Wastewater contamination and urbanization contribute to the spread of antibiotic resistance in aquatic environments. This is a particular concern in areas receiving chronic pollution of untreated waste via combined sewer overflow (CSO) events. The goal of this study was to expand knowledge of CSO impacts, with a specific focus on multidrug resistance. We sampled a CSO-impacted segment of the James River (Virginia, USA) during both clear weather and an active overflow event and compared it to an unimpacted upstream site. Bacteria resistant to ampicillin, streptomycin, and tetracycline were isolated from all samples. Ampicillin resistance was particularly abundant, especially during the CSO event, so these isolates were studied further using disk susceptibility tests to assess multidrug resistance. During a CSO overflow event, 82% of these isolates were resistant to five or more antibiotics, and 44% were resistant to seven or more. The latter statistic contrasts starkly with the upstream reference site, where only 4% of isolates displayed resistance to more than seven antibiotics. DNA sequencing (16S rRNA gene) revealed that ~35% of our isolates were opportunistic pathogens, comprised primarily of the genera Stenotrophomonas, Pseudomonas, and Chryseobacterium. Together, these results demonstrate that CSOs can be a significant source of viable clinically-relevant bacteria to the natural environment and that multidrug resistance is an important understudied component of the environmental spread of antibiotic resistance.

中文翻译：

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城市化河流中耐多药细菌的多样性：以混合污水溢出的潜在风险为例

废水污染和城市化加剧了抗生素耐药性在水生环境中的传播。在通过联合下水道溢流 (CSO) 事件接收未经处理的废物长期污染的地区，这是一个特别关注的问题。本研究的目标是扩大对 CSO 影响的认识，特别关注多药耐药性。我们在晴朗的天气和活跃的溢流事件期间对詹姆斯河（美国弗吉尼亚州）受 CSO 影响的一段进行了采样，并将其与未受影响的上游站点进行了比较。从所有样品中分离出对氨苄青霉素、链霉素和四环素具有抗性的细菌。氨苄青霉素耐药性特别高，尤其是在 CSO 事件期间，因此使用磁盘敏感性试验进一步研究了这些分离株，以评估多药耐药性。在 CSO 溢出事件期间，这些分离株中有 82% 对 5 种或更多抗生素耐药，44% 对 7 种或更多抗生素耐药。后者的统计数据与上游参考站点形成鲜明对比，其中只有 4% 的分离株显示出对超过七种抗生素的耐药性。DNA测序（16S rRNA基因）显示，约 35% 的分离株是机会性病原体，主要由狭养单胞菌属、假单胞菌属和金杆菌属组成。总之，这些结果表明，CSO 可以成为自然环境中临床相关活细菌的重要来源，并且多药耐药性是抗生素耐药性环境传播的一个重要的未充分研究的组成部分。