Bacteriology USMLE Step 1 Practice Question
A 68-year-old woman presents with fever (38.9°C), malaise, and knee swelling 10 days after prosthetic knee arthroplasty. Vital signs show HR 102/min, BP 138/88 mmHg, RR 18/min, SpO2 98% on room air. Joint aspirate reveals catalase-positive, coagulase-negative gram-positive cocci in clusters; WBC 18,500/μL with left shift. She denies recent antibiotic use. Which virulence factor most likely enabled this organism's persistence on the prosthetic surface?
Answer choices
- AProtein A binding the Fc region of IgG
- BCapsular antiphagocytic protein composed of D glutamate
- CM protein inhibiting complement deposition
- DPolysaccharide biofilm productionCorrect answer
- EHeat stable enterotoxin activating guanylate cyclase
- FCoagulase production forming a fibrin clot around the organism
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