WBR0055

Author	PageAuthor::William J Gibson
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Microbiology
Sub Category	SubCategory::Musculoskeletal/Rheumatology, SubCategory::General Principles, SubCategory::Infectious Disease
Prompt	[[Prompt::A soldier suffers from an open leg wound after an explosion. He is treated upon returning to base, but he soon develops widespread purefaction of the wound site with bubbles arising in nearby muscle and subcutaneous tissue. What is the mechanism of the toxin in the causative organism?]]
Answer A	AnswerA::Bring MHCII and TCR together to stimulate leukocytes.
Answer A Explanation	AnswerAExp::Incorrect - this is the mechanism of the Staph Aureus Toxic Shock Syndrome toxin and Strep Pyogenes Endotoxin A.
Answer B	AnswerB::Phospholipase
Answer B Explanation	AnswerBExp::Correct - See Explanation
Answer C	AnswerC::Cleaves SNARE protein
Answer C Explanation	AnswerCExp::Incorrect - This is the mechanism of Botulinum and Tetanus toxin, which disables neurotransmitter release at the synaptic cleft.
Answer D	AnswerD::Inactivate 60S ribsosome by cleaving rRNA
Answer D Explanation	AnswerDExp::Incorrect - This is the mechanism of the toxin produced by Shigella and EHEC.
Answer E	AnswerE::Increases cAMP by intrinsic enzymatic activity.
Answer E Explanation	AnswerEExp::Incorrect - This is the mechanism of the edema factor toxin produced by Bacillus Anthracis.
Right Answer	RightAnswer::B
Explanation	[[Explanation::The patient in this vignette is suffering from gas gangrene, caused by Clostridium Perfringens. C. Perfringens is found in soil and the environment as spores, which can enter open wounds. The organism produces alpha toxin, a phospholipase which degrades cell membranes, thereby producing tissue destruction. Infections can progress rapidly, leading to myonecrosis and the formation of gas as tissue is destroyed. Potentially lethal sepsis can ensue within hours without proper treatment. The treatment for gas gangrene is wound debridement and often amputation of the affected area with adjuvant penicillin. Educational Objective: Clostridium Perfringens produces gas gangrene and alpha toxin, a phospholipase which degrades tissues. Tags: #Microbiology #Pathophysiology Educational Objective: References: ]]
Approved	Approved::Yes
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