Bacteriology USMLE Step 1 Practice Question
A 67-year-old man with a prosthetic heart valve presents with fever (38.9°C), new systolic murmur, and malaise 6 months post-replacement. Vital signs show HR 102/min, BP 118/76 mmHg, RR 18/min, SpO2 98% on room air. Blood cultures grow gram-positive cocci in chains that are catalase-negative and alpha-hemolytic. Echocardiography reveals vegetation on the prosthetic valve. He denies recent dental procedures or IV drug use. Which organism is most likely responsible?
Answer choices
- AStaphylococcus epidermidis
- BEnterococcus faecalis
- CStreptococcus agalactiae
- DStaphylococcus aureus
- EViridans group StreptococcusCorrect answer
- FStreptococcus pneumoniae
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