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Blocks the release of inhibitory neurotransmitters GABA and glycine
1%
5/410
Blocks the presynaptic release of acetylcholine at the neuromuscular junction
0%
2/410
Inactivates mammalian 60S ribosomal subunit
14%
56/410
Stimulates release of cytokines
3%
11/410
Stimulates adenylate cyclase (increasing cAMP)
80%
328/410
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Enterotoxigenic E. coli (ETEC) causes diarrhea via production of a heat-labile toxin that stimulates adenylate cyclase, thus increasing levels of cAMP. ETEC causes diarrhea via secretion of toxins. ETEC can produce both a heat-stable (ST) and heat-labile toxin (LT). Both toxins can cause watery diarrhea. LT acts in a mechanism similar to that of cholera toxin. In particular, LT stimulates adenylate cyclase to produce increased levels of cAMP, which causes an increased secretion of chloride ions by cells in the gastrointestinal tract. This leads to water efflux, and subsequent watery diarrhea. The ST toxin acts on guanylate cyclase. A mnemonic that is helpful for remembering the mechanisms of these toxins is: "Labile like the Air, Stable like the Ground." (That is, LT acts on Adenylate cyclase; ST acts on Guanylate cyclase.) The linked video discusses the most common and important subtypes of E. coli in more detail, including ETEC. Incorrect Answers: Answer 1: Blocking release of inhibitory neurotransmitters GABA and glycine is the mechanism of tetanus toxin. Answer 2: Blocking the presynaptic release of acetylcholine at the neuromuscular junction is the mechanism of botulinum toxin. Answer 3: Shiga-like toxin inactivates the mammalian 60S ribosomal subunit. Answer 4: Pyrogenic exotoxins stimulate release of cytokines causing rash, fever, toxic shock syndrome, and can be produced by S. aureus and S. pyogenes.
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