Which mycobacterium is the causative agent of Buruli ulcer, and what is the primary virulence factor responsible for the characteristic extensive skin and soft tissue necrosis with undermined edges?

• A Mycobacterium marinum — photochromogen pigment causing phototoxic tissue destruction
• B Mycobacterium haemophilum — lipid-rich capsule resisting phagocytic killing
• C Mycobacterium ulcerans — mycolactone toxin (a macrolide polyketide toxin) ✓
• D Mycobacterium fortuitum — beta-lactamase causing antibiotic resistance leading to necrosis

Explanation

Buruli ulcer (third most common mycobacterial disease after TB and leprosy) is caused by Mycobacterium ulcerans, a Runyon Group III slowly growing mycobacterium. Its key virulence factor is mycolactone, a diffusible polyketide toxin that suppresses immune responses locally (by inhibiting monocyte activation and inducing apoptosis) and causes coagulative necrosis of subcutaneous fat, leading to the characteristic painless ulcer with undermined necrotic edges. Diagnosis is by PCR or Ziehl-Neelsen stain of tissue. M. marinum causes swimming pool granuloma at cooler body sites without extensive necrosis.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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