Bacteriology USMLE Step 1 Practice Question
A 17-year-old male presents with a painful, fluctuant abscess on his thigh following football practice. Vital signs show BP 118/76, HR 92, RR 16, Temp 38.2°C, SpO2 98% on room air. Gram stain reveals gram-positive cocci in clusters. Culture confirms Staphylococcus aureus; WBC 11,200/μL. He denies recent antibiotic use. Which virulence factor most helps this organism evade opsonization by binding the Fc portion of IgG?
Answer choices
- AProtein ACorrect answer
- BIgA protease
- CPolysaccharide capsule containing D glutamate
- DCord factor
- EM protein
- FCoagulase converting fibrinogen to fibrin around the organism
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