Eawag, Swiss Federal Institute of Aquatic Science and Technology, CH-6047 Kastanienbaum or CH-8600 Dübendorf, Switzerland; Department of Environmental Systems Science, ETH Zurich, Swiss Federal Institute of Technology, Zurich, Switzerland.
Key Laboratory of Coastal Environment and Resources of Zhejiang Province, School of Engineering, Westlake University, Hangzhou, China; Institute of Advanced Technology, Westlake Institute for Advanced Study, Hangzhou, China.
Water Res. 2021 Jun 1;197:117050. doi: 10.1016/j.watres.2021.117050. Epub 2021 Mar 15.
River networks are one of the main routes by which the public could be exposed to environmental sources of antibiotic resistance, that may be introduced e.g. via treated wastewater. In this study, we applied a comprehensive integrated analysis encompassing mass-flow concepts, chemistry, bacterial plate counts, resistance gene quantification and shotgun metagenomics to track the fate of the resistome (collective antibiotic resistance genes (ARGs) in a microbial community) of treated wastewater in two Swiss rivers at the kilometer scale. The levels of certain ARGs and the class 1 integron integrase gene (intI1) commonly associated with anthropogenic sources of ARGs decreased quickly over short distances (2-2.5 km) downstream of wastewater discharge points. Mass-flow analysis based on conservative tracers suggested this decrease was attributable mainly to dilution but ARG loadings frequently also decreased (e.g., 55.0-98.5 % for ermB and tetW) over the longest studied distances (6.8 and 13.7 km downstream). Metagenomic analysis confirmed that ARG of wastewater-origin did not persist in rivers after 5 ~ 6.8 km downstream distance. sul1 and intI1 levels and loadings were more variable and even increased sharply at 5 ~ 6.8 km downstream distance on one occasion. While input from agriculture and in-situ positive selection pressure for organisms carrying ARGs cannot be excluded, in-system growth of biomass is a more probable explanation. The potential for direct human exposure to the resistome of wastewater-origin thus appeared to typically abate rapidly in the studied rivers. However, the riverine aquatic resistome was also dynamic, as evidenced by the increase of certain gene markers downstream, without obvious sources of anthropogenic contamination. This study provides new insight into drivers of riverine resistomes and pinpoints key monitoring targets indicative of where human sources and exposures are likely to be most acute.
河流网络是公众接触环境抗生素耐药性的主要途径之一，这些耐药性可能通过处理后的废水等途径进入环境。在这项研究中，我们应用了一种综合的集成分析方法，包括质量流概念、化学分析、细菌平板计数、抗性基因定量和鸟枪法宏基因组学，以追踪处理后废水中耐药组（微生物群落中抗生素抗性基因的集合）在瑞士两条河流中的命运，研究范围为一公里。在废水排放点下游 2-2.5 公里的短距离内，某些抗生素抗性基因（ARGs）的水平和通常与人为 ARG 源相关的 1 类整合子整合酶基因（intI1）迅速下降。基于保守示踪剂的质量流分析表明，这种下降主要归因于稀释，但 ARG 负荷也经常下降（例如 ermB 和 tetW 下降 55.0-98.5%）在研究距离最长（下游 6.8 和 13.7 公里）的情况下。宏基因组学分析证实，废水中的 ARG 在下游 56.8 公里处的河流中无法持续存在。在一个时期，sul1 和 intI1 的水平和负荷甚至在下游 56.8 公里处急剧增加。虽然不能排除农业输入和携带 ARG 的生物的原位正选择压力，但生物量的系统内生长是更可能的解释。因此，在研究的河流中，人类直接接触废水起源的耐药组的可能性似乎迅速减弱。然而，河流水体耐药组也具有动态性，下游某些基因标记的增加证明了这一点，而没有明显的人为污染来源。这项研究为河流耐药组的驱动因素提供了新的见解，并确定了关键的监测目标，表明人类来源和暴露最有可能在何处发生。
