What is EHEC? EHEC or enterohaemorrhagic E. Coli is one type of Escherichia colii strains which known as the caused of bloody diarrhea. Hemorrhagic colitis (HC) or bloody diarrhea can advance to the possibly deadly hemolytic uremic syndrome (HUS) that known as the special characteristics that distinguish EHEC from other strain.
Escherichia coli is a gram-negative, rod-shaped bacterium and normaly met in the intestine of humans and warm-blooded animals. Majority strains of E. coli are not dangerous. Some strains even so, such as enterohaemorrhagic E. coli (EHEC), can induce terrible foodborne disease. It is transferred to humans mainly through consumption of contaminated foods, such as raw or undercooked ground meat products and raw milk. Faecal contamination of water and other foods, as well as cross-contamination during food preparation (with beef and other meat products, contaminated surfaces and kitchen utensils), will also lead to infection.
The following are the types of eschericia coli strains:
- Enterohemorrhagic Escherichia coli (EHEC):Attaches to colonic enterocytes and releases virulence factors, most commonly shiga-like toxins (Stx), which disrupt protein synthesis, leading to cell death and subsequent bloody diarrhea. Release of toxins can lead to systemic complications. E coli O157:H7 is the most commonly recognized EHEC.
- Enteropathogenic E coli (EPEC): Utilizes an adhesion protein, intimin, to bind to small bowel epithelial cells, subsequently destroying the normal microvillar architecture and a leading cause of diarrhea in infants.
- Enteroinvasive E coli (EIEC):Similar to Shigella infection, leading to a secretory diarrhea/dysentery. An intracellular pathogen, which can invade and replicate within macrophages and epithelial cells.
- Enterotoxigenic E coli (ETEC):A noninvasive strain that binds to small bowel enterocytes and produces heat-labile (LT) or heat-stable (ST) enterotoxins. It is the most common cause of traveler’s diarrhea.
- Enteroaggregative E coli (EAEC):A strain of noninvasive bacteria that bind to the intestinal mucosa and adhere to each other, creating a thick biofilm with release of secretory enterotoxins and cytotoxins. Usually associated with chronic diarrhea in children in developing countries.
- Diffusely adherent E coli (DAEC):Colonizes the small bowel, leading to the development of fingerlike projections that wrap around the bacteria.
Escherichia coli enteric infection, as with all diarrheal illnesses, affects all ages and races and both sexes. However, people at the extremes of age, and immunocompromised patients, are more susceptible, especially to complications and prolonged infection.
E coli infections generally have an incubation period of 1 to 3 days, although in some circumstances incubation can be as long as 8 days. Patients present with gastroenteritis, diarrhea being the principal symptom. It may be associated with additional GI symptoms, such as abdominal pain or discomfort, anorexia, or nausea, although vomiting is unusual. Systemic symptoms, including lethargy or fever, may be present. However, Enterohemorrhagic E coli (EHEC) have more specific clinical sign. The shiga-like toxin in EHEC causes a bloody diarrhea with abdominal pain, fever and vomiting may also occur.
The production of verotoxin or Shiga toxins (Stx) is the characteristic of EHEC. Of these, O157:H7 is the most often implicated in illness worldwide. The infectious dose for O157:H7 is estimated to be 10 – 100 cells. The toxin plays a role in the intense inflammatory response produced by EHEC strains and may explain the ability of EHEC strains to a life-threatening disease, such as haemolytic uraemic syndrome (HUS).
HUS is characterized by acute renal failure, haemolytic anaemia and thrombocytopenia. It is estimated that up to 10% of patients with EHEC infection may develop HUS, with a case-fatality rate ranging from 3% to 5%. . It can cause neurological complications (such as seizure, stroke and coma) in 25% of HUS patients and chronic renal sequelae, usually mild, in around 50% of survivors. The incidence of EHEC infections varies by age group, with the highest incidence of reported cases occurring in children aged under 15 years.
In order to identify pathogenic species such as E coli O157:H7, stool should be cultured on specialist plates such as sorbitol MacConkey agar (SMAC). Stool cultures can confirm the diagnosis, with serotyping used to identify the exact strain. The presence of EHEC can be confirmed by performing serological testing to identify the shiga-like toxins using typing antiserum, enzyme-linked immunosorbent assay (ELISA), immunofluorescence, immunochemistry, or latex agglutination. Alternatively, PCR can identify the genes encoding these toxins.
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