Two typical residual surfactants facilitate the dissemination of antibiotic resistance genes: mechanisms of conjugation and community-level implications.

Since the outbreak of the COVID-19 pandemic, the reinforcement of personal hygiene practices has led to a significant increase in surfactant residues in municipal wastewater. As a reservoir of antibiotic resistance genes (ARGs), municipal wastewater has been reported to facilitate the conjugative transfer of ARGs by surfactants. However, the intrinsic mechanisms driving this process and the broader impact of surfactants on ARGs fate in real wastewater systems remain poorly understood. Here, we demonstrate that residual cetyltrimethylammonium bromide (CTAB) and sodium dodecylbenzenesulfonate (SDBS) promote ARGs transfer both between Escherichia coli (E. coli) strains and from E. coli to municipal wastewater indigenous microbiota. Exploration of the underlying mechanisms revealed that CTAB exerts its effects primarily by increasing cell membrane permeability, inducing oxidative stress, and activating the SOS response. Further investigation showed that CTAB increases membrane permeability through direct binding to membrane proteins. SDBS primarily acted by enhancing bacterial motility and reducing barriers to cell contact. Additionally, modulation of glutamate and aspartate metabolism supported the conjugative transfer process by providing supplementary energy. Furthermore, we found that harboring multidrug-resistant plasmids conferred a survival advantage to bacterial hosts in municipal wastewater environments, thereby promoting the enrichment of ARGs. These findings elucidate novel mechanisms underlying surfactant-facilitated dissemination of ARGs, revealing a significant but overlooked environmental risk associated with residual surfactants in wastewater.