Contamination Rates and Antimicrobial Resistance in Enterococcus spp., Escherichia coli, and Salmonella Isolated from "No Antibiotics Added''-Labeled Chicken Products

In the United States, products from chickens that were not administered antimicrobial medications during growout can contain labels stating "no antibiotics added.'' Here we compared microbial profiles of chicken products labeled as coming from birds raised without antimicrobial medications (N=201; NON) with chicken products carrying conventional labels (N=201; CONV). There were no differences in percentages of samples positive for Enterococcus spp. (CONV: 17.4%; NON: 21.3%) or Escherichia coli (CONV: 25.9%; NON: 22.3%). The number of samples positive for Salmonella was low in both groups, but statistically higher in the NON samples (5.0%) versus CONV samples (1.5%; p < 0.05). Conversely, CONV samples contained higher concentrations of coliforms (CONV: 3.0 log(10)CFU/mL; NON: 2.5 log(10)CFU/mL; p < 0.05). E. coli (N=190) and Enterococcus spp. isolates (N=113) were tested for resistance to common antimicrobials. E. coli isolates from CONV samples were more frequently resistant to at least one antimicrobial (CONV: 61.3%; NON: 41.2%; p < 0.05). Enterococcus spp. isolates from both groups were equally likely to be resistant to at least one antimicrobial, but Enterococcus spp. isolates from CONV samples were more likely to be resistant to erythromycin, kanamycin, and gentamicin (p < 0.05). Taken together, these data suggest that NON samples may more frequently carry Salmonella; however, E. coli and Enterococcus spp. found on CONV are more likely to be resistant to some antimicrobials.