Bacteriology USMLE Step 1 Practice Question
A 41-year-old woman with a 10-pack-year smoking history presents with an 8-week progressive cough productive of scant sputum, night sweats, and unintentional weight loss of 12 pounds. She denies hemoptysis, fever, or dyspnea. Vital signs are BP 118/76 mmHg, HR 92 bpm, RR 18/min, temperature 37.8°C, and SpO2 95% on room air. Physical examination reveals crackles in the right upper lobe. Chest radiograph shows a cavitary infiltrate in the right upper lobe. Sputum smear microscopy performed with Ziehl-Neelsen staining demonstrates acid-fast bacilli. Which of the following structural features of the causative organism is most responsible for its resistance to standard antibiotics and desiccation?
Answer choices
- AGram-negative outer membrane containing lipopolysaccharide
- BThick peptidoglycan layer with teichoic acid polymers
- CLipid-rich cell wall with mycolic acids covalently bound to arabinogalactanCorrect answer
- DPolysaccharide capsule surrounding a thin peptidoglycan layer
- EGlycoprotein outer envelope with minimal peptidoglycan content
- FChitinous cell wall with ergosterol-containing membranes
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