2 Enteropathogenic E. coli subgroups that correlate well with toxicoinfection belong to the Enteropathogenic(EPEC) and enterotoxigenic(ETEC) types. They produce diarrheal diseases when ingested in large numbers through contaminated foods and water. The symptoms are more like those in cholera. The incidence is high in many developing countries and is directly related to poor sanitation.
3 CharacteristicsMany serotypes in both subgroups are involved in human gastroenteritis. They are Gram-negative small curved rods, nonsporulating and motile(nonmotile strains can be present). The strains are facultative anaerobes and can grow effectively in both simple and complex media and many foods. Growth occurs between 10-50C, with optimum at 30-37C. Some strains can grow below 10C. The cells are sensitive to pasteurization.
4 HabitatAll strains in both subgroups can establish in the small intestine of humans without producing symptoms. The carriers can shed the organisms in feces and can contaminate food and water directly or indirectly. Many animals, including domestic ones, can also harbor different serotypes of both subgroups and contaminate soil, water and food. In animals, many serotypes may not produce disease symptoms.
5 Toxins and Toxin Production The strains in ETEC subgroup produce two types of enterotoxins: Heat labile(LT). And heat stable(ST). A strain can produce either LT or ST or both. LT toxin is an antigenic protein, similar to cholera toxin that induces fluid secretion by epithelial cells of small intestine. ST is lower in M.Wt and is nonantigenic. It also increases fluid secretion by intestinal cells, but through a different mode of action.
6 The genetic determinants of the enterotoxins in ETEC are plasmid linked and can be transferred to other E. coli strains. The production of enterotoxins by ETEC strains is influenced by media composition, culture age, and alteration of a culture during growth. Optimum production occurs in a nutritionally rich medium at pH 8.5. Aeration of broth facilitates good toxin production. The toxins are detected in growing culture within 24 h at 35C. However, the toxin can be produced by the cells growing at 25-40C
7 Disease and SymptomsEPEC strains were initially thought to be associated with infant diarrhea in many tropical and developing countries, causing high mortality. In contast, ETEC strains are regarded as the cause of traveler”s diarrhea, a nonfata diarrheal disease. However, some consider that various EPEC strains can cause traveler”s diarrhea. Ingestion of several millions of viable cells is necessary for the symptoms to occur within h. Symptoms include mild to severe diarrhea that lastsfor24-30 h. In severe cases, dehydration and shock may accompany diarrhea. Those who develop symptoms may shed the organisms in feces after recovery.
8 Food AssociationMany types of foods, including meat products, fish, milk and dairy products, vegetables, baked products, and water have been associated with gastroenteritis of E. coli origin in many countries. These include serotypes from both EPEC and ETEC subgroups. Direct and indirect contamination of these foods (and water) with fecal materials, along with improper storage temperature and inadequate heat treatment, were involved in these incidences.
9 PreventionPrevention contamination of food and water, directly or indirectly by fecal matter. Effective sanitation in water supplies and treating and disposing sewage. Prevent contamination of food due to poor personal hygiene by people who shed the pathogen. If the pathogen is present in very small numbers in a food, temperature abuse of the food can facilitate multiplication of cells to high levels necessary for the disease symptoms. Thus, food should be refrigerated or eaten quickly , preferably after heating.
10 Detection MethodsSelective enrichment of sample(food, water and feces). Isolation of pathogens on selective agar medium. Biochemical characterization of suspected isolates. Confirmation tests to detect toxins involve one or more serological tests e.g. ELISA.