There is a risk that residues of antibiotics and other antimicrobials in hospital and municipal wastewaters could select for resistant bacteria. Still, direct experimental evidence for selection is lacking. Here, we investigated if effluent from a large Swedish hospital, as well as influent and effluent from the connected municipal wastewater treatment plant (WWTP) select for antibiotic resistant Escherichia coli in three controlled experimental setups. Exposure of sterile-filtered hospital effluent to a planktonic mix of 149 different E. coli wastewater isolates showed a strong selection of multi-resistant strains. Accordingly, exposure to a complex wastewater community selected for strains resistant to several antibiotic classes. Exposing individual strains with variable resistance patterns revealed a rapid bactericidal effect of hospital effluent on susceptible, but not multi-resistant E. coli. No selection was observed after exposure to WWTP effluent, while exposure to WWTP influent indicated a small selective effect for ceftazidime and cefadroxil resistant strains, and only in the E. coli mix assay. An analysis of commonly used antibiotics and non-antibiotic pharmaceuticals in combination with growth and resistance pattern of individual E. coli isolates suggested a possible contribution of ciprofloxacin and β-lactams to the selection by hospital effluent. However, more research is needed to clarify the contribution from different selective agents. While this study does not indicate selection by the studied WWTP effluent, there is some indications of selective effects by municipal influent on β-lactam-resistant strains. Such effects may be more pronounced in countries with higher antibiotic use than Sweden. Despite the limited antibiotic use in Sweden, the hospital effluent strongly and consistently selected for multi-resistance, indicating widespread risks. Hence, there is an urgent need for further evaluation of risks for resistance selection in hospital sewers, as well as for strategies to remove selective agents and resistant bacteria.

医院和市政废水中的抗生素和其他抗菌素残留物可能会选择抗药性细菌。仍然缺乏用于选择的直接实验证据。在这里，我们调查了瑞典一家大型医院的废水以及相连的市政废水处理厂（WWTP）的废水和废水是否通过三种受控实验设置选择了抗药性大肠杆菌。无菌过滤的医院污水暴露于149种不同大肠杆菌的浮游混合物中废水分离株显示出对多抗性菌株的强烈选择。因此，暴露于选择对几种抗生素具有抗性的菌株的复杂废水群落中。暴露具有可变抗性模式的单个菌株显示医院流出物对易感但对多抗性的大肠杆菌具有快速杀菌作用。暴露于WWTP流出物后未观察到选择，而暴露于WWTP流入物表明对头孢他啶和对头孢氨苄耐药的菌株只有很小的选择性作用，并且仅在大肠杆菌混合试验中有效。结合个别大肠杆菌的生长和耐药模式分析常用抗生素和非抗生素药物分离株提示环丙沙星和β-内酰胺类药物可能对医院出水的选择产生影响。但是，需要更多的研究来阐明不同选择剂的贡献。尽管该研究未表明所研究的污水处理厂废水的选择，但仍有迹象表明市政进水对β-内酰胺耐药菌株具有选择性作用。在抗生素使用量高于瑞典的国家，这种影响可能更为明显。尽管在瑞典抗生素的使用受到限制，但医院的出水强烈且稳定地被选择用于多重耐药，这表明存在广泛的风险。因此，迫切需要进一步评估医院下水道中抗药性选择的风险，以及去除选择剂和抗药性细菌的策略。