Which of the following bacteria acts by increasing cAMP:
Correct Answer: Vibrio cholerae
Description: Ans. (a) Vibrio cholerae Cholera toxin (CT) Protein enterotoxin Composed of 2 subunit: A - (Active monomeric moiety) B - (Pentameric binding moiety) Mechanism of action: The B-pentamer binds to GM, ganglioside, a glycolipid on the surface of epithelial cells that serves as toxin receptor | The activated A subunit (A,) irreversibly transfers ADP ribose from NAD to regulatory component of adenyl cyclase | Up regulation of adenylate cyclase | Intracellular increase in cAMP In intestine cAMP inhibits the absorptive sodium transpo system in the villus cells and activates the secretory chloride system in the crypt cells. Thus, increased cAMP leads to leads to accumulation of sodium chloride in the intestinal lumen. To maintain osmolality water moves passively to the lumen and isotonic diarrhea stas. Note Though peurbation of the adenylate cylase pathway is the primary mechanism of cholera; cholera toxin also enhances the intestinal secretions prostaglandins and/or neural histamine receptors. Remember: Mechanism of action of some impoant bacterial toxin. Heat labile toxin of E. coli - | cAMP Heat stable toxin of E. coli - Increase cGMP Botulism toxin - Inhibit release of acetylcholine from peripheral nerves. Tetanus toxin - Inhibit release of glycine and GABA at presynaptic terminals. Diphtheria toxin - Inhibit protein synthesis by inactiviting EF-2.
Category:
Microbiology
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