Distillers grains (DGs) are useful animal feeds but during ethanol production, antimicrobials may be added which can result in residues in DGs. The Center for Veterinary Medicine issued an assignment in 2010 to survey DGs for antimicrobial residues. From the 46 samples tested, residues were found as follows: (samples positive, average ppm as is); virginiamycin (vir) (4, 0.14), penicillin (pen) (1, 0.17), and erythromycin (ery) (1, 0.50). In response, a study was designed to determine the impact that low levels of antimicrobial may have upon bacteria representative of the human GI tract. Enterococcus sp and Campylobacter sp with known minimum inhibitory concentrations were exposed to low levels (≤1.0 µg/ml) of pen, vir, a pen/vir blend (93%/7%), and ery. The strains were evaluated for decreased susceptibility to the test antimicrobials. Results indicate that low levels of pen, vir and the pen/vir blend did not select for strain variants with decreased susceptibility. In contrast, ery gave mixed results. There was no selection for resistance in Campylobacter sp. (0.5 µg/ml) or in Enterococcus sp. (0.1 µg/ml). However, resistant variants of Enterococcus sp were observed with 0.25 and 0.5 µg/ml ery. It was concluded that pen and vir (≤1.0 µg/ml) or ery (0.1 µg/ml) did not select for resistant variants. However exposure of Enterococcus sp. to ery (0.25 and 0.5 µg/ml) did select for resistant phenotypes. Given these results it is suggested that ery residues in distillers grains be more fully evaluated given the importance of this antimicrobial in clinical medicine.