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 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 most likely causal organism?]] |
| Answer A | AnswerA::Bring MHCII and TCR together to stimulate leukocytes. |
| Answer A Explanation | [[AnswerAExp::Incorrect: This is the mechanism of the Staphylococcus aureus' Toxic Shock Syndrome toxin and Streptococcus pyogenes' Endotoxin A. Because of their unique ability to stimulate leukocytes without co-stimulatory factors, these toxins are called "superantigens".]] |
| Answer B | AnswerB::Phospholipase |
| Answer B Explanation | AnswerBExp::'''Correct:''' Clostridium perfringens produces gas gangrene and alpha toxin, a phospholipase that degrades tissues. |
| Answer C | AnswerC::Cleaves SNARE protein |
| Answer C Explanation | AnswerCExp::'''Incorrect:''' Both Botulinum and Tetanus toxin cleave SNARE protein at synapses, thereby disabling neurotransmitter release at the synaptic cleft. |
| Answer D | AnswerD::Inactivate 60S ribsosome by cleaving rRNA |
| Answer D Explanation | AnswerDExp::'''Incorrect:''' The toxins produced by Shigella and EHEC inactivate the 60S ribosome by cleaving rRNA. |
| Answer E | AnswerE::Increases cAMP by intrinsic enzymatic activity. |
| Answer E Explanation | [[AnswerEExp::Incorrect: Edema factor toxin produced by Bacillus anthracis increases cAMP by increasing enzymatic activity.]] |
| 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 that degrades tissues. References: First Aid 2014 page 127 |
| Approved | Approved::Yes |
| Keyword | WBRKeyword::Microbiology, WBRKeyword::Bacteria, WBRKeyword::Toxin, WBRKeyword::Mechanism, WBRKeyword::Gangrene |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |