ABPath Medical Microbiology 3 — Questions and Answers
Question 1: Which organism produces a green pigment (pyocyanin) and a grape-like odor in culture?
- Pseudomonas aeruginosa (Correct answer)
- Escherichia coli
- Klebsiella pneumoniae
- Proteus mirabilis
Correct answer: Pseudomonas aeruginosa
P. aeruginosa produces pyocyanin and a fruity/grape-like odor.
Question 2: A stool culture on sorbitol-MacConkey shows sorbitol-nonfermenting colonies. Which pathogen is suspected?
- E. coli O157:H7 (Correct answer)
- Shigella dysenteriae
- Salmonella typhi
- Vibrio cholerae
Correct answer: E. coli O157:H7
E. coli O157:H7 does not ferment sorbitol, distinguishing it on SMAC agar.
Question 3: Which encapsulated yeast stains with India ink in CSF and causes meningitis in AIDS patients?
- Cryptococcus neoformans (Correct answer)
- Histoplasma capsulatum
- Candida glabrata
- Coccidioides immitis
Correct answer: Cryptococcus neoformans
Cryptococcus has a polysaccharide capsule visualized by India ink.
Question 4: Which bacterium is the most common cause of hospital-acquired Clostridioides difficile risk after broad-spectrum antibiotics?
- Clostridioides difficile (Correct answer)
- Bacteroides fragilis
- Enterococcus faecium
- Clostridium perfringens
Correct answer: Clostridioides difficile
C. difficile overgrows after antibiotic disruption of normal flora, causing pseudomembranous colitis.
Question 5: A blood culture grows lactose-fermenting, mucoid, string-test-negative gram-negative rods. Which organism?
- Klebsiella pneumoniae (Correct answer)
- Pseudomonas aeruginosa
- Salmonella enterica
- Serratia marcescens
Correct answer: Klebsiella pneumoniae
Klebsiella is a mucoid, lactose-fermenting gram-negative rod due to its prominent capsule.
Question 6: Which serologic marker indicates immunity to hepatitis B after vaccination?
- Anti-HBs antibody (Correct answer)
- HBsAg
- Anti-HBc IgM
- HBeAg
Correct answer: Anti-HBs antibody
Anti-HBs is the protective antibody present after vaccination or recovery.
Question 7: Which parasite is transmitted by ingesting undercooked pork and forms cysts in muscle?
- Trichinella spiralis (Correct answer)
- Taenia saginata
- Giardia lamblia
- Entamoeba histolytica
Correct answer: Trichinella spiralis
Trichinella spiralis larvae encyst in striated muscle after ingesting undercooked pork.
ABPath Medical Microbiology 3
Which organism produces a green pigment (pyocyanin) and a grape-like odor in culture?