Description
Enterohemorrhagic E. coli (EHEC) have been isolated from patients who have hemorrhagic colitis and hemolytic-uremic syndrome (HUS). To date, O157:H7 is the most frequently encountered EHEC strain in stools from these patients. This is probably due to the fact that conventional diagnostic strategies such as O157 latex agglutination assays rely on the unique sorbitol negative fermentation property of this strain. The major weakness in this approach is that at least 50 other EHEC serotypes have been reported to be associated with the development of hemorrhagic colitis and HUS. One virulence trait of all EHEC strains is the ability to produce cytotoxin(s) called Shiga toxin (ST) or verotoxin (VT) ST-I and ST-II are the two most common toxins and individual EHEC strains have the ability to produce both or either, in varying quantities. Therefore, ST production and not individual (O157:H7) serotype identification is a better diagnostic strategy for the determination of EHEC associated disease. Cytotoxin can be identified by a specific cytotoxin assay described by Karmali. The cytotoxin assay, however, is labor intensive, requires tissue culture facilities, has not been standardized and may take up to 72 hours to confirm the presence of cytotoxin. Exploiting the EHEC attribute to produce these toxins, EHEC was developed for the direct detection of ST producing strains from stool specimens or culture systems