The effects of acidifying agents on the growth, antimicrobial resistance, and plasmid genome of <i>Salmonella enterica</i> serovar Infantis

This study evaluated if acidifying agents used for ammonia control and pathogen reduction in poultry houses have a deleterious effect on the survival and growth of Salmonella Infantis. Changes in antimicrobial resistance (AMR) and the gene composition of the plasmid of emerging S. Infantis (pESI) were also investigated. When S. Infantis was exposed to sodium bisulfate (SBS) and acidified copper sulfate (ACS), a bacteriostatic effect on Salmonella was observed at recommended concentrations, whereas ACS at double concentration had a bactericidal effect. No difference in the maximum growth and lag phase time (P > .05) between the pESI-carrying (pESI+) and pESI-free (pESI-) strains was observed, suggesting that there was a minimal benefit or burden imposed by pESI. However, several evolved isolates of the pESI+ strains lost resistance to sulfamethoxazole and trimethoprim-sulfamethoxazole in the presence of SBS, potentially by losing the associated genes. Furthermore, applying ACS to litter microcosms post-inoculation with pESI+ strains significantly reduced the gene abundance of S. Infantis and pESI replicon (P < .05), while SBS reduced the gene abundance of pESI- strains. This study suggests that acidifiers such as ACS pose a selective pressure on pESI+ S. Infantis and broader studies are needed to investigate their efficacy for pathogen and AMR reduction in pre-harvest broiler production.