MICROBIOLOGY

Which of the following Mycobacterium species is associated closely with HIV/AIDS patient infections? A. M. ulcerans B. M. avium-intracellulare complex C. M. gordonae D. M. bovis

B. M. avium-intracellulare complex Feedback The Mycobacterium avium-intracellulare complex is closely associated with infections in immunocompromised HIV/AIDS patients. Infections in this population with M. avium-intracellulare complex can be fatal.

The stool specimen from a patient admitted to the hospital with symptoms of appendicitis has a culture with the following characteristics: Gram-negative bacillus Catalase positive Urease positive Weakly fermentative TSI Slant is A/A These reactions suggest that the organism is MOST likely: A. Yersinia enterocolitica B. Escherichia coli C. Plesiomonas shigelloides D. Pasteurella multocida

A. Yersinia enterocolitica Feedback Considering the reactions given in this case study, Yersinia enterocolitica would be the best choice. Most strains of Plesiomonas shigelloides, Escherichia coli, and Pasteurella multocida are urease negative. Also, Plesiomonas shigelloides demonstrates a K/A reaction on a TSI slant.

The colonies shown in the blood (BAP) agar (upper) and MacConkey (MAC) agar (lower) biplate are a 24 hour growth from an aerobic blood culture bottle that became positive at 12 hours after inoculation. The appearance of the colonies on MAC agar rules out the following two bacterial species: A. Pseudomonas aeruginosa B. Klebsiella pneumoniae C. Streptococcus pneumoniae D. Escherichia coli

B. Klebsiella pneumoniae D. Escherichia coli Feedback Although Pseudomonas aeruginosa may produce mucoid colonies on MAC agar, it does not ferment lactose, which is evident from the pink pigmentation of the colonies. S. pneumoniae colonies may be mucoid, but cannot grow in the presence of the bile salts and the crystal violet dye contained in MAC agar. Both K. pneumoniae and E. coli can produce mucoid, lactose fermenting colonies on MAC agar. The colonies of E. coli, however, tend to be dry and the surrounding medium also tends to turn pink or red from strong lactose fermentation. Thus, the colonies seen here are most consitent with K. pneumoniae.

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

D. Cysteine-blood agar Feedback Although cysteine-blood agar was traditionally used, F. tularensis will also grow on commercially available Thayer-Martin and chocolate agar which have been enriched with supplemental nutrients.

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

D. MHA; direct colony suspension; 35oC; cefoxitin disk; 24 hour incubation Feedback Mueller-Hinton agar is the standard medium for Kirby Bauer testing on Staphylococcus isolates. The direct colony suspension method, utilizing a 0.5 McFarland standard, should be used to prepare the inoculum. A full 24-hour incubation is required. A 30 µg cefoxitin disk is recommended to detect mecA mediated resistance. Incubation above 35°C may not allow for the detection of resistance.

Adult Ascaris lumbricoides worms live in the: A. Lungs B. Liver C. Small Intestines D. Large Intestines

C. Small Intestines Feedback Although the larval form of Ascaris migrates through the lung, where it can cause Loeffler's syndrome, the mature form lives in the duodenum or proximal jejunum within the small intestines. The adults are very large worms, and can measure up to 35 cm in length.

What effect may bacterial contamination have on urine pH? The bacteria may make the pH more alkaline. The bacteria may make the pH more acidic. The bacteria would not affect urine pH.

The bacteria may make the pH more alkaline. Feedback A urine pH above 8.0 may indicate that a specimen has been held unpreserved too long, which allows multiplication of urea-splitting bacteria with resultant increase in pH.

The media used to isolate Legionella pneumophilia should contain which of the following additives? X and V factors Hemin and vitamin K Charcoal and yeast extract Dextrose and laked blood Lactose and vitamin E

Charcoal and yeast extract Feedback When yeast extract and activated charcoal are added into Feeley Gorman (F-G) agar, the components enhanced the ability to support the growth of Legionella spp. Yeast extract serves as the protein source. Activated charcoal decomposes hydrogen peroxide and other toxic products to allow for a better yield of Legionella spp. growth.

A decrease in which of the following in AIDS patients results in increased susceptibility to infection: A. CD 4+ cells B. CD 8+ cells C. HIV antibodies D. HIV antigens

A. CD 4+ cells Feedback It is the CD 4+ cells that help aid our immune system in attacking foreign antigens by initiating the body's response. CD 8+ also help in the role of immunity by attaching to infected cells to initiate cell destruction. A decrease in HIV antibodies would not leave the host more suseptible to infection since the antibody is directed at the HIV virus only. Finally, a decrease in HIV antigens will also not cause a host to become more suseptible to infections.

The protein component that surrounds the genome is called a: A. Capsid B. Spike C. Co-receptor D. Syncytia

A. Capsid Feedback The protein component that surrounds the genome is called a capsid.

An aerobic gram negative coccobacillus was isolated from a nasopharyngeal swab 48 hours after culture from a 6 month old with the following culture characteristics on Bordet-Gengou agar: Small zones of beta-hemolysis Urease: positive Oxidase: negative Motility: negative The MOST probable identification of this isolate is: A. Pasteurella multocida B. Bordetella pertussis C. Bordetella parapertussis D. Bordetella bronchiseptica

Bordetella parapertussis Feedback The clinical and laboratory findings most closely match that of a Bordetella species; particularly a Bordatella parapertussis infection. Bordetella pertussis is oxidase positive but urease negative, while B. parapertussis is oxidase negative and urease positive. B. bronchosepticus is positive for both enzymes.

A recto-sigmoidoscopy revealed pseudomembranes in a patient with severe diarrhea following prolonged treatment with ampicillin. Which of the following organisms is MOST likely to be isolated? A. Bacteroides fragilis B. Clostridium botulinum C. Clostridium difficile D. Fusobacterium nucleatum E. Klebsiella oxytoca

C. Clostridium difficile Feedback Clostridium difficile is a gram-positive, anaerobic, spore-forming bacillus that produces a strong toxin. C difficile is a common cause of antibiotic-associated diarrhea and pseudomembranous colitis.

A definitive diagnosis of malaria can be made by: A. Serological testing B. Culture techniques C. Demonstration of the organisms in peripheral blood D. Biochemical reactions

C. Demonstration of the organisms in peripheral blood Feedback Diagnosis of malaria may require thick smears as well as conventional thin blood smears.

Which one of the following is the INCORRECT match between organism and the appropriate diagnostic procedure? A. Trichinella spiralis - serologic testing B. Cryptosporidium - modified acid-fast stain C. Echinococcus granulosus - routine ova and parasite examination D. Schistosoma haematobium - examination of urine sediment E. Mycobacterium tuberculosis - acid fast stain

C. Echinococcus granulosus - routine ova and parasite examination Feedback Since Echinococcus granulosus tends to form cysts in lung or liver tissue, diagnosis usually requires ultrasound, CT, or MRI to detect the location of one or more brood cysts. Diagnosis can also be confirmed by examining cyst tissue or contents for evidence of the parasite. Finally, diagnosis can also be made through serologic exam or skin testing.

Which one of the following statements is false? A. Rickettsial infections are usually best diagnosed by specific serology, rather than the Weil-Felix test B. Ehrlichiosis is transmitted by the lonestar tick C. Rickettsia rickettsii causes Rocky mountain spotted fever D. Rocky mountain spotted fever is almost always geographically restricted to the Rocky mountain region

D. Rocky mountain spotted fever is almost always geographically restricted to the Rocky mountain region Feedback The last choice in this question is false. Rocky mountain spotted fever is NOT geographically restricted to the Rocky mountain region. In fact, according to the CDC, this disease is widely distributed east of the Rocky Mountains and also occurs in limited areas on the Pacific Coast.

This non-hemolytic Streptococcus was isolated from the blood culture of a patient recently diagnosed with colon cancer. The image below demonstrates 6.5% NaCl broth and bile esculin agar. With further testing, this isolate will most likely be identified as: A. Streptococcus pneumoniae B. Enterococcus spp. C. Streptococcus pyogenes D. Streptococcus bovis

D. Streptococcus bovis Feedback Streptococcus bovis is the correct answer because Group D streptococcus, not Enterococcus, is demonstrated by a negative 6.5% NaCl tube and a positive bile esculin agar. Streptococcus bovis belongs to this group and is associated with bacteremia in patients with colon cancer. Streptococcus pneumoniae and Streptococcus pyogenes are bile esculin negative. Enterococcus spp. grow in 6.5% NaCl broth.

This suspicious form, found in a stool sample, measures 15 micro meters. The correct answer is highlighted below Entamoeba histolytica Entamoeba hartmanni Entamoeba coli Pseudoparasite

Entamoeba coli Feedback Entamoeba hartmanni and Entamoeba histolytica are basically identical with the exception of size. Entamoeba hartmanni is typically smaller that Entamoeba histolytica measuring less than 10 micro meters.

Which of the following is NOT a characteristic of Burkholderia pseudomallei? A. Has been reported as the cause of laboratory- acquired infection B. Oxidase positive C. Non-motile D. Catalase positive

Feedback B. pseudomallei is motile, a characteristic that differentiates it from the non-motile B. mallei. Burkholderia species is a dangerous and highly virulent organism that can cause laboratory-acquired infections. It should NOT be manipulated on an open bench. B. pseudomallei is oxidase positive, while B. mallei is oxidase variable. Both organisms are catalase positive and testing MUST be performed with extreme caution in a biosafety cabinet (BSC) due to the creation of aerosols. Both organisms are indole also negative. Motility: B. mallei: Non-motile B. pseudomallei: Motile

If a TSI agar slant shows a neutral or slightly alkaline slant, acid butt, no/gas production, and no H2S production, the organism might be: A. Salmonella typhi B. Proteus vulgaris C. Shigella dysenteriae D. Proteus mirabilis

C. Shigella dysenteriae Feedback Salmonella and Proteus both produce H2S, while Shigella does not. Therefore, out of the choices listed, it could only be Shigella.