diarrheagenic Escherichia coli isolates are clas- sified into specific groups including enterohemorrhagic E coli (EHEC), enteropathogenic E coli (EPEC), enterotoxigenic E. coli (ETEC), and enteroinvasive E. coli (EIEC) based on their virulence factors,. mechanisms of pathogenicity, clinical syndromes, and distinct OH serotypes (Nataro and Kaper 1998; Meng and oth- ers 2001). Pathogenic E. coli are important food-borne pathogens with EHEC receiving the most emphasis based on disease symptoms. Most EHEC infections in the United States the UK are caused serotype 0157 others 2001; 2003), and more than 75000 cases of food-borne disease attributable to E coli O157: H7 occur every year (Perna and ot hare onn11.