Bacterium
Viridans streptococci
Alpha-hemolytic optochin-resistant oral strep
VIR-ih-danz strep-tuh-KOK-eye
High-yield clue
Alpha-hemolytic, optochin-resistant, and bile-insoluble, they seed subacute endocarditis on damaged valves after dental procedures cause transient bacteremia.
Overview
A heterogeneous group of alpha-hemolytic oral streptococci (including S. sanguinis, S. mitis, S. mutans) that are normal mouth flora. They are the classic teaching cause of subacute bacterial endocarditis on previously damaged valves.
Classification
- Gram-positive
- Cocci in chains
- Alpha-hemolytic
- Optochin-resistant
- No Lancefield group antigen
Lab & identification clues
- Alpha-hemolytic (green) colonies
- Optochin-resistant (pneumococcus is sensitive)
- Bile-insoluble (pneumococcus is soluble)
- No capsule
Associations
- Subacute bacterial endocarditis
- Transient bacteremia after dental work
- Members: S. sanguinis, S. mitis, S. mutans
Commonly confused with
- Streptococcus pneumoniae
- Enterococcus species
Your notes
Original student-study summary. Sources checked: OpenStax Microbiology 2e, NCBI Bookshelf Medical Microbiology, and CDC topic pages where applicable; reviewed 2026-06. Educational only; no diagnosis, treatment, dosing, or specimen-handling guidance.