WBR0300

Author	[[PageAuthor::Serge Korjian M.D. (Reviewed by Alison Leibowitz) (Reviewed by Serge Korjian)]]
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::Exotoxin A is an important virulence factor of Pseudomonas aeruginosa. The toxin blocks protein synthesis by ADP ribosylation of elongation factor 2 (EF2). The Pseudomonas aeruginosa Exotoxin A is usually inactivated by heating at 60 °C for several minutes.]]
Answer B	AnswerB::''Vibrio cholerae'' exotoxin
Answer B Explanation	[[AnswerBExp::The Vibrio cholerae exotoxin is a protein complex part of a large group of bacterial exotoxins referred to as "A/B toxins" in essence because they are formed from two subunits. The toxin is responsible for the massive, watery diarrhea characteristic of cholera infection. It acts by by causing ATP-mediated efflux of chloride ions into the gut lumen. The Vibrio cholerae exotoxin is usually inactivated by heating at 60 °C 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 withstanding temperatures as high as 100 °C 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 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). This disables the inhibition of adenylyl cyclase activity, leading to increased concentrations of cAMP. The Bordetella pertussis Exotoxin is usually inactivated by heating at 60 °C 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 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: Staphylococcal enterotoxin B is an exotoxin, produced by Staphylococcus aureus, known to be extremely heat-stable. It is classically associated with acute food poisoning. References: Balaban N, Rasooly A. Staphylococcal enterotoxins. International Journal of Food Microbiology. 2000;61(1):1-10.]]
Approved	Approved::Yes
Keyword	[[WBRKeyword::Staphylococcus aureus]], WBRKeyword::Staphylococcal enterotoxin B, WBRKeyword::Heat-stable exotoxin, WBRKeyword::toxin, WBRKeyword::staph, WBRKeyword::food-borne illness, WBRKeyword::toxic shock syndrome, WBRKeyword::exotoxin, WBRKeyword::endotoxin
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