Between April 1996 and March 1997 we examined 5093 samples of raw beef and lamb
products for the presence of E. coli O157. Samples were purchased from 81 small butchers'
shops in south Yorkshire. In March 1997 we also examined five samples of dried mint for the
presence of E. coli O157.
Strains of E. coli O157 were isolated by enrichment culture in modified buffered peptone
water followed by immunomagnetic separation and culture of magnetic beads onto cefixime
tellurite sorbitol MacConkey agar. Strains were characterized by phage typing, toxin
genotyping and plasmid analysis.
Strains of E. coli O157 were isolated from 72 (1·4%) of 5093 samples; it was isolated from
36 (1·1%) of 3216 samples of beef products and from 29 (2·9%) samples of lamb products.
The highest prevalence was found in lamb sausages and lamb burgers where E. coli O157 was
isolated from 3 (4·1%) of 73 and 18 (3·7%) of 484 samples respectively. Strains of E. coli
O157 were isolated most frequently during early summer. Strains of E. coli O157 were also
isolated from 2 of 5 samples of dried mint although we did not determine how the mint had
All isolates of E. coli O157 were Verocytotoxin-producing as determined by both Vero cell
assay and DNA hybridization for the genes encoding Verocytotoxin and all were positive for
the eaeA gene. A combination of phage typing, toxin genotyping and plasmid profile
subdivided the 72 strains of E. coli isolated into 20 different subtypes, of which 18 were
indistinguishable from strains isolated previously from cattle and sheep; of these 18 strains, 8
were indistinguishable from strains isolated from human cases of infection during the study