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Enterotoxigenic Enterotoxigenic E. coli E. coli  A A watery diarrhea, nausea, abdominal cr watery diarrhea, nausea, abdominal cr amps and low-grade fever for 1-5 days. amps and low-grade fever for 1-5 days.  T T ravellers diarrhea ravellers diarrhea and and diarrhea in child diarrhea in child ren in developing countries ren in developing countries  Transmission is via contaminated food or Transmission is via contaminated food or water. water. Enterotoxigenic Enterotoxigenic E. coli E. coli  diarrhea like cholera diarrhea like cholera  milder milder  nursery travellers diarrhea nursery travellers diarrhea  caused by LT, ST, or LTST. caused by LT, ST, or LTST. Enterotoxigenic Enterotoxigenic E. coli E. coli  Heat labile toxin Heat labile toxin – like choleragen like choleragen – Adenyl cyclase activated Adenyl cyclase activated – cyclic AMP cyclic AMP – secretion waterions secretion waterions  Heat stable toxin Heat stable toxin – Guanylate cyclase activated Guanylate cyclase activated – cyclic GMP cyclic GMP – uptake waterions uptake waterions LT vs ST activity LT vs ST activity E.coli- E.coli- Enteroinvasive EIEC Enteroinvasive EIEC  The organism attaches to the intestinal mucosa v ia pili  Outer membrane proteins are involved in direct penetration, invasion of the intestinal cells, and d estruction of the intestinal mucosa.  There is lateral movement of the organism from one cell to adjacent cells.  Symptoms include fever,severe abdominal cramp s, malaise, and watery diarrhea followed by scant y stools containing blood, mucous, and pus.  resembles shigellosis Enteroinvasive Enteroinvasive E. coli E. coli EI EI EC EC  Dysentery - resembles shigellosis - elder children and adult diarrhea E.coli- E.coli- c. Enteropathogenic EPEC c. Enteropathogenic EPEC  Malaise and low grade fever diarrhea, vomiting, nausea, non-bloody stools  Bundle forming pili are involved in attachment to the intestinal mucosa.  This leads to changes in signal transduction in t he cells, effacement of the microvilli, and to inti mate attachment via a non-fimbrial adhesion c alled intimin.  This is a problem mainly in hospitalized infants and in day care centers. E.coli- E.coli- d. Enterohemorrhagic EHEC d. Enterohemorrhagic EHEC  Hemorrhagic – bloody, copious diarrhea – few leukocytes – afebrile  hemolytic-uremic syndrome – hemolytic anemia – thrombocytopenia low platelets – kidney failure • Usually O157:H7 Transmission electron micrograph Enterohemorrhagic Enterohemorrhagic E. coli E. coli  Vero toxin Vero toxin – “ “ shiga-like” shiga-like”  Hemolysins Hemolysins  younger than 5 year s old,causing hemor rhagic colitis oli oli 肠肠肠肠肠肠肠肠 肠肠肠肠肠肠肠肠  a cause of persistent, watery diarrhea with vo miting and dehydration in infants.  That is autoagglutination in a ‘stacked brick’ arrangement.  the bacteria adheres to the intestinal mucosa and elaborates enterotoxins enteroaggregativ e heat-stable toxin, EAST.  The result is mucosal damage, secretion of la rge amounts of mucus, and a secretory diarrh ea. E.coli- E.coli- Enteroaggregative EAggE Enteroaggregative EAggE C C  Mucous associated autoagglutinins cause aggre gation of the bacteria at the cell surface and res ult in the formation of a mucous biofilm.  The organisms attach via pili and liberate a cyt otoxin distinct from, but similar to the ST and LT enterotoxins liberated by ETEC.  Symptoms incluse watery diarrhea, vomiting, d ehydration and occasional abdominal pain. Various Types of E. coli Various Types of E. coli Summary of Summary of E.coli E.coli str str ains that cause gastr ains that cause gastr oenteritis. oenteritis. Sanitary significance Sanitary significance  Totoal bacterial number: number of bact Totoal bacterial number: number of bact eria contained per ml or gm of the sampl eria contained per ml or gm of the sampl e; the standard of drinking water is less t e; the standard of drinking water is less t han 100. han 100.  Coliform bacteria index: the number of c Coliform bacteria index: the number of c oliform bacteria detected out per 1000 m oliform bacteria detected out per 1000 m l sample; the standard of drinking water l sample; the standard of drinking water is less than 3 is less than 3  Genetically E. coli and Shigella are genetically highly closely related. For practical reasons primarily to avoid confusion they are not placed in the same genus. Not surprisingly there is a lot of overlap between diseases caused by the two organi sms.  1 Enteropathogenic E. coli EPEC. Certain serotypes are commonly found associated with infant diarrhea. The use of ge ne probes has confirmed these strains as different from other groups listed below. There is a characteristic morphological l esion with destruction of microvilli without invasion of the organism that suggests adhesion is important. Clinically one o bserves fever, diarrhea, vomiting and nausea usually with non-bloody stools.  2 Enterotoxigenic E. coli ETEC produce diarrhea resembling cholera but much milder in degree. Also cause traveler’s diarrhea. Two types of plasmid-encoded toxins are produced. a Heat labile toxins which are similar to choleragen see c holera section below. Adenyl cyclase is activated with production of cyclic AMP and increased secretion of water and ion s. b Heat stable toxins; guanylate cyclase is activated which inhibits ionic and water uptake from the gut lumen. Watery d iarrhea, fever and nausea result in both cases.  3 Enteroinvasive E. coli EIEC produce dysentery indistinguishable clinically from shigellosis, see bacillary dysentery below.  4 Enterohemorrhagic E. coli EHEC. These are usually serotype O157: H7. These organisms can produce a hemorrhagic colitis characterized by bloody and copious diarrhea with few leukocytes in afebrile patients. Outbreaks are often caused by contaminated hamburger meat. The organisms can disseminate into the bloodstream producing systemic hemolytic-ure mic syndrome hemolytic anemia, thrombocytopenia and kidney failure. Production of Vero toxin biochemically similar to shiga toxin thus also known as shiga-like is highly associated with this group of organisms; encoded by a phage. He molysins plasmid encoded are also important in pathogenesis.  As noted above, there are at least 4 etiologically distinct diseases. However, in the diagnostic laboratory generally the gro ups are not differentiated and treatment would be on symptomatology. Generally fluid replacement is the primary treatme nt. Antibiotics are generally not used except in severe disease or disease that has progressed to a systemic stage e.g.hemol ytic-uremia syndrome. Two major classes of pili are produced by E. coli : mannose sensitive and mannose resistant pili. The former bind to mannose containing glyocoproteins and the latter to cerebrosides on the host epithelium allowing attac hment. This aids in colonization by E. coli. Shigella Shigella  S. flexneri, S. boydii, S. sonnei, S. S. flexneri, S. boydii, S. sonnei, S. dysenteriae dysenteriae – bacillary dysentery bacillary dysentery – shigellosis shigellosis  bloody feces bloody feces  intestinal pain intestinal pain  pus pus Genral Genral features features  Pili. Pili.  Most strains can not ferment lactos Most strains can not ferment lactos e; S. sonnei can slowly_ ferment lac e; S. sonnei can slowly_ ferment lac tose. tose.  According to O antigen, 4 groups According to O antigen, 4 groups  Easily causing drug-resistence. Easily causing drug-resistence. Shigellosis Shigellosis  within 2-3 days within 2-3 days – epithelial cell damage epithelial cell damage Shiga toxin Shiga toxin  enterotoxic enterotoxic  cytotoxic cytotoxic  inhibits protein synthesis inhibits protein synthesis – lysing 28S rRNA