Chapter 27HostmicrobeMed micro13th ed2

Hock inducedbytoxicshocksyndromeantigenofstaph

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Unformatted text preview: pithelial cytoplasmic membrane A1 activates adenylate cyclase to produce cAMP which brings about secretion of chloride and bicarbonate ions from mucosal cells in intestinal lumen which causes water secretion into lumen Enterotoxins Enterotoxins Shigella dysenteriae enterotoxin (called Shiga toxin) and a similar Shiga­like toxin produced by enteropathogenic Escherichia coli (O157:H7 strain) are protein synthesis inhibiting AB toxins but they specifically kill small intestine cells, leading to bloody diarrhea. Cholera, Salmonella, Shigella, and Escherichia produce enterotoxins when colonizing intestine Other food poisoning, like Staphylococcus, Clostridia, and Bacillus cereus produce toxin in food; thus toxin ingested. Cholera Enterotoxin Cholera Enterotoxin Cholera enterotoxin causes massive fluid loss from the intestine AB toxin: B binds to GM1, a ganglioside, a glycolipid found in cell membrane of intestinal epithelial cells A chain crosses membrane, activates adenylate cyclase: ATP cAMP cAMP induces secretion of Cl­ & bicarbonate ions from mucosal cells into intestinal lumen. As ion concentration increases, water secreted into lumen. Massive fluid loss resulting in life threatening dehydration & electrolyte depletion. Endotoxins Endotoxins o o o o o Gram­negative bacteria produce lipopolysaccharides as part of the outer layer of their cell envelope. Lipid A portion responsible for toxicity, polysaccharide fraction makes complex water soluble & immunogenic. These are called endotoxins because they are generally cell­bound but are released in large amounts when the cells are lysed Stimulates host cells to release proteins called endogenous pyrogens causing fever Other symptoms: diarrhea, rapid decrease in lymphocyte, leukocyte, and platelet numbers, release of cytokines : & generalized inflammation, death (by hemmoragic shock and tissue necrosis) Disseminated intravascular coagulation (DIC): multiple clots then bleeding. Not as toxic as exotoxins. Ex: LD50 for mice is 200­400 µg for endotoxin but LD50 for botulinum toxin is about 25 picograms (pg), about 10 million times less. Endotoxin Endotoxin 250o C for 30 minutes for inactivation Major problem if contamination of medical devices LPS affects macrophages, monocytes, and neutrophils by binding to a receptor on these cells & transfer to a CD 14. LPS­CD14 then complexes with a Toll­like receptor to initiate a response that releases cytokines & tumor necrosis factor alpha: later immunology chapter Next Chapter: Physical, Chemical & Anatomical Next Chapter: Physical, Chemical & Anatomical Barriers to Infection...
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