Cyromazine accelerates the dissemination of antimicrobial resistance genes by promoting the conjugative transfer of the SXT integrative conjugative element.

Antimicrobial resistance (AMR) is an urgent public health challenge, and the horizontal transfer of antimicrobial resistance genes (ARGs) mediated by mobile genetic elements (MGEs) accelerates its spread worldwide. Despite the recognized role of integrative conjugative elements (ICEs) in conjugative gene transfer, ICE-mediated horizontal gene transfer (HGT) remains underexplored, particularly for SXT ICEs, which are widely disseminated and relevant to animal and human health. Cyromazine, a widely used veterinary drug frequently detected in livestock feces and associated environments, is linked to an increased abundance of ARGs, but the underlying mechanisms remain unclear. Here, we investigate the impact of cyromazine on SXT ICE-mediated ARG transfer and delineate potential mechanisms. We show that cyromazine promotes intra- and inter-species conjugative transfer of SXT ICE and validate this effect in vivo. In environmentally relevant models (feces, soil, and water), cyromazine further enhances SXT ICE transfer and reshapes the community structure of transconjugants. Potential mechanisms include cyromazine-induced ROS accumulation and SOS activation, which may promote SXT ICE excision and induce conjugation-related operons. Enhanced energy production and disrupted membrane homeostasis may further facilitate transfer. Collectively, these findings narrow the gap in ICE-mediated AMR transmission and suggest cyromazine could intensify AMR spread by stimulating SXT ICE conjugative transfer.