Salmonella and antimicrobial-resistant bacteria recovered from livestock feed components include Escherichia coli ST167 expressing NDM-5 carbapenemase

Abstract

Antimicrobial-resistant bacteria, including both pathogens and commensal organisms, can be introduced into livestock populations by a variety of mechanisms including contaminated water, animal and human movement, and animal feed. We hypothesized that animal feed is an important mechanism for introduction of both Salmonella and commensal reservoir bacteria harboring mobile antimicrobial-resistance genes into livestock populations. The identification of high-risk feed components may allow targeted interventions that will reduce carriage of these organisms in food animals and ultimately improve food safety. We collected 666 livestock feed component samples from 16 individual local mills (n = 263) and from 2 corporations with multiple feed mills located across the US (n = 403). Salmonella enterica were recovered from 7.2 % of samples (n = 48) and were more likely to be found (P < 0.02) in blended feeds, animal protein components, and oilseed meals. We also recovered two carbapenem-resistant Enterobacterales isolates (0.3 %), both E. coli sequence type 167 O101:H9 carrying an IncF plasmid mediated bla_NDM-5, from two dried distiller’s grain samples sourced from two states in the upper Midwest. Antimicrobial-resistant commensal bacteria were found in all feed component types, although the overall prevalence of each resistance phenotype was below seven percent except for AmpC β-lactamase producing strains (19.5 %). The identification of feed components with higher risk of contamination suggests that targeted interventions could potentially reduce feed contamination. Contamination reduction efforts focusing on feed components with heating and cooling steps may reduce the proliferation of pathogens and resistant bacterial strains in finished feed fed to livestock.