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General Features Genera: Streptococcus, Enterococcus Gram-positive cocci, catalase-negative, usually in pairs/chains Hemolysis on blood agar used for classification: Beta (complete): S. pyogenes (Group A), S. agalactiae (Group B) Alpha (partial, green): S. pneumoniae, Viridans group Gamma (none): Enterococcus spp., S. bovis Classification Lancefield grouping (cell wall carbohydrates): Groups A, B, C, D, F, G Key tests: PYR, CAMP, Hippurate hydrolysis, Esculin, Bacitracin, Optochin, Bile solubility, NaCl tolerance.
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Enterococcus spp. (Group D, γ-hemolytic) Species: E. faecalis, E. faecium Virulence: Biofilm formation, antibiotic resistance (↑ VRE risk) Diseases: Nosocomial infections, UTI, endocarditis, wound infections Lab ID: Growth in 6.5% NaCl, Bile-esculin+, PYR+ Nutritionally Variant Streptococci (Abiotrophia, Granulicatella) Require B6/pyridoxine or satellite growth with S. aureus Disease: Endocarditis.