Antimicrobial resistance (AMR) poses a significant public health challenge, as AMR bacteria and their genes persist in environments such as farms and water systems. AMR bacteria can infect humans through contaminated food, water, or direct contact. We hypothesize that both intermittent exposure to clinical antimicrobials and environmental residues might exacerbate this colonization, leading to gut dysbiosis and facilitating the spread of resistance genes. This could enhance the survival and persistence of AMR bacteria and promote AMR gene transfer among bacterial communities in the gut.

To investigate this, we utilized a mouse model to examine the conjugative transfer of a mobile AMR plasmid from a Salmonella Heidelberg donor to Enterobacteriaceae in the gut under treatments of intermittent clinical doses of ampicillin and sub-clinical levels of tetracycline in drinking water. Fecal samples were collected from mice at regular intervals to isolate AMR bacteria on selective agar media. DNA was extracted from these samples for future 16S rRNA sequencing to analyze microbial community shifts and qPCR targeting ARGs to examine plasmid transfer dynamics.

Preliminary results show that the donor Salmonella Heidelberg persisted for four months in all treatment groups except the control, which had no antimicrobial exposure. The donor reached a high density immediately after each ampicillin treatment and gradually became undetectable. The AMR plasmid was transferred to commensal E. coli and to an introduced recipient Salmonella Heidelberg. While detailed sequencing and bioinformatics analyses are pending, initial findings highlight the significant impacts of antimicrobial exposure on the persistence of AMR bacteria and the transfer of AMR plasmids within the gut microbiota.