Jawetz Microbiology Mcq (2027)

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?

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? 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) Trophozoite – glycolysis via hexose monophosphate shunt

A) Ganciclovir – inhibits DNA polymerase after phosphorylation by viral kinase B) Acyclovir – requires viral thymidine kinase for activation C) Foscarnet – directly inhibits viral DNA polymerase without prior phosphorylation D) Cidofovir – incorporates into DNA after diphosphate conversion E) Brivudine – inhibits viral thymidine kinase Answer: C – VZV retinitis in advanced HIV can be acyclovir-resistant due to thymidine kinase mutations. Foscarnet does not require viral TK; it directly blocks DNA polymerase. Acyclovir (B) would fail if TK-deficient. Ganciclovir (A) requires viral kinase (UL97 for CMV; VZV TK less efficient). Brivudine (E) also requires TK. 3. Gram-Positive Cocci – Subtle Differentiation A blood culture from a patient with subacute bacterial endocarditis grows catalase-negative, gram-positive cocci in chains. The organism is bile-esculin positive, grows in 6.5% NaCl, and produces a yellow pigment on blood agar. Which additional test confirms the species, and what is the key virulence factor? They are metabolically dormant but survive

A) Mycolic acid chain length – Mycobacterium marinum B) Lipoarabinomannan (LAM) structure – Mycobacterium kansasii C) Phthiocerol dimycocerosate (PDIM) – Mycobacterium leprae D) Sulfolipids – Mycobacterium tuberculosis E) Phenolic glycolipids – Mycobacterium ulcerans Answer: A – M. marinum causes fish tank granuloma, grows optimally at 30-32°C, not at 37°C. Mycolic acid chain composition affects membrane fluidity. M. leprae (C) does not grow on artificial media. PDIM is important for M. tuberculosis virulence but not temperature restriction. 10. Mixed Infection – Synergy A human bite wound becomes necrotizing within 24 hours. Gram stain shows mixed pleomorphic gram-negative rods and tiny gram-positive cocci in chains. The infection is more severe than either isolate alone. Which pair of organisms and their synergistic virulence mechanism is correct?