Streptococcus viridans group - MegaMicro

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Streptococcus viridans group

Microbiology > Bacteriology > Gram-positive bacteria > Gram-Positive Cocci > Streptococci
·         Gram (+) cocci
·         Not encapsulated
·         Non-sporulating
·         No Lancefield carbohydrate antigen in cell wall  
·         Biofilm former
S. sanguinis:
·         NORMALLY inhabits oropharynx epithelium
·         Can seep into bloodstream (i.e. flossing)
·         Can adhere to platelet-fibrin clumps on PREVIOUSLY damaged heart valves that were damaged from group A Strep (i.e. from Rheumatic fever affecting mitral valve)
·         This can lead to subacute bacterial endocarditis (SBE)  
S. mutans
·         Can attach to teeth via extracellular dextran
·         Converts sugars to lactic acid via fermentation →decrease in pH → destruction of tooth enamel → dental caries
S. intermedius
·         A member of normally GI flora
·         Can progress to abscesses in low-O2 environment of brain/abdomen
·         Neutropenic patients have been shown to be at increased risk of susceptibility to S. viridians (Tunkel, et. al)
·         Incidence of SBE: 11-15 per 100,000 patients
Laboratory diagnosis:
·         Catalase (-)
·         Alpha hemolytic (appear green on blood agar plate due to partial hemolysis) *note “viridis” in Latin means “green”
·         Bile-esculin insoluble (solution will appear cloudy)
·         Optochin resistant (no halo will form around optochin disc)
·         Quellung reaction (-)
Disease Manifestations:
·         Systemic: Subacute Bacteria Endocarditis (SBE) (S. sanguinis/S. bovis)
o   Patients can present with fever, general malaise
o   Osler’s nodes on hands and feet (due to deposition of immune complexes): tender, erythematous lesions on hands and feet
o   Janeway lesions (non-tender, erythematous lesions on hands and feet)
o   Can cause Bacteremia which can progress to Endocarditis
·         Local: Biofilm formation can lead to dental caries (S. mutans). Infection of anaerobic strain can form brain/abdominal abscesses (S. intermedius)
Related concepts

Key Words
  • Caries
  • SBE
  • Mutans
  • Intermedius

      • Helpful Youtube video describing S. viridans and similarities/differences to S. pneumoniae
  • Harpavat, S. and Nissim, S. “Viridans Streptococci”. Lippincott’s Microcards, 3rd Ed. Lippincott Williams and Wilkins. 2012.
  • Tunkel, et al., “Infections Caused by Viridans Streptococci in Patient with Neutropenia”. Clin Infect Dis. (2002) 34 (11): 1524-1529.

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