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

Antimicrobial resistance (AMR) is one of the most urgent challenges in public health, and the horizontal transfer of antibiotic resistance genes (ARGs) mediated by mobile genetic elements (MGEs) drives its widespread global dissemination. Although integrative conjugative elements (ICEs) outnumber conjugative plasmids, research on ICE-mediated horizontal gene transfer (HGT) remains largely lacking, especially concerning SXT ICEs, which are highly prevalent, pose significant risks, and are directly related to human health. Cyromazine is a widely used feed additive, with high detection rates in the feces of farmed animals and related environments. It has also been shown to increase the abundance of ARGs, and the potential driving mechanisms urgently require further exploration. Thus, we investigated the impact of cyromazine on SXT ICE-mediated ARGs transfer and elucidated its underlying mechanisms. Our study demonstrates that cyromazine promotes SXT ICE conjugative transfer both intra- and inter-species. This facilitating effect confirmed in mouse intraperitoneal and intestinal conjugation models. The potential mechanisms include cyromazine-induced ROS accumulation and triggering of the SOS response, which could promote SXT ICE excision and activate conjugation-related operons. Furthermore, enhanced energy metabolism and altered lipid metabolism further facilitate SXT ICE transfer. Collectively, our study partially fills the gap in understanding ICE-mediated AMR transmission dynamics, and highlighting that the exacerbated AMR crisis is associated with cyromazine-stimulated high-frequency SXT ICE conjugation in vitro and in vivo.