Escherichia coli O157:H7 is a foodborne pathogenic bacterium that can reside undetected in the gastrointestinal tract of cattle because colonization by this bacterium is asymptomatic. Recent research has indicated that swine can carry and transmit this pathogen as well. The development of more advanced and sensitive detection techniques has improved the limit of detection and increased sensitivity for this important pathogen. This study was undertaken to determine the prevalence of E. coli O157 in cattle and swine in Mexico with the more sensitive detection technique of immunomagnetic bead separation. Samples (n = 60 per farm) were taken from four cattle and four swine farms (n = 240 cattle samples, n = 240 swine samples) located throughout central Mexico in October 2001. The prevalence of E. coli O157 was found to be only 1.25% on cattle farms and 2.1% on swine farms. The prevalence in cattle in this study is lower than that reported in the United States and could be related to the lower reported prevalence of E. coli O157 in humans in Mexico. However, further research is needed to verify prevalence throughout other regions of Mexico, as well as prevalence during other seasons of the year.

Aims: This study was carried out to determine the survival time of Escherichia coli, Salmonella choleraesuis, Aujeszky's Disease virus and Blue Eye Disease virus in ensilages based on the solid fraction of pig faeces. Methods and Results:The four micro-organisms were inoculated into microsilos based on the solid fraction of pig faeces, sorghum and molasses. They were left for 0, 7, 14, 28 and 56 days, after which the state of each microsilo was evaluated, and isolation of the inoculated agents was attempted. The four inoculated agents were isolated only on day 0 of ensilage. The viral agents were identi®ed through the cytopathic effect and¯uorescence. Conclusions, Signi®cance and Impact of the Study: It is concluded that ensilages based on the solid fraction of pig faeces appear to reduce the risk of the transmission of the agents inoculated in this study and help to reduce the environmental impact by using the solid in animal feed.

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