Characterization of Escherichia coli and Salmonella enterica from cattle feed ingredients

The objectives of this study were (1) to evaluate the frequency with which feed ingredients or mixed feeds in cattle feedlots were contaminated with Escherichia coli and Salmonella spp. and (2) to evaluate the antimicrobial susceptibility patterns of non-type-specific Escherichia coli and Salmonella spp. recovered from feed ingredients or mixed feeds. Approximately 30 individual samples were collected from each of several feed commodities present on two cattle feedlots each month for 1 year. Half of the samples were cultured for Escherichia coli, and the other half were cultured for Salmonella spp. E. coli was recovered from 48.2% (516/1070) of the samples and from all feed ingredient types at least once. Salmonella spp. were recovered from 5.3% (57/1070) of samples. Overall, 40.3% (207/514) of E. coli isolates and 54.4% (31/57) of Salmonella spp. isolates were susceptible to all antimicrobials tested in the panel. Bacterial contamination of feed ingredients used at cattle feedlots with enteric bacteria is relatively common. In some cases, the enteric organisms are resistant to one or more antimicrobials. Feed ingredients may be a source of genetic elements associated with antimicrobial resistance for feedlot cattle. To be successful in minimizing foodborne pathogens and antimicrobial resistance in the cattle feedlot setting, it is important to consider the myriad of potential sources of these organisms or genetic elements.