A 45-year-old man with a history of rheumatic mitral valve disease and poor dental hygiene presents with 3 weeks of low-grade fever, malaise and weight loss. Blood cultures grow alpha-hemolytic streptococci that are optochin resistant. Which organism is responsible?
- A Streptococcus pyogenes
- B Viridans group streptococci ✓
- C Streptococcus pneumoniae
- D Enterococcus faecalis
Correct answer: B. Viridans group streptococci
Explanation
Viridans group streptococci such as Streptococcus sanguis and mutans are alpha-hemolytic, optochin resistant, and normal inhabitants of the oral cavity. They seed previously damaged valves following dental procedures or poor dentition and cause subacute endocarditis with an indolent course over weeks. Streptococcus pneumoniae is optochin sensitive, pyogenes is beta-hemolytic, and enterococci more typically follow genitourinary or gastrointestinal instrumentation and can grow in bile and high salt.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.