WBR0300
| Author | [[PageAuthor::Rim Halaby, M.D. [1]]] |
|---|---|
| Exam Type | ExamType::USMLE Step 1 |
| Main Category | MainCategory::Microbiology |
| Sub Category | SubCategory::General Principles |
| Prompt | [[Prompt::A researcher is studying the properties of bacterial toxins. After isolating and purifying several bacterial toxins using thiol-disulfide exchange affinity chromatography, he exposes the purified product to a number of harsh conditions. In one experiment, he heats the product to 70C and then injects a small amount 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 is usually destroyed with heating at 60 C for a few minutes. |
| Answer B | AnswerB::Vibrio cholerae exotoxin |
| Answer B Explanation | AnswerBExp::The Vibrio cholerae exotoxin is also destroyed with heating at 60 C for a few minutes. |
| 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 is usually destroyed with heating at 60 C for several minutes. |
| Answer E | AnswerE::Bordetella pertussis Exotoxin |
| Answer E Explanation | AnswerEExp::The Bordetella pertussis Exotoxin is usually destroyed with heating at 60 C for several minutes. |
| Right Answer | RightAnswer::C |
| Explanation | [[Explanation::Staphylococcal enterotoxin B is an exotoxin produced by Staphylococcus aureus and classically associated with food poisoning. This exotoxin is encountered in contaminated meat and dairy products where the bacteria are allowed to thrive. Even with heating of food products, enterotoxin B has been shown to withstand temperatures as high as 100 C for several minutes, long after the bacteria have been destroyed. This feature is unique among most exotoxins that are usually very heat labile and do not withstand heat fluctuations. The toxin is also resistant to the gut proteases allowing it to cause disease shortly after it is ingested. Beyond regular food poisoning, Staphylococcal enterotoxin B has been shown to possess a super-antigen quality that allows it to cause toxic shock syndrome (TSS) by crosslinking MHCII to TCRs with great affinity.
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| Approved | Approved::No |
| Keyword | WBRKeyword::Staphylococcus aureus, WBRKeyword::Staphylococcal enterotoxin B, WBRKeyword::Heat-stable exotoxin |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |