The elimination of potentially pathogenic bacteria in wastewater treatment plants (WWTPs) attracts much attention in public health. Reports on the occurrence of the emerging hospital pathogen Acinetobacter baumannii in wastewaters do not include a continuous monitoring at all WWTP stages. The objective of this study was to characterize A. baumannii recovered from the water and sludge line of the secondary WWTP in Zagreb, Croatia over the period of one year. Recovery of A. baumannii was performed using CHROMagar Acinetobacter plates. Antimicrobial susceptibility testing was performed with broth microdilution and results interpreted using EUCAST breakpoints for clinical isolates of A. baumannii. Molecular characterization was performed by WGS and cgMLST. The secondary WWTP treating the urban wastewater is constantly receiving viable A. baumannii along with genes encoding carbapenem resistance, and emitting them via effluent into the environment. Furthermore, A. baumannii from influent are incorporated into activated sludge flocs in aeration basin. A. baumannii can survive the technological process of anaerobic mesophilic sludge digestion, and is finally destroyed in alkaline lime-treated stabilised sludge. The majority (102/119) of A. baumannii isolates were carbapenem-resistant, while antibiotic-susceptible isolates (17/119) were rarely recovered from all WWTP stages. Carbapenem-resistant isolates belonged to international clonal lineage IC2 carrying OXA-23 and IC1 carrying OXA-72, while the susceptible isolates belonged to IC5 or were unclustered. Increased resistance to antibiotics, together with the appearance of carbapenem- and even pandrug-resistant isolates in effluent as compared to influent wastewater, suggests the need of additional disinfection of effluent prior to its discharge into the natural recipient.

废水处理厂（WWTP）中潜在致病细菌的消除在公共卫生领域引起了广泛关注。关于废水中新出现的医院病原体鲍曼不动杆菌的发生的报告并未包括在所有污水处理厂阶段的连续监测。这项研究的目的是表征从克罗地亚萨格勒布二级污水处理厂的水和污泥管线中回收的鲍曼不动杆菌，历时一年。使用CHROMagar不动杆菌平板进行鲍曼不动杆菌的回收。用肉汤微稀释液进行抗菌药敏试验，并使用EUCAST断点解释鲍曼不动杆菌临床分离株的结果。分子表征是通过WGS和cgMLST进行的。处理城市废水的二级污水处理厂不断接受可行的鲍曼不动杆菌和编码碳青霉烯抗性的基因，并通过污水排放到环境中。此外，来自进水的鲍氏不动杆菌被掺入曝气池中的活性污泥絮凝物中。鲍曼不动杆菌可以在厌氧中温污泥消化的工艺过程中幸存下来，并最终在碱性石灰处理的稳定污泥中被破坏。鲍曼不动杆菌的大部分（102/119）分离株对碳青霉烯类耐药，而在所有污水处理厂阶段都很少回收对抗生素敏感的分离株（17/119）。耐碳青霉烯的分离株属于携带OXA-23的国际克隆谱系IC2和携带OXA-72的IC1，而易感分离株属于IC5或未聚类。与进水废水相比，对废水的抗生素耐药性增强，以及在废水中出现对碳青霉烯类甚至泛药耐药的分离株，表明在将废水排入自然接收器之前，需要对其进行额外的消毒。