Blood cultures from a patient who developed infective endocarditis three weeks after mechanical aortic valve replacement grow a methicillin-resistant coagulase-negative staphylococcus. Which organism is the most common cause of endocarditis presenting within 60 days of valve surgery?

• A Viridans group streptococci
• B Haemophilus species (HACEK group)
• C Streptococcus gallolyticus (bovis)
• D Staphylococcus epidermidis (coagulase-negative staphylococcus) ✓

Explanation

Early prosthetic valve endocarditis, defined as occurring within 60 days of surgery, is most commonly caused by coagulase-negative staphylococci such as Staphylococcus epidermidis acquired perioperatively, often with surgical wound involvement. Late prosthetic valve endocarditis mirrors native valve disease, with viridans streptococci and Staphylococcus aureus predominating. HACEK organisms are slow-growing fastidious Gram negatives responsible for a small minority of cases.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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