Streptococcus pyogenes
General: Group A beta-hemolytic strep.
Clinical:
- Normal:
- Abnormal: Pharyngitis most common, also rheumatic fever, glomerulonephritis, scarlet fever, toxic-shock-like syndrome (~45% mortality), and necrotizing fasciitis (~25% mortality).
Resistance: Bacitracin susceptible. Usually very sensitive to penicillin; may use erythromycin or cephalosporins if penicillin allergic.
Morphology: Gram+ cocci in pairs and chains. Some strains are encapsulated by hyaluronic acid antigenically similar to mammalian, and is associated with virulence.
Growth characteristics: VP- Group A (Lancefield) beta-hemolytic strep which form large colonies (as opposed to small colony VP+ Group A S. anginosus). Usually isolated on blood agar in 5% CO2, possibly with trimethoprim-sulfamethoxazole. There is also high-specificity Group A antigen detection. There are also type-specific proteins; M protein is associated with virulence and is subdivided into classes I and II (only class I M proteins cause rheumatic fever; T (trypsin-resistant) protein is a positive marker for M protein negative strains. Other components include F protein and lipoteichoic acid, which facilitate binding to host cells. Streptococcal pyrogenic exotoxins (Spes) include SpeA, SpeB, SpeC, and SpeF mediate shock and organ failure due to toxic-shock-like syndrome.
Common/important pathogens: