Potential risk-factors affecting Salmonella sp. and Escherichia coli occurrence and distribution in Midwestern United States swine feed mills

Aim: This study aimed to evaluate the patterns and potential risk factors associated with the occurrence of Salmonella sp. and Escherichia coli in selected United States swine feed mills. Methods and Results: A total of 405 samples were collected during fall 2018, spring and summer 2019 from selected sites including floors, equipment, shoes and feed in six feed mills in the US Midwest region. Each sample was analysed for the presence of Salmonella and E. coli with culture methods and confirmed by PCR. A survey regarding production volumes, hygiene practices and microbial testing capabilities was conducted in each facility All mills had at least one sampling site positive for either Salmonella or E. coli. Of the 405 samples, 4.7, and 14.1% were positive for Salmonella sp., and E. coli respectively. Sites with higher percentages of positive samples were the receiving, manufacturing, and control area floors. The survey responses indicated that the age of the mill might be a risk factor for bacterial contamination: the older the facility, the higher the number of positive samples. Other risk factors evaluated, such as the production capacity, did not appear to relate to bacterial prevalence. Conclusion: The data documents the presence of E. coli and Salmonella in selected US swine feed mills, and an association between E. coli occurrence and number of ingredient suppliers to feed mill. Significance and Impact of the Study: This information could be used to understand risk factors affecting the occurrence of Salmonella sp. and E. coli in feed mills and help implement monitoring and mitigation strategies for public health.