Antimicrobial resistance in commensal Escherichia coli and Enterococcus spp. is influenced by production system, antimicrobial use, and biosecurity measures on Spanish pig farms.

Overall, this study evidences that the production system and, to a lesser extent, the biosecurity measures, contribute to the AMR development in commensal E. coli and Enterococcus spp., with antimicrobial usage as the main differential factor, and demonstrates the potential value of these bacteria as bioindicators on pig farms in AMR surveillance programs.