A 60-year-old man with poor dental hygiene develops subacute bacterial endocarditis affecting the mitral valve. Blood cultures grow alpha-hemolytic, optochin-resistant, bile-insoluble Gram-positive cocci. Which organism is the most likely cause?
- A Streptococcus mutans (viridans group) ✓
- B Streptococcus pyogenes
- C Streptococcus pneumoniae
- D Staphylococcus epidermidis
Correct answer: A. Streptococcus mutans (viridans group)
Explanation
Alpha-hemolytic, optochin-resistant, bile-insoluble organisms are viridans group streptococci, the most common cause of subacute endocarditis following dental procedures in patients with pre-existing valve disease. S. pneumoniae is optochin-sensitive. S. pyogenes is beta-hemolytic (Group C). S. epidermidis causes prosthetic valve endocarditis, not native valve disease, and is catalase-positive.
Reference: Jawetz, Melnick, & Adelberg's Medical Microbiology, 28th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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