Antimicrobials USMLE Step 1 Practice Question
A 67-year-old man with COPD presents with community-acquired pneumonia. Vital signs show HR 102, RR 22, SpO2 88% on 2L oxygen, BP 128/76, and temperature 38.5°C. Sputum culture reveals gram-negative rods; chest X-ray shows left lower lobe infiltrate. He is started on levofloxacin. On day 3, he develops severe watery diarrhea. C. difficile toxin assay is positive; no recent hospitalization documented. Which antimicrobial property predisposed him to this complication?
Answer choices
- AReduced gastric acid production increasing bacterial overgrowth
- BDirect epithelial toxicity to the colonic mucosa
- CBroad-spectrum coverage causing disruption of normal gut floraCorrect answer
- DAllergic reaction specific to gram-negative bacterial antigens
- EInhibition of intestinal peristalsis causing bacterial translocation
- FImpaired production of short-chain fatty acids by intestinal bacteria
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