Wednesday, March 14, 2012

Gastroenteritis associaed with Escherichia coli

E.coli may cause several types of diarrheal illness. There are five major categories of diarrhegenic E.coli, based on definite virulence factors, clinical manifestations produced, epidemiology, and different O:H stereotypes.

These include the following:
• Enteropathogenic Escherichia coli (EPEC), which cause infantile entritis, especially in tropical countries.
• Enteropathogenic Escherichia coli (EPEC), which are responsible for community acquired diarrheal disease in areas of poor sanitation and are the commonest cause of traveller’s diarrhea.
• Entero-invasive Escherichia coli (EIEC), which cause an illness resembling Shigella dysentery in patients of all ages.
• Enterohemorrhagic Escherichia coli (EHEC), which caused disease in developed countries. Stereotype O157:H7.
• Entero-aggregative Escherichia. coli (EaggEC), which cause chronic diarrhaeal disease in certain developing countries (Nataro, 2001). Phenotypic assay based on virulence characteristics.
Identification of diarrheagenic E.coli strains requires that these organisms can be differentiated from nonpathogenic members of the normal flora. Serotypic markers correlate, sometimes very closely, with specific categories of diarrheagenic E.coli, however, these markers are rarely sufficient in and themselves to reliably identify a strain as diarrheagenic (an exception may be strains of serotype O157:H7, a serotype that serves as a marker for virulent enterohemorrhagic E.coli strains, nevertheless, EHEC of serotypes other than O157:H7 are being identified with increasing frequency in sporadic and epidimic cases). In addition to its limited sensitivity and specificity serotyping is tedious and expensive and is performed reliable only by a small number of reference laboratories. Thus, detection of diarrheagenic E.coli has focused increasingly on the identification of characteristics which themselves determine the virulence of these organisms. This may include detection of the genes encoding these traits (Nataro and Kaper, 1998).

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