ASCP Practice Questions Microbiology

A diarrheal stool can be suspected of harboring Vibrio cholerae if it: A. Is well formed and shows blood streaks B. Is soft, dark and positive for occult blood C. Contains a high concentration of segmented neutrophils D. Is watery with a high pH

D; The diarrhea caused by Vibrio cholera is watery and contains large concentrations of sodium, bicarbonate and other electrolytes, producing an alkaline pH. The diarrhea is caused by the action of cholera toxin on the intestinal epithelial cells, with the end result of stimulating adenyl cyclase (cyclic AMP), which in turn inhibits the readsorption of sodium across the brush border membrane and stimulates the excretion of bicarbonate and potassium into the bowel lumen. In the absence of mucosal invasion by the bacteria, blood or neotrophils are not found in the stool specimen.

Match the culture media with possible organism 1. Macconkey agar 2. Lowenstein-Jensen media 3. Thayer-Martin 4. PPLO agar A. Shigella B. Mycobacteria C. Neisseria D. Mycoplasma

1. A 2. B 3. C 4. D Mycobacteria: Lowenstein-Jensen media Shigella: Macconkey agar Mycoplasma: PPLO agar Neisseria: Thayer-Martin media

Nocardia farcinica has been distinguished from other members of the Nocardia asteroides complex because most strains are resistant to erythromycin and other antibiotics commonly used to treat nocardia infections, and are more commonly recovered from patients with severe underlying illness. Characteristics that are helpful in the preliminary identification of this species include: More than 1 answer applies A. The ability to grow at 45°C B. Reduction of nitrates to nitrites C. A white opacity around colonies on Middlebrook agar D. Turning of arylsulfatase media in 2 weeks

A & C; The ability of Nocardia farcinica to grow at 45°C and to develop a white opacification around colonies growing on Middlebrook agar were cited by Carson and Hellyar (J Clin Microbiol 32:2270-2271, 1994) as two of the key characteristics by which this subspecies can be separated from other members of the Nocardia asteroides complex. All members of the Nocardia asteroides complex reduce nitrates; therefore, this is not a differentiating characteristic. The turning of arylsulfatase media in 2 weeks is a distinguishing characteristic for another member of the Nocardia asteroides complex, namely, Nocardia nova (Wallace, et al: J Clin Microbiol 29:2407-2411, 1991).

D; The tiny colonies seen in the upper photograph are surrounded by a narrow zone of beta hemolysis. The lower photomicrograph confirms that the isolate is a streptococcus. The small size of the colonies and the butter scotch odor are clues to the identification of Streptococcus anginosus (S. milleri in the European literature), which characteristically carries the F antigen. S. anginosus is one of the more common isolates from hepatic abscesses, although Group G would be a close contender. The bacterial colonies of the other streptococci listed are considerably larger after 36 hours incubation and the zones of hemolysis are much wider and more distinct.

A 30 year old man with chronic persistent hepatitis developed an abscess in the right hepatic lobe. A needle aspiration revealed purulent material. The small colonies shown in the upper photograph were isolated after 36 hours incubation at 35°C. They emitted a butter scotch odor. The lower photomicrograph reveals the gram stain features. The antigen most likely carried by this isolate is: A. Group A B. Group B C. Group G D. Group F

B; 10^3 colony forming units per milliliter of a gram negative bacillus is the correct answer. There are less than ten colonies so the colony count is 10^3 colony forming units per milliliter. If it was 10^4, there would be more than 10 and less than a hundred colonies. 10^5 colony forming units per milliliter would be 100 or more colonies. It is a gram negative bacillus because it is growing on MacConkey agar. Gram positive cocci and rods are inhibited by the bile salts and crystal violet in MacConkey agar.

A clean catch urine was streaked to a sheep blood agar plate and a MacConkey plate with a one microliter loop. The images below demonstrate what grew. How would you report the colony count and growth? (See next flashcard for MacConkey plate pic) A. 10^4 colony forming units per milliliter of a gram positive bacillus. B. 10^3 colony forming units per milliliter of a gram negative bacillus. C. 10^5 colony forming units per milliliter of a gram positive coccus. D. 10^5 colony forming units per milliliter of a gram negative bacillus.

Exudate from a burn submitted on a swab for bacterial culture grew a gram-negative bacillus that was oxidase-positive, produced an alkaline slant and butt on TSIA, was resistant to numerous antibiotics, and produced a green, water-soluble pigment. This organism would be identified as: The correct answer is highlighted below A. Pseudomonas fluorescens B. Pseudomonas aeruginosa C. Stenotrophomonas maltophilia D. Burkholderia cepacia

B; Pseudomonas aeruginosa is the correct answer. Pseudomonas fluorescens, Stenotrophomonas maltophilia, and Burkholderia cepacia do not produce a green, water-soluble pigment.

from gastric biopsies in which organisms were seen in the tissue sections. He was advised to switch from the Campy BAP selective medium to Skirrow's blood agar because the latter is: A. Free of cephalothin B. Incorporates lysed horse instead of sheep blood C. Free of amphotericin B D. Has reduced concentrations of vancomycin and trimpthoprim

A; Indeed, Helicobacter pylori is highly susceptible to cephalothin and other cephalosporins; therefore, any medium that contains this class of antibiotics will fail in its recovery from clinical specimens. Therefore, switching to a medium such as Skirrow's that is free of cephalothin will solve the recovery problem. H. pylori will grow equally as well in media containing sheep or horse blood, and the presence or absence of amphotericin B has no effect on recovery. The concentrations of vancomycin (10mg/L) and trimethoprim (10ug/mL) are the same in Campy BAP and Skirrow's medium; also, neither of these antibiotics inhibit the growth of H. pylori.

The ends of rod-shaped bacteria may appear: (More than 1 correct answer applies) A. budding B. tapered C. filamentous D. rounded

B & D; When describing rod-shaped bacteria, the terms "rounded ends" or "tapered ends" may help to identify the type of bacteria present. The term budding frequently describes yeast, but not rod-shaped bacteria. Filamentous may describe the appearance of certain bacteria such as Nocardia, but is not used to describe the ends of rod-shaped bacteria.

Each of the following bacterial species are commonly associated with wound infections following a dog bite except: A. Staphylococcus intermedius B. Bordetella bronchicanis C. Pasteurella multicida D. Capnocytophaga cyanodegmi

B; Although the species name of Bordetella bronchicanis (bronchiseptica) indicates an association with dogs ("canis"), the linkage is as an agent or respiratory tract infections in animals (tracheobronchitis or "kennel cough" in dogs, atrophic rhinitis in pigs, pneumonia and otitis media in rabbits and guinea pigs) (Ehrhardt M, et al: Bordetella bronchiseptica: pathogen vs commensal. Clin Microbiol Newslett 8:26-27, 1986). Although humans, particularly those who are immunosurppressed, may acquire B. bronchicanis respiratory infections by contact with dogs, wound infections following dog bites is not part of the clinical spectrum of this organism. In contrast, Staphylococcus intermedius, Pasteurella multicida and Capnocytophaga cyanodegmi are all known to be associated with dog bites, to the point that when one of these species is recovered, either from a wound or a blood culture, an animal source must be presumed.

The end product of the fermentative metabolism that characterizes members of the Enterobacteriaceae is: A. CO2 and water B. Nitrogen gas C. Pyruvic acid D. Various mixed acids

D; Although the fermentation of glucose passes through pyruvic acid as a pivotal compound, the end products of fermentative metabolism are the mixed acids such as acetic, formic, butyric, propionic, etc. The production of these acids is responsible for the conversion of the color of Kligler iron agar (pink to yellow) that is common to all members of the Enterobacteriaceae. CO2 and water are the end products of oxidative metabolism. Nitrogen gas is formed from the complete denitrification of nitrates or nitrites.

Which are true statements regarding hospital-associated methicillin-resistant Staphylococcus aureaus (HA-MRSA) and community-associated MRSA (CA-MRSA)? The correct answer is highlighted below A. Resistance for both strains is conferred by the mecA gene. B. HA strains tend to demonstrate resistance to more drug classes than CA strains. C. CA tends to be associated with the PVL gene and skin and soft tissue infections. D. All of the above.

D; PBP2a, which has a reduced binding affinity for beta-lactams, and remains active in cell wall synthesis even in the presence of beta-lactam antibiotics, is coded by the mecA gene. Both HA and CA strains of MRSA possess the mecA gene, although CA strains typically possess a smaller variant of that gene. CA strains may be susceptible to some antibiotics that HA strains are resistant to. CA strains are also associated with the PVL gene, which code for enzymes that produce tissue necrosis and leukocyte destruction.

B; The development of the red pigment after inoculation with the test organism, as seen with ultraviolet illumination, on the delta aminolevulinic acid paper disk indicates the production of protoporphyrin intermediates. Each of the Haemophilus species listed in this exercise except Haemophilus influenzae, has the capability of synthesizing hemin from the aminoluvulinic acid substrate and therefore is not X factor dependent. Haemophilus influenzae is both V and X-factor dependent; therefore, would not have the capability of producing the fluorescing protoporphyrin intermediates as seen with this disk test.

Look, oh look at the little red dot, Tell me, O tell me, who I am not. A. Haemophilus parainfluenzae B. Haemophilus influenzae C. Haemophilus parahaemolyticus D. Haemophilus aphrophilus

C; Staphylococcus saprophyticus is the correct answer because this organism is resistant to novobiocin. It is a common cause of urinary tract infections in young sexually active females. The other organisms are susceptible to novobiocin and would have a zone of inhibition 16 mm or larger.

This is a catalase-positive, coagulase-negative gram-positive coccus isolated from a urine specimen from a 20-year-old college student. The image below is a Mueller Hinton plate streaked with a 0.5 MacFarland standardized inoculum and a 5 microgram disk of novobiocin after overnight incubation. What is the identification of the isolate? A. Staphylococcus epidermidis B. Staphylococcus aureus C. Staphylococcus saprophyticus D. Staphylococcus lugdenensis

A; Notice in the photograph the somewhat pinkish iridescence of the colonies growing MacConkey agar. This is characteristic of the nonfermenter Acinetobacter baumannii, which has emerged as one of the most frequent causes of hospital acquired pneumonia. Moraxella catarrhalis is both a diplococcus that can appear similar to Acinetobacter baumannii in gram stains and can cause respiratory infections in patients with chronic obstructive pulmonary disease or chronic bronchitis. However, the organism does not grow on MacConkey agar and the infections are usually not considered to be hospital acquired. Neisseria lactamica is a gram negative diplococcus and will not grow on MacConkey agar. Burkholderia cepacia can cause pulmonary infections, particularly in patients with cystic fibrosis; however, the organism is a bacillus and not a coccobacillus and does not produce the pinkish iridescence when grown on MacConkey agar.

a common cause of nosocomial hospital acquired pneumonia, can be presumptively identified as: A. Acinetobacter baumannii B. Burkholderia cepacia C. Moraxella catarrhalis D. Neisseria lactamica

Match the names of each of the Staphylococcus species with A if it can produce acid from mannitol and with B if it is mannitol negative. 1. Staphylococcus aureus 2. Staphylococcus saprophyticus 3. Staphylococcus epidermidis 4. Staphylococcus xylosus

1. A 2. B 3. B 4. A Mannitol salt agar was formerly used as a selective media for recovering Staphylococcus aureus from specimens contaminated with mixed bacteria. It grows well in the presence of salt and develops yellow colonies from the production of acid from mannitol. The large majority of strains of other staphylococci, such as S. saprophyticus and S. epidermidis, do not produce acid from mannitol and appear as white colonies on mannitol salt agar. However, as numerous additional coagulase negative staphylococci were discovered, many other species, including S. xylosus, were also found to be mannitol positive. Therefore, this medium no longer as the selectivity of former times.

The Quellung test is useful for which of the following : A. Differentiate between Staphylococcus and Streptococcus B. Serological typing of Streptococcus pneumoniae C. Isolation of various strains of Staphylococcus D. Isolation of various strains of Streptococcus

B; Capsular swelling results from the addition of specific capsular antibody to an isolate of the organism. This test is generally not required for routine diagnosis.

An unknown isolate has been inoculated to two agar plates on which either a CAMP test ( A) or an optochin disk test (B) has been performed. Match each of the conditions listed with A or B depending upon which positive test the bacterial species recovered would be most likely associated. 1. Meningitis in the newborn 2. Adult meningitis 3. Neonatal sepsis 4. Otitis media 5. Community acquired pneumonia A. CAMP test B. Optochin disk test

1. A 2. B 3. A 4. B 5. B The positive CAMP test identifies this isolate as Streptococcus agalactiae (Group B); the positive sensitive optochin disk test identifies this isolate as Streptococcus pneumoniae. Streptococcus agalactiae primarily causes infections in neonates, contracted primarily from the mother's vaginal canal during parturition. Therefore, in this exercise, meningitis in the newborn and neonatal sepsis are correct. Streptococcus pneumoniae is more likely to cause infections in older children and adults, of which meningitis, otitis media and community acquired pneumonia are the more likely associations within the context of this exercise.

The bacterial species commonly causing bronchopneumonia in foals, that can cause a slowly progressive tuberculosis-like pulmonary infection in humans is: The correct answer is highlighted below A. Nocardia asteroides B. Streptococcus equi C. Rhodococcus equi D. Moraxella catarrhalis

C; Rhodococcus equi is a "diphtheroidal-like" gram positive bacillus that causes bronchopneumonia in foals and other farm animals. Human pulmonary infections are acquired via inhalation of soil-infected dust or dander from infected animals. The disease in humans is more slowly progressive and may mimic tuberculosis, on occasion progressing to cavitary lesions (Van Etta, et al: Rev infect dis D:1012-1018, 1983). Persons with immunosuppression (including AIDS), or with lymphomas are most susceptible. Nocardia asteroides can cause tuberculosis-like pulmonary infections in humans, but is not associated with bronchopneumonia in foals. Streptococcus equi causes a mucopurulent discharge of the upper respiratory tract in horses, a disease called strangles. These group C streptococci may cause acute pharyngitis in humans, but only rarely causes acute pneumonia. Moraxella catarrhalis may be associated with chronic bronchitis in humans, but does not cause pulmonary infections in horses or other animals.

C; The structure that is indicated by the arrow is a pseudohyphae. Pseudohyphae are made up of multiple buds of yeast that do not detach, thereby forming chains. The organism that was identified was Candida albicans.

This Gram stain was prepared from a sputum specimen and is viewed under oil immersion (1000X). What is the structure that is indicated by the arrow? A. Epithelial cell B. Gram-positive streptococci C. Pseudohyphae/yeast D. Artifact

Match the names or the organisms listed with the bucket indicating whether each is cryophlic (can grow as low as 4°C) or is themophilic (grows at temperatures of 42°C or higher). 1. Campylobacter jejuni 2. Yersinia enterocolitica 3. Listeria monocytogenes 4. Pseudomonas aeruginosa A. Thermophylic B. Cryophilic

1. A 2. B 3. B 4. A Of the bacterial species listed in this exercise, Listeria monocytogenes and Yersinia enterocolitica are cryophilic and can grow at refrigerator temperatures. This is one important implication in that these two organisms are possible infective agents in cases of transfusion related septicemia as the organisms can survive and replicate at the storage temperature of blood products. Pseudomonas aeruginosa and Campylobacter jejuni have the property that they can grow at 42°C, the latter optimally at the higher temperature requiring a separate incubator if recovery from clinical specimens is to be maximized.

The ability of streptococci to spread within the tissues and cause rapidly advancing cellulitis is due to the production of several virulence factors. Match each of the virulence factors with its specific manifestation. 1. Streptokinase 2. Streptolysin S 3. Pyrogenic exotoxins 4. Hyaluronidase A. Hydrolysis of fibrin clots B. Depolymerization of ground substance in connective tissue C. Leucotoxic killing of phagocytes D. Scarlet fever rash

1. A 2. C 3. D 4. B The "spreading factors" produced by streptococci include hyaluronidase, which depolymerizes the ground substance of the connective tissue removing any barriers to the spread of the bacterial cells; and, streptokinase, which hydrolyzes any clots that may hinder spread. Streptolysin S is toxic to many cell types, including neutrophils and mononuclear phagocytes, allowing uninhibited proliferation of the bacterial cells.

Please match the names of each of the infectious diseases humans may incur from the animals that can transmit the disease. 1. Cats 2. Pigs 3. Rabbits 4. Chicken A. Brucellosis B. Pasteurellosis C. Salmonellosis D. Tularemia

1. B 2. A 3. D 4. C Infected chicken meat is a common source for Salmonella species. Rabbits can transmit tularemia. Infected cats are able to transmit Pasteurella multocida (found in the oropharynx). Finally, pigs have been implicated in the transmission of Brucella spp.

From the list of bacterial species, match each with the name of the test that would be most helpful in making a species identification. Your answers are on the left. The correct answers are on the right and highlighted. 1. Mycobacterium tuberculosis 2. Streptococcus pneumoniae 3. Providencia stuartii 4. Campylobacter jejuni A. Optochin B. Niacin accumulation C. Indoxyl acetate D. Phenylalanine deaminase

1. B 2. A 3. D 4. C Optochin is ethyl hydrocupreine hydrochloride, a compound to which Streptococcus pneumoniae is susceptible, in contrast to viridans streptococci and alpha hemolytic group D. Streptococci that are resistant. The ability to hydrolyze indoxyl acetate is a helpful identifying characteristic for Campylobacter jejuni and certain other Campylobacter species, separating them from Helicobacter species, all of which are incapable of hydrolyzing this compound. Niacin accumulation historically has been a helpful characteristic in the identification of Mycobacterium tuberculosis; however, currently, this species is most commonly identified by nucleic acid probe assays. Phenylalanine deaminase is a key characteristic in the identification of Proteus and Providencia species.

Match each of the activities listed with the name of the most likely bacterial agent that would cause an associated infection. 1. Incurring a deep cat scratch 2. Ingestion of unpasteurized milk 3. Stepping on a rusty nail 4. Skinning small game A. Listeria monocytogenes B. Clostridium tetani C. Pasteurella multocida D. Erysipelothrix rhusiopathiae

1. C 2. A 3. B 4. D Listeria monocytogenes is a bacterial species that is widespread in nature, not uncommonly infecting cattle and goats that forage in open fields. The organisms concentrate in the animal milk and can be transmitted to humans who ingest unpasteurized milk. Erysipelothrix is an infection caused by Erysipelothrix rusiopathiae, a bacterium that causes septicemia and arthritis in swine, calves, lambs, other farm animals and wild small game. Humans most commonly incur a skin infection (usually of the hands or fingers), upon direct contact with infected animal tissue. Hunters and veterinarians, who often handle potentially infected animals, are particularly vulnerable to incurring cutaneous infections, particularly if they have open abrasions, scratches or open punctures of the skin. Pasteurella maltocida is a prevalent bacterial species inhabiting the oropharynx of cats and dogs. Humans can become infected through bites or scratches of these animals, particularly from the scratches of cats that habitually preen themselves with their own salivary secretions.

The red ring at the top of the media in this tube indicates a positive indole reaction. The precursor substance in the medium from which the indole is produced is: A. Tryptophan B. p-dimethylaminobenzaldehyde C. Pyruvic acid D. Peptone

A; Indole, along with pyruvic acid and ammonia, are the chemical products resulting from the deamination of the amino acid tryptophan, under the action of the enzyme tryptophanase, produced by indole-positive bacterial species. P-dimethylaminobenzaldehyde is the reagent added to the incubated media to detect the presence of indole. As stated above, pyruvate is one of the byproducts along with indole in the deamination of tryptophan. Peptone is added to the medium as an enrichment for bacterial growth. Indirectly, if the peptone contains large quantities of tryptophan, it could serve as a source of indole production. Nevertheless, the intended answer here is tryptophan.

A; Bacteroides fragilis is the anaerobe most commonly recovered from human infections, particularly those that occur "below the diaphragm". It is commonly associated with parappendiceal abscesses. The organism grows readily on anaerobic blood agar in an anaerobic atmosphere and produces small, gram negative bacilli with rounded ends, as seen in the upper photograph. Characteristic of the genus is the ability to grow in 20% bile and to hydrolyze esculin (shown by the growth in the bile quadrant and black pigment in the esculin quadrant in the lower photograph), two key characteristics that separate the B. fragilis group from Prevotella species and Porphyromonas species, which are negative for both. Fusobacterium nucleatum can also be associated with intra abdominal cavity abscesses; however, the bacterial cells are slender and tapered and growth is inhibited by 20% bile, esculin is not produced but the indole reaction is positive.

An eleven year old boy developed signs and symptoms of acute appendicitis. At surgery, the appendix was found to be ruptured and encased in a 3 cm in diameter abscess. Aspiration material was inoculated to an anaerobic blood agar plate. Small, gray, nonhemolytic, semiopaque colonies grew anaerobically in 36 hours. The upper photograph illustrates the gram stain features of the organism; the lower photograph is a Presumpto plate indicating the biochemical reactions (reading clockwise from the 12 o'clock quadrant): growth in 20% bile agar, indole negative, esculin hydrolysis positive and lecithinase negative. The bacterial species most likely associated with the abscess is: The correct answer is highlighted below A. Bacteroides fragilis B. Fusobacterium nucleatum C. Porphyromonas asaccharolytica D. Prevotella intermedia

C; On return of the German Cholera Commission from India in April, 1884 after a successful mission that uncovered the bacterial cause of cholera, Robert Koch was received by the Kaiser and awarded a metal by Chancellor von Bismark. Although Pasteur and his assistant Emile Roux had attempted to discover the cause of cholera during the French Expedition in Egypt the year before, the sudden death of Thuillier from cholera ended an unsuccessful campaign. Max von Pettenkofer, a Munich hygienist who avidly believed that cholera was caused by soil contact, almost died after ingesting a cholera-infected water cocktail, trying to prove his point that water was not incriminated.

Anthrax, tuberculosis, and cholera, Years and years of toil and bother, Royal reception by the Chancellor, Forever acclaimed the "Bacillus Father". A. Louis Pasteur B. Emile Roux C. Robert Koch D. Max von Pettenkofer

If a blood agar plate and an EMB plate are both inoculated with 0.001 ml of urine, and 90 colonies of Staph aureus grew on the blood agar plate, what should be reported? Choose the single best answer A. 90 colony forming units/mL of Staphylococci aureus B. 90,000 colony forming units/mL of Staphylococci aureus C. 9,000 colony forming units/mL of Staphylococci aureus D. 9 colony forming units/mL of Staphylococci aureus

B; 90,000 colony forming units/mL of Staphylococci aureus should be reported. Calculate the number of bacteria in the urine sample by multiplying the colony count X the dilution of the calibrated loop (1/1000). If there are 90 colonies on the EMB, 90 X 1000 dilution = 90,000 colony forming units/ml of urine.

A,B,C, & D; The beta hemolytic streptococci most commonly recovered from clinical specimens fall in to the Lancefield groups A, B, C, and G. Of the answers listed, all would be helpful in making a presumptive identification. Streptococci are catalase negative while the Staphylococci are catalase positive - helpful in establishing a genus identification. Group A streptococci are PYR Positive, susceptible to low concentrations of bacitracin ("A" disk) and, along with Group B streptococci, are resistant to SXT. The specific group antigen can be demonstrated by follow-up serological tests.

Beta hemolytic colonies grew from the blood culture bottle after 18 hours incubation (see image). Which of following tests would be helpful in making a preliminary identification? (Choose all that apply) A. PYR B. Catalase C. Bacitracin susceptibility D. SXT susceptibility

A human spirochetal disease associated with contact with rats is: A. Lyme disease B. Relapsing fever C. Leptospirosis D. Syphilis

C; Although human infections of leptospirosis have classically been associated with contact with rats, particularly soil, water and materials soiled with rat urine, other domestic animals may be infected as well. Spirilum minor is another spirochete that also is carried by rats, and humans become infected primarily from rat bites. Lyme disease, caused by the spirochete Borellia bergdorferi, is transmitted to humans from the bite of infected Ixodes ticks. Human relapsing fever may be louse-borne or tick-borne. Louse-borne relapsing fever is caused by the spirochete, Borellia recurrentis, transmitted by the human louse, Pediculus humanus. Tick-borne relapsing fever is caused by Borellia hermsii, carried by the tick vector Ornithidorus hermsii. Trepenoma pallidum, the agent of syphilis, is strictly a human pathogen not affecting animals.

An abdominal wound culture grows E. coli on the aerobic culture. The anaerobic culture has growth of two gram negative rods, one of which is aerobic. The other gram negative rod has 2+ growth on BBE plate and is resistant to Kanamycin, Colistin, and Vancomycin disc. This organism can be identified as: A. Veillonella B. Prevotella fragilis C. Bacteroides fragilis group D. Fusobacterium necrophorum

C; Bacteroides Bile Esculin Agar (BBE) is an enriched selective and differential medium for the isolation and presumptive identification of obligately anaerobic gram-negative bacilli of the Bacteroides fragilis group. BBE contains gentamicin at a concentration which inhibits most facultative anaerobes. With a few exceptions, Bacteroides species are resistant to kanamycin and vancomycin and show variable susceptibility to colistin.

Different species of Neisseria can be differentiated from each other by: A. Oxidase test B. Catalase test C. Carbohydrate utilization D. Nitrate test

C; Carbohydrate utilization tests are usually employed to identify various Neisseria sp.

Which of the following media contains the X and V factors necessary for the growth of Haemophilus influenzae: A. MacConkeys agar B. Sheep blood agar C. Chocolate agar D. Brain-heart infusion agar

C; Chocolate agar contains both the X factor (hemin) and V factor (coenzyme nicotine adenine dinucleotide) which are necessary for growth of H. influenzae. It is prepared by adding sheep blood to agar at 80o C to lyse the red cells.

Which of the following fungal infections is endemic in the southwestern US desert regions? The correct answer is highlighted below A. Histoplasmosis B. Blastomycosis C. Coccidioidomycosis D. Sporotrichosis

C; Coccidioidomycosis is strictly endemic in the southwestern US desert regions. The geographic distribution of blastomycosis in the United States tends to be centered more in the upper Mississippi river drainage system and adjacent tributaries. Histoplasmosis is more concentrated in the lower Mississippi river valley and adjacent tributaries and, sporotrichosis has a broad geographic distribution, sparing only the higher western mountainous regions.

Which of the following would be the most appropriate temperature for long term storage of viral cultures: The correct answer is highlighted below A. 4° C B. -20° C C. -70° C D. Room temperature

C; Cultures can be stored at either -20° or -70°, but -70° is preferred for long term storage.

As a gram positive coccus I've become a bit fancy, Short chains and motile, plus I carry the gene VanC. A. Enterococcus faecium B. Staphylococcus aureus C. Enterococcus cassiloflavus D. Streptococcus pneumoniae

C; Enterococcus cassiloflavus is unique among the gram positive cocci (except for E. gallinarum which has similar properties) of being motile and carrying an intrinsic chromosomal mutation gene called Van C that confers low grade resistance to vancomycin. In contrast, many strains of Enterococcus faecium have high level vancomycin resistance through expression of an inducible, transposon-mediated gene, called Van A. Resistance to vancomycin has not developed with Staphylococcus aureus; rather, many strains have become methicillin resistant through expression of a gene called MecA. Many strains of Streptococcus pneumoniae have developed penicillin resistance via the alteration of penicillin binding proteins, a mechanism similar to the ampicillin resistance expressed by many strains of Enterococcus species.

In order to speciate a swarming Proteus organism found on an eosin methylene blue agar plate, the BEST approach would be to: A. inoculate to a 4% agar plate and subculture to McConkey's B. determine motility and lysine decarboxylase activity C. determine Indole production, phenylalanine and urease activity D. determine utilization of sodium acetate and citrate E. inoculate a tube of thioglycolate broth

C; In order to speciate a swarming Proteus mirabilis organism found on an eosin methylene blue agar plate, the BEST approach would be to determine Indole production, phenylalanine and urease activity. P. mirablis is strongly urease and phenylalanine positive. P. mirabilis is usually indole-negative- which is helpful to differentiate this organism from P. vulgaris which is indole-positive.

The cytochrome oxidase-positive bacterial species that is DNAse negative, ornithine positive, and is associated with gastroenteritis in children is most likely: A. Aeromonas hydrophila B. Aeromonas sobria C. Plesiomonas shigelloides D. Shigella sonnei

C; The genus name plesiomonas is derived from the Greek word meaning "neighbor", indicating a close association with Aeromonas species. However, both A. hydrophyla and A. sobria produce DNAse and do not hydrolyze ornithine, two key characteristics by which they are separated from Plesiomonas shigelloides. The latter species also is more likely than Aeromonas species to cause gastroenteritis in children (McNeeley, et al: Plesiomonas: Biology of the organism and diseases in children. Pediatr Infect Dis 3:176-181, 1984), following ingestion of contaminated water or unwashed vegetables. Shigella sonnei can cause gastroenteritis in children; however, it is cytochrome oxidase negative and belongs to the Family Enterobacteriaceae.

c Illustrated in the photograph are colonies that are distinctly pitting the agar surface. This property, in conjunction with the detection of a bleach-like odor, provides a presumptive identification of Eikenella corrodens. E. corrodens skin infections are almost always related to human bites, in contrast to infections with Capnocytophaga canimorsus, which are related to dog bites. In addition, the colonies of C. canimorsus show and "gliding motility" rather than the pitting seen here. Although the colonies of Moraxella lacunata (as the species name indicates) may pit the surface of agar, they do not have a bleach odor and would be extremely rarely associated with wound infections. Although Haemophilus aphrophilus can cause wound infections, the colonies do not pit the agar nor do they have a bleach odor.

Illustrated in this photograph are colonies growing on the surface of a chocolate agar plate. The colonies were recovered from a subcutaneous infection of the forearm and had a bleach odor. The most likely identification is: Choose the single best answer a. Moraxella lacunata b. Haemophilus aphrophilus c. Eikenella corrodens d. Capnocytophaga canimorsus

B; Of the Mycobacterium species listed in this exercise, M. kansasii and M. marinum are the two photochromogens, fitting the description of the colonies included in the question. Of these, M. marinum would not grow at 35°C; therefore, the intended answer in this exercise is M. kansasii. M. tuberculosis is neither a photochromogen nor scotochromogen, producing only buff-pigmented colonies no matter what the light exposure. M. gordonae is a scotochromogen, and produces yellow-pigmented colonies, both in the presence and in the absence of light.

Illustrated in this photograph are two Middlebrook 7H-11 plates incubated at 35°C, on which are growing colonies of an unknown Mycobacterium species. The plate on the left was incubated in the dark; the plate on the right had been exposed to light for 24 hours. The most likely identification is: The correct answer is highlighted below A. Mycobacterium gordonae B. Mycobacterium kansasii C. Mycobacterium tuberculosis D. Mycobacterium marinum

A; The zone of growth inhibition around the bacitracin (left) disk is presumptive evidence for a beta hemolytic streptococcus, group A. It should be remembered that approximately 10% of group C and group G streptococci may produce narrow zones of hemolysis around the bacitracin (left) disk; however, each of these species is also susceptible to SXT (right). Occasional strains of group B streptococci may also be susceptible to bacitracin and they also are resistant to bacitracin; however, it would be an extremely rare isolate from throat cultures. Therefore, the reactions shown in this photograph along with the site of recovery allows the most likely report of, "beta-hemolytic streptococcus, presumptive group A by bacitracin."

Illustrated in this photograph is a blood agar plate inoculated with a beta hemolytic streptococcus obtained from a throat culture of a patient with acute pharyngitis. A 0.04ug bacitracin (left) disk and a SXT disk (right) had been placed in the areas of streaking. The reactions observed allow the most likely presumptive identification of a streptococcus belonging to Lancefield group: A. Group A B. Group B C. Group C D. Group G

D; One of the most important discoveries in microbiology during the past decade has been the identification of Helicobacter pylori as a major cause of peptic ulcer disease. This organism, initially called Campylobacter pyloridis, is found only in the mucus-secreting epithelial cells of the stomach. The organism can survive in the environment of inhospitably low pH of the gastric mucosa through extremely active urease production, surrounding itself in a cloud of neutralizing ammonium ions. Salmonella typhi does cause ulcerative bowel disease; however, the ulcers are in the colon due to break down of the infected lymphoid tissue in Pyers patches. Yersinia paratuberculosis also causes invasive enteritis of the colon, although mucosal ulceration is less common, with granulomatous inflammation of the lamina propria and adjacent mesenteric lymph nodes being the more common manifestation. Campylobacter hyointestinalis is also primarily a pathogen of the lower ileum and colon, where it causes an invasive enteritis similar to that caused by Campylobacter jejuni.

Illustrated in this photograph is an H & E-stained section of a gastric biopsy obtained from a patient with suspected peptic ulcer disease. Based on the biopsy findings, the bacterial species that would most likely be recovered is: A. Salmonella typhi B. Campylobacter hyointestinalis C. Yersinia paratuberculosis D. Helicobacter pylori

C; The bacterial species that best fits the four positive reactions of the characteristics shown here is Klebsiella oxytoca. The partial or weak urease reaction (slant only) in particular is in keeping with the genus Klebsiella, although some Enterobacter species may show a similar reaction. In this exercise, however, Enterobacter cloacae is ruled out because none of the species produce indole. K. oxytoca is the only Klebsiella species that is indole positive. Salmonella typhimurium does not produce indole and is urease inactive; Citrobacter koseri is VP negative.

Illustrated in this photograph, reading from left to right, are biochemical reactions for indole, Voges Proskauer, Simmons citrate and Christensen's urea. The bacterial species providing the best fit for the reactions illustrated is: A. Salmonella typhimurium B. Citrobacter koseri C. Klebsiella oxytoca D. Enterobacter cloacae

See previous

See previous

D; The white, opaque, entire colonies seen in the blood agar plate is most consistent with a Staphylococcus species, supported by the loose clustering of the gram-positive bacterial cells seen in the photomicrograph. Note in the photomicrograph that the bacterial cells are relatively small and have a distinct tendency to form tetrads. This picture is more consistent with a coagulase negative Staphylococcus species, rather than Staphylococcus aureus, making a primary wound source less likely. Septicemias caused by coagulase-negative staphylococci are more likely to be related to infected indwelling catheters than any other source.

The bacterial species shown on the blood agar plate and illustrated in the photomicrograph was recovered from a blood culture of a patient with fever. The most likely source of infection is: (See next picture) A. The urinary tract B. The respiratory tract C. An indwelling catheter D. Cutaneous wound

A & C; Eikenella corrodens is part of the normal flora of the upper respiratory tract of humans. Infections commonly occur when human saliva of one individual is introduced into the subcutaneous tissue of another, either directly from human bites or other forms of trauma such as occurs in bare knuckle fist fights ("clenched fist" infections). Intravenous drug users, who habitually lick the needle before insertion ("skin popping"), also have a high incidence of cellulitis from E. corrodens. Juvenile periodontitis is more commonly caused by another member of the HACEK group of fastidious gram negative bacilli, Actinobacillus actinomycetemcomefans; or, by Capnocytophaga species. E. corrodens does not reside in the oropharynx of dogs; therefore, is not related to infections caused by dog bites.

The fastidious gram negative bacillus, often producing pitting of the agar around the colonies growing on blood agar, as illustrated in this photograph, producing a bleach-like odor is most commonly associated with one or more of the following conditions: More than 1 answer applies A. "Clenched fist" infection of the hand B. Juvenile periodontitis C. "Skin-popping" cellulitis D. Dog bite cellulitis

B; Enterobacter aerogenes ferments lactose, is motile, does not produce indole and is both VP and citrate positive, consistent with the reactions seen here. C. freundii produces similar reactions except 100% of strains are VP negative. K. pneumoniae also produces similar reactions, but can be ruled out because all strains are non motile. Proteus mirabilis fits the pattern of reactions shown here, except it is a non fermenter and would produce an alkaline slant/acid deep reaction on KIA.

The reactions seen in the tubes presented in this photograph reveals a motile, gas producing, lactose fermenter that produces acetyl methyl carbinol in VP broth and utilizes sodium citrate as the sole source of carbon. The most likely identification is: The correct answer is highlighted below A. Citrobacter freundii B. Enterobacter aerogenes C. Klebsiella pneumoniae D. Proteus mirabilis

1. A 2. B 3. C 4. D The most common cause of acute pharyngitis is the group A, beta hemolytic streptococcus, definitively identified by demonstrating a zone of growth inhibition around the 0.04ug bacitracin ("A") disk, shown in Frame C. Of the responses listed, neonatal meningitis would most likely be caused by the group B, beta hemolytic streptococci (S. agalactiae), identified by the production of the arrowhead-shaped zone of hemolysis (CAMP reaction) shown in Frame A. Enterococcus species is a common cause of urinary tract infection, with this species being identified by its ability to produce PYR (Frame D, red pigment in upper left quadrant) and to hydrolyze esculin, as demonstrated by the production of a diffuse black pigment when grown on esculin containing agar (Frame D, lower quadrant). Streptococcus pneumoniae is one of the common causes of lobar pneumonia, the definitive laboratory identification of which is made by demonstrating susceptibility to ethyl hydrocupreine hydrochloride (Optochin) as shown by the zone of growth inhibition around the "P" disk demonstrated in Frame B.

The streptococci and related organisms can cause a variety of infections. Match each of the clinical manifestations of streptococcal diseases listed with the corresponding photograph that illustrates the identifying characteristic of the associated bacterial agent for each. 1. Neonatal meningitis 2. Lobar pneumonia 3. Acute pharyngitis 4. Acute cystitis

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

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

A; Salmonella spp. is the correct answer because the isolate is a non-lactose and sucrose fermenter on TSIA, positive for H2S, lysine decarboxylase positive, urea negative, citrate positive, phenylalanine deamination negative, indole negative, and ornithine positive. Shigella would be H2S negative, lysine negative, urea negative, citrate negative, phenylalanine negative, and nonmotile. Proteus vulgaris would not decarboxylase lysine and ornithine, and is citrate negative, phenylalanine positive, and produce indole. Citrobacter freundii would usually ferment lactose or sucrose, not decarboxylase lysine, and would be phenylalanine and indole negative.

This member of the Enterobacteriaceae is shown on triple sugar iron agar, lysine iron agar, urea agar, citrate agar , phenylanine deaminase agar, and motility indole ornithine agar. It should be identified as: The correct answer is highlighted below A. Salmonella spp. B. Shigella spp. C. Proteus vulgaris D. Citrobacter freundii

C; This organism is a Plasmodium ring form. Note that this form consists of a "ring" of cytoplasm that is connected by a chromatin dot. Plasmodium species are the only parasites listed that actually invade unsuspecting red blood cells.

This parasite is found in blood. A. Plasmodium schizont B. Leishmania amastigote C. Plasmodium ring form D. Trypanosoma promastigote