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Prevalence of Escherichia coli 0157 in cattle

Escherichia coli 0157 is an impor tant foodborne pathogen. Fortunately foodborne incidents associated with this organism in Australia are rare but its effects are frequently severe. In addition,it is a major public health concern in some countries which import Australian beef, especially the USA which has its own testing regimes.

The prevalence and concentration of E.coli 0157 in cattle faeces have been identified as important factors which influence the risk associated with the consumption of contaminated beef products in the USA. As information on the presence of E.coli 0157 at the various stages of production is being accumulated, the factors that can influence the faecal shedding of the organism by cattle are being identified. These include an animal's age, diet and husbandry.

In Australia, beef cattle are produced on pasture or are finished on grain-supplemented diets in feed lots (lot fed). Food Science Australia workers have recently published the results of a study to determine if the diet and husbandry practices in these two production systems correlate with the prevalence and numbers of total E.coli and E.coli 0157 shed by cattle raised in each system (Journal of Applied Microbiology 97 2004: 362).

For the purposes of this study, lot fed animals were defined as those fed a grain enriched diet for at least 60 days prior to slaughter. The number of lot fed cattle sampled in each State was determined by the number of cattle on feed in Australia. The number of grass fed cattle sampled from each State was determined from that State's production as a percentage of total national production. The survey was conducted during the period of widespread drought in Australia and this may have changed husbandry practices in some areas, influencing the results of the survey.

The workers found that there was no significant difference in the prevalence of toxigenic E.coli 0157 between grass fed and lot fed cattle at slaughter. E.coli 0157 were isolated from 15 percent of faecal samples from lot fed cattle and 10 percent from grass fed cattle. A total of 310 samples were analysed.

This incidence is somewhat lower than reported in US lot fed cattle, 23–28 percent, and Italian cattle, 17 percent. Sample size and the method of analysis can affect estimations of prevalence.

There was also no significant difference between the number of generic E. coli shed by lot fed cattle and grass fed cattle.

The research workers conclude that while feeding history did not significantly affect the prevalence or numbers of generic E.coli or E.coli 0157 in cattle at slaughter, further studies are necessary. These could yield information that would help identify risks associated with carcass contamination from infected animals. Further data in this area is required to aid in the development of a whole-of-chain approach for managing the risks of exposure to E.coli 0157.

This research was co-funded by CSIRO and Meat & Livestock Australia.
For further information contact:
Dr Trish Desmarchelier or Dr Narelle Fegan at Food Science Australia, Tel:+61 7 3214 2000.