Samples of rectal faeces were collected immediately after slaughter fr
om 400 cattle each month for a 1-year period and from 1000 each of she
ep, pigs and poultry over the same period. Samples were examined for E
scherichia coli O157 by enrichment culture in buffered peptone water w
ith vancomycin, cefixime and cefsulodin followed by immunomagnetic sep
aration and culture of magnetic particles onto cefixime tellurite sorb
itol MacConkey agar. E. coli O157 was isolated from 752 (15.7%) of 480
0 cattle, 22 (2.2%) of 1000 sheep and from 4 (0.4%) of 1000 pigs, but
not from any of 1000 chickens. Of the cattle sampled, 1840 (38.4%) wer
e prime beef animals, 1661 (34.6%) were dairy animals being culled and
the status could not be determined for the other 1299 (27%) animals.
E. coli O157 was found in 246 (13.4%) of the 1840 beef cattle and 268
(16.1%) of the 1661 dairy cattle. The monthly prevalence of E. coli O1
57 in cattle was 4.8-36.8% and was at its highest in spring and late s
ummer. Seventeen of the 22 isolates from sheep were also made over the
summer period. All E. coli O157 isolates from sheep and 749 (99.6%) o
f the 752 E. coli O157 isolates from cattle were verocytotoxigenic as
determined by Vero cell assay and DNA hybridization, eaeA gene positiv
e, contained a 92 kb plasmid and were thus typical of strains causing
infections in man. In contrast isolates from pigs were non-toxigenic,
eaeA gene negative and did not contain a 92 kb plasmid and would, ther
efore, be unlikely to be a source of infection for man.