Shiga toxin-producing Escherichia coli, faecal coliforms and coliphage in animal feeds

Aims: Animal feeds (n = 226), collected from pastures or feeding troughs on UK farms and from feed manufacturers’ bulk stores, were analysed for Escherichia coli harbouring shiga-toxin genes (stx), faecal coliforms, coliphages and stx-harbouring bacteriophages. Methods and Results: Samples comprised of 79 fresh grasses, 26 silages and 121 dried or heat-processed feeds (DPF). Five of the 79 (6·3%) fresh grass samples contained stx2-E. coli. stx-E. coli were not detected in the silages or DPF that were examined. Faecal coliforms were detected in 75/79 (94·9%) of fresh grasses, 19/26 (73·1%) of silages and 36/121 (29·8%) of processed feeds. Coliphages were detected in 63/79 (79·7%) and 18/26 (69·2%) of fresh grasses and silages, respectively. Coliphages were isolated at a significantly lower prevalence of 5% (6/121) from processed feeds. Although stx2-phage was isolated from the enrichment of a single grass sample, stx-phages were not detected in any of the silage or processed feeds. We did not detect stx1-phage in any of the samples collected. Conclusions: Pastures have the potential to act as transmission vectors for stx-harbouring E. coli for grazed livestock. Significance and Impact of the Study: This is the first study to report on the prevalence of E. coli harbouring stx genes, faecal coliforms, coliphages and stx-harbouring bacteriophages in a range of feedstuffs destined for consumption by UK livestock. This study provides information on the risk of feeds to the spread of stx-phages between livestock and/or the environment.