|
Enterotoxigenic ''Escherichia coli'' (ETEC) is a type of ''Escherichia coli'' and the leading bacterial cause of diarrhea in the developing world, as well as the most common cause of travelers' diarrhea.〔(World Health Organization. Enterotoxigenic ''Escherichia coli'' (ETEC). )〕 Insufficient data exist, but conservative estimates suggest that each year, approximately 210 million cases and 380,000 deaths occur, mostly in children, from ETEC.〔(World Health Organization. Institute for Vaccine Research. Enterotoxigenic ''escherichia coli'' (ETEC). )〕 A number of pathogenic isolates are termed ETEC, but the main hallmarks of this type of bacteria are expression of one or more enterotoxins and presence of fimbriae used for attachment to host intestinal cells. ==Enterotoxins == Enterotoxins produced by ETEC include heat-labile enterotoxin (LT) and heat-stable enterotoxin (ST). Some strains of ETEC produce a heat-labile exotoxin (LT) that is under the genetic control of a plasmid. The strain also triggers fimbrial adhesion that extends from the surface of the E. coli cell and has a B subunit that attaches to the GM1 ganglioside at the brush border of the small intestine epithelium cell and stimulates the entry of the A subunit into the cell, where the latter activates adenylyl cyclase.() This increases the amount of cAMP, and results in intense and prolonged hypersecretion of chlorides and water; while also inhibiting the reabsorption of sodium. The gut lumen contains large amount of fluid, and motility, leading to diarrhea that can last for several days. LT is an antigen that can cross-react with the enterotoxin to stimulate the production of neutralizing immunoglobulin antibodies in the serum of previously infected people with enterotoxigenic E coli. People that reside in locations that have high prevalence of this strain are likely to possess antibodies to said strain and are less prone to presenting with diarrhea if re-exposed to the strain. () Some strains of ETEC produce another toxin called heat-stable enterotoxin (ST) which are regulated by a heterogeneous group of plasmids. ST activates guanylyl cyclase in the signal pathway of the enteric epithelial cells and triggers fluid secretion. Also, some ST E. coli strains are capable of making LT; the strain that contains both ST and LT toxins produces a more severe diarrhea. The plasmids carrying the genes for enterotoxins may also encode genes used for the colonization factors that initiate the attachment of E. coli strains to the intestinal epithelium. Mnemonic: Labile like the Air (cAMP), Stable like the Ground(cGMP). 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Enterotoxigenic Escherichia coli」の詳細全文を読む スポンサード リンク
|