Escherichia coli O157 is a foodborne pathogen that can be transmitted by contaminated ground beef and is shed naturally in cattle feces. Recent reports indicated that feeding distillers' grains (DG) to cattle increased fecal shedding and prevalence of E. coli O157. In Minnesota, feeding DG with solubles (DGS) to livestock became widespread within the last 10 years, but there is no report about the prevalence of E. coli O157 in beef cattle in this state. This study was undertaken to survey the fecal prevalence of E. coli O157 in cattle fed diets containing DG and its association with environmental conditions and management practices. Fecal samples were collected from three feedlots during a 1-year period. All animals in those feedlots were fed different DGS levels. E. coli O157 presence was determined using a combination of enrichment, immunomagnetic separation, plating onto sorbitol MacConkey agar, and confirmation of isolates by immunoassay and multiplex virulence genes polymerase chain reaction analysis. Overall, E. coli O157 was confirmed in 9.7% of samples. Prevalence during summer was 30% and declined to less than 10% the rest of the year. In animals grouped by dietary DGS concentration, no significant difference in prevalence (12.0 and 5.5%) was detected between the low and the high average groups (less and more than 20%). Previous feeding of DGS before arriving to the feedlot also had no influence on fecal prevalence. The presence of several interacting variables, uncontrolled in a real-life feedlot environment, was the likely reason for our observation and suggested that at the levels studied, DGS had no effect on the STEC O157 prevalence in cattle populations.

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Enterohaemorrhagic Escherichia coli (EHEC) serotype O157:H7 is carried asymptomatically by cattle gastrointestinal tract and the inclusion of distillers grains solids (DGS) in feed is thought to be a factor in the prevalence and persistence of EHEC O157 in a herd. The present study surveys the faecal prevalence of E. coli O157 in cattle processed at an abattoir in the Upper Midwest and its association with environmental factors and feeding practices. Faecal samples were collected from pre-processing cows during a 1-year period. E. coli O157 prevalence was estimated isolation of putative positives and confirmation of isolates by immunoassay and multiplex virulence genes PCR analysis. Overall, E. coli O157 was confirmed in 11.2% of samples. Prevalence during winter was the highest at 14% followed by summer (11.6%) and declined to less than 8% the rest of the year. Winter was the only season that had a statistically significant effect on prevalence. As a category unto itself, DGS feeding before arrival had no significant influence on faecal prevalence. However, we found a significant interaction of DGS feeding and summer. This observation is extremely relevant because it corroborates a previous study and suggests possible feeding practices to abate EHEC O157 presence during harvest.