This study attempted to isolate Escherichia coli O157:H7 from the rectal feces of 125 clinically normal dairy cattle of different age groups and to determine the virulence potential of the isolates. Isolation was carried out in several steps which included enrichment in tryptic soy broth, direct plating in selective sorbitol MacConkey agar medium containing cefixime and potassium tellurite, and inoculation of non-sorbitol fermenting colonies in standard biochemical media. Organisms identified by the biochemical tests were tested for slide agglutination using adsorbed O rabbit antisera against E. coli O157 antigen. Isolates were also subjected to PCR assay for detection of E. coli O157:H7 and verotoxin genes. E. coli O157:H7 was not found as shown by non-agglutination to O157 antigen of the three recovered nonsorbitol fermenting isolates and non-amplification of E. coli O157:H7 standard primers. Isolates from one cattle gave a 1.9 kilobase product, characteristic of E. coli possessing verotoxin (VT)2, giving a herd prevalence of 0.8%. This study showed that verotoxin-producing E. coli (VTEC) non-O157 was carried by seemingly healthy dairy cattle and that this organism was not widespread in this farm. Nevertheless, the occurrence of VTEC in this herd could result in human infections.

Keywords: dairy cattle; non-O157 Escherichia coli, verotoxin, VTEC