Enteropathogenic E.coli infection:

·         Most strains of E.coli are common members of the enteric microflora in the human colon and are not pathogenic. Few strains are potential foodborne pathogens.

·         They produce potent enterotoxins and may cause life-threatening diarrheal disease and urinary tract infections.

Six virulence groups of diarrheagrnic E.coli.

1.       Enterotoxigenic E.coli (ETEC)

·         ETEC strain produces one or both of two distinct enterotoxins- heat stable (ST) and heat-labile (LT).

·         The genes for ST and LT production and for colonization factors are plasmid-borne.

·         The colonizing factors are generally fimbriae or pili.

·         ST binds to glycoprotein receptor coupled to guanylate cyclase on the surface of intestinal epithelial cells.

·         Activation of guanylate cyclase stimulates the production of cGMP, which leads to secretion of electrolytes and water into the lumen of the small intestine causing watery diarrhea, characteristic of an ETEC infection.

·           LT binds to specific gangliosides (GM1) on epithelial cells. Upon binding, A polypeptide chain catalyzes ADP ribosylation of G protein that activates adenylate cyclase, and increases cAMP production, resulting in hypersecretion of electrolytes and water into the intestinal lumen.

·         These strains are the Leading cause of Traveller’s diarrhea.

·         Primary vehicles are food such as - fresh vegetables and water

·         The local population is usually resistant to the infecting strains presumably they have acquired resistance to the endemic ETEC strain.

·         Caused by ingestion of 10⁶ – 10¹⁰ viable cells/gm that must colonize the small intestine and produce the enterotoxins.

·         Fever and sudden diarrhea.

2.       Enteroinvasive E.coli (EIEC)

·         Causes diarrhea by penetrating and multiplying within the intestinal epithelial cells.

·         Causes invasive disease in the colon, the produces watery sometimes bloody diarrhea.

·         EIECs are taken up by phagocytes, but escape lysis in the phagolysosomes, grow in the cytoplasm, and move into other cells.

·         Strains generally do not produce enterotoxins.

·         The incubation period is between 2-48 hrs with an average of 18 hrs.

·         Salmon is common food vehicle.

3.       Enteropathogenic E.coli (EPEC)

·         EPEC attach to the brush border of intestinal epithelial cells and cause a specific type of cell damage called effacing lesions.

·         Effacing lesion or attaching-effacing lesion (AE) represent the destruction of brush border microvilli adjacent to adhering bacteria.

·         This cell destruction leads to subsequent diarrhea.

·         Possesses adherance factor plasmids that enable adherance to the intestinal mucosa

·         EPEC causes diarrheal disease in infants and small children.

·         Do not cause invasive disease or produce toxins.

4.       Enterohemorrhagic E.coli (EHEC)

·         EHEC strains affect only the large intestine and produce large quantities of Shiga like toxins.

·         EHEC strains carry the bacteriophage encoded genetic determinants for shiga-like toxin (Stx-1 and Stx-2 proteins).

·         EHEC produces lesions causing hemorrhagic colitis with severe abdominal pain and cramps followed by bloody diarrhea.

·             Stx-1 and Stx-2 have also been implicated in Hemolytic uremic syndrome, a severe hemolytic anemia that leads to kidney failure.

·         Most widely distributed EHEC is E.coli O157: H7.

·         The bacteria grow in the small intestine and produce toxins.

·         Consumption of contaminated uncooked or undercooked meat (mass-processed ground beef).

·         Dairy products, fresh fruits, raw vegetables contamination by fecal material from cattle carrying E.coli.

·         Symptoms: abdominal cramps, nausea, vomiting, fever, dehydration.

·         Approx. 4 days incubation period.

·         Symptoms lasts for 3 to 7 days.

·         Bloody red stools is a unique symptom for this syndrome.

·         Infection dose low as 10 cfu.

5.       Enteroaggregative E.coli (EAGGEC)

·         EAggEC strains adhere to epithelial cells in localized regions, forming clumps of bacteria with stacked brick appearance.

·         Some strains produce a Heat-stable enterotoxin (ST)

·         Carry plasmid needed for the production of fimbriae responsible for aggregative expression and outer membrane protein (OMP).

·         Persistant diarrhea lasts > 14 days.

6.       Diffusely adhering E.coli (DAEC)

·         DAEC strains adhere over the entire surface of epithelial cells and usually cause disease in immunologically naive or malnourished children.

·         May have an undefined virulence factor

7.       Travellers Diarrhea:

·         E.coli can be the common cause of “traveller’s diarrhea”, a common enteric infection causing watery diarrhea in travellers to developing countries.

·         Primary causal agent- ETEC and some EPEC strains.

·         Other orgainsms are rotaviruses, noroviruses, Shigella spp, Klebsiella pneumoniae and Enterobacter cloacae.

Prevention:

·         Chill foods rapidly in small quantities

·         Cook food throughly

·         Practise personal hygiene

·         Protect and treat water

·         Dispose of sewage in a sanitary manner

·         Prepare food in a sanitary manner

·         Traveller’s diarrhea can be prevented by avoiding consumption of local water and uncooked food.