by Marla Luther, PhD, Center for Veterinary Medicine, FDA

The expansion of the fuel ethanol industry markedly increased the volume of distillers products being produced and marketed as animal feed ingredients. The FDA’s Center for Veterinary Medicine (CVM) acknowledged a potential risk of distillers products contaminated with antibiotic residues to animals and the potential human food safety concerns if antibiotic residues accumulate in the milk, meat and/or eggs. Therefore, the FDA developed an analytical method to analyze distillers products for antibiotic residues and gained intelligence about the extent of antibiotic residues using the preliminary method to survey a limited number of distillers products.

In order to monitor and regulate antibiotic residues in distillers products, CVM needed an analytical method capable of identifying and quantifying these compounds. The CVM’s Office of Research (OR) developed a multiclass, multiresidue method for the detection and estimation of level of twelve antibiotics: ampicillin, penicillin G, tetracycline, oxytetracycline, chlortetracycline, bacitracin A, virginiamycin M1, chloramphenicol, erythromycin A, clarithromycin, tylosin, and streptomycin as well as monensin, an ionophore. The method was published in “Multiclass, multiresidue method for the detection of antibiotic residues in distillers grains by liquid chromatography and ion trap tandem mass spectrometry,” in the Journal of Chromatography. One component of the method validation, method ruggedness, was tested using incurred samples collected by field investigators during 2008 (see Nationwide Survey of Distillers Grains for Antibiotic Residues, December 19, 2007).

In the 2008 survey, samples were collected for informational purposes in order to determine the extent of antibiotic residues and to estimate their levels in distillers products produced by U.S. ethanol production facilities. The FDA sought to gather 60 distiller grain samples from domestic ethanol processors for research purposes only, specifically to assist with method validation. Due to multiple inquiries for FDA’s findings, CVM is providing this summary of its activities and sampling results.

From the 60 domestic samples that were requested, a total of 49 domestic samples were sent to the CVM and used to test the ruggedness of the method undergoing the single lab method validation process. The 49 domestic samples included 28 dried distillers grain samples, 17 wet distillers grains samples, and 4 distillers grains solubles (stillage) samples. These samples were analyzed using the method being developed by CVM. The data were evaluated using Guidance for Industry #118, “Mass Spectrometry for Confirmation of the Identity of Animal Drug Residues.” Using these criteria, samples were identified as not containing antibiotic residues, containing tentatively identified residues, or containing confirmed residues of one or more antibiotics.

Preliminary results showed antibiotic residues were detected in 28 of the samples with the most prevalent being virginiamycin (17 samples), erythromycin (10 samples), and tylosin (5 samples). Although antibiotic residues were detected in 28 samples, quantifiable antibiotic residues were found in only 17 of the samples. Virginiamycin was estimated in 10 samples at levels of 0.1 ppm to 0.5 ppm, on a dry weight basis. Erythromycin was estimated in 7 samples at levels of 0.1 ppm to 1.5 ppm, on a dry weight basis. There were no other antibiotics found at levels high enough to estimate.

The progress in FDA’s ability to regulate antibiotic residues in distillers products is two-fold. First, analysis of these samples demonstrated that the method developed by OR is generally applicable to the variable distillers product matrices. Subsequent to this survey, the method was disseminated in Laboratory Information Bulletin 4438, “Analysis of Antibiotics in Distillers Grains Using Liquid Chromatography and Ion Trap Tandem Mass Spectrometry.” A follow-up survey in 2010 used the method in other FDA laboratories, ensuring the method and techniques could be reliably and accurately used for regulatory purposes. A summary of the FY2010 survey is available on the FDA website in, “Report of FY 2010 Nationwide Survey of Distillers Products for Antibiotic Residues.” Second, the detection of residues in distillers products confirms that the use of antibiotics as a processing aid in ethanol fermentation should be regulated to ensure animal and human health when these products are used as animal feed ingredients. CVM is preparing a guidance document for industry on the presence of antibiotics in distillers products as a result of the use of antibiotics in ethanol production. CVM is also reviewing food additive petitions for the use of virginamycin, penicillin and erythromycin in ethanol production.

Additional Information:

December 19, 2007 Nationwide Survey of Distillers Grains for Antibiotic Residues

De Alwis, H. and D. N. Heller, J. Chromatogr.A 1217 (2010) 3076-3084.

Guidance for Industry #118, “Mass Spectrometry for Confirmation of the Identity of Animal Drug Residues

Detection of Antibiotic Residues in Distillers Grains

September 30, 2009 FY 2010 Nationwide Survey of Distillers Grains for Antibiotic Residues

Report of FY 2010 Nationwide Survey of Distillers Products for Antibiotic Residues