The rise of bacterial antimicrobial resistance (AMR) poses a major threat to both human and animal health. Addressing this challenge requires a comprehensive understanding of how AMR spreads across interconnected One Health compartments, including humans, animals, and the environment. Limiting the dissemination of AMR in and through the environment demands insights into ecological and evolutionary drivers, including biotic factors such as microbial community composition, host range, interspecies interactions, and predation, as well as abiotic factors such as temperature, nutrient availability, pollutants, and hydrological connectivity. These drivers act in concert with environmental dispersal barriers that shape the persistence and mobility of resistant bacteria, resistance genes, and mobile genetic elements.

This presentation explores the key processes underpinning environmental AMR spread, with a focus on microbial invasion, horizontal gene transfer, and selective pressures that favor resistant populations. Particular attention is given to how environmental microbial communities can either resist or facilitate the establishment of incoming resistant bacteria and mobile resistance genes.

The presentation discusses how community diversity, niche occupation, and biotic interactions can act as natural barriers to AMR dissemination, and how these barriers may be weakened by chemical stressors, altered environmental conditions, or ecological disturbance. It further considers how natural and anthropogenic drivers can promote plasmid transfer, reshape microbial communities, and amplify resistance risks. Finally, the presentation outlines how understanding these eco-evolutionary mechanisms can inform environmental surveillance, risk assessment, and future strategies to limit or reverse AMR dissemination.