Enumeration of Escherichia coli O157 in cattle faeces using most probable number technique and automated immunomagnetic separation

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Abstract
Aims: To determine the numbers of Escherichia coli O157 present in the faeces of naturally infected cattle. Methods and Results: A combination of the most probable number (MPN) technique and automated immunomagnetic separation (AIMS) was used to enumerate E. coli O157 in cattle faeces from both pasture‐fed and grain‐fed animals. A total of 22 E. coli O157 positive faecal samples were enumerated for E. coli O157 (10 from pasture‐fed and 12 from grain‐fed animals). The numbers of E. coli O157 in cattle faeces varied from undetectable (−1 of faeces) to 2·4 × 104 MPN g−1. There was no significant difference (P = 0·06) between the numbers of E. coli O157 in pasture‐fed or grain‐fed cattle faeces, although the geometric mean (antilog of the mean of log10 transformed MPN values) was higher in grain‐fed (130 MPN g−1) than in pasture‐fed (13 MPN g−1). Conclusions: Although the number of samples tested is small, the results indicate that E. coli O157 make up a small proportion of the total E. coli population present in cattle faeces. Significance and Impact of the Study: Information on the numbers of E. coli O157 present in cattle will assist in developing more robust quantitative risk assessments and formulating intervention strategies.

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