A 5-year-old child presents with sudden onset fever, a 'strawberry tongue,' and sandpaper-like rash that blanches on pressure, sparing the perioral area. The most likely organism produces a toxin that causes rash by its specific mechanism. What toxin and mechanism is responsible for the rash of scarlet fever?
- A Exfoliatin (ET-A and ET-B) from S. aureus phage group II — cleaves desmoglein-1 in granular layer
- B Toxic shock syndrome toxin-1 (TSST-1) from Staphylococcus aureus — superantigen causing diffuse macular erythema
- C Streptococcal pyrogenic exotoxins (SPE-A, SPE-B, SPE-C) — superantigens that activate up to 20% of T cells non-specifically, causing massive cytokine release and erythroderma ✓
- D Diphtheria toxin from Corynebacterium diphtheriae — inhibits EF-2 causing local tissue necrosis with membrane formation
Correct answer: C. Streptococcal pyrogenic exotoxins (SPE-A, SPE-B, SPE-C) — superantigens that activate up to 20% of T cells non-specifically, causing massive cytokine release and erythroderma
Explanation
The rash of scarlet fever is caused by streptococcal pyrogenic exotoxins (SPE-A, SPE-B, SPE-C — also called Dick's toxin or erythrogenic toxin) produced by GAS (Group A Streptococcus, S. pyogenes). These toxins are superantigens: they cross-link MHC class II on APCs with the Vβ-region of TCR, non-specifically activating 5–30% of all T lymphocytes and triggering massive cytokine storm (IL-1, IL-2, TNF) causing systemic erythroderma. Exfoliatin causes scalded skin syndrome (SSSS). TSST-1 causes staphylococcal TSS.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.