SpeB

S. pyogenes carries an unusually rich virulence arsenal, and the pyrogenic exotoxins are central to its most severe syndromes. SpeB is a broad-spectrum cysteine protease that cleaves extracellular matrix proteins, immunoglobulins, and complement components, degrading tissue and impairing host defence, and it is implicated in the rapid fascial spread of necrotizing fasciitis, the so-called flesh-eating disease, in which pain out of proportion to visible findings, systemic toxicity, and crepitus or bullae demand emergent surgical debridement alongside penicillin and clindamycin. Clindamycin is added specifically because it inhibits ribosomal protein synthesis and therefore shuts down toxin production, an effect independent of bacterial killing and not shared by beta-lactams. SpeA and SpeC are superantigens that bind MHC class II and T-cell receptor beta chains outside the peptide groove, activating up to twenty per cent of T cells and triggering a cytokine storm with fever, rash, hypotension, and multiorgan failure. Streptococcal toxic shock differs from staphylococcal in that blood cultures are usually positive and a portal of entry is usually evident.