A) PYR positive – fibrinogen binding protein B) Optochin resistant – pneumolysin C) Bacitracin sensitive – M protein D) Hippurate hydrolysis – CAMP factor E) Lancefield group D antigen – cytolysin Answer: A – The organism is Enterococcus faecalis (bile-esculin +, 6.5% NaCl +). Among enterococci, E. faecalis is PYR positive (distinguishes from E. faecium sometimes). Key virulence for endocarditis includes aggregation substance and gelatinase. Option A’s “fibrinogen binding protein” refers to microbial surface component recognizing adhesive matrix molecules (MSCRAMMs). CAMP factor is Strep. agalactiae . Hippurate hydrolysis is S. agalactiae . 4. Anaerobes – Deep Concept A diabetic foot ulcer culture grows foul-smelling, gram-negative bacilli, resistant to kanamycin and vancomycin, but sensitive to metronidazole. Which enzyme system is directly inhibited by metronidazole in this organism?
A) HSV-1 – trigeminal ganglia – sunlight/UV B) VZV – dorsal root ganglia – emotional stress C) EBV – B lymphocytes – plasmapheresis D) CMV – salivary gland endothelial cells – trauma E) HHV-6 – microglia – rituximab therapy Answer: A – HSV-1 reactivation is classically triggered by UV light, fever, stress. VZV reactivation (shingles) often has no clear trigger but can be stress/age-related; sunlight is not classic. EBV latency in B cells; reactivation more with immunosuppression. CMV latency in monocytes; plasmapheresis not a trigger. HHV-6 in microglia; reactivation post-transplant, not rituximab specifically. 8. Spirochetes – Diagnostic Pitfall A patient with a painless genital ulcer and inguinal lymphadenopathy has a darkfield microscopy positive for spirochetes. However, the RPR is negative. Which of the following best explains this seronegative primary syphilis? jawetz microbiology mcq
A) Flucytosine – inhibits thymidylate synthase B) Amphotericin B – binds ergosterol C) Caspofungin – inhibits β-(1,3)-D-glucan synthase D) Voriconazole – inhibits lanosterol 14α-demethylase E) Terbinafine – inhibits squalene epoxidase Answer: C – The description matches Aspergillus fumigatus (galactomannan +, green colony with red reverse). Echinocandins (caspofungin) target β-glucan, which is abundant in Aspergillus cell wall. Although voriconazole is drug of choice for invasive aspergillosis, the question asks for mechanism “specifically suited” to a unique cell wall component – β-glucan is more specific to fungal cell wall (not in human cells). Amphotericin B (B) targets ergosterol but also binds cholesterol, less specific. 6. Parasitology – Relapse Mechanism A returned traveler from Southeast Asia had 3 days of fever, chills, and sweats every 48 hours, now asymptomatic without treatment. Six months later, he develops identical symptoms. Which structure of Plasmodium vivax is responsible for this pattern, and what is its unique metabolic feature? A) PYR positive – fibrinogen binding protein B)
A) Trophozoite – glycolysis via hexose monophosphate shunt B) Schizont – proteolysis of hemoglobin C) Hypnozoite – dormant stage in hepatocytes with slow metabolic rate D) Gametocyte – anaerobic respiration E) Merozoite – pentose phosphate pathway only Answer: C – P. vivax and P. ovale form hypnozoites in the liver, causing relapse months after primary infection. They are metabolically dormant but survive. Primaquine targets them. The 48-hour periodicity is tertian malaria. 7. Virology – Unusual Latency Which DNA virus is correctly paired with its primary site of latency AND a unique reactivation trigger that does NOT involve immunosuppression? faecium sometimes)
A) Superoxide dismutase B) Catalase C) Pyruvate-ferredoxin oxidoreductase D) Cytochrome c oxidase E) Beta-lactamase Answer: C – The organism is Bacteroides fragilis group. Metronidazole is a prodrug reduced by ferredoxin (or pyruvate-ferredoxin oxidoreductase) in anaerobic bacteria; the reduced form damages DNA. Resistance can occur via nim genes that reduce metronidazole to inactive metabolites. Option A (SOD) is present in aerotolerant anaerobes but not metronidazole target. 5. Mycology – Antifungal Mechanism A patient with prolonged neutropenia develops a pulmonary cavity. A serum galactomannan antigen is positive. The isolate grows a greenish-brown colony with a red reverse on Sabouraud dextrose agar. Which drug’s mechanism is most specifically suited for this organism’s unique cell wall component?