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
Frequently asked questions
What is Viridans streptococci?
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.
What is the Gram stain of Viridans streptococci?
Viridans streptococci is Gram positive.
What are the lab clues for Viridans streptococci?
Lab clues for Viridans streptococci include Alpha-hemolytic (green) colonies, Optochin-resistant (pneumococcus is sensitive), Bile-insoluble (pneumococcus is soluble), and No capsule.
What is Viridans streptococci commonly confused with?
Viridans streptococci is commonly confused with Streptococcus pneumoniae and Enterococcus species.
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.