Bacteriology

PATHOGENIC STRAINS OF ESCHERICHIA COLI THAT CAUSES DIARRHEAL DISEASES IN MAN

Written by MicroDok

1. ENTEROPATHOGENIC E. COLI (EPEC): EPEC strains causes diarrhea in infants and children in developing countries. EPEC strains adhere strictly to the epithelial cells of the intestines by means of an adhesion molecule and start proliferating. They cause lesions known as effacing or attaching-effacing lesions that affects the microvilli of the intestines, and this lead to profuse and prolonged diarrhea in infants. Vomiting can also be accompanied in an EPEC strain infection. The diarrhea caused by EPEC strains is generally self-limiting but can be chronic and last longer in the infected children. The mode of transmission of this type of E. coli­-associated diarrheal disease is via the feacal-oral route.

2. ENTEROTOXIGENIC E. COLI (ETEC): ETEC strains are the main causative agents of traveler’s diarrhea in people visiting developing countries. It causes watery diarrhea in both infants and adults. ETEC strains produce a variety of enterotoxins that are responsible for the watery diarrhea they produce in their host. The enterotoxins (which are heat-stable and heat-labile in nature) bind to the epithelial cells of the intestines where they stimulate guanylate cyclase that activates the production of cyclic guanosine monophosphate (cGMP). This action mediates the inhibition of sodium ions (Na+) and stimulates the secretion of chloride ions (Cl) and/or electrolytes and water into the lumen of the small intestine that finally result into watery diarrhea. The mode of transmission of this type of E. coli­-associated diarrheal disease is via the feacal- oral route especially through the consumption of foods contaminated with human feaces.

3. ENTEROHAEMORRHAGIC E. COLI (EHEC): EHEC strains are the causative agents of haemorrhagic colitis (a life-threatening bloody diarrhea), and they mainly affect the colon (large intestine) unlike other pathogenic strains of E. coli that attack solely the small intestines. They cause severe abdominal pain followed by bloody diarrhea and haemolytic uraemic syndrome (HUS) in humans. EHEC strains produce verotoxins (a shiga-like toxin) and are sometimes called verocytotoxin-producing E. coli (VTEC) because their toxin is cytotoxic on Vero cells (that originated from kidney cells of African green monkeys) in tissue cultures. Consumption of food stuffs such as beef and other meat products from animals colonized by the bacteria are the main source of acquiring the pathogen. Spinach and unpasteurized fruit juices can also aid in the transmission of EHEC strains. EHEC disease (bloody diarrhea) is a disease of the developed countries. It occurs at a low frequency in developing countries. E. coli 0157:H7 serotype is a major form of EHEC strains as both are genetically related. The mode of transmission of this type of E. coli­-associated diarrheal disease is via the feacal-oral route.

4. ENTEROINVASIVE E. COLI (EIEC): EIEC strains cause E. coli-associated dysentery that resembles shigellosis. Shigellosis is caused by Shigella dysenteriae. Though EIEC infection may occur worldwide, children under the age of 5 years old and who live in developing countries are mostly affected by the disease. EIEC is toxigenic (i.e. it produces enterotoxins), and they penetrate the colonic mucosa and/or epithelial cells of the intestine where they cause inflammatory ulcerations that result in dysentery. The stool of infected patients is usually accompanied with blood, mucous, and pus cells. Contaminated food and water are the main source of acquiring the EIEC infections. The mode of transmission of this type of E. coli­-associated diarrheal disease is via the feacal-oral route.

5. ENTEROAGGREGATIVE E. COLI (EAEC): EAEC strains are the causative agents of food-borne disease in developed countries and chronic and acute diarrhea in people living in developing countries. They cause vomiting and watery diarrhea in infants and children living in developing nations. EAEC strains are notorious in adhering tightly to the intestinal mucosa of its human host to form biofilms or aggregates of bacterial cells. This type of E. coli-associated diarrhea is often associated with neonatal-nursery outbreaks in hospital settings. The mode of transmission of this type of E. coli­-associated diarrheal disease is via the feacal-oral route.

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MicroDok

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