Unraveling the antibiotic resistome in backwater zones of large cascade reservoirs: Co-occurrence patterns, horizontal transfer directions and health risks

The widespread occurrence of antibiotic resistant genes (ARGs) throughout aquatic environments has raised global concerns for public health. However, the profiles and patterns of antibiotic resistome in backwater zone of cascade reservoirs, where water flow is slowed down, are still poorly understood. Here, we proposed a metagenomic analysis framework to comprehensively reveal the diversity, abundance, co-occurrence patterns and transfer direction of ARGs in cascade reservoirs system and evaluated their health risks through a procedure based on contigs. A total of 364 ARGs subtypes conferring resistance to different antibiotics classes were detected in our water samples, and the dominant ARGs (macB, bacA, vanRA, bcrA) were similar in different reservoirs. Meanwhile, the distribution of ARGs was influenced by the presence of biotic factors such as metal resistant genes (MRGs) and mobile genetic elements (MGEs), as well as abiotic factors such as dissolved oxygen (DO) and pH. Remarkably, ARGs (vanR, rosB, MexT) co-occurred with plasmids and virulence factor genes (VFGs), which can lead to the emergence and spread of highly virulent and antibiotic resistant bacteria in microbial communities. Overall, this study helps administrators to better understand the complex patterns of ARGs in backwater zones of large cascade reservoirs and provides a proper procedure for detecting the presence of high-risk of ARGs.