WBR0300
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| Author | [[PageAuthor::Serge Korjian M.D. (Reviewed by Serge Korjian, Yazan Daaboul, M.D., and Template:AJK)]] |
|---|---|
| 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 (158 °F) and then injects a sample into anesthetized rats. Which of the following bacterial toxins is likely to elicit symptoms following injection?]] |
| Answer A | AnswerA::''Pseudomonas aeruginosa'' exotoxin A |
| Answer A Explanation | [[AnswerAExp::Exotoxin A is an important virulence factor of Pseudomonas aeruginosa. The toxin inhibits protein synthesis by ADP ribosylation of elongation factor 2 (EF2). The Pseudomonas aeruginosa exotoxin A is usually inactivated by heating at 60 °C (140 °F) for several minutes.]] |
| Answer B | AnswerB::''Vibrio cholerae'' exotoxin |
| Answer B Explanation | [[AnswerBExp::The Vibrio cholerae exotoxin is part of a group of bacterial toxins referred to as A/B toxins, owing to the presence of 2 subunits. The toxin is responsible for the massive, watery diarrhea characteristic of cholera infection. It acts by causing ATP-mediated efflux of chloride ions into the gut lumen. The Vibrio cholerae exotoxin is usually inactivated by heating at 60 °C (140 °F) for several minutes.]] |
| Answer C | AnswerC::Staphylococcal enterotoxin B |
| Answer C Explanation | AnswerCExp::Staphylococcal enterotoxin B is unique among exotoxins for being very heat stable. It is able to withstand extreme temperatures as high as 100 °C (212 °F) for several minutes. |
| Answer D | AnswerD::Tetanospasmin |
| Answer D Explanation | [[AnswerDExp::Tetanospasmin is an extremely potent neurotoxin produced by Clostridium tetani. The toxin causes spastic paralysis by inhibiting the release of γ-aminobutyric acid (GABA) from presynaptic neurons. Tetanospasmin is also inactivated by heating at 60 °C (140 °F) for several minutes.]] |
| Answer E | AnswerE::''Bordetella pertussis'' exotoxin |
| Answer E Explanation | [[AnswerEExp::The Bordetella pertussis exotoxin is also an A/B toxin that acts by binding the Gi subunit of G protein-coupled receptors (GPCRs). The binding process disables the inhibition of adenylyl cyclase activity, leading to increased concentrations of cyclic AMP (cAMP). The Bordetella pertussis exotoxin is usually inactivated by heating at 60 °C (140 °F) for several minutes.]] |
| 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 withstands extreme temperatures as high as 100 °C (212 °F) 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 following ingestion. Beyond regular food poisoning, Staphylococcal enterotoxin B possesses a super-antigen (SAG or SAg) quality and may result in toxic shock syndrome (TSS) by cross-linking MHC-II to T-cell receptors (TCR) with great affinity. Educational Objective: Staphylococcal enterotoxin B is an exotoxin that is produced by Staphylococcus aureus. It is extremely heat-stable and is classically associated with food poisoning. |
| Approved | Approved::Yes |
| Keyword | WBRKeyword::Staphylococcus aureus, WBRKeyword::Staphylococcal enterotoxin B, WBRKeyword::Heat-stable exotoxin, WBRKeyword::Food poisoning, WBRKeyword::Toxin, WBRKeyword::Staph, WBRKeyword::Food-borne illness, WBRKeyword::Toxic shock syndrome, WBRKeyword::Exotoxin, WBRKeyword::enterotoxin |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |