Tracking dissemination of antimicrobial resistance from a hospital to surface water via a municipal wastewater treatment plant using a carbapenemase gene

Antibiotic resistant bacteria originating from hospitals are ultimately discharged to municipal wastewater treatment plants (WWTP), which may serve as important reservoirs for the spread of antibiotic resistant genes. This study traced and quantified the presence of a rare but clinically relevant antimicrobial resistance gene; Klebsiella pneumoniae carbapenamase (KPC)-and the viable organisms which carried the gene (KPCO) in hospital, non-hospital wastewater discharges, various compartments within the WWTP, and receiving water and sediment samples. The KPC gene was present in high concentration along with viable and multispecies KPCO in the hospital wastewater and in the forepart stages of the WWTP, but not detected in the final effluent. KPCO were not detected in multiple non-hospital sources of wastewater discharges tested. The treatment train used in the sampled WWTP was found to help remove and reduce KPCO load. Using whole-genome sequencing, a KPC-producing Klebsiella oxytoca strain identical to strains seen in the patients and hospital was isolated from the downstream receiving water on one sampling event. This study systematically demonstrates dissemination of KPCO from hospital point sources to environment via municipal WWTP. KPCE were also found to persist in the biosolids, but were not detected in the processed composting products. Understanding hospitals as the origin and source of spread of some of the most clinically urgent antimicrobial resistant organisms may help direct interventions to improve efficiency and reliability of elimination of antimicrobial resistant organisms via enhancement of wastewater treatment and reduce their loading into the environment.

源自医疗机构的耐药菌（antibiotic resistant bacteria）最终会被排放至市政污水处理厂（wastewater treatment plants, WWTP），而后者可能成为耐药基因（antibiotic resistant genes）传播的重要储库。本研究针对一种罕见但具有临床相关性的抗菌耐药基因（antimicrobial resistance gene）——肺炎克雷伯菌碳青霉烯酶（Klebsiella pneumoniae carbapenamase, KPC），以及携带该基因的活菌（KPCO），对医疗机构污水、非医疗机构污水排放口、市政污水处理厂内各处理单元、受纳水体及沉积物样品中的目标物开展了溯源与定量分析。
KPC基因在医疗机构污水及市政污水处理厂前端工段中呈高浓度检出，且伴随活菌及多菌种KPCO，但在最终出水中未被检出。在本次研究检测的多个非医疗机构排放的污水源中，均未检出KPCO。本次采样的市政污水处理厂所采用的处理工艺链，可有效去除并降低KPCO的负载量。
通过全基因组测序（whole-genome sequencing），本研究在一次采样事件中从下游受纳水体中分离出一株产酸克雷伯菌（Klebsiella oxytoca），其与患者及医疗机构中检出的菌株完全一致。本研究系统证实了KPCO通过市政污水处理厂从医疗机构点源向环境的传播路径。
KPCE还可在生物固体（biosolids）中持续存在，但在经处理的堆肥产品中未被检出。将医疗机构视为部分临床亟需的耐药菌的传播起源与源头，可为相关干预措施提供指导：通过强化污水处理工艺提升耐药菌的消除效率与可靠性，并降低其向环境中的排放负荷。