A patient develops toxic shock syndrome after a soft tissue infection. Blood culture grows Streptococcus pyogenes. The superantigenic toxin responsible for massive T-cell activation in streptococcal TSS is:

• A Streptokinase (fibrinolysin)
• B Streptolysin O (SLO)
• C Streptococcal pyrogenic exotoxin A (SPEA / erythrogenic toxin A) ✓
• D M protein

Explanation

Streptococcal pyrogenic exotoxin A (SPEA, also called erythrogenic toxin A) functions as a superantigen that cross-links MHC class II on APCs with the Vβ region of T-cell receptors, causing polyclonal T-cell activation and massive cytokine release (cytokine storm), the mechanism of streptococcal toxic shock syndrome and scarlet fever rash. Streptolysin O is an oxygen-labile cytolysin. M protein mediates antiphagocytic virulence. Streptokinase dissolves fibrin.

Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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