Sedimentary antimicrobial-resistome coupling patterns across rural-urban waterway interfaces

Both antimicrobials and their corresponding resistance genes (ARGs) are acknowledged micropollutants in aquatic environments, whose interactions are implicated in driving environmental antimicrobial resistance (EAR) and posing threat to human health. The in situ ARGs proliferation and/or selective maintenance with the co-presence of antimicrobials and ARGs were argued in sediment of a rural-urban waterway network in Ningbo, China, where the Yao and Fenghua rivers converge to form the Yong River before draining into the East China Sea. Twenty-three out of the 31 selected antimicrobial compounds and 183 out of the 323 targeted ARGs were quantified in 41 surface sediment samples (0-10 cm). ARG categorical expression potential (relative abundance normalized by the number of quantified genes within each category) showed significant positive antimicrobial-ARG coupling in the Fenghua and Yong rivers, but a non-significant correlation in the Yao River. At the category level, persistent antimicrobials (e.g., tetracyclines in relation to tetracycline resistance genes) and multidrug resistance (aggregate antimicrobial residues in relation to multidrug resistance genes) exhibited evident positive associations, suggesting in situ proliferation under stronger selection. However, rapidly degradable antimicrobials (e.g., sulfonamides in relation to sulfonamide resistance genes) showed non-significant category-matched coupling, consistent with maintenance dynamics. Non-corresponding antimicrobial-ARG couplings dominated in co-occurrence network, implying mobile genetic elements (MGE) -enabled co-/broad-selection rather than strict one-to-one correspondence proliferation. Physicochemical factors were limited and river-specific, while integrons repeatedly emerged as significant drivers of antimicrobial-ARG coupling across rivers, supporting a key role for MGEs in cross-category ARG dissemination. These findings support watershed-scale mitigation combining point-source input reduction with nutrient and sediment-hydrodynamic management to reduce EAR risks.