Effects of feeding wet corn distiller's grains with solubles with or without monensin and tylosin on the prevalence and antimicrobial susceptibilities of fecal food-borne pathogenic and commensal bacteria in feedlot cattle

¹ Department of Diagnostic Medicine and Pathobiology, Kansas State University, Manhattan, Kansas 66506
² Department of Animal Sciences and Industry, Kansas State University, Manhattan, Kansas 66506

^* To whom correspondence should be addressed. E-mail: tnagaraj{at}vet.k-state.edu.

	Abstract

Distiller' grains, a co-product of ethanol production from cereal grains, are comprised principally of the bran, protein, and germ fractions and are commonly supplemented in ruminant diets. The objective of this study was to assess the effect of feeding wet distiller's grains with solubles (WDGS) and monensin and tylosin on the prevalence and antimicrobial susceptibilities of fecal food-borne and commensal bacteria in feedlot cattle. Cattle were fed 0 or 25% WDGS in steam-flaked corn-based diets with the addition of no antimicrobials, monensin, or monensin and tylosin. Fecal samples were collected from each animal (n = 370) on d 122 and 136 of the 150 d finishing period, and cultured for Escherichia coli O157. Fecal samples were also pooled by pen (n = 54) and cultured for E. coli O157, Salmonella, commensal E. coli and Enterococcus species. Antimicrobial resistance was assessed by determining antimicrobial susceptibilities of pen bacterial isolates and quantifying antimicrobial resistance genes in fecal samples by real-time PCR. Individual animal prevalence of E. coli O157 in feces collected from cattle fed WDGS was higher (P < 0.001) compared to cattle not fed WDGS on d 122, but not on d 136. There were no treatment effects on the prevalence of E. coli O157 or Salmonella spp. in pooled fecal samples. Antimicrobial susceptibility results showed Enterococcus isolates from cattle fed monensin or monensin and tylosin had greater levels of resistance towards macrolides (P = 0.01). There was no effect of diet or antimicrobials on concentrations of 2 antimicrobial resistance genes, ermB or tetM, in fecal samples. Results from this study indicate that WDGS may have an effect on prevalence of E. coli O157 and the concentration of selected antimicrobial resistance genes, but does not appear to affect antimicrobial susceptibility patterns in Enterococcus and generic E. coli isolates.

Key Words: antimicrobial feed additives, antimicrobial susceptibility, cattle, distiller's grains, Escherichia coli O157