Evaluation of plant-based antimicrobials in controlling antimicrobial resistance gene spread in poultry production...

Antimicrobial resistance poses a looming global health challenge impacting human, animal, and environmental health sectors, with horizontal gene transfer (HGT) playing a critical role in the dissemination of resistance genes among bacteria. To address this challenge effectively, a comprehensive strategy encompassing animal health and environmental management is essential. Therefore, this study aims to investigate the efficacy of phytochemicals on the conjugative transfer of an antimicrobial resistance gene, bla _TEM, between multidrug-resistant Salmonella Heidelberg, a major food-borne pathogen in poultry and commensal Escherichia coli. The effect of four phytochemicals, namely trans-cinnamaldehyde (TC), carvacrol (CR), beta-resorcylic acid (BR), and caprylic acid (CA) were determined across diverse environments, including bacteriological broth, chicken manure, and water. Further, the efficacy of in-feed supplementation of TC, CR and TC-CR combinations in reducing HGT frequency in broiler chicken ceca ex vivo was also studied. The HGT frequency was calculated as the ratio of the number of transconjugant CFU per mL to the number of recipient CFU per mL. Exposure to CR and BR reduced transconjugant counts and HGT frequency in broth and chicken manure, while CR and CA showed similar effects in water (p < 0.05). Additionally, in-feed supplementation 0.5% TC decreased HGT frequency in chicken ceca ex vivo (p < 0.05). There was also a significant reduction in the transcription of conjugation genes in Salmonella treated with phytochemicals (p < 0.05). These findings suggest the potential of phytochemicals to mitigate the spread of bla _TEM in the poultry production continuum, although additional studies in a large number of samples, including chickens, are imperative to validate these results.