S123: Impact of using virginiamycin in the fuel ethanol production process on distillers grains coproducts

Antibiotics are frequently used to reduce bacterial contamination in commercial fuel ethanol fermentations, but there is concern that antibiotic residues may persist in the distillers grains (DDG) coproducts.  A study was conducted at the National Corn-to-Ethanol Research Center to trace the antibiotic virginiamycin through the ethanol production process, and to evaluate the impact of feeding the resultant DDGs on antibiotic sensitivity of commensal bacteria in cattle.  Three fermentor runs were performed with a commercial virginiamycin product: F1, no antibiotic; F2, 2 ppm dose; and F3, 20 ppm dose.  Using LC/MS, virginiamycin M was detected in beer, whole stillage, thin stillage, syrup, wet-cake, and DDGs from the F3 run.  Furthermore, antibiotic activity was detected by bioassay in DDGs from both the F2 and F3 runs (0.7 ppm and 8.9 ppm virginiamycin, respectively).  The DDGs were incorporated into feedlot rations containing 8% of each respective DDG batch and fed to crossbred beef steers.  No changes (P > 0.05) in antimicrobial susceptibilities of fecal E. coli isolates were observed due to treatment.  More antibiotic resistance was observed in fecal Enterococcus isolates, but this was related to the species rather than treatment.  Treatment had little effect on prevalence of resistance genes in Enterococcus isolates, the exception being the ermB gene which was higher in the control and 2 ppm treatments on some collection days.  Although biologically active virginiamycin may persist in DDGs, it appears that feeding these DDGs should have minimal impact on dissemination of antibiotic resistance among enteric bacteria.