Antibiotics, antibiotic resistance genes, and environmental drivers: Assessment of resistance pollution along the Yangtze River Basin.

Antibiotic resistance pollution presents a significant global health challenge. The present study systematically investigated the occurrence of 50 antibiotics in the dissolved, suspended particulate matter phases, and surface sediments at 30 locations across the Yangtze River Basin (YRB). Eleven extracellular and intracellular antibiotic resistance genes (eARGs and iARGs) in surface sediments were quantified using fluorescence-based real-time quantitative polymerase chain reaction. Additionally, key relationships between ARGs, antibiotic concentrations, mobile genetic elements, microbial communities, and environmental factors were explored. Results revealed high levels of antibiotic contamination in the dissolved phase, with the cumulative concentration of the 50 target antibiotics ranging 857-7560 ng/L across various sections of the YRB. While iARGs predominated in absolute abundance, eARGs showed higher relative abundance. Mechanistic of intI1-mediated horizontal gene transfer as the principal pathway for the dissemination of ARGs. Redundancy analysis revealed that antibiotic concentrations, environmental factors, and microbial communities collectively explained 57.69 % of the variation in ARGs distribution. Among these, environmental variables such as conductivity and dissolved oxygen indirectly promote the enrichment of ARGs by influencing microbial communities. This study provided a theoretical basis for developing targeted prevention and control strategies against antibiotic resistance pollution in this extensive and economically critical watershed.