Bacteriology USMLE Step 1 Practice Question
A 51-year-old man sustains a deep crush injury to his leg during a farm accident. Two days later, he presents with severe pain, crepitus, and foul-smelling purulent discharge. Vital signs show BP 98/62, HR 124, RR 22, temperature 39.2°C. Rapidly progressive tissue necrosis is evident on examination. Laboratory studies reveal elevated creatine kinase (8,500 U/L) and myoglobinuria. He denies recent antibiotic use. Which toxin most directly causes the myonecrosis in this infection?
Answer choices
- AAdenylate cyclase that increases intracellular cyclic AMP
- BProtease that cleaves SNARE proteins
- CEndotoxin composed of lipid A
- DSuperantigen that cross links T cell receptor and MHC class II
- ELecithinase that degrades cell membrane phospholipidsCorrect answer
- FTheta toxin (perfringolysin O) forming pores in cholesterol-containing membranes
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