BOC 5 Microbiology

Which selective medium is used for the isolation of gram-positive microorganisms?

Columbia CNA with 5% sheep blood Columbia CNA agar contains colistin and nalidixic acid, which inhibit most gram-negative organisms. Eosin methylene blue is selective and inhibits gram-positive organisms and modified Thayer Martin is selective and inhibits gram-positive organisms, gram-negative bacilli and yeast.

A culture from an infected dog bite on a small boys finger yielded a small, gram-negative coccobacillus that was smooth, raised and beta-hemolytic on blood agar. The isolate grew on MacConkev agar, forming colorless colonies. The organism was motile, catalase positive, oxidase positive, reduced nitrate, and was urease positive within 4 hours. No carbohydrates were fermented. The most likely identification of this isolate is:

Bordetella bronchiseptica Bordetella bronchiseptica are normal flora the respiratory tract of various animals. reaction is that it is rapidly urea Positive (within 4 hours). Brucella is also urea positive, but does not grow on MacConkey

An aerobic, gram-negative coccobacillus was isolated on Bordet-Gengou agar from a nasopharyngeal swab 48 hours after culture from a 6-month-old infant with suspected pertussis. The organism exhibited the following characteristics: MacConkey agar: no growth urea: negative at 4 hours, positive at 24 hours oxidase: negative cataiase: positive The most probable identification of this isolate is:

Bordetella parapertussis The oxidase and urea reactions differentiate Bordetella pertussis and B parapertussis. B pertussis is oxidase positive and urea negative.

Relapsing fever in humans is caused by:

Borrelia recurrentis Relapsing fever is caused by Borrelia recurrentis and is transmitted by the human body louse. Relapsing fever is characterized by the acute onset of high fever lasting 3-7 days, interspersed with periods of no fever lasting days to weeks.

An anaerobic, spore-forming, nonmotile, gram-positive bacillus isolated from a foot wound is most likely;

Clostridium perfringens Actinomyces and Eubacterium are anaerobic gram-positive bacilli that do not form spores; Bacillus is not an anaerobic organism. Clostridium perfringens is a spore- forming anaerobe organism.

Which one of the following organisms could be used as the positive quality control test for lecithinase on egg yolk agar?

Clostridium perfringens Clostridium perfringens is lecithinase positive. Bacteroides, Fusobacterium and Clostridium sporogenes are lecithinase negative.

The reverse CAMP test, lecithinase production, double zone hemolysis, and Gram stain morphology are all useful criteria in the identification of:

Clostridium perfringens The reverse CAMP test, production of lecithinase, and demonstration of double zone hemolysis are tests and characteristics used for the identification of Clostridium perfringens.

An anaerobic gram-positive bacilli with subterminal spores was isolated from a peritoneal abscess.The most likely identification of this organism is:

Clostridium septicum Bacillus cereus is not an anaerobic organism; Eubacterium and Bifidobacterium are anaerobic gram-positive bacilli that do not form spores. Clostridium septicum forms subterminal spores.

A strict anaerobe that produces terminal spores is:

Clostridium tetani Corynebacterium species and Propionibacterium species do not produce spores, and Bacillus is an aerobic organism.

Lab workers should always work under a biological safety hood when working with cultures of:

Coccidioides immitis The arthroconidia of Coccidioides immitis are highly infectious; cultures must be handled with care to minimize aerosols.

A small, gram-negative bacillus is isolated from an eye culture. It grows only on chocolate agar and is oxidase-negative. The most likely organism is:

Haemophilus influenzae Growth only on chocolate agar is typical for Haemophilus influenzae, which is a gram- negative coccobacillus that causes upper respiratory infections.

The expected colony count in a suprapubic urine from a healthy individual is:

0 CFU/mL Urine in the bladder is normally sterile. Suprapubic aspiration removes urine directly from the bladder and yields a specimen free of urethral contamination.

A neonatal blood culture collected through a catheter grows a small yeast. Microscopically, the yeast appear round at one end, with a budlike structure on a broad base at the other end. Growth is enhanced around olive oil-saturated discs. The organism isolated is:

Malassezia furfur Malassezia furfur causes catheter-related only sepsis, requires lipids for growth, and is a small yeast with a wide bud.

A cell culture line used for the recovery of Chlamydia trachomatis from clinical specimens is:

McCoy McCoy cells, in addition to buffalo green monkey kidney cells, are susceptible to infection with Chlamydia trachomatis, and are used routinely for the recovery of C trachomatis in culture.

The nitrate test for mycobacteria can be performed with a reagent impregnated paper strip or by the use of standard reagents. In order to quality control the test properly, which of the following should be used for a positive control?

Mycobacterium tuberculosis Mycobacterium tuberculosis is the {LY only mycobacterium listed that is nitrate eduction positive.

A nonchromogen that grows best at 42°C and is highly resistant to antibiotics is:

Mycobacterium xenopi Mycobacterium xetiopi grows best at 42°-45°C and is not pigmented.

Which of the following reagents should be used as a mucolytic, alkaline reagent for digestion and decontamination of a sputum for mycobacterial culture?

N-acetyl-L-cystine and NaOH The most widely used digestion- decontamination method is the N-acetyl-L- cysteine-2% NaOH method.

Primary amoebic encephalitis may be caused by:

Naegleria fowleri Naegleria fowleri is the etiologic agent of primary amoebic encephalitis.

Coagglutination is associated with:

Neisseria gonorrhoeae One of the less commonly used methods for identification of Neisseria gonorrhoeae grown in culture is coagglutination.

Clinical resistance to penicillin correlates most frequently with beta-lactamase production in:

Neisseria gonorrhoeae Penicillin resistance in Streptococcus pyogenes and S agalactiae have not been described. Neisseria meningitidis is rarely resistant to penicillin, which can be beta-lactamase mediated in some isolates. The primary mechanism of penicillin resistance in Ngonorrhoeae is beta-lactamase.

An autopsy performed on an 8-year-old child revealed Waterhouse-Friderichsen syndrome. Blood and throat cultures taken just prior to death were positive for which organism?

Neisseria meningitidis Waterhouse-Friderichsen syndrome is a known complication of severe Neisseria meningitidis infection.

An organism recovered from a sputum has the following characteristics: Culture: growth at 7 days on Lowenstein-Jensen agar, incubated under aerobic conditions with C02 at 35°C Gram stain: delicate branching gram-positive bacilli acid-fast stain: branching, filamentous, "partially" acid-fast bacterium These results are consistent with which of the following genera?

Nocardia Nocardia are capable of growing on Lowenstein-Jensen agar within 7 days and demonstrate branching, beaded gram- positive bacilli on Gram stain. Nocardia are partially acid fast, and are stained best with the modified acid-fast stain.

A branching gram-positive, partially acid-fast organism is isolated from a bronchial washing on a 63-year-old woman receiving chemotherapy. The organism does not hydrolyze casein, tyrosine or xanthine. The most likely identification is:

Nocardia asteroides Nocardia asteroides are partially acid fast, and do not hydrolyze the substrates casein, tyrosine, or xanthine.

A fibrous skin nodule is removed from the back of a patient from Central America. A microfilaria seen upon microscopic exam of the nodule is:

Onchocerca volvulus Onchocerca volvulus is the only only microfilaria that is detected in the skin snips of patients with raised skin nodules. The microfilaria of Wuchereria, Brugia and Loa loa are found in the blood of infected patients

A fungus superficially resembles Penicillium species but may be differentiated because its phialides are Iong and tapering and bend away from the central axis. The most probable identification is:

Paecilomyces d Elongated and tapered phialides (tenpins) are characteristic of Paecilomyces.

Organisms that can be easily identified to the species level from the ova in fecal specimens include:

Paragonimus westermani, Hymenolepis nana Of the organisms listed, only Paragonimus and Hymenolepis can be identified to the species level by the appearance of their ova in stool.

>100,000 CFU/mL of a gram-negative bacilli were isolated on MacConkey from a urine specimen. Biochemical results are as follows: glucose: acid, gas produced indole: negative urea: positive TDA: positive H2S: positive The organism is most likely:

Proteus mirabilis Morganella and Providencia do not produce H2S; the indole reaction differentiates P mirabilis and P vulgaris.

Which of the following characteristics best distinguishes Mycobacterium scrofulaceum from Mycobacterium gordonae?

Tween® hydrolysis Tween® hydrolysis differentiates Mycobacterium gordonae (Tween® positive) from M scrofulaceum

Which of the following sets of organisms may exhibit a brick red fluorescence?

Veillonella parvula and Prevotella melaninogenica Prevotella, Porphyromonas and Veillonella produce colonies that fluoresce brick red.

One of the enterotoxins produced by enterotoxigenic Escherichia coli in traveler's diarrhea is similar to a toxin produced by:

Vibrio cholerae The toxin produced by enterotoxigenic E coli is similar in action and amino acid sequence to cholera toxin.

A 4-year-old is admitted with symptoms of meningitis, and a Gram stain of the cerebrospinal fluid reveals small, pleomorphic, gram-negative coccobacilli. After 24 hours incubation at 35°C, small, moist, gray colonies, which are oxidase negative, are found on the chocolate agar plate only. Which of the following biochemical data would be consistent with this isolate?

X factor: no growth V factor: no growth XV factor: growth horse blood: no hemolysis These are classic gram stain, growth and biochemicals for Haemophilus influenzae.

Which one of the following gram-negative bacilli ferments glucose?

Yersinia enterocolitica Alcaligenes, Pseudomonas and Acinetobacter are all nonfermenters; Yersinia is a member of the Enterobacteriaceae and, by definition, ferments glucose.

An 8-year-old girl was admitted to the hospital with a three-day history of fever, abdominal pain, diarrhea, and vomiting. A stool culture grew many lactose-negative colonies that yielded the following test results: oxidase: negative TSI: acid slant/acid butt indole: negative urease: positive ornithine decarboxylase: positive sucrose: positive H^S: negative motility at 25°C: positive The most probable identification of this organism is:

Yersinia enterocolitica Edwardsiella produces H2S; E coli is indole positive; Providencia has a TSI reaction of alkaline/acid. Yersinia typically shows motility at 25°C and not 35°C.

An isolate from a stool culture gives the following growth characteristics and biochemical reactions: MacConkey agar: colorless colonies Hektoen agar: yellow-orange colonies TSI: acid slant/acid butt, no gas, no H2S urea: positive These scieening reactions are consistent with which of the following enteric pathogens?

Yersinia enterocolitica Shigella has colorless colonies on both MacConkey and Hektoen agars. Yersinia is lactose negative, but Hektoen agar (has both lactose and sucrose) produces yellow colonies from the fermentation of sucrose. V parahaemolyticus needs at least 1% NaCl to grow and Campylobacter does not grow on MacConkey or Hektoen agars.

A 10-year-old boy was admitted to the emergency room with lower right quadrant pain and tenderness. The following laboratory results were obtained: (IMAGE) The admitting diagnosis was appendicitis. During surgery the appendix appeared normall an enlarged node was removed and cultured. Small gram-negative bacilli were isolated from the room temperature plate. The organism most likely is:

Yersinia enterocolitica The history of the patient suggests an appendicitis-like syndrome, which is consistent with Yersinia enterocolitica. Also, Yenterocolitica grows better at 25°C.

A 25-year-old man who had recently worked as a steward on a transoceanic grain ship presented to the emergency room with high fever, diarrhea and prostration. Axillary lymph nodes were hemorrhagic and enlarged. A Wayson stain of the aspirate showed bacilli that were bipolar resembling safety pins. The most likely identification of this organism is:

Yersinia pestis Yersinia pestis is classically described as having a "safety pin" appearance on Wayson stain. This patient's presentation is classic for bubonic plague.

Colds and other acute respiratory diseases are most often associated with:

adenovirus Adenovirus infections are common. It causes up to 5% of all respiratory infections, and the prevalence of infection is higher (up to 14%).

The diagnosis of Neisseria gonorrhoeae in females is best made from:

an endocervical culture Clinical history does not distinguish Neisseria gonorrhoeae from Chlamydia trachomatis. Because of the presence of nonpathogenic Neisseria in the female genital tract, Gram stain does not differentiate these organisms from Ngonorrhoeae. Culture of an appropriate genital tract specimen is required to confirm identification.

The etiologic agent of botulism is:

an exotoxin producer The toxin produced by Clostridium botulinum is a neurotoxin that is excreted by the organism in food materials, and is then ingested.

A sputum specimen received at 8 AM for an AFB smear reveals acid-fast bacilli. An additional sputum is submitted that afternoon. This specimen was concentrated by the NALC-sodium hydroxide method and inoculated on 2 Lowenstein-Jensen slants and held for 8 weeks at 35°C in 5%-10% C02. No growth occurs. The best explanation is that:

an improper specimen was submitted for culture Early-morning sputum specimens are optimal for AFB culture.

Gram stain of a thigh wound showed many gram-positive spore-forming bacilli. The specimen was placed on brain heart infusion blood agar and incubated aerobically at 35°C for 3 days. At the end of that time, the plates showed no growth. The most likely explanation is that some of the specimen should have been incubated:

anaerobically The specimen Gram stain suggests the presence of Bacillus or Clostridium. Since no growth was observed aerobically, the specimen should be inoculated to media that are incubated anaerobically.

A stool specimen for ova and parasite examination contained numerous rhabditiform larvae. Which factor does not aid in the identification of larvae?

appearance of the genital primordium The rhabditiform larvae of hookworm and Strongyloides stercoralis can be differentiated by the size of their genital primordium. Strongyloides has a prominent genital primordium and a small buccal cavity. Hookworm larvae have a longer buccal cavity, and the genital primordium is not evident. S. stercoralis larvae have a notched tail whereas hookworm larvae have a tapering tail.

Penicillium can best be separated from Aspergillus by:

arrangement of the conidia on the conidiophore Microscopic morphology (arrangement only of the conidia on the conidiophore) is used to differentiate Penicillium from Aspergillus.

In a suspected case of Hansen disease (leprosy), a presumptive diagnosis is established by:

detection of weakly acid-fast bacilli in infected tissue Mycobacterium leprae cannot be cultured in vitro. A clinical diagnosis is made, supported by the presence of AFB in a biopsy specimen.

A beta-hemolytic, catalase-positive, gram-positive coccus is coagulase negative by the slide coagulase test. Which of the following is the most appropriate action in identification of this organism?

do a tube coagulase test to confirm the slide test Staphylococcus aureus are usually beta- hemolytic. Some strains may not produce bound coagulase detected by the slide coagulase test. A tube coagulase is performed to detect free coagulase and should be performed on colonies with typical S aureus morphology that are slide coagulase- negative.

Plesiomonas shigelloides is a relatively new member of the family Enterobacteriaceae. What characteristic separates it from other members of the Enterobacteriaceae?

it is oxidase positive Enterobacteriaceae ferment glucose and are oxidase negative. Plesiomonas was a member of the Vibrio family in part because it is oxidase positive. However, it was moved to the Enterobacteriaceae family despite its positive oxidase reaction.

Mycoplasmas differ from bacteria in that they:

lack cell walls Mycoplasma are smaller than other bacteria and lack a cell wall. Instead, they possess a trilaminar cell membrane. Because they lack a cell wall, they cannot be stained with Gram stain.

Refer to the following image: The organism depicted is a(n):

flagellate The image displays the trophozoite form of Giardia lamblia, a flagellated protozoan parasite.

Middlebrook 7H10 and 7H11 media must be refrigerated in the dark, and incubated in the dark as well. If these conditions are not met, the media may prove toxic for mycobacteria because:

formaldehyde may be produced If exposed to light, agar-based media such as 7H11 may release formaldehyde, which is toxic to mycobacteria.

A yellow colony from a wound culture tested catalase-positive and coagulase-negative. The organism stained as gram-positive cocci in clusters. Which of the following tests would differentiate between a coagulase-negative Staphylococcus and Micrococcus?

furazolidone (100 pg/disk) susceptibility Micrococcus and Staphylococcus can be differentiated by susceptibility to furazolidone (100 pg/disk). Staphylococcus is susceptible and Micrococcus is resistant.

The following results were obtained from a culture of unknown origin: Gram stain: gram-negative diplococci indophenol oxidase: positive glucose: positive maltose: negative sucrose: negative The most likely source of the specimen would be the:

genitourinary tract Based on the biochemicals listed the most likely identification of the organism is Neisseria gonorrhoeae. N gonorrhoeae is most commonly isolated from the genitourinary tract.

Which of the following is most often used to prepare a slide from a plate culture of a dermatophyte for microscopic observation?

lactophenol cotton blue Lactophenol cotton blue is used as the mounting medium, since lactic acid acts as a clearing agent, phenol acts as a killing agent, glycerol prevents drying, and cotton blue gives color to the structures.

Which of the following is the most reliable test to differentiate Neisseria lactamica from Neisseria meningitidis?

lactose degradation Both Neisseria meningitidis and N lactamica produce acid from maltose and grow on modified Thayer martin agar- N lactamica ferments lactose, N meningitidis does not.

An outbreak of Staphylococcus aureus has occurred in a hospital nursery. In order to establish the epidemiological source of the outbreak, the most commonly used typing method is:

pulsed-field gel electrophoresis The most commonly used method to determine the relatedness of 2 or more bacterial strains is pulsed-field gel electrophoresis.

When staining acid-fast bacilli with Truant auramine-rhodamine stain, potassium permanganate is used as a:

quenching agent The counterstain acts as a quenching agent and reduces the background fluorescence of cellular debris.

Which of the following characteristics best differentiates Bordetella bronchiseptica from Alcaligenes species?

rapid hydrolysis of urea Both organisms are oxidase positive; Bordetella bronchiseptica is urea positive in 4 hours.

Members of the family Enterohacteriaceae share which one of the following characteristics?

reduce nitrate to nitrite Members of Enterobacteriaceae are oxidase negative, ferment glucose, and reduce nitrate to nitrite.

Characteristically, enterococci are:

relatively resistant to penicillin Enterococci are bile esculin-positive, hippurate-negative and have the ability to grow in 6.5% NaCl. Enterococci are relatively resistant to penicillin and require combination therapy to treat serious infections.

Quality control testing of CHROMagar™ Candida medium shows very weakly colored colonies after incubation at 25°C, ambient atmosphere for 48 hours. The technologist should:

repeat the quality control tests but incubate at 35°C CHROMagar™ produces the best color only development when incubated at 35°-37°C.

The species of mycobacteria that will give a positive niacin test is Mycobacterium:

tuberculosis A positive niacin reaction differentiates Mycobacterium tuberculosis from M leprae, M kansasii and M fortuitum.

A positive niacin test is most characteristic of Mycobacterium:

tuberculosis A positive niacin test differentiates only Mycobacterium tuberculosis from most other mycobacteria.

A digested and decontaminated sputum is inoculated into a Bactec™ 12B bottle and incubated in air at 37°C. On day 14, a positive growth index is obtained, and the auramine-rhodamine stain is positive. Broth from the initial bottle is inoculated into one Bactec™ 12B bottle, and one Bactec™ 12B bottle with NAP. After reincubation, the inoculated growth bottle shows an increase in growth index, while the bottle containing NAP shows no increase. The organism cultured from the sputum is most likely Mycobacterium:

tuberculosis Mycobacterium tuberculosis and M bovis cannot grow in the presence of NAP, while other mycobacteria can grow in the presence of NAP.

A gastroenterologist submits a gastric biopsy from a patient with a peptic ulcer. To obtain presumptive evidence of Helicobacter pylori, a portion of the specimen should be added to which media?

urea broth Helicobacter pylori produces large amounts of extracellular urease and is positive for urea within 2 hours.

Chlamydial infections have been implicated in:

urethritis and conjunctivitis Chlamydia trachomatis is a well-known cause of sexually transmitted infections, including urethritis and cervicitis, as well as inclusion conjunctivitis and pneumonia in neonates. It also causes trachoma and lymphogranuloma venereum.

A 2-week-old culture of a urine specimen produced a few colonies of acid-fast bacilli, which were rough and nonpigmented. The niacin test was weakly positive and the nitrate test was positive. Which of the following is the most appropriate action when a presumptive identification has been requested as soon as possible?

wait a few days and repeat the niacin test; report presumptive Mycobacterium tuberculosis if the test is more strongly positive The niacin test can be repeated in several days from the initial tube rather than setting up new biochemicals that would take longer

Acinetobacter Iwoffii differs from Neisseria gonorrhoeae in that the former:

will grow on MacConkey and EMB media Both organisms are gram-negative. Neisseria gonorrhoeae is fastidious and does not grow on MacConkey or EMB agar, but Acinetobacter does. Neisseria is oxidase positive and Acinetobacter is oxidase negative.

On day 3 of a fungal culture, grayish cottony growth is observed that is filling the container. The most likely mold isolated is a:

zygomycete Zygomycetes grow rapidly and fill the dish with cotton candy-like growth.

Refer to the following image: A 24-year-old woman, who just returned from vacationing in Russia, became ill with steatorrheal diarrhea. The above organism was found in her stool. The patient most likely is suffering from:

giardiasis Diarrhea associated with lamblia is caused by the consumption of contaminated water and results in greasy, foul-smelling stools.

The preferred carbon source for mycobacteria is:

glycerol Mycobacteria use glycerol as a carbon source in the presence of mineral salts.

Which compound, detected by Lugol iodine, is used in the nonimmunologic detection of Chlamydia trachomatis in cell culture?

glycogen Iodine staining can be used to detect only the glycogen-rich cytoplasmic inclusions in Chlamydia trachomatis infected cells. These inclusions stain brown with iodine.

An acid-fast bacillus recovered from an induced sputum had the following characteristics: pigmentation: yellow in the dark, turning a deeper yellow-orange after 2 weeks of light exposure nitrate reduction: negative Tween® hydrolysis: positive at 5-10 days urease: negative Based on this information, the organism is most likely Mycobacterium:

gordonae The characteristics given differentiate Mycobacterium gordonae from the other mycobacteria listed. M szulgai and flavescens are nitrate reduction positive, and M scrofulaceum is negative for Tween® hydrolysis.

The Image depicts a Gram stain (final magnification l,000x) of a knee fluid from a patient who has recently undergone knee replacement surgery: The best interpretation of this Gram stain is:

gram-positive cocci suggestive of Streptococcus The Gram stain depicts gram-positive cocci arranged in chains. Members of the genus Streptococcus characteristically grow in pairs and chains, and tend to chain more in fluid. Staphylococci are also gram-positive cocci that can appear singly, in pairs, short chains or, more typically, clusters.

A beta-hemolytic streptococci that is bacitracin-sensitive and CAMP-negative is:

group A Group A streptococci (Streptococcus pyogenes) are susceptible to bacitracin and CAMP test negative.

A beta-hemolytic Streptococcus that is bacitracin-resistant and CAMP-positive is:

group B Group B streptococci (Streptococcus agalactiae) are resistant to bacitracin and CAMP test positive.

The organism most commonly associated with neonatal purulent meningitis is:

group B streptococci All of the organisms listed are potential causes of meningitis. Group B Streptococcus is associated with neonatal meningitis and meningitis in the elderly.

A gamma-hemolytic Streptococcus that blackens bile esculin agar but does not grow in 6.5% NaCl broth is most likely:

group D Streptococcus Group D streptococci and Enterococcus produce a positive bile esculin test; however, of these 2, only Enterococcus grows in the presence of 6.5% NaCl.

Which one of the following results is typical of Campylobacter fetus subspecies fetus?

growth at 37°C Most Campylobacter grow at 42°C, except C fetus. C fetus grows best at 37°C and is catalase and oxidase positive.

If present, a characteristic that is helpful in separating Pseudomonas aeruginosa from other members of the Pseudomonas family is:

growth at 42*C Pseudomonas aeruginosa grows at 42°C, but this temperature is inhibitory for other Pseudomonas species.

An organism has been identified as a member of the fluorescent group of Pseudomonas. Which of the following sets of tests should be used to determine the species of the organism?

growth at 42°C, pyocyanin production, gelatinase production Growth at 42°C and pyocyanin production are classic tests for the identification of Pseudomonas aeruginosa. Gelatin hydrolysis separates Pseudomonas putida (negative) from Pseudomonas fluorescence (positive).

A beta-hemolytic streptococcus that has been isolated from an ear culture grows up to the edge of a 0.04 unit bacitracin disk. Which of the following tests would help to determine if the organism is Enterococcus?

growth in 6.5% NaCl broth Of the biochemicals listed, only growth in 6.5% NaCl will aid in the identification of Enterococcus, which has the ability to grow in the presence of high salt concentrations.

In processing clinical specimens and fungal isolates, laboratory workers may contract systemic fungal infections through:

inhalation Inhalation is a common mode of transmission for fungal spores. Specimens for fungal culture should be processed in a biological safety cabinet to minimize the potential for aerosol spread.

Virus transport medium containing penicillin, gentamicin and amphotericin is used to collect and transport specimens for virus culture because this medium:

inhibits bacterial and fungal growth antibiotics and antifungal agents are added to viral transport medium to inhibit the growth of bacteria and fungus.

Microorganisms resembling L-forms have been isolated from the blood of patients treated with antibiotics that:

interfere with cell wall synthesis Bacterial L-forms are bacteria that lose their cell wall as a result of therapy with cell wall-active antibiotics, such as beta-lactam antibiotics. Unlike Mycoplasma species, which permanently lack a cell wall, the lack of a cell wall in L-forms is a result of environmental conditions. Once beta-lactam therapy is discontinued, an L-form has the capability to regrow the cell wall.

Which of the following indicates the presence of a viral infection in tissue smears or biopsies?

intranuclear inclusions In tissue smears or biopsy specimens, the presence of virally infected cells is indicated by intranuclear or intracytoplasmic inclusions.

Structures important in the microscopic identification of Coccidioides immitis are:

irregular staining, barrel-shaped arthrospores Cultures of Coccidioides immitis produce alternating arthrospores.

Which of the following clean catch urine culture colony counts indicates the patient likely has a urinary tract infection?

10^3 CFU/mL Patients with infection often have at least 100,000 bacteria/mL of urine in the bladder. However one third of young women with symptomatic cystitis have less than 100,000 bacteria/mL of urine. The Infectious Disease Society of America consensus definition of cystitis is greater than or equal to 1,000 CFU/mL of a uropathogen.

A sheep blood agar plate inoculated with 0.001mL of urine grows 70 colonies of Staphylococcus aureus. How many colony forming units per mL of urine be reported?

70,000 When 0.001 mL of urine is plated, the growth of one colony is equivalent to 1000 CFU/mL. Thus 70 colonies is 70,000 CFU/mL.

Refer to the following illustration... Examine the broth microdilution suceptibility test shown above and determine the MIC for gentamicin.

<2 µg/mL When reading a broth microdilution susceptibility test, growth in each well is determined by comparison with the growth control well and indicated by turbidity. The well with the lowest concentration of antibiotic displaying no growth is read as the minimum inhibitory concentration (MIC).

The Gram stain from a blood culture shows gram-positive cocci in chains. No growth occurs on blood agar plates incubated both aerobically and anaerobically. Additional testing should be done to detect the presence of:

Abiotrophia defectiva Nutritionally deficient streptococci such as Abiotrophia do not grow on sheep blood agar without the addition of cysteine or proximity to S aureus colonies.

A diabetic foot swab from a 82-year-old woman with recurrent infections is submitted for culture. The Gram stain reveals: many neutrophils, no squamous epithelial cells many gram-negative bacilli many gram-positive cocci in chains The physician requests that all pathogens be worked up. In addition to the sheep blood and MacConkey agar plates routinely used for wound cultures, the technologist might also process a(n):

CNA agar plate CNA agar is a selective medium rutinelly used in the isolation of gram positive aerobic and anaerobic organisms. Since the Gram stain indicates a mixture of gram-positive and gram-negative organisms, use of CNA will aid in the recovery of the gram-positive cocci in culture.

A vaginal/rectal swab is collected from a pregnant patient to screen for group B Streptococcus colonization. What is the best medium to use for specimen inoculation?

LIM broth Detection of group B Streptococcus (GBS) in the genital and gastrointestinal tracts of pregnant women can identify infants at risk for GBS infection. The CDC currently recommends the collection of vaginal and rectal swabs or a single swab inserted first into the vagina and then the rectum at 35-37 weeks gestation. The swab(s) should be inoculated into a selective broth medium such as LIM broth (Todd-Hewitt broth with colistin and nalidixic acid). The use of vaginal/rectal swabs and selective broth medium greatly increases the recovery of GBS.

Chocolate agar base containing vancomycin, colistin, anisomycin, and trimethoprim is also known as:

Martin Lewis agar Martin Lewis agar is a modification of the modified Thayer Martin formulation, and contains a higher concentration of vancomycin and anisomycin instead of nystatin. These modifications provide better inhibition of gram-positive organisms and Candida.

Which of the following organisms may be mistaken for Neisseria gonorrhoeae in Gram stained smears of uterine cervix exudates?

Moraxella osloensis Moraxella osloensis is a gram-negative coccobacillus that is often plump and occurs in pairs and demonstrates a morphology similar to Neisseria. The presence of this organism in endocervical specimens contaminated with vaginal secretions can lead to over interpretation of smears for N gonorrhoeae.

A 24-year-old man presents with pain on urination and urethral discharge. A Gram stain of the discharge is seen in the image: (IMAGE) What is the most likely identification of this organism?

Neisseria gonorrhoeae Gonococcal urethritis in adult males is often diagnosed by the observation of gram-negative diplococci within or closely associated with neutrophils in smears prepared from urethral discharge. The Gram stain in males has a sensitivity of 90%-95% and a specificity of 95%-100% for diagnosing gonorrhea in symptomatic males.

The best medium for culture of Bordetella pertussis is:

Regan-Lowe agar Regan-Lowe agar is an enriched and selective medium for the isolation of B pertussis. Cephalexin is added to inhibit nasopharyngeal flora. It provides better isolation of B pertussis than Bordet-Gengou medium.

Which of the following tests is used to monitor bactericidal activity during antimicrobic therapy in cases of endocarditis?

Schlichter The serum bactericidal, or Schlichter, test can be used to assess the activity of patient's serum when they are receiving long-term therapy for endocarditis or osteomyelitis. High titers of antibacterial activity in the serum suggest adequate dosing, a nontolerant isolate or normal elimination of the antibiotic.

Which of the following media can be used to culture Campylobacter jejuni?

Skirrow medium Skirrow medium is an enriched selective blood agar medium used for the isolation of Campylobacter from specimens with mixed flora. CIN and bismuth sulfite agars are selective and differential for Yersinia enterocolitica and Salmonella, respectively. CNA agar is selective for gram- positive organisms.

Production of beta-lactamase is inducible in which of the following:

Staphylococcus aureus Some bacteria such as Enterococcus sp, H influenzae and Neisseria gonorrhoeae continually produce beta-lactamase. S aureus produces beta-lactamase only after exposure 70 to an inducing agent (such as penicillin). C diphtheriae and S pyogenes do not produce beta-lactamase.

The optochin (ethylhydrocupreine hydrochloride) disk is used for the identification of:

Streptococcus pneumoniae Optochin susceptibility is used to differentiate S pneumoniae, which are susceptible, from other alpha-hemolytic streptococci, which are resistant.

Which one of the following organisms does not require susceptibility testing to the antimicrobial indicated when isolated from a clinically significant source?

Streptococcus pyogenes-penicillin Susceptibility testing should be performed when the susceptibility of the organism cannot reliably be predicted and resistance is known or suspected. Susceptibility testing of penicillins for treatment of S pyogenes does not need to be performed routinely since resistance has not been documented.

Which of the following is the most appropriate organism and media combination?

Yersinia enterocolitica—cefsulodin-irgasan-novobiocin (CIN) CIN agar is a selective and differential medium for the isolation and differentiation of Y enterocolitica. This medium contains sodium desoxycholate, crystal violet, cefsulodin, irgason (triclosan), and novobiocin as selective agents, and mannitol as the carbohydrate.

The optimal wound specimen for culture of anaerobic organisms should be:

a syringe filled with pus, obtained before administration of antibiotics The use of swabs for collection of specimens for anaerobic culture is discouraged. Aspiration with a needle and syringe is recommended. Whenever possible cultures should be obtained before the administration of antibiotics to optimize organism recovery.

Which of the following is the most appropriate method for collecting a urine specimen from a patient with an indwelling catheter?

aspirate urine aseptically from the catheter tubing Indwelling catheters are closed systems, and should not be disconnected for specimen collection. Urine samples should not be collected from catheter bags, and Foley catheter tips are unsuitable for culture because they are contaminated with colonizing organisms. Urine from indwelling catheters should be collected by aseptically puncturing the tubing (collection port).

The most rapid method for detection of Francisella tularensis is:

polymerase chain reaction Methods for rapid diagnosis of Francisella tularensis include fluorescent antibody staining of smears and tissues, antigen detection in urine detection of lipopolysaccharide using specific monoclonal antibodies and PCR. Only PCR has gained widespread use. PCR is appealing because smears and cultures are usually negative, and organism isolation may be hazardous. Serological diagnosis may take weeks to confirm.

When performing a Kovac indole test, the substrate must contain:

tryptophan The indole test is used for determining an organism's ability to produce indole from deamination of tryptophan by tryptophanase.

When performing a stool culture, a colony type typical of an enteric pathogen is subcultured on a blood agar plate. The resulting pure culture is screened with several tests to obtain the following results: TSI: acid butt, alkaline slant, no gas, no H2S phenylalanine deaminase: negative motility: positive serological typing: Shigella flexneri (Shigella subgroup B) The serological typing is verified with new kit and controls. The best course of action would be to:

verify reactivity of motility medium with positive and negative controls All of the biochemical and serological reactions listed are consistent with an identification of Shigella flexneri, with the exception of motility. All Shigella are nonmotile.

In a disk diffusion susceptibility test, which of the following can result if disks are placed on the inoculated media and left at room temperature for an hour before incubation?

zones of larger diameter would result A delay of more than 15 minutes between placing the disks on an inoculated plate and incubation permits excess prediffusion of the antimicrobial agent from the disk. This would result in a larger than expected zone diameter.

The proper blood-to-broth ratio for blood cultures to reduce the antibacterial effect of serum in adults is:

1:10 Human blood contains substances that may inhibit microbial growth. Diluting blood in culture broth reduces the concentration of these substances as well as any antibiotics that may be present. The recommended blood broth ratio is 1:5-1:10. Dilutions less than this may cause the blood to clot trapping organisms in the clot. Greater dilutions may increase the time to detection

How many hours after eating contaminated food do initial symptoms of staphylococcal food poisoning typically occur?

2-6 hours Staphylococcus aureus produces an enterotoxin that is associated with food poisoning. Symptoms typically appear within 2-6 hours.

The scolex of Taenia saginata has:

4 suckers The scolex of Taenia saginata is square with 4 suckers and no hooks.

The optimal incubator temperature for isolation of the Campylobacter jejuni/coli group is:

42°C Campylobacter jejuni/coli grow better at 42°C than 37°C and other organisms in the colon are inhibited at this high temperature.

Optimum growth of Campylobacter jejuni is obtained on suitable media incubated at 42°C in an atmosphere containing:

6% 02, 10%-15% C02, 85%-90% nitrogen Campylobacter is microaerophilic, and requires a decreased oxygen and increased carbon dioxide atmosphere for growth.

A clean catch urine sample from a nursing home patient is cultured using a .001 mL loop. It grows 67 colonies of a lactose fermenter that has the following biochemical reactions: TSI: acid/acid oxidase: negative motility: positive indole: negative citrate: positive VP: positive lysine decarboxylase: negative ornithine decarboxylase: positive urea: negative What should the microbiologist report?

67,000 CFU/mL Enterobacter cloacae The correct quantitation on a urine sample is obtained by counting the colonies and multiplying them by the dilution factor, which in this case is 1000 because a .001 pL loop was used for culture. The biochemicals are characteristic of Enterobacter cloacae.

Which of the following is the most useful morphological feature in identifying the mycelial phase of Histoplasma capsulatum?

8-14 µm tuberculate macroconidia The presence of tuberculate macroconidia indicates a presumptive identification of H capsulatum. The identification must be confirmed using nucleic acid probes or exoantigen testing.

An AFB broth culture is positive for acid-fast bacilli at 1 week while the agar slant shows no growth. The most likely explanation for this is:

AFB grow more rapidly in liquid media Liquid medium is recommended to provide more rapid recovery of AFB than solid medium. Isolation rates of mycobacteria is also higher with liquid medium.

A patient with a nosocomial pneumonia has a sputum Gram stain that shows many neutrophils and numerous small gram-negative coccobacilli. The organism grew in 24 hours as a mucoid, hemolytic colony on blood agar and a colorless colony on a MacConkey agar. The organism had the following characteristics: oxidase: negative catalase: positive nitrate: negative ONPG: negative ornithine decarboxylase: negative lysine decarboxylase: negative The organism is:

Acinetobacter baumannii Alcaligenes and Moraxella are oxidase positive; Stenotrophomonas is a gram-negative bacillus and is lysine and ONPG positive; Acinetobacter baumais nitrate and ONPG negative, and it is a gram- negative coccobacillus.

The Gram stain of drainage from a pulmonary sinus tract shows many WBCs and 3+ branching gram-positive bacilli. Colonies grow on anaerobic media after 3 days incubation. They are yellow-tan and have a molar tooth appearance. The most likely genus is:

Actinomyces Bacteroides and Fusobacterium are anaerobic gram-negative bacilli and Nocardia is an aerobic gram-positive bacillus stain and colony morphology described classic for Actinomyces.

While swimming in a lake near his home, a young boy cut his foot, and an infection developed. The culture grew a nonfastidious gram-negative, oxidase positive, beta-hemolytic, motile bacilli that produced deoxyribonuclease. The most likely identification is:

Aeromonas hydrophila Enterobacteriaceae, such as E coli, Serratia and Enterobacter, are oxidase negative. The only selection that is oxidase positive is Aeromonas. It is associated with wounds contaminated with water.

Fluid from a cutaneous black lesion was submitted for routine bacterial culture. After 18 hours of incubation at 35°C there was no growth on MacConkey agar, but 3+ growth on sheep blood agar. The colonies were nonhemolytic, nonmotile, 4-5 mm in diameter and off-white with a ground glass appearance. Each colony had an irregular edge with comma-shaped outgrowths that stood up like "beaten egg whites" when gently lifted with an inoculating needle. A Gram stain of a typical colony showed large, gram-positive rectangular bacilli. The organism is most likely:

Bacillus anthracis Bacillus anthracis are large, rectangular gram-positive bacilli that produce colonies with an irregular edge (often described as a "medusa-head" appearance) on blood agar. Colonies are nonhemolytic, catalase positive and nonmotile.

Which organism commonly causes food poisoning by consumption of foods containing excessive populations of organisms or preformed enterotoxin?

Bacillus cereus Bacillus cereus is the etiologic agent of 2 distinct types of food poisoning syndromes. Spores can survive cooking and germinate. Vegetative cells multiply and produce toxin.

An organism from a peritoneal abscess is isolated on kanamycin-vancomycin laked blood agar and grows black colonies on BBE agar. It is nonpigmented, catalase positive, and indole negative. The genus of this organism is:

Bacteroides Bacteroides fragilis grows on BBE agar and because it can hydrolyze esculin produces black colonies. B fragilis is also catalase positive and indole negative.

Which of the following genera include anaerobic gram-negative nonsporulating bacilli?

Bacteroides Brucella and Pasteurella are aerobic, gram-negative bacilli, and Actinomyces is on anaerobic gram-positive bacillus. Bacteroides species are anaerobic, gram-negative bacilli.

Which of the following pairs of organisms usually grow on kanamycin, vancomycin, laked blood agar?

Bacteroides and Prevotella Kanamycin-vancomycin laked blood agar is a selective medium used for the isolation of Bacteroides or Prevotella.

Which organism is the most common anaerobic bacteria isolated from infectious processes of soft tissue and anaerobic bacteremia?

Bacteroides fragilis Anaerobic gram-negative bacilli predominate among anaerobes in clinical infections. Bacteroides fragilis is the most common isolated anaerobic bacteria in clinical specimens.

Which one of the following anaerobes would be negative for indole?

Bacteroides fragilis Bacteroides fragilis is indole negative, unlike Fusobacterium nucleatum and Porphyromonas asaccharolytica. Proteus mirabilis is an indole negative, aerobic organism.

The presence of 20% bile in agar will allow growth of:

Bacteroides ovatus Bile tolerant Bacteroides species will grow on agar with 20% bile (BBE agar), while Fusobacterium, Prevotella, and Porphyromonas are sensitive to 20% bile and will not grow on BBE agar. This reinforces the usefulness of bile esculin agar for differentiation of anaerobic gram-negative bacilli.

The stock cultures needed for quality control testing of oxidase production are:

Escherichia coli/Pseudomonas aeruginosa Of the organisms listed only Pseudomonas aeruginosa is oxidase positive.

A 17-year-old female with cystic fibrosis is diagnosed with pneumonia. A sputum sample grew gram-negative bacilli with yellow, smooth colonies that have the following biochemical reactions: oxidase: positive TSI: alk/alk glucose: oxidized fluorescence: negative lysine decarboxylase: positive The most likely organism is:

Burkholderia cepacia Burkholderia cepacia is associated with ONLY respiratory infections in cystic fibrosis patients, and the biochemicals are typical for this organism.

The Epstein-Barr virus is associated with which of the following?

Burkitt lymphoma The classic clinical syndrome associated with Epstein-Barr virus (EBV) infection is infectious mononucleosis. However, in immunocompromised patients, EBV is associated with posttransplant lymphoproliferative disorders, and malignancies such as Burkitt lymphoma.

An isolate of an unknown beta-hemolytic Streptococcus is streaked perpendicular to a streak of beta-lysin-producing Staphylococcus aureus. After incubation a zone of arrowhead hemolysis is noted at the interface of the 2 streaks. What is the name of the test and the presumptive identification of the unknown Streptococcus?

CAMP test and S agalactiae The question describes the CAMP test, which is positive for Streptococcus agalactiae.

A stool sample is sent to the laboratory for culture to rule out Clostridium difficile. What media should the microbiologist use and what is the appearance of the organisms on this media?

CCFA: yellow, ground glass colonies Selective media are needed to isolate Clostridium difficile from stool and CCFA is also differential—fermentation of lactose produces classic colony morphology for this organism.

A Campylobacter species isolated from a stool culture gives the following biochemical reactions: nalidixic acid: susceptible cephalothin: resistand hippurate hydrolysis: positive oxidase: positive catalase: positive This biochemical profile is consistent with:

Campylobacter jejuni Campylobacter jejuni and C coli are closely only related and both are pathogens. The test that differentiates the two is hippurate hydrolysis.

Which of the following must be incubated in a microaerophilic environment for optimal recovery of the organism?

Campylobacter jejuni Most Campylobacter species grow best under lower oxygen tension in an atmosphere of 5% oxygen, 10% carbon dioxide and 85% nitrogen. E coli and Proteus mirabilis are facultative anaerobes and Pseudomonas aeruginosa is an aerobe.

The morphological characteristics of a yeast grown in rabbit plasma are shown in the image: The most likely identification of this yeast isL

Candida albicans Candida albicans produce tubular structure with no constrictions (germ tubes) when incubated in rabbit plasma.

The formation of germ tubes presumptively identifies:

Candida albicans Candida albicans produces germ tubes.

Which of the following statements concerning the germ tube test is true?

Candida albicans and Candida tropicalis can be used as positive and negative controls, respectively Candida albicans (positive) and C tropicalis (negative) can be used as control organisms for quality control of the germ tube test.

A urine culture from a patient with a urinary tract infection yields a yeast culture with the following characteristics: failure to produce germ tubes hyphae not formed on cornmeal agar urease-negative assimilates trehalose The most likely identification is:

Candida glabrata Of the yeasts listed, only UCandida glabrata is urease negative and does not produce pseudohyphae.

Iodine staining of a McCoy cell monolayer culture of a cervical swab reveals a large brown intracytoplasmic inclusion. What is the most likely infecting organism?

Chlamydia trachomatis Iodine staining can be used to detect omy the glycogen-rich cytoplasmic inclusions in Chlamydia trachomatis infected cells. These inclusions stain brown with iodine.

A Wright stain on a conjunctival smear from a neonate shows granular cytoplasmic perinuclear inclusions. This is indicative of:

Chlamydia trachomatis The presence of typical intracytoplasmic inclusions are particularly useful in diagnosing Chlamydia trachomatis inclusion conjunctivitis. Multinucleated giant cells are seen in cells infected with herpes simplex and varicella zoster virus. Cytomegalovirus produces large cells with intranuclear inclusions.

A 29-year-old man is seen for recurrence of a purulent urethral discharge 10 days after the successful treatment of culture proven gonorrhea. The most likely etiology of his urethritis is:

Chlamydia trachomatis Up to 1/3 of patients with Neisseria gonorrhoeae infection are also co¬infected with Chlamydia trachomatis. Patients with identified infection with one organism are usually treated for both infections.

A genus that is found in soil and water and causes infections in immunocompromised patients has the following characteristics: sheep blood agar: violet pigment MacConkey agar: growth 42°C incubation: growth oxidase: positive OF glucose: fermenter indole: negative The genus is:

Chromobacterium The violet pigment on sheep blood agar is a characteristic for the genus Chromobacterium. Serratia is oxidase negative, and Campylobacter does not produce a pigment and does not grow on MacConkey agar.

An organism that demonstrates budding yeast cells with wide capsules in an India ink preparation of spinal fluid is probably:

Cryptococcus neoformans Cryptococcus neoformans is a cause of meningitis in immunocompromised patients, and produces a polysaccharide capsule.

An HIV-positive patient began to show signs of meningitis. A spinal fluid was collected and cultured for bacteria and fungus. A budding, encapsulated yeast was recovered. Which organism is consistent with this information?

Cryptococcus neoformans Cryptococcus neoformans is a of meningitis in immunocompromised patients, and produces a polysacchar.de capsule.

Staib medium (birdseed agar) is useful in the identification of which of the following?

Cryptococcus neoformans Cryptococcust neoformas is the only yeast that produces brown colonies (due to melanin production) on birds agar.

Differentiation of Mycobacterium avium from Mycobacterium intracellulare can be accomplished by:

DNA probe Mycobacterium avium and M intracellulare have the same biochemical pattern, but can be differentiated by the use of DNA probes.

At the present time Clostridium difficile toxin can be detected by:

EIA Latex agglutination identifies the organism, but does not distinguish between toxigenic and nontoxigenic strains, while EIA can detect toxins. Fluorescent staining and HPLC are not used for detection of C difficile toxins.

The examination of human feces is no help in the detection of:

Echinococcus granulosus The diagnostic stages of Strongyloides, Entamoeba and Ancylostoma can be detected in the stool of infected patients. The diagnostic stage of Echinococcus granulosus is not detected in an infected patients stool.

A fecal specimen, inoculated to xylose lysine deoxycholate (XLD) and Hektoen enteric (HE) produced colonies with black centers. Additional testing results are as follows: Biochemical screen - Result glucose - positive H2S - positive lysine decarboxylase - positive urea - negative ONPG - negative indole - positive Serological test - Result polyvalent - no agglutination group A - no agglutination group B1 - no agglutination group C - no agglutination group D - no agglutination group Vi - no agglutination The most probable identification is:

Edwardsiella tarda Shigella is H2S negative, while Salmonella, Edwardsiella and Proteus are H2S positive. Proteus mirabilis is indole negative, so a lack of agglutination with Salmonella antisera indicates the presence of Edwardsiella.

A child was bitten on the arm by her sibling and the resulting wound grew a slender gram-negative bacilli that has the following characteristics: growth on SBA: colonies that "pit" the agar colonies odor: like bleach catalase: negative oxidase: positive TSI: no growth The identification of this organism is:

Eikenella corrodens "Pitting the agar" and the bleach smell of the colonies are hallmark characteristics of Eikenella corrodens.

Protozoan cysts are found in a wet mount of sediment from ethyl-acetate concentrated material. The cysts are without peripheral chromatin on the nuclear membrane. Each cyst has 4 nuclei, and each nucleus has a large karyosome, which appears as a refractive dot. These oval cysts are most likely:

Endolimax nana While Entamoeba hartmanni and, Endolimax nana are a similar size, E hartmanni has similar peripheral chromatin to E histolytica, while E nana has none. E histolytica cysts are larger and round when compared to E nana. Chilomastix is a flagellated protozoan, and has only 1 nucleus.

Refer to the following image. An inexperienced parasitology student may confuse the above organism with:

Entamoeba histolytica The cysts of Entamoeba coli and E histolytica may appear similar to the unexperienced technologist. E coli cysts are larger and contain more than 4 nuclei in each cyst.

A patient is suspected of having amebic dysentery. Upon microscopic examination of a fresh fecal specimen for ova and parasites, the following data were obtained: a trophozoite of 25 pm progressive, unidirectional crawl evenly distributed peripheral chromatin finely granular cytoplasm This information probably indicates:

Entamoeba histolytica The trophozoite of Entamoeba histolytica ranges in size from 12-60 pm, which is significantly larger than Endolimax nana. The nucleus of E histolytica displays evenly distributed peripheral chromatin unlike E coli, which has coarse peripheral chromatin and I butschlii, which has none.

Which of the following may be used as a positive quality control organism for the bile esculin test?

Enterococcus faecalis Enterococcus is positive for the bile esculin test while Streptococcus pyogenes and staphylococci are negative.

Infection of the urinary tract is most frequently associated with:

Escherichia coli >80% of uncomplicated UTIs are caused by E coli.

Which of the following organisms can grow in the small bowel and cause diarrhea in children, traveler's diarrhea, or a severe cholera-like syndrome through the production of enterotoxins?

Escherichia coli E coli can produces several different types of toxins that result in different gastroenteritis manifestations.

An organism gave the following reactions: TSI: acid slant/acid butt; no H2S gas produced indole: positive motility: positive citrate: negative lysine decarboxylase: positive urea: negative VP: negative This organism most likely is:

Escherichia coli These biochemicals are characteristic for E coli. Klebsiella pneumoniae is indole negative and nonmotile. Shigella dysenteriae is nonmotile and Enterobacter cloacae is indole negative.

Quality control of the spot indole test requires the use of ATCC cultures of:

Escherichia coli/Enterobacter cloacae Quality control of indole requires both a positive and a negative control. E coli and E cloacae respectively produce a positive and negative reaction with indole.

A jaundiced 7-year-old boy, with a history of playing in a pond in a rat-infested area, has a urine specimen submitted for a direct dark-held examination. No organisms are seen in the specimen. Which medium should be inoculated in an attempt to isolate the suspected organism?

Fletcher semisolid The clinical syndrome described is most likely the icteric form of Leptospira interrogans. The most commonly used medium for culture is Fletcher semisolid agar. Cultures are incubated in the dark for up to 6 weeks at 28°-30°C and examined weekly by darkfield microscopy

Crust from a cauliflower-like lesion on the hand exhibited brown spherical bodies 6-12 µm in diameter when examined microscopically. After 3 weeks of incubation at room temperature, a slow-growing black mold grew on Sabouraud dextrose agar. Microscopic examination revealed Cladosporium, Phialophora and Fonsecaea types of sporulation. The probable identification of this organism is:

Fonsecaea pedrosoi Only Fonsecaea pedrosoi produces cladiosporium, phialophora and fonsecaea types of sporulation simultaneously.

An isolate from a cornea infection had the following culture results: Sabouraud dextrose: white & cottony at 2 days, rose color at 6 days slide culture: slender sickle shape macroconidia The most likely organism is:

Fusarium Fusarium frequently cause cornea infections and have sickle-shaped macroconidia.

A thin, gram-negative bacillus with tapered ends isolated from an empyema specimen grew only on anaerobic sheep blood agar. It was found to be indole positive, lipase negative, and was inhibited by 20% bile. The most probable identification of this isolate would be:

Fusobacterium nucleatum Fusobacterium nucleatum is classically only described as a long, slender, gram-negative bacillus with tapered ends. Inhibition of growth by 20% bile and a positive indole reaction narrow the selection process.

Which feature distinguishes Erysipelothrix rhusiopathiae from other clinically significant non-spore-forming, gram-positive, facultatively anaerobic bacilli?

H2S production Erysipelothrix rhusipathiae is the only gram-positive bacillus that produces hydrogen sulfide when inoculated into triple sugar iron agar.

Multiple blood cultures from a patient with endocarditis grew a facultatively anaerobic, pleomorphic gram-negative bacilli with the following characteristics: hemolysis: negative MacConkey agar: no growth sheep blood agar: growth in 5%-10% CO2 chocolate agar: growth in 5%-10% CO2 catalase: negative V factor: not required X factor: not required oxidase: negative nitrate: positive, reduced to nitrites indole: negative The most likely identification is:

Haemophilus aphrophilus Biochemicals and growth characteristics are indicative of Haemophilus aphrophilus. Brucella and Cardiobacterium are oxidase positive, and Actinobacillus are catalase positive.

A cerebrospinal fluid has been inoculated onto sheep blood and chocolate agar plates and into a tube of trypticase soy broth. All media were incubated in an atmosphere of 5%C02. Which of the following organisms would usually be isolated by this procedure?

Haemophilus influenzae Haemophilus influenzae is recovered on chocolate agar. Francisella and Bordetella pertussis are fastidious and require special media for growth. Bacteroides is an anaerobe that will not grow aerobically.

An organism that exhibits the satellite phenomenon around colonies of staphylococci is:

Haemophilus influenzae Haemophilus influenzae requires X and V factors. Sheep blood agar supplies X factor, and the staphylococci produce V factor, so colonies grow around staph colonies.

A 4-year-old boy is admitted to the hospital with suspected meningitis. He has not had most of the childhood vaccines. The suspected pathogen is:

Haemophilus influenzae Haemophilus influenzae was previously the most common cause of bacterial meningitis in young children. However, the Haemophilus influenzae type B vaccine has been in use for several years, resulting in a low incidence of H influenzae causing meningitis. This patient has not had most childhood vaccinations, so he is susceptible to H influenzae.

A gram stain of a touch prep from a gastric biopsy shows gram-negative bacilli that are slender and curved. The most likely pathogen is:

Helicobacter pylori Helicobacter pylori is known to cause gastritis and is a gram-negative, curved bacillus.

Many fungal infections are transmitted to man via inhalation of infectious structures. Which of the following is usually contracted in this manner?

Histoplasma capsulatum Histoplasma capsulatum is most frequently transmitted by inhalation.

Gram stain examination of a CSF specimen indicates the presence of yeast-like cells with gram- positive granular inclusions. Which of the following techniques should be used next to assist in the identification of this organism?

India ink Cryptococcus may not stain well on Gram stain. Rapid identification is important when yeast is detected in CSF, the presence of capsules seen in an India ink preparation would be presumptive for C neoformans.

Of the following bacteria, the most frequent cause of prosthetic heart valve infections occurring within 2-3 months after surgery is:

Staphylococcus epidermidis Staphylococcus epidermidis is the most common cause of prosthetic valve endocarditis.

Sodium bicarbonate and sodium citrate are components of which of the following?

JEMBEC system The JHMBEC system is a transport and inoculation medium used for direct plating of specimens for Ngonorrhoeae. Chocolate- based selective medium is inoculated with the specimen. This is placed in an impermeable plastic bag with a bicarbonate- sodium citrate pellet that absorbs moisture to generate a carbon dioxide-rich environment,

Which ot the following sets of tests best differentiates Salmonella and Citrohacter species?

KCN, malonate, beta-galactosidase, lysine decarboxylase Salmonella are positive for lysine decarboxylase and most are negative for KCN, malonate, and ONPG. Citrobacter are negative for lysine decarboxylase and positive for growth in KCN.

A sputum culture from an alcoholic seen in the ER grows gray, mucoid, stringy colonies on sheep blood agar. The isolate grows readily on MacConkey agar and forms mucoid, dark pink colonies. The colonies yield the following test results: ONPG: + indole: = glucose: + oxidase: = citrate: + VP: + The organism is most likely:

Klebsiella pneumoniae Klebsiella is the only distractor that is VP positive, and the other biochemical reactions are typical for K pneumoniae.

The stock cultures needed for quality control testing of motility are:

Klebsiella pneumoniae/Escherichia coli Of the organisms listed only Klebsiella pneumoniae is nonmotile.

A jaundiced 7-year-old boy, with a history of playing in a pond in a rat infested area, has a urine specimen submitted for a direct darkfield examination. Several spiral organisms are seen. Which of the following organisms would most likely be responsible for the patient s condition?

Leptospira interrogans Leptospira are spiral-shaped organisms with hooked ends. They are ubiquitous in water (eg, lakes, ponds) and associated with renal infection in animals. Leptospirosis is a zoonosis, and humans are usually infected via direct or indirect contact with the urine of infected animals (including rats). Between 5%-10% of patients with leptospirosis have the icteric form and develop jaundice, and may develop acute renal failure.

The best medium for culture of Mycobacterium tuberculosis is:

Lowenstein-Jensen medium Lowenstein-Jensen is an egg-based medium used to isolate AFB. The other media are not used for the isolation of AFB.

Which of the following combinations of media provides an egg base, agar base, and a selective egg or agar base media?

Lowenstein-Jensen, Middlebrook 7H11, Lowenstein-Jensen Gruft Lowenstein-Jensen is an egg-based medium, 7H11 is an agar-based medium, and Lowenstein-Jensen Gruft is a selective egg- based medium.

A light yellow colony from a skin lesion grew aerobically and tested as catalase positive and coagulase negative. The organism gram stained as positive cocci in clusters. The organism was modified oxidase positive, bacitracin (0.04U) susceptible and resistant to lysostaphin. What is the identification of this organism?

Micrococcus luteus Micrococcus is modified oxidase positive, bacitracin (0.04U) susceptible and resistant to lysostaphin.

Culture of a strand of hair, that fluoresced yellow-green when examined with a Wood lamp, produced a slow-growing, flat gray colony with a salmon-pink reverse. Microscopic examination demonstrated racquet hyphae, pectinate bodies, chlamydospores, and a few abortive or bizarre¬shaped macroconidia. The most probable identification of this isolate is:

Microsporum audouinii Hair that fluoresces yellow-green under a Woods lamp indicates the presence of a Microsporum species. The colony morphology and microscopic characteristics are consistent with M audouinii.

A specimen of hair that fluoresced under a Wood lamp was obtained from a child with low-grade scaling lesions of the scalp. Cultures revealed a fungus with mycelium and very few macroconidia or microconidia. This fungus is most likely:

Microsporum audouinii The absence of conidia differentiates Microsporum audouinii from the other dermatophytes listed.

A Gram stain performed on a sputum specimen revealed gram-negative diplococci within PMNs. Oxidase testing is positive and carbohydrate degradation tests are inert. The organism is:

Moraxella catarrhalis The Neisseria species listed all ferment several carbohydrates, Moraxella catarrhalis is biochemically inert and does not ferment carbohydrates.

Which one of the following species of Mycobacterium does not usually fluoresce on fluorochrome stain?

Mycobacterium fortuitum Rapidly-growing mycobacteria such as Mycobacterium fortuitum may be <10% acid fast and may not stain with fluorochrome

A 27-year-old scuba diver has an abrasion on his left thigh. A culture of this wound grew an acid-fast organism at 30°C. This isolate most likely is:

Mycobacterium marinum Mycobacterium marinum causes infections as a result of trauma to the skin and exposure to contaminated fish tanks or salt water. Its optimal growth temperature is 28e-30°C.

When grown in the dark, yellow to orange pigmentation of the colonies is usually demonstrated by:

Mycobacterium scrofulaceum Mycobacterium scrofulaceum is a only scotochromogen.

A gram negative bacillus with bipolar staining was isolated from a wound infection caused by a bite from a pet cat. The following characteristic reactions were seen: oxidase: positive glucose OF: fermentative catalase: positive motility: negative MacConkey agar: no growth Which of the following is the most likely organism?

Pasteurella multocida Pasteurella multocida does not grow on MacConkey agar, and is associated with wounds resulting from dog and cat bites. Vibrio cholerae is motile and Pseudomonas and Aeromonas grow on MacConkey.

Which one of the following anaerobes is inhibited by sodium polyanethol sulfonate (SPS)?

Peptostreptococcus anaerobius SPS in blood culture media enhances recovery of most bacteria, including anaerobes. However, Peptostreptococcus anaerobius is inhibited by SPS.

A 44-year-old man was admitted to the hospital following a 2-week history of low-grade fever, malaise and anorexia. Examination of a Giemsa stain revealed many intraerythrocytic parasites. Further history revealed frequent camping trips near Martha's Vineyard and Nantucket Island, but no travel outside the continental United States. This parasite could easily be confused with:

Plasmodium falciparum c The patients history is suggestive of Babesia infection. Babesia microti ring forms are similar to Plasmodium falciparum. A travel history is helpful in determining the cause of infection.

A 1-2 mm translucent, nonpigmented colony, isolated from an anaerobic culture of a lung abscess after 72 hours, was found to fluoresce brick-red under ultraviolet light. A Gram stain of the organism revealed a coccobacillus that had the following characteristics: growth in bile: inhibited vancomycin: resistant kanamycin: resistant colistin: susceptible catalase: negative esculin hydrolysis: negative indole: negative The identification of this isolate is:

Prevotella melaninogenica Both Prevotella and Porphyromonas colonies fluoresce brick red. Porphyromonas is susceptible to vancomycin and can be catalase positive.

A urine culture had the following culture results: sheep blood: swarming Columbia CNA: no growth MacConkey: 1. >100,000 CFU/mL nonlactose-fermenter; 2. >100,000 CFU/mL nonlactose-fermenter with red pigment The isolates from MacConkey agar had the following biochemical reactions: Test - Isolate 1 - Isolate 2 TSI - alk/acid - alk/acid urea - positive - negative TDA - positive - negative H2S - positive - negative The organisms are most likely:

Proteus mirabilis and Serratia marcescens Serratia can produce a red pigment; Proteus mirabilis swarms, is TDA positive and produces H2S.

The stock cultures needed for quality control testing of deamination activity are:

Proteus mirabilis/Escherichia coli Of the organisms listed only Proteus mirabilis is phenylalanine deaminase positive

A 64-year-old male with lymphoma has a positive blood culture at 18 hours incubation. The organism is a nonlactose fermenting gram-negative bacillus on MacConkey agar. Further testing gives the following reactions: oxidase: negative TSI: alkaline/acid, no hydrogen sulfide motility: positive indole: positive citrate: positive ornithine decarboxylase: negative urea: positive phenylalanine deaminase: positive VP: negative

Providencia These are typical biochemical reactions for Providencia. Key reactions that sepaiate it from most other enteric organisms aie lack of hydrogen sulfide production and phenylalanine deaminase positivity. Citrate and ornithine reactions differentiate Providencia and Morganella.

In the USA, the most common organism causing eumycotic mycetoma is:

Pseudallescheria boydii Pseudallescheria boydii is a common cause ONLY of eumycotic mycetoma.

Pus from a draining fistula on a foot was submitted for culture. Gross examination of the specimen revealed the presence of a small (0.8 mm in diameter), yellowish, oval granule. Direct microscopic examination of the crushed granule showed hyphae 3-4 µm in diameter and the presence of chlamydospores at the periphery. After 2 days a cottony, white mold was seen that turned gray with a gray to black reverse after a few days. When viewed microscopically, moderately large hyaline septate hyphae with long or short conidiophores, each with a single pear-shaped conidium, 5-7 x 8-10 µm, were seen. The most likely identification is:

Pseudallescheria boydii microscopic characteristics differentiate Pseudallescheria boydii from the ther fungi listed.

A nonfermenting gram-negative bacillus is isolated from a wound. The nitrate and oxidase are strongly positive. The growth on sheep blood agar has a grape-like odor. The organism is:

Pseudomonas aeruginosa Pseudomonas aeruginosa often has a sweet odor that smells like grapes.

An organism isolated from the surface of a skin burn is found to produce a diffusible green pigment on a blood agar plate. Further studies of the organism would most likely show the organism to be:

Pseudomonas aeruginosa Pseudomonas aeruginosa produces the blue-green pigment, pyocyanin.

An organism was inoculated to a TSI tube and gave the following reactions: alkaline slant/acid butt, H2S, gas produced This organism most likely is:

Salmonella typhimurium Salmonella is the only distractor that produces H2S. Also, Klebsiella and E coli produce acid/acid reactions in TSI.

The stock cultures needed for quality control testing of deoxyribonuclease (DNase) production are:

Serratia marcescens/Escherichia coli Of the organisms listed only Serratia marcescens is DNase positive.

Which one of the following genera is among the least biochemically reactive members of the Enterobacteriaceae?

Shigella Shigella is lactose negative, most species do not produce gas, are VP, urea, lysine decarboxylase and citrate negative, and they are nonmotile.

A TSI tube inoculated with an organism gave the following reactions: alkaline slant, acid butt, no H2S, no gas produced This organism is most likely:

Shigella dysenteriae Salmonella produce H2S in TSI and Yersinia produces an acid slant and acid butt. Shigella fits this biochemical profile.

Which of the following is a dimorphic fungus?

Sporothrix schenckii Dimorphism differentiates Sporothrix from the other fungi listed.

A mold grown at 25°C exhibited delicate septate hyaline hyphae and many conidiophores extending at right angles from the hyphae. Oval, 2-5 µm conidia were formed at the end of the conidiophores giving a flowerlike appearance. In some areas "sleeves" of spores could be found along the hyphae as well. A 37°C culture of this organism produced small, cigar-shaped yeast cells. This organism is most likely:

Sporothrix schenckii The characteristics listed define Sporothrix and differentiate it from other dimorphic fungi.

A gram-positive coccus isolated from a blood culture has the following characteristics: optochin susceptibility: negative bacitracin (0.04 U) susceptibility: negative bile esculin hydrolysis: negative hippurate hydrolysis: positive catalase: negative This organism is most likely:

Streptococcus agalactiae Streptococcus agalactiae is catalase and bile esculin hydrolysis negative and bacitracin and optochin resistant. Streptococcus agalactiae hydrolyzes hippurate.

Which of the following organisms is, to date, considered universally susceptible to penicillin:

Streptococcus pyogenes Haemophilus influenzae and Neisseria gonorrhoeae do not have predictable susceptibility to penicillin. Corynebacterium diphtheriae is not universally susceptible to penicillin. To date, no penicillin resistance has been demonstrated in Streptococcus pyogenes.

An important cause of acute exudative pharyngitis is:

Streptococcus pyogenes Streptococcus pyogenes is the cause of exudative pharyngitis, commonly called strep throat.

The term "internal autoinfection" is generally used in referring to infections with:

Strongyloides stercoralis Strongyloides stercoralis rhabditiform larvae are capable of transforming into filariform (infective) larvae in the intestines of immunocompromised patients. This establishes an autoinfective cycle.

The causative agent of cysticercosis is:

Taenia solium Humans may become infected with Taenia solium by either ingesting the larval form or ova. If ova are ingested the parasite cannot complete the life cycle, and cysticerci encyst in various tissues including the brain.

Multifocal brain lesion in AIDS patients is commonly caused by:

Toxoplasma gondii a The most common cause of ring- enhancing brain lesions in a patient with HIV/AIDS is Toxoplasma gondii.

Which organism fails to grow on artificial media or in cell cultures?

Treponema pallidum Chlamydia trachomatis, Neisseria gonorrhoeae and herpes simplex virus can all be isolated in culture. Direct culture of Treponema pallidum on artificial media has not been achieved. Darkfield microscopy and serological techniques are used to diagnose T pallidum infection.

Darkfield microscopy is can be used to visualize:

Treponema pallidum Darkfield microscopy can be performed to visualize Treponema pallidum in genital or skin lesions. Darkfield examination allows for the visualization of Tpallidum s typical morphology and motility

A college student attended a beach party where raw oysters and other shellfish were consumed. The next day, he had symptoms of septicemia. The blood cultures grew gram-negative bacilli with the following characteristics: oxidase: positive MacConkey agar: pink colonies 0/129 (150 micrograms): susceptible Thu most likely organism is:

Vibrio vulnificus The consumption of raw shell fish is only a risk factor for Vibrio vulnificus and the biochemical reactions support a Vibrio species. V vulnificus is one of the only vibrios that ferments lactose.

Appropriate culture requirements for a specimen from a patient suspected of having tularemia include:

a media with cysteine such as buffered charcoal yeast extract agar Francisella tularensis is the causative agent of tularemia. It has a specific growth requirement for cysteine.

Which of the 2 different antimicrobial agents listed below are commonly used and may result in synergistic action in the treatment of endocarditis caused by Enterococcus faecalis?

a penicillin derivative and an aminoglycoside Enterococcus species are relatively resistant to beta-lactam agents and aminoglycosides. Combination therapy with a beta-lactam agent or vancomycin and an aminoglycoside provide a synergistic combination to effectively treat enterococcal infections.

Establishing the pathogenicity of a microorganism isolated from a child's throat and identified as Corynebacterium diphtheria would depend upon:

a positive toxigenicity test In order to determine if an isolate of Corynebacterium diphtheriae produces toxin, testing for the presence of diphtheria toxin mttst be performed using methods such as the Elek test or PCR.

Proper collection of a sample for recovery of Enterobius vermicularis includes collecting:

a scotch tape preparation from the perianal region The ova of Enterobius vermicularis cannot be demonstrated in a routine ova and parasite examination. The adult female Enterobius worm migrates out of the anus, and lays her eggs in the perianal folds. A scotch tape preparation of the skin of the perianal folds is used to collect ova.

Acceptable specimens for culture of anaerobic bacteria that cause disease include:

abscesses Anaerobes normally inhabit skin and mucous membranes as part of the normal flora. Distractors b, c, and d are virtually always unacceptable for anaerobic culture, because they normally contain anaerobic organisms. It is difficult to interpret culture results from these specimens and distinguish between pathogens and normal flora.

Children who have infections with beta-hemolytic streptococci can develop:

acute glomerulonephritis Noninfectious sequelae associated with infection with Streptococcus pyogenes are glomerulonephritis and rheumatic fever.

An aspirate of a deep wound was plated on blood agar plates aerobically and anaerobically. At 24 hours there was growth on the anaerobic plate only. The next step in the evaluation of this culture is to:

begin organism identification A probable anaerobe is the only organism growing so the microbiologist can proceed with identification.

Haemophilus influenzae becomes resistant to ampicillin when the organism produces a(n):

beta-lactamase enzyme The beta-lactamase enzyme produced by Haemophilus influenzae inactivates the antibiotics that have a beta-lactam ring in their structure, such as penicillins and cephalosporins.

Streptococcus pneumoniae can be differentiated best from the viridans group of streptococci by

bile solubility Bile solubility testing of alpha-hemolyt streptococci differentiates S pneumoniae (soluble) from other alpha-hemolytic streptococci such as viridans streptococci (insoluble).

Psittacosis is transmissible to man via contact with:

birds Chlamydophila psittaci, the agent of psittacosis, is transmitted to humans via inhalation of nasal secretions, as well as infected fecal or feather dust, of psittacine birds (parrot family).

The method of choice to detect Acanthamoeha sp from corneal ulcer scrapings is:

blood agar flooded with a 24-hour growth of E coli The recommended technique for culturing Acanthamoeba is the use of nonnutrient agar seeded with a lawn of E coli. Specimens with suspected Acanthamoeba are inoculated onto a freshly inoculated lawm of E coli, incubated and observed for 7 days. Identification is based on the characteristic patterns of locomotion and morphologic features of the trophic and cystic forms.

Propionibacterium acnes is most often associated with:

blood culture contamination Propionibacterium acnes is part of the normal flora of the skin, so it is frequently isolated from improperly collected blood cultures.

Biochemical reactions of an organism are consistent with Salmonella. A suspension is tested in polyvalent antiserum A through G and Vi antiserum. There is agglutination in the Vi antiserum only. What should be done next?

boil suspension of the organism for 10 minutes to inactivate the Vi antigen If the Vi antigen is present, it will not permit agglutination of the polyvalent antisera. The Vi antigen is heat labile, so boiling will remove it and appropriate agglutination can take place.

A gram-negative bacillus has been isolated from feces, and the confirmed biochemical reactions fit those of Shigella. The organism does not agglutinate in Shigella antisera. What should be done next?

boil the organism and retest with the antisera Some Shigella produce capsular antigen that mask the cell wall and boiling removes the capsule.

Which of the following specimens is considered to be the most sensitive for the recovery of Brucella in cases of chronic infection?

bone marrow Bone marrow is considered the most sensitive specimen for the recovery of Brucella.

Which species of Mycobacterium includes a BCG strain used for vaccination against tuberculosis?

bovis Mycobacterium tuberculosis can remain viable but dormant in macrophages for many years.

A smear of skin tissue reveals fluorescent septate hyphae. The smear was prepared using:

calcofluor white Calcofluor white binds to cellulose and chitin present in fungal cell walls.

The disease-producing capacity of Mycobacterium tuberculosis depends primarily upon:

capacity to withstand intracellular digestion by macrophages Mycobacterium tuberculosis can remain viable but dormant in macrophages for many years.

A yeast isolate from a CSF specimen produced the following results: India ink: no encapsulated yeast cells cryptococcal antigen: negative urea: negative germ tube: negative What should the technologist do next to identify this organism?

carbohydrate assimilation Conventional tests, such as carbohydrate assimilation, must be performed for definitive identification of the yeast in this CSF specimen, especially in light of the fact that the yeast is both cryptococcal antigen and germ tube negative.

An organism previously thought to be nonpathogenic, Moraxella catarrhalis, is now known to be associated with opportunistic respiratory infection and nosocomial transmission. Characteristici dentification criteria include:

carbohydrates negative (asaccharolytic) Moraxella catarrhalis is an oxidase- positive gram-negative diplococcus that is usually beta-lactamase positive. It does not ferment carbohydrates.

Tubercle bacilli are specifically stained by:

carbol fuchsin Mycobacteria form stable complexes with Kinyoun carbol fuchsin.

The primary isolation of Neisseria gonorrhoeae requires:

carbon dioxide Neisseria gonorrhoeae requires an enhanced C02 atmosphere for optimal growth.

A patient has a suspected diagnosis of subacute bacterial endocarditis. His blood cultures grow non-spore-forming pleomorphic gram-positive bacilli in the anaerobic bottle. What test(s) will give a presumptive identification of this microorganism?

catalase and spot indole Propionibacterium acnes is part of the normal flora on the skin and is a common blood culture contaminant. The Gram stain given is typical for P acnes, and it is catalase and indole positive.

The best method to demonstrate the ova of Enterobius vermicularis is:

cellophane tape preparation The ova of Enterobius vermicularis cannot be demonstrated in a routine ova and parasite examination. The adult female Enterobius worm migrates out of the anus, and lays her eggs in the perianal folds. A scotch tape preparation of the skin of the perianal folds is used to collect ova.

A batch of trichrome-stained slides for ova and parasite examination contains numerous minute crystals, which totally obscure the microscopic field. Which of the following measures is most appropriate remedial action?

change the iodine alcohol solution to obtain a strong tea-colored solution, restain Incomplete removal of mercuric chloride may cause the smear to contain refractive crystals. Since the 70% ethanol-iodine solution removes the mercury, it should be changed at least weekly to maintain the strong tea color.

Two blood cultures are positive for yeast from a patient with an intravenous catheter. One culture grew Candida albicans, while the other grew Candida krusei. Which medium should the technologist use to subculture the blood bottles to in order to verify that the cultures are pure?

chromogenic agar Chromogenic agar is extremely effective only in detecting mixed yeast populations in clinical specimens.

The most critical distinction between Staphylococcus aureus and other Staphylococcus is:

coagulase production Coagulase production is the primary biochemical used to differentiate S aureus from other coagulase-negative staphylococci.

Characteristics of the genus Capnocytophaga include:

colonies are large and spreading after 2-4 days Capnocytophaga requires increased C02, ferments glucose, sucrose, and lactose, and is a gram-negative bacillus. Capnocytophaga produces characteristic spreading colonies.

An unusual number of Mycobacterium gordonae have been isolated. The most likely source is:

contamination by water organisms Mycobacterium gordonae is widely distributed in soil and water, and is generally considered nonpathogenic.

The most sensitive test for the initial diagnosis of cryptococcal disease is:

cryptococcal antigen Cryptococcal latex antigen test has been proven to be significantly more sensitive than staining methods.

Which of the following procedures should be performed to confirm that an unknown mold is one of the pathogenic dimorphic fungi?

culture conversion to yeast form Several monomorphic molds resemble the filamentous phase of dimorphic molds, so conversion to yeast phase must be performed for identification of dimorphic molds.

A laboratory aid receives a bronchoscopy sample with the request for culture of Legionella. The assistant asks a microbiologist for direction on plating protocol. The correct response from the microbiologist is:

culture on buffered charcoal yeast extract agar with antibiotics Buffered charcoal yeast extract agar is recommended for culture of specimens for Legionella.

Serum samples collected from a patient with pneumonia demonstrate a rising antibody titer to Legionella. A bronchoalveolar lavage (BAL) specimen from this patient had a positive antigen test for Legionella but no organisms were recovered on buffered charcoal yeast extract medium after 2 days of incubation. The best explanation is that the:

culture was not incubated long enough Media for isolation of Legionella should be incubated at 35°-37°C for at least 7 days.

A first morning sputum is received for culture of mycobacteria. It is digested and concentrated by the N-acetyl-L-cysteine alkali method. Two Lowenstein-Jensen slants are incubated in the dark at 35°C with 5%-10% C02. The smears reveal acid-fast bacilli, and after 7 days no growth appears on the slants. The best explanation is:

cultures held for insufficient length of time Many species of mycobacteria are slow growing, and may take up to 12 weeks for growth.

The recovery of some Cryptococcus species may be compromised if the isolation media contains:

cycloheximide Cycloheximide is known to inhibit the growth of some fungal pathogens, including Cryptococcus neoformans.

Refer to the following image. This structure depicts a:

cyst of a nonpathogenic amoeba The image displays the cyst form of Entamoeba coli, a nonpathogenic parasite.

A first morning sputum specimen is received for acid-fast culture. The specimen is centrifuged, and the sediment is inoculated on 2 Lowenstein-Jensen slants, which are incubated at 35°C in 5%-10% C02. After 1 week, the slants show abundant growth over the entire surface. Stains reveal gram-negative bacilli. To avoid this problem:

decontaminate the specimen with sodium hydroxide d Specimens contaminated by normal flora must be decontaminated prior to inoculation of media; NaOH is the most common decontaminant.

The most meaningful laboratory procedure in confirming the diagnosis of clinical botulism is:

demonstration of toxin in the patients serum Botulism infection is confirmed by reference laboratories such as the CDC by demonstrating toxin in serum, feces, gastric contents or vomitus.

Antifungal susceptibility tests for yeasts are:

more useful in identifying resistant strains Many factors influence clinical response to an antifungal agent; studies have shown that strains that are resistant in vitro are less likely to show a clinical response in vivo.

Rickettsiae infecting man multiply preferentially within which of the following cells?

endothelial Rickettsia species infect and multiply within vascular endothelial cells.

Its important to differentiate between Enterococcus and group D streptococcus because:

enterococci often show more antibiotic resistance than group D streptococci Enterococcus species are more resistant to antimicrobial therapy than group D streptococci such as S hovis.

What material should be used to prepare slides for direct smear examination for virus detection by special stains or FA technique?

epithelial cells from the base of the lesion Since viruses are intracellular organisms, the collection of cellular material is required to be able to demonstrate virus using stains or fluorescent techniques. Scrapings of the base of a vesicle are required to collect cellular material.

The appropriate specimen for the diagnosis of mucormycosis is:

eschar biopsy Mucormycosis is an aggressive infection where biopsy, curettage or fine-needle aspiration is essential for diagnosis.

Listeria can be confused with some streptococci because of its hemolysis and because it is:

esculin positive Listeria may be confused with some streptococci because Listeria is beta- hemolytic and is capable of hydrolyzing esculin.

Photochromogens produce pigment when:

exposed to light for 1 hour Pigment production is controlled by an oxygen-dependent, light-inducible enzyme in photochromogenic mycobacteria.

A catheterized urine is inoculated onto blood and MacConkey agar using a 0 01 mL loop After 48 hours, 68 colonies of a small translucent nonhemolytic organism grew on blood agar but not MacConkey. Testing reveals small gram-positive, catalase-negative cocci. The preliminary report and follow-up testing would be:

growth of 6,800 colomes/mL of a Streptococcus species, esculin hydrolysis and NaCl growth test to follow The number of colonies isolated is multiplied by 100 when a 0.01 mL loop is used for inoculation. Gram-positive, catalase negative cocci are indicative of streptococci.

A mycobacterial isolate that causes multiple skin nodules, grows at 30°C and requires hemin for growth is Mycobacterium:

haemophilum Mycobacterium haemophilum grows best at 30°C, requires hemin or ferric ammonium citrate for growth, and causes subcutaneous lesions presenting as multiple skin nodules.

Refer to the following image: (IMAGE) Trophozoites of the cyst shown above are likely to:

have slow, undefined motility Trophozoites of Entamoeba coli demonstrate slow and undefined motility.

Encephalitis is most commonly associated with which of the following viruses?

herpes simplex Herpes simplex virus is the most common cause of fatal sporadic encephalitis in the United States.

Definitive identification of Neisseria gonorrhoeae is made with the.

hydrolysis of carbohydrates Of the choices provided, only fermentation of carbohydrates provides definitive identification of Neisseria gonorrhoeae.

Which of the following would best differentiate Streptococcus agalactiae from Streptococcus pyogenes?

hydrolysis of sodium hippurate Of the biochemicals listed only hydrolysis of sodium hippurate will differentiate Streptococcus agalactiae {[positive) from S pyogenes (negative).

A first morning sputum is received for culture of acid-fast bacilli. It is digested and concentrated by the N-acetyl-L-cysteine alkali method. Two Sabouraud dextrose slants are incubated in the dark at 35°C with 5%-10% C02. The smears reveal acid-fast bacilli, but the slants show no growth after 8 weeks. The explanation is:

improper media used Sabouraud dextrose is fungal media; mycobacterial media should have been inoculated.

The advantage of thick blood smears for malarial parasites is to:

improve detection of the organisms The increased amount of blood placed on the slide of a thick smear for blood parasites improves the sensitivity of the smear. Thick smears should be performed on all requests for blood parasites.

Blood cultures from a case of suspected leptospiremia should be drawn:

in the first 7-10 days of infection Leptospira organisms can be readily detected by culturing blood during the first week of illness. After this time the organisms disappear from blood and are excreted from the urine for up to 1 month.

Nutritionally deficient streptococci are:

in the genera Granulicatella and Abiotrophia Organisms that used to be categorized as nutritionally variant or deficient streptococci have been reclassified into the genera Abiotrophia and Granulicatella.

A sputum specimen from a patient with a known Klebsiella pneumoniae infection is received in the laboratory for fungus culture. The proper procedure for handling this specimen is to:

include media that have cycloheximide and chloramphenicol added to inhibit bacterial organisms and saprophytic fungi Since fungi grow more slowly than bacteria, a medium with antimicrobials is included to assist in the recovery of fungi. Chloramphenicol is an antibacterial agent active against Klebsiella and most other bacteria.

A urine specimen was submitted for isolation of cytomegalovirus (CMV). The urine was inoculated into human fibroblast tissue culture tubes. After 72 hours, no cytopathic effect was observed in the culture tubes. The most appropriate course of action is to:

incubate the culture tubes for 2-3 weeks longer Cytomegalovirus is a slow-growing herpesvirus, and may require up to 3 weeks to grow in conventional viral culture.

AFB smears of a lymph node biopsy from a child are positive. At the end of 8 weeks, the AFB cultures are no growth. To enhance the possibility of recovery of the causative organism, the technologist should:

incubate the cultures an additional 4 weeks Mycobacterium malmoense requires up to Y 12 weeks for growth.

The lab has been using a latex agglutination assay to detect Clostridium difficile in stools, which identifies a nontoxin cell wall antigen. The lab is considering adoption of an EIA method that detects Clostridium difficile toxin A. Which of the following would provide the best comparison?

latex agglutination vs EIA vs cell culture cytotoxin assay One must compare the sensitivity of o^y latex agglutination that is currently used in the laboratory with the proposed EIA method for toxin A detection. The cell culture cytotoxin assay should be included as a gold standard for toxin detection.

Group B, beta-hemolytic streptococci may be distinguished from other hemolytic streptococci by vhich of the following procedures?

latex antigen typing Growth in 6.5% NaCl, growth in bile esculin medium and susceptibility are not used in the routine identification of Streptococcus agalactiae. Polysaccharide typing for group B antigen is routinely used for identification of S agalactiae.

A beta-hemolytic gram-positive coccus was isolated from the cerebrospinal fluid of a 2-day-old infant with signs of meningitis. The isolate grew on sheep blood agar under aerobic conditions and was resistant to a bacitracin disc. Which of the following should be performed for the identification of the organism?

latex antigen typing The most likely organism isolated from this specimen is Streptococcus agalactiae. Polysaccharide antigen typing will confirm the identification of S agalactiae and differentiate it from other beta-hemolytic streptococci.

The function of N-acetyl-L-cysteine in the reagent for acid-fast digestion-decontamination procedure is to:

liquefy the mucus N-acetyl-L-cysteine (NALC) is a mucolytic agent; the concentration of NALC may be increased to digest thick, mucoid specimens.

The microscopic structures that are most useful in the identification of dermatophytes are:

macroconidia and microconidia Dermatophytes include 3 genera that are generally differentiated by their macroconidia and microconidia formation.

The major features by which molds are routinely identified are:

macroscopic characteristics and microscopic morphology Macroscopic characteristics and microscopic morphology are observations used for the routine identification of molds.

Which of the following is a growth requirement for the isolation of Leptospira?

medium containing 10% serum plus fatty acids Leptospira cultures are incubated in the dark for up to 6 weeks in ambient air at 28°-30°C, and examined weekly by darkfield microscopy. Fletcher semisolid agar contains peptone, bee extract and rabbit serum, which create an enriched medium to support the growth of leptospires.

Assuming the agent isolated from a patient's spinal fluid produces a positive oxidase test, the most likely diagnosis is:

meningococcal meningitis Of the possible types of meningitis listed, only Neisseria meningitidis is oxidase positive.

The best procedure to differentiate Listeria monocytogenes from Corynebacterium species is:

motility at 25°C Corynebacterium and Listeria are catalase-positive and gram-positive bacilli. Listeria demonstrates "tumbling motility that is best demonstrated following growth at 25°C. A few species of Cory neb acterium species are motile when grown at 35°C.

Respiratory syncytial virus is best isolated using a(n):

nasopharyngeal aspirate Respiratory syncytial virus (RSV) infected the ciliated respiratory epithelium of the upper respiratory tract. A nasopharyngeal swab or aspirate is the optimal specimen for RSV recovery.

On a culture suspected to be Mycobacterium tuberculosis, the most important test to perform is:

niacin production Growth rate, colony morphology and positive niacin differentiates Mycobacterium tuberculosis from other mycobacteria.

Shigella species characteristically are:

nonmotile The biochemical characteristic that best fits Shigella is that it is nonmotile. Shigella are urease negative and oxidase negative. Shigella are lactose nonfermenters.

A vaginal smear is submitted for a Gram stain for Neisseria gonorrhoeae. The technologist finds the following results on the Gram stain: many white blood cells few epithelial cells many gram-positive bacilli few gram-negative diplococci few gram-positive cocci in chains The technologist should:

not read or report a Gram stain on a vaginal specimen Because of the presence of nonpathogenic Neisseria in the female genital tract, Gram stain does not differentiate these organisms from Ngonorrhoeae. For this reason Gram stain results should not be reported on vaginal specimens.

AFB smear positive respiratory specimens may be reliably identified as Mycobacterium tuberculosis the same day the smear was read by:

nucleic acid amplification Several commercial PCR tests are available that identify Mycobacterium tuberculosis from positive respiratory specimens.

Examination of a fungal culture from a bronchial washing reveals white, cottony aerial mycelium. A tease preparation in lactophenol cotton blue shows the structures shown in the image: (IMAGE) The most rapid test for definitive identification is:

nucleic acid probe Nucleic acid probe test specific for only Coccidioides immitis can be completed in <4 hours.

Which one of the following results is typical of Campylobacter jejuni:

optimal growth at 42°C Campylobacter jejuni will grow at 37°C, but prefers 42°C. It is oxidase and catalase positive and motile.

In preparing an India ink slide, the technician should ensure that the:

proper amount of reagent is added Interpretation of India ink preparations can be hindered if too much India ink is added, blocking the transmission of light. Equal parts of India ink and CSF should be combined.

An urethral swab obtained from a man with an urethral exudate was plated directly on chocolate agar and modified Thayer-Martin agar, and a Gram stain was made. The Gram stain showed gram-negative diplococci. The culture plates were incubated at 35°C, but had no growth at 48 hours. The most likely failure for organism growth is that the:

organism requires CO2 for growth Neisseria gonorrhoeae requires an enhanced carbon dioxide atmosphere for optimal growth.

Haemophilus influenzae is most likely considered normal indigenous flora in the:

oropharynx Haemophilus influenzae is indigenous flora of the upper respiratory tract.

The method used for processing specimens for mycobacterial culture contaminated with Pseudomonas is:

oxalic acid The oxalic acid method is superior to alkali methods for processing specimens contaminated with Pseudomonas.

Differentiating tests that will separate Burkholderia from Stenotrophomonas include:

oxidase Both organisms are gram-negative bacilli and grow on MacConkey agar. Neither ferments glucose. Stenotrophomonas is oxidase negative, while most other nonfermenters are oxidase positive.

A gram-negative diplococcus that grows on modified Thayer-Martin medium can be further confirmed as Neisseria gonorrhoeae if it is.

oxidase positive and glucose positive, maltose negative Neisseria gonorrhoeae is oxidase positive and ferments glucose but not maltose.

The genus of virus associated with anogenital warts, cervical dysplasia and neoplasia is:

papillomavirus Human papilloma virus (HPV) infects epithelial tissues throughout the body, including skin, larynx, and anogenital tissue. Persistent infection with oncogenic types of HPV and integration of HPV DNA into the cellular genome is a pathway leading to HPV- induced neoplasia, such as cervical cancer.

An isolate on chocolate agar from a patient with epiglottitis was suggestive of Haemophilus species. Additional testing showed that the isolate required for growth and was nonhemolytic. The organism is most likely Haemophilus:

parainfluenzae Haemophilus parainfluenzae requires NAD for growth but not hemin. This distinguishes it from H influenzae. H haemolyticus is hemolytic, and H ducreyi does not cause epiglotittis.

After 24 hours a blood culture from a newborn grows catalase-negative, gram-positive cocci. The bacterial colonies are small, translucent and beta-hemolytic on a blood agar plate. Biochemical test results of a pure culture are: bacitracin: resistant CAMP reaction: positive bile esculin: not hydrolyzed 6.5% NaCi broth: no growth Assuming that all controls react properly and reactions are verified, the next step would be to:

perform a Streptococcus group typing The colony description and biochemical results presented describe Streptococcus agalactiae. The identification of this organism is confirmed by streptococcus antigen typing.

A physician calls the laboratory to verify a result of Mycobacterium tuberculosis, stating that the clinical history of the patient is not compatible with tuberculosis. On review of the patient's culture, the smear was negative and the culture became positive at 5 weeks in the broth culture only. Additionally, it was determined that another patient's specimen that was processed the same day was 4+ AFB on smear and the culture was positive at 10 days for Mycobacterium tuberculosis. The lab should:

perform molecular fingerprinting on both isolates If the molecular fingerprint is the same, the smear-negative culture should be considered a false positive, and the laboratory should review its processing procedures.

Refer to the following image: The egg depicted above is most likely to be found in children suffering from:

perianal itching The most common sign of Enterobius vermicularis infection is intense perianal itching.

Mycobacteria that produce pigment only after exposure to light are classified as:

photochromogens Photochromogens produce nonpigmented colonies only when grown in darkness, but pigmented colonies after exposure to light.

Artifacts found in a stool specimen that can be confused with ova or cysts are:

pollen grains Pollen grains are common artifacts in stool specimens submitted for ova and parasite examination. Their appearance is similar to protozoan cysts.

The one characteristic by which an unknown Cryptococcus species can be identified as Cryptococcus neoformans is:

positive phenol oxidase test Cryptococcus neoformans is the only clinically encountered yeast that is phenol oxidase positive.

A Gram stain of organisms on Loeffler agar showed pleomorphic gram-positive bacilli. The organism should be subcultured to:

potassium tellurite Media containing potassium tellurite is used for the recovery of Cory neb acterium diphtheriae.

The characteristic that is most commonly associated with the presence of strict anaerobic bacteria and can be taken as presumptive evidence of their presence in a clinical specimen is the:

presence of a foul, putrid odor from tissue specimens and cultures Anaerobic bacteria characteristically produce foul-smelling metabolic end products.

A formed stool is received in the laboratory at 3 AM for ova and parasite exam. The night shift technologist is certain that the workload will prevent examination of the specimen until 6 AM when the next shift arrives. The technologist should:

preserve the specimen in formalin until it can be examined Formed stool is unlikely to contain trophozoites so direct examination of the stool is not necessary. The stool should be preserved as soon as possible to preserve any cysts, ova or larvae that may be present in the specimen.

A bronchial washing is processed for acid-fast bacilli. Which of the following precautions should be taken in order to prevent infection of laboratory personnel?

process all specimens in a biological safety hood Specimens processed for mycobacterial culture must be processed in a biological safety cabinet to minimize aerosol transmission of the organism.

Which characteristic best differentiates Acinetobacter species from Moraxella species?

production of indophenol oxidase Both Acinetobacter and Moraxella display resistance to penicillin, and some species grow on MacConkey agar. Acinetobacter are oxidase negative, and Moraxella are oxidase positive.

A liquid stool specimen is collected at 10:00 PM and brought to the laboratory for culture and ova and parasite examination. It is refrigerated until 10:10 AM the next day, when the physician requests that the technologist look for amoebic trophozoites. The best course of action would be to:

request a fresh specimen Protozoan trophozoites are fragile and begin to disintegrate as soon as they are passed. Liquid stool specimens should be preserved within 30 minutes of passage in order to adequately preserve parasite morphology. If a liquid specimen cannot be properly preserved, another specimen should be collected.

Characteristics of the HACEK group of bacteria include:

requirement of 5%-10% C02 for growth The HACEK group of organisms ONLY are gram-negative bacilli that require increased C02 for growth. They are commonly associated with endocarditis, and include Haemophilus species (especially H aphrophilus), Actinobacillus actinomycetemcomitans, Cardiobacterium hominis, Eikenella corrodens, and Kingella species.

In reviewing the number of Mycobacterium isolates for the current year, it was noted that there were 76% fewer isolates than the previous year (115 vs 28). The technologist in charge of the area has documented that the quality control of media, reagents and stains has been acceptable and there has been no gross contamination of the cultures noted. The most appropriate course of action to pursue would be:

review the digestion and decontamination procedure The concentration of sodium hydroxide may be too strong due to decreased recovery of AFB and lack of contaminated cultures.

Refer to the following image: Upon finding the above in a fecal concentrate, the technologist should:

review the fecal concentration carefully for the presence of other microorganisms that may be pathogenic Entamoeba coli is a nonpathogenic protozoan. Its presence indicates the ingestion of fecally contaminated food or water and should lead to a closer review of the specimen for pathogenic parasites or the collection of additional specimens.pathogenic

Which of the following is considered a primary drug for the treatment of Mycobacterium tuberculosis?

rifampin Primary drugs for the treatment of Mycobacterium tuberculosis include isoniazid, rifampin, pyrazinamide, and ethambutol.

Characteristics necessary for the definitive identification of Mycobacterium tuberculosis are:

rough, nonpigmented colony, slow growth at 37°C, niacin production-positive, nitrate reduction-positive Growth rate, colony morphology, niacin production, and nitrate reduction differentiate Mycobacterium tuberculosis from other mycobacteria.

Skin scrapings obtained from the edge of a crusty wrist lesion were found to contain thick-walled, spherical yeast cells (8-15 µm in diameter) that had single buds with a wide base of attachment. Microscopic examination of the room temperature isolate from this specimen would probably reveal the presence of:

round or pear-shaped small conidia attached to conidiophores of irregular lengths The microscopic morphology of the yeast phase is characteristic of Blastomyces. The microscopic morphology of the mycelial phase of Blastomyces is round or pear-shaped small conidia attached to conidiophores of irregular lengths.

Refer to the following illustration. The specimen of choice for finding the above parasite is:

scotch tape preparation The ova of Enterobius vermicularis cannot be demonstrated in a routine ova and parasite examination. The adult female Enterobius worm migrates out of the anus and lays her eggs in the perianal folds. A scotch tape preparation of the skin of the perianal folds is used to collect ova.

The mycobacteria that produce a deep yellow or orange pigment both in the dark and light are:

scotochromogens Scotochromogens produce deep yellow or orange pigment when grown in either light or darkness.

Polyvinyl alcohol used in the preparation of permanently stained smears of fecal material:

serves as an adhesive Polyvinyl alcohol is an adhesive and is used in the preparation of smears for stains, such as trichrome.

A Gram stain of a necrotic wound specimen showed large gram-positive bacilli. There was 3+ growth on anaerobic media, with colonies producing a double zone of hemolysis. To identify the organism, the microbiologist should:

set up egg yolk agar plate The Gram stain and double zone of hemolysis are characteristics of Clostridium perfringens. C perfringens is lecithinase positive on the egg yolk agar test for lecithinase and lipase.

An aspirated specimen of purulent material was obtained from a brain abscess. After 24 hours incubation, pinpoint colonies grew on sheep blood and small, yellowish colonies grew on chocolate. Gram stain of the organism showed gram-negative cocci. Results of carbohydrate degradation studies were as follows: glucose: acid maltose: acid sucrose: acid lactose: negative Additional testing revealed that the organism was oxidase positive and beta-galactosidase negative. The organism is most likely Neisseria:

sicca Neisseria sicca is the only Neisseria species of those listed that ferments glucose, maltose and sucrose.

Which of the following is the best aid in the identification of Epidermophyton floccosum macroconidia?

smooth walls, club-shaped Smooth walled, club-shaped macroconidia are characteristic of Epidermophyton fioccosum.

Biochemical reactions of an organism are consistent with Shigella. A suspension is tested in antiserum without resulting agglutination. However, after 15 minutes of boiling, agglutination occurs in group D antisera. The Shigella species is:

sonnei Boiling removed the capsule so that the antiserum could react with cell wall antigen. Group D Shigella is S sonnei.

MacConkey media for screening suspected cases of hemorrhagic E coli 0157:117 must contain:

sorbitol Sorbitol replaces lactose in MacConkey. E coli 0157:H7 does not ferment sorbitol, whereas other species of E coli are positive for fermentation of sorbitol. This makes the media a good screen for 0157:H7.

When stool examination is negative, the preferred specimen for the diagnosis of paragonimiasis is:

sputum Adult Paragonimus worms live in cystic cavities in the lungs. Eggs are laid by the adult and transferred to the bronchial tree with sputum. Ova may be found in sputum or swallowed and passed in stool.

Ureaplasma urealyticum are difficult to grow in the laboratory on routine media because of their requirement for:

sterols Ureaplasma urealyticum, like other Mycoplasma, lacks a cell wall and possesses an extremely small genome. As a result, this organism has limited biosynthetic capabi ity and fastidious growth requirements. Culture medium should contain serum (provides sterols), growth factors such as yeast extra and a metabolic substrate.

The following growth results were observed on media inoculated with a foot abscess aspirate and incubated in 3%-5% CO2. SBA: 2+ large gray colonies PEA: no growth chocolate: 3+ large gray colonies MacConkey: 3+ lactose fermenters trypticase soy broth: gram-negative bacilli and gram-positive bacilli Biochemicals were set up on the colonies from the MacConkey agar plate. What should the microbiologist do next?

subculture TSB to SBA aerobic and SBA anaerobic In this culture there is an aerobic or facultative gram-negative bacillus and a second organism growing in the TSB only (a gram-positive bacillus). This leads one to think it could be an anaerobe because it did not grow on any of the media incubated in 3%-5% C02. The aerotolerance test is the first step in determining if an anaerobe is present.

A blood culture bottle with macroscopic signs of growth is Gram stained and the technician notes small, curved gram-negative bacilli resembling "gull wings." It is subcultured to blood and chocolate agar, and incubated aerobically and anaerobically. After 24 hours, no growth is apparent. The next step should be to:

subculture the bottle, and incubate in microaerophilic conditions Campylobacter are gram-negative, curved bacilli that require microaerophilic conditions for growth.

Penicillium species is isolated from a bone marrow culture of a patient that traveled to southeast Asia. After 7 days the isolate produces a red pigment that diffuses into the medium. The technologist should:

transfer a colony to BHI at 35°C Penicillium marneffeiis a dimorphic fungi only that produces a diffusible red pigment.

A fungal isolate from the sputum of a patient with a pulmonary infection is suspected to be Histoplasma capsulatum. Tuberculate macroconidia were seen on the hyphae of the mold phase which was isolated at room temperature on Sabouraud dextrose agar containing chloramphenicol and cycloheximide (SDA-CC). A parallel set of cultures incubated at 35°C showed bacterial growth on SDA, but no growth on SDA-CC. Which of the following is the appropriate course of action?

subculture the mold phase to moist BHI-blood media, incubate at 35°C Conversion of thermally dimorphic fungi in culture requires the use of moist enriched (blood-containing) agar incubated at 35°C.

The porphyrin test was devised to detect strains of Haemophilus capable of:

synthesis of hemin The porphyrin test is an alternative method for detecting heme-producing species of Haemophilus. It detects whether or not the organism converts the substrate delta-amino levulinic acid into porphyrins porphobilinogen, which are intermediates synthesis of Factor X.

The laboratory receives a blood culture from a veterinarian who has been ill for many weeks with fevers in the afternoon and evenings, arthritis, and fatigue. The blood culture is positive after 5 days, and the organism has the following characteristics: Gram stain: small, gram-negative coccobacilli sheep blood agar: growth after 48 hours with small, smooth, raised colonies What should the microbiologist do next?

take extra safety precautions for possible Brucella Brucella causes undulant fever and is a cause of fever of unknown origin. It is slow growing, and is associated with laboratory- acquired infections. It is also a potential agent of bioterrorism. Suspected Brucella isolates should not be tested in automated or manual identification systems.

All species of the genus Neisseria have the enzyme to oxidize:

tetramethyl-phenylenediamine Since all Neisseria species are oxidase positive, they possess the enzyme to oxidize tetramethyl-phenylenediamine.

A control strain of Clostridium should be used an anaerobe jar to assure:

that an anaerobic environment is achieved Several Clostridium species are obligate anaerobes, and will only grow in an anaerobic environment. The growth of one of these clostridium species would confirm that an anaerobic environment has been achieved in anaerobic jar.

During the past month, Staphylococcus epidermidis has been isolated from blood cultures at 2-3 times the rate from the previous year. The most logical explanation for the increase in these isolates is that:

there has been a break in proper skin preparation before drawing blood for culture Appropriate skin antisepsis is the most important factor in preventing contaminated blood cultures. Staphylococcus epidermidis is a common blood culture contaminant because it is a common inhabitant of the skin.

Anaerobic infections differ from aerobic infections in which of the following?

they are usually polymicrobic Most infections involving anaerobes are polymicrobic and can include obligate aerobes, facultative anaerobes, microaerophilic bacteria in addition to anaerobic bacteria.

A community hospital microbiology laboratory is processing significant numbers of stool cultures because of an outbreak of diarrhea following heavy rains and flooding in the county. A media that should be incorporated in the plating protocol is:

thiosulfate citrate bile salts sucrose for Vibrio species Thiosulfate citrate bile salt agar is a selective media for Vibrio, an it a so differentiates sucrose-fermenting species, such as Vcholerae and Valginolyticus.

Three sets of blood cultures were obtained from an adult patient with fever and suspected endocarditis. The aerobic bottle of one set had growth of Staphylococcus epidermidis at 5 days of incubation. This indicates that:

the organism is most likely a contaminant Coagulase-negative staphylococci are commonly associated with contaminated blood cultures; however, they are also increasing as a cause of true bacteremia. Significant bacteremia in a patient with endocarditis is usually continuous and low grade. In most cases, all blood cultures drawn will yield positive results. The facts that only 1 bottle of 1 set was positive, and that the bottle did not become positive until day 5 of incubation, indicate that this isolate is most likely a contaminant.

Upon review of a sputum Gram stain, the technician notes that the nuclei of all of the neutrophils present in the smear are staining dark blue. The best explanation for this finding is:

the slide was inadequately decolorized with acetone/alcohol Problems with analysis of Gram staining generally result from errors including interpretation of the slide (smear prepared too thick), excessive heat fixing, and improper decolorization. Inadequate decolorization with acetone/alcohol results in a smear in which host cells (neutrophils and squamous cells), as well as bacteria, all appear blue.

A Gram stain from a swab of a hand wound reveals: moderate neutrophils no squamous epithelial cells moderate gram-positive cocci in chains moderate large gram-negative bacilli Select the appropriate media that will selectively isolate each organism.

Columbia CNA, MacConkey Columbia CNA agar is a selective medium used for the isolation of gram- positive organisms. The medium contains colistin and nalidixic acid, which inhibits gram-negative organisms. MacConkey agar is a selective and differential medium used for the isolation of gram-negative organisms. The medium contains bile and crystal violet, which inhibits gram-positive organisms.

A pregnant patient is screened at 36 weeks gestation for group B Streptococcus (GBS). A vaginal swab is collected and cultured in Todd-Hewitt broth with 8 pg gentamicin/mL and 15 pg nalidixic acid/mL. The broth is subcultured onto sheep blood agar after 24 hours of incubation. No GBS are seen on the subculture and the results are reported as negative. The patient later goes on to deliver an infant with early onset GBS disease. What is the most likely reason for the negative GBS culture?

a vaginal swab was collected instead of a vaginal/rectal swab Group B Streptococcus (GBS) colonizes only both the genital and gastrointestinal tracts of pregnant women. Collection of a vaginal and rectal specimen is recommended by the CDC to maximize GBS detection in this population. Patients should be screened at 35-37 weeks gestation. In addition selective broth culture is recommended (Todd-Hewitt broth with antibiotics) although other selective media are also available. When selective broth culture is used it should be incubated for 18-24 hours prior to subculture onto blood agar.

In a quality control procedure on a new batch of Mueller-Hinton plates using a stock culture of Staphylococcus aureus (ATCC 25923), all the disk zone sizes are too small. The most likely reason for this is that the:

bacterial suspension was not diluted to the proper concentration Quality control zone sizes that are too small could indicate that the organism inocdum is too high, plates were poured too thick, or that the potency of the antibiotic disks is too low.

The ONPG test allows organisms to be classified as a lactose fermenter by testing for following?

beta-galactosidase Through the action of the enzyme beta- galactosidase, ONPG cleaves into galactose and o-nitrophenol (a yellow compound).

A penicillin-resistant Neisseria gonorrhoeae produces:

beta-lactamase Antimicrobial resistance in Neisseria gonorrhoeae is widespread. The production of beta-lactamase (penicillinase) breaks open the beta lactam ring of penicillin, destroying its activity. Thus, Ngonorrhoeae that produce beta lactamase are resistant to penicillin.

Gram-positive cocci in chains are seen on a Gram stain from a blood culture. The organism grows as a beta-hemolytic colony. Further tests that could be performed include:

bile esculin, PYR, bacitracin, and hippurate Bile esculin, PYR, bacitracin and hippurate are biochemicals/tests used in the presumptive or definitive identification of beta-hemolytic streptococci such as S pyogenes, S agalactiae and Enterococcus.

Viridans streptococci can be differentiated from Streptococcus pneumoniae by:

bile solubility Bile solubility testing of alpha-hemolytic streptococci differentiates S pneumoniae (soluble) from other alpha-hemolytic streptococci, such as viridans streptococci (insoluble).

Diagnosis of typhoid fever can be confirmed best by culture of:

blood The sensitivity of blood culture is only 50%-70%. Stool cultures are positive in <50% of patients and urine cultures are positive even less frequently. Bone marrow has a sensitivity of up to 90%. Higher colony counts are present in bone marrow and counts are not decreased by up to 5 days of antimicrobial therapy prior to specimen collection.

A sputum specimen is received for culture and Gram stain. The Gram stained smear from this specimen is seen in the image (total magnification 100x): (image) The technologist's best course of action would be to:

call the patient care area and request a new specimen There are several sputum-screening systems for assessing the quality of respiratory specimens. In general, neutrophils are a positive indicator of quality, and squamous epithelial cells are a negative indicator of quality, suggesting oropharyngeal contamination. This specimen contains an abundance of squamous cells (> 10/low power field), and would be unacceptable for culture.

Gram stain examination from a blood culture bottle shows dark blue, spherical organisms in clusters. Growth on sheep blood agar shows small, round, pale yellow colonies. Further tests should include:

catalase production and coagulase test The Gram stain and culture growth describe a Staphylococcus species. Catalase production confirms that the organism belonged to the genus Staphylococcus and coagulase is used to differentiate S aureus from coagulase-negative staphylococci.

The most common cause for failure of a GasPak™ anaerobic jar to establish an adequate environment for anaerobic incubation is:

catalysts that have become inactivated after repeated use The 2 most common causes of failure of the GasPak™ system is a defective gasket in the jar lid that allows escape of gas from inside the jar and inactivated catalyst pellets.

In the Kirby-Bauer disc diffusion susceptibility test, which variable is critical when testing Pseudomonas species for antibiotic susceptibility to aminoglycosides?

cation content of media Variations in the concentrations of divalent cations primarily calcium and magnesium affect the results of aminoglycoside, tetracycline and colistin tests with P aeruginosa isolates. A cation concentration that is too high results in smaller zone sizes, and a concentration that is too low increases zone sizes.

The enterotoxin produced by certain strains of hemolytic, coagulase positive Staphylococcus aureus:

causes one type of bacterial food poisoning Staphylococcus aureus produces an enterotoxin that is associated with short- incubation food poisoning.

Which of the following combinations is useful for confirming the presence of extended spectrum beta-lactamases in E colil?

ceftazidime + clavulanic acid Extended spectrum beta lactamases (ESBL) are inhibited by clavulanic acid. Confirmatory tests of the presence of ESBL are based on the enhanced activity of a beta-lactam antibiotic, usually cefotaxime or ceftazidime, when it is tested with clavulanic acid compared to the activity of the beta- lactam tested alone.

First generation cephalosporins can be adequately represented by:

cephalothin Cephalothin is a first-generation cephalosporin, cefotetan and cefoxitin are second-generation cephalosporins, and ceftriaxone is a third generation cephalosporin.

Media used to support to support growth of Legionella pneumophilia should contain which of the following additives?

charcoal and yeast extract Buffered charcoal yeast extract medium is a specialized enrichment medium for the isolation of Legionella. The nutritive base includes yeast extract. Charcoal is added to the medium as a detoxifying agent.

A 10-year-old child with cystic fibrosis presents with cough and shortness of breath. Her sputum Gram stain is seen in the image: (IMAGE) Based on the Gram stain what would be the best medium and incubation condition to optimize recovery of the organism seen?

chocolate agar incubated in C02 The Gram stain demonstrates numerous neutrophils and small, pleomorphic gram- negative bacilli suggestive of Haemophilus. H influenzae is an important cause of lower respiratory tract infections in patient with pre-existing lung disease such as cystic fibrosis. Haemophilus are fastidious, and require the use of an enriched medium such as chocolate agar and incubation at 35°-37°C in a moist environment supplemented with 5%-10% C02.

Cerebrospinal fluid from a febrile 25-year old man with possible meningitis is rushed to the laboratory for a stat Gram stain and culture. While performing the Gram stain, the technologist accidentally spills most of the specimen. The smear shows many neutrophils and no microorganisms. Since there is only enough CSF to inoculate one plate, the technologist should use a:

chocolate agar plate Enriched media such as chocolate agar has no inhibitory effects on bacterial growth and contains additional nutrients that supports the growth of fastidious organisms such as H influenzae and Neisseria.

Proper media for culture of a urethral discharge from a man include:

chocolate and modified Thayer-Martin agars Chocolate agar and chocolate agar-based selective media should be used for recovery of Neisseria gonorrhoeae from urethral discharge. Chocolate agar provides the nutrients required by N gonorrhoeae and selective media contains antimicrobial agents that inhibits other organisms and permits recovery of pathogenic Neisseria.

A reliable test for distinguishing Staphylococcus aureus from other staphylococci is:

coagulase Coagulase is the biochemical test used to distinguish S aureus (positive) from coagulase-negative staphylococci (negative).

In the disk diffusion method of determining antibiotic susceptibility, the size of the inhibition zone used to indicate susceptibility has been determined by:

correlating the zone size with minimum inhibitory concentrations The zone size observed has no meaning in and of itself. Interpretive standards are derived from a correlation between zone sizes and minimum inhibitory concentrations. Usually a large number of organisms from a given species or group (eg, Enterobacteriaceae) are tested.

An antibiotic used to suppress or kill contaminating fungi in media is:

cycloheximide Cyclohexamide, which inhibits protein synthesis, is the common agent used in Mycosel ' or mycobiotic agar to inhibit faster-growing saprophytic fungi. Penicillin and streptomycin do not inhibit fungi. Amphotericin B is not routinely used as an additive in fungal media.

The best medium for culture of Francisella tularensis is:

cystine glucose blood agar Francisella tularensis is fastidious and not readily recovered in culture. Cysteine blood glucose agar is an enriched medium with beef heart infusion, peptones, glucose and rabbit blood. It also includes cystine, which is required by F tularensis for growth.

In disk diffusion susceptibility testing, as an antimicrobial agent diffuses away from the concentration of antibiotic is:

decreased The amount of antibiotic used in disk diffusion susceptibility testing is standardized and constant. Once the disk is placed on the inoculated plate and makes contact with the agar, the antibiotic in the disk begins to diffuse out. As it diffuses into the media, the concentration of antibiotic gets lower the further it diffuses from the disk.

A medium that aids in the presumptive identification of organisms based on their appearance on the medium is called:

differential Differential media contain compounds, often carbohydrates, that provide a presumptive identification based on colony color or a precipitate around the colony. Examples include MacConkey, Hektoen and xylose lysine desoxycholate agar.

Which of the following methods is inadequate for the detection of vancomycin-intermediate S aureus?

disk diffusion The disk diffusion procedure will not differentiate S aureus strains with reduced susceptibility to vancomycin (MICs 4-8 pg/mL) from susceptible stains even when incubated for 24 hours.

Which type of microscope would be most useful in examining viruses and the structure of microbial cells?

electron Due to the small size of viruses, they are not visible using light microscopy. Electron microscopy is used to visualize viruses and the internal structure of microorganisms.

Which of the following is the most appropriate specimen source and primary media battery?

endocervical-chocolate, Martin Lewis Chocolate agar and chocolate agar-based selective media (Martin Lewis) are routinely used for the recovery of Neisseria gonorrhoeae from genital specimens. Sputum and urine specimens are routinely processed using a general purpose media (blood agar) and a selective agar (EMB or MacConkey). In addition chocolate agar is routinely included to enhance recovery of fastidious organisms such as H influenzae. CSF is routinely processed using blood and chocolate agars.

A D test is performed on an isolate of Staphylococcus aureus to determine inducible clindamycin resistance: (IMAGE) Based on the result seen in the image how should the erythromycin and clindamycin be reported?

erythromycin: resistant; clindamycin: susceptible The image displays a negative D test result. There is no flattening of the zone of inhibition around the clindamycin disk adjacent to the erythromycin disk. Thus, there is no inducible clindamycin resistance, and the isolate is reported as clindamycin- susceptible, while the erythromycin is reported as resistant.

After satisfactory performance of daily disk diffusion susceptibility quality control is documented, the frequency of quality control can be reduced to:

every week Daily disk diffusion quality control can be converted to weekly testing when 30 days of consecutive testing demonstrates no more than 3 antibiotic/organism combinations outside of the acceptable limits.

A liquid fecal specimen from a three-month-old infant is submitted for microbiological examination. In addition to culture on routine media for Salmonella and Shigeli. this specimen should be routinely:

examined for the presence of Campylobacter sp Campylobacter continues to be the most common enteric pathogen isolated from patients with diarrhea. Routinely fecal specimens should be cultured for Salmonella, Shigella and Campylobacter. Fecal specimens are not routinely cultured for enterotoxigenic E coli or C botulinum. E hartmanni is a onpathogenic parasite and does not cause diarrhea.

An aspirate of a deep wound was plated on blood agar plates and incubated aerobically and anaerobically. At 24 hours there was growth on both plates. This indicates that the organism is a(n):

facultative anaerobe Facultative anaerobes are organisms that can grow under both aerobic and anaerobic conditions.

Which of the following antibiotics would routinely be tested and reported for isolates of Pseudomonas aeruginosa?

gentamicin Aminoglycoside antibiotics such as gentamicin are active against Pseudomonas and routinely tested and reported on these isolates. Penicillin, erythromycin, and clindamycin are not active against Pseudomonas.

Enzymatic drug modification is a mechanism of resistance for which antimicrobial?

gentamicin Aminoglycoside modifying enzymes modify aminoglycosides, such as gentamicin, resulting in poor binding to the bacterial ribosome. Resistance to levofloxacin, vancomycin and sulfamethoxazole is a result of nonenzymatic alteration of the antimicrobial target causing reduced antibiotic binding or activity.

Which 2 diseases are usually preceded by infection with beta-hemolytic streptococci?

glomerulonephritis, rheumatic fever Noninfectious sequelae associated with infection with Streptococcus pyogenes are glomerulonephritis and rheumatic fever.

SPS is used as an anticoagulant for blood cultures because it:

inactivates neutrophils and components of serum complement Most commercially available blood culture media contain sodium polyanetholsulfonate (SPS) in concentrations between 0.025 and 0.05%. SPS has anticoagulant activity, and inactivates neutrophils as well as some antibiotics including gentamicin and polymyxin. It also precipitates components of serum complement.

To quality control the autoclave, a vial of Bacillus stearothermophilus is autoclaved and should then be:

incubated at 56°C Bacillus stearothermophilus is commonly used as an indicator organism for the appropriate functioning of autoclaves. Unlike most Bacillus species, B stearothermophilus grows at 56°C.

Which one of the following combinations of organisms would be appropriate as controls to test the functions listed?

indole-negative Escherichia coli and Proteus mirabilis Of the combinations listed, the use of E coli and Proteus mirabilis will produce a positive and negative result for indole respectively. The remainder of the organisms are all positive for the test described

In order to isolate Campylobacter coli/jejuni, the fecal specimen should be:

inoculated onto selective plating media and incubated in reduced oxygen with added CO2 at 42°C Campylobacter coli/jejuni require a microaerophilic atmosphere for optimal recovery. The use of selective media is recommended for recovery from fecal specimens. Selective media for Campylobacter contains antibiotics to inhibit the growth of enteric gram-negative flora. Unlike other enteric pathogens, C coli/jejuni grow well at 42°C.

When evaluating a new susceptibility testing system, if the new system characterizes a susceptible isolate as resistant, this is termed a:

major error When evaluating susceptibility testing systems the following conventions are used: a very major error occurs when the system characterizes a resistant isolate as susceptible; a major error occurs when the system characterizes a susceptible isolate as resistant; and a minor error occurs when the system characterizes a susceptible or resistant isolate as intermediate, or an intermediate isolates as susceptible or resistant.

The lowest concentration of antibiotic that inhibits growth of a test that inhibits growth of a test organism is the:

minimum inhibitory concentration The MIC is a basic laboratory measurement of the activity of an antibiotic against an organism. It is the lowest concentration of antibiotic that inhibits visible growth of the organism. It does not represent the concentration of antibiotic that is lethal to the organism.

The most sensitive substrate for the detection of beta-lactamases is:

nitrocefin The chromogenic cephalosporin test using nitrocefin is the most sensitive and specific test for detection of beta lactamase. Acidimetric tests employing penicillin are less expensive, but not as sensitive, as the nitrocefin assay.

Which of the following antimicrobials would be inappropriate to report on an E coli isolated from a wound culture?

nitrofurantoin Certain antimicrobials, such as nitrofurantoin and norfloxacin, are used only or primarily to treat urinary tract infections. These agents should not be reported for pathogens recovered from other sites of infection.

A urine Gram stain shows gram-positive cocci in clusters. The organism tested catalase positive. To speciate this organism from culture, the technician should perform a coagulase test and a/an:

novobiocin susceptibility The organism in this urine culture is a Staphylococcus species. Coagulase will differentiate S aureus from coagulase- negative staphylococci (CNS) and novobiocin susceptibility will differentiate S saprophyticus from other CNS. S saprophyticus is a common cause of urinary tract infections in young females.

An expectorated sputum is sent to the laboratory for culture from a patient with respiratory distress. The Gram stain of the specimen shows many squamous epithelial cells (>25/lpf) and rare neutrophils. The microscopic appearance of the organisms present include: moderate gram-positive cocci in chains and diplococci moderate gram-negative diplococci moderate palisading gram-positive bacilli all in moderate amounts This Gram stain is most indicative of:

oropharyngeal flora Sputum specimen quality is assessed to determine if the specimen is representative of the site of infection. The presence of white blood cells is an indicator of infection, and presence of squamous epithelial cells is an indicator of oropharyngeal contamination. In this specimen, >25 epithelial cells per low power field is an indicator of poor specimen quality, and the bacteria present are representative of oropharyngeal flora.

A 73-year-old man diagnosed as having pneumococcal meningitis is not responding to his penicillin therapy. Which of the following tests should be performed on the isolate to best determine this organism's susceptibility to penicillin?

oxacillin disk diffusion With the exception of the oxacillin disk screening test, disk diffusion is not recommended for testing S pneumoniae against beta-lactam agents. S pneumoniae does not produce beta-lactamase, so beta- lactamase testing would not be useful. The Schlichter test is not a method for determining an organisms susceptibility to a given agent.

Quality control results for disk diffusion susceptibility tests yield the following results: aminoglycoside zones too small and penicillin zones too large. This is most likely due to the:

pH of Mueller-Hinton agar being too low Mueller-Hinton agar used for disk diffusion susceptibility testing is standardized at pH 7.2-7.4. Penicillins function better in an acidic environment, so zone sizes would become larger if the media pH is too low. Aminoglycosides, on the other hand, are less effective in an acidic environment, so zone sizes would become smaller if the pH of the media is too low. Plates should not be incubated in a carbon dioxide atmosphere, which lowers the pH of the media.

An antibiotic that inhibits cell wall synthesis is:

penicillin Penicillin inhibits penicillin binding proteins that are essential to peptidoglycan (cell wall) synthesis. Chloramphenicol inhibits protein synthesis, colistin increases cell membrane permeability, and sulfamethoxazole inhibits folate metabolism.

Which of the following groups of specimens would be acceptable for anaerobic culture?

pleural fluid, brain abscess Materials collected from sites not harboring indigenous flora (sterile body fluids, abscess exudate and tissue) should be cultured for anaerobic bacteria. However, since anaerobes normally inhabit the skin and mucus membranes as part of the indigenous flora, specimens such as urine, sputum, and vaginal, eye and ear swabs are not acceptable for culture.

In the optochin (ethylhydrocupreine hydrochloride) susceptibility test, if there is a zone of inhibition of 19-30 mm surrounding the disk following overnight incubation at 37"C, the colony most likely consists of:

pneumococci Optochin susceptibility is used to differentiate S pneumoniae, which are susceptible, from other alpha-hemolytic streptococci, which are resistant.

A 21-year-old patient presents with pharyngitis. A throat swab is collected and submitted for anaerobic culture. This specimen should be:

rejected as unacceptable Many anaerobic bacteria are commensal flora in the oropharynx. Anaerobic bacteria do not cause pharyngitis. The most common cause of pharyngitis is Streptococcus pyogenes. Other causes include Arcanobacterium haemolyticum, Corynebacterium diphtheriae, Neisseria gonorrhoeae and viruses.

A technologist is reading a Gram stain from a CSF and observes many neutrophils and lancet-shaped gram-positive diplococci. Which set of chemistry and hematology CSF results would most likely be seen in someone with this type of infection? CSF results - WBC - Glucose - Protein A - increased - increased - increased B - decreased - decreased - decreased C - increased - decreased - increased D - decreased - increased - decreased

result C The classic CSF alterations associated with bacterial meningitis are a high WBC count with a neutrophil predominance as well as a low CSF glucose and a high CSF 72 protein.

An Enterococcus isolated from multiple blood cultures in a patient endocarditis should be:

screened for high level aminoglycoside resistance Systemic enterococcal infections, such as endocarditis, are commonly treated with a cell-wall-active agent and an aminoglycoside. These agents act synergistically to kill the organism. If the organism is resistant to one or both, there is no synergy, and the combination will fail. It is important to detect aminoglycoside and beta-lactam resistance in these cases. Enterococci have intrinsic moderate level resistance to aminoglycosides. Acquired resistance corresponds to very high MICs (greater than 500 pg/mL) for gentamicin and is termed high level resistance.

When processing throat swabs for a group A Streptococcus culture, the medium of choice is:

sheep blood agar Sheep blood agar is preferred because clear-cut patterns of hemolysis are obtained.

Tests for beta-lactamase production in Haemophilus influenzae:

should be performed on all blood and CSF isolates As many as 20%-40% of H influenzae produce beta-lactamases. Detection of these enzymes should be performed on any isolate considered to be a pathogen using the chromogenic cephalosporin (nitrocefm) test.

A Staphilococcus aureus isolate has an MIC of 4ug/mL to oxacillin. There is uncertainty as to whether this represents an oxacillin (heteroresistant) resistant strain or a hyperproducer of beta-lactamase. Strain - Oxacillin - Amoxicillin-clavulanic acid strand A - Sus - Sus stand B - Sus - Res strand C - Res - Sus strand D - Res - Res Based on the above results for oxacillin and amoxicillin, which strand is heteroresistant?

strand D A Staphylococcus aureus isolate with an MIC of 4 pg/mL is resistant to oxacillin.. As per the Clinical and Laboratory Standards Institute (CLSI) recommendations a heteroresistant strain would be defined as a methicillin (oxacillin) resistant S aureus (MRSA/ORSA). An MRSA/ORSA isolate would be reported as resistant to all beta lactam agents, beta lactam/beta lactamase inhibitor combinations, such as amoxicillin- clavulanic acid, and carbapenems.

Anaerobic susceptibility testing is helpful in the management of patients with:

synovial infections There is evidence that antimicrobial resistance among anaerobic organisms is significant, and that inappropriate therapy correlates with poor patient outcomes. Susceptibility testing is useful when anaerobes are isolated from normally sterile sites such as synovial fluid. Rectal abscesses and pilonidal sinuses are polymicrobial in nature, and often resolved by surgical management.

Salmonella enteritidis is isolated from multiple blood cultures in a patient with fever. Susceptibility results are as follows: ampicillin-susceptible; ceftriaxone-susceptible; ciprofloxacin-susceptible; trimethoprim/sulfamethoxazole-resistant. What is the next best step?

test the isolate against nalidixic acid and if resistant report the ciprofloxacin as resistant Extraintestinal isolates of Salmonella should be tested for resistance to nalidixic acid in addition to fluoroquinolones. Fluoroquinolones susceptible stains of Salmonella that are resistant to nalidixic acid may be associated with clinical failure or delayed response to therapy. In the case where ciprofloxacin is susceptible and nalidixic acid is resistant the nalidixic acid result should be used for reporting.

Susceptibility testing is performed on a Staphylococcus aureus isolate from a blood culture with the following results: oxacillin: resistant cefazolin: susceptible clindamycin: susceptible erythromycin: susceptible trimethoprim/sulfamethoxazole: susceptible vancomycin: susceptible What should the technologist do next?

the cefazolin result should be changed to resistant since the oxacillin result is resistant Oxacillin resistant staphylococci are resistant to all beta-lactam agents, beta-lactam/beta-lactamase inhibitor combinations and carbapenems. Results for these antibiotics should be reported as resistant or should not be reported.

The susceptibility results below are reported on an Enterococcus faecalis isolated from peritoneal fluid. ampicillin: susceptible vancomycin: resistant clindamycin: susceptible levofloxacin: resistant linezolid: susceptible The physician calls questioning the results. Which of the following should have been done before the report was released?

the clindamycin result should have been removed from the report since it is inactive against Enterococcus Enterococcus species may appear active in vitro to clindamycin, cephalosporins and trimethoprim/sulfamethoxazole but are not effective clinically and should not be reported as susceptible.

Susceptibility testing performed on quality control organisms using a new media lot number yielded zone sizes that were too large for all antibiotics tested. The testing was repeated using media from a previously used lot number, and all zone sizes were acceptable. Which of the following best explains the unacceptable zone sizes?

the depth of the media was too thin All Mueller-Hinton agar used for disk diffusion susceptibility testing should be poured to a depth of 4mm. If the depth of the media is <4mm, this may be associated with excessively large zones and false- positive susceptibility results. Agar that is >4mm in depth may cause excessively small zone sizes.

Which of the following is the most important variable in the recovery of organisms in patients with bacteremia?

the volume of blood cultured The volume of blood collected is the single most important variable in the recovery of organisms in patients with bloodstream infections. Since many cases of adult bacteremia are of low magnitude, there is a direct relationship between the yield of blood culture (positivity) and volume of blood collected. The collection of multiple blood culture sets from a single venipuncture is an unacceptable practice due to the potential for contamination. The practice of terminal subculture of blood culture bottles at 5 days is no longer recommended. The use of chlorhexadine for skin antisepsis does not affect organism recovery, but aids in decreasing blood culture contamination.

Vibrio parahaemolyticus can be isolated best from feces on:

thiosulfate citrate bile salts (TCBS) agar TCBS is a highly selective and differential medium for the recovery of most Vibrio species including V parahaemolyticus. Hektoen and Salmonella-Shigella agars are selective and differential for the isolation and differentiation of enteric pathogens such as Salmonella and Shigella. EMB is a selective and differential medium for gram-negative enteric bacilli.

Which of the following factors would make an organism appear to be more resistant on a disk diffusion susceptibility test?

too many organisms in the inoculum To ensure the reproducibility of disk diffusion testing, the inoculum must be standardized. If the inoculum is too dense (too many organisms), zone sizes would be smaller than expected and appear falsely resistant.

Which one of the following specimen requests is acceptable?

urine for culture of acid-fast bacilli Urine is an appropriate specimen for the detection of renal tuberculosis. Since feces contain anaerobic organisms as part of the indigenous flora, it is an unacceptable specimen for anaerobic culture. Foley catheter tips are also not acceptable for culture, because they are contaminated with colonizing organisms. Gram stain smears of rectal swabs for Ngonorrhoeae should also not be performed, since the presence of organisms with similar morphologies may lead to overinterpretation of smears.

The procedure that assures the most accurate detection of mecA-mediated oxacillin resistance in routine broth microdilution susceptibility testing against S aureus is:

use of cefoxitin for testing Cefoxitin is used as a surrogate for mecA-mediated oxacillin resistance in S aureus. S aureus with cefoxitin MICs >4 pg/mL are considered oxacillin resistant. The Clinical Laboratory Standards Institute (CLSI) recommends addition of 2% NaCl, incubation at 35±2°C, and incubation for 24 hours when performing susceptibility testing of S aureus against oxacillin.

When using a control strain of Staphylococcus aureus, the technologist notices that the zone around the oxacillin disk is too small. Which of the following is the most likely explanation?

use of outdated oxacillin disks Deterioration of the antimicrobial agent in the disk will cause the zone sizes to be too small (falsely resistant). Standardization of the inoculum turbidity to less than a 0.5 McFarland standard would result in an inoculum that is too light and resulting zone sizes that are too large. Incubation of the plates at 35°C and inoculating plates within 10 minutes of preparation would not have an adverse effect on zone sizes.

The steam autoclave method of sterilization:

uses 15 lbs of pressure for 15 minutes The traditional gravity displacement steam sterilization cycle is 121°C for 15 minutes at 15 pounds per square inch. Ethylene oxide is an alternative sterilization method.

The ability to detect oxacillin-resistant Staphylococcus aureus may be enhanced by:

using Mueller-Hinton broth with 2% NaCl For optimum detection of oxacillin- resistant S aureus, a suspension with a turbidity equivalent to a 0.5 McFarland standard should be inoculated into a cation- adjusted Mueller-Hinton broth with 2% NaCl. Plates should be incubated at 35 ± 2°C for 24 hours. Temperatures above 35°C may not detect oxacillin resistance.