Infectious disease

Viridans Streptococci song

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Viridans Streptococci

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Key points in this song10

Viridans streptococci are alpha-hemolytic, optochin-resistant, and bile-insoluble, distinguishing them from *S. pneumoniae*, which is optochin-sensitive and bile-soluble.
*Streptococcus mutans* and *S. sanguis* colonize dental plaque and cause subacute bacterial endocarditis (SBE) after dental procedures by binding fibrin-platelet aggregates on damaged valves via dextran production.
Viridans streptococci are the most common cause of subacute (low-grade) native valve endocarditis, classically involving the mitral valve in patients with pre-existing rheumatic heart disease or mitral valve prolapse.
Unlike *S. pyogenes*, viridans streptococci are NOT associated with rheumatic fever or glomerulonephritis.
*S. bovis* (now reclassified as *S. gallolyticus*) is a viridans-group organism whose bacteremia is strongly associated with colorectal cancer and warrants colonoscopy workup.
Viridans streptococci lack Lancefield group antigens and are identified by their inability to grow in 6.5% NaCl, distinguishing them from enterococci.
*S. intermedius* group (milleri group) can cause abscess formation in the brain, liver, and lung, unlike other viridans streptococci.
Penicillin G remains the drug of choice for viridans streptococcal endocarditis; gentamicin is added synergistically for severe or penicillin-tolerant cases.
Viridans streptococci are a leading cause of bacteremia and sepsis in neutropenic patients receiving chemotherapy, particularly following mucositis-induced mucosal breakdown.
On blood agar, viridans streptococci produce alpha-hemolysis (green, partial hemolysis), reflecting incomplete red blood cell destruction by hydrogen peroxide.