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
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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- Fall '13
- Virulence factors, Protein biosynthesis, elongation factor