A 60-year-old develops infective endocarditis after dental extraction. Blood cultures grow alpha-hemolytic streptococci that are optochin-resistant and bile-insoluble. The most likely organism is:
- A Streptococcus mutans (viridans group) ✓
- B Streptococcus pneumoniae
- C Enterococcus faecalis
- D Streptococcus pyogenes
Correct answer: A. Streptococcus mutans (viridans group)
Explanation
Viridans streptococci (e.g., S. mutans, S. sanguinis) are alpha-hemolytic, optochin-resistant, and bile-insoluble; they colonize the oral cavity and are the most common cause of subacute infective endocarditis following dental procedures. S. pneumoniae is alpha-hemolytic but optochin-sensitive and bile-soluble. Enterococcus faecalis is gamma-hemolytic and shows bile-esculin hydrolysis. S. pyogenes is beta-hemolytic.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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