Microbiology · Streptococci and enterococci
Viridans streptococci !
- Bacterium
- Gram-positive
- Exam priority: medium
Mouth streptococci that cause tooth decay and subacute endocarditis; S. gallolyticus is linked to colon cancer.
Updated 2026-11-01
Also called: S. mutans, S. sanguinis, S. mitis, S. gallolyticus (formerly S. bovis)
At a glance
- Gram
- Gram-positive
- Shape
- Cocci in chains
- Oxygen
- Facultative anaerobe
- Family
- Streptococcaceae
- Stain
- Gram positive; catalase negative; alpha-haemolytic
Morphology
- Gram-positive cocci in chains
- Alpha (green) haemolysis
- Optochin resistant and bile insoluble
Transmission
- Normal flora of the mouth and gut (not contagious)
- Enter the blood after dental procedures or through inflamed gums
Isolation precautions
What the care team adds to standard precautions.
- Standard
Virulence factors
- Dextrans: adhesion to enamel and to fibrin-platelet clots on damaged valves
- S. mutans ferments sugars into acid that demineralises enamel
Diseases it causes
- Subacute endocarditis on damaged valves Infective endocarditis →
- Dental caries (S. mutans) Dental caries →
- S. gallolyticus bacteraemia linked to colorectal cancer Colorectal cancer →
Clinical picture
- Prolonged fever, a new murmur, fatigue and weight loss (subacute endocarditis)
Diagnosis
- Serial blood cultures
- Optochin resistant, bile insoluble
- Echocardiogram when endocarditis is suspected
- Colonoscopy if S. gallolyticus is isolated
Treatment
They are usually susceptible to penicillin or ceftriaxone; susceptibility guides endocarditis treatment. Prophylaxis before dental procedures is reserved for high-risk patients, such as those with prosthetic valves.
Drug class only; doses and regimens are set by the clinician from the current guideline.
In Pharmacology:
Prevention
- Oral hygiene and caries control
- Dental antibiotic prophylaxis only for high-risk cardiac patients
Test yourself
Think of the answer, then tap the question to see it.
Which test distinguishes viridans streptococci from pneumococcus?
Optochin: viridans are resistant and pneumococcus is sensitive.
Which test is indicated for a patient with S. gallolyticus bacteraemia?
A colonoscopy, because of the link with colorectal cancer.
Which factor lets viridans streptococci stick to damaged valves?
Dextrans, which adhere to fibrin and platelet deposits.
Related
Related conditions
← Back to the group: Streptococci and enterococci
Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Endocarditis: MedlinePlus Medical Encyclopedia (MedlinePlus (NLM), 2024); Dental cavities: MedlinePlus Medical Encyclopedia (MedlinePlus (NLM), 2024).
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Representative model, for educational purposes only.