Antibiotic residues in distillers grains (DG) were inactivated during the production process or are present in sub-lethal concentrations, according to recently published research at the University of Minnesota and involving SGS North America, Inc.

The study, on the presence and biological activity of antibiotics used in fuel ethanol and corn co-product production by D.M. Paulus Compart and colleagues, has been published in Journal of Animal Science.

The researchers say that antibiotics are used in ethanol production to control bacteria from competing with yeast for nutrients during starch fermentation. However, there is no published scientific information on whether antibiotic residues are present in DG, co-products from ethanol production, or whether they retain their biological activity.

The objectives of this study were to quantify concentrations of various antibiotic residues in DG and determine whether residues were 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 analysed for dry matter, crude protein, neutral detergent fibre (NDF), crude fat, sulphur, phosphorus and pH to describe the nutritional characteristics of the samples evaluated. Samples were also analysed for the presence of erythromycin, penicillin G, tetracycline, tylosin and virginiamycin M1, using liquid chromatography and mass spectrometry. Additionally, virginiamycin residues were determined, using a US Food and Drug Administration-approved bioassay method.

Samples were extracted and further analysed for biological activity by exposing the sample extracts to 10⁴ to 10⁷ colony-froming units (CFU) per mL concentrations of sentinel bacterial strains Escherichia coli ATCC 8739 and Listeria monocytogenes ATCC 19115. Extracts that inhibited bacterial growth were considered to have biological activity.

Physiochemical characteristics varied among samples but were consistent with previous findings.

Thirteen per cent of all samples contained low (≤1.12mg per kg) antibiotic concentrations.

Only one sample extract inhibited growth of Escherichia coli at 10⁴CFU per mL but this sample contained no detectable concentrations of antibiotic residues.

No extracts inhibited Listeria monocytogenes growth.

Paulus Compart conclude their data indicates that the likelihood of detectable concentrations of antibiotic residues in DG is low; and if detected, they are found in very low concentrations.

The inhibition in only one DG sample by sentinel bacteria suggests that antibiotic residues in DG were inactivated during the production process or are present in sub-lethal concentrations.

Reference

^{Paulus Compart D.M., A. M. Carlson, G.I. Crawford, R.C. Fink,F. Diez-Gonzalez, A. DiCostanzo and G.C. Shurson. 2013. Presence and biological activity of antibiotics used in fuel ethanol and corn co-product production. J. Anim. Sci. 91(5):2395-2404. doi: 10.2527/jas.2012-5714}