A 4-year-old child from a poorly immunized community develops fever, pharyngitis, and a grayish-white pseudomembrane over the tonsillar pillars extending to the uvula, which bleeds when attempts are made to remove it. The child has a 'bull neck' appearance. Which toxin mechanism is responsible for myocarditis in this condition?
- A ADP-ribosylation of EF-2 (elongation factor 2) inhibiting protein synthesis ✓
- B Superantigen activation of T-cells causing cytokine storm
- C Cleavage of SNARE proteins inhibiting acetylcholine release
- D Activation of adenylyl cyclase causing fluid secretion
Explanation
Diphtheria toxin is encoded by the tox gene of bacteriophage β-corynephage infecting Corynebacterium diphtheriae. It consists of two fragments: Fragment B (binding domain) binds to cell surface receptors; Fragment A (active domain) is translocated into the cytoplasm, where it ADP-ribosylates elongation factor-2 (EF-2, also called translocase), irreversibly inhibiting translocation during protein synthesis, halting protein production in all cells. In cardiac myocytes, this causes myocarditis (arrhythmias, heart block, heart failure — the most common cause of death in diphtheria). Superantigen mechanism is streptococcal/staphylococcal; SNARE cleavage is botulinum toxin; adenylyl cyclase activation is cholera toxin.
Reference: Ghai Essential Pediatrics, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.