Transmission and Evolution of Antibiotic Resistance Genes and Antibiotic-Resistant Bacteria in Animals, Food, Humans and the Environment

Antimicrobial resistance (AMR) constitutes one of the most severe and pressing threats to global public health, food security, and environmental integrity. This review synthesizes current evidence across interconnected One Health domains-humans, animals, food, and the environment-to delineate the scope, mechanisms, and drivers of AMR transmission. Our analysis reveals three principal findings. First, the scope of AMR is alarmingly extensive, with antibiotic-resistant bacteria (ARB) and genes (ARGs) now pervasive across all four ecological compartments, transcending traditional clinical boundaries. Second, this widespread distribution is critically facilitated by horizontal gene transfer mechanisms, particularly via mobile genetic elements such as plasmids, which enable ARGs to disseminate rapidly between diverse bacterial populations across different ecosystems. Third, we identify multiple interconnected drivers that actively promote this cross-ecosystem spread, encompassing both evolutionary and transmission drivers. By characterizing these critical transmission pathways and underlying drivers, this review provides an integrated framework to identify critical transmission risks and inform integrated strategies for mitigating antimicrobial resistance across One Health domains.