Published On: Thu, Jun 16th, 2011

In the News – Amid new E coli cases.What is E.coli ?

What is E. coli?

Escherichia coli (E. coli) are gram-negative bacteria that can survive in an environment with or without air (facultative anaerobes) and, depending on the environment, may or may not produce thin hair-like structures (flagella or pili) that allow the bacteria to move and to attach to human cells. These bacteria commonly live in the intestines of people and animals worldwide. There are many strains (over 700 serotypes) of E. coli. Most of the E. coli are normal inhabitants of the small intestine and colon and do not cause disease in the intestines (non-pathogenic). Nevertheless, these non-pathogenic E. coli can cause disease if they spread outside of the intestines, for example, into the urinary tract (where they cause bladder or kidney infections), or into the blood stream (sepsis). Other E. coli strains (enterovirulent E. coli strains or EEC) cause “poisoning” or diarrhea even though they usually remain within the intestine by producing toxins or intestinal inflammation. There are four to six groups (some researchers combine groups) of E. coli strains that comprise EEC.

  • EHEC (enterohemorrhagic E. coli)
  • ETEC (enterotoxigenic E. coli)
  • EPEC (enteropathogenic E. coli)
  • EIEC (enteroinvasive E. coli
  • EAEC (enteroadherent E. coli
  • EAggEC (enteroaggregative E. coli)

E. coli were first isolated by T. Escherich in 1885 and were named after him. The over 700 serotypes are identified by small antigenic changes in their surface “O” antigens (lipopolysaccharides or molecules on the bacterial surface of gram-negative bacteria), for example E. coli 0157 or E. coli 055. These serotypes are identified by immunological tests. E coli strains are further distinguished by “H” protein antigens (different types of flagella that make the bacteria motile). Consequently, a particular E. coli strain can be identified as H, followed by a number, and this identifier is added to the “O” name; for example, E. coli 0157:H7. Although this name designation seems complicated, researchers and clinicians use these antigenic identifiers to track specific E. coli strains that cause outbreaks of disease.

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