Gram ⊕ cocci in chains. - Bacitracin sensitive, β-hemolytic, pyrrolidonyl arylamidase (PYR) ⊕.- Hyaluronic acid capsule and M protein inhibit phagocytosis.

Cause:- Pyogenic – pharyngitis, cellulitis, impetigo ("honey-crusted" lesions), erysipelas- Toxigenic – scarlet fever, toxic shock-like syndrome, necrotizing fasciitis- Immunologic – rheumatic fever, glomerulonephritis

- Antibodies to M protein enhance defense but can give rise to rheumatic fever.- ASO titer or anti-DNase B antibodies indicate recent infection.- Strains causing impetigo can induce glomerulonephritis.

Jones criteria: Guidelines to diagnose rheumatic fever (Joint pain, ♥ Carditis, Nodules, Erythema marginatum, Syndeham chorea)

Scarlet fever – blanching, sandpaper-like body rash, strawberry tongue, and circumoral pallor in the setting of group A streptococcal pharyngitis (erythrogenic toxin ⊕).