A comparison of two pre-enrichment media prior to immunomagnetic separation for the isolation of E. coli O157 from bovine faeces.

To compare the sensitivity of two pre-enrichment broth media prior to immunomagnetic separation for the isolation of Escherichia coli O157 from cattle faeces. One-gram portions of 721 cattle faeces collected from 43 farms were pre-enriched in buffered peptone water containing vancomycin, cefixime and cefsulodin (BPW-VCC) and buffered peptone water without additives (BPW-WOA), respectively. A total of 137 samples were positive for E. coli O157: 127 pre-enriched with BPW-WOA and 89 pre-enriched in BPW-VCC. Representative isolates were tested for phage type, verotoxin and eae (E. coli attaching and effacing) gene sequences, resulting in the recognition of eight different types. All the E. coli O157 types recognized were isolated by both methods except for three different strains, each of which were isolated only on a single occasion: two by BPW-WOA and another by BPW-VCC. The results clearly demonstrate, under the conditions of this study, that BPW without antibiotics was the superior pre-enrichment medium for the isolation of E. coli O157 from cattle faeces. The use of BPW-WOA in preference to BPW-VCC for the isolation of E. coli O157 from cattle faeces in future research and outbreak studies should lead to a higher number of positive isolates.