Prevalence of antibiotic resistance genes in different drinking water treatment processes in a northwest Chinese city

Antibiotic resistance genes (ARGs) are an emerging issue which are receiving increasing concerns in drinking water safety. However, the factors (e.g. treatment processes and water quality) affecting the removal efficiency of ARGs in the drinking water treatment plants (DWTPs) is still unclear. This work investigated the ARG profiles in each treatment process of two DWTPs located in a northwest Chinese city. The results showed that tetracycline and sulfonamide resistance genes were predominant among the 14 targeted ARGs. After the treatment, the Z water treatment plant which demonstrated a higher removal rate of ARGs (ranging from 50 to 80%), compared to the S plant (50-75%). And the average removal rate of tetracycline resistance genes (tetA, tetG, tetQ, tetX) was about 49.18% (S plant) and 67.50% (Z plant), as well as the removal rate of 64.2% and 72.9% for sulfonamide resistance (sul1 and sul2) at S and Z water plants, respectively. It was found that the relative abundance of main microbial communities (such as Bacteroidota, Actinobacteria, Verrucomicrobiota, Roseomonas), alpha-diversity index, as well as the abundance of pathogenic bacteria were all significantly reduced after different treatment processes. Network co-occurrence analysis revealed that Methylocystis possibly was the potential host for most ARGs, and sul1 was found across a broad spectrum of microorganisms in the drinking water environment. Adonis analysis showed that heavy metals and microbial communities explain solely 44.1% and 35.7% of variances of ARGs within DWTPs. This study provides insights into the contamination status and removal efficiencies of ARGs in DWTPs, offering valuable references for future studies on ARG removal, propagation, and diffusion patterns in drinking water treatment.