Beyond the “Green”: Understanding Viridans Streptococci

Viridans streptococci are a heterogeneous group of alpha-hemolytic, gram-positive cocci arranged in chains and are part of the normal commensal flora of the oral cavity, upper respiratory tract, gastrointestinal tract and female genital tract. Unlike other pathogenic Streptococcus species, they lack Lancefield group antigens and are generally considered less virulent. The name "viridans" derives from the Latin word for "green," referring to the greenish discoloration produced around colonies on blood agar due to partial hemolysis.

This group encompass numerous species and hold considerable significance despite being commensals. In immunocompromised or neutropenic patients, particularly those undergoing chemotherapy, viridans streptococci can cause serious bloodstream infections and septic shock. They are the leading cause of subacute bacterial endocarditis, particularly in patients with pre-existing valvular heart disease or prosthetic valves, gaining entry into the bloodstream following dental procedures, poor oral hygiene or minor mucosal trauma. Certain species are notably associated with dental caries and deep-seated pyogenic abscesses.

So, accurate identification and antimicrobial susceptibility testing of viridans streptococci are essential. Precise species-level identification helps differentiate viridans streptococci from more pathogenic or morphologically similar organisms guiding appropriate treatment decisions and infection control measures.

To conclude, ever dismiss the green on a culture plate. Sometimes, beneath its quiet hue, Viridans streptococci whisper clues to hidden pathology waiting not merely to be seen, but to be understood.

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