The MOST common causative organism in subacute infective endocarditis affecting a previously abnormal (but not prosthetic) valve is:

• A Staphylococcus aureus
• B Viridans group streptococci (e.g., S. sanguinis) ✓
• C Enterococcus faecalis
• D Streptococcus bovis (S. gallolyticus)

Explanation

Viridans group streptococci are the most common cause of subacute infective endocarditis on previously abnormal native valves (rheumatic, bicuspid aortic). They are low-virulence oral commensals that enter the bloodstream during dental procedures, adhering to pre-existing platelet-fibrin thrombi on damaged valve endothelium. Staphylococcus aureus is the most common cause of acute endocarditis on normal valves and prosthetic valves.

Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.