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Systemic Bacteriology · NEET PG Preparation Microbiology

A 35-year-old immigrant worker presents with a non-healing, painless ulcer on his hand that has a black eschar, surrounded by massive non-pitting ede…

Practice question from Systemic Bacteriology (NEET PG Preparation Microbiology), with the correct answer and a step-by-step solution.

medium · MCQ · Q-8EC16E

A 35-year-old immigrant worker presents with a non-healing, painless ulcer on his hand that has a black eschar, surrounded by massive non-pitting edema. He reports working with imported goat wool. Gram stain of the wound exudate reveals large, encapsulated, gram-positive bacilli in chains resembling 'boxcars'. Which of the following is the primary virulence factor responsible for the systemic manifestations and edema in this condition?

  1. A.Exotoxin A (inhibits protein synthesis via EF-2 elongation factor)
  2. B.Tripartite toxin consisting of protective antigen, lethal factor, and edema factorCorrect answer
  3. C.Heat-labile enterotoxin increasing intracellular cAMP
  4. D.Cord factor (trehalose 6,6'-dimycolate) inhibiting phagolysosome fusion

Solution

The clinical presentation is classic for cutaneous anthrax caused by Bacillus anthracis. B. anthracis produces a tripartite exotoxin composed of Protective Antigen (PA), Lethal Factor (LF), and Edema Factor (EF). PA binds to cellular receptors, allowing LF (a zinc metalloprotease that inactivates MAP kinase kinases) and EF (an adenylate cyclase that increases cAMP) to enter the cell, causing edema and necrosis.

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