Location: Food and Feed Safety Research
Title: Evaluation of feeding distiller's grains, containing virginiamycin, on antimicrobial susceptibilities in fecal isolates of Enterococcus and Escherichia coli and prevalence of resistance genes in cattle Authors
Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 24, 2013
Publication Date: February 3, 2014
Repository URL: http://handle.nal.usda.gov/10113/58591
Citation: Edrington, T.S., Bischoff, K.M., Loneragan, G.H., Nisbet, D.J. 2014. Evaluation of feeding distiller's grains, containing virginiamycin, on antimicrobial susceptibilities in fecal isolates of Enterococcus and Escherichia coli and prevalence of resistance genes in cattle. Journal of Animal Science. 92:1144-1149. Interpretive Summary: Distiller’s grains are a by-product of the ethanol industry and are fed to cattle. To prevent bacterial contamination during the ethanol production process, antibiotics may be used, residues of which may end up in the distiller’s grains. We conducted a study to determine if feeding distiller’s grains produced in fermentations using different levels of antibiotics and containing known concentrations of antibiotic residues would influence antimicrobial susceptibility and the prevalence of resistance genes in cattle. Distiller’s grains were fed to beef steers for 49 days and fecal samples were collected and cultured for Escherichia coli and Enterococcus throughout the experimental period. Results indicate that although antibiotic residues were in the distiller’s grains fed to these cattle, the effects, if any, on antimicrobial susceptibility and the prevalence of resistance genes were mild. This is good news for the ethanol and cattle feeding industries.
Technical Abstract: Dried distiller’s grains (DG), produced from fermentations using no antibiotic (Control) or dosed with 2 or 20 ppm virginiamycin product and containing 0, 0.7, and 8.9 ppm virginiamycin, respectively, were fed to cattle and effects on antibiotic sensitivity and prevalence of resistance genes in commensal bacteria were examined. Twenty-four head of crossbred beef steers were fed one of four diets [containing 8% of each of the 0, 2, and 20 ppm DG and a fourth utilizing 8% of the control DG + 22.5 g/ton V-Max50™ (virginiamycin, positive control)] for 7 weeks. Fecal samples were collected throughout the experimental period, cultured for Escherichia coli and Enterococcus, and isolates examined for antimicrobial susceptibility, resistance genes (vatE, ermB, and msrC in Enterococcus), and integrons (E. coli). No treatment differences (P > 0.05) were observed in antimicrobial susceptibility of the E. coli isolates. Enterococcus isolates were resistant to more antibiotics; however this was influenced by the species of Enterococcus, not treatment (P > 0.10). No differences (P > 0.05) were observed for the prevalence of the msrC gene. The prevalence of ermB was higher (P < 0.05) in the control isolates after 4 and 6 weeks, while at week 7, prevalence was greater (P < 0.01) in the 2 and 20 ppm treatments. Taken together, the minor treatment differences observed for the presence of ermB coupled with the lack of effect on antimicrobial susceptibility patterns suggest that feeding DG containing virginiamycin residues should have minimal, if any, impact on dissemination of antibiotic resistance.