Escherichia coli O157 in cattle and sheep at slaughter, on beef and lamb carcasses and in raw beef and lamb products in South Yorkshire, UK.

A 1 year study of Escherichia coli O157 in cattle and sheep at slaughter, on beef and lamb carcasses and in raw beef and lamb products from retail butchers' shops was performed in the Sheffield area. Each month, samples of rectal faeces were collected immediately after slaughter from 400 cattle and 600 sheep, and 400-430 samples of raw meat products were purchased from butchers' shops. Meat samples were also obtained from 1500 beef and 1500 lamb carcasses. All samples were examined for E. coli O157 by enrichment culture, immunomagnetic separation and culture of magnetic particles onto cefixime tellurite sorbitol MacConkey agar. Raw meat products were also examined for numbers of generic E. coli by a standard membrane culture method. E. coli O157 was isolated from 620 (12.9%) of 4800 cattle, 100 (7.4%) of 7200 sheep, 21 (1.4%) of 1500 beef carcasses, 10 (0.7%) of 1500 lamb carcasses and from 22 (0.44%) of 4983 raw meat products. E. coli O157 was isolated more frequently from lamb products (0.8%) than from beef products (0.4%). Numbers of generic E. coli in meat products reached seasonal peaks in July and August with counts of > 10(4)/g occurring more frequently in lamb products (50.8 and 42.4%, respectively) than in beef products (19.3 and 23.8%, respectively). The majority of E. coli O157 strains, from animals, carcasses and meat samples, were isolated during the summer. Most were verocytotoxigenic as determined by Vero cell assay and DNA hybridisation, eaeA gene positive and contained a 92 kb plasmid. The isolates were compared with 66 isolates from human cases over the same period. A combination of phage type, toxin genotype and plasmid analysis allowed subdivision of all the E. coli O157 isolates into 96 subtypes. Of these subtypes, 53 (55%) were isolated only from bovine faecal samples. However, 61 (92%) of the 66 isolates from humans belonged to 13 subtypes which were also found in the animal population.