Antibiotics are utilized in ethanol production to control unwanted bacteria from competing with yeast for nutrients during ethanol fermentation. However, there is no published scientific information on whether antibiotic residues in distillers grains (DG) co-products from ethanol production retain their biological activity. Therefore, the objective of this study was to quantify the concentration of various antibiotic residues in DG and determine if those residues are biologically active. Twenty distillers wet grains and 20 distillers dried grains samples were collected quarterly from nine states and 43 ethanol plants in the United States. Samples were analyzed for DM, CP, NDF, crude fat, S, P, pH, and titratable acidity. Samples were also analyzed for the presence of erythromycin, penicillin G, tetracycline, tylosin, and virginiamycin using liquid chromatography and mass spectrometry. Additionally, virginiamycin residues were determined using an FDA-approved method of analysis. Samples were further analyzed for biological activity by exposing sample extracts to varying levels of the sentinel bacteria Escherichia coli ATCC 8739 and Listeria monocytogenes ATCC 19115. Residues that inhibited bacterial growth were considered to have biological activity. Data were analyzed using the mixed procedure of SAS 9.2. Physiochemical characteristics varied among samples, but were consistent with previous findings. Ten percent of samples contained erythromycin residues at concentrations up to 0.87 ppm on a DM basis. Less than one percent of the samples contained penicillin G residues at concentrations up to 0.11 ppm on a DM basis. Less than one percent of samples contained tetracycline residues at concentrations up to 1.12 ppm on a DM basis. None of samples contained tylosin residues. Additionally, 1.3% of samples contained virginiamycin residues at concentrations up to 0.6 ppm on a DM basis. Only one residue sample inhibited growth of E. coli at 104 CFU/g, but this sample contained none of the five antibiotic residues evaluated. No residues inhibited L. monocytogenes growth. These data suggest the likelihood of detectable residues in DG is low, and if they are present, they are found at very low concentrations. It appears that antibiotic residues in DG are inactivated during the production process or are present in sublethal concentrations. There is concern that low concentrations of antibiotics in DG may lead to development of antibiotic resistance in bacteria, especially if antibiotics are present in sublethal doses. However, the risk to human health appears to be minimal. Therefore, future studies on the utilization of antibiotics in ethanol fermentation should focus on the transfer of antibiotic-resistant genes through the ethanol fermentation process and resulting DG production.
University of Minnesota M.S. thesis. June 2012. Major: Animal science. Advisor: Dr. Alfredo DiCostanzo. 1 computer file (PDF); viii, 81 pages.
Compart, Devan Marie Paulus.
Fate and biological activity of antibiotics used in ethanol production..
Retrieved from the University of Minnesota Digital Conservancy,
Content distributed via the University of Minnesota's Digital Conservancy may be subject to additional license and use restrictions applied by the depositor.