Bacteriology USMLE Step 1 Practice Question
A 38-year-old man presents with a 3-month history of productive cough, unintentional 8-kg weight loss, and night sweats. Vital signs show BP 118/76, HR 92, RR 18, temp 37.8°C, and SpO2 98% on room air. Chest X-ray reveals cavitary lesions in the right upper lobe. Sputum smear microscopy is positive for acid-fast bacilli. He denies immunosuppressive medication use. The organism is phagocytosed by alveolar macrophages but persists intracellularly. Which virulence factor most directly contributes to this persistence by inhibiting phagolysosome formation?
Answer choices
- AProtein A
- BPolysaccharide capsule
- CSulfatidesCorrect answer
- DM protein
- ELipid A
- FCord factor (trehalose dimycolate)
See the full explanation
Get the correct-answer rationale, why each distractor is wrong, the underlying mechanism, and high-yield associations — plus adaptive practice that targets your weak areas — with a free MedBoardPRO account.