WBR0300
| Author | [[PageAuthor::Rim Halaby, M.D. [1] (Reviewed by Alison Leibowitz)]] |
|---|---|
| Exam Type | ExamType::USMLE Step 1 |
| Main Category | MainCategory::Microbiology |
| Sub Category | SubCategory::General Principles |
| Prompt | [[Prompt::After isolating and purifying several bacterial toxins using thiol-disulfide exchange affinity chromatography, a researcher studying the properties of bacterial toxins exposes the purified product to a number of harsh conditions. In one experiment, he heats the product to 70 °C and then injects a sample into anesthetized rats. Which of the following bacterial toxins is likely to elicit symptoms after injection?]] |
| Answer A | AnswerA::Pseudomonas aeruginosa Exotoxin A |
| Answer A Explanation | AnswerAExp::The Pseudomonas aeruginosa Exotoxin A typically cannot withstand a few minutes of heating to 60 °C. |
| Answer B | AnswerB::Vibrio cholerae exotoxin |
| Answer B Explanation | AnswerBExp::The Vibrio cholerae exotoxin typically cannot withstand a few minutes of heating to 60 °C. |
| Answer C | AnswerC::Staphylococcal Enterotoxin B |
| Answer C Explanation | AnswerCExp::Staphylococcal enterotoxin B is unique among exotoxins for being very heat stable withstanding temperatures as high as 100 C for several minutes. |
| Answer D | AnswerD::Tetanospasmin |
| Answer D Explanation | AnswerDExp::Tetanospasmin typically cannot withstand a few minutes of heating to 60 °C. |
| Answer E | AnswerE::Bordetella pertussis Exotoxin |
| Answer E Explanation | AnswerEExp::The Bordetella pertussis Exotoxin typically cannot withstand a few minutes of heating to 60 °C. |
| Right Answer | RightAnswer::C |
| Explanation | [[Explanation::Staphylococcal enterotoxin B is an exotoxin, produced by Staphylococcus aureus, that is often associated with food poisoning. This exotoxin can be encountered in contaminated meat and dairy products where the conditions are optimal for Staphylococcus aureus to thrive. Enterotoxin B has been shown to withstand temperatures as high as 100 °C for several minutes, long after the bacteria have been destroyed. Staphylococcal enterotoxin B's ability to withstand high temperatures is atypical of exotoxins, which are often extremely heat labile and usually do not tolerate heat fluctuations. Staphylococcal enterotoxin B is resistant to the gut proteases, enabling it to cause disease shortly after ingestion. Beyond regular food poisoning, Staphylococcal enterotoxin B possesses a super-antigen quality, leading to toxic shock syndrome (TSS) by crosslinking MHCII to TCRs with great affinity. Educational Objective: |
| Approved | Approved::Yes |
| Keyword | [[WBRKeyword::Staphylococcus aureus]], WBRKeyword::Staphylococcal enterotoxin B, WBRKeyword::Heat-stable exotoxin |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |