Table 2_Riverine antibiotic resistome along an anthropogenic gradient.xlsx

The introduction of antibiotic-resistant bacteria into riverine systems through the discharge of wastewater treatment plant (WWTP) effluent and agricultural waste poses significant health risks. Even when not pathogenic, these bacteria can act as reservoirs for antibiotic resistance genes (ARGs), transferring them to pathogens that infect humans and animals. In this study, we used fluorescence in situ hybridization, qPCR, and metagenomics to investigate how anthropogenic activities affect microbial abundance and the resistome along the Holtemme River, a small river in Germany, from near-pristine to human-impacted sites. Our results showed higher bacterial abundance, a greater absolute and relative abundance of ARGs, and a more diverse ARG profile at the impacted sites. Overall, the ARG profiles at these sites reflected antibiotic usage in Germany, with genes conferring resistance to drug classes such as beta-lactams, aminoglycosides, folate biosynthesis inhibitors, and tetracyclines. There were also variations in the ARG profiles of the impacted sites. Notably, there was a high abundance of the oxacillin resistance gene OXA-4 at the downstream site in the river. In the metagenome assembly, this gene was associated with a contig homologous to small plasmids previously identified in members of the Thiotrichaceae. The likely in-situ host of the putative plasmid was a close relative of Thiolinea (also known as Thiothrix) eikelboomii, a prominent member of WWTP microbiomes worldwide. Our results show that the effluent from WWTPs can introduce bacteria into the environment that act as shuttle systems for clinically relevant ARG.

通过排放污水处理厂（wastewater treatment plant, WWTP）出水与农业废弃物，将耐药菌引入河流生态系统，会造成显著的健康风险。即便此类细菌不具备致病性，也可作为抗生素抗性基因（antibiotic resistance genes, ARGs）的储存库，将抗性基因转移至感染人类与动物的病原菌体内。本研究采用荧光原位杂交、定量聚合酶链反应（quantitative polymerase chain reaction, qPCR）与宏基因组学技术，探究了德国小型河流霍尔滕默河（Holtemme River）从近原生状态到受人类活动干扰的河段中，人为活动对微生物丰度与抗性组（resistome）的影响。研究结果显示，受人类活动干扰的河段中，细菌丰度更高，抗生素抗性基因的绝对与相对丰度均显著提升，且抗性基因谱更为多样。总体而言，这些河段的抗生素抗性基因谱反映了德国的抗生素使用现状，涵盖编码对β-内酰胺类、氨基糖苷类、叶酸生物合成抑制剂以及四环素类等药物类别具有抗性的基因。受干扰河段的抗生素抗性基因谱亦存在差异。值得注意的是，该河下游河段中，奥沙西林抗性基因OXA-4的丰度极高。在宏基因组组装结果中，该基因所在的重叠群（contig）与此前在硫丝菌科（Thiotrichaceae）物种中发现的小型质粒具有同源性。该推定质粒的潜在原位宿主为艾克宝莫硫线菌（Thiolinea eikelboomii，亦称发硫菌Thiothrix eikelboomii）的近缘物种，该菌是全球范围内污水处理厂微生物群落的优势类群。本研究结果表明，污水处理厂出水可将充当临床相关抗生素抗性基因穿梭系统的细菌引入自然环境中。