Thermal death of Escherichia coli O157:H7 in cattle feeds.

AIMS: To determine if the temperatures used in feed manufacture are likely to destroy Escherichia coli O157. METHODS AND RESULTS: Two commercial feeds were ground and inoculated with E. coli O157 cells. The feeds were heated to 50, 55, 60, 65 or 70 degrees C. Heating produced quadratic survivor curves, with rapid initial decreases. The survival characteristics of E. coli O157 differed in the two feeds. The reductions observed in one feed may not have been due to heat alone. There was evidence that indigenous anti-E. coli O157 factor(s) in one feed acted with the heat and contributed to the observed rates of bacterial death. Heating at 70 degrees C for 20 or 120 s resulted in approx. 1.3 and 2.2 log reductions in E. coli O157 numbers respectively. Lesser reductions were observed at lower temperatures. CONCLUSIONS: The time/temperature combinations used in commercial pelleting processes would not effectively kill high numbers of E. coli O157. SIGNIFICANCE AND IMPACT OF THE STUDY: This is the first study to look at the survival of E. coli O157 strains after heat treatment within concentrated animal feed. The study provides information on the likely risk of E. coli O157 surviving the animal feed manufacturing process.

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 stx(2)-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 stx(2)-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 stx(1)-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.

An evaluation of raw milk microorganisms as markers of on-farm hygiene practices related to milking.

Dairy farm hygiene audits were undertaken at 24 farms during summer and winter and the results compared with transformed bacterial indicator levels in raw milk samples collected during each audit. The bacterial indicators measured were total viable counts, Escherichia coli, coliforms, Bacillus spp., Bifidobacteria spp., and Pseudomonas spp. The results of initial comparisons using Pearson product-moment correlation coefficients showed presumptive relationships between some bacterial groups and the subjective quantitative audit scores. When investigated further using linear regression, the presumptive relationships were found to be influenced by external factors. Possible reasons for the low correlations between on-farm hygiene and bacterial indicator counts in raw milk were further investigated. Measurements of the uncertainty associated with the bacteriological results were undertaken and revealed geometric relative standard deviations that ranged from 0.019 to 1.05. Toward the higher end of this scale, the uncertainty associated with the laboratory estimations of bacterial numbers may have been large enough to blur hygiene score-marker bacteria relationships. The samples obtained from on-farm raw milk storage tanks were representative of the whole tank contents and not a significant source of error. Although total bacterial counts are widely acknowledged by the milk industry as not always giving a true measure of on-farm hygiene during milking, we were unable to find any marker bacteria that showed consistently higher correlations and were thus better suited as indicators of on-farm hygiene.