Distribution Characteristics And Driving Mechanism Of Antibiotic Resistance Genes In Recreational Coastal Waters Around Qinhuangdao,China

In recent years,bacterial resistance has seriously threatened human public health and ecological safety.The key for antibiotic resnstance of bacteria is to carry corresponding antibiotic resistance genes（ARGs）.As emerging contaminants,ARGs can not only replicate with the growth of bacterial host,but also can translate among different bacterial species through horizontal gene transfer mediated by Mobile Genetic Elements（MGEs）,by which increasing the possibility of ARGs entering human pathogens.Estuarine and offshore areas are ecosystems formed by the convergence of ocean and reiver or land,which accumulate a large amount of terrigenous pollution,including heavy metals,antibiotics,ARGs and antibiotic resistant bacteria,which may cause the accumulation of terrigenous ARGs in offshore environment and form selective pressure on ARGs.Marine recreational water is an important placr for human activities in coastal cities.Monitoring ARGs pollution in water is one of the important ways to prevent drug-resistant bacteria infections.However,the distribution and driving mechanism of ARGs in recreational coastal waters（RCWs）remains to be studied.In this study,we analyzed the ARGs and bacterial communities in water samples taken from five RCWs and their adjacent estuaries in the Qinhuangdao area of Hebei Province,China,using high throughput quantitative PCR and 16S r RNA gene amplicon sequencing technique.（1）The relative abundances of ARGs from different RCWs varied greatly,and occurred at levels close to,or even higher than,those in the neighboring estuaries,ranging from 9.4×10^-2 to 2.5 copies/16S r RNA gene.A total of 159 different ARGs able to express resistance to almost all antibiotics were detected in all of the water samples.Therefore,it’s highly possible for human to obtain ARGs from the environment in RCWs through direct contact.（2）Patterns of ARGs occurrence were significantly correlated with those of bacterial communities（Mantel test,P<0.05）.In addition,a partial redundancy analysis showed that differences in bacterial communities accounted for 50.3%of the total ARG variations,which was much higher than the sum of the contribution of mobile genetic elements（MGEs,18.1%）and the other selected environmental factors（8.3%）.Therefore,bacterial communities are the main drivers of ARGs in typical RCWs in Qinhuangdao,meanwhile mobile genetic elements and any environmental factors that may disrupt the microbial composition in RCWs should be valued.（3）Principal coordinate analysis based on Bray-Curtis distance revealed the similarities between ARG profiles in the RCWs and in their adjacent estuaries.Estuaries affect ARGs in RCWs to some extent through seawater dispersion or ocean flow,thereby causing pollution to RCWs.These results implied that it is necessary to develop proper regulations and monitoring strategies of related influencing factors in RCWs for reducing risks of ARGs on human health.This study is conducive to understanding the overall abundance and ecological risk of ARGs in coastal environment,and provides a theoretical basis for scientific prevention and control of ARGs in RCWs.