Streptococcus

General: Historically defined by phenotypic characteristics, but are definitively identified by genetic analysis. Identification algorithms typically still use phenotypic methods unless specifically indicated, as it is cheaper, faster, and easier.

Clinical:

• Normal: Mucosa; predominant component of respiratory, gastrointestinal, and genital tract flora.
• Abnormal: Usually Streptococcus pyogenes; cellulitis, pharyngitis, endocarditis, impetigo/pyoderma, necrotizing fasciitis, streptococcal toxic shock syndrome/toxic-shock-like syndrome.

Resistance:

Morphology: Gram+ cocci seen in pairs or chains. Alpha, beta, or gamma hemolytic. Lancefield antigen classification of A, B, C, D, F, or G; except for D (alpha or gamma), they are beta-hemolytic.

Growth characteristics: Catalase- facultative anaerobes, metabolize carbohydrates by fermentation, producing primarily lactic acid.

Common/important pathogens:

• Streptococcus agalactiae
• Streptococcus anginosus
• Streptococcus bovis
• Streptococcus dysgalactiae
• Streptococcus pneumoniae
• Streptococcus pyogenes