Plasmid-mediated antimicrobial resistance in non-typhoidal Salmonella: serotype-specific mechanisms and ecological implications.

Non-typhoidal Salmonella (NTS) is a leading cause of foodborne illness, with multidrug-resistant (MDR) strains challenging treatment and food safety. Serotype-specific plasmid associations underlie distinct antimicrobial resistance (AMR) risks: IncHI2 plasmids in S. Typhimurium, virulence-plasmid exclusion in S. Enteritidis, pESI megaplasmids in S. Infantis, and multi-plasmid carriage in S. Indiana. These profiles shape persistence in livestock, processing, and retail settings, raising the likelihood of resistance spread along the farm-to-fork continuum. Plasmid interactions, including helper-mediated mobilization, IS26-driven recombination, and fusion events, accelerate the emergence of mosaic or hybrid plasmids that combine resistance and virulence, enhancing adaptability in food-associated environments. Ecological factors such as gut microbiota, biofilms, and exposure to disinfectants or microplastics further promote plasmid transfer and maintenance. Within a One Health framework, integrating food chain surveillance, predictive modeling, and microbiota-targeted or CRISPR-based tools provides opportunities to monitor, predict, and disrupt plasmid dissemination. By combining serotype-specific, evolutionary, and ecological perspectives, this review highlights key mechanisms driving AMR in NTS and identifies actionable intervention points to reduce MDR Salmonella risks in the food chain.