Antibiotics are used in commercial fuel ethanol production facilities to control bacterial contamination, according to Dr Marla Luther of the Center for Veterinary Medicine at the FDA in a new report Nationwide Survey of Distillers Products for Antibiotic Residues for 2010. The FDA’s Center for Veterinary Medicine (CVM) has taken steps to determine the impact of the use of antibiotics in commercial fuel ethanol production facilities because ethanol co-products, primary distiller’s grains – also known as DDGS – are used as animal feed ingredients.

The Division of Animal Feeds within CVM issued a field assignment during fiscal year 2010 to survey distiller’s products for antimicrobial residues. Samples were collected for informational purposes in order to learn more about the antibiotics used during the production of distillers products and to determine the antibiotic levels in these distillers products. Due to the interest in this area, CVM is providing this summary of the sampling results.

The assignment was issued under the FDA Feed Contaminants Program and requested that 60 samples be collected and analysed for antibiotics. A total of 46 samples were collected by FDA investigators and these samples were sent to FDA laboratories for analysis. These 46 samples consisted of 18 domestic–import samples (samples were in domestic commerce in the US when collected but the country of origin was outside the US) and 28 domestic samples (samples were in domestic commerce in the US when collected and the country of origin was the US).

FDA laboratories analyzed the 46 samples for residues of up to 12 antibiotics (ampicillin, penicillin G, chlortetracycline, oxytetracycline, tetracycline, clarithromycin, erythromycin, streptomycin, virginiamycin M1, bacitracin A, chloramphenicol, tylosin) and monensin using the method found in Laboratory Information Bulletin (LIB) 4438. This method was entitled ‘Analysis of Antibiotics in Distillers Grains Using Liquid Chromatography and Ion Trap Tandem Mass Spectrometry’. The FDA laboratories also determined the percentage moisture in each sample using ‘AOAC Official Method 934.01 (4.1.03) Loss on Drying (moisture) at 95-100°C for Feeds’.

CVM has completed its examination of the samples. Although, five of the 46 samples collected were initially reported as positive for antibiotics (above the limit of quantitation [LOQ] of the method) by the FDA laboratories, upon further evaluation of the analytical worksheets one sample was found to have a level of virginiamycin M1 that was below the LOQ verified by the laboratory and thus was no longer considered to contain antibiotics. The limit of quantification using the LIB 4438 method is 0.1ppm for virginiamycin M1, 0.5ppm for erythromycin and 1.0ppm for penicillin.

Consequently, FDA/CVM’s final analysis finds that four of the 46 samples were quantifiable in the laboratory for antibiotics. The four positive samples contained a total of five antibiotic residues. Of the four positive samples, three were domestic samples and one was domestic–import sample.

The results of the three positive domestic samples are detailed below. Virginiamycin M1 was detected at around 0.16mg per kg (parts per million or ppm) on a dry weight basis in one sample. Erythromycin was detected at around 0.58ppm on a dry weight basis in another sample. The final positive domestic sample contained virginiamycin M1 at about 0.15ppm on a dry weight basis and penicillin G at about 0.24ppm on a dry weight basis. Although the amount of penicillin found (0.24 ppm) is lower than the LOQ for penicillin, the laboratory was able to accurately quantify this sample for penicillin below 1ppm.

The positive domestic import sample was from Canada and around 0.18ppm of virginiamycin M1 was detected by the FDA laboratory on a dry weight basis. This finding was not confirmed by CVM/FDA scientists because the analytical worksheets were not available.

The sampling assignment results are providing FDA with a better idea of the extent and level of antibiotics in distillers products. CVM will take this information into consideration as it develops a policy for antibiotic residues in distillers products. Since the primary objective of this assignment was to collect data on antibiotic residues in distillers products to support policy development, CVM does not anticipate regulatory follow-up.