Antimicrobial resistance and the human gut microbiome-a food safety perspective.

The gastrointestinal environment is where the resident gut microbiome encounters foodborne microorganisms, antimicrobial resistance genes (ARGs), and bioactive substances from food, all of which may influence the acquisition and dissemination of antimicrobial resistance (AMR). Although resistant bacteria and ARGs are frequently detected in food and food production environments, their contribution to the gut resistome remains unclear. Most ingested microbes are transient and constrained by ecological barriers; however, the conditions that enable horizontal gene transfer in vivo are not well characterized. Multiple factors (e.g., microbial composition and density, the presence of mobile genetic elements, antimicrobial residues, and host physiology) can modulate ARG persistence and mobility, but their relative impact within the gut ecosystem and its associated resistome needs to be better understood. Resistance acquisition also depends on fitness costs and adaptive responses within complex microbial communities. Methodological variability and limited in vivo data further limit comparability and interpretation. This review summarizes current knowledge of AMR dynamics in the gut following dietary exposure and highlights significant knowledge gaps that limit our understanding of factors influencing ARG transfer and persistence in the gastrointestinal environment. Reducing these uncertainties is crucial for strengthening AMR risk assessment and designing more effective mitigation strategies.