The use of antimicrobials in the animal industry has increased the prevalence of antimicrobial resistant commensal bacteria in food products derived from animals, which could be associated with antimicrobial resistance in human pathogens. To reduce the influx of antibiotic-resistant bacteria (and genes) to the human microbiota, restrictions on antimicrobials (in food animals) have been implemented in different countries. We investigated the impact of antimicrobial restriction on the frequency of antimicrobial resistant bacteria and genes in pigs. We analyzed the antibiotic susceptibility and resistome of coliforms isolated from animals which were subjected to diets with and without antibiotics during 2 generations. No differences in antimicrobial resistance or antimicrobial resistance genes (richness or abundance) were found when we compared animals fed with and without antibiotics. Fitness costs of antimicrobial resistance in bacteria (in the field) seems to be overestimated.

Withdraw of prophylactic antimicrobials does not change the pigs' resistome