Wednesday, March 14, 2012

Enterotoxin production

Enterotoxin production.
Shigella and EIEC infections are both characterized by a period of watery diarrhea that precedes the onest of scantly dysenteric stools containing blood and mucus. Indeed, in the majority of infections with EIEC and many with Shigella, only watery diarrhea occurs.

Nataro et al. (1995b) cloned and sequenced a plasmid borne gene from EIEC (designated sen), which encodes a novel protein of predicted size 63k Da. It was shown that a mutation of the sen gene causes a significant diminution of the entertoxic activity of the parent strain. And that the purified sen protein elicits rises in ISC without a significant effect on tissue conductance (Nataro, 2001). Clinical considerations.
The clinical infections is characterized by fever, several abdominal cramps, malaise and watery diarrhea, accompanied by toxemia. Scantly stool containing pus, muces and blood follows the watery diarrhea (Mahon and Manuselis 2000). Detection and diagnosis.
I- EIEC strains may be non motile and do not ferment lactose, cross reactions between Shigella and EIEC O antigens have been seen. Isolates may be mistaken for non pathogenic E.coli although EIEC do not decarboxylate lysine, more than 80% of E.coli decarboxylate lysin, for this reasons cases of diarrheal illness resulting from EIEC may be underreported (Mahon and Manuselis, 2000).

Recently, DNA probes to identify EIEC strains have been studied and compared with the sereny test. DNA probes to screen stool samples for EIEC have developed which eliminate the need for various other tests to identify EIEC.
Also a PCR assay with primers derived from also effective in a multiplex PCR system to identify EIEC strains simultaneously with other E.coli categories (Nataro and Kaper 1998).
II- EIEC strains can be difficult to distinguish from Shigella spp and from other E.coli strains including nonpathogenic strains. In general identification of EIEC entails demonstrating that the organism posses the biochemical profile of E.coli, yet with the genotypic or phenotypic characteristics of Shigella spp. The classical phenotypic assay for Shigella and EIEC identification is the sereny test, which correlate the ability of the strain to invade epithelial cells and spread from cell to cell (Green Wood et al., 2002 and Mahon and Manuselis, 2000).

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