingredient added to culture media to enhance the recovery of the dimorphic fungi by preventing the overgrowth of more rapidly growing, saprophytic molds is: - Brain heart infusion base - Chloramphenicol - Thiamine - Cycloheximide

- Cycloheximide Cycloheximide is an antifungal agent that binds to the 80S ribosome of many eukaryotes and prevents protein synthesis by blocking the transfer of RNA to the growing polypeptide chain. The dimorphic fungi have developed resistance to this antifungal agent, and can grow in culture media to which it has been added, in contrast to most rapidly growing saprophytes. Brain heart infusion is often used as an enrichment to enhance the primary recovery of dimorphic fungi from clinical materials; however, also enhances the growth of other fungal species as well. Thiamine is an enrichment needed for the growth of a few select fungal species; notably, the dermatophyte Trichophyton tonsurans. It has little influence on the growth of the dimorphic fungi. Chloramphenicol is added to culture media to prevent the overgrowth of bacteria.

The historical medium of choice for isolation of Francisella is: - Chocolate agar - Cysteine blood glucose agar - Modified Thayer-Martin agar - MacConkey agar

- Cysteine blood glucose agar The correct answer is cysteine blood glucose agar. Cysteine blood glucose agar is the historical medium of choice for isolation of Francisella, as it usually does not grow without cysteine. Chocolate agar and modified Thayer-Martin agar are able to support the growth of Francisella, but are not the historical medium of choice. MacConkey agar is not able to support the growth of Francisella.

Which of the following media would you use to isolate Francisella tularensis: - Sheep-blood agar - Lowenstein-Jensen media - Bordet-Gengou media - Cysteine-blood agar

- Cysteine-blood agar Cysteine-blood agar is the traditional media used when F. tularensis is suspected. However, F. tularensis will also grow on chocolate agar and Thayer-Martin agar, which have been enriched with supplemental nutrients. This reduces the necessity of having a selective agar available solely for the cultivation of F. tularensis. Sheep blood agar is generally considered a universal media for culture; however, the fastidious nature of F. tularensis does not allow it to grow on sheep blood agar. Lowenstein-Jensen media is used for the cultivation of mycobacteria and actinomycetes. Bordet-Gengou media is used for the selective culturing of Bordetella pertussis and Bordetella parapertussis.

Stenotrophomonas maltophilia and Burkholderia cepacia share each of the following characteristics EXCEPT: - Decarboxylation of lysine - Cytochrome oxidase activity - Production of colonies with a yellow pigment - Good growth on MacConkey agar

- Cytochrome oxidase activity Cytochrome oxidase is the correct response. Stenotrophomonas maltophilia is cytochrome oxidase negative and Burkholderia cepacia is cytochrome oxidase positive. Both Burkholderia cepacia and Stenotrophomonas maltophilia were previously included in the genus Pseudomonas. These were the two pseudomonads that characteristically produced yellow colonies and decarboxylated lysine. The departure of Stenotrophomonas maltophilia from the genus was heralded by its lack of cytochrome oxidase activity. Most strains of Burkholderia cepacia are cytochrome oxidase positive, although the reaction may be weak in some cases. Therefore, of the characteristics listed, cytochrome oxidase activity is the only one that is different for the two species. Both organisms can decarboxylate lysine. Both organisms produce a yellow pigment. B. cepacia produces yellow, serrated colonies while S. maltophilia produces smooth, glistening yellow to tan colonies. Both species grow well on MacConkey agar.

What system is used in the clinical laboratory to monitor a patient's current clinical values for a test with previous values? - Calibrators - Delta checks - Controls - Competencies

- Delta checks Delta checks compare a patient's current clinical values for a test with previous values. These checks are used in part to detect pre-analytical errors such as patient misidentification or specimen mix-ups, before the results are released to the physician. When a significant change is observed in the test result within a short period of time (eg, 24 hours), one possible explanation is that the specimens did not come from the same person. An investigation of the reason for the change should be perform in order to clarify the reason for the delta check.Calibrators, controls, and competencies are part of the quality assessment and quality control in the clinical laboratory, but they do not monitor patient's current results to previous results.

The Laboratory Response Network (LRN) consists of all of the following except: - Sentinel laboratories - Department of Defense (DOD) - Reference laboratories - National laboratories

- Department of Defense (DOD) The Laboratory Response Network (LRN) is a three tier system. Sentinel laboratories receive patient samples, rule out pathogens, and transfer suspicious specimens to reference laboratories. Reference laboratories perform confirmatory testing on pathogens. National laboratories are responsible for the definitive characterization of agents. The Department of Defense assists with any confirmed bioterrorism incidents.

Which of the following statements is correct regarding the glutamate dehydrogenase (GDH) assay for Clostridium difficile? - The GDH test can differentiate toxin producing strains of C. difficile from nontoxigenic strains. - The GDH assay is a valuable confirmatory test for C. difficile. - Detection of the GDH gene and 16srRNA genes for C. difficile without the presence of a toxin gene indicates a carrier or nonpathogenic state. - GDH assays can be used as stand-alone assays.

- Detection of the GDH gene and 16srRNA genes for C. difficile without the presence of a toxin gene indicates a carrier or nonpathogenic state. GDH or glutamate dehydrogenase is an enzyme produced by C. difficile. Detection of the GDH gene or 16rRNA genes without the presence of a toxin gene is indicative of a nonpathogenic strain or the carrier state. Toxin A or Toxin B must be detected to confirm a toxigenic, pathogenic state. The GDH assays does not differentiate between toxin producing strains of C. difficile and nontoxigenic strains. The GDH assay is used as a screening test, and not a confirmatory test. Toxin A or Toxin B must be detected to demonstrate a pathogenic strain of C. difficile. Enzyme assays for the GDH antigen have been associated with a high negative predictive value. However, positive samples are not always associated with a toxin producing strain and require a second assay to confirm the presence of a toxigenic strain.

Which is the incorrect statement about sample labeling requirements? - Prelabeled tubes should be used. - The label should have the patient's first and last name. - The label should have a unique identification number. - The date of collection should be included.

- Prelabeled tubes should be used. The sample must be labeled at bedside. To prevent a possible sample mix-up, prelabeled tubes should never be used. The label must include first and last name of the patient; unique identification number; date of collection; and signature, initials, or method to identify the phlebotomist.

This parasite measures 12 µm and is found in the stool. It may easily be mistaken for fecal debris, and reported incorrectly as a a nonpathogenic fecal contaminant. - Entamoeba coli cyst - Endolimax nana trophozoite - Dientamoeba fragilis cyst - Dientamoeba fragilis trophozoite

- Dientamoeba fragilis trophozoite Dientamoeba fragilis is a flagellated intestinal protozoan. The trophozoites of Dientamoeba fragilis measure from 5-15 µm and are the only trophozoites of protozoan flagellates that contain two nuclei with each made up of 4 to 8 chromatin dots, as is shown in the image. Most other trophozoites of the protozoan flagellates contain a single nucleus. The cysts of Entamoeba coli, a protozoan amoeba, usually measure from 15 -25 µm and are usually round and 8 nuclei are usually visible in the mature cyst. Coarse granular peripheral chromatin is present. The trophozoites of Endolimax nana, a protozoan amoeba, are smaller and usually measure from 8 -10 µm with a single nucleus with variable nuclear chromatin. Dientamoeba fragilis does not have a cyst stage.

A 54-year-old Finnish male presented at the local clinic with abdominal pain, weight loss, overall weakness and digestive discomfort. Patient history revealed that the man's diet was rich in raw fish. A complete blood count (CBC) was performed and revealed macrocytic anemia. A stool for parasitic examination was ordered. This suspicious form was seen upon initial screening of the sample. It measures 70 µm by 48 µm. This patient is most likely suffering from an infection with: - Clonorchis sinensis - Paragonimus westermani - Fasciolopsis buski - Diphyllobothrium latum

- Diphyllobothrium latum Diphyllobothrium latum, the freshwater broad fish tapeworm, is the largest human tapewom. The intermediate hosts of D. latum include crustaceans and freshwater fish. Infection is obtained through the consumption of fresh water fish. The parasite is identified when eggs are visualized in a wet preparation of a fresh stool sample. The eggs are ovoid, operculated (have a lid), with a terminal knob, and often appear yellow-brown. Eggs are approximately 58-75 µm x 40-50 µm in size and pass in abundance in the stool. Eggs are sometimes confused with those of Paragonimus. Clonorchis sinensis, known as the Chinese liver fluke, requires a freshwater snail as an intermediate host. Eggs of C. sinensis are identified in fresh stool using a sedimentation method and a wet mount with or without iodine. Eggs are 28-30 µm x 14-18 µm. They have shouldered opercula with a small knob at the end opposite the operculum and are yellow-brown in color. Paragonimus westermani is the most common and widely distributed lung fluke. Freshwater snails are required as an intermediate host. Eggs are found in stool after adult worms produce eggs in the lungs, which are then expectorated and swallowed. P. westermani eggs measure 80-120 µm x 45-60 µm and are operculated with opercular shoulders, thick shells, and are brownish-yellow in color. They may be misidentified as D. latum, but maybe differentiated by the opercular shoulders and thickened shell and the end opposite the operculum. Fasciolopsis bruski is an intestinal trematode that requires a snail as an intermediate host. Infections are acquired by ingestion of raw or undercooked water plants. The eggs of F. bruski are oval and elongated, transparent, and yellow-brown with an operculum at one end. Eggs are large and measure 130-140 µm x 80-85 µm. Eggs are indistinguishable from those of Fasciola hepatica.

The packets of small, spherical immature ova (upper photomicrograph) may be observed in the ovaries of tapeworms indigenous in dogs and cats. Human infections are uncommon but on occasion stool specimens of young children with mild diarrhea who have had contact with household pets may include proglottids as represented by the lower photograph. Select the presumptive identification of this tapeworm from the multiple choice answers listed below. - Diphyllobothrium latum - Dipylidium caninum - Taenia saginata - Hymenolepis nana

- Dipylidium caninum Dipylidium caninum ova are small and aggregate in packets within the ovaries of the adult worm as shown in the upper image. The proglottids are longer than wide (lower image 2), and distinctly have bilateral genital pores from which the ova are discharged externally through vitelline ducts (Dipylidium = "di-pyle" or "double orifice"). The organism is found more commonly in children who have had contact with infected dogs and cats. Diphyllobothrium latum is transmitted through the ingestion of eggs in infected fish. D. latum ova are large, oval in outline, with a thin smooth shell. A distinctive, inconspicuous non-shouldered operculum is present at one end. Internal cleavage extends to the inner shell membrane. The proglottids are distinctively wider than long, with a branching uterus within simulating a compact rosette. Genital pores are absent. Taenia saginata is associated with cattle. T. saginata ova are spherical in shape, measure 30 - 45 µm in diameter and have a thick shell with striations. Three pairs of hooklets are observed within. The proglottids are rectangular in outline and possess over 13 lateral uterine branches. Hymenolepis nana is transmitted direct ingestion of the egg or by the ingestion of infected arthropods such as fleas. H. nana ova are large, averaging 50 µm in diameter, are oval in outline with a smooth outer shell. Contained within is an inner membrane with three pairs of hooklets. The adult worms are small and thin, simulating mucous threads, and proglottids are obscure.

The eggs of this parasite arrange themselves in membrane-enclosed clusters known as packets: - Hymenolepis nana - Diphyllobothrium latum - Dipylidium caninum - Taenia species

- Dipylidium caninum The correct answer is Dipylidium caninum. The egg packets of Dipylidium caninum consist of approximately 5 to 30 eggs. Each egg resembles the typical six-hooked onchosphere. Hymenolopsis nana also exhibits eggs that contain six hooklets, but has a pair of polar filaments on either side of the membrane. Diphyllobothrium latum eggs have a smooth shell with inconspicuous non-shouldered operculum at one end and a knoblike thickening on the other. Taenia species have eggs that are spherical with a thick shell containing radial striations and three pairs of hooklets in the oncosphere.

Which of the following statements is true regarding the various non-molecular methods used for influenza testing? - Direct fluorescent antibody (DFA) staining on specimen smears can provide rapid results but are dependent on the availability of trained personnel to accurately interpret the smears. - The shell vial methodology provides a more rapid result that meets all clinical needs. - Traditional viral culture provides both rapid and sensitive results. - Enzyme immunoassay (EIA) or immunochromatographic membrane techniques provide both rapid and very sensitive alternatives.

- Direct fluorescent antibody (DFA) staining on specimen smears can provide rapid results but are dependent on the availability of trained personnel to accurately interpret the smears. Direct Fluorescent Antibody smears are a rapid methodology if trained personnel are available. Shell vials can provide more rapid results than traditional culture methods, but do require 24 to 48 hours of incubation and sensitivity will vary. Traditional culture provides very good sensitivity is achieved but requires extended incubation. Of the non-molecular methods, EIA's or immunochromatographic are the most easily performed and most rapid, but do not have desirable sensitivity.

The laboratory test most commonly used to establish a definitive diagnosis of primary syphilis is: - Rapid plasma reagin (RPR) - Recovery of spirochetes via culture - Direct fluorescent antibody test - Fluorescent treponemal antibody (FTA) with adsorption test

- Direct fluorescent antibody test The direct fluorescent antibody test is the definitive method for diagnosing early syphilis. The antibodies produced in response to infection with Treponema pallidum are detectable during primary syphilis. Levels will continue to increase as the disease progresses to secondary syphilis. The RPR is a screening test. The test detects the presence of cardiolipin and other indicators that correlate to disease activity, however, it is not highly specific and does not correlate with disease activity. Spirochetes cannot be recovered outside of the body and thus cannot be cultured. FTA with adsorption is done to diagnose late latent or tertiary syphilis.

The use of molecular testing to identify the presence of Methicillin-Resistant Staphylococcus aureus (MRSA) is not always the best method because false-positive results can occur. However, the main purpose for performing molecular testing on surveillance cultures for MRSA is all of the following, EXCEPT? - Shorter turnaround time - High sensitivity - Reduction of patient isolation days - Does not require culture confirmation

- Does not require culture confirmation Does not require culture confirmation is the correct answer because molecular testing for MRSA has a very high sensitivity, which can lead to false-positive results requiring the use of culture confirmation. Shorter turnaround time, High sensitivity, and Reduction of patient isolation days are all incorrect answers because these are reasons why molecular testing for MRSA are performed. The major advantage of MRSA molecular testing is the reduction in turnaround time, which can reduce the number of isolation days if the patient tests negative for MRSA.

Which of the following serological tests would be used for the diagnosis of Q-fever? - Weil-Felix test - Quellung test - EIA or indirect immunoflourescence - Cold agglutinin test

- EIA or indirect immunoflourescence Serology testing utilizing indirect immunofluorescences or EIA is the most commonly used methodology. IFA is considered the reference method due to its high specificity and sensitivity in both acute and chronic infections. It is also reliable, cost-effective, and easy to perform. The Weil-Felix test detects cross-reacting rickettsia antibodies by using Proteus vulgaris. The Quellung test utilizes antibodies to bind to the bacterial capsule, which can be used to identify serotypes of Streptococcus pneumoniae. Cold agglutinins are autoantibodies that cross-react with red blood cells (RBCs). They cause RBCs to clump together when the person is exposed to cold temperatures and increases the chances of those RBCs getting destroyed.

Clenched-fist cellulitis is commonly found in patients whom have been in a physical altercation. Which organism below is the most likely cause of this condition? - Neisseria gonorrhoeae - Staphylococcus aureus - Streptococcus anginosus group - Eikenella corrodens

- Eikenella corrodens The correct response is Eikenella corrodens as it is normal flora of the mouth and those that have been in an altercation and have punched someone in the mouth, can often become infected with this bacteria. Neisseria gonorrhoeae is a sexually transmitted infection that can cause acute urethritis in males and cervicitis in females, as well as pharyngitis, conjunctivitis, anorectal infections and some disseminated infections as well. This organism is not part of the normal human flora. Staphylococcus aureus, while part of the normal skin flora of many individuals, does not cause clenched-fist cellulitis. S. aureus been isolated from other cellulitis infections and is also the causative organism in scalded skin syndrome, can cause toxic shock syndrome, bacteremia and many other infections. Streptococcus anginosus group, while part of the normal oral and GI flora, are viridans streptococci. This group may group with Lancefield groups A, C, F, G or L and have been associated with abscesses and bacteremia caused by invasive pyogenic infections.

All of the following statements regarding the HBV vaccine are correct, EXCEPT: - The vaccine is effective in 90% of cases. - Employers may require a fee to administer the vaccine. - Side effects are rare and minimal. - The vaccine is administered over a six-month period.

- Employers may require a fee to administer the vaccine. The correct answer is employers may require a fee to administer the vaccine. Employers CANNOT charge employees a fee to administer the vaccine. The OSHA standard requires that the vaccine be administered free of charge to employees who are at risk for exposure to infection. The vaccine is at least 90% effective when administered as prescribed by the manufacturer, which involves three doses administered over a six-month period. Side effects are rare, but may include redness and pain at the site of injection.

A 12-year-old female went to her doctor for her yearly back-to-school check-up. She was in good health and was asymptomatic at the time of the examination. Due to the increased incidence of parasites in the area, the doctor ordered a stool for parasite examination as part of the routine physical testing. Multiple suspicious forms, measuring approximately 9 µm each were seen. Which of the following is most likely the identification of these forms? - Endolimax nana - Entamoeba coli - Iodamoeba butschlii - Pseudoparasite

- Endolimax nana As the question denotes, this child is was asymptomatic. All options given are nonpathogenic parasites, including the pseudoparasite. Based on size with the non-pathogenic ameba Endolimax nana. The organism may be identified in part by its small size (trophozoites less than 12 µm). Examination of the photograph shown indicates that the organism lacks peripheral chromatin, another key identifying feature, with a central or eccentric karyosome. Since the child is healthy and asymptomatic, it is likely that she will not require treatment. While Entamoeba coli and Iodamoeba butschlii are both nonpathogenic, both have larger trophozoite forms. E. coli trophozoites tend to range 15 to 50 µm and the nucleus has a large karyosome with clumped chromatin or irregular. I. buschlii are smaller than E. coli but larger than E. nana and range 8-20 µm. The nucleus may look to have a halo on a permanent stain with a central or eccentric karyosome and fanning chromatin. A pseudoparasite is an artifact such as fiber, fat, or other undigested material that resembles a parasite but is actually not.

Which cyst is identified in Section D of the image shown? - Entamoeba coli - Giardia intestinalis - Entamoeba histolytica - Endolimax nana

- Endolimax nana Endolimax nana cysts are shown in section D of the image and are characterized as a spherical to oval. They contain 1-4 nuclei, but mature cyst most commonly have 4 nuclei. They have a large blot-like karyosome, usually centrally located. There is no peripheral chromatin. The cytoplasm may have granules or other small non-descript masses. Chromatin bars are not found. Entamoeba coli cysts are shown in section B of the image and have a thick cell wall the surrounds the cyst. The cyst can contain 1-8 nuclei. The nuclei contain an eccentric karyosome with uneven peripheral chromatin. Young cysts can contain a glycogen mass, and if large, can displace the nuclei to opposite ends of the cyst. Chromatoid bars are also present and often show pointed or splintered ends. Giardia intestinalis cysts are shown in section A of the image and are ovoid in shape. Immature cysts have 2 nuclei and 2 median bodies. Mature cysts contain 4 nuclei and 4 median bodies. The cytoplasm is also retracted from the cell wall and can show a visible space in the cyst. Entamoeba histolytica cysts are shown in section C of the image and are round in shape. One to 4 nuclei are present in the cyst. They contain a central karyosome with even peripheral chromatin. Young cysts have a chromatoid bar, as shown in this image. Young cysts can also show a glycogen mass, which typically disappears as the cyst matures. It is important to note that ingested red blood cells are not seen in the cyst stage, but are characteristic in the trophozoite stage.

Loeffler's medium is useful in making the presumptive identification of isolates suspicious for Corynebacterium diphtheriae recovered from oropharyngeal cultures because it: - Inhibits the growth of contaminating bacteria - Detects the production of H2S - Enhances granule formation as seen in methylene blue stains - Screens out the toxin producing strains

- Enhances granule formation as seen in methylene blue stains Although the identification of Corynebacterium diphtheriae in upper respiratory specimens cannot be made by the study of direct smears, the accentuated granule formation seen in methylene blue stains of isolates grown on this medium is a helpful property in determining which strains should be further studied, either by subculture to tellurite medium or for toxicity studies. Loeffler's medium is a rich, non-inhibitory culture medium on which many bacterial species readily grow; however, bacterial cells suspicious for Corynebacterium diphtheriae can be readily identified because of the metachromatic granules (Babes-Ernst granules). Corynebacterium diphtheriae does not produce H2S gas and there are no detectors in the medium even if the gas were produced. The medium does not differentiate toxin-producing from non-toxin-producing strains.

The 20 µm in diameter cyst illustrated in the photograph had been observed microscopically in a trichrome stained mount prepared from a stool specimen of a patient with low grade, intermittent diarrhea. What is the presumptive identification? - Entamoeba histolytica - Entamoeba coli - Entamoeba hartmanni - Iodamoeba bütschii

- Entamoeba coli Entamoeba coli is the correct response. Note that there are 5 nuclei, each with a distinctly eccentrically placed karyosome and a chromatin ring that is irregular in width and blotchy in distribution. The usual size range is 15-25 µm. Entamoeba histolytica is an incorrect response. E. histolytica cysts are on the average smaller than those of E. coli, have no more than 4 nuclei within which the karyosomes are centrally placed, and have an even distribution of chromatin around the outer ring. The usual size range is 12-15 µm. Entamoeba hartmanni is an incorrect response. E. hartmanni cysts are small, rarely larger than 10µm, and possess less than 5 nuclei, each with a small central karyosome and even distribution of chromatin in the outer ring, simulating what is observed with Entamoeba histolytica. Iodamoeba bütschii is an incorrect response. I. bütschii cysts typically have only a single nucleus, no peripheral chromatin. The karyosome is larger with eccentric refractile granules. The usual size range is 10-12 µm.

Not all strains of Entamoeba histolytica appear to be pathogenic, and recent molecular studies indicated that there was a non-pathogenic variant of Entamoeba histolytica. What is this non-pathogenic variant? - Entamoeba hartmanni - Entamoeba moshkovkii - Entamoeba dispar - Entamoeba coli

- Entamoeba dispar Several DNA sequencing assays are available to separate the non-pathogenic variant, Entamoeba dispar, from Entamoeba histolytica. It is important to know that these assays are available in cases where the recovery of an isolate identified as Entamoeba histolytica by conventional methods may not have a clinical correlation. Entamoeba hartmanni is similar to E. histolytica butdoes not possess the exclusive genetic composition representing pathogenicity. Entamoeba moshkovkii is an infectious agent to humans and is morphologically identical to E. hystolytica. It is identified as a GI pathogen. Entamoeba coli is not pathogenic, but it is easily distinguished from E. histolytica. As the trophozoites and cysts of Entamoeba coli are easy to identify when seen in stool specimens, antigen testing has not been necessary.

This parasite resides in the mouth where, when present, measures approximately 17 µm. - Entamoeba histolytica cyst - Entamoeba gingivalis trophozoite - Acanthamoeba species cyst - Trichomonas vaginalis trophozoite

- Entamoeba gingivalis trophozoite Entamoeba gingivalis resembles Entamoeba histolytica both in size and in nuclear characteristics however, Entamoeba histolytica is commonly found in the large intestine. Entamoeba gingivalis may contain numerous cytoplasmic inclusions such as red blood cells, white blood cells, and bacteria and is most frequently recovered from the mouth. Acanthamoeba species is typically isolated from the CNS and eye whereas Trichomonas vaginalis is typically isolated from genital specimens.

Recovered in a stool sample, this suspicious form measures 7 µm. What is the MOST likely identification? - Entamoeba coli - Entamoeba hartmanni - Entamoeba histolytica - Entamoeba gingivalis

- Entamoeba hartmanni The correct answer is Entamoeba hartmanni. Entamoeba histolytica, Entamoeba hartmanni, and Entamoeba gingivalis have the same basic nuclear structures - evenly distributed peripheral chromatin which surrounds a small central karyosome. The contents potentially located in the cytoplasm vary among the organisms as does the specimens of choice for their recovery (stool for the former two and mouth scrapings for the latter). Entamoeba hartmanni is the most likely identification due to its recovery in stool, typical morphologic characteristics, and relatively small size (less than 10 µm). Entamoeba coli is at a minimum 20 µm, has a large eccentric karyosome and a chunky distribution of nuclear chromatin. None of these characteristics are observed in this photo.

Which of the following organisms is considered to be pathogenic? - Entamoeba histolytica - Entamoeba coli - Chilomastix mesnili - Trichomonas hominis

- Entamoeba histolytica Entamoeba histolytica is the only organism of those listed that is considered to be pathogenic. It occurs in as many as 10% of the world's population and is considered a leading cause of parasitic deaths. It is transmitted through ingestion of the infective stage (the cyst), which occurs through hand-to-mouth contamination and food or water contamination. It may also be transferred via unprotected sex. Improperly treated water supplies are additional sources of possible infection. Historically, it has been prevalent in homosexual communities because it causes frequent asymptomatic infections in homosexual men, particularly in western countries. It may be diagnosed by standard methods such as wet prep and permanent staining techniques on a suspected stool sample, as well as alternative methods such as antigen tests, ELISA, indirect hemagglutination (IHA), gel diffusion precipitin (GDP) and indirect immunofluorescence(IIF).

A unidentified colony was inoculated to the surface of a filter paper strip impregnated with cytochrome oxidase reagent (dimethyl-p-phenylenediamine dihydrochloride) as shown in the picture on the right. The family of bacteria ruled out by the reaction seen is: - Pasteurellae - Neisseriaceae - Enterobacteriaceae - Pseudomonadaceae

- Enterobacteriaceae The correct answer is Enterobacteriaceae. The key biochemical reactions by which the family Enterobacteriaceae can be identified include fermentation of carbohydrates, reduction of nitrates to nitrites and the absence of cytochrome oxidase activity. Some or all of the members of the other families of bacteria listed produce cytochrome oxidase. A positive spot oxidase test, as shown in this photograph, is a useful in separating these families of bacteria from members of the Enterobacteriaceae family.

Which of the following parasites has the egg as the infective stage of the parasite for humans? - Enterobius vermicularis - Taenia solium - Trypanosoma cruzi - Schistosoma mansoni

- Enterobius vermicularis Enterobius vermicularis (also known as Pinworm) infects humans after ingestion of eggs. The eggs migrate to the digestive tract, to the small intestine, where they hatch and release larvae. Although Schistosoma mansoni and Taenia solium have eggs in their corresponding life cycles, this form is not the infective stage for human infections. Taenia solium infects humans after ingestion of pork contaminated with cysticercus larva. This larva consists of a scolex surrounded by a thin-walled cyst filled with fluid. The larvae will emerge in the small intestine, mature, and release eggs. Those eggs are consumed by the animal species (pig), in which the larva will deposit in the tissues. Trypanosmoa cruzi does not have an egg stage at all. T. cruzi is a hemoflagellate and requires an arthropod vector (the reduviid bug) for transmission. When the bug bites a human, infective trypomasitgotes are deposited next to the bite. Humans will scratch the bite and rub these into the area and into the host. Schistosoma mansoni infection occurs through the water-residing cercaria, which enters the human body by drilling into the skin. They migrate to the bloodstream where they mature and reside in the veins surrounding the intestinal tract. The females lay eggs. The eggs reach water and release the miracidium that must find a snail host to develop into cercaria. The egg is not the infective form for humans.

The 30 X 50 µm ovum illustrated in the image are most commonly observed by microscopic examination of transparent adhesive tape mounts of perianal skin of children who have complained of nocturnal anal pruritus. What is the most likely presumptive identification? - Cystoisospora belli - Necator americanus - Enterobius vermicularis - Trichuris trichiura

- Enterobius vermicularis Enterobius vermicularis is a correct response. The eggs are collected using a sticky paddle or a piece of clear cellophane tape pressed against the perianal region. Enterobius ova are oval in outline with flattening along one margin, simulating a deflated football. The shell is smooth and slightly thickened. A well-developed larva is commonly observed internally, which retracts away from the inner shell membrane, leaving an open space. Cystoisospora belli is an incorrect response. Cystoioocysts are also oval in outline and have a smooth, thin outer shell. Internally, a single spherical sporocyst may be observed, but more typically mature oocysts are noted which contain two sporocysts. One is advised to search further in a smear preparation for detection of oocysts with double sporocysts to ensure an accurate identification. Necator americanus is an incorrect response. Necator ova, although also oval in outline, are not flattened on one side and the outer shell is thin and transparent. Although the inner yolk sac retreats, leaving a clear space beneath the shell, further development into an embryo is not observed. Trichuris trichiura is an incorrect response. Trichuris ova are easy to recognize with their barrel-shape and a distinctive protruding, convex, hyaline polar plug at each end. The shell is smooth but relatively thick and the internal developing embryo reaches the inner lining of the shell without leaving an open space.<

The upper photograph is of a 10 mm long nematode adult; the lower photograph is a close in view illustrating the transparent wing-like alar anterior expansion (blue arrow). These adult nematodes occupy the intestine and may occasionaly be seen at the anal opening of patients with diarrhea. Select from the answer choices below the presumptive identification of this nematode. - Trichuris trichiura - Ascaris lumbricoides - Enterobius vermicularis - Ancylostoma duodenale

- Enterobius vermicularis Enterobius vermicularis is the correct response. Illustrated in each of the photomicrographs are two key identifying features of this 10 mm long Enterobius vermicularis adult worm- the pointed tail ("pinworm") and the anterior alar wing-like expansion (blue arrow). Trichuris trichiura is an incorrect response. Trichuris adults are somewhat longer, measuring up 40 - 50 mm long. Male Trichuris worms have a thin caudal extremity with a 360 degree terminal coil, from which the colloquial name "whipworm" is derived. In intestinal infections, the head is buried in the epithelium and worms are rarely seen in stool specimens. Ascaris lumbricoides is an incorrect response. Ascaris worms are thick in diameter and very long (15 - 35 cm). Male worms have a smooth cuticle and a curved, non-pointed tail. Ancylostoma duodenale is an incorrect response. Ancylostoma (hookworm) adult worms measure up to 1.5 cm in length, and are distinguished by their mouth part that is fitted with a double pair of chitinous teeth. The tail section is rounded rather than pointed. In addition, rhabditiform larvae have a long, narrow buccal cavity and an inconspicuous genital primordium.

The upper image is a photomicrograph of a Gram stain prepared from a positive blood culture obtained from a 68 year old female with an indwelling urinary bladder catheter. Smooth, gray, faintly beta hemolytic colonies were recovered in subcultures of the positive bottle. The tubes shown in the lower photograph are: ------> an esculin slant (left) displaying intense brown coloration ------> a 6.5% sodium chloride broth (right) showing cloudy growth The most likely identification is: - Non-Enterococcus Group D - Streptococcus mitis - Enterococcus faecalis - Staphylococcus saprophyticus

- Enterococcus faecalis Enterococcus faecalis is the correct answer. The Gram stain illustrates gram-positive cocci in pairs and short chains consistent with Enterococcus species. The hydrolysis of esculin and ability to grow in 6.5% sodium chloride are characteristics consistent with that species. Enterococcus faecalis can be alpha, beta, or gamma hemolytic on sheep blood agar. Non-Enterococcus Group D is incorrect. The presence of the group D antigen is common with Enterococcus species; however, other Gram positive cocci can also possess the group D antigen so additional biochemical testing is needed for identification. Pediococcus species and Streptococcus gallolyticus can both possess the group D antigen. Streptococcus gallolyticus will be bile esculin positive, will not grow in 6.5% sodium chloride, and is pyrrolidonyl arylamidase (PYR) negative. Pediococcus species will be PYR test negative whereas Enterococcus species will be PYR positive. Variable reactions by Pedicoccus species with bile esculin and 6.5% sodium chloride can occur. Streptococcus mitis is incorrect. S. mitis cannot grow in high concentrations of salt and only rarely is involved in urinary tract infections. In addition, this species is an alpha streptococcus species and will be PYR negative separating this organism from Enterococcus species, which are PYR positive. Staphylococcus saprophyticus is incorrect. This species is involved in urinary tract infections, particularly in middle-aged females and can grow in 6.5% sodium chloride; however, it appears as Gram positive cocci in clusters rather than in chains and does not hydrolyze esculin.

A Gram stain of serous exudate is shown in the image. What should the tech report to the physician? - Gram-positive cocci present - Gram-positive cocci in tetrads and clusters present - Gram-positive cocci suggestive of Staphylococcus species present - Bacteria present

- Gram-positive cocci in tetrads and clusters present In reporting out Gram stains, one should not go beyond what objective observation will allow. In this case, bacterial cells are observed, which are spherical and gram-positive. Their arrangement in tetrads and clusters might be helpful to the physician, suggesting a Staphylococcus species. However, one should stop short of naming the genus in an official report, as the large gram-positive cocci in tetrads is also suggestive of Micrococcus species, for which human infections have not been reported.

Which one of these Gram-positive species has a high incidence of vancomycin-resistance? - Aerococcus species - Enterococcus faecium - Group D streptococci - Streptococcus pyogenes

- Enterococcus faecium Vancomycin-resistance in Enterococcus faecium is close to 90% in blood cultures in the U.S. In addition to Enterococcus faecium, E. faecalis is also isolated in nosocomial infections such as UTI or bacteremia. Leuconostoc and Pediococcus are other Gram-positive cocci that demonstrate resistance to vancomycin. Aerococcus species, Group D streptococci, and Streptococcus pyogenes are usually susceptible to vancomycin. Aerococcus is an opportunistic pathogen causing infection similar to other gram-positive cocci. Group D streptococci are part of the viridans group found as normal flora, but may cause infections such as bacteremia and endocarditis. Streptococcus pyogenes is found as normal flora existing on skin and in the oropharynx, but may cause serious infections such as pharyngitis, necrotizing fasciitis, TSS, and rheumatic fever.

A dermatophyte that produces thin-walled, two or three-celled macroconidia in clusters, and no microconidia, most likely belongs to the genus: - Microsporum - Trichophyton - Epidermophyton - Ajellomyces

- Epidermophyton One of the key characteristics in the identification of Epidermophyton floccosum is the inability of this dermatophyte to produce microconidia. Two to four-celled, club-shaped macroconidia are produced, usually in clusters of two or three. Both Microsporum species and Trichophyton species produce microconidia, the latter genus in profusion. The organism name, Ajellomyces dermatitidis is actually the same organism as Blastomyces dermatitidis, just a different form. The genus Blastomyces dermatitidis does not belong to the dermatophytes; rather it belongs to the group of fungi known as Systemic Mycoses. It produces an abundance of microconidia which are single, circular and produced on short conidiophores that resemble lollipops.

Illustrated in the top photograph is a 4-day growth of silky, light gray-white to yellow colonies grown on Sabouraud's dextrose agar incubated at 30° C, recovered from an "athlete's foot" infection (tinea pedis) of a young football player. Note the projection of delicate hyphae to the periphery of the colonies. The identification can be made by observing the conidia formations in the lactophenol blue stained mount prepared from the surface of one of the colonies. With these observations, select the species identification from the multiple choices. - Trichophyton mentagrophytes - Trichophyton tonsurans - Epidermophyton floccosum - Microsporum gypseum

- Epidermophyton floccosum Epidermophyton floccosum is the correct selection. The silky gray-yellow colonies with outward projecting delicate hyphal strands are highly suggestive of E. floccosum. The more definitive identification is made by observing the microscopic appearance of the three to five celled macroconidia that are typically large and club-shaped with smooth walls, and attached directly and laterally from hyaline hyphae. Microconidia are never produced. E. floccosum is an anthropophilic dermatophyte that is an important cause of tinea cruris (jock itch) and tinea pedis (athlete's foot). Trichophyton mentagrophytes colonies are either cottony or granular depending on maturation and are tan to cream colored. Microscopically are observed small spherical microconidia irregularly spaced in loose clusters along thin hyphae. Macroconidia are produced singly and contain four to five cells separated by cross-walls. They are smooth and cigar-shaped. Trichophyton tonsurans colonies are yellow to buff, and suede-like without peripheral hyphal extensions. Typically, the colonies have a rust-colored reverse. Microscopically observed are the distinctive relatively large, tear-drop or club-shaped microconidia produced laterally in a "birds on the fence" pattern on each side of hyaline hyphae. Microsporum gypseum colonies are cinnamon-brown with outward projecting delicate hyphae. In stained microscopic mounts, large multi-celled fusiform macroconidia are observed, each at the tip of a slender conidiophore, with the distal cells being rounded rather than with a tapered tip.

A D-test is performed on gram positive cocci to determine inducible resistance to clindamycin when the isolate is sensitive to clindamycin and resistant to which antibiotic? - Methicillin - Vancomycin - Cefoxitin - Erythromycin

- Erythromycin The correct answer is erythromycin. When erythromycin tests resistant and clindamycin is susceptible, an isolate should be tested for inducible clindamycin resistance. A positive test is indicated by a blunting of the zone of inhibition between the two disks, demonstrating a "D" around the clindamycin disk, giving it the name, "the D-test". The D-test is based on a modified double disk diffusion test and is only used to detect inducible macrolide resistance, none of the other antibiotics listed are macrolides.

Which organisms are the appropriate stock cultures for quality control testing of oxidase production? - Escherichia coli / Klebsiella pneumoniae - Salmonella typhimurium / Escherichia coli - Escherichia coli / Pseudomonas aeruginosa - Proteus mirabilis / Escherichia coli

- Escherichia coli / Pseudomonas aeruginosa When performing quality control, organisms should always be used that can show both a positive and negative reaction for the testing, to ensure both reactions are occurring properly. The oxidase test is a test used to differentiate the Enterobacteriaceae family (except Plesiomonas) from Pseudomonas species, which are oxidase positive. All of the organisms in this question are part of the Enterobacteriaceae, thus they are oxidase negative. The only organism that is oxidase positive is Pseudomonas aeruginosa. The correct answer is Escherichia coli, which is oxidase negative and Pseudomonas aeruginosa, which is oxidase positive. Both positive and negative reactions would be checked using these organisms. E. coli and Klebsiella pneumonaie are both part of the Enterobacteriaceae and oxidase negative, thus a positive and negative reaction would not be obtained for quality control. Salmonella typhimurium and E. coli are both part of the Enterobacteriaceae and oxidase negative, thus a positive and negative reaction would not be obtained for quality control. Proteus mirabilis and E. coli are both part of the Enterobacteriaceae and oxidase negative, thus a positive and negative reaction would not be obtained for quality control.

Illustrated in the upper image is an 8-day-old old green black colony growing on the surface of Sabouraud Dextrose Brain Heart Infusion (SABHI) agar, obtained from a superficial skin lesion characteristic of chromomycosis. The black pigment extends to the reverse side of the colony. The identification can be made by observing the characteristic fruiting body as illustrated in the lower image. What is the most likely identification of this fungi? - Exophiala jeanselmei - Cladophialophora carrionii - Fonsecaea pedrosoi - Phialophora verrucosa

- Exophiala jeanselmei The correct answer is Exophiala jeanselmei. Exophiala jeanselmei exhibits slow growth and the black pigment on the surface that extends to the reverse of the colony is distinctive for chromomycosis. The dark-staining septate hyphae containing a distinctive conidiophore with a pointed terminal end, giving rise to clusters of elongated pigmented conidia is the exophiala type sporulation characteristic of Exophiala jeanselmei. Fonsecaea pedrosoi colonies are not specific. Sporulation is of the acrotheca type that is characterized by the branching of conidiophores produced from the ends of septate hyphae, simulating the prongs of a coat rack. Short chains of elliptical conidia are produced from the tips of these conidiophores. Cladophialophora carrionii colonies are also not specific. Sporulation is characterized by the production of long straight chains of elliptical, dark-staining conidia each separated by a delicate scar known as a dysjunctor. The long conidiophores with a pointed end are not observed with Cladosporium sp. Phialophora verrucosa colonies are not distinctive. Sporulation is characterized by the production of short urn-shaped phialides with a narrow bottle-like opening derived laterally from elongated conidiophores. Spherical of oval-shaped, yellow pigmented conidia are produced from within each phialide, forming loose aggregates at the terminal opening.

Which of the following best describes the morphological characteristics of Mucor species of fungi? - Slow growing (30 days), cream to tan and waxy; tissue form shows broad based budding with double contoured walls - Rapid growing (3-5 days), blue-green to gray-green colonies; tissue form shows septate hyphae with dichotomous branching - Moderate growth colonies (21-30 days), wrinkled, brown in appearance; tissue form shows budding cells are attached to the parent cell by a narrow neck - Extremely rapid growing (1-3 days), wooly and gray to brown, or gray-black colonies; tissue form shows large, ribbonlike, twisted pieces of aseptate hyphae with occasional septa

- Extremely rapid growing (1-3 days), wooly and gray to brown, or gray-black colonies; tissue form shows large, ribbonlike, twisted pieces of aseptate hyphae with occasional septa The correct answer is "Extremely rapid growing (1-3 days), wooly and gray to brown, or gray-black colonies; tissue form shows large, ribbonlike, twisted pieces of aseptate hyphae with occasional septa." Mucor species are similar to Rhizopus species in morphology and growth and both cause Mucormycosis, a potentially severe fungal infection. These fungi are extremely fast growing which rules out all other options given. Slow growing, waxy with broad based budding is more characteristic of Blastomyces species, while the rapid growing blue-green colonies with septate hyphae is most likely Aspergillus species. Paracoccidiodes colonies can be wrinkled and may be brown while the budding cells are attached to parent cell by a narrow neck.

One of the key biochemical characteristics by which Escherichia coli serogroup O157 can be screened from stool specimens is? - Failure to ferment sorbitol - Failure to ferment lactose - Positive methyl red - Lack of motility

- Failure to ferment sorbitol MacConkey agar, with sorbitol (SMAC) instead of lactose, is a screening culture media helpful in the detection of E. coli O157 from stool specimens. E. coli O157 produces heavy growth on SMAC, but does not ferment sorbitol. However, SMAC should not be the only test to identify potential O157 strains. In general, all species of the genus Escherichia ferment lactose and produce a positive methyl red reaction. Most species of E. coli are motile; nonmotile species are not limited to any serogroup, but do exist in some O157 isolates.

The common name of which parasite is the sheep liver fluke? - Fasciolopsis buski - Fasciola hepatica - Clonorchis sinensis - Paragonimus westermani

- Fasciola hepatica Fasciola hepatica is commonly known as the sheep liver fluke. When the organism infects sheep, it causes a disease known as liver rot. Humans ingest metacercaria on raw water vegetation. Once ingested the larvae migrate through the intestinal wall and peritoneal cavity and travel to the liver. In general terms, the common names of these particular parasites are derived from the area of the human body where they tend to inhabit. Knowledge of the parasite life cycles is helpful in making this determination. Fasciolopsis buski is commonly referred to as the giant intestinal fluke, Clonorchis sinensis is the Chinese liver fluke and Paragonimus westermani is known as the lung fluke.

The 20 mm mature adult fluke illustrated in the photograph has a normal habitat in the liver bile ducts. Humans become infected by ingesting raw or undercooked water plants contaminated with infective metacercaria. These adult flukes are only observed during surgery involving the liver or at autopsy. Intermittent upper abdominal discomfort and low grade jaundice may be experienced. From the multiple choices listed, select the presumptive identification of this fluke. - Clonorchis sinensis - Fasciola hepatica - Fasciolopsis buski - Paragonimus westermani

- Fasciola hepatica The adult Fasciola hepatica is 20 - 30 mm in size and has a cone like cephalic protrusion. Anterior and ventral suckers are clearly visible. Being hermaphrophilic, it contains a short convoluted uterus observed anterior, and delicately branched testes located posterior. C. sinensis flukes are less than half the size (7 - 15 mm) and are bottle-shaped with a long protruding cephalic head. They contain highly visible, broad branched testes occupying the posterior part of the fluke from which the genus name clonorchis ("branched testes") is derived. F. buski flukes are large, measuring up to 70 mm long, and inhabit the small intestine, particularly the duodenum and jejunum. Distinctive is the rounded cephalic end rather than a cone-shaped anterior protrusion. Being hermaphrophilic, a convoluted branching anterior uterus and delicate branching testes is observed posteriorly. P. westermani flukes are relatively small (10 - 16 mm) with a flattened oval shape. One end is contracted and the other is the form of a broad smooth curve. Being hermaphrophilic, irregularly lobed testes lie oblique to one another in the posterior third of the adult fluke along side a lobed ovary and a closely coiled uterus lying anterior. Adult flukes primarily occupy the lungs.

A 55-year-old female, who recently returned from an extensive trip to China, presented to her physician complaining of diarrhea and abdominal cramps. The doctor ordered a complete blood count (CBC), comprehensive metabolic panel (CMP), and stool for culture and parasite examination (O & P). The CBC revealed pronounced eosinophilia. The CMP and stool culture were unremarkable. The O & P revealed suspicious forms like the one below that each measured approximately 140 µm by 80 µm. This patient is most likely infected with: - Paragonimus westermani eggs - Diphyllobothrium latum eggs - Fasciola/Fasciolopsis eggs - Ascaris lumbricoides eggs

- Fasciola/Fasciolopsis eggs Fasciola/Fasciolopsis eggs is the correct answer because these eggs measure 130-140 µm x 63-90 µm. Fasciola/Fasciolopsis are indistinguishable and recovery of an adult worm is necessary to speciate these organisms. Paragonimus westermani eggs are incorrect because patients infected with Paragonimus westermani typically suffer from respiratory difficulties. The organism produces eggs similar to those shown here that are recovered in sputum specimens. Eggs from this organism measure 80-120 µm x 39-67 µm and even though it has an operculum, the operculum is flattened with raised opercular shoulders. Diphyllobothrium latum eggs is incorrect because eggs are generally smaller in size (measuring 58-76 µm x 40-51 µm) than those depicted here and possess a small terminal knob opposite the operculum. Infected patients complain of several symptoms including digestive difficulties and abdominal discomfort. Ascaris lumbricoides eggs is incorrect because these eggs typically measure 45-95 µm x 35-50 µm and does not have an operculum. The egg in this image is much larger and has an operculum.

If a bacteria produces the enzyme tryptophanase to break down the amino acid tryptophan, which of the following tests will be positive with Kovac's reagent? - Oxidase test - Esculin test - Catalase test - Indole test

- Indole test The indole (modified Kovacs' reagent) is used to assess the ability of certain bacteria to produce indole by the deamination of tryptophan. Indole reacts with aldehyde in the Kovac's reagent to produce a red color. An alcoholic layer holds the red color as a ring at the top of the tube used for the indole test.

This parasite is found worldwide, particularly in areas in which sheep and cattle are raised. The natural host for the completion of this parasite's life cycle is the sheep. Humans often serve as accidental hosts. Which of the following conditions may be associated with the presence of this stool parasite from a human measuring 130-150 µm long by 60-90 µm wide? - Paragonimiasis - Fasciolopsiasis - Fascioliasis - Ascariasis

- Fascioliasis The disease caused by Fasciola hepatica is called Fascioliasis. The egg shown here resembles that of either Fasciola hepatica or Fasciolopsis buski. The eggs of both flukes are identical and are considered indistinguishable. They both consist of an oblong undeveloped miracidium equipped with a distinct operculum. However, the upper limit of size is considered Fasciola hepatica. Both of these parasites are transmitted through ingestion of raw infected water plants. Additionally, the geographic distribution of Fasciola hepatica is worldwide and the natural host for completion of the life cycle is the sheep. Recovery of the adult flukes is necessary to confirm the identification between the two organisms. The parasitic organism Paragonmus westermani causes the disease paragonimiasis. It is transmitted through the ingestion of undercooked crayfish or crabs and occurs in several areas of the world: Asia, Africa, India, and South America. Once ingested this fluke migrates through the intestinal wall eventually going into lung tissue. The eggs/ova of Fasciolopsis buski resemble Fasciola hepatica but are slightly smaller in size, and the location of where the adult worms take up residence in the human host differs: F. buski in the small intestine and F. hepatica in the bile ducts. The parasite Fasciolopsis buski causes the disease fasciolopsiasis. Additionally the geographic distribution of F. buski is limited to areas of the Far East and it has animals such as rabbits, pigs, and dogs as the reservoir hosts. All of these diseases are caused by trematodes except for ascariasis which is a worldwide infection caused by the large intestinal roundworm/Nematode of Ascaris lumbricoides. This parasite's egg is smaller in size than the other answer choices presented. Infection occurs through direct ingestion of the ova usually as a result of using human feces as a fertilizer.

The image shows a variety of colony elevations. Which colony elevation description matches with figure B in the image? - High Convex or Dome - Low Convex - Flat - Raised

- Flat Elevation is observed in colonies by tilting the culture plates and looking at the side of the colony to view how the colony is raised off the agar plate. Figure B shows a flat colony as there is not much elevation shown off the surface. High Convex or Dome is shown in Figure A. The colony has a high elevation off the agar surface and is dome-shaped. Low Convex is shown in Figure C. The colony elevation is a bit lower but still rather convex, or round in shape. Raised is shown in Figure D. The colony is not rounded, so it is not convex, and is only slightly elevated off the media surface. Other colony elevations include umbilicate, which has a central depression in the colony, and umbonate which as a central elevation in the colony.

Illustrated in the top image is a slow-growing, 8-day-old colony with velvety brown, deep radial grooves and a black periphery consistent with one of the agents of chromomycosis. In the bottom image, note the conidiophores produced from the sides of the hyphae producing short, branching phialides, giving rise to clusters of elliptical conidia. From the list of choices shown below, select the correct presumptive identification of this isolate. - Phialophora verrucosa - Cladophialophora carrionii - Fonsecaea pedrosoi - Exophiala species

- Fonsecaea pedrosoi Fonsecaea pedrosoi is the correct response. The colony morphology is not species specific but with the dark brown to black mycelium, an agent of chromomycosis can be presumptively suspected. Microscopically is shown the branching phialides giving rise to small clusters of elliptical conidia. This represents the acrotheca-type sporulation, most consistent with Fonsecaea pedrosoi. There is considerable strain variation within the genus Fonsecaea, and other species may produce sporulation as seen with Cladosporium or Rhinocladiella species, at times making a definitive identification somewhat difficult. Phialophora verrucosacolonies are also slow-growing with a nondistinctive olive brown to gray-black mycelium. Identification is made by the elongated narrow bottle-like phialides with collarettes from which loose clusters of conidia are produced. Cladophialophora carrionii colonies are also slow growing with a smooth, olive-gray surface mycelium and black pigmentation of the reverse side. Being non-specific, the identification is made by observing the distinctive cladosporium type sporulation in which long unbranched chains of elliptical conidia are produced, with each pair separated by a scar-like dysjunctor. Exophialaspeciescolonies are also slow growing but are more flat and velvety in consistency at maturity. Sporulation is of theExophiala-type in which long and narrow phialides end each with a distinctive sharply pointed terminal end, from which clusters of elongated pigmented conidia are produced.

Illustrated in the upper image is a 4 day growth of a fungus colony on Sabouraud's dextrose agar. Note the cottony to woolly surface, and the distinctive lavender, pink pigmentation. The lower image is of a lactophenol cotton blue pigmented view of long, narrow multi-celled macro-conidia that are sickle-shaped. Based on these observations, select the genus identification of this isolate. - Curvularia - Acremonium - Fusarium - Paecilomyces

- Fusarium Fusarium is the correct answer because colonies are distinctive for the lavender pink to reddish pigmentation. The production of long, sickle-shaped (canoe/banana) segmented macro-conidia is also distinctive. Identification of Fusarium species is important as infections may result in mycotic keratitis. Curvularia is incorrect because Curvularia produces black pigmented colonies. Upon microscopic examination, knobby conidiophores with boomerang-shaped conidia containing four cells can be seen. Acremonium is incorrect because colonies are gray to light shades of yellow with a smooth surface. Small spherical to club-shaped conidia are arranged in loose clusters, each borne at the tip of a long, slender conidiophore ending in a blunt tip. A septum is observed at the base of each conidiophore. Acremonium can resemble Fusarium, but Acremonium produces septate hyphae with fine and narrow phialides that produce oval conidia. Paecilomyces is incorrect even though they can produce pink to lilac colonies. Microscopically, the colonies will demonstrate septate, hyaline hyphae with branching conidiophores that have long, slender, tapered phialides. The conidia will be oval shaped in chains.

The colonies illustrated in the top photograph are 48-hour-old colonies growing on the surface of blood agar that had been incubated anaerobically. The colonies are small, gray-white and convex with irregular borders and internal flecking. Long, slender fusiform Gram negative bacilli with tapered ends are seen in the Gram stain as observed in the bottom photomicrograph. The indole reaction is strongly positive and glucose fermentation is variable; other biochemical reactions are negative except for H2S production by some strains. This isolate is commensal in the upper respiratory tract and has been associated with hospital acquired aspiration pneumonia, lung abscesses, and empyema in hospitalized patients. Based on these observations, select from the multiple choices the name of this isolate. - Veillonella parvula - Prevotella melaninogenica - Bacteroides fragilis - Fusobacterium nucleatum

- Fusobacterium nucleatum Fusobacterium nucleatum is the correct response. Colonies on anaerobic BA are small, gray-white and convex with irregular borders and internal flecking. Beta hemolysis is not observed. In Gram stains, long and slender Gram negative bacilli with distinctly tapered ends are seen. Some strains show weak glucose fermentation, but other carbohydrates are negative (asaccharolytic). Indole and H2S reactions are positive. F. nucleatum should be considered when isolates as presented in this exercise are recovered from induced sputum specimens of hospitalized patients who develop upper respiratory infections. Veillonella parvula colonies on anaerobic blood agar are small, entire, smooth without flecking, convex, and non- hemolytic. Gram stains are distinctive from F. nucleatum. Observed are short Gram negative cocci distributed singly and in loose clusters. Carbohydrate fermentation is absent (asaccharolytic). Additional biochemical assays may be required to make a definitive identification. Being part of the microbiota of the mouth and upper respiratory tract, V. parvula is often recovered in mixed cultures with other bacterial species, or less commonly from blood cultures from hospitalized patients with bacteremia and endocarditis. Prevotella melaninogenica colonies are smooth, concave, and black pigmented. The presence of broad zones of beta hemolysis surrounding the colonies is also distinctive. Small Gram negative cocci lying singly are observed on Gram stains. Most biochemical reactions including indole and H2S are negative. Glucose and lactose are fermented. P. melaninogenica is endemic in the oral cavity and may be recovered from cultures obtained from dental cavity infections. Isolates have also been recovered from human bite wounds. Bacteroides fragilis colonies on anaerobic blood agar are 1-4 mm in diameter, gray, convex, entire with smooth borders, semi-opaque, and free of flecking. Hemolysis is not observed. Older colonies may show internal ring-like whorls. Short, Gram negative cocco-bacilli with rounded ends are observed in Gram stains. Indole and esculin hydrolysis reactions are positive. Glucose and select other carbohydrates are fermented.

Which combination of test/quality control organisms is correct? (One organism positive for the test and one organism negative for the test) - Coagulase: Staphylococcus saprophyticus and Staphylococcus epidermidis - H2S production: Proteus mirabilis and Salmonella serotype Typhi - Phenylalanine deamination: Escherichia coli and Yersinia enterocolitica - Indole: Escherichia coli and Proteus mirabilis

- Indole: Escherichia coli and Proteus mirabilis Escherichia coli is indole positive and Proteus mirabilis is indole negative. Staphylococcus saprophyticus and Staphylococcus epidermidis are both coagulase negative. Proteus mirabilis and Salmonella serotype Typhi both produce H2S. Escherichia coli and Yersinia enterocolitica are both negative for phenylalanine deamination.

Leuconostoc species are streptococcus-like bacteria used in the dairy and pickling industries that have recently caused opportunistic infections in humans. The need to make the laboratory identification is compounded because these bacteria are intrinsically resistant to vancomycin. Which characteristic is most helpful in separating Leuconostoc species from other streptococcus-like organisms? - Gas from glucose in MRS broth - Leucine aminopeptidase (LAP) activity - Ability to grow in 6.5% NaCl (salt tolerance) - Ability to grow at 10° C

- Gas from glucose in MRS broth Leuconostoc species may be misidentified as Enterococcus, alpha-hemolytic streptococci, Pediococcus, Lactococcus, or lactobacilli (Facklam R, Elliott JA: Clin Microbiol Rev; 1995 Oct; 8(4):479-95). The detection of gas from glucose in Mann, Rogosa and Sharpe (MRS) broth (available from Difco Laboratories) overlaid with petrolatum is the one characteristics that differentiates Leuconostoc species from the other streptococcal-like organisms. All of the other characteristics listed in this exercise are either variable for Leuconostoc species or are shared by other streptococcal-like organisms and therefore are not discriminatory tests.

The Enterotest may be used to recover which of the following parasites? - Balantidium coli - Giardia duodenalis - Cryptococcus species - Entamoeba coli

- Giardia duodenalis Giardia duodenalis is the correct answer because the Enterotest is designed to retrieve duodenal material for parasite analysis. The process takes approximately 4 hours and involves the swallowing of a weighted gelatin capsule. After the four-hour "incubation period," the capsule is extracted out of the patient through the mouth and the contents are then examined. This test is helpful in the recovery of Strongyloides stercoralis, Giardia duodenalis, Cryptosporidium species, microsporidia, and Clonorchis sinensis. Balantidium coli is incorrect because this ciliate is best found in stool specimens. Humans acquire the infection by ingesting the infective cyst from contaminated food and water. Cryptococcus species is incorrect because this is a yeast and not a parasite. Cryptococcus species is typically seen in immunocompromised patients. Entamoeba coli is incorrect because this protozoa is best isolated from stool specimens. Humans acquire the infection by ingesting the infective cyst from contaminated food and water.

A large number of antigen detection procedures and assays are available to diagnose clinically suspected parasitic diseases in the absence of finding ova or other forms of parasites in stool preparations or other body fluids. Illustrated in the photograph are antigen positive-staining green dots at sites where small drops of duodenal aspirated fluid had been applied to the test reagents. Trophozoites of this protozoan occupy the upper gastrointestinal tract and the excreted ova may not find the way down the long stretch of bowel to be excreted in stool specimens. From the list of multiple choice selections, indicate the genus/species in which antigen detection may be required to make a diagnosis. - Entamoeba dispar - Giardia duodenalis - Dientamoeba fragilis - Endolimax nana

- Giardia duodenalis Giardia duodenalis is the intended response. It is not uncommon, particularly in cases of light infections, that one of any number of assays to detect Giardia antigens might be performed on duodenal secretions when giardiasis is clinically suspected. Giardia trophozoites primarily occupy the upper intestine, particularly the duodenum, and the low number of ova produced may not reach the caecum and may not be observed in stool specimens. Antigen assays may also be performed to determine if a patient had been cured after treatment. Although antigen tests might be performed on stool specimens to differentiate this non-pathogenic strain from Entamoeba histolytica, the trophozoites of both E. dispar and E. histolytica occupy the epithelial wall of the colon and antigens would only be found in fecal excretions and not in duodenal fluid. Dientamoeba fragilis is not the intended response. Antigen immunoassays and sequence analyses are being developed to detect the presence of D. fragilis antigens in stool specimens to exclude a diagnosis of Giardiasis. D. fragilis only have a trophozoite form in its life cycle and trophozoites in stool specimens may be difficult to recover. As trophozoites occupy the lower bowel, antigens would not be detected in duodenal fluid. Endolimax nanatrophozoites are primarily found in the epithelium of the large bowel and characteristic trophozoites and ova may be found in stool specimens. Being indigenous in the large bowel and colon would preclude antigen detection in duodenal secretions.

Identify the parasite seen in the image that is sometimes found in stool as well as in duodenal contents. The organism in the image measures 15 µm in length. - Trichomonas tenax trophozoite - Chilomastix mesnili cyst - Giardia duodenalis trophozoite - Trichomonas hominis cyst

- Giardia duodenalis trophozoite The Giardia duodenalis trophozoite is noted for its resemblance of "an old man wearing glasses" and looks like it is looking back at you. Keys to its identification include its symmetrical appearance and obvious axostyle. T. tenax, C. mesnili, and T. hominis all contain only 1 nucleus.

All of the following parasites are appropriately matched with its respective means of locomotion, EXCEPT: - Trichomonas sp. - flagella - Entamoeba sp. - pseudopods - Giardia sp. - no locomotion - Balantidium sp. - cilia

- Giardia sp. - no locomotion The correct answer is Giardia sp. - no locomotion. Giardia sp. use flagella to exhibit "falling leaf" motility. Giardia intestinalis is the most frequent cause of parasitic gastrointestinal disease in the United States. In addition to direct microscopic mounts, immunofluorescent detection and antigen detection are widely used to screen for its presence in stool samples. Trichomonas sp. also use flagella as a means of locomotion. Trichomonas vaginalis is one of the most common STDs. Entamoeba sp. extend their pseudopods as a means of locomotion. Entamoeba histolytica causes amebic dysentery in roughly 10% of individuals that are exposed and death rates from amebic dysentery are as high as 70% in endemic areas. Balantidium sp. has short cilia covering its entire surface that allow it to move. Balantidium coli is the only ciliate known to infect humans. It is found most commonly in swine and infections are most prevalent where pigs are raised and slaughtered.

In rapid carbohydrate fermentation testing, Neisseria gonorrhoeae ferments the following sugar(s): - Glucose only - Glucose and maltose - Glucose, maltose, and lactose - Glucose, maltose, lactose, and sucrose

- Glucose only Neisseria gonorrhoeae is able to rapidly ferment glucose only. Neisseria gonorrhoeae is not able to ferment maltose, lactose, or sucrose; only glucose.

Which of the following is most commonly used as a routine staining technique in the clinical microbiology laboratory? - Wright's - Gram - Giemsa - Wright's/Giemsa

- Gram The Gram stain is the principle stain used for microscopic examination of bacteria and is one of the most important bacteriologic techniques within the microbiology laboratory. The two most commonly used hematology stains are Wright's stain and Giemsa stain. Many clinical laboratories use a commercial stain for hematology that is a combination of Wright's and Giemsa.

The Western Blot for HIV-1 infection identification looks for HIV p24 and what other two protein bands to confirm HIV-1 infection? - gp41 or gp160 - gp16 or gp161 - gp61 or gp140 - gp141 or gp60

- gp41 or gp160 Western blot analysis is frequently used as a HIV confirmation test. The Western Blot test detects specific protein bands that are present when an individual has been infected with the HIV virus. This assay is interpreted as positive when at least 2 of the 3 following bands are present: p24, gp41, and gp160.

Which of the following best describes the organisms seen in this illustration: - Gram-positive - Gram-negative - Gram-variable - Acid-fast

- Gram-variable The organisms in this image are demonstrating a gram-variable phenomenon. For the most part, the organisms are staining primarily gram-negative, however, on the tips of some of the rods, there is a gram-positive staining morphology. This can be defined as gram-variable. Gram-positive organisms stain dark purple due to the crystal violet. During the gram stain procedure, crystal violet dye is added first to the slide for 30 sec. The crystal violet is washed off with water and Gram's iodine is added to the slide. The crystal violet and iodine form a complex together that does not wash out in organisms with thick cell walls containing teichoic acid. Therefore, these organisms retain the purple color and do not counterstain with safranin. Gram-negative organisms stain pink from the counterstain, safranin dye. These organisms do not have a thick cell wall for the crystal violet and iodine complex to adhere to. So during the gram stain procedure after the crystal violet and iodine complex is washed out, the slide is stained with safranin dye. This is a pink dye and all organisms including epithelial cells stain pink with this dye. Acid-fast stain is used for Mycobacteria. The carbolfuchsin stain binds to mycolic acid in the cell walls, which is red in color. After the de-colorization stage, the sample is stained with methylene blue. So, any Mycobacterium in the sample will stain red and all other organisms and cells will stain blue.

Asaccharolytic use of glucose would be indicated by which of the following reactions in OF glucose tubes? - Yellow at the top of the open tube and green in the closed tube - Green in both tubes with a little blue at the top of the open tube - Yellow in both tubes - Green at the top of the open tube, yellow in the bottom of the open tube and yellow in the closed tube

- Green in both tubes with a little blue at the top of the open tube The correct answer is green in both tubes with a little blue at the top of the open tube. Asaccharolytic describes an organism that cannot utilize glucose either oxidatively or via fermentation; therefore, there would be no color change (stays green) in either tube. When glucose is utilized in OF tubes, a high concentration of acid produced during fermentation or oxidation will turn the bromothymol blue indicator in OF media from green to yellow. The closed tube will appear yellow if an organism is able to ferment glucose. The open tube will appear yellow if an organism is able to oxidize glucose. Yellow at the top of the open tube and green in the closed tube would indicate that an organism is able to oxidize glucose. Yellow in both tubes would indicate that an organism is able to ferment and oxidize glucose. Green at the top of the open tube, yellow in the bottom of the open tube and yellow in the closed tube would indicate that the organism is able to ferment glucose (which only occurs in anaerobic conditions). The yellow observed in the bottom of the open tube is evidence of the need for anaerobic conditions.

All of the following descriptions about Pasteurella species are true, EXCEPT: - Forms large amounts of indole. - Grows well on MacConkey agar. - Many infections are caused by domestic animals. - P. multocida is the species most frequently isolated from humans.

- Grows well on MacConkey agar. The correct answer is grows well on MacConkey agar. Pasteurella spp. generally do not grow on MacConkey agar, but generally grow well on sheep blood agar or chocolate agar at 37°C. They are catalase, oxidase and indole positive. Most infections are caused by dog and cat bites or scratches, and are caused by P. multocida.

An eleven-year-old girl was seen in the emergency room with sudden onset of sore throat, fever and dysphagia, the latter accompanied by an intermittent sensation of choking. The bacterial species shown in the upper photograph of a chocolate agar plate was recovered from a throat culture. The most likely bacterial species based on the test shown in the lower photograph is: - Corynebacterium diphtheriae - Haemophilus influenzae - Haemophilus parainfluenzae - Abiotrophia (nutritionally variant streptococci)

- Haemophilus influenzae Acute epiglottitis, both in the pediatric and the adult population, may present a life threatening emergency from airway obstruction. Haemophilus influenzae type b is the cause of this acute infection. Although similar symptoms may be experienced during the early stages of diphtheria, C. diphtheriae is not X or V-factor dependent and would grow more diffusely over the surface of the agar shown in the lower photograph. Although H. parainfluenzae may cause mild inflammation of the upper respiratory tract, the symptoms are usually mild and obstructive epiglottitis does not occur. H. parainfluenzae is only V factor dependent; therefore, would grow circumferentially around the V and XV disks, not between the X and V disks as shown here. Abiotrophia (formerly known as nutritionally deficient streptococci) require pyridoxal rather than NAD and hemin; therefore, would grow more diffusely over the surface of the plate shown in the lower photograph.

A pediatric patient arrived at the doctor complaining of itching eyes that appeared red and slightly purulent. When a sample was submitted to the laboratory, the sample grew only on the chocolate plate as seen in the upper image. When performing a satellite test, the image on the bottom is observed. What is the most likely identity of the organism causing this patient's symptoms? - Moraxella catarrhalis - Haemophilus influenzae - Streptococcus pneumoniae - Listeria monocytogenes

- Haemophilus influenzae The correct answer is Haemophilus influenzae. Haemophilus influenzae will grow on the chocolate plate as observed in the upper image. It will also exhibit growth on the satellite test as observed in the lower image. In pediatric patients, it is the leading cause of conjunctivitis, which is the condition described in the question above. Moraxella catarrhalis and Streptococcus pneumoniae would grow on sheep blood agar in addition to the chocolate agar, thus it would not be necessary to perform a satellite test, as the organisms would not grow in a satellite formation. Both organisms are common causes of conjunctivitis, but would not grow as described above. Listeria monocytogenes would grow on sheep blood agar and chocolate agar at standard incubation temperature (35-37°C), but grows optimally at 30-35°C. Since it grows well on both sheep blood agar and chocolate agar, it would be unnecessary to perform the satellite test.

Which organism matches the reactions shown? Left tube: Motility agar (note subsurface flare shown by arrows) Middle tube: Esculin hydrolysis (+) Right tube: Voges-Proskauer(VP) (+) - Erysipelothrix rhusiopathiae - Arcanobacterium haemolyticum - Corynebacterium spp. - Listeria monocytogenes

- Listeria monocytogenes L. monocytogenes is motile (optimum at room temperature or 25°C), hydrolyzes esculin (black), and gives a positive VP reaction (red). Erysipelothrix rhusiopathiae is negative for all these tests. E. rhusiopathiae may have colony and Gram stain features similar to that of Listeria monocytogenes however, E. rhusiopathiae produces H2S in Kligler and Triple Sugar Iron Agar while L. monocytogenes does not. Corynebacterium spp. and Arcanobacterium haemolyticum are not motile.

Illustrated in this photograph is the surface of a 5% sheep blood agar plate on which are growing colonies of yellow pigmented Staphylococcus species. Note the tiny semi-translucent colonies that satellite around some of the colonies. Pleomorphic gram-negative bacilli were seen on gram stain. The most likely identification is: - Neisseria elongata - Moraxella catarrhalis - Haemophilus influenzae - Granulicatella species

- Haemophilus influenzae The satelliting of small colonies around Staphylococci and other bacterial species as observed in this photograph is always suspicious for Haemophilus species. Haemophilus species require X (hemin) and/or V (NAD) Factors for growth. The Staphylococci produce Factor V as a by-product of metabolism and make it available for the organism to use. X factor is available from the sheep's blood agar. Haemophilus influenzae requires both X and V Factors and therefore will only grow where both of these supplements are available, right around the Staphylococcal colonies. Neisseria elongata, although a gram negative bacillus rather than a coccus, is not pleomorphic and does not have X and V factor requirements. It therefore would grow randomly on blood agar if present. Moraxella catarrhalis is a gram negative diplococci, not a gram negative bacilli. It also does not have an X and V factor requirement and thus would grow randomly on the blood agar plate without relationship to the Staphylococcus species colonies. Granulicatella species, previous known as nutritionally variant streptococci, can also be known as "satelliting strep". They require sulfhydryl compounds for growth. They would produce similar appearing satelliting colonies as seen here; however, they are gram positive cocci and not gram negative bacilli.

Which of the following species of bacteria is positive for rapid urease production, as demonstrated by a color change in urea agar from yellow to pink within two hours? - Salmonella enterica - Escherichia coli - Helicobacter pylori - Campylobacter jejuni

- Helicobacter pylori Rapid urease testing may be useful in the presumptive identification of Helicobacter pylori from gastric biopsy specimens. Positive results are indicated by a color change from yellow to pink, as the ammonia produced from urea hydrolysis creates alkalinization using phenol red as the pH indicator. Salmonella enterica, Escherichia coli, and Campylobacter jejuni are also Gram-negative rods implicated in enteric infections, but are urease negative. Stool specimens are routinely screened for Salmonella, Escherichia, and Campylobacter.

The mechanism by which certain strains of Enterococcus species have developed resistance to the synergistic combination of an aminoglycoside and beta-lactam antibiotics is considered: - Alteration of penicillin binding proteins - Beta lactamase activity against the beta-lactam moiety - High level gentamicin resistance - Efflux of antibiotics from the bacterial cell

- High level gentamicin resistance The correct answer is high level gentamicin resistance. Enterococci have an intrinsic resistance to aminoglycoside antibiotics because they are not able to efficiently cross the bacterial cell wall. Therefore, the addition of a beta lactam antibiotic such as penicillin has the effect of making the cell wall permeable to the aminoglycoside that can then gain access to its ribosomal binding site. High level synergy resistance develops when the bacterium alters the ribosomal binding site so that even high intracellular concentrations of aminoglycoside are ineffective. Alteration of penicillin binding proteins is the mechanism by which S. pneumoniae has developed resistance to penicillin. Only a low percentage of strains of Enterococcus species produce beta lactamases, which do not affect the synergy resistance phenomenon. Active transport or efflux of antibiotics from the bacterial cell is a resistance mechanism active against tetracyclines and macrolides.

Which one of the following organisms can be isolated from bone marrow specimens? - Histoplasma capsulatum - Staphylococcus aureus - Aeromonas hydrophilia - Aspergillus fumigatus

- Histoplasma capsulatum Histoplasma capsulatum is the correct answer because this mold is considered a systemic mold and can disseminate throughout the reticuloendothelial system causing infection. Primary sites of dissemination are lymph nodes, liver, spleen, and bone marrow. Infections are common in immunocompromised patients. Staphylococcus aureus is incorrect because this organism commonly causes skin infections and is not routinely found in bone marrow specimens. Aeromonas hydrophilia is incorrect because this organism can cause both wound infections and intestinal infections. In addition, this organism is typically found in ponds and streams and infections can occur through inoculation by fish fins or fishing hooks. Aspergillus fumigatus is incorrect because this organism is commonly found in respiratory secretions, skin, ear, eyes, and sinuses. This mold is not typically found in bone marrow specimens.

In the late 1990's, an outbreak of pneumonia was experienced by several high school students involved in a clean-up day held in a Midwestern community. One student experienced a severe disseminated infection. The colony growing on Sabouraud Dextrose with Brain Heart Infusion (SABHI) agar and incubated at 30o C and shown on the top photograph was recovered from an induced sputum specimen. The colony matured in 8 days, presenting a hair-like, cottony surface mycelium. The identification was confirmed by observation of the lactophenol tease mount obtained from the surface of the mycelium. From the list of choices below, select the name of this isolate. - Coccidioides immitis - Sporothrix schenckii - Blastomyces dermatitidis - Histoplasma capsulatum

- Histoplasma capsulatum Histoplasma capsulatum is the correct response. Although the appearance of the colony is not species specific, the delayed growth and hair-like, cobweb surface of the mycelium would suggest a dimorphic fungus. The identification of Histoplasma was made microscopically based on the appearance of the 10 - 20 um, circular, roughened, spike- like (tuberculate) macroconidia being borne along delicate hyphae, as illustrated in the image. Coccidioides immitis colonies are not distinctive from other dimorphic molds except in cases where focal areas of dark pigment from hemoglobin absorption may be observed. Distinctive microscopically of the mold form are the barrel-shaped arthroconidia that are separated by empty spaces (dysjunctors). Sporothrix schenckii mold colonies are distinctive among the dimorphic fungi by growing rapidly. Distinctive microscopically is the production of delicate, septate hyphae from which are borne laterally oval, smooth conidia measuring 2-4 mm in diameter. Conidia of S. schenckii are arranged either laterally along the side of the hyphae or more characteristically in daisy-like clusters from the tips of straight, delicate conidiophores. Blastomyces dermatitidis mold colonies are not specific and identification is made microscopically by observing thin background hyphae giving rise to long or short conidiophores from the tips of which are borne small spherical to oval deep-staining conidia often referred to as "lollipops". Hyphae with arthroconidia separated by dysjunctors) are not observed.

All of the following agents can be handled using biosafety level 2 practices, EXCEPT: - Marburg virus - Methicillin resistant Staphylococcus aureus (MRSA) - Herpes simplex virus - Candida albicans

- Marburg virus The correct answer is Marburg virus. Marburg virus requires biological safety level 4 practices for handling since it is considered a dangerous agent that poses a high risk of life-threatening diseases and the ability to be transmitted via aerosols which could cause laboratory related infections. Marburg virus is part of the filoviruses that produce hemorrhagic fever. MRSA, Herpes simplex virus, and Candida albicans can all be handled using biosafety level 2 practices.

What is the medium of choice for isolating Gardnerella vaginalis? - Modified Thayer-Martin (MTM) agar - Malonate broth - Human blood bilayer Tween (HBT) agar - New York City (NYC) medium

- Human blood bilayer Tween (HBT) agar HBT agar is a selective layered medium for the isolation of Gardnerella vaginalis from clinical specimens. Antimicrobial agents, colistin, nalidixic acid, and amphotericin B suppress vaginal normal flora growth. Addition of human blood permits differentiation by the observation of beta hemolysis around colonies. Peptone and polysorbate 80 are the key enrichments. MTM agar is used for recovering Neisseria gonorrhoeae and Neisseria meningitidis from specimens with mixed microbiota. Malonate broth is used in the identification of Enterobacteriaceae, namely Salmonella. NYC medium is used primarily to isolate Neisseria gonorrhoeae and Neisseria meningitidis from specimens with mixed microbiota. It can also support the growth of Ureaplasma urealyticum.

In the upper photograph is a short, thin, thread-like adult worm. In the lower photograph is show the scolex of this worm, with a protruding armed scolex and a row of hooklets. Also known as the "dwarf tapeworm", what is this cestode that commonly infects children? - Taenia saginata - Hymenolepis nana - Taenia solium - Diphyllobothrium latum

- Hymenolepis nana Hymenolepis nana is known as the small "dwarf" size and the tiny scolex as seen under low-power magnification with a distinctive protruding armed rostellum and a circle of hooklets are key to its identification. Taenia solium scolex have an armed rostellum, but are larger and more flattened on the anterior surface, and are non-protruding. The rostellum has a double row of hooklets as well as four suckers. Taenia saginata scolex have only four suckers and have a flat anterior end that is devoid of an armed rostellum. Diphyllobothrium latum scolex are elongated and narrow with a dorso-ventral groove (bothrium) surrounded on either side by lateral lip-like folds (phyllo).

Rocky Mountain spotted fever (RMSF), caused by Rickettsia rickettsii, is MOST reliably diagnosed by which laboratory technique? - Blood culture - Electron microscopy - IFA testing - Serial dilution

- IFA testing The gold standard for diagnosis of RMSF is the indirect immunofluorescence antibody (IFA) assay with R. rickettsii antigen, demonstrating a significant (four-fold) rise in antibody titer in two serum samples. Timing of the samples should be at onset of symptoms, and within a few weeks, allowing time for antibodies to develop. However, treatment should be initiated before confirmation. Blood culture, electron microscopy, and serial dilution are not usual methods for confirming RMSF.

A stool specimen can be suspected of harboring Vibrio cholerae if it possess which of the following characteristics? - If the stool is well formed and shows blood streaks. - If the stool is soft, dark, and positive for occult blood. - If the stool contains a high concentration of segmented neutrophils. - If the stool is watery with a high pH and flecks of mucus.

- If the stool is watery with a high pH and flecks of mucus. The diarrhea caused by V. cholera is watery and contains large concentrations of sodium, bicarbonate, and other electrolytes, producing an alkaline pH. The diarrhea is caused by the action of cholera toxin on the intestinal epithelial cells, with the end result of stimulating adenyl cyclase (cyclic AMP), which in turn inhibits the readsorption of sodium across the brush border membrane and stimulates the excretion of bicarbonate and potassium into the bowel lumen. A stool specimen comprised of primarily fluid and flecks of mucous (known as rice water stools) is a distinctive feature when cholera toxin activity is present. In the absence of mucosal invasion by the bacteria, blood or neotrophils are not found in the stool specimen.

All of the following statements about blood cultures are correct EXCEPT? - A specific amount of blood is required to fill blood culture bottles to optimize the growth and detection of bacteria. - If two separate sets (two bottles each set) of blood cultures are requested, draw them both from the same site at the same time. - Prior to performing the venipuncture, allow the cleansing agent to air dry completely on the skin to ensure sterilization of the venipuncture site. - If two separate sets (two bottles each set) of blood cultures are requested, it is recommended to draw each set from different sites. Some recommend collecting the sets at different times (approximately an hour apart).

- If two separate sets (two bottles each set) of blood cultures are requested, draw them both from the same site at the same time. A blood culture collection usually consists of one set of two bottles. Blood cultures are commonly ordered in multiple sets drawn from separate sites at different times. The different sites for collection have demonstrated more of a difference in the yield of the bacteria than collecting at different times. Each bottle must be inoculated with a specific blood volume to maximize growth and detection of bacteria. Under-filled bottles may cause false-negative results. Each bottle must be inoculated with a specific blood volume to maximize growth and detection of bacteria. Under-filled bottles may cause false-negative results. To minimize contamination of the blood cultures due to skin flora, the venipuncture site is first treated with 70% isopropyl alcohol to remove any fat on the surface of the skin. Next, an antiseptic agent is used on the site to kill any surface or subsurface bacteria that may contaminate the blood culture. Two commonly used antiseptics are iodine tincture and chlorhexidine. Iodine tincture may not be used due to patient allergies. A blood culture collection usually consists of two separate sets (two bottles each set) to increase the volume of blood which increases the likelihood of isolating the bacteria. In addition, the bottles are collected from different locations to increase the sensitivity and yield of the bacteria that may demonstrate periodicity in the bloodstream. It is also recommended to collect the sets at different times but studies have demonstrated no significant differences in the yield between sets drawn at the same time compared to those collected with time in between the collections.

Which one of the following statements is true regarding the 2009 H1N1 virus? - Novel 2009 H1N1 virus is an influenza B virus. - Novel 2009 H1N1 virus only infects pigs and horses. - In 2009, the novel H1N1 virus spread during warmer months. - The Novel H1N1 virus spread in colder months.

- In 2009, the novel H1N1 virus spread during warmer months. The novel H1N1 virus of 2009 spread in warmer weather months, distinguishing it from seasonal flu viruses that are known to peak in cold weather months. H1N1 is a recombination of human, avian, and swine influenza viruses which is how it spread so fast and during warmer months. It can infect several types of animals and is an Influenza A virus.

Elizabethkingia is the new genus name for the bacterium formerly called Chryseobacterium meningosepticum, an important agent of neonatal mentingitis (now E. meningoseptica). What biochemical characteristic is unique for the family Flavobacteriaceae among the nonfermenters? - Indole production - Esculin hydrolysis - Glucose oxidation - Resistance to penicillin

- Indole production Among the nonfermenters, the production of indole points to one of the Flavobacteriaceae, including E. meningoseptica. Indole production is weak; therefore, extraction with xylene and reaction with Ehrlich's rather than Kovac's reagent is required for its detection in the standard laboratory procedure. Esculin hydrolysis, oxidation of glucose and susceptibility profiles to penicillin are variable among the Flavobacteriaceae and do not represent characteristics unique to this group.

The area of suppressed growth surrounding a disk impregnated with an antimicrobial on a sensitivity plate is referred to as the zone of: - Resistance - Breakpoint - MIC - Inhibition

- Inhibition A zone of inhibition is the area around an antibiotic-infused paper disk that does not show any bacterial growth. The antibiotic-impregnated on the disk will diffuse into the agar in the area surrounding the disk. If the bacteria are sensitive to the antibiotic, they cannot grow near the disk. The size of the zone is proportional to how sensitive the organism is. If the organism is resistant to the antibiotic, it will grow very close to the disk. Resistance is an interpretive category of a susceptibility test that indicates the antimicrobial agent is not appropriate for treatment. Breakpoints are the specific concentrations of antimicrobial agents that differentiate the interpretations for susceptibility testing into the sensitive, intermediate or resistant categories. The MIC, or the minimum inhibitory concentration, is the lowest concentration of an antimicrobial agent that completely inhibits visible bacterial growth.

Which fungal culture media is used for the primary recovery of pathogenic fungi exclusive of dermatophytes? - Inhibitory mold agar - Potato flake agar - Mycosel agar - (SABHI) Sabouraud Dextrose with Brain Heart Infusion agar

- Inhibitory mold agar Inhibitory mold agar, brain-heart infusion agar with antibiotics and yeast-extract phosphate agar are all used for the primary recovery of pathogenic fungi exclusive of dermatophytes. Potato flake agar is used for the primary recovery of saprobic and pathogenic fungi. Mycosel agar is used for the primary recovery of dermatophytes. Sabouraud Dextrose with Brain Heart Infusion agar is used for the primary recovery of saprobic and pathogenic fungi.

A 20-year-old female was admitted into the hospital complaining of 10 to 15 bloody mucous stools per day, fever, gastrointestinal disturbances, abdominal pain, and nausea. The preliminary O & P report went out as "Probable Entamoeba histolytica trophozoites and cysts, confirmation pending." What is this patient most likely suffering from? - Traveler's diarrhea - Extraintestinal amebiasis - Intestinal amebiasis - Giardiasis

- Intestinal amebiasis According to the National Institutes of Health (NIH), the following symptoms are closely associated with intestinal amebiasis: Abdominal cramps Fever Diarrhea Vomiting Abdominal tenderness Fatigue Excessive gas Rectal pain while having a bowel movement Unintentional weight loss Bloody stools: Passage of liquid stools with streaks of blood Passage of 10 - 20 stools per day

Illustrated in the photomicrograph is an amebic cyst as observed in a stool specimen obtained from a patient with low-grade, intermittent diarrhea. Observe the distinctive cytoplasmic vacuole and "ball in socket" nucleus. Select from the list of responses the species identification of this amoeba. - Iodamoeba butschlii - Entamoeba hartmanni - Chilomastix mesnili - Endolimax nana

- Iodamoeba butschlii Iodamoeba butschlii is the correct response. The typical cyst is small, ranging from 5 to 20 µm. Distinctive is the "ball-in-socket" nucleus, and the large cytoplasmic vacuole that stains positive with iodine, a distinctive feature from which the genus name "Iodamoeba" is derived. These are considered non-pathogenic. Entamoeba hartmanni cysts, as the genus name suggests, possesses a distinct "entamoeba type" nucleus (one or two nuclei) with a central karyosome and peripheral chromatin ring, rather than as a "ball-in-socket". The small size is similar to that of Iodamoeba butschlii. Chilomastix mesnili cysts are lemon to pear-shaped, with a hyaline knob observed to one side. A single nucleus with a small karyosome is observed adjacent to which is seen a curved cytostome, having the appearance of a "shepherd's crook". Endolimax nana cysts are small (5 - 10 µm), and are distinctive for having 4 nuclei when mature, each with a blot-like karyosome.

Each parasite listed below is correctly matched with its respective vector, EXCEPT: - Iodamoeba butschlii - pig - Trypanosoma cruzi - reduviid bug - Plasmodium vivax - mosquito - Loa loa - fly

- Iodamoeba butschlii - pig The correct answer is Iodamoeba butschlii - pig. Iodamoeba butschlii is transmitted via the fecal-oral route and humans become infected when they ingest the infective cysts. The morphological characteristic that is typically found inside the cyst is a single, large, well defined glycogen vacuole. Trypanosoma cruzi is transmitted by the feces of the reduviid bug when it bites. This allows trypomastigotes to enter the human bloodstream. Plasmodium vivax is transmitted by the saliva of a female mosquito that contains sporozoites that enter the human bloodstream. Loa loa is transmitted by the bite of a fly containing larvae. The larvae migrate to the subcutaneous tissue and mature to microfilariae.

A patient grew out Mycobacterium tuberculosis (MTB) from an acid fast bacilli (AFB) sputum culture. The physician called requesting information on drugs of choice for the treatment of MTB. Which of the following antitubercular agents would be recommended for treatment? - Isoniazid - Ciprofloxacin - Kanamycin - Rifabutin

- Isoniazid Isoniazid is the correct answer because this antitubercular agent is one of five of the primary drugs used to treat MTB infections. Other primary agents used in treating MTB infections are Streptomycin, Rifampin, Ethambutol, and Pyrazinamide. Initial isolates of MTB are tested against all five agents and used as a first line treatment option. Ciprofloxacin, Kanamycin, and Rifabutin are incorrect answers because they are secondary antitubercular agents used to treat MTB infections. Other secondary antitubercular agents used in the treatment of MTB are: Ethionamide, Capreomycin, Doxycycline or minocyline, Ofloxacin, Cycloserine, and Trimethoprim-sulfamethoxazole. If resistance to any of the primary drugs is detected, a combination of secondary drugs can be used.

Bob is a MLT at the local VA hospital. Tonight he is assigned to perform set-up and read Gram stains on newly received specimens in the Microbiology department. He ported reported a superficial wound Gram stain as having Gram negative rods, when he realized he must have over decolorized the slide and the rods reported are actually Gram positive. What should Bod do next? - Issue a preliminary report - Issue a final report - Issue a corrected report - It is too late to change the report

- Issue a corrected report Bob should immediately issue a corrected report and contact the caregiver to inform him/her of the changes. Such reports need to be clearly designated and that "corrected" results reports clearly state that the new result is a change from a previously reported result. A preliminary report is a report given to the caregiver while the culture is pending. A final report is given to the caregiver once the identification of the organism is made and antimicrobial sensitivities are determined (if such culture requires it).

Norcardia species can be isolated from cutaneous specimens and can produce sulfur granules. These granules can be found in tissue specimens and can aid in detecting aerobic actinomycetes. To help identify the presence of sulfur granules in tissue specimens, which of the following methods will be most beneficial? - Gram stain - Acid fast stain - KOH Mount - Gomori methenamine-Silver (GMS)

- KOH Mount KOH Mount is the correct answer because this is a rapid test that can detect sulfur granules in tissue. By performing a KOH mount on tissue specimens, proteinaceous material can be digested in order to detect the presence of sulfur granules. Aerobic actinomycetes, such as, Actinomadura species, Nocardia species, and Streptomyces species can grow in tissue as small, hard colonies, which are referred to as sulfur granules. Gram stain is incorrect because this test will detect the presence of Gram positive or Gram negative organisms. By performing a Gram stain test, the presence of aerobic actinomycetes can be detected by the presence of Gram positive branching rods. This test will not detect the presences of sulfur granules. Acid fast stain is incorrect as this test is used to assist in identifying Nocardia species because Nocardia is weakly or partially acid-fast positive. This test does not detect the presence of sulfur granules. Gomori methenamine-Silver (GMS) is incorrect because this test is used to detect aerobic actinomycetes filaments from tissue specimens. It does not detect the presence of sulfur granules.

In the image, what morphologic structure is shown in section D on this parasite form? - Karyosome - Chromatoid bars - Uneven peripheral chromatin - Cytoplasm

- Karyosome The parasite pictured here is an Entamoeba coli cyst. The area in section D is the karyosome. The karyosome is seen in amebas as the mass inside the nucleus, which is made up of a mass of chromatin. Chromatoid bars are shown in section C. These can be squared or round-ended bar-like structures seen in cysts. They contain condensed RNA material. Uneven peripheral chromatin is seen in section B. Peripheral chromatin is a ring of chromatin that surrounds the karyosome. Uneven means that it is not distributed evenly around the nucleus and as seen here, can be thicker or thinner in some areas. Cytoplasm is shown in section A. The cytoplasm is the fluid that fills the cells and contains all the cells organelles including the nuclei.

Carbolfuchsin binds to mycolic acid in cell walls with high lipid/wax content and is retained after decolorizing, preventing counterstaining with methylene blue. This principle describes: - Kinyoun acid-fast staining - Gram staining - Negative staining of yeast capsules - Schaefer-Fulton bacterial endospore staining

- Kinyoun acid-fast staining This principle describes Kinyoun acid-fast staining, which is used for mycobacteria and other cells that do not stain with traditional stains. Gram staining is the most widely used stain in microbiology, used to separate bacteria into two categories based on cell wall composition. India ink and nigrosin are negative stains used to visualize capsules surrounding certain yeasts, including Cryptococcus. Schaefer-Fulton is a bacterial endospore stain using malachite green and safranin.

An 87-year old patient had a foot wound that grew gram-negative rods on McConkey agar as pink to dark pink oxidase-negative colonies along with the following results: TSI: A/A Indole: neg. MR: neg. VP: pos. Citrate: pos. H2S: neg. Urea: pos. Motility: neg. Ornithine: neg. Antibiotic susceptibility: Carboxicillin and ampicillin resistant, all others sensitive. What is the MOST likely organism? - Serratia marcescens - Proteus vulgaris - E. coli - Klebsiella pneumonia

- Klebsiella pneumonia Considering the reactions given in this case study, Klebsiella pneumonia would be the best choice. Serratia marcescens can be eliminated by the fact that it is motility + and urea negative, as well as ornithine +. Proteus vulgaris can be eliminated due to its production of H2S, the fact that it is indole +, the MR/VP reaction is positive/negative, it is citrate +, and motility +. E. coli can be eliminated due to its production of gas on the TSI slant. E. coli is also indole +, MR/VP = positive/negative, citrate negative, urea negative, motility +, ornithine +.

From the choices listed below, choose the most likely associated bacterial species represented in the image as pink, runny, mucoid colonies at 48 hours incubation on MacConkey (MAC). - Haemophilus species - Pseudomonas aeruginosa - Klebsiella pneumoniae - Proteus species

- Klebsiella pneumoniae The colonies of Klebsiella pneumoniae are characteristically mucoid from the production of abundant capsular material. K. pneumoniae is a lactose fermenter, indicated by pink coloration on MacConkey as the pH decreases. Colonies of Enterobacter may also produce this type of colony appearance. Although Haemophilus species may also produce capsular material, Haemophilus species do not grow on MAC. Enrichment agar such as CHOC is used for isolation. Pseudomonas aeruginosa is a non-fermenter that may demonstrate ß-hemolysis on blood agar, with flat, spreading colonies and a metallic sheen. Many strains of P. aeruginosa produce pigments that appear green, and strains may have a fruity odor. Colonies of Proteus species typically swarm when grown on blood agar, and do not ferment lactose. Proteus species are a common cause of urinary tract infection and tend to produce a distinctly alkaline urine pH because of strong urease activity and the release of ammonia.

Which of the following sites is used most often for CSF collection? - Ventricles - L1-L2 - Subarachnoid - L3-L4

- L3-L4 CSF is routinely collected by lumbar puncture between the third, fourth, or fifth lumbar vertebra. CSF is produced in the choroid plexuses of the two lumbar ventricles and the third and fourth ventricles. The Subarachnoid is the space where CSF flows and its located between the arachnoid and pia mater.

From the choices listed below, which organism is classified as an aerotolerant anaerobe? - Clostridium novyi - Staphylococcus aureus - Lactobacillus species - Neisseria species

- Lactobacillus species Lactobacillus species are aerotolerant anaerobes, tolerating brief exposure to O2, but not able to carry out metabolic processes unless an anaerobic environment is sustained. Clostridium novyiis one of the most oxygen-susceptible anaerobes, with cells being killed within 10 minutes of exposure to atmospheric air. This species is often used as a quality control strain to indicate an adequate anaerobic environment in anaerobe tents and jars. Staphylococcus aureus is classified as a facultative anaerobe, preferentially using oxygen for growth, but able to grow in the absence of oxygen. Most Neisseria species are aerobic, but some are capnophilic, requiring 5-10% CO2.

Small, smooth, gray-white, 24-hour colonies are seen growing on the surface of sheep blood agar with faint alpha-hemolysis. This isolate is most often part of the normal flora, serving in several body sites as a protection against harmful bacteria through production of lactic acid. The gram stain reveals long, slender gram-positive bacilli lying singly and in short chains. It is a non-branching, non-spore-former. From the multiple choices, select the presumptive identification of this isolate. - Actinomyces species - Rothia dentocariosa - Corynebacterium striatum - Lactobacillus species

- Lactobacillus species Lactobacillus species are aerotolerant anaerobes. The colonies growing on sheep blood agar after 24 hours incubation are gray white, convex, smooth and non-discriminatory. Observation of narrow zones of light alpha hemolysis would help to make a presumptive identification. The microscopic observation of long, slender, non-spore forming gram-positive bacilli arranged in short and long chains is characteristic. Additional assays may be required to confirm the identification. Actinomyces species colonies may vary in texture and color. Actinomyces species are aerotolerant anaerobes. Actinomyces species are gram-positive, non-spore-forming bacilli that may be filamentous, beaded, or branching. Rothia dentocariosa is a gram-positive bacilli or cocco-bacilli observed in diphtheroidal arrangements. Filamentous forms are seen in older cultures. Hemolysis is not observed. Corynebacterium striatum colonies are relatively small, convex, smooth, and non-hemolytic. Small club-shaped, gram-positive bacilli are in small clusters or in picket fence or Chinese letter arrangements are observed in Gram stains.

A 10-year-old male presented to the local Appalachian Mountain clinic complaining of vomiting, fever, and severe abdominal pain. Patient history revealed that the child lives in the area in substandard conditions and receives only one balanced meal per day. A stool was collected and submitted for parasite study. This suspicious form, measuring 50 µm by 35 µm was found. This patient is most likely infected with: - Hookworm - Large intestinal roundworm - Threadworm - Whipworm

- Large intestinal roundworm Large intestinal roundworm is the correct answer. The picture shown here is an egg of Ascaris lumbricoides, common name - large intestinal roundworm. Hand-to-mouth transmission is a common mechanism of transmitting the organism, particularly in children. Size range 45-75 µm x 35- 50 µm. Brown in color with a very thick shell that may appear decorticated. Hookworm is incorrect because Ancylostoma duodenale (Old World hookworm) and Necator americanus (New World hookworm) are hookworms that produce eggs with a very thin shell that measure 55-75 µm x 35-45 µm and appear colorless. Threadworm is incorrect because Strongyloides stercoralis is known as the human threadworm and measures 50-58 µm x 30-34 µm. The eggs look very similar to the hookworm eggs, but somewhat smaller. Whipworm is incorrect because Trichuris trichiura is known as the whipworm and measures 50-54 µm x 22-23 µm. The eggs are barrel or football shaped, have bipolar plugs, and are brown in color.

In an urinalysis, tests are performed that serve as a method of screening for urinary tract infections. Which of following tests detects the presence of inflammatory cells? - Niacin test - Nitrate reduction test - Leukocyte esterase test - Catalase test

- Leukocyte esterase test

The minimum time of retention for microbiology instrument records is? - Life of the instrument - 2 years - 5 years - 7 years

- Life of the instrument Life of the instrument is the correct answer. Instrument records must be retained for the life of the instrument to prove that validation and correlation studies were performed prior to putting into use. 2 years is incorrect. Test reports including all preliminary reports, accession list, requisitions, work cards, QA/QC, instrument maintenance, incident reports, and reportable disease reports must all be kept for a minimum of 2 years. 5 years is incorrect. Personnel and safety records are required to be kept for a minimum of 5 years. 7 years is incorrect as this does not represent a minimum retention time for microbiology records.

A tech is interpreting a urine culture from a catheter as the source. There is 1 colony of Staphylococcus epidermidis present on the blood agar which was streaked with a 0.001 loop. What should the tech do next? - Reject culture due to contamination - Perform sensitivity on S. epidermidis - Report culture as no growth - List S. epidermidis as a possible contaminant

- List S. epidermidis as a possible contaminant Catheterized specimens can have contamination from collection. The catheter can help to prevent contamination from the urethra, however, the collection of the urine from an indwelling catheter can become contaminated if not collected properly or if the port is not cleaned before collection. Thus, any catheterized specimens should be assessed as possibly contaminated. S. epidermidis is a normal flora organism on the skin and a frequent contaminant in urine cultures from collection. Due to the nature of the organism, low colony count (1,000 cfu/mL), and the potential for contamination from the catheter, the organisms should be listed as a contaminant. Urine cultures are not rejected due to contamination, they are reported with the organism listed as a contaminant. Rejection of specimens occurs prior to culture set up for any inappropriate sources or incorrect handling or storage procedures that may have occurred. A sensitivity should not be performed on the S. epidermidis due to the normal flora nature, low colony count, and possibility of contamination. Providing a sensitivity would indicate that the organism is clinically significant, when it is not and could lead to inappropriate patient treatment. The culture should not be reported as no growth. There is one colony and that cannot be overlooked and should be addressed.

A tech is working on a urine culture and finds the following isolate: Escherichia coli: 5,000 cfu/mL How should the tech continue with the culture work up? - Perform sensitivity on E.coli - Reject the culture due to contamination - Report the culture as no growth - List the E.coli as a possible contaminant

- List the E.coli as a possible contaminant Even though E.coli is a urinary pathogen, the low colony count (<10,000 cfu/mL) does not correlate with clinical infection. The organism should be listed as a possible contaminant due to the low colony count. Sensitivity should not be performed on E.coli due to the low colony counts. This can lead to inappropriate treatment for the patient. Urine cultures are not rejected due to contamination, they are reported with the organism listed as a contaminant. Rejection of specimens occurs prior to culture set up for any inappropriate sources or incorrect handling or storage procedures that may have occurred. Listing E.coli without performing a sensitivity, does not provide any clinically relevant data for the physician and can lead to inappropriate treatment. The culture should not be reported as no growth. There is are colonies and that cannot be overlooked and should be addressed.

Which bacterial species is a common agent of neonatal bacteremia? - Streptococcus pyogenes - Listeria monocytogenes - Staphylococcus aureus - Enterococcus faecium

- Listeria monocytogenes Listeria monocytogenes is a common cause of neonatal diseases, bacteremia and/or meningitis. The route of disease is not well understood, but thought to come from contaminated foods with subsequent spread through the intestines. Specifically for pregnant women, Listeria monocytogenes infections can occur from ingestion of contaminated foods and infect the fetus in vitro. During an infection, the organism will be transported in the blood stream of the mother and deposits in the uterus and fetus. This can lead to pre-mature labor or spontaneous abortions. If the fetus is born, infection with Listeria monocytogenes can be seen in the newborn. There are two types of newborn infections, early and late-onset disease. Early onset is typically seen with an intrauterine infection and present at birth. The most common disease manifestation for early onset is sepsis. Late-onset infection is typically seen several days to weeks after birth and typically manifests as meningitis. Streptococcus pyogenes is the causative agent of Strep throat. It can also been seen in some skin infections, but is not usually seen in neonatal infections specifically. Staphylococcus aureus is a significant pathogen and causes many types of infections. In neonates, we can see Staphylococcus aureus cause scalded skin syndrome, which is a skin disease from staphylococcal toxins the baby is exposed to during birth. Enterococcus faecium is normal flora in the intestines and most commonly cause urinary tract infections.

Observed in the top photographs are colonies growing on blood agar after 24 hours incubation, obtained from a positive blood culture. The colonies are tiny and surrounded by narrow zones of beta hemolysis. The initial presumptive identification was that of a Streptococcus and a CAMP test was set up. A follow up Gram stain (middle image) revealed Gram positive bacilli in loose clusters rather than cocci. The lower image demonstrates a rectangular zone of hemolysis in the CAMP test, compared to the arrow-head shape of a control Streptococcus. From these observations, select the most likely presumptive identification of this isolate. - Listeria monocytogenes - Erysipelothrix rhusiopathiae - Arcanobacterium haemolyticum - Lactobacillus species

- Listeria monocytogenes Listeria monocytogenes is the correct response. Colonies on blood agar are initially small, gray to yellow-white, surrounded by narrow zones of beta hemolysis and look almost exactly like Streptococcus agalactiae. Characteristic of L. monocytogenes is a positive CAMP reaction with a rectangular zone of beta hemolysis in contrast to the arrow-head shape produced by Streptococcus agalactiae. The other test the tech could have used to verify the colony was a Streptococcus was catalase. Streptococcus is catalase negative and Listeria is catalase positive. To confirm Listeria monocytogenes, motility testing (umbrella-shaped) and bile esculin (positive) could be performed. Erysipelothrix rhusiopathiae colonies are also small and gray white on blood agar, but hemolysis is absent. Catalase is negative. The CAMP test is negative. To confirm the identification, the organism is H2S positive, Voges-Proskauer negative, and creates a test-tube brush-like appearance in a gelatin stab. Arcanobacterium haemolyticum colonies on blood agar are also small and beta hemolytic also and are catalase negative. Gram stain of the colony typically shows some branching bacilli, instead of the straight bacilli seen in the Gram stain. Distinctive is a reverse CAMP reaction in which the zones of hemolysis are in a cup-shaped downward projection rather than extending upward. Motility and esculin reactions are negative. Lactobacillus species colonies on blood agar are also small and gray-white, but are surrounded by zones of alpha rather than beta hemolysis. The CAMP test is negative.

Illustrated in this photograph to the right is a sulfide indole motility (SIM) tube (left) and an esculin hydrolysis slant (right) after inoculation with an unknown gram positive bacillus and incubation at 30°C for 24 hours. Based on the reactions observed, the most likely identification is: - Listeria monocytogenes - Erysipelothrix rhusiopathiae - Kurthia species - Lactobacillus species

- Listeria monocytogenes The correct answer is Listeria monocytogenes. The SIM tube illustrates the typical subsurface umbrella-shaped motility characteristic of Listeria monocytogenes. The motility is best demonstrated at incubation temperatures of 25° - 30°C. The hydrolysis of esculin as indicated by the black pigment in the right tube helps to confirm this identification as all of the other bacterial species listed are esculin negative. This is an important differentiation from Kurthia species, most strains of which are motile. E. rhusiopathiae and Lactobacillus species are not motile.

The Knott technique serves as a means of identifying: - Plasmodium vivax - Babesia microti - Loa loa - Strongyloides stercoralis

- Loa loa Loa loa is the correct answer. The Knott technique is a procedure in which the red blood cells are lysed and the bodies of microfilariae are killed and straightened for better identification. The specimen is then centrifuged to concentrate it and the sediment is spread on a side and stained for review. Plasmodium vivaxis best identified using thick and thin blood smears to see the parasite in red blood cells. Babesia microti are best identified using thick and thin blood smears. Strongyloides stercoralis may be identified using standard techniques (direct and concentrated wet preparations and permanent stains) used for examining stool specimens.

Which of the following culture media should be used to attempt to recover mycobacteria from a clinical specimen? - MacConkey agar - Lowenstein-Jensen (LJ) medium - PPLO agar - Modified Thayer-Martin agar

- Lowenstein-Jensen (LJ) medium The use of a solid-based medium, such as LJ medium, in combination with a liquid-based medium is recommended for routine culturing of specimens for the recovery of acid fast bacilli. Lowenstein-Jensen media is solid-based, and the most commonly used egg-based medium. MacConkey agar is selective, differential, primary plating medium. It selects for Gram negative rods, and differentiates them into lactose fermenters and non-lactose fermenters. PPLO agar is used to isolate Mycoplasma spp. Colonies may appear with a dense center and less dense edge, looking like a fried egg. Modified Thayer-Martin agar is a selective enrichment medium used for recovering Neisseria gonorrhoeae and Neisseria meningitidis from specimens with mixed microbiota.

Erythema migrans, spirochetemia, and chronic arthritis are three stages in the progress of: - Leptospirosis - Lyme disease - Syphilis - Rat bite fever

- Lyme disease Indeed, erythema migrans, blood-borne distribution of spirochetes to many organs and tissues, and the evolution of chronic arthritis are the hallmarks of classic Lyme disease. Leptospirosis is characterized initially by high fever, headache, malaise and muscle pain, associated with septicemic spread of the spirochetes. Skin rashes may develop, particularly in the pretibial areas of the legs. Jaundice from liver disease and renal failure are complications. Syphilis is a complex disease syndrome, initiated by a painless chancre at the site of infection, a secondary phase when the spirochetes become blood-borne and are widely disseminated, accompanied by a maculopapular rash and gray white plaques called condylomata lata. Latent or late syphilis is characterized by several complications, including chronic meningitis, aortitis, and aortic aneurysm, and a peripheral nerve disease known as tabes dorsalis. Rat bite fever is characterized by initial chills, fever and headache, and complicated low grade recurrent fever for months or years, potentially complicated by endocarditis.

Which of the following substances produced by Group A Streptococci is responsible for producing type specific immunity? - Streptolysin O - Streptolysin S - M antigen - T antigen

- M antigen The correct answer is M antigen The M antigen (also known as M protein) is also the major virulence factor of group A beta hemolytic streptococci. It prevents phagocytosis of the organism. Although antibodies to the M protein confer lifelong immunity, there are over 60 different M proteins, so recurrent S. pyogenes infections can easily occur in a given individual. Streptolysin O lyses leukocytes, platelets and RBCs. It is highly immunogenic and antibodies are formed quickly upon exposure. Streptolysin S also lyses leukocytes, but it is nonimmunogenic. T antigen is not an antigen associated with group A beta hemolytic streptococci.

Pericarditis may occur as a complication from endocarditis caused by Staphylococcus aureus. Virulence mechanisms attributed to the spread of this organism include all of the following EXCEPT: - Hyaluronidase - Protein A - Coagulase - M protein

- M protein M protein is a virulence factor of Streptococcus pyogenes, which increases resistance to phagocytosis and facilitates attachment to mucosal cells. Pathogenicity of Staphylococcus aureus is due to several virulence factors, including hyaluronidase, protein A, and coagulase; causing damage to cells and tissues and enhancing the spread of the bacteria.

Which of the following Mycobacterium species is closely associated with infections in HIV positive patients? - M. ulcerans - M. avium-intracellulare complex - M. simiae - M. bovis

- M. avium-intracellulare complex The correct answer is Mycobacterium avium-intracellulare complex. The Mycobacterium avium-intracellulare complex is closely associated with infections in HIV positive patients, in fact, these infections can be fatal. The infection often presents as a systemic bacterial infections that responds unpredictably to the standard multidrug regimen. M. ulcerans very rarely causes mycobacteriosis and has no predilection for HIV positive patients. M. simiae is implicated as a cause of pulmonary disease in patients with preexisting lung damage. M. bovis causes tuberculosis primarily in cattle, but is able to produce tuberculosis in humans with no predilection for HIV positive patients.

A microbiology laboratory recently purchased a rapid identification instrument that uses a laser on the microorganisms, which produces an ion cloud. These ions are then separated in a tube and travel within the tube to a detector. The time of travel will be measured and a mass spectrum will be produced. Which of the following techniques uses this methodology? - API 20E - Vitek - Microscan - MALDI-TOF

- MALDI-TOF MALDI-TOF is the correct answer because the name describes its methodology (Matrix-Assisted Laser Desorption Ionization Time of Flight mass spectrometry). With this methodology, an organism will be placed directly onto a plate and a chemical matrix will be applied. Afterwards, a laser will be applied to the sample and the matrix will absorb the energy creating an ion cloud. These ions will travel through a tube called a flight tube. The lighter ions will travel faster through the tube to the detector while the heavier ions will travel slower. The detector will measure the time of flight and report out a mass spectrum. This spectrum will be compared to other spectrums within the data library for identification. API 20E is incorrect as this method uses dried substrates within capsules located on strips. The strip is inoculated with a bacterial suspension and incubated for 4-6 hours. The reactions will be read, and numbers will be recorded based on the reactions. The number sequence will be entered into a data base and the organism matching that number is reported. Vitek is incorrect because it is similar to the API 20E. The Vitek also uses dried substrates within a card. The cards are resuspended with a bacterial suspension, incubated, and read within the instrument. Microscan is incorrect because it uses a microtiter tray that is inoculated with a bacterial suspension. The inoculated trays are loaded into the instrument and incubated for a specific amount of time. After incubation, the instrument will automatically add the reagents. Once the reagents are added, the instrument will read and report out the organism identification.

Which of the following scenarios represents appropriate detection of MRSA by the Kirby Bauer method? - Mueller-Hinton agar (MHA); direct colony suspension; 37oC; cefoxitin disk; 36 hour incubation - MHA; direct colony suspension; 35oC; oxacillin disk; 18 hour incubation - MHA; direct colony suspension; 35oC; cefoxitin disk; 18 hour incubation - MHA; direct colony suspension; 35oC; cefoxitin disk; 24 hour incubation

- MHA; direct colony suspension; 35oC; cefoxitin disk; 18 hour incubation Mueller-Hinton agar is the standard medium for Kirby Bauer testing on Staphylococcus isolates. The direct colony suspension method, utilizing a 0.5 McFarland standard, should be used to prepare the inoculum. A 16 to 20-hour incubation is required. A 30 µg cefoxitin disk is recommended to detect mecA mediated resistance. Incubation above 35°C may not allow for the detection of resistance. Oxacillin is recommended only for MIC detection with an incubation of at least 24 hours at 35°C, not for disk diffusion testing.

The appropriate media for the isolation of anaerobic bacteria from any source would normally include all of the following except: - CDC blood agar - MacConkey agar - Phenylethyl alcohol agar (PEA) - Kanamycin-vancomycin-laked blood agar (KVLB)

- MacConkey agar In order to assess anaerobes in clinical specimens, the best media to use are those that have not been exposed to oxygen. Typically, all cultures include one type of anaerobic blood agar, such as CDC agar, that has been prereduced to remove any molecular oxygen that could inhibit growth of anaerobes. Phenylethyl alcohol agar (PEA) can be used in anaerobic cultures because the media supports the growth of almost all obligate anaerobes (gram positive and gram negative) and gram positive facultative anaerobes. Kanamycin-vancomycin-laked blood agar (KVLB) supports the growth of anaerobic gram negative bacilli such as Bacteroides and Prevotella species. MacConkey agar is a selective and differential agar that is used for aerobic gram negative bacilli, such as differentiating the Enterobacteriaceae family. MacConkey agar does not support the growth of anaerobic bacteria and should not be used for anaerobic cultures.

The cellular immune response plays a role in whether a person exposed to Mycobacterium tuberculosis will develop tuberculosis disease (TB). Which of the following factors will make a person most at-risk of progressing from infection to active disease if exposed to M. tuberculosis? - Amount of exposure - Malnutrition - Alcoholism - Age of patient

- Malnutrition Mycobacterium tuberculosis, the causative agent of tuberculosis (TB), is spread by airborne particles called droplet nuclei. After initial infection, the disease usually goes to an asymptomatic and non-infectious phase called latent tuberculosis infection (LTBI). The risk of a patient with a positive TB screening test progressing to active disease ranges from about 3% to 15% throughout their lifetime. Malnutrition can have a significant impact on whether or not an exposed patient will progress from LTBI to active disease. While the patient's age, amount of exposure to the organism, and health status also play roles in the likelihood of developing active TB infection, malnutrition, with or without these other factors, is the most significant factor contributing to the progression of the disease.

Matrix-assisted laser desorption-ionization time-of-flight (MALDI-TOF) is used for identification of aerobic bacterial isolates on a urine culture bench. Upon placing the target into the MALDI-TOF instrument, no peaks were found on any target spots, including the quality control. What caused this issue? - Quality control organism was not added to the target wells - Matrix solution was not added to the target wells - The target was not cleaned properly - Quality control organism has deteriorated

- Matrix solution was not added to the target wells Matrix solution is required for the MALDI-TOF to properly identify the organisms, by extracting proteins from the organisms on the target. Once the proteins are extracted with matrix, they each generate a distinct signal (peak) and then spectrum. This spectrum is compared to know spectra in a database to identify the organisms. Since there were no peaks found on the target, this points to the fact that no proteins were extracted to make those peaks. Also, since all the target spots did not work, including the quality control, this points to a procedural error that occurred with all the target wells. If there was no quality control organism applied to the target, just the quality control target wells would have no peaks. At least some of the other target wells should have peaks found if matrix solution is added correctly. Since all the target wells had no peaks, the problems stem from more than the quality control. Targets are cleaned after use and if not cleaned properly, identifications may show as mixed or may not match with colony morphology if residual organism is left on the target. Residual organisms from improper cleaning would show as peaks, just incorrect peaks. If the quality control organism has deteriorated, just the quality control target wells would have an issue of no peaks or no identification. With all target wells showing no peaks, the matrix was not added to extract the proteins.

Which of the following life cycle stage is properly matched to it's location within the host? - Sporozoites in erythrocytes - Merozoites in erythorocytes - Gametocytes in liver cells - Trophozoite in liver cells

- Merozoites in erythorocytes The correct answer is merozoites inside of erythrocytes. The typical malarial life cycle occurs in the following order in the human host: Sporozoites (in liver cells) à Merozoites (in liver cells) à Trophozoites (in erythrocytes) à Schizont (in erythrocytes) à Merozoites (in erythrocytes) à Gametocytes (in erythrocytes)

Beginning with human infection, which of the following is the first stage of the Wuchereria bancrofti life cycle? - Infective stage develops in insect - Ingested by blood sucking insect - Mature in circulatory system, body cavity, or connective tissue in humans - Microfilariae in blood or skin of humans

- Microfilariae in blood or skin of humans The mosquito is the intermediate host for the microfilaria and humans are the definitive host and the reservoir for Wuchereria bancrofti. - Microfilariae in blood or skin of humans is the correct answer as this is the first step of the filarial nematode lifecycle. - Ingested by blood sucking insect is incorrect as this is the second step. - Infective stage develops in insect is incorrect as this is the third step. - Enter humans when insect takes blood meal is incorrect as this is the fourth step. - Mature in circulatory system, body cavity, or connective tissue of humans is incorrect as this is the fifth step. - The final step is adult worms found in humans.

Illustrated in the photomicrograph is a high-power view of the elements within a duodenal aspirate preparation using a Weber Stain (Chromotope 2R, Fast Green, phosphotungstic acid). This stain is used to identify the tiny 1.5 µm pink-red staining spores, many with central transverse septa as: - Cryptosporidium parvum - Cystoisospora belli - Microsporidium species - Cyclosopora cayetanensis

- Microsporidium species Microsporidium species is the correct response. The small size of the spores, the positive red staining with the Weber stain, and the central transverse septa are distinctive for Microsporidium. The oocysts of Cryptosporidium parvum, Cystoisospora belli, and Cyclospora cayetanensis are larger than Microsporidium spores, ranging from 5 - 30 µm, and are negative for the Weber stain, but positive for the modified acid-fast stain. They do not possess an internal pink-staining band.

Carbapenemases are produced by various organisms such as Enterobacteriaceae, Pseudomonas aeruginosa, and Acinetobacter species. Detecting the presence of carbapenemase activity in these organisms is important to prevent spreading of the resistant organisms. Which of the following methods is used to detect the presence of carbapenemase producing organisms? - D test - Modified Hodge Test - ESBL Test - Beta-lactamase test

- Modified Hodge Test Modified Hodge Test is the correct answer because the presence of a carbapenemase can be detected by this method. This method is also referred to as the clover-leaf test. This test uses a carbapenem-susceptible Escherichia coli that is plated to a Mueller-Hinton agar and then carbapenem disks are placed onto the plate. The test organisms are inoculated in a straight line from the disks and growth of the Escherichia coli around the test organism at the intersection of the streak and the zone of inhibition indicates the presence of a carbapenemase. D test is incorrect. The D test is used to detect inducible clindamycin resistance by plating the test organism on a Mueller-Hinton plate and then placing erythromycin and clindamycin disks. If a D zone of inhibition is present after a 24 hour incubation at 37° C, the organism has an inducible resistance to clindamycin, due to the erm gene. ESBL Test is incorrect. This test detects organisms that produce extended spectrum beta-lactamases to the cephalosporin class of antibiotics. To detect an ESBL producing organism, antibiotic disks cefotaxime and cefotaxime-clavulanate and ceftaxidime and ceftaxidime-clavulanate are placed on a Mueller-Hinton agar plated with the test organism. If there is a zone difference between the antibiotic with and without the clavulanate, then the presence of an ESBL is indicated. Beta-lactamase test is incorrect. This test is a rapid test to detect penicillin resistance. Beta-lactamase breaks down the beta-lactam ring found in penicillin.

Identification of intestinal microsporidial spores is usually done by using which of the listed stains? - Modified trichrome stain - Modified acid-fast stain - Gram stain - Giemsa stain

- Modified trichrome stain Modified trichrome stain is the stain of choice for identifying intestinal microsporidium spores.Modified acid-fast stains are primarily used in identification of Cryptosporidium oocysts.Bacteria is usually identified by using the Gram stain.Giemsa stain is the stain of choice for the identification of malarial parasites.

All of the following are reasons why molecular methods for the detection of methicillin-resistant Staphylococcus aureus (MRSA) have gained increasing attention, except: - Active surveillance protocols are being utilized by more institutions on a more comprehensive basis. - Identification of carriers can reduce risk of transmission. - Molecular methods are less expensive than culture methods. - Molecular methods offer the prospect of reduced turnaround times for the availability of MRSA status.

- Molecular methods are less expensive than culture methods. All of the options are correct except that molecular methods are less expensive than culture methods. Direct test costs of PCR methods are likely to be greater than any culture method. Many institutions have implemented active surveillance, both upon admission and throughout the patient stay for MRSA and/or MSSA (methicillin sensitive Staphylococcus aureus). Early identification of carriers allows for implementation of precaution protocols and reduced transmission to other patients. Depending on the culture medium employed, PCR methods offer the prospect of providing screening results 24 to 48 hours earlier than culture methods and are the new gold standard for detection of MRSA from the anterior nares.

Which of the following organisms are aerobic, Gram negative diplococci that do not ferment sugars and is DNAse positive? - Neisseria lactamica - Moraxella catarrhalis - Kingella kingae - Veillonella parvula

- Moraxella catarrhalis Moraxella catarrhalis is a common laboratory isolate that is distinguished from other Gram negative diplococci, including Neisseria species and Kingella species, by not fermenting any of the commonly tested carbohydrates and is DNAse positive. It is also aerobic. N. lactamica is a Gram negative diplococci but ferments glucose, maltose lactose, while K. kingae is a Gram negative coccobacilli that ferments glucose and maltose. Veillonella parvula is an infrequently recovered anaerobic Gram negative diplococcus that also has the properties of being asaccharolytic and failing to hydrolyze DNA.

The colonies shown in this 5% sheep blood agar (left) and MacConkey agar (right) split frame photograph are most likely those of: - Escherichia coli - Enterobacter sakasakii - Proteus mirabilis - Morganella morganii

- Morganella morganii The colonies shown on the 5% blood agar plate are relatively large, dirty gray and are not swarming. The colonies growing on MacConkey agar show no red pigmentation; therefore, the bacterial species is a non-lactose fermenter. Of the responses given, only Proteus and Morganella are non-lactose fermenters and would give the appearance of colorless colonies on MacConkey agar. Morganella morganii, which does not swarm on blood agar, is the correct choice.Escherichia coli is a lactose fermenter and would produce red colonies on MacConkey agar.Enterobacter sakasakii is a lactose fermenter and would produce red colonies on MacConkey agar. In addition, E. sakasakii would produce yellow pigmented colonies on 5% sheep blood agar, not seen in this photograph.Proteus mirabilis would produce colonies similar in appearance to those seen here on MacConkey agar but would swarm on 5% sheep blood agar with a spreading, film covering the surface.Therefore, by exclusion, the non-lactose fermenter, Morganella morganii, which also does not swarm on blood agar, is the correct choice.

Which molecular methodology is used to detect multiple targets in a single sample of CSF when meningitis/encephalitis is suspected? - Nested PCR - Multiplex PCR - Northern blot - Broad range PCR

- Multiplex PCR The correct answer is multiplex PCR. Multiplex assays are designed to detect a variety of microorganisms that cause the same disease. This question references meningitis/encephalitis panels, which are panels used to screen CSF samples for the most common bacterial, viral, and fungal causes. Nested PCR is a modification of PCR that was designed to increase the sensitivity of the reaction. It involves two primer sets directed at the same target, with the first set mirroring traditional primers and the second set "nested" inside of the first set. Northern blot is a way of isolating RNA that is known to be present, which is not the case in most CSF samples submitted to the laboratory. Broad range PCR is used to detect a larger group of microorganisms, rather than a single species. This is generally used to identify if any organism in a "broad-range" of microorganisms is present. This is not useful when performing an analysis to determine if a variety of unrelated organisms are present.

Illustrated in the photograph are 14-day-old colonies of a Mycobacterium species growing on Middlebrook 7H10 agar, with development of yellow pigmentation after exposure to environmental light. From the choices listed below, select the correct presumptive identification of this photochromogenic Mycobacterium species. - Mycobacerium chelonae - Mycobacerium marinum - Mycobacerium scrofulaceum - Mycobacerium gordonae

- Mycobacerium marinum Mycobacterium marinum is the correct response. Of the Mycobacterium species included in this exercise, Mycobacterium marinum is the only photochromogen. Mycobacterium kansasii is another photochromogenic mycobacterium commonly recovered from clinical specimens and additional assays would be required to make the differential identification. Mycobacerium chelonae is a nonchromogen and the small gray white colonies do not develop pigment after exposure to light. Another identifying feature from M. chelonae is the rapid growth of colonies within 3 - 5 days. Mycobacterium scrofulaceum also produces yellow colonies, but from the onset of growth before exposure to light, characteristic of one of the scotochromogens. Mycobacterium gordonae is also a scotochromagen and colonies are yellow pigmented even when incubated in the dark, not requiring exposure to light for yellow pigment to develop.

Which of the following is the most common cause of nontuberculous mycobacteria (NTM) lung disease? - Mycobacterium ulcerans - Mycobacterium scrofulaceum - Mycobacterium kansasii - Mycobacterium avium complex (MAC)

- Mycobacterium avium complex (MAC) Mycobacterium avium complex (MAC) is the most common cause of NTM lung disease. Mycobacterium ulcerans causes painless nodules under the skin, but could also cause a shallow ulcer that could be severe. It also is a rare cause of mycobacteriosis. Mycobacterium kansasii is the second most common cause of NTM lung disease. Mycobacterium scrofulaceum is rare, and causes cervical lymphadenitis in children.

Small, gray-white colonies, growing on 7-H10 agar as illustrated in the upper left image, were recovered from an upper respiratory specimen after 7 days of incubation. This Mycobacterium species in the past was not often recovered from human infections until the discovery of AIDS when it became an agent of pulmonary infections, as well as other systemic infections. Most notably, the colony isolates exhibit a pale yellow pigmentation that does not intensify with light exposure (see upper right image). These acid-fast bacilli illustrated in the lower image are short and found singly or in loose clusters. From these observations, what is the MOST likely identification? - Mycobacterium marinum - Mycobacterium tuberculosis - Mycobacterium avium/intracellulare - Mycobacterium kansasii

- Mycobacterium avium/intracellulare The correct answer is Mycobacterium avium/intracellulare. Mycobacterium avium/intracellulare colonies are small, smooth and dome-shaped early in incubation. After prolonged incubation colonies may become rough and when recovered from patients with AIDs, often develop a pale yellow pigmentation. Microscopic examination of an acid-fast smear reveal short cocco-bacilli free of beading or banding. Most biochemical reaction are non-reactive. Human infections occur primarily from ingestion of contaminated water and food and are of low virulence, except in patients with AIDs where disseminated disease may be encountered. Additional procedures may be required to make a definitive identification. Mycobacterium marinum colonies on Lowenstein Jensen (LJ) and 7H10 agars tend to be small to intermediate in size, entire, smooth to rough, convex, and non-pigmented when grown in the dark. Upon exposure to light, a deep yellow pigmentation develops, one of the characteristics of a photo-chromogen. In acid-fast preparations acid fast bacilli are relatively long and straight, with cross bars often visible. Most infections with M. marinum involve the skin, particularly when open wounds or skin abrasions come in contact with a contaminated water source. Environmental habitats include salt water estuaries, inadequately chlorinated swimming pools, tropical fish aquariums, warm-water spas, and water cooling towers. Mycobacterium tuberculosis colonies are rough and gray-white without pigmentation, both prior to and with exposure to light (non-chromogenic). Bacterial cells observed in acid-fast stains prepared from surgical specimens or exudates are thin, slightly curved, red-pigmented and beaded. In acid-fast smears prepared from colonies growing on agar surfaces long, narrow bacilli are arranged in distinct serpentine cords. Additional procedures may be required to confirm a presumptive identification. Mycobacterium kansasii colonies early in incubation are small, smooth and gray-white. With prolonged incubation after exposure to light, more roughened yellow pigmented colonies are observed, characteristic of one of the photochromogens. The bacilli observed in acid-fast smears are typically long, straight and broad. Cross bands and bars may also be observed. Chronic pulmonary infection resembling classic tuberculosis is the common clinical manifestation and additional procedures may be required to confirm a presumptive identification.

An acid-fast bacillus recovered from a post-surgery wound of a young child had the following characteristics: Rapid growth (3-5 days) on blood and chocolate agar Nitrate positive Niacin negative Urease positive Catalase 68ºC positive Iron uptake positive Which of the following Mycobacterium species does this represent? - Mycobacterium tuberculosis - Mycobacterium fortuitum - Mycobacterium kansasii - Mycobacterium avium-intracellulare

- Mycobacterium fortuitum Mycobacterium fortuitum is correct because Mycobacterium fortuitum demonstrates rapid growth, is nitrate positive, niacin negative, and urease positive, while demonstrating a positive iron uptake test. M. fortuitum is known to grow on routine bacteria media. Mycobacterium tuberculosis is incorrect because Mycobacterium tuberculosis is niacin positive, catalase negative, and iron uptake negative. In addition, M. tuberculosis is not a rapid grower. Mycobacterium kansasii is incorrect because Mycobacterium kansasii is niacin negative, nitrate positive, and a photochromogen. Mycobacterium avium-intracellulare is incorrect because it is niacin and nitrate negative. In addition, M. avium-intracellulare is a nonphotochromogen.

Which of the following is the most likely identification of an acid fast bacilli recovered from an induced sputum with these culture findings? Slow growth at 37 C Niacin test = negative Pigmented photochromogenic Nitrate test = positive Catalase = positive - Mycobacterium kansasii - Mycobacterium tuberculosis - Mycobacterium simiae - Mycobacterium chelonei

- Mycobacterium kansasii The correct answer is Mycobacterium kansasii. Mycobacterium kansasii colonies are photochromagenic (form a pigment when exposed to light, but are non-pigmented in the dark); they are strongly catalase positive, strong nitrate reducers, and negative for niacin accumulation. M. kansasii produces a chronic lung infection that closely resembles pulmonary tuberculosis. Mycobacterium tuberculosis is positive for catalase production, able to reduce nitrate, but it is non-pigmented and positive for niacin accumulation, which does not fit with the information given above. Mycobacterium simiae is photochromogenic and catalase positive, but it does not reduce nitrate and it is positive for niacin accumulation. Mycobacterium chelonei is a rapidly growing mycobacterium that is also non-pigmented and does not reduce nitrate.

What is the MOST likely identification of an acid-fast bacillus that demonstrates the following characteristics? ---> Slow growth ---> Cream to tan colored colonies when grown in the dark ---> Development of yellow pigment upon exposure to light - Mycobacterium kansasii - Mycobacterium chelonei - Mycobacterium avium complex - Mycobacterium scrofulaceum

- Mycobacterium kansasii The correct answer which best fits the characteristics in this question is Mycobacterium kansasii, commonly known as the "yellow bacillus". The description of the organism is consistent with that of a photochromagen, a member of the mycobacteria that is nonpigmented (buff to tan color) when grown in the dark and which develops a yellow pigment when grown in the presence of consistent light. Mycobacterium chelonei is considered a rapid grower with growth occurring in less than 7 days; it is nonpigmented. Mycobacterium scrofulaceum is classified as a scotochromagen and produces smooth, buttery, deep-yellow to orange pigmented colonies when grown in the either the light or dark. Mycobacterium avium complex is a nonphotochromagen with colonies that are nonpigmented (tan to buff color) in the light and in the dark.

All of the following Mycobacterium species will cause tuberculosis, EXCEPT? - Mycobacterium bovis - Mycobacterium africanum - Mycobacterium leprae - Mycobacterium microti

- Mycobacterium leprae Mycobacterium leprae does not cause tuberculosis. It is associated with two major forms of disease; tuberculoid leprosy and lepromatous leprosy. Along with Mycobacterium tuberculosis, M. bovis, M. africanum, M. microti, M. canetti, M. caprae, and M. pinnipedii can each cause tuberculosis and are members of the tuberculosis species complex.

Illustrated in the top photograph are acid-fast bacilli as they may appear in acid-fast stains prepared from a direct mount of infected tissue. These acid fast bacilli are thin, slightly curved, red-pigmented and beaded. The acid fast bacilli, as illustrated in the bottom photograph, aggregate in serpentine chords in stained mounts prepared from colonies growing on agar. From these observations, select the presumptive identification of this mycobacterium. - Mycobacterium kansasii - Mycobacterium avium/intracellulare - Mycobacterium tuberculosis - Mycobacterium fortuitum

- Mycobacterium tuberculosis Mycobacterium tuberculosis is the correct response. Bacterial cells observed in acid-fast stains that are prepared from surgical specimens or exudates are thin, slightly curved, red-pigmented and beaded. Bacilli observed microscopically in acid-fast stains prepared from colonies growing on agar surfaces are distinctly arranged in serpentine cords. Presumptive identifications can be made from these acid-fast preparations and additional biochemical reactions are available both in commercial kits or electronic instruments for confirmation. Mycobacterium kansasii bacilli as observed in acid fast stains prepared from clinical materials are typically long, straight and broad. Cross bands and bars may also be observed. Arrangement of bacilli in serpentine chords are not observed in acid-fast stains prepared from growing colonies. With experience when these bacilli are observed, a presumptive identification can be made. Observation of yellow, pigmented colonies growing on the surface of agar plates will confirm the presumptive identification. Mycobacterium avium/intracellulare bacilli are short and cocco-bacillary, uniform in staining and free of cross banding. Arrangement of bacilli in serpentine chords is not observed in acid fast stains prepared from colonies. Additional biochemical reactions may be required to make a more definitive identification when acid-fast stain morphology is not distinctive. Mycobacterium fortuitum bacilli as observed in acid-fast preparations are pleomorphic with a mixture of short, thick rods admixed with filamentous forms. Bacilli at times may appear beaded or swollen, but aggregation into serpentine chords is not observed. Additional biochemical reactions may be required to make a more definitive identification when acid-fast stain morphology is not distinctive.

Which of the following Mycobacterium species is positive for nitrate reduction? - Mycobacterium tuberculosis - Mycobacterium bovis - Mycobacterium simiae - Mycobacterium ulcerans

- Mycobacterium tuberculosis Out of the choices, Mycobacterium tuberculosisis the only one that will reduce nitrates. Mycobacterium bovis, <Mycobacterium simiae and Mycobacterium ulcerans will not reduce nitrates.

A 32-year-old male was seen in the emergency room with gastrointestinal discomfort. Upon questioning the patient it was learned that he first began feeling ill after spending a day at the park where he swam and played volleyball barefooted. He first noticed a lesion on his foot. Later, he developed vague respiratory symptoms. Now his largest complaint is severe abdominal pain along with occasional vomiting. This patient is most likely suffering from a parasitic infection with: - Echinococcus granulosus - Necator americanus - Entamoeba histolytica - Trichuris trichuria

- Necator americanus The correct answer is Necator americanus. Necator americanus is the only option listed that gains entry to the host by penetrating intact human skin. Ancylostoma duodenale and Strongyloides stercoralis are also able to enter the host by penetrating intact skin and migrate through the body causing respiratory symptoms and eventually intestinal discomfort. Echinococcus granulosus enters the host by ingestion of eggs. The eggs are carried to the liver, lung and/or brain and develop hydatid cysts. Entamoeba histolytica enters the host by ingestion of a mature cyst. Once inside the host, the cyst will multiply by binary fission and the trophozoite emerges. Trichuris trichuria enters the host by ingestion of an embryonated egg from which larvae hatch once they enter the intestine.

Sexually active women can develop peritonitis in the form of perihepatitis, inflammation of the liver surface, due to which of the following organisms? - Streptococcus pneumoniae - Neisseria gonorrhoeae - Mycobacterium tuberculosis - Staphylococcus saprophyticus

- Neisseria gonorrhoeae Neisseria gonorrhoeae is the correct answer because in sexually active young women, both Neisseria gonorrhoeae and Chlamydia trachomatis are common agents of peritoneal infection. However, peritonitis caused by these organisms leads to perihepatitis, which is an inflammation of the surface of the liver, called Fitz-Hugh-Curtis Syndrome. Streptococcus pneumoniae is incorrect even though this organism can cause peritonitis in both children and adults; however, it is not linked to sexual activity. Mycobacterium tuberculosis is incorrect even though this organism can cause peritonitis. Peritonitis infections caused by this mycobacterium species are typically seen in patients who have traveled to South America, Southeast Asia, or Africa. Staphylococcus saprophyticus is incorrect. This organism is seen in sexually active women; however, it is seen as a cause of urinary tract infections and peritonitis.

A patient came into the emergency department with symptoms of meningitis. The patient was suspected of having a blocked cerebral shunt, which can cause meningitis. The shunt was drained and sent to the microbiology laboratory for culture. All of the following organisms are associated with shunt infections EXCEPT? - Coagulase Negative Staphylococcus - Klebsiella pneumoniae - Escherichia coli - Neisseria meningitidis

- Neisseria meningitidis Neisseria meningitidis is the correct answer because this organism in typically not seen in cerebral shunt infections even though it is a cause of meningitis. The following organisms are most often seen in shunt infections: Coagulase negative Staphylococcus, Staphylococcus aureus, Cutibacterium (Propionibacterium) acnes, Viridans group streptococci, Pseudomonas aeruginosa, Klebsiella pneumoniae, Escherichia coli, and Serratia marcescens. Cerebral shunts are placed to allow fluid to drain from the brain into the peritoneal cavity. All of the above organisms can be found in the intestinal tract; therefore, it makes sense that these organisms can be seen in shunt infections. Coagulase negative Staphylococcus, Klebsiella pneumoniae, and Escherichia coli are incorrect answers because they all have been found to cause cerebral shunt infections.

An organism grew out of a spinal shunt. The protocol for growth of this organism is to notify infection control and the public health department. In addition, any health care worker who came in contact with the patient must be treated promptly with antibiotic prophylaxis. Which of the following organisms requires this type of protocol? - Neisseria meningitidis - Neisseria gonorrhoeae - Enterococcus species - Staphylococcus aureus

- Neisseria meningitidis Neisseria meningitidis is the correct answer because this organism is easily spread person-to-person through respiratory droplets leading to life-threatening meningitis. Any person who comes in contact with someone with Neisseria meningitidis must be treated to prevent spreading or succumbing to the infection. Neisseria meningitidis is the leading cause of fatal bacterial meningitis in children and adults. Neisseria gonorrhoeae is incorrect because this organism is spread through sexual contact or spread from mother to newborn during birth. Neisseria gonorrhoeae is the leading cause of sexually transmitted disease and causes purulent urethritis in males and pelvic inflammatory disease in women. Enterococcus species is incorrect. The isolation of Enterococcus species from CSF is always important, but the presence of this organism can indicate strongyloidiasis. Strongyloides parasite can cause an hyperinfection in the intestines and as a result cause damage to the bowel. This can lead to septicemia. Enterococcus species is a common gut bug and in strongyloidiasis (disseminated infections) enterococcus can be a finding in CSF infections. However, treatment does not require antibiotic prophylaxis of those who had contact with the patient and it is not spread by respiratory droplets. Staphylococcus aureus is incorrect. This organism is important when isolated, but it is not spread by person-to-person contact through respiratory droplets and does not require antibiotic prophylaxis of those who came in contact with the patient with meningitidis.

Gram-negative cocci that occur in pairs with their adjacent sides flattened, giving them a "coffee bean" appearance (indicated by the arrows in the image), are typical of which of the following bacteria? - Streptococcus pneumoniae - Neisseria species - Staphylococcus species - Micrococcus species

- Neisseria species Neisseria species is the correct answer because gram-negative cocci that occur in pairs with their adjacent sides flattened are typical of Neisseria species, including Neisseria meningitidis and Neisseria gonorrhoeae. The bacteria in the gram stain that is represented by the image is Neisseria gonorrhoeae. Streptococcus pneumoniae is incorrect because this species is gram positive cocci in pairs and chains. They appear oval in shape and are known as lancet-shaped gram positive cocci. Staphylococcus species is incorrect because Staphylococcus species are gram positive cocci in clusters. Micrococcus species is incorrect because Micrococcus species are large gram positive cocci that can appear in pairs, tetrads, and clusters.

Dracunculus medinensis belongs to this category of parasites? - Cestode - Nematode - Filaria - Trematode

- Nematode Dracunculus medinensis ("guinea worm") is a tissue nematode (roundworm). The organism is typically recovered in the adult form in infected ulcers. Ingesting water that contains infected copepods initiates human infection. Due to eradication efforts, infection is rare. Cestodes (tapeworms) are transmitted to humans by ingestion of a larval stage. The tapeworm attaches to the intestine of a human host with a scolex. Tapeworms have segments called proglottids that produce eggs which are infective to the intermediate host. Filaria are roundworms of blood and tissue transmitted by insects such as mosquitoes, flies, or midges. The adult worms live in human lymphatics, muscles, or connective tissues. Microfilariae are the infective stage for the insect, which develop into filariform larvae, which are introduced into the human circulation. Trematodes (flukes) are flatworms that may infect the liver, lung, intestine, or blood. The life cycle of a fluke requires water for eggs to mature, with a snail as a first intermediate host.

Trichuris trichiura belongs to which of the following helminth groups? - Filariae - Trematodes - Nematodes - Cestodes

- Nematodes Nematodes is the correct answer because nematodes are nonsegmented, elongated, cylindrical worms with a well-developed digestive tract and reproductive system. Trichiuris trichiura is an example of an intestinal nematode. Filariae is incorrect because filariae are tissue roundworms that infect humans. They are transmitted by blood sucking arthropod vectors such as mosquitos or flies. Wuchereria bancrofti is an example of a filariae. Trematodes is incorrect because they require at least one intermediate host. Most trematodes are hermaphroditic. Fasciolopsis buski is an example of an intestinal trematode. Cestodes is incorrect because they are commonly referred to as tapeworms. Tapeworms have long, ribbon-like bodies with a structure for attachment. Taenia solium is an example of an intestinal cestode.

Enterococcus faecium is: - Often vancomycin resistant - Susceptible to the aminoglycosides - Arabinose negative - Motile

- Often vancomycin resistant Characteristics of Enterococcus faecium include: gram-positive cocci, Lancefield antigen group D, primarily alpha-hemolytic (or nonhemolytic), and commonly vancomycin resistant. Vancomycin-resistant enterococci (VRE) have become a global problem. Enterococcus faecium is also resistant to the aminoglycosides, is arabinose positive, and is non-motile.

What is one of the BIGGEST challenges with isolating Francisella? - The production of wide zones of hemolysis - Organism growth is slow. - The overgrowth other organisms. - The production of greenish colonies like Pseudomonas.

- Organism growth is slow. Francisella is slow growing on primary isolation culture media and produces poorly staining, small gram-negative coccobacilli on Gram stain. Because F. tularensis is included on the list of bioterrorism agents, suspicious isolates should be referred immediately to a public health laboratory in lieu of attempting an in-laboratory identification.

A wound specimen was received into the laboratory and a large Gram positive rod was isolated. The microbiologist suspected the isolate was a probable Bacillus anthracis and had to rule in/out before reporting. All of the following tests must be performed before calling the species Bacillus anthracis EXCEPT? - Catalase - Motility - Presence of hemolysis - Oxidase

- Oxidase Oxidase is incorrect because this test is most often performed on nonfermentative Gram negative rods; however, the bioterrorist agent Brucella can be tested with oxidase to help rule in this species. Brucella stains as tiny Gram negative coccobacilli and is oxidase positive. Catalase, Motility, and Presence of hemolysis are all used to identify Bacillus anthracis. Bacillus anthracis is catalase positive, nonmotile, and is nonhemolytic. This organism is a large Gram positive rod, grows large colonies on sheep blood agar, and the colonies can stand up like a beaten egg.

All of the following are characteristics of Brucella are EXCEPT: - Oxidase negative - Stain faintly as gram negative coccobacilli or short rods - Urea positive - Nonmotile

- Oxidase negative Brucella are oxidase positive. This along with other characteristics can be used to differentiate them from similar organisms. Brucella also stain faintly as gram negative coccobacilli or short rods, are urea positive and nonmotile. They are also catalase positive.

The bacterial species producing the set of reactions seen in the oxidative/fermentative (OF) glucose tubes illustrated in this photograph at the right is a (an): - Fermenter - Aerobe - Oxidizer - Nonoxidizer

- Oxidizer The development of a yellow color by a bacterial species inoculated into OF medium indicates the production of acid from the carbohydrate contained. The reaction seen in this photograph; that is, acid production only in the oxygen exposed, uncovered tube, is indicative of an oxidizer. OF medium is used to determine if an organism can use carbohydrates oxidatively, fermentatively, or not at all. In OF medium, positive reactions are indicated by a yellow color, as the bromothymol blue indicator becomes yellow in an acidic environment. Green or blue-green are alkaline reactions and are interpreted as negative. A carbohydrate fermenter would produce a yellow pigmentation in both tubes the open and the closed tubes. Aerobes are microorganisms that live and grow in the presence of oxygen and does not refer to its ability to use carbohydrates. This organism is not a fermenter because fermenters give a positive (yellow) reaction in both the open and closed (tube covered with mineral oil) tubes. A non-oxidizer or nonsaccharolytic organism would produce no color change in either of the tubes, as the carbohydrate is not utilized by either mode of metabolism. Both tubes would appear blue/green or blue, indicating an alkaline reaction.

The colonies observed on the agar surface in the top photograph represent 4 day-old yeast colonies converted from a mold colony suspicious for a dimorphic fungus. The identification is made by microscopically observing the characteristic morphology of the yeast cells as illustrated in the bottom photomicrograph. What is this species? - Blastomyces dermatitidis - Histoplasma capsulatum - Sporothrix schenckii - Paracoccidioides brasiliensis

- Paracoccidioides brasiliensis Paracoccidioides brasiliensis is distinctive by the production of multiple small, spherical, narrow-neck buds attached to central spherical yeast cell that resemble a mariner's wheel. When grown at 22°C, it forms a variety of different colonies, but when grown on BHI blood agar at 37°C the colonies convert to the yeast phase seen in the photograph. Blastomyces dermatitidis yeast colonies are not distinctive on agar and microscopic evaluation is required. The mold phase is seen with one budding daughter cell attached to the mother cell with a distinctive broad base, and are grown on blood agar at 37°C. Histoplasma capsulatum produces small 2-4 µm in diameter yeast cells when grown at 37°C, often in loose clusters. Many of the yeast cells show small buds surrounding the cell with a double walled appearance. When seen in tissue sections, these small yeast cells are typically inside macrophages and resemble Candida glabrata. Sporothrix schenckii yeast colonies are not distinctive, but key is the microscopic observation of elongated cigar-body like yeast forms that can measure up to 10 µm. This organism is dimorphic and it is important to look at forms created at 22°C and 37°C for diagnosis.

Which of the following parasites migrate either to or through the lungs in their corresponding life cycle? - Fasciola species - Taenia solium - Entamoeba histolytica - Paragonimus westermanni

- Paragonimus westermanni Paragonimus westermanni is the correct answer because this organism is found in the lungs of the host. The adult worms are encapsulated in the lungs and produce eggs that leave the lungs through the bronchioles by stimulating a cough in the host. The eggs are then swallowed and excreted in feces. Fasciola species is incorrect as this species is found in the bile ducts. The adult worms produce eggs in the bile duct that are then excreted from the body in the feces. Taenia solium is incorrect because this species is caused by the ingestion of contaminated pork and is found in the intestines in the form of eggs or proglottids. Entamoeba histolytica is incorrect because this amoeba is found in the intestines and occurs from the ingestion of contaminated food and water.

Matrix-assisted laser desorption-ionization time-of-flight (MALDI-TOF) is used for identification of aerobic bacterial isolates on a urine culture bench. Upon placing the target into the MALDI-TOF instrument, no peaks were found on one of the patient samples (out of 20 patients). The quality control passed. What caused this issue? - Too much matrix was added to the well - Too much patient sample was added to the well - Patient sample was not added to the well - Two patient samples were added to the same well in error

- Patient sample was not added to the well Quality control and other patient samples gave good results, so the most likely issue is that patient sample was inadvertently not added to the well. When using the MALDI-TOF identification, it is important to keep track of the target wells that are being used and to place the appropriate patients in the appropriate wells. Matrix is used to extract the proteins from the patient samples and is essential in making the peaks and spectrum for identification. If too much matrix is used, the identification will most likely still provide some type of peaks but may not give as good of an identification. Too much patient sample added to the wells can cause poor identification, but if sample is added to the wells, peaks should be found. Since there were no peaks found, that indicates that sample was not applied to the wells. Two patient samples could be added to the same well in error. If this occurs, typically the identification would come back as low or mixed, but since both patient samples are in the well, some peaks should be found.

All of the following patients may submit an urine specimen from an indwelling catheter EXCEPT? - Patient seen for an annual physical - Hospitalized patient - Long-term care facility patient - Oncology patient

- Patient seen for an annual physical Patient seen for an annual physical is correct because a patient seen for an annual physical will most likely submit a clean catch midstream urine specimen. Such patients they are not in need of an indwelling catheter. A clean catch midstream urine specimen is the least invasive and preferred collection procedure for urine specimens. Hospitalized patient, long-term care facility patient, and oncology patient are all incorrect answers because all these patient types are more likely to have an indwelling urinary catheter. Patients with indwelling urinary catheters are likely to develop bacteriuria, which can spread to a more severe infection.

Which of the following would ensure positive patient identification prior to specimen collection? - Patient's full name and mother's maiden name. - Patient's full name and room number. - Patient's full name and hospital or medical record number. - Patient's full name and age.

- Patient's full name and hospital or medical record number. At least two patient identifiers should be used to positively identify a patient prior to specimen collection. A patient's name alone is not sufficient as several people may have the same name. If the patient's name along with a unique identifier, such as a hospital/medical record number or date of birth is used, positive identification is assured. The patient's name and hospital or medical record number must be verified on the patient's wristband. A room number is not a unique identifier as a patient could potentially be moved to a different room. A patient's mother's maiden name is not a unique identifier, even in combination with the patient's name. A patient's age is also not unique to that individual, even in combination with the patient's name. A birth date may be used in combination with the patient's name if no other unique identifying number is available. It may be the only alternative for outpatients that do not have medical records, hospital, or other unique numbers associated with their names. If a patient is able to respond, it is also important to ask the patient to state his or her name.

The fungal colony illustrated in the upper image, observed after 4 days incubation at 30°C, was recovered from dialysis fluid of a 60 year-old patient who had been receiving multiple antibiotics for treatment of bacterial peritonitis. The colony surface is cottony and green in pigmentation. The lower image is of a methylene-blue stained section of fruiting heads observed in a mount prepared from a small sample of the colony surface. Based on the colony morphology and microscopic features, what is the genus identification of this isolate. - Paecilomyces - Penicillium - Scopulariopsis - Fusarium

- Penicillium Penicillium is the correct response. Characteristic are fruiting heads in the form of a "penicillus" each at the tip of a conidiophore that branches into primary metulae from which in turn are produced secondary phialides. Long chains of small, spherical conidia are produced from the blunt tips of the phialides. Paecilomyces fruiting heads are similar to those of Penicillium sp., with the exception that only a single row of phialides that terminate in a tip are observed. The tips of the Paecilomyces phialides are long and tapered, terminating in a point. The conidia are irregular in size, with the "older" terminal ones being distinctly larger. Scopulariopsis colonies are also have a yellow brown pigmentation but the microscopically the conidia produced in chains are two to three times larger than those of Penicillium spp. and Paecilomyces sp. They are spherical, except for the presence of a distinct flat or truncated base. Fusarium colonies are distinctly magenta to pink-red with red pigment diffusing into the agar. Microscopically long boat-shaped multi-celled macro-conidia are observed each with a hair-like "foot-cell" extending from one end.

In the microbiology laboratory, four specimens are received at the same time. The specimen that should be processed immediately is: - Unpreserved sputum - Feces in preservative - Tissue for quantitation - Pericardial fluid

- Pericardial fluid Of the specimens listed, pericardial fluid is classified as a level 1 critical specimen. Level 1 specimens should be processed immediately due to the invasiveness of collection and the potential of life-threatening illness. Unpreserved specimens, such as sputum, are classified as level 2 specimens, and should follow level 1 specimens in order of processing. If not processed quickly, level 2 specimens may degrade or demonstrate overgrowth of contaminating flora. Level 3 specimens that require quantitation, such as urine or tissue, should also be processed quickly for accurate results. Appropriate storage or preservation should be initiated for level 2 or 3 specimens if delay in processing occurs. Lastly, level 4 specimens, such as urine or feces in preservative, are processed after levels 1-3, but within laboratory guidelines.

This organism is a slow-grower on Sabouraud Dextrose Brain Heart Infusion (SABHI) agar. It was recovered from a chronic recurrent cyst of the skin of the lower leg. The brown hair-like surface pigmentation appears brown-black when observed on the reverse of the colony. The identification is made by the microscopic appearance of fruiting heads. The image shows hyphae that are dark with flask-shaped phialides which form on the tips of the condiophores. What is the name of this fungus? - Phialophora verrucosa - Exophiala jeanselmei - Cladophialophora carrionii - Fonsecaea pedrosoi

- Phialophora verrucosa Phialophora verrucosa is the slow-growing, brown hair-like colony with the dark brown-black reverse side is consistent with one of the agents of chromoblastomycosis. They have flask-shaped phialides with collarettes. The conidia are oval, one celled and occur in balls at the tips of the phialides. Exophiala jeanselmei colonies are also slow growing but more velvety in consistency. The phialides are long and narrow, ending with a distinctive pointed terminal end, giving rise to clusters of elongated pigmented conidia, in keeping with the Exophiala-type sporulation. Fonsecaea pedrosoi primary one celled conidia formed on sympoidal conidiophores. The hyphae are dark and primary conidia at the tip of the condiophore support one to four secondary conidia. Cladophialophora carrionii is characterized by the production of long straight chains of elliptical, dark-staining conidia. Conidium close to the tip of conidiophore are termed shield cell.

Illustrated in the photograph is the 4 day slow growth of colonies recovered on an anaerobic culture. Note the small size of the colonies growing on anaerobic blood agar, distinctive for brown-black pigmentation surrounded by a wide zone of beta hemolysis. Gram stain revealed small, gram-negative coccobacilli. Most strains are biochemically inactive, although glucose and lactose fermentation are positive (saccharolytic). A common source would be from an infection of the oral cavity or from an infected human bite wound. From these observations, select from the multiple choices the identification of this isolate. - Veillonella parvula - Prevotella melaninogenica - Bacteroides fragilis - Fusobacterium nucleatum

- Prevotella melaninogenica Prevotella melaninogenica is the correct response. The presumptive identification can be suspected from the observation of black pigmented colonies, suggested by the species name. The presence of broad zones of beta hemolysis surrounding the colonies is also distinctive. Small gram-negative cocci lying singly are observed on gram stains. Most biochemical reactions are negative with the exception of the fermentation of glucose and lactose. P. melalinogenica is endemic in the oral cavity and may be recovered from cultures obtained from dental cavity infections. Isolates have also been recovered from human bite wounds. Veillonella parvula colonies on anaerobic blood agar are small, entire, convex, translucent, non-pigmented and non-beta hemolytic. Gram-negative cocci lying singly and in loose clusters are observed in Gram stains. Carbohydrate fermentation is absent (asaccharolytic). Additional biochemical assays may be required to make a definitive identification. Being part of the microbiota of the mouth and upper respiratory tract, V. parvula is often recovered in mixed cultures with other bacterial species, or less commonly from blood cultures from hospitalized patients with bacteremia and endocarditis. Bacterioides fragilis colonies on anaerobic blood agar are 1-4 mm in diameter, gray, convex, entire, semi-opaque, and non-pigmented and non-hemolytic. Older colonies may show internal ring-like whorls. Gram negative coccobacilli with rounded ends are observed in Gram stains. Indole and esculin hydrolysis reactions are positive. Glucose and select other carbohydrates including sucrose are fermented. B . fragilis, endogenous in the gastrointestinal tract, is a common isolate from a variety of infections. Fusobacterium nucleatum colonies on anaerobic blood agar are small, gray-white and convex with irregular borders and internal flecking. Beta hemolysis is not observed. Distinctive on gram stain are long and slender gram negative bacilli with tapered ends. Indole is positive. Carbohydrate fermentation of individual sugars is variable but positive among various bacterial strains (sacchrolytic). F. nucleatum is most commonly recovered from induced sputum specimens from hospitalized patients who develop upper respiratory infections.

The dematiaceous colony illustrated here grew to a diameter of 3 - 4 cm in 5 days. Which of the following fungi can be ruled out based on the information given? - Phialophora verrucosum - Exserohilum species - Alternaria species - Ulocladium species

- Phialophora verrucosum The correct answer is Phialophora verrucosum. Phialophora verrucosum, one of the agents of chromomycosis grows slowly, producing colonies no more than 1 cm in diameter after 7 days incubation. All of the other fungi listed grow rapidly, forming mature colonies within 5-7 days of incubation. The dematiaceous molds can be broadly separated into two major groups: those that take 7 or more days of incubation to mature (slow growers) and those that take only 5-7 days of incubation to mature (rapid growers). These are all possible causes of phaeohyphomycosis (mycotic infections caused by dematiaceous fungi).

Illustrated in the top image is a 4-day growth of a dark brown, entire colony with a narrow outer white zone. The surface mycelium is glabrous and finely granular. As this colony is not specific, the fungal species identification must be made on stained mounts prepared from the surface of the mycelium. In the lactophenol blue mount shown in the bottom photomicrograph is the characteristic sac-like structure, a pycnidium, within which are contained small spiral, hyaline, one-celled conidia. Select the name of the fungal species represented in these photographs. - Chaetomium species - Phoma species - Ulocladium species - Culvularia species

- Phoma species Phoma species is the correct response. Although the colony morphology is not distinctive, the rather smooth to peppery appearance of the surface mycelium indicate that hyphae and not conidia are present. The identification can be made microscopically by observing the large, smooth walled sac-like structure that is known as a pycnidium. Within the pycnidia are small, spherical, hyaline one-celled conidia. Chaetomium species contain flask-shaped perithecia which, in contrast to those of Phoma species, are large and distinct due to extension of hair-like extensions. Ascospores are released within the perithecium. Ulocladium species produce colonies that are rapidly growing, ranging from gray, olive-green, or black. Ulocladium species contain multi-celled, angular, cross-walled conidia on sympodial conidiophores. Curvularia species produce colonies that are rapidly growing, cottony, and gray to black. Microscopically, multi-celled, crescent shaped conidia with 3-5 unequally-sized cells are seen on conidiophores.

Refer to the image on the right demonstrating macroscopic images of hyaline molds. All of the following are accurate descriptions of the expected microscopic findings, EXCEPT: - Photo A: single-celled, smooth walled microconidia - Photo B: dense aggregates of echinulate, brown-black conidia - Photo C: loose clusters of elliptical conidia arranged in a "diphtheroid" pattern - Photo D: chains of large, lemon-shaped annelloconidia

- Photo A: single-celled, smooth walled microconidia The correct answer is Photo A: single-celled, smooth walled microconidia. Photo A: The cottony white colony with a lemon yellow apron is typical of Microsporum canis, which microscopically would exhibit Multi-celled, rough walled macroconidia with a tapered terminal cell. Photo B: The peppered brown-black colony is typical of Aspergillus niger, which is microscopically described as dense aggregates of echinulate, brown-black conidia. Photo C: The pastel-rose pigmented colony is typical of Acremonium species, which are microscopically described as loose clusters of elliptical conidia arranged in a 'diphtheroid' pattern. Photo D: The buff-brown colony with radial rugae is typical of Scopulariopsis species, which are microscopically described as chains of large, lemon-shaped annelloconidia.

Perianal itching is the major symptom of infection with both forms of the organism pictured here. This parasite is the causative agent of what condition? - Whipworm infection - Roundworm infection - Pinworm infection - Hookworm infection

- Pinworm infection Adult female pinworms migrate outside of the human anus, when the body is at rest, where they lay their eggs. Perianal itching is the major symptom experienced by individuals (usually children) who are infected by Enterobius vermicularis (pinworm). The eggs are typically flattened on one side. Trichuris trichiura (whipworm) have eggs in stool that appear as brown, barrel-shaped structures with hyaline polar plugs at each end. Ascaris lumbricoides is the most common and the largest roundworm. The ovum is a thick, oval, mammillated (outer protrusions) and embryonated egg. Hookworm infections can occur with Necator americanus and Ancylostoma duodenale. The eggs and larvae of the two species are indistinguishable from each other. The eggs are oval and thin-shelled and contain a clearly visible four- to eight-cell stage embryo.

To enhance recovery of bacteria, proper inoculation of broth media may be accomplished by: - Placing a few drops of liquid specimen directly into the tube of broth - Placing the inoculating loop into the liquid specimen, then sterilizing the loop before placing into the tube of broth - Rehydrating a dried-up swab specimen with saline before adding the swab to the tube of broth - Placing the swab specimen into the tube of broth, while maintaining the temperature at 4°C before and after inoculation

- Placing a few drops of liquid specimen directly into the tube of broth Broth media may be used to supplement plating protocols to enhance bacterial detection. Broth media may be inoculated directly with a few drops of liquid specimen or by placing the swab into the broth. Sterilizing the inoculating loop should be performed before touching the specimen for inoculation, and after media is inoculated. Dried-up specimens should be rejected, because bacteria require moisture for growth. To enhance recovery of pathogenic bacteria, most cultures should be incubated at human body temperature (35-37°C).

An 85-year-old female nursing home patient was treated empirically with a cephalosporin for a urinary tract infection, but later failed therapy. The physician then requested a culture and sensitivity on a new urine specimen which grew >100,000 CFU/mL of Escherichia coli. After reviewing the Kirby-Bauer disc susceptibility plate and susceptibility interpretations, what is the resistance mechanism (if any) for this organism? - Plasmid-mediated AmpC - CRE - Carbapenem Resistant Enterobacteriaceae - ESBL - Extended-Spectrum Beta Lactamase - No resistance mechanism detected

- Plasmid-mediated AmpC Plasmid-mediated AmpC is the correct answer. Cefoxitin and all the first, second, and third generation cephalosporins are resistant with the exception of Cefepime. Ertapenem and Imipenem are both susceptible. Aztreonam is intermediate. This resistance pattern is indicative of a plasmid-mediated AmpC. AmpC is a cephalosporinase that hydrolyzes all beta lactam antibiotics except Cefepime and the carbapenems. AmpCs are also not inhibited by clavulanate. Plasmid-mediated AmpCs have been reported in Serratia species, Providencia species, Citrobacter freundii, Enterobacter species, Morganella morganii, Aeromonas species, and Pseudomonas aeruginosa. Susceptibility disk tests should be performed on these organisms if any of the following screens are positive: Cefoxitin is non-susceptible; ESBL screen test is positive, but the ESBL confirmatory test is negative; if both Cefoxitin and Ceftazidime have an MIC >16 µg/mL and the ESBL confirmatory test is negative. This post-analytic comment should be added to the final report: "Plasmid-mediated transmissible resistance mechanism detected (AmpC). Patient requires contact isolation." CRE- Carbapenem Resistant Enterobacteriaceae is incorrect as there is no resistance pattern or clover-leaf like indention present. ESBL is incorrect as the addition of clavulanic acid to cefotaxime or ceftazidime does not increase the zone size. No resistance mechanism detected is incorrect as there clearly is a pattern of resistance present.

This image depicts a blood smear made from a patient with symptoms resembling malaria. Please identify the species listed below that matches the parasite forms shown in the image with arrows. - Plasmodium vivax - Plasmodium malariae - Plasmodium falciparum - Pseudoparasite

- Plasmodium falciparum This is a true parasitic infection. The species pictured here is Plasmodium falciparum. Plasmodium falciparum ring forms often contain two chromatin dots instead of one, as commonly seen in the other Plasmodium species, and are usually more delicate. Also shown in this image is the characteristic banana- or crescent-shaped gametocyte. Plasmodium vivax is typically characterized by seeing enlarged red blood cells with parasite forms in them as it usually invades the younger red blood cells (reticulocytes). The trophozoite is typically ameboid and may display large vacuoles and the gametocyte is rounded and fills the cell. Plasmodium malariae presents with a compact trophozoite that may have a band appearance as it extends across the entire cell. The schizont is also typically seen in a blood smear which has an average of eight merozoites which may be arranged in a "loose daisy petal" arrangement.

All of the organisms are listed with a common site of recovery for that parasite, EXCEPT: - Giardia lamblia - duodenal contents - Trichuris trichuria - stool - Plasmodium falciperum - ocular secretions - Paragonimus westermanni - sputum

- Plasmodium falciperum - ocular secretions The correct answer is Plasmodium falciperum - ocular secretions. Plasmodium falciperum is commonly found in the peripheral blood and can be recovered from liver biopsies as well. It is part of the blood and tissue flagellates group. It is known to cause severe CNS complications where a patient will complain of severe headaches, will be confused and will eventually lapse into a coma. Giardia lamblia is found in both stool and duodenal contents. Trichuris trichuria is found in stool samples, as the eggs are shed in the feces. Paragonimus westermanni is found in sputum, as it is known to inhabit the lungs.

This parasite was found on a Giemsa stained blood smear. The form shown in the image at the arrow is best described as: - Plasmodium schizont - Leishmania amastigote - Plasmodium ring form - Trypanosoma promastigote

- Plasmodium ring form This organism is a Plasmodium ring form. Note that this form consists of a "ring" of cytoplasm that is connected by a chromatin dot. Schizogony (merogony) is a form of asexual multiple fission in Plasmodium where the nucleus divides many times followed by division of the cytoplasm. These dividing cells are known as schizonts. Plasmodium schizonts contain from 6-24 merozoites depending on the species. The Leishmania amastigote form is an intracellular parasite found in the cells of the reticuloendothelial system with an oval shape and containing a nucleus and a kinetoplast. Trypanosoma cruzi trypomastigotes are usually a "C" or "U" shape and are found in stained blood smears as either a long, slender form or short, stubby form with the nucleus in the center of the body and a large oval kinetoplast. The trophozoite has a flagellum which extends along the outer edge of an undulating membrane.

The cytochrome oxidase-positive bacterial species that is DNAse negative, ornithine decarboxylase positive, and is associated with gastroenteritis in children after the ingestion of contaminated water is most likely: - Aeromonas hydrophila - Salmonella enterica - Plesiomonas shigelloides - Shigella sonnei

- Plesiomonas shigelloides Plesiomonas shigelloides is an oxidase positive organism that is associated with gastrointestinal infections in children. This infection is typically acquired after the ingestion of contaminated water. It is also DNAse and ornithine decarboxylase negative. Aeromonas hydrophila is similar to Pleisiomonas as they are both oxidase positive, associated with contaminated water, and cause gastrointestinal infections in children. However, Aeromonas hydrophila produces DNAse and it does not hydrolyze ornithine, two key characteristics by which they are separated from Plesiomonas shigelloides. Salmonella enteritidis is similar to Pleisiomonas as it causes gastrointestinal infections and it is ornithine decarboxylase positive and DNAse negative. The key characteristic that differentiates it from Pleisiomonas is that it is oxidase negative. Shigella sonnei is similar to Pleisiomonas as it can cause gastroenteritis. It is also ornithine decarboxylase positive and DNAse negative; however, it differs from Pleisiomonas as it is cytochrome oxidase negative.

A bone biopsy from a jaw sent to a microbiology laboratory for culture grew out an Actinomyces species. What would be the most probable contributing factor to this infection? - Poor circulation - Poor oral hygiene - Break in skin - Pelvic infection

- Poor oral hygiene Poor oral hygiene is the correct answer because Actinomyces species is found as normal flora of the human mouth. In addition, Capnocytophaga species can also cause osteomyelitis (infection of bone). If good oral care is not maintained by brushing teeth daily or routine visits to a dentist, these organisms can invade the oral mucosa and infect the bone in the jaw. Poor circulation is incorrect. Osteomyelitis that occurs due to poor circulation is usually found in the extremities in patients with diabetes. Diabetics may develop ulcers on the feet, which patients may not feel due to neuropathy. The infection will spread from the foot and invade the bone of the foot. Break in the skin is incorrect as infections from human or animal bites usually invade the bone of that area. Eikenella corrodens, seen in human bites, and Pasteurella multocida, seen in animal bites, have been isolated in osteomyelitis cases. Pelvic infection is incorrect as a pelvic infection in females may result in mixed infections with aerobic and anaerobic organisms and infect the pelvic bone and not the jaw.

Illustrated in the photographs are smooth, entire, gray-white colonies growing on blood agar that are faintly beta hemolytic (left). Light pink-red pigmented entire, smooth colonies grew on MacConkey agar (right). These isolates were recovered from a skin infection incurred by a 28 year old man after swimming in a lake. The pink-red pigmentation of colonies on MacConkey agar suggest lactose fermentation. Biochemical reactions included Acid/Acid KIA reactions indicating fermentation of glucose. Oxidase was positive. Other positive reactions include indole, DNAse, and esculin. Additional biochemical tests identified this isolate as Aeromonas species. The pink-red colonies growing on MacConkey may suggest one of the Enterobacteriaceae. Which of the following choices will exclude this possibility? - Beta hemolysis on blood agar - Pink red colonies on MacConkey Agar - Positive oxidase reaction - Positive esculin reaction

- Positive oxidase reaction All Enterobacteriaceae species are negative for oxidase. This test result rules out Enterobacteriaceae as a possible identification of the organism. Some species in Enterobacteriaceae family demonstrate beta hemolysis on 5% sheep blood agar. Colony morphology alone is not acceptable to rule out Enterobacteriaceae for this organism. Non-lactose fermenting Enterobacteriaceae will produce clear to light pink-red colonies on MacConkey agar. Lactose fermenting organisms produce an opaque pink pigment. Aeromonas species may be misidentified as Enterobacteriaceae to the inexperienced eye. All species within the Enterobacteriaceae family produce a negative esculin reaction.

What is the anatomical feature of a tapeworm that possesses both male and female reproductive structures? - Brood capsule - Proglottid - Rostellum - Scolex

- Proglottid The correct answer is proglottid. Proglottids comprise is the major portion of the body of tapeworms and they contain both male and female reproductive organs. The uterine branches will become packed with eggs once mature. The brood capsule is a cyst containing a scolex, typically found in Echinococcus granulosus. The rostellum is the crown of the scolex that may or may not have hooklets to assist the tapeworm in attaching to the intestinal wall. The scolex is the anterior portion of the tapeworm that has hooklets and/or suckers to allow the worm to attach to the intestinal mucosa.

A urine sample yielded a lactose-negative, Gram-negative bacillus on primary isolation. Biochemical testing showed the following reactions: Oxidase negative H2S positive Urea positive Phenylalanine deaminase positive The organism which most closely fits this profile belongs to the genus: - Escherichia - Providencia - Proteus - Salmonella

- Proteus Proteus is the correct answer because only Proteus, Providencia, and Morganella produce phenylalanine deaminase. This rules out Escherichia and Salmonella. Proteus is also H2S positive, while Providencia is not.

Which of the following stool pathogens would demonstrate the following reactions: TSI: A/A with H2S production LIA: R/A - Morganella spp. - Providencia spp. - Proteus spp. - Citrobacter spp.

- Proteus spp. Proteus spp. would demonstrate the reactions listed. Morganella spp. would be R/A in the LIA, but in the TSI, would be K/A, or K/A with gas. Providencia spp. would be R/A in the LIA, but in the TSI, would be A/A, K/A, or K/A with gas. Citrobacter spp. would be K/A in the LIA, and in the TSI, would be K/A with gas and H2S, K/A with gas, A/A with H2S, A/A with gas, or A/A.

The trichrome stain is most commonly used to identify which class of parasites? - Protozoa - Nematodes - Cestodes - Trematodes

- Protozoa The correct answer is protozoa. Trichrome stains are used to identify intestinal protozoa, such as Entamoeba histolytica, Endolimax nana, and Giardia lamblia. Trophozoite and cyst morphology can be better visualized using permanent stains, such as the trichrome stains, due to their small size. Wet mounts are generally used for rapid identification of nematodes, cestodes and trematodes.

What bacterial species is rarely part of normal microbiota of healthy humans? - Pseudomonas aeruginosa - Burkholderia cepacia - Burkholderia mallei - Pseudomonas fluorescens

- Pseudomonas aeruginosa Pseudomonas aeruginosa is found in the environment (soil, water, plants) and it survives well in domestic environments (e.g., hot tubs, whirlpools, contact lens solutions) and hospital environments (e.g., sinks, showers, respiratory equipment). It is rarely part of normal microbiota of healthy humans. Burkholderia cepacia is found in the environment (soil, water, plants). It survives well in hospital environments and may colonize respiratory tract of patients with cystic fibrosis. It is not part of normal human microbiota. Burkholderia malleiis the causative agent of glanders in horses, mules, and donkeys. It is not part of human microbiota.Pseudomonas fluorescensis found in the environment (soil and water). It is not part of the normal human microbiota.

The organism growing on Blood Agar and MacConkey Agar in the attached photograph was recovered from the burn wound of a patient. The Gram stain is also attached. This organism is a non-fermenter and can grow at increased temperatures (42 °C). Upon additional testing, the organism was positive for pyocyanin production. Which of the following is the most likely presumptive identification of this organism? - Burkholderia cepacia - Delftia (formerly Comamonas) acidovorans - Pseudomonas stutzeri - Pseudomonas aeruginosa

- Pseudomonas aeruginosa Pseudomonas aeruginosa is the correct response. The spreading, mucoid colonies growing both on Blood and MacConkey agars are characteristic. Colonies growing on MacConkey agar have a greenish pigmentation (not well demonstrated in this photograph) from the production of pyocyanin, best observed when growing on PseudoCel agar. P. aerugniosa is capable of growing at 42 °C. Elongated Gram negative bacilli arranged in parallel bundles is also characteristic of P. aeruginosa. Oxidase, Arginine and Acetamide reactions are positive. Most isolates are resistant to Polymyxin B. P. aeruginosa is a common cause of nosocomial infections including infections following burns. It is often found in moist environments such as pools, hot tubs, catheters, and humidifiers. Burkhoderia cepacia colonies on blood and MacConkey agar do not spread, are relatively small, smooth and entire with a buff yellow pigmentation. The colonies on MacConkey agar are light gray without green pigmentation indicating lack of pyocyanin production. Gram stains reveal short Gram negative bacilli arranged singly and in loose clusters. Arginine and acetamide reactions are negative. Also resistant to polymyxin B. Delftia (formerly Comamonas) acidovorans colonies on blood agar are tiny and non-spreading. Greenish pigmentation of colonies on MacConkey agar are negative indicating lack of pyocyanin production. Gram stain reveals straight or slightly curved Gram negative bacilli arranged singly. Arginine and acetamide reactions are negative. Pseudomonas stutzeri colonies on blood agar are distinctly flat and wrinkled with a yellow pigmentation. Colonies on MacConkey agar are gray white characteristic of a non-fermenter and devoid of pyocyanin green pigmentation. The Gram stain appearance and most other biochemical characteristics are comparable to P. aeruginosa. Most strains of P. stutzeri are sensitive to polymyxin B.

The bacterial species, a typical colony of which is illustrated in this photograph, and a common bacterial cause of otitis externa, also known as "swimmer's ear", can be identified as: - Serratia marcescens - Pseudomonas aeruginosa - Alcaligenes odorans - Streptococcus pneumoniae

- Pseudomonas aeruginosa The photograph illustrates a colony that appears smooth to mucoid in consistency, with a distinct green discoloration. Blood agar may assume a green discoloration from the breakdown of erythrocytes and the release of pigmented biliverdin products, either from alpha hemolysis or from deterioration. For example, most strains of Alcaligenes odorans produce a green discoloration of the media. Streptococcus pneumoniae is alpha hemolytic, and many strains may also appear mucoid. However, neither of these species produce pyoverdin and neither has been associated with "swimmer's ear". Some strains of Serratia marcescens produce pigments; however, the hue is generally on the brown, yellow or red side of the color spectrum. The green pigment seen in this photograph is pyocyanin, a chief identifying characteristic of P. aeruginosa. P. aeruginosa is a hydrophilic organism and a known bacterial agent of otitis externa, aka: "swimmer's ear", at a site where moisture tends to accumulate.

All of the following organisms are known to be resistant to vancomycin EXCEPT? - Staphylococcus aureus - Enterococcus faecium - Enterococcus faecalis - Rhodococcus equii

- Rhodococcus equii Rhodococcus equii is the correct answer because Rhodococcus species are susceptible to most antibiotics and can be treated with erythromycin and rifampin, gentamicin, tobramycin, ciprofloxacin, vancomycin, and imipenem. Staphylococcus aureus is incorrect because this species is known to have vancomycin resistance, hence, the species names Vancomycin Intermediate Staphylococcus aureus (VISA) and Vancomycin Resistant Staphylococcus aureus (VRSA). Enterococcus faecium and Enterococcus faecalis are both incorrect because both organisms have an acquired resistance to vancomycin as well other classes of antibiotics. Vancomycin resistance can occur due to alterations in the molecular structure of cell components, which decreases the vancomycin binding allowing cell wall formation to continue. In addition, excess peptidoglycan production can also lead to vancomycin resistance.

A CSF specimen was sent to the laboratory for analysis. A glucose, protein, and cell count were performed. Based on the following results, what would be the probable cause? Analyte Result Glucose 15 mg/dL Protein 150 mg/dL Leukocytes 1,000 cells/mm3 neutrophils - Normal CSF - Viral infection - Purulent infection - Tuberculosis or fungal infection

- Purulent infection Purulent infection is correct. For a CSF to be considered purulent, the glucose value should be <45 mg/dL, the protein value should be >100 mg/dL, and the leukocyte count should average 800 cells/mm3 (range 5-20,000 cells/mm3) with polymorphonuclear cells predominating. The glucose value is low because bacterial organisms are using the glucose as an energy source for growth and the protein value is elevated due an increase in cellular presence. Normal CSF is incorrect. To be considered normal, the glucose value must be within 45-100 mg/dL, the protein must be within 15-50 mg/dL, and the leukocyte count must be within 0-5 cells/mm3 with no predominant cell line. Viral infection is the incorrect answer. In a viral infection, the spinal fluid will have a normal glucose value (range 45-100 mg/dL), a slightly elevated protein value (range 15-50 mg/dL), and an average leukocyte count of 80 cells/mm3 (range 0-5 cells/mm3) with mononuclear cells predominating. Tuberculosis or fungi infection is incorrect. In this type of infection, the glucose value is low to normal, the protein value is >50 mg/dL, and the leukocyte count is around 100 cells/mm3 with mononuclear cells predominating.

The pigment produced on the King's medium agar plate illustrated in this photograph is: - Phenylalanine - Fluorescein - Pyocyanin - Biliverdin

- Pyocyanin Pyocyanin is a phenazine dye that is uniquely produced by Pseudomonas aeruginosa, accounting for the blue pus that characterizes purulent infections caused by this organism. Phenylalanine is an amino acid that, upon deamination to phenyl pyruvic acid, produces a green color when reacted with ferric chloride. Fluorescein is also a pigment produced by P. aeruginosa; however, it is an iridescent yellow to the naked eye and produces a brilliant blue green fluorescence when observed with UV light. Bilverdin is an oxidative break down product of hemoglobin, which often is observed as a gray green discoloration of blood agar.

Some strains of Group F Strep can carry the group A antigen, potentially leading to a false positive identification of group A, Streptococcus pyogenes. A spot test that is helpful in differentiating these two species and thus preventing a false report is: - Catalase - Bile solubility - Pyrrolidonyl-b-naphthylamide (PYR) - Cytochrome oxidase

- Pyrrolidonyl-b-naphthylamide (PYR) Most strains of group A Streptococcus pyogenes are PYR positive, and therefore can be differentiated from other beta hemolytic streptococci, all of which are negative. All of the streptococci are catalase negative; therefore, this is not a helpful discriminating test. Bile solubility is a test that is helpful in distinguishing Streptococcus pneumoniae (bile soluble) from all other streptococci, which are bile resistant. The streptococci do not possess cytochrome oxidase activity; therefore, this is not a discriminatory test.

Matrix-assisted laser desorption-ionization time-of-flight (MALDI-TOF) is used for identification of aerobic bacterial isolates on a urine culture bench. Upon placing the target into the MALDI-TOF instrument, no peaks were found on the quality control wells, but the patient isolates gave good identifications. What caused this issue? - Quality control organism was not added to the target wells - Matrix solution was not added to the target wells - The target was not cleaned properly - Incorrect wells were used for analysis

- Quality control organism was not added to the target wells The only wells on the target that had an issue were the quality control wells, which indicate that the quality control was not added, or it could have deteriorated. Since the other patient wells gave a good identification, the issue lies with the quality control only. Matrix solution is required for the MALDI-TOF to properly identify the organisms, by extracting proteins from the organisms on the target. Once the proteins are extracted with matrix, they each generate a distinct signal (peak) and then spectrum. This spectrum is compared to known spectra in a database to identify the organisms. Matrix is required for all wells, including the quality control. Since the patient wells gave good identifications, the matrix was applied to the target. Targets are cleaned after use and if not cleaned properly, identifications may show as mixed or may not match with colony morphology if residual organism is left on the target. Residual organisms from improper cleaning would show as peaks, just incorrect peaks in the quality control wells. If the incorrect wells were used for analysis, there should be some type of result for those wells, just not the correct quality control result.

All of the following viruses are classified as retroviruses, EXCEPT? - Human immunodeficiency virus (1 & 2) - Human T-lymphotropic virus type 1 - Human T-lymphotropic virus type 2 - Rabies virus

- Rabies virus The rabies virus is in the family of Rhabdoviridae (common name, Rhabdovirus). The virion consists of single-stranded RNA with a helical nucleocapsid surrounded by a lipid bilayer envelope. Retroviruses are enveloped RNA viruses, and each virion contains two identical copies of single-stranded RNA. The family Retroviridae include Human immunodeficiency virus 1 & 2 and Human T-lymphotropic virus 1 & 2.

To screen for Vancomyin-Resistant Enterococci, which of the following culture sites is most appropriate? - Rectal - Nasal - Groin - Throat

- Rectal Rectal is the correct answer. To screen for Vancomyin-Resistant Enterococci (VRE), rectal or stool swabs will provide the best sensitivity. Open skin lesions and mucosal surfaces can be sampled, but the sensitivity is low. Nasal swabs are not recommended for VRE screening. Nasal, Groin, and Throat are incorrect answers because these culture sites are most appropriate for MRSA screening.

What color would the agar be around a colony of Staphylococcus epidermidis growing on mannitol salt agar (MSA)? - Yellow - Red - Brown - Clear

- Red Mannitol salt agar is commonly used for selective differentiation of staphylococci. It contains peptone base, mannitol, and a phenol red indicator. At a 7.5% salt concentration, it inhibits the growth of most bacteria. No change in the color of the original agar (red) indicates that mannitol was not fermented, which S. epidermidis would show. A change in the agar color to yellow indicates mannitol fermentation by the organism. S. aureus and S. saprophyticus would both show this. A brown or clear appearance in the agar is not traditionally seen as a reaction result using MSA.

A protected brush specimen was received into the microbiology laboratory from an ICU patient and cultured using a 0.001-mL loop. The culture grew 3 colonies of Pseudomonas aeruginosa. Which of the following is the correct way to report out the organism? - Report out 3 CFU/mL of Pseudomonas aeruginosa - Report out 300 CFU/mL of Pseudomonas aeruginosa - Report out 3,000 CFU/mL of Pseudomonas aeruginosa - Report out as glucose nonfermenting Gram-negative rods.

- Report out 3,000 CFU/mL of Pseudomonas aeruginosa Report out 3,000 CFU/mL of Pseudomonas aeruginosa is the correct answer. Quantitative cultures can be performed in two ways. A serial dilution method or a calibrated-loop method. When a 0.001-ml loop (1-µL) is used with the calibrated-loop method, the number of colonies growing is multiplied by 1,000 and then reported. In addition, any time Pseudomonas aeruginosa is present in significant amounts, even if not the predominating organism, the organism is reported. Report out 3 CFU/mL of Pseudomonas aeruginosa is incorrect because this does not represent the correct calculation when using a 0.001-mL (1-µL) loop in culturing a protected brush specimen. Report out 300 CFU/mL of Pseudomonas aeruginosa is incorrect because this represents the correct colony count when using a 0.01-mL (10-µL) loop in culturing a protected brush specimen. If a 0.01-mL (10-µL) was used, the number of colonies will be multiplied by 100 resulting in this answer. In the question presented, a 0.001-mL loop was used. Report out as Glucose nonfermenting gram-negative rods is incorrect because this is reported when more than one morphology of Gram negative rods that are either oxidase positive and grows on MacConkey or are nonreactive on KIA or TSI slants. In the question presented, only Pseudomonas aeruginosa grew and there was no mention of multiple morphologies.

An alpha hemolytic slightly concave isolate from a respiratory specimen gave a zone of inhibition of 18 mm around the optochin disk. What should the next step be? - Report the isolate as optochin sensitive. - Report this organism as Streptococcus pneumoniae. - Report this organism as Viridans streptococci. - Repeat the optochin susceptibility test.

- Report this organism as Streptococcus pneumoniae. The correct answer is to report this organism as Streptococcus pneumoniae. Streptococcus pneumoniae is susceptible to optochin, where all other alpha hemolytic streptococcus species are resistant. A zone measuring greater than or equal to 16 mm is considered susceptible. Streptococcus pneumoniae is a virulent pathogen, mainly due to its capsular polysaccharides. Streptococcus pneumoniae strains that lose the ability to produce a capsule are nonpathogenic. Optochin disks are used for identification, not antimicrobial susceptibility testing. With a susceptible optochin result, this isolate is not a Viridans streptococci. There is no need to repeat the optochin susceptibility, as this zone is sufficient for interpretation.

Gram stain of a spinal fluid revealed pleomorphic, gram-negative rods. Colonies that appeared on chocolate agar after 24 hours of incubation were gray, opaque, and medium in size. A musty odor was noted when the plate was opened. Gram stain of the colonies on chocolate agar showed small, gram-negative coccobacilli. No growth was seen on sheep blood or MacConkey agar. The next step taken by the technologist to identify this isolate would be to show that the organism: - Ferments lactose and produces indole - Decarboxylates lysine - Requires cysteine - Requires X and V factors

- Requires X and V factors Requires X and V factors is the correct answer because the description is typical of Haemophilus influenzae. The best way to identify Haemophilus species is by showing a requirement for X and V factors. Haemophilus species does not ferment lactose, decarboxylate lysine, or require cysteine for growth. Haemophilus species may produce acid from glucose and xylose, but not lactose or sucrose. In addition, Haemophilus species does not grow on sheep blood agar and will give a coccobacilli gram stain morphology.

In the hookworm life cycle, which of the following is considered the noninfective larval form?: - Rhabditiform - Filariform - Proglottids - Cercariae

- Rhabditiform Rhabditiform is the correct answer because in the hookworm lifecycle, eggs are released in feces and hatch in the soil. The rhabditiform larvae (noninfective) will hatch from the egg and mature into filariform (infective) larvae. The filariform larvae then will penetrate the skin or be ingested. From there, the filariform will migrate to the heart, lungs, trachea, and them be swallowed and enter the intestines. The adult worms will then enter the intestines and the cycle will start over. Filariform is incorrect because this is the infective stage of the hookworm that will either penetrate the skin or be ingested. Proglottids is incorrect because proglottids are not seen in hookworms. Proglottids are seen in tapeworms and are egg producing segments. Cercariae is incorrect because cercariae is found in snails that lead to trematode infections, such as Fasciolopsis buski. The cercariae will mature into metacercariae and infect fish. Humans will ingest the infected fish and the metacercariae will develop into adult worms.

A suspected nocardioform bacterial species was recovered from sputum. The isolate produced mucoid colonies with pink pigment after 4 days on SBA, as shown in the associated image. Staining demonstrated diphtheroid, Gram positive rods with a few branching filaments. It also stained partially acid fast. The most likely identification is: - Rhodococcus equi - Corynebacterium pseudotuberculosis - Klebsiella pneumoniae - Cutibacterium (Propionibacterium) acnes

- Rhodococcus equi Rhodococcus equi is classified as an aerobic actinomycete and nocardioform bacteria. Colonies of R. equi produce salmon-pink pigment, especially with extended incubation. Growth on SBA may resemble lactose-fermenting Klebsiella on MAC. Corynebacterium pseudotuberculosis is a Gram positive rod, diphtheroidal in arrangement, and does not form filaments. It produces small, yellowish-white colonies on SBA. Klebsiella pneumoniae is Gram negative rod, and does not produce filaments or stain acid fast. It grows as mucoid, gray-white colonies on SBA. Cutibacterium (Propionibacterium) acnes is a Gram positive, anaerobic rod with diphtheroid-like arrangement that does not produce branching filaments like Cutibacterium (Propionibacterium) propionicus. On anaerobe blood agar, colonies are circular, entire, convex, and glistening. It is often a contaminant from skin, but may cause more serious infection.

The optochin (ethylhydrocupreine hydrochloride) disk is most often used for the identification of which organism? - Staphylococcus aureus - Haemophilus influenzae - Streptococcus pyogenes - Streptococcus pneumoniae

- Streptococcus pneumoniae The optochin test detects whether or not an organism is susceptible to optochin (ethylhydrocupreine hydrochloride). Optochin tests the fragility of the bacterial cell membrane and causes Strep pneumoniae to lyse due to changes in surface tension. The optochin test is widely used in the form of filter paper discs, impregnated with ethylhydrocupreine hydrochloride, which are applied directly to inoculated plates before incubation. So, optochin inhibits Strep pneumoniae, but does not affect other Strep. (They are resistant) Haemophilus influenzae and Staph aureus would not be plated with an optochin disk.

Which yeast species is most likely the colony morphology as seen in the bottom right image - Candida albicans - Rhodotorula species - Cryptococcus neoformans - Geotrichum candidum

- Rhodotorula species Rhodotorula species can virtually be recognized by the distinctive orange red pigmentation of the colonies, as seen in the bottom right image. The colonies also appear mucoid as in the picture due to the presence of a capsule. Candida albicans is seen in the lower left image. The image shows pasty, yellow-white colonies from which "feet" extend out from the margins. The margins of the colonies are irregular with short extensions into the surrounding agar, which is characteristic for C. albicans. Cryptococcus neoformans is seen in the upper left image. The large cream colonies that appear mucoid are characteristic for Cryptococcus due to the presence of a capsule. Geotrichum candidum is seen in the upper right image. The colonies appear white to cream and smooth to wrinkled, with radiating edges.

Which physician is known for their discovery of Bacillus anthracis and Mycobacterium tuberculosis? - Louis Pasteur - Paul Ehrlich - Robert Koch - Edward Jenner

- Robert Koch Robert Koch is the correct answer because in 1876, Robert Koch published his work on Bacillus anthracis. In 1882, he published his findings on Mycobacterium tuberculosis. Through his published work on Bacillus anthracis, Robert Koch proved the first proof that the germ theory of disease was valid. Louis Pasteur is incorrect because Louis Pasteur is known for his discovery of Staphylococcus, Streptococcus, and Pneumococcus as well as the theory of contamination, which lead to the development of pasteurization. Paul Ehrlich is incorrect because he is known for the discovery of disease treatments with chemicals, hence, the term chemotherapy. Ehrlich and his colleague, Sahachiro Hata, developed Salvarsan, which was used in the treatment of syphilis. Edward Jenner is incorrect because he is known for his discovery of using cowpox to protect against smallpox.

History records an outbreak with the sudden onset of high fever, headache, and abdominal pain among 93 persons who had attended a public church dinner the week before. The photograph of an XLD agar plate is representative of the organism that may have been recovered from blood cultures from any one of these 93 persons. The most likely identification is: - Escherichia coli - Salmonella serotype Typhi - Shigella sonnei - Edwardsiella tarda

- Salmonella serotype Typhi The clinical history as presented is classic for typhoid fever. The HE agar plate shows the recovery of non-lactose fermenting colonies (clear appearance) some of which have black centers. This picture is consistent with Salmonella serotype Typhi, although Edwardsiella tarda is a possibility but can be ruled out because it does not cause a typhoid fever type syndrome. Escherichia coli will appear yellow without H2S production on XLD agar, and doesn't fit the clinical presentation in this case. Shigella sonnei would appear clear on XLD agar, but would not produce H2S, and doesn't fit the clinical presentation in this case.

Adult forms of the following worms are all hermaphroditic, EXCEPT: - Hymenolepis - Taenia - Schistosoma - Clonorchis

- Schistosoma Schistosoma spp. are blood flukes. They differ from all other flukes (trematodes) in that both male and female forms exist. The female lives in an involuted chamber, the gynecophoral canal, which extends the length of the male. Since both male and female forms exist, Schistosoma are not hermaphroditic. Hymenolepis spp. and Taenia spp. are tapeworms (cestodes) containing both male and female reproductive organs, therefore they are hermaphroditic. Clonorchis spp. are flukes (trematodes) that contains both male and female reproductive organs, therefore they are hermaphroditic.

This suspicious form, found in urine, measures 120 µm by 50 µm. What is the appropriate identification? - Schistosoma japonicum - Pseudoparasite - Trichomonas vaginalis - Schistosoma haematobium

- Schistosoma haematobium The only egg, as seen in the photograph, typically recovered in urine samples is that of Schistosoma haematobium. This organism is characterized by its distinct shape, particularly the presence of a large terminal spine opposite a rounded end. The standard method of diagnosis is by the detection of characteristic eggs in feces for Schistosoma japonicum which has a small lateral spine. Since this is showing an actual egg form of a parasite, it would not be considered a pseudoparasite. Although Trichomonas vaginalis may be recovered from a urine sample, it is relatively small in size (average length = 13 µm) and assumes the characteristic flagellate trophozoite appearance.

This suspicious form, found in urine, measures 120 µm by 50 µm. What is the identification? - Schistosoma japonicum egg - Pseudoparasite - Trichomonas vaginalis trophozoite - Schistosoma haematobium egg

- Schistosoma haematobium egg Schistosoma haematobium typically measures 110-170 µm by 38-70µm. The oblong shape of the egg is characteristic for Schistosoma species. The arrow in the picture is pointing to the terminal spine that is diagnostic for Schistosoma haematobium. S. haematobium resides in the veins surrounding the bladder and is found in urine, rather than in stool samples. Schistosoma japonicum has the same oblong egg shape. This parasite is the smallest of the Schistosoma species typically measuring 50-85 µm by 38-60 µm. This egg is also differentiated from the other species based on the presence of a lateral spine, opposed to a terminal spine. Additionally, S. japonicum resides in the veins surrounding the intestinal tract or blood passages to the liver, and thus are recovered in stool, not urine. Pseudoparasite means a false or fake parasite, such as matter in a sample that resembles a parasite, but is not one. Based on the oblong shape and terminal spine, this is Schistosoma haematobium. Trichomonas vaginalis is a sexually transmitted infection and the specimen of choice for diagnosis is a wet prep, however, it may be recovered from a urine sample. T. vaginalis it is relatively small in size, typically 8-15 µm but some can be as large as 30 µm in size. T. vaginalis trophozoite is characterized by an ovoid, round, or pear-like shape, with flagella. The flagella may not be apparent, but typically the organism will be motile in the preparation. T. vaginalis also has a single, ovoid nucleus, but it is not visible in unstained preparations.

The portion of a tapeworm used for attachment to the host's intestine is called the: - Hexacanth - Proglottid - Rostellum - Scolex

- Scolex The scolex is the mouth-like part at the anterior end of a tapeworm used for attaching to the lining of the intestines. A hexacanth (or oncoshpere) is the larval tapeworm (embryo) within the egg of a tapeworm. Hooklets may be visible inside the hexacanth. This stage is infective if ingested. Proglottids are a chain of egg-producing units which compose the majority of an intestinal tapeworm (cestode). The proglottids at the anterior end of the tapeworm are the youngest. The older, gravid proglottids at the posterior end may detach and release eggs. The rostellum is the crown of the scolex (mouthpart used for attachment) that may have hooklets or be smooth with sucking parts. The presence or hooklets, suckers, or both are useful in the identification of species with similar egg characteristics.

The egg in the image to the right, measuring 80 µm, was observed in the stool specimen of a patient complaining of fever, diarrhea, and weight loss. Low grade eosinophilia of 12% was detected in a peripheral blood count. Based on this information, what is the most likely identification of this trematode species? - Schistosoma haematobium - Schistosoma mansoni - Fasciola hepatica - Schistosoma japonicum

- Schistosoma japonicum The correct answer is Schistosoma japonicum. Schistosoma japonicum eggs typically measure around 80 µm and exhibit an oval to spherical shape. A small knob extending from the side of the outer thin, smooth shell is distinctive for S. japonicum. The adult fluke resides in the small intestine and may invade the intestinal wall. A heavy proliferation of eggs is most commonly detected in the microscopic examination of fecal specimens. Schistosoma haematobium eggs are oval in outline and characterized by their large size (averaging 140 µm) and the extension of a relatively small pointed spike from the shell at one of its narrow ends. These eggs are also more commonly observed in the urine and only rarely found in the feces. Schistosoma mansoni eggs are characterized by their large size (average of 140 µm), oval outline and the distinctive large, pointed spike projecting from the side of the outer thin shell, rather than from one of the ends. Fasciola hepatica eggs are large, averaging 140 µm. The outer shell is thin and smooth, but with an indistinct non-shouldered operculum at one of its narrow margins, rather than having the pointed spikes as seen with certain Schistosoma species.

Illustrated in the high power view of an H & E-stained tissue section is a granuloma involving the wall of the large intestine. Based on the observation of a sharp spike projecting from the cyst shell (arrow), what is the identification of this parasitic egg? - Schistosoma japonicum - Clonorchis sinensis - Schistosoma mansoni - Schistosoma haematobium

- Schistosoma mansoni Compared to the size of the surrounding inflammatory cells (8 - 10 µm), the size of this ovum is quite large, exceeding at least 10 times their size. The distinguishing characteristic leading to the identification of this invasive ovum as Schistosoma mansoni is the large, spiked lateral spine projection from the side of the shell. Schistosoma japonicum ova are smaller, measuring an average of 80 µm, and are spherical in outline and distinctive for the presence of a small, knob (or hooked spine) at one side of the shell rather than a pointed projected spike. Clonorchis sinensis ova are small, measuring no more than 35 µm, and are urn-shaped with a smooth shell with prominent shoulders. Mature ova may present a small knob extending from the posterior outer margin. Schistosoma haematobiumova are large, averaging 140 µm, with a thin, smooth shell. Distinctive is the small, spiked spine that projects from the terminal margin rather than from the side. It is more commonly seen in the wall of the urinary bladder rather than of the intestine.

Which of the following organisms is considered a Helminth? - Trypanosoma brucei rhodesiense - Leishmania braziliensis - Entamoeba histolytica - Schistosoma mansoni

- Schistosoma mansoni Schistosoma mansoni is a blood fluke, or Helminth, that can cause local infections of dermatitis that lasts for 3 days. However, if the larvae travel through the body it can cause fever, malaise and urticaria that can last up to 4 weeks. Trypanosomes brucei rhodesiense is a Protozoa that causes East African sleeping sickness. The infection starts as a tender, red inflammation at bite that progresses to a hemolymphatic disease in about 3 weeks. The infection can then progress to the CNS where it can cause paralysis and eventually death. Leishmania braziliensis is a Protozoa that causes mucocutaneous leshmaniasis that destroys the mucosal lining in the face. This can leave hosts significant damage. Entamoeba histolytica is an intestinal amebae that is usually asymptomatic, but can cause abdominal infections. Asymptomatic patients pose a threat because they are contagious and can pass infection to others.

Which one of the following parasites migrates through the circulation (blood) before maturing in the portal venous system? - Schistosoma mansoni - Enterobius vermicularis - Taenia saginata - Trichuris trichiura

- Schistosoma mansoni Schistosoma mansoni is a fluke that resides in the portal system venules, primarily those of the lower intestine. Cercariae (the free-swimming larval stage of the fluke) is released from infected snails (the intermediate host) into freshwater estuaries. Humans that are in the water may become infected through skin penetration by the cercariae. The cercariae then enters the blood circulation, finally settling into the intrahepatic portal blood vessels of the intestine where it matures. Enterobius vermicularis is an intestinal nematode that enters the host by ingestion or inhalation of the eggs. The eggs hatch and the worm matures in the intestine. Taenia saginata is an intestinal cestode that enters the host via undercooked or raw beef infected with larvae. The larvae are released into the small intestine where the worm attaches to the mucosa and matures. Trichuris trichiura is an intestinal nematode that enters the host by ingestion of embryonated eggs. The larvae are released in the intestine where they mature into adult worms.

A 16-year-old male champion athlete went to his doctor complaining of a persistent cough, fever, bloody diarrhea and overall weakness. Upon questioning the patient, it was learned that he had recently competed in a freshwater swimming competition in the Caribbean. Examination revealed a dermatitis on the patient's right calf. A battery of tests were ordered including a CBC, chemistry profile, and a stool for culture and parasitic examination. The CBC revealed the presence of eosinophilia. The other hematology and chemistry tests were unremarkable. The culture was negative. A suspicious egg form was seen on all parasite preparations made from the stool sample submitted. This form measured 165 µm by 68 µm and had a large lateral spine. (See image to the right) This patient is most likely suffering from an infection with: - Schistosoma japonicum - Fasciolopsis buskii - Schistosoma mansoni - Fasciola hepatica

- Schistosoma mansoni Schistosoma mansoni is correct because they are found in Africa, South America, West Indies, and in Puerto Rico. The eggs are elongated and oval in shape. They measure 114-180 µm and have a large lateral spine. Human contraction of the schistosomes occurs following swimming in contaminated fresh water. Infective cercariae, residing in such water, drill into human skin and establish a residence in select blood vessels of the body. Schistomsoma japonicum is incorrect because it is most endemic to Africa, Asia, and India. The eggs are elongated and oval and measure 55-85 um. They also have a small knob-like projection. Fasciolopsis buskii and Fasciola hepatica are incorrect answers because they are typically found in the Far East. The eggs are ellipsoid in shape and measure 130-140 µm. They are very large and can have a colorless shell. Both species are nearly indistinguishable from each other.

The ONPG (ortho-nitrophenyl-Beta-D-galactopyranoside) test is used to: - Separate Gram positive cocci based on production of catalase. - Separate late lactose fermenters from lactose negative bacteria based on the production of beta-galactosidase. - Differentiate alpha hemolytic streptococci based on bile solubility. - Differentiate Gram negative bacilli based on cytochrome oxidase production.

- Separate late lactose fermenters from lactose negative bacteria based on the production of beta-galactosidase. Structurally like lactose, ONPG is useful in the detection of late or slow lactose fermenters. Lactose fermentation requires two enzymes, beta-galactosidase which degrades lactose into glucose and galactose and lactose permease which transfers lactose into the bacterial cell. Late lactose fermenters possess beta-galactosidase, but not lactose permease. Lactose negative bacteria do not have beta-galactosidase or lactose permease. Catalase is detected by mixing a colony of bacteria with hydrogen peroxide and observing for bubbles, which indicates oxygen production. One important use is to separate the staphylococci, which are catalase positive from the streptococci, which are catalase negative. Bile solubility is used to separate Streptococcus pneumoniae from other alpha hemolytic streptococci. Surface- active agents, such as sodium deoxycholate can to lyse S. pneumoniae, while other alpha hemolytic streptococci are resistant to these surface-active agents. Cytochrome oxidase, in the presence of oxygen, oxidizes tetramethyl-para-phenylenediamine dihydrochloride to form a colored compound, indophenol. The test is useful in the separation of gram negative bacilli; all Enterobacteriaceae are oxidase negative and some of the nonfermentative gram negative bacilli, such as Pseudomonas are oxidase positive. The genus Neisseria is also oxidase positive.

Shigella serotyping is performed by using a polyvalent somatic (O) antisera. A Shigella species grew from culture and serotyped as Group D. Which of the following Shigella species serotypes as Group D? - Shigella boydii - Shigella dysenteriae - Shigella sonnei - Shigella flexneri

- Shigella sonnei Shigella sonnei is the correct answer because this species types as Group D. Shigella sonnei infection is caused by the ingestion of contaminated food and water. The mode of pathogenicity is due to invasion of the intestinal mucosa, which will be demonstrated by the presence of white blood cells in stool specimens. Shigella boydii is incorrect because this species types as Group C. Shigella boydii infection is caused by the ingestion of contaminated food and water. The mode of pathogenicity is due to invasion of the intestinal mucosa, which will be demonstrated by the presence of white blood cells in stool specimens. Shigella dysenteriae is the incorrect answer because this species types as Group A. Shigella dysenteriae produces the most severe form of illness and can lead to hemolytic uremic syndrome (HUS). However, all Shigella species can cause dysentery that includes watery diarrhea, fever, and abdominal cramps. As the infection progresses, blood and mucus can be seen in stool specimens. Shigella flexneri is incorrect because this species types as Group B. Shigella flexneri infection is caused by the ingestion of contaminated food and water. The mode of pathogenicity is due to invasion of the intestinal mucosa, which will be demonstrated by the presence of white blood cells in stool specimens.

Please see the image. Which illustration corresponds with the classification of bacteria seen in section A? - Bacilli - Spiral (spirochetes) - Cocci - Curved bacilli (Vibrios)

- Spiral (spirochetes) Section A of the illustration shows spiral shaped organisms consistent with spirochete organisms. Bacilli are shown in illustration F. Cocci are shown in illustration B. Curved bacilli consistent with Vibrios are shown in illustration D.

An infective agent of skin wound infections and an agent of toxic shock syndrome, the large, entire, golden-yellow, smooth convex colonies on blood agar were recovered from a swab specimen after 48 hours incubation at 37o C. In the image to the right, clusters of gram-positive cocci were observed microscopically in a gram stain prepared from one of the colonies. The coagulase reaction was positive. With these observations, select the name of this isolate from the choices given. - Staphylococcus aureus - Staphylococcus saprophyticus - Micrococcus luteus - Rothia mucilaginosis

- Staphylococcus aureus Staphylococcus aureus is the correct response. The smooth, golden yellow colonies on blood agar ("aureus") along with the grape-like clustering of gram positive cocci on gram stain are distinctive for a presumptive identification of Staphylococcus aureus. The identification can be confirmed by observing a positive coagulase test. S. aureus is the primary bacterial cause of Toxic Shock Syndrome. Staphylococcus saprophyticus colonies are smooth but not pigmented and the gram-positive cocci in slide preparations are in small loose clusters and in tetrads, not in non-grape like clusters. The coagulase test is negative. Demonstrating resistance to novobiocin is an additional identifying characteristic to differentiate it from other coagulase negative staphylococci. S. saprophyticus is most commonly an agent of urinary tract infections. Micrococcus luteus colonies are also smooth and pigmented, but with a deep golden yellow rather than a lighter lemon yellow. The genus identification of Micrococcus can be made by observing gram positive cocci arranged in distinctive tetrads. The coagulase test is negative. Identification can be confirmed by demonstrating susceptibility to bacitracin ("A" disc) and resistance to fuaxolidone. Isolates are usually clinically insignificant. Rothia mucilaginosis colonies are clear to light pink-gray and are distinctly mucoid and adherent to the agar surface. Gram positive cocci, as observed in gram stains, are in pairs or short, filamentous chains. Rothia is indigenous in the oral cavity and may be recovered in cases infections following dental plaque procedures.

The slide coagulase test is a rapid method for identifying which of the following organisms? - Staphylococcus hominis - Streptococcus pneumoniae - Staphylococcus aureus - Neisseria gonorrhoeae

- Staphylococcus aureus The coagulase slide test is used to differentiate S. aureus from coagulase negative staphylococci. Since not all isolates of S. aureus are detected by the slide coagulase test, suspicious organisms negative by the slide test must be confirmed by the tube coagulase test.

Which of the following Staphylococcus species will produce yellow colonies on mannitol salt agar? - Staphylococcus aureus - Staphylococcus saprophyticus - Staphylococcus epidermidis - Staphylococcus haemolyticus

- Staphylococcus aureus The correct answer is Staphylococcus aureus. Mannitol salt agar was formerly used as a selective media for recovering Staphylococcus aureus from specimens contaminated with mixed bacteria. It grows well in the presence of salt and develops yellow colonies from the production of acid from mannitol. The large majority of strains of other staphylococci, such as S. saprophyticus,S. epidermidis, and S. haemolyticus, do not produce acid from mannitol and appear as white colonies on mannitol salt agar.

Which of the following is the most common etiologic agent identified in prosthetic valve endocarditis? - Staphylococcus epidermidis - Staphylococcus aureus - Streptococcus sanguis - Streptococcus mutans

- Staphylococcus epidermidis Intravascular catheters are a leading cause of bloodstream infections. S. epidermidis is the most common agent isolated from prosthetic valve endocarditis, with S. aureus being the second most common. Streptococcus sanguis and Streptococcus mutans are commonly isolated from patients with infective endocarditis (infection of the endocardium).

A Staphylococcus species recovered from a blood culture was found to produce acid from sucrose and maltose and showed alkaline phosphatase activity. The Staphylococcus was also coagulase negative. The same organism was also found in a culture from the central line tip. The most likely identification is: - Staphylococcus saprophyticus - Staphylococcus schleiferi - Staphylococcus epidermidis - Staphylococcus aureus

- Staphylococcus epidermidis Staphylococcus epidermidis is a normal flora organism on the skin, but a common cause of infections from medical devices. The organism can produce biofilms on catheters and other medical devices. The biofilm is a complex interaction between the device, host, and bacteria. A large number of organisms may aggregate in the biofilm and then be shed into the bloodstream or other nearby sites depending on the biofilm placement. Sometimes in blood cultures, Staphylococcus epidermidis can be seen as a contaminant from the skin during collection. However, by the organism presence in both the blood and line cultures, this can be determined as an infection from the central line. S. epidermidis also produces acid from sucrose and maltose and has alkaline phosphatase activity, important characteristics included in most algorithms and identification systems. They are also coagulase negative. Staphylococcus saprophyticus is coagulase negative, and does produce acid from sucrose and maltose, but is alkaline phosphatase negative. These organisms are laso typically found in the urinary system as a cause of urinary tract infections, specifically in women, and rarely found on the skin or mucous membranes. Staphylococcus schleiferi is also coagulase negative Staphylococcus but it does not produce acid from sucrose and maltose. It is alkaline phosphatase positive. These organisms are also typically considered contaminants or causes of opportunistic infections. Staphylococcus aureus is a coagulase positive Staphylococcus and would be eliminated based on that result alone. S. aureus however, is alkaline phosphatase positive as well as produces acid from sucrose and maltose.

Which of the following organisms typically produces umbilicate (depressed center, concave) colonies? - Yeast - Staph aureus - Proteus mirabilis - Streptococcus pneumoniae

- Streptococcus pneumoniae Streptococcus pneumoniae is known for umbilicate colonies that have been compared to coins due to the depressed centers and raised edges. This is due to old colonies undergoing autolysis, collapsing their centers. Yeast colonies are typically creamy, white, with "feet" or "pedicles" extending from the colony edges. Staph aureus produces convex colonies. Proteus mirabilis produces a hazy blanket of growth, known as "swarming" that extends well beyond the streak lines, overtaking the culture media.

The organism in the attached photos was isolated from a sputum specimen. The blood agar plates were incubated at 37° C. The upper photo shows 24 hour incubation and the lower photo shows 48 hour incubation. The Gram stain showed lancet-shaped Gram positive cocci in pairs. What is the most likely identification of this organism? - Streptococcus pneumoniae - Enterococcus species - Streptococcus anginosus - Streptococcus bovis group

- Streptococcus pneumoniae Streptococcus pneumoniae is the correct response. The large mucoid appearing colonies indicate the synthesis of capsular polysaccharide characteristic of S. pneumoniae. Narrow zones of alpha hemolysis may be observed. This identification is further supported by observing the colony auto-hydrolysis after prolonged incubation, resulting in sunken centers in what have been referred to as "checker pieces". The presumptive identification is supported by the characteristic lancet-shaped Gram positive cocci in pairs on the Gram stain. Enterococcus species colonies are relatively small, measuring 1 - 2 µm in diameter, and are dry and gray-white typically non-hemolytic or alpha hemolytic. Alterations in morphology do not appear after prolonged incubation. In Gram stain mounts, Gram-positive cocci are round or elongated and are arranged in short chains. Streptococcus anginosus (Group F) colonies are tiny and translucent, surrounded by narrow zones of beta hemolysis. Alterations in morphology do not appear after prolonged incubation. In Gram stained mounts, small spherical Gram positive cocci are arranged in short and long chains. Streptococcus bovis group (Group D) colonies are relatively small, gray-white, non-hemolytic and dry in consistency. Alterations in morphology do not appear after prolonged incubation. Small, spherical Gram positive cocci are arranged in short chains and not in lancet-shaped pairs.

The most frequent cause of bacterial meningitis in adults and in children is: - Streptococcus pneumoniae - Neisseria meningitidis - Haemophilus influenzae - Escherichia coli

- Streptococcus pneumoniae Streptococcus pneumoniae is the most common cause of meningitis in adults and in children. Neisseria meningitidis causes meningitis in adults and in children, but not as frequently as S. pneumoniae. Haemophilus influenzae and E. coli usually cause meningitis in infants (1 month to 23 months of age). Other organisms can also cause bacterial meningitis, particularly Streptococcus agalactiae, in neonates (less than one month old) and infants (1 to 23 months of age), and Listeria monocytogenes in infants and in adults older than 65 years of age.

The microscopic image shown here is a direct Gram stain of sputum obtained from a 70-year-old man complaining of cough, sputum production, and chest pain. This organism was alpha-hemolytic on blood agar, catalase negative, optochin ("P disk") susceptible, and bile soluble. What is the identity of this organism? - Klebsiella pneumoniae - Haemophilus influenzae - Streptococcus pneumoniae - Mycoplasma pneumoniae

- Streptococcus pneumoniae The Gram stain illustrated here shows many background segmented neutrophils and a pure culture of Gram positive diplococci most consistent with Streptococcus pneumoniae. This bacterial species typically causes lobar pneumonia. Conditions that reduce host defenses, such as chronic alcoholism and malnutrition, or that compromise the mucociliary clearance mechanisms of the respiratory mucosa such as COPD and tobacco-related bronchitis predispose individuals to pneumococcal pneumonia. Klebsiella pneumoniae, Haemophilus influenzae,andMycoplasma pneumoniaealso cause pneumonia. However,K. pneumoniaeandH. influenzaeare Gram-negative.M. pneumoniaecauses "atypical" pneumonia, as it lacks a cell wall and does not Gram stain.

A 67-year-old man was seen in the emergency room complaining of cough, fever, and piercing right posterior chest pain. X-ray of the chest revealed consolidation of the right middle lobe of the lung. A sputum culture grew the bacterial species shown in the upper photograph. The lower photomicrograph illustrates a gram-stain of the sputum specimen. The most likely cause of the pneumonia is: - Klebsiella pneumoniae - Enterococcus faecalis - Staphylococcus intermedius - Streptococcus pneumoniae

- Streptococcus pneumoniae The clinical setting of lobar pneumonia in an elderly patient is most likely associated with Streptococcus pneumoniae. The mucoid, alpha hemolytic colonies seen in the blood agar plate and the gram-positive diplococci seen in the sputum specimen are virtually confirmatory. Enterococcus faecalis can produce a gram stain similar to that illustrated; however, the colonies are not mucoid and lobar pneumonia by this species would be less likely. Klebsiella pneumoniae can appear as mucoid colonies on blood agar and can cause lobar pneumonia similar to that described; however, the bacterial cells are gram negative bacilli. Staphylococcus intermedius would more likely cause a necrotizing bronchopneumonia, the colonies are not mucoid and the cocci arrange in loose clusters or tetrads rather than pairs.

Complete hemolysis of sheep blood agar as demonstrated by the image below would be seen in which of the following catalase-negative isolates? - Streptococcus pneumoniae - Streptococcus pyogenes - Staphylococcus aureus - Enterococcus faecium

- Streptococcus pyogenes The correct answer is Streptococcus pyogenes S.pyogenes produces colonies that are about 0.5 mm in diameter, appear translucent with a smooth surface and have a beta-hemolytic zone that is up to four times the diameter of the colony. Streptococcus pneumoniae is alpha-hemolytic which demonstrate a green area of partial hemolysis around the colonies. Staphylococcus aureus will produce beta-hemolysis, but is catalase positive. Enterococcus faecium generally produces alpha-hemolytic colonies, but can also produce non-hemolytic colonies.

Illustrated in the top photograph are alpha-hemolytic, entire, gray-white convex colonies that are of a bacterial species that was found to be susceptible to vancomycin. In the lower photomicrograph, gram-positive cocci arranged in chains and in loose clusters that are not species distinctive are seen. Select the bacterial species that are uncommonly vancomycin resistant. - Staphylococcus species - Leuconostoc species - Pediococcus species - Streptococcus species

- Streptococcus species Streptococcus species is the correct response. Although isolated strains of an alpha hemolytic streptococcus may be vancomycin resistant, most are susceptible. Leuconostoc species is incorrect. Leuconostoc species can produce alpha or gamma hemolysis and can resemble viridans streptococci when growing on blood agar; however, this species is intrinsically resistant to vancomycin. When this species is isolated from clinical specimens, it must be ruled out as a contaminate. Pediococcus species is incorrect. Pediococcus species can produce alpha or gamma hemolysis and can resemble viridans streptococci when growing on blood agar; however, this species is intrinsically resistant to vancomycin. When this species is isolated from clinical specimens, it must be ruled out as a contaminate. Staphylococcus species is incorrect. Staphylcoccus species are not categorically vancomycin resistant; however, this resistance has become a major problem with Staphylococcus aureus that are recovered from a variety of human specimens, particularly strains recovered from hospitalized patients.

In cases of suspected intestinal parasitic disease, select the name of the parasite, as illustrated by the 50 µm ovum in this image, that may be detected in upper respiratory secretions when stool specimen preparations are negative. - Ancylostoma duodenale - Necator americanus - Strongyloides stercoralis - Fasciola hepatica

- Strongyloides stercoralis Strongyloides stercoralis is the correct response. As adult Strongyloides nematodes occupy the respiratory tract, larvae and ova may be observed in preparations made from upper respiratory secretions, when stool specimens may be negative. Ova measure 50-58 µm x 30-34 µm and may not reach the lower intestinal tract. Ancylostoma duodenale is incorrect. Although Ancylostoma ova appear similar to those of Strongyloides, the adult worm is located in the upper intestinal tract. Ova are only found in intestinal secretions, particularly in stool specimens, and would not appear in respiratory secretions. The ova measure 55-75 µm x 35-45 µm. Necator americanus is incorrect. Although Necator ova appear similar to those of Strongyloides, the adult worm is located in the upper intestinal tract. Ova are only found in intestinal secretions, particularly in stool specimens, and would not appear in respiratory secretions. The ova measure 55-75 µm x 35-45 µm. Fasciola hepatica is incorrect. Although Fasciola ova appear similar to those of Strongyloides, they are twice the size. Fasciola adults reside in the liver and bile ducts, excreting ova into the intestinal tract where they can be observed in stool specimens, but never in upper respiratory secretions.

The rhabditiform larva shown in this image was observed in a mount prepared from a diarrheal stool specimen. This patient also complained of persistent cough and increased shortness of breath. From the list of answer choices below, what presumptive identification can be made? - Strongyloides stercoralis - Trichuris trichiura - Ancylostoma duodenale - Necator americanus

- Strongyloides stercoralis Strongyloides stercoralis is the correct response. Diagnostic is the short buccal cavity (arrow) as observed in the anterior section of the rhabditiform larva. Not observed in this photograph is the genital primordium that commonly is seen 1/3 the distance from the tail. Trichuris trichiura is an incorrect response. Trichuris larvae hatch soon after ingestion of an infective ovum and develop into adult worms in the small intestine producing eggs that are passed in stool. Ancylostoma duodenale is an incorrect response. The buccal cavities of the rhabditiform larvae of this hookworm species are long differentiating it from the short buccal cavity of Strongyloides. Necator americanus is an incorrect response. The buccal cavities of the rhabditiform larvae of this hookworm species are long differentiating it from the short buccal cavity of Strongyloides.

A fresh stool sample was submitted to the laboratory for an ova and parasites examination on a 30-year-old male who presented to a local clinic complaining of gastrointestinal discomfort and overall weakness. The sample was immediately processed and this suspicious form was seen. No other suspicious forms were observed. What is the most likely identification of this parasite? - Strongyloides stercoralis - Ancylostoma duodenale - Trichuris trichiura - Necator americanus

- Strongyloides stercoralis The correct answer is Strongyloides stercoralis. The eggs of hookworms (Ancylostoma duodenale and Necator americanus) and Strongyloides stercoralis are basically indistinguishable whereas the rhabditiform larvae of each have specific characteristic features. Knowing the age of the specimen as well as whether the patient is experiencing severe diarrhea or not help to predict what morphologic forms of each organism will most likely be present. The eggs of hookworm are common in fresh samples whereas those of S. stercoralis are typically seen only when the patient is suffering from severe diarrhea. Rhabditiform larvae of hookworm are usually found only in old specimens (those which have been unfixed and left at room temperature) and those of S. stercoralis are common in fresh samples as depicted in this question. Trichuris trichiura does not produce visible larvae in human stool samples.

Infections with Eikenella corrodens is associated with: - Ingestions of food contaminated with saliva - Bites from canines or felines - Trauma associated with human teeth - Inhalation of respiratory droplets

- Trauma associated with human teeth Eikenella corrodens is found in the human mouth and gastrointestinal tract. Infections occur following trauma associated with human teeth including human bites or clench-fist punches to the face. Endocarditis has occurred due to endogenous flora. Although Eikenella corrodens is found in the human mouth, transmission is not associated with the ingestion of food contaminated with saliva. Eikenella corrodens is part of the normal flora of the human mouth. It is not associated with bites from canines or felines. Inhalation of respiratory droplets is not a known route of infection for Eikenella corrodens.

A stool specimen has been left at room temperature overnight. The next day, many motile larvae with a short buccal cavity are seen upon microscopic exam, but there are no ova observed. What is the most likely identification and life stage of this parasite? - Necator americanus - rhabditiform larvae - Strongyloides stercoralis - adult - Ancylostoma duodenale - filariform larvae - Strongyloides stercoralis - rhabditiform larvae

- Strongyloides stercoralis - rhabditiform larvae The correct answer is Storongylodes stercoralis - rhabditiform larva. The presence of a short buccal cavity is the key identifying characteristic. S. stercoralis is also known as the "threadworm" is unique in its ability to survive as a free-living worm in addition to inside a host. Many patients are asymptomatic, but exhibit an increased eosinophil count due to the reaction of our immune system. The buccal cavities of Hookworm (Necator americanus and Ancylostoma duodenale) rhabditiform larvae are 3 times longer than S. stercoralis. If a stool specimen is not preserved within 24 hours of passage, eggs of Hookworms and Strongyloides can continue to develop resulting in the release of rhabditiform larvae. After an extended period in the environment, these larvae will develop into male and female worms that in turn produce infective form filariform larvae. In this example, there hasn't been a long enough period of exposure to the environment to allow for maturation.

A combination of nontreponemal testing (VDRL or RPR) and treponemal testing (TP-PA or EIA) is used to confirm: - Chlamydia - Genital herpes - Syphilis - Gonorrhea

- Syphilis Of the sexually transmitted infections listed here, syphilis is caused by the spirochete, Treponema pallidum subsp. pallidum. Treponemal tests detect antibodies to treponemal antigens, whereas nontreponemal tests screen for reagin antibodies, which are less specific. The combination of tests aids in diagnosis of this complex disease. Chlamydia is the most common sexually transmitted bacterial infection in the U.S. It is caused by Chlamydia trachomatis. Screening tests for C. trachomatis infection often include EIA or NAAT. Genital herpes is a viral infection caused by HSV-1 or HSV-2. NAATs are rapid, sensitive, and specific tests for detection of HSV. Gonorrhea is caused by the bacterial infection with Neisseria gonorrhoeae. Diagnosis is made through direct gram stain and culture, or NAAT.

Based on the morphologic features of this 40 µm (in diameter) ovum, as seen in the upper photomicrograph with the accompanying scolex of the adult worm illustrated in the lower image, select the presumptive identification of this cestode from the multiple choice answers listed below. - Taenia saginata - Taenia solium - Hymenolepis nana - Diphyllobothrium latum

- Taenia solium Taenia solium is the correct response. Although the spherical ova with their thick, striate shell and internal hooklets does not rule out Taenia saginata, the scolex of T. solium, with its distinctive rostellum armed with a ring of hooklets, serves to exclude T. saginata, the scolex of which is flat and rounded and devoid of an armed rostellum. Taenia saginata ova are similar in appearance to those of T. solium, with a thick striated shell and three pairs of hooklet observed interiorly. Distinctive is the scolex of the adult worm with a round, smooth anterior end devoid of an armed rostellum. Hymenolepis nana ova have a thin outer non-striated shell and an inner membrane within which three pairs of hooklets are contained. The scolex of the adult worm also has an armed rostellum, but in contrast to T. solium, is small and projects outward. Diphyllobothrium latum ova are large (up to 70 µm), and have a thin smooth shell with a distinctive, inconspicuous non-shouldered operculum at one end. The scolex of the adult worm is long and narrow with a dorso-ventral groove surrounded on either side by lateral lip-like folds.

Of the following parasites, which parasitic scolex has a rostellum, hooklets, and 4 suckers? - Taenia saginata scolex - Diphyllobothrium latum scolex - Hymenolepis nana scolex - Taenia solium scolex

- Taenia solium scolex Taenia solium scolex is correct because this parasite scolex has a rostellum, hooklets, and 4 suckers. Taenia saginatascolex is incorrect because this parasite scolex has 4 suckers with no rostellum or hooklets. Diphyllobothrium latum scolex is incorrect because this parasite scolex has no rostellum or hooklets, but has two shallow grooves or bothria. Hymenolepis nana scolex is incorrect because this parasite scolex has a rostellum, no hooklets, and 4 suckers.

The ovum, illustrated in this photograph, is in an immature stage of development, and is surrounded by residual yolk sack material and membrane. It measures 50 µm in diameter. What is the presumptive identification of this ovum? - Dipylidium caninum - Taenia species - Hymenolepis nana - Diphyllobothrium latum

- Taenia species Taenia species is the intended response. The key distinguishing features are the spherical to oval outline and the distinctive thick shell with radiating striations. At this stage of development, this enclosed immature ovum does not have distinguishing characteristics. Dipylidium caninum is an incorrect response. Dipylidium ova can be excluded because they typically occur in packets. Ova contain a 6-hooked oncosphere but are smaller, 25 - 40 µm. Hymenolepis nana is an incorrect response. Hymenolepis ova can be excluded as their outer shell is thin, smooth, and devoid of radial striations.Diphyllobothrium latum is an incorrect response. Diphyllobothrium ova are large, measure up to 75 µm, and are elliptical to barrel shape. The outer shell is smooth, thin, and not striated. At this stage, a visible shouldered operculum probably would not yet have developed.

The 40 µm in diameter ovum illustrated in the photograph may be observed in the stool specimens of individuals presenting with minimal abdominal discomfort and low grade diarrhea. Pairs of hooklets are observed internally in the absence of an internal membrane. Select from the multiple choice answers the presumptive identification of this cestode ovum. - Hymenolepis diminuta - Diphyllobothrium latum - Taenia spp. - Dipylidium caninum

- Taenia spp. Taenia species is the correct response. Characteristics of Taenia ova include the spherical outline and smooth, thick shell with distinctive radial striations. Although the pairs of hooklets observed internally might suggest Hymenolepis species, the absence of an internal membrane is exclusive. Hymenolepis diminuta is an incorrect response. Hymenolepis ova, although similar in size and shape with those of Taenia species, have a thin non-striated outer shell and a distinctive inner membrane enclosing the three pairs of hooklets. Diphyllobothrium latum is an incorrect response. Diphyllobothrium ova are large (up to 70 µm), have a smooth shell with a distinctive, inconspicuous non-shouldered operculum at one end. Internal cleavage that is devoid of hooklets extends to the inner shell membrane. Dipylidium caninum is an incorrect response. Dipylidium ova are small, have a thin smooth shell, and are spherical and arranged in packets within the ovary of the adult worm. An internal membrane and hooklets are absent.

Illustrated in the upper image is a 6-day-old colony growing on the surface of Sabouraud Dextrose agar. Note the distinct light green and pink granular colony surrounded with a reddish margin with diffusion of the wine-red pigment into the agar. This type of colony may be recovered from a sputum specimen of a person with travel history to Southeast Asia. The lower image is of a microscopic mount stained with lactophenol blue. From these characteristics, select the identification of this fungal isolate. - Purpureocillium (Paecilomyces) lilacinum - Scopulariopsis - Talaromyces (Penicillium) marneffei - Fusarium

- Talaromyces (Penicillium) marneffei Talaromyces (formerly Penicillium) marneffei is the correct selection. Yeast-like cells similar to Histoplasma capsulatum may be detected in Wright-stained smears from biopsy specimens. The microscopic features of this fruiting head (shown here) are distinctive for Penicillium species. Unusual is the red diffusible pigmentation surrounding the colony as observed on the agar plate. This species is geographically endemic to Southeast Asia, but travelers to that part of the world may become infected. The infection may spread similar to that of disseminated histoplasmosis, particularly in patients with AIDS when a rapid identification is necessary followed by appropriate therapy.The selection of Purpureocillium (formerly Paecilomyces), Scopulariopsis and Fusarium can be recorded as incorrect responses as none of these fungal genera produce the diffusible wine red pigment as observed in the colony demonstrated here. Also, the distinctive fruiting head of Talaromyces, like Penicillium species, also serves to eliminate these fungi from consideration. Purpureocillium philiades may resemble Penicillium species, but are usually longer and more tapered. Scopulariopsis produces chains of globe-shaped conidia arising from annellides. Fusarium produce banana-shaped macroconidia.

Beta-lactam antibiotics interfere with cell wall synthesis by all of the following, EXCEPT: - Binding with a transpeptidase - Preventing the final stage of peptidoglycan synthesis - Interfering with PBPs - Targeting the 30S ribosomal subunit

- Targeting the 30S ribosomal subunit Transpeptidase enzymes catalyze the final stage of peptidoglycan synthesis during cell wall formation. Beta-lactam antibiotics bind with these enzymes, interfering with their function. The transpeptidase enzymes are also referred to as PBP's, or penicillin-binding proteins. Aminoglycosides and tetracyclines interfere with the 30S ribosomal subunit (protein synthesis inhibitors).

Who should a technologist contact if an organism is isolated that cannot be ruled out as a potential agent of bioterrorism? - The local police department - The Federal Bureau of Investigation (FBI) - The Laboratory Response Network (LRN) reference laboratory - The Centers for Disease Control (CDC)

- The Laboratory Response Network (LRN) reference laboratory The correct answer is the Laboratory Response Network (LRN) reference laboratory. In the event that a potential agent of bioterrorism is suspected, the appropriate internal staff should contact your LRN reference laboratory. The sentinel laboratory should NOT make the decision that a bioterrorism event has occurred, thus should not contact law enforcement, or public health officials.

All of the following are primary routes of transmission for intestinal amoebae, EXCEPT? - The ingestion of cysts in contaminated food - The bite of an insect - The ingestion of cysts in contaminated drink - Hand-to-mouth contamination

- The bite of an insect The bite of an insect is correct because insect bites are responsible for the spread of hemoflagellates, Plasmodium species and the filariae. The ingestion of cysts in contaminated food, drink, or hand-to mouth contamination is incorrect because these are common routes of infection for amoebae such as Entamoeba histolytica and Escherichia coli. In addition, all of the ways that intestinal amoebae may be transmitted result in ultimate ingestion of infective cysts. Hand-to-mouth contamination occurs due to the lack of proper hand hygiene.

What is successful molecular identification of methicillin-resistant Staphylococcus aureus (MRSA) based upon? - The detection of the mecA gene. - The detection of the S. aureus orfX gene. - The detection of S. aureus nuc and coa genes. - The detection of the S. aureus genes (orfX, nuc, or coa) gene and the mecA gene.

- The detection of the S. aureus genes (orfX, nuc, or coa) gene and the mecA gene. The mecA gene, confers oxacillin/methicillin resistance, but it can be present in both S. aureus and coagulase negative species. Thus, there must also be a gene to identify the organism is S. aureus to determine that it is MRSA. Examples of these genes are orfX, nuc, and coa genes. Detection of both genes indicates the organism is S. aureus and oxacillin resistant and thus the organism is MRSA. Other gene markers that can be used for S. aureus are femA, femB, or sa442 genes. The detection of the mecA gene determines oxacillin resistance in the organism, but does not identify that the organism is S. aureus and instead could be a coagulase negative species. This would not allow the determination of MRSA. The detection of the S. aureus orfX gene or nuc and coa genes both indicate the organism is S. aureus but does not indicate anything about the resistance to oxacillin. This would not allow a determination of MRSA.

All of the following are true concerning clinical specimens that are gram stained before culturing, EXCEPT: - The gram stain allows you to judge the quality of the specimen. - The gram stain provides the clinician with same day information regarding possible pathogenic organisms. - The gram stain eliminates the need for a culture. - The gram stain provides internal quality control when direct smear results are compared to culture results.

- The gram stain eliminates the need for a culture. The correct answer is the gram stain eliminates the need for a culture. A Gram stain does not replace a culture; cultures still need to be processed even though a Gram stain was performed. Gram-stained direct smears can be used to: - Judge the quality of the specimen. - Provide the clinician with same-day information regarding possible pathogenic organisms, pending results of culture and sensitivity. - Provide internal quality control when direct smear results are compared to culture results.

A cerebral spinal fluid was collected from a lumbar puncture to evaluate for possible meningitis. Four tubes were collected and sent to the microbiology laboratory for analysis. Which of the four tubes is preferred for microbiology studies? - Tube 1 - Tube 2 - Tube 3 - Tube 4

- Tube 2 Tube 2 is the correct answer because this tube will be more concentrated and allow for the recovery of low numbers of bacterial organisms causing meningitis. In addition, this specimen will most often be free of blood cells or bacteria introduced by the spinal tap procedure. Tube 1 is incorrect as this tube is used for chemistry studies such as glucose and protein. These tests are least affected by the presence of blood cells and bacteria introduced by the lumbar puncture procedure. Tube 3 and tube 4 are incorrect answers as both tubes can be used for cell count and differential testing because these tubes should be free from cells introduced by the lumbar puncture procedure.

A tech working in the laboratory receives a phone call from a doctor who is upset that his patient has a negative urine culture. The doctor indicates that the urinalysis result is positive for leukocyte esterase so the culture should be positive. The doctor feels that the urine culture was not properly handled. How can you explain the discrepancy in the urinalysis and culture to the doctor? - Incorrect agar plates were used for culture - The culture may have been stored incorrectly, causing the organisms to lose viability - The patient could have another infection, such as a sexually transmitted infection (STI) - The culture may have been set up with a 0.01 loop instead of a 0.001 loop

- The patient could have another infection, such as a sexually transmitted infection (STI) The presence of leukocyte esterase in a urinalysis points to the presence of white blood cells, which indicate inflammation, not necessarily infection. Nitrates were not noted on the urinalysis, which typically point to a urinary tract infection with our most common pathogen, enteric bacteria. Since urinalysis is done on a centrifuged sample, the correlation between culture (non-centrifuged) and urinalysis can sometimes not agree. However, if there is a discrepancy between urinalysis and culture, the most likely scenario is that there is a different type of infection occurring and white blood cells from the inflammatory process are being shed in the urine. The most common of these infections would be a sexually transmitted infection, such as Neisseria gonorrhoeae or Chlamydia trachomatis, which would not grow on routine urine culture media. Incorrect agar plates used for culture is not likely as the tech that was reading the urine culture should have recognized a discrepancy and re-plated the culture if needed. Improper storage of the urine sample (typically at room temperature instead of refrigeration) would typically cause organisms to overgrow opposed to lose viability. The 0.001 loop size is used for routine urine cultures. The 0.01 loop size is used for urine from sterile sources and allows more specimen to be plated, to help recover small amounts of organism. If the 0.01 loop was used, it would help to improve organism recovery from the sample, not reduce recovery.

A laboratory test flags a critical result. The technologist repeats the test, and it again flags as a critical result. Which of these scenarios correctly describes all the actions that need to be taken after this occurs? - The technologist immediately releases the result. - The technologist phones the clinical person handling the patient's care (caregiver) and reports the critical test result. - The technologist phones the patient's caregiver, reports the critical result, documents his placement of the call, who was notified, time, and date of notification. - The technologist phones the patient's caregiver, reports the result, and asks the caregiver to read back the information; documents his placement of the call, who was notified, time, and date of notification.

- The technologist phones the patient's caregiver, reports the result, and asks the caregiver to read back the information; documents his placement of the call, who was notified, time, and date of notification. Critical laboratory test results that are given over the phone must only be given to a clinical person (person in charge of the patient's care). The person who receives the result should be asked to read back the information that is given to verify that it was heard correctly. The person who reported and called the result, the person who was notified, and the date and time of notification should be documented along with the test result.

What is the purpose of allowing a prepared KOH mount to sit for 30 minutes? - To dissolve the background keratin and reveal fungal elements. - To dissolve the chitin in the fungal elements. - To dissolve the peptidoglycan of the bacteria. - A prepared KOH mount should not be allowed to sit, it should be viewed immediately.

- To dissolve the background keratin and reveal fungal elements. The correct answer is to dissolve the background keratin and reveal fungal elements. 10% potassium hydroxide (KOH) dissolves the keratin present in direct patient samples to allow for easier visualization of fungal elements if present. KOH does not dissolve fungal elements or peptidoglycan.

When serotyping Salmonella, Shigella, and Escherichia coli 0157:H7, typing should be performed from a non-sugar-containing medium, such as 5% sheep blood agar. The reason for this is which of the following? - To prevent false positive results - To prevent false negative results - To prevent both false positive and false negative results - It does not matter what type of media as there is no interference in serotyping

- To prevent false positive results To prevent false positive results is the correct answer because sugar containing media, such as MacConkey and Triple Sugar Iron agar, can cause the organism to autoagglutinate and give false positive serotyping results. To prevent false negative results is incorrect because false positive serotyping results occur not false negative. To prevent both false positive and false negative results is incorrect because only false positive serotyping results occur not false negative serotyping results. It does not matter what type of media as there is no interference in serotyping is incorrect because the type of media does matter due to autoagglutination of organisms grown on glucose containing media.

What is the role of a sentinel laboratory within the Laboratory Response Network (LRN)? - To make the decision that a bioterrorism event has occurred and notify the press - To rule-out critical biological agents or to refer them to a Laboratory Response Network (LRN) reference laboratory - To detect and confirm (rule-in) the presence of a threat agent - To test environmental samples during a suspected bioterrorism event

- To rule-out critical biological agents or to refer them to a Laboratory Response Network (LRN) reference laboratory The role of a sentinel laboratory in the Laboratory Response Network (LRN) is to use standardized procedures to rule out critical biological agents or refer them to one of the Laboratory Response Network (LRN) reference laboratories. It is NOT the role of a sentinel laboratory to determine that a bioterrorism event has occurred. It is the role of the LRN reference laboratory to detect and confirm (rule-in) the presence of a threat agent. The sentinel laboratory should NOT accept environmental samples for testing during a suspected bioterrorism event due to the unknown nature of the sample.

Which obligate intracellular parasite may be transmitted to humans though accidental ingestion of infective oocysts from cat feces when gardening or changing a litterbox? - Babesia species - Trypanosoma cruzi - Toxoplasma gondii - Leishmania species

- Toxoplasma gondii Toxoplasma gondii is the causative agent of toxoplasmosis, a mild or asymptomatic infection in immunocompetent individuals. However, pregnant mothers and immunocompromised patients should avoid any potential fecal contamination from pets or other animals, as congenital transmission and infection in immunosuppressed patients may be severe. Trypanosoma cruzi is transmitted by the triatomid, or reduviid bug. The trypomastigote form is the primary diagnostic stage in the blood during acute infection. T. cruzi causes Chagas disease. In the U.S., donated blood is screened for antibodies to T. cruzi. Leishmaniasis is a zoonotic disease caused by Leishmania species in which canines and rodents serve as reservoirs, with sand flies as the insect vectors. Finding intracellular or extracellular amastigotes is diagnostic. Babesia species are responsible for babesiosis, a zoonotic intraerythrocytic human infection. The vector is a tick, and the reserviors are mice and deer. Diagnosis is made by viewing tetrad ring forms within erythrocytes in stained blood smears.

Which of the following parasites enters its host through ingestion of infected pork? - Schistosoma mansoni - Trichinella spiralis - Necator americanus - Ascaris lumbricoides

- Trichinella spiralis Trichinella spiralis enters its host through the ingestion of undercooked pork containing encysted larvae. The larvae are released in the intestine and the offspring migrate to muscle tissue to complete the maturation cycle. One of the blood flukes, Schistosoma mansoni, infects human hosts through direct skin penetration by cercariae, which then enter veins in the large intestine. Migration occurs to the portal blood in the liver, and eggs are deposited that circulate from the liver to the intestine for excretion. Transmission of the hookworm, Necator americanus, occurs through direct skin penetration of filariform larvae from the soil. The larvae enter circulation and migrate through the lungs and into the digestive tract. Maturation occurs in the small intestine, and eggs are shed in feces. Ascaris lumbricoides infection is also soil-transmitted, but ingested eggs cause infection. Larvae are released in the intestine, and migrate through the lungs and into the digestive tract, where maturation is completed in the intestine.

Illustrated in the photomicrograph is an H & E - stained section of skeletal muscle illustrating the larval form of an invading parasite (arrow). Humans become infected by ingesting raw or poorly cooked infected animal meat. An epidemic occurred in the 1800's during the North Pole expedition when explorers were eating the raw and undercooked meat of infected indigenous polar bears that they had killed for food. What is the species shown? - Onchocerca volvulus - Trichinella spiralis - Trypanosoma cruzi - Ancylostoma duodenale

- Trichinella spiralis Trichinella spiralis is shown as the distinctive coiled larval form. The larva characteristically have a 2 ½ spiral coil. Humans ingest the infected meat, and the larva penetrate the intestinal wall where it migrates through the circulatory system into the muscles. The muscle fiber becomes swollen and edematous with a chronic inflammatory reaction in the surrounding stroma. Oncherca volvulus may be observed in the tissue sections of inflammatory abscesses of infected subcutaneous tissue. Within the adult worm are observed a myriad of elongated tubular shaped microfilaria that do not coil. Muscle fiber is not commonly involved as the infection primarily involves subcutaneous tissue or eyes which can lead to blindness. Trypanosoma cruzi infections are most commonly diagnosed by observing C-shaped trypomastigotes circulating in the peripheral blood. On occasion, tissue invasion may result in the release of amastigotes into striated skeletal muscle.These amastigotes are small, circular in shape, and have a central karyosome.These amastigotes do not coil. Ancylostoma caninum are hookworms that infect humans. Eggs are deposited in feces which mature in the soil to a rhabditiform larvae. This larvae develops into the infectious, filariform larvae that penetrates the skin. It migrates to the small intestine where it attaches and releases eggs in feces.

This parasite, found in striated muscle, is responsible for which of the following conditions? - Trichinosis - Elephantiasis - River blindness - East African sleeping sickness

- Trichinosis The correct answer is trichinosis. The organism pictured is Trichinella spiralis. This organism is an intestinal-tissue nematode whose larvae encyst by coiling in muscle tissue. Humans are an accidental host that becomes infected when encysted larvae are ingested through poorly cooked pork. Elephantiasis can be caused by three different microfilariae: Wucheria bancrofti, Brugia malayi or Loa loa. All three are introduced to humans by larvae that are transmitted by the bite of an infected insect. River blindness is caused by Onchocerca volvulus. It is called such because of the ocular involvement that leads to varying degrees of loss of sight. Microfilariae are found in the nodule following the bite of a fly and may cause localized infection or wander to infect other tissues, including the eye. East African sleeping sickness is caused by Trypanosoma brucei subspecies rhodesiense. It is transmitted to humans by the bite of an infected tse tse fly transmitting epimastigotes.

The image shows a scavenger that lives in the mouth and measures about 10 µm. What is the identification of the organism? - Trichomonas hominis cyst - Entamoeba gingivalis trophozoite - Trichomonas vaginalis cyst - Trichomonas tenax trophozoite

- Trichomonas tenax trophozoite The image of the organism shows a pear-like shape, typical of a trophozoite form versus a cyst form, which is more circular. There are predominant flagella that extend from the anterior end of the organism, which puts it into the flagellate group of organisms. There is one nucleus present with a predominant axostyle, which runs the length of the organism and wraps around the nucleus. The nucleus is filled with chromatin granules. The organism is identified as Trichomonas tenax trophozoite. It also has an undulating membrane that is two-thirds the length of the organism. T. tenax can range in size from 5-14 µm. The organism is found in mouth scrapings, tonsillar crypts, and pyorrheal pockets. Trichomonas hominis has no known cyst form, only trophozoite forms. The trophozoite can be differentiated from T. tenax by the position of the nucleus and axostyle. The nucleus is present in the anterior portion of the organism, instead of more centralized in T. tenax, and also contains a central karyosome. The axostyle extends down from the nucleus, and does not wrap around the nucleus. T. hominis also has a full body length undulating membrane. The organism is typically found in contaminated milk and recovered from the stool, but is considered a non-pathogen. Entamoeba gingivalis trophozoite is in the ameba group, not the flagellates. Since is is an ameba, the organism moves via pseudopodia instead of flagella. The flagella present in this picture rules out Entamoeba gingivalis. The organism does live around the gum line of teeth and in tartar, gingival pockets, and tonsillar crypts. Trichomonas vaginalis also has no know cyst form, only trophozoite forms. The trophozoite can be differentiated from T. tenax because it typically has granules present along the axostyle. Also, T. vaginalis has a very short undulating membrane, about half the total length of the organism. T. vaginalis is a sexual transmitted organism and can cause urethritis and vaginitis.

All of the following parasites are correctly matched with its respective primary symptom, EXCEPT: - Enterobius vermicularis - perianal itching - Plasmodium falciparum - fever and chills - Trichomonas vaginalis - diarrhea - Endolimax nana - usually no symptoms

- Trichomonas vaginalis - diarrhea The correct answer is Trichomonas vaginalis. Trichomonas vaginalis is most commonly associated with vaginal discomfort, a green frothy discharge, odor, pain, itching, and irritation. Enterobius vermicularis typically causes perianal itching due to the female worms laying their eggs in this region Plasmodium falciparum, a causative agent of malaria, is characterized by fever and chills. Endolimax nana is not considered to be a pathogen, according to the CDC.

The trophozoite state of the intestinal flagellate Giardia duodenalis has what characteristic? - Two nuclei - An undulating membrane - Two flagella - Lack of a sucking disc

- Two nuclei The trophozoite state of the intestinal flagellate Giardia duodenalis is characterized by two nuclei. It has been described as "someone looking at you". Pentatrichomonas hominis is an example of an intestinal flagellate with an undulating membrane. The trophozoite is usually shaped like a pear and utilizes four lateral flagella for propulsion. It also has a large sucking disk which it uses to attach to a host's intestinal wall lining.

The upper image to the right depicts a small circular white colony with a downy surface, recovered from a skin scraping specimen after 7 days of growth on agar supplemented with thiamine and inositol. The identification is made by observing the aerial hyphae (middle image) and the underlying chains of pigmented chlamydospores among the hyphae (lower image). Based on this information, what is the most likely identification of this dermatophyte? - Microsporum gypseum - Trichophyton tonsurans - Trichophyton verrucosum - Epidermophyton floccosum

- Trichophyton verrucosum The correct answer is Trichophyton verrucosum. Trichophyton verrucosum exhibits a small-growing white downy colony which is not distinctive. The indication that the colony grew on agar containing thiamine and inositol may be a clue that one of the Trichophyton species, particularly T. verrucosum was suggested. The antler-type hyphae and the chains of darkly pigmented chlamydospores as observed along the underlying hyphae indeed are the microscopic features for T. verrucosum. Microsporum gypseum colonies are more rapidly growing, maturing in 3 - 5 days, and have a more sugary or granular surface as conidia are produced. Microscopically, large and multi-segmented macroconidia with rounded ends are produced from conidiophores borne laterally from nonbranching septate hyphae. Triphophyton tonsurans colonies are also slow growing, but have a granular buff-colored surface with prominent radial rugae. Microscopically, club-shaped and spherical conidia are produced laterally from nonbranching septate hyphae. Chlamydospores are not produced. Epidermophyton floccosum colonies are more rapidly growing, maturing in 3 - 5 days, and have a khaki-green pigment with peripheral radiating hyphal strands when mature. Microscopically, large club-shaped macroconidia with 3 - 5 cells are characteristic. Neither microconidia nor chlamydospores are produced.

Nematodes are round and elongated and typically look like an earthworm. Nematodes can be found in decaying vegetation or moist soil. Of the following organisms listed, which one is considered a nematode? - Trichuris trichiura - Diphyllobothrium latum - Taenia solium - Hymenolepis diminuta

- Trichuris trichiura Trichuris trichiura or whipworm is common in tropical or subtropical areas. It is the second most common nematode in the United States. Diphyllobothrium latum, Taenia solium, and Hymenolepis diminuta are all cestodes. Cestodes are also known as tape worms and are capable of self-fertilization.

Whipworm infection may be diagnosed in stool specimens by microscopic observation of adult worms or barrel-shaped eggs with polar plugs. Which species is known as the whipworm? - Trichuris trichiura - Ascaris lumbricoides - Necator americanus - Enterobius vermicularis

- Trichuris trichiura Whipworm infection, or trichuriasis, is caused by Trichuris trichiura. It is a soil-transmitted parasite. Eggs are brown, barrel-shaped, and have a polar plug at each end. Heavy infections may lead to rectal prolaspe. Necator americanus (hookworm), and Ascaris lumbricoides are also soil-transmitted. Necator americanus eggs are oval, and usually contain the 4 to 8-cell stage when observed. However, N. americanus eggs and rhabditiform larva are indistinguishable from Ancylostoma duodenale, and are reported as "hookworm." Ascaris lumbricoides eggs are oval, with a thick wall, and often have a brown, mammillated outer layer. Enterobius vermicularis is another roundworm, known as the pinworm. Eggs may be spread in the environment. The eggs are colorless, oval, and slightly flattened on one side. Whipworm, hookworm, pinworm, and Ascaris have a worldwide distribution.

The image shown here is a thin blood smear stained with Giemsa. Identify the parasitic organism present in the blood smear, which is transmitted by the triatomid bug, or "kissing bug." - Trichomonas hominis - Trypanosoma brucei rhodesiense - Trypanosoma cruzi - Leishmania species

- Trypanosoma cruzi Although Trypanosoma species cannot be differentiated on a blood smear, of the choices listed, Trypanosoma cruzi is transmitted by the triatomid, or reduviid bug. A complete patient history must be obtained to determine species. The trypomastigote form is the primary diagnostic stage in the blood during acute infection, shown here. T. cruzi causes Chagas disease. In the U.S., donated blood is screened for antibodies to T. cruzi. Trichomonas hominis is a non-pathogenic, intestinal flagellate that must be differentiated from pathogenic species. It is small trophozoite form with prominent axostyle, four anterior flagella, one nucleus, and an undulating membrane. Trypanosoma brucei rhodesiense causes East African trypanosomiasis, or sleeping sickness. The tsetse fly is the insect vector, and game animals serve as reservoirs. Without treatment, trypomastigotes spread to the CNS in the second stage of the disease, resulting in death. Leishmaniasis is a zoonotic disease caused by Leishmania species in which canines and rodents serve as reservoirs, with sand flies as the insect vectors. Finding intracellular or extracellular amastigotes is diagnostic. The most severe infection, kala-azar, is caused by L. donovani.

Coccidia parasites are often acquired by fecal-oral routes by ingesting contaminated food or water. All of the following are coccidia parasites EXCEPT? - Sarcocystis species - Cryptosporidium parvum - Trypanosoma cruzi - Isospora belli

- Trypanosoma cruzi Trypanosoma cruzi is incorrect becasue it is a hemoflagellate that is spread from an insect vector (reduviid or kissing bug). Even though it is transmitted via an insect vector like Plasmodium and Babesis species, it does not have a sexual stage of reproduction. Trypanosoma cruzi replicates asexually by binary fission. Sarcocystis species, Cryptosporidium parvum, and Isospora belli are all coccidian parasites that are acquired through the ingestion of contaminated food and water. Plasmodium species and Babesia species fall into the category coccidia/sporozoa, but are spread via an insect vector. Coccidia and sporozoa have life cycles that include both asexual and sexual reproduction.

Xenodiagnosis has historically been used to identify: - Leishmania donovani - Trichinella spiralis - Trypanosoma cruzi - Echinococcus granulosus

- Trypanosoma cruzi Trypanosoma cruzi is the correct answer. Xenodiagnosis is a lengthy process that involves allowing a non-infected kissing bug to feed on a patient suspected of suffering from Chagas disease. The bug is monitored and allowed to let the parasite evolve. At the appropriate time, the bug droppings are examined for the presence of the diagnostic Trypanosoma cruzi trypomastigotes. Leishmania donovani is incorrect. Leishmania donovani is diagnosed by performing a bone marrow from the sternum or iliac crest and looking for the presence of amastigote forms. Trichinella spiralis is incorrect. Trichinella spiralis is diagnosed by performing a muscle biopsy and examining the biopsy for encysted larval forms. Echinococcus granulosus is incorrect. Echinococcus granulosus eggs are only found in dogs, since they are the definitive host, and humans are the intermediate host. Echinococcus granulosus is diagnosed in humans by a fluid aspirate from a hydatid cyst. Serological testing can also be performed in humans to make a diagnosis.

Regarding specimens for legal testing, which one of the following is false? - Chain of custody must be maintained at all times. - Sealed collection kits should be opened in the presence of the donor individual. - Use an alcohol prep pad when cleaning the phlebotomy site prior to collecting a blood alcohol specimen. - Carefully follow the instructions in the collection kit, as you may be called to testify as to how you collected the specimen, and documented its authenticity.

- Use an alcohol prep pad when cleaning the phlebotomy site prior to collecting a blood alcohol specimen. Alcohol preps must not be utilized when collecting blood samples for alcohol levels. The alcohol left on the draw site may contaminate the blood entering into the tube. Iodine or other site preparation cleaning pads should be used instead of alcohol preps to avoid contamination of the blood sample. The chain of custody must be maintained at all times for a specimen for legal testing, the sealed collection kits should be opened in the presence of the donor individual, and the collection kits instructions should be followed carefully as the phlebotomist may be called to court to testify how they collected and documented the specimen.

Isolation and detection of Gardnerella vaginalis from vaginal secretions is improved by which of the following? - Utilization of human blood agar - Incubation at 35-37º C ambient air - Cold enrichment - Utilization of Thayer-Martin agar

- Utilization of human blood agar Human blood agar is an enriched media that supports the growth of Gardnerella vaginalis. The media usually contains 5% human blood without the presence of inhibitors. G. vaginalis produces a characteristic diffuse beta-hemolysis in the presence of human blood, and can, therefore, be distinguished from other similar-appearing organisms. Gardnerella requires incubation at 35-37ºC in 5-10% CO2, not ambient air. Cold enrichment is one of the methods of detecting Listeria species. It is not utilized to isolate Gardnerella which requires 35-37ºC for growth. Thayer-Martin agar is used to selectively isolate Neisseria species. Gardnerella grows well on 5% sheep blood and chocolate agars, CNA, and HBT agar but not on Thayer-Martin agar.

A physician suspected that a young, sexually active woman had bacterial vaginosis. Which of the following specimen sources is the correct specimen of choice to support a bacterial vaginosis infection? - Urethral - Endocervical - Vaginal - Cervical

- Vaginal Vaginal is the correct answer because bacterial vaginosis causes vaginitis, which is inflammation/infection of the vaginal mucosa. Bacterial vaginosis (BV) is commonly associated with Gardnerella vaginalis and is characterized by a foul, smelling discharge. The discharge is made up of sloughed epithelial cells that are covered with tiny, gram-variable rods. These cells are referred to as clue cells. To provide a clinical diagnosis of BV three or more of the following must be present: gray discharge, clue cells should be seen on wet mount, pH >4.5, and a fishy odor after the addition of 10% KOH to the discharge on a slide. Urethral is incorrect because this specimen type is best for the recovery of Neisseria gonorrhoeae and Trichomonas vaginalis. Endocervical and cervical are incorrect answers because these specimen types are best for the recovery of Trichomonas, gonococci, herpes, mycoplasma, and chlamydia.

Which of the following conditions is caused by the Human Papilloma Virus? - Mononucleosis - Venereal Warts - Common Cold - Gastroenteritis in infants

- Venereal Warts Venereal Warts is the correct answer because venereal warts is caused by the human papilloma virus and has been linked to cervical cancer in women. Mononucleosis is incorrect because this is caused by the Epstein Barr Virus (EBV). EBV has also been linked to Burkitt lymphoma and other lymphoproliferative disorders. Common cold is incorrect because this viral infection is caused by the Rhinovirus. Gastroenteritis in infants is incorrect because this is caused by the Rotavirus. Rotavirus is common during the winter and spring seasons.

Which of the following organisms are Gram negative? - Bacillus - Vibrio - Staphylococcus - Nocardia

- Vibrio Vibrio species are Gram negative, oxidase-positive bacilli which are inhabitants of water. These organisms are the causative agents of cholera (V. cholerae) to wound infections. Bacillus, Staphylococcus, and Nocardia are all Gram positive bacteria. Bacillus species are environmental bacteria that cause foodborne gastroenteritis (B. subtilis and B. cereus) and anthrax (B. anthracis). Staphylococcus are found on skin and fomites and cause UTIs, wound infections, toxic shock syndrome, among other infections. S aureus is the most commonly isolated, pathogenic Staphylococci. Nocardia species cause skin and lymphocutaneous infections. Pulmonary infections may disseminate hematologically to the CNS.

Which of the following organisms is known to be a strict halophilic organism? - Vibrio vulnificus - Staphylococcus aureus - Erysipelothrix rhusiopathiae - Salmonella typhi

- Vibrio vulnificus Vibrio vulnificus is the correct answer. Vibrio vulnificus is a halophilic (salt-loving) vibrio that causes wound or intestinal infections by direct contact with contaminated sea water or food. This organism will not grow without sodium chloride. Staphylococcus aureus is incorrect because this organism does not require salt in order to grow. Staphylococcus aureus can grow in ambient air or CO2 at 35° C to 37° C. Staphylococcus aureus can be recovered from the blood stream; however, more commonly it causes localized infections such as boils and carbuncles or deep visceral abscesses. Erysipelothrix rhusiopathiae is incorrect because Erysipelothrix rhusiopathiae is a facultative anaerobe that can grow in high salt concentrations; however, salt is not required for growth. Erysipelothrix rhusiopathiae causes localized infections of the skin, called erysipeloid, secondary to direct penetration of contaminated animal tissue or hides. Salmonella typhi is incorrect because this organism can grow in ambient air at 35° C to 37° C, but salt is not required for growth. Salmonella typhi is caused by ingesting contaminated food or water, which can then invade the blood stream causing a form of sepsis called typhoid fever.

Oxacillin resistance in clinical strains of staphylococci is confirmed by the detection of _______ gene. - vanA - vanB - mecA - mefA

- mecA The gold standard for identification of oxacillin resistance in staphylococci is the detection of the mecA gene using commercial latex or molecular detection methods. Of the six described phenotypes of glycopeptide resistance in enterococci, VanA and VanB are the most clinically significant. VanA confers high level resistance to both vancomycin and teicoplanin; VanB confers moderate to high resistance to vancomycin only.mefA gene offers resistance to macrolides in Streptococcus pneumonia and other viridans streptococi.

A CSF specimen was sent to the laboratory for analysis. A glucose, protein, and cell count were performed. Based on the following results, what would be the probable cause? Analyte Result Glucose 50 mg/dL Protein 100 mg/dL Leukocytes 80 cells/mm3 mononuclear - Normal CSF - Viral infection - Purulent infection - Tuberculosis or fungi infection

- Viral infection Viral infection is the correct answer. In a viral infection, the spinal fluid will have a normal glucose value (range 45-100 mg/dL), a slightly elevated protein value (range 15-50 mg/dL), and an average leukocyte count of 80 cells/mm3 (range 0-5 cells/mm3) with mononuclear cells predominating. Normal CSF is incorrect. To be considered normal, the glucose value must be within 45-100 mg/dL, the protein must be within 15-50 mg/dL, and the leukocyte count must be within 0-5 cells/mm3. Purulent infection is incorrect. For a CSF to be considered purulent, the glucose value should be <45 mg/dL, the protein value should be >100 mg/dL, and the leukocyte count should average 800 cells/mm3 with polymorphonuclear cells predominating. The glucose value is low because bacterial organisms are using the glucose as an energy source for growth and the protein value is elevated due an increase in cellular presence. Tuberculosis or fungi infection is incorrect. In this type of infection, the glucose value is low to normal, the protein value is >50 mg/dL, and the leukocyte count is around 100 cells/mm3 with mononuclear cells predominating.

An 18 year old immigrant from the Philippines presented to the local clinic shortly after relocating to the United States complaining of fever and chills. Examination of the young adult revealed enlarged lymph nodes. Blood was drawn and submitted for culture and parasitic examination. The culture was negative. This suspicious form was seen on the Giemsa-stained blood smear. It measures 225 µm in length. This patient is most likely infected with: - Onchocerca volvulus - Wuchereria bancrofti - Brugia malayi - Loa loa

- Wuchereria bancrofti This form is definitely a microfilaria roundworm of the blood and tissue due to its nuclear appearance, shape and size. Wuchereria bancrofti infect the lymphatics and blood of humans, and can be detected by the sheathed microfilaria with nuclei that do not extend to the tip of the tail. Onchocerca volvulus is not the likely culprit since it is usually recovered in infected nodules or subcutaneous tissue (not in blood) and lacks the protective sheath shown on this organism. Nuclei are similar to W. bancrofti since they do not extend to the tip of the tail. Brugia malai has the same clinical symptoms as W. brancrofti, but is distinguished by having nuclei that extend to the tip of the tail with space that separates the two terminal nuclei. Loa loa can be detected in the blood or by having the adult worm in the conjunctiva of the eye. This microfilaria is also sheathed, but the nuclei extend to the tip of the tail without spaces between the nuclei.

A small gram-negative rod isolated from an eye grows on chocolate agar and it produces satellite growth around staphylococci colonies on sheep blood agar. The organism requires: - X factor and V factor - X factor only - V factor only - Neither X factor nor V factor

- X factor and V factor The correct answer is X factor and V factor. Haemophilus influenzae (which requires X factor and V factor) will grow in the hemolytic zone of Staphylococcus aureus on blood agar plates. Sheep blood agar plates (SAP) provide Haemophilus with X factor (hemin) and the hemolysis of red blood cells by S. aureus releases V factor (NAD). The X and V factors (hemin and NAD, respectively) diffuse into the surrounding medium and promote the growth of Haemophilus in the area surrounding staphylococcus colonies in a process called satelliting. For Haemophilus spp., the satellite test substitutes for the V factor test. If the organism required X factor only, it would be able to grow on SAP, as well as chocolate agar. If the organism required V factor only, it would not show satelliting on the SAP and would only grow on the chocolate agar. If the organism did not require either X factor or V factor, it would grow on the SAP and chocolate agar.

Which of the following organisms causes disease by direct invasion of tissues? - Clostridium botulinum - Vibrio cholerae - Yersinia enterocolitica - Shigella sonnei

- Yersinia enterocolitica Yersinia enterocolitica produces enteritis by direct penetration of the bowel mucosa, resulting in terminal ileitis, lymphadenitis and acute enterocolitis. Clostridium botulinum (toxins A, B and E most common), Vibrio cholerae (cholera enterotoxin) and Shigella sonnei(Shiga toxin) produce disease not by invasion of the tissues, but by the release of toxins that act on specific receptors. Botulinum toxin is an extremely potent neurotoxin, preformed in poorly preserved canned foods contaminated with Clostridium botulinum organisms. The toxin blocks acetylcholine release at peripheral nerve endings. Shiga and cholera-type toxins bind to gangliosides in the epithelial cell membranes, primarily blocking sodium absorption, resulting in a severe watery diarrhea syndrome.

What bacteria is responsible for the bubonic plaque? - Mycobacterium tuberculosis - Yersinia pestis - Vibrio cholerae - Corynebacterium diphtheriae

- Yersinia pestis Yersinia pestis causes bubonic plague and is transmitted from infected rats and other rodents to humans by the bite of rat fleas. Mycobacterium tuberculosis is the causative agent of most cases of human tuberculosis and can be prevented by respiratory isolation. Vibrio cholerae causes epidemics and pandemics of the diarrheal disease cholera. Not all strains of Corynebacterium diphtheriae are toxin producing strains. Only the toxin producing strains will cause diphtheria.

In the performance of which of the following procedures may eggs with opercula be difficult to recover from or detect in stool specimens? - Sedimentation - Direct saline mount - Zinc sulfate flotation - Direct iodine mount

- Zinc sulfate flotation Zinc sulfate flotation is the correct response. Although the zinc sulfate flotation technique is a time honored procedure for the recovery of helminth eggs, with the advantage that the background fecal "junk" is not present, those eggs with an operculum will fill up with fluid and sink to the bottom of the tube and will not be present in the surface eluate. Sedimentation indicates that the parasites are concentrated at the bottom of the tube following centrifugation. An ovum with an operculum will already sink to the bottom of the tube in the sedimentation procedure and will be recovered and detected. A direct saline mount is made by mixing a drop of saline with unfixed stool. This ovum most likely will be present and detected in a direct saline mount. The direct iodine mount is made by mixing a drop of iodine with unfixed stool. The presence of an operculum does not prevent the staining of this ovum that will be present and detected in an iodine mount.

Orthonitrophenyl-b-D-galactopyranosidase (ONPG) is produced by several bacterial species. It acts by cleaving the beta galactosidase bond of certain disaccharides, such as lactose. An ONPG-positive bacterial species, however, may appear as a "late lactose user" because of the absence of what? - ß -galactosidase - Oxidase - ß-galactoside permease - Decarboxylase

- ß-galactoside permease Lactose fermentation is dependent on the activity of two enzymes, the first being ß-galactosidase. The second enzyme, ß-galactoside permease, functions by transporting lactose molecules into the bacterial cell via the cell walls where they settle in the endoplasm. It is here where hydolysis by specific galactosidases can take place. In the absence of the permease enzyme, lactose molecules rely on mutant cells to produce permease at which time lactose can penetrate the cell wall. This process is time-consuming and thus results in delayed lactose fermenters, also known as "late lactose users." Catalase, oxidase, and decarboxylase are enzymes that have other functions in the bacterial cell, not involved in lactose metabolism.