Antimicrobial effects, and selection for AMR by non-antibiotic drugs on bacterial communities

Antimicrobial resistance (AMR) is a major threat to human, veterinary, and agricultural health. AMR can be directly selected for by antibiotics, and indirectly co-selected for by biocides and metals. Some evidence suggests that non-antibiotic drugs (NADs) can co-select for AMR, but previous work focused on exposing single model bacterial species to predominately high concentrations of NADs. Here, we determined the antimicrobial effect and selective potential of three commonly used NADs against a complex bacterial community using a combination of culture based, metagenomic, and metratranscriptomic approaches. We found that three of five NADs tested on growth significantly reduced growth of a bacterial community, although only one (17-{beta}-estradiol) selected for an AMR marker using qPCR. Whole metagenome sequencing indicated that there was no clear strong selection by NADs for antibiotic resistance genes, nor effects on community composition. However, some changes in relative abundance of metal resistance genes were observed after exposure to diclofenac, metformin, and 17-{beta}-estradiol. Together, these results indicate that the NADs tested likely do not strongly select for AMR at both clinically and environmentally relevant concentrations.