Abstract
Carbapenemase-producing bacteria (CPB) are rare, multidrug resistant organisms most commonly associated with hospitalized patients. Metropolitan wastewater treatment plants (WWTP) treat wastewater from large geographic areas which include hospitals and may serve as epidemiologic reservoirs for the maintenance or expansion of CPB that originate from hospitals and are ultimately discharged in treated effluent. However, little is known about the potential impact of these WWTP CPB on the local surface water and their risk to the public health. In addition, CPB that are present in surface water may ultimately disseminate to intensively-managed animal agriculture facilities where there is potential for amplification by extended-spectrum cephalosporins. To better understand the role of WWTPs in the dissemination of CPB in surface waters, we obtained samples of treated effluent, and both upstream and downstream nearby surface water from 50 WWTPs throughout the US. A total of 30 CPB with clinically-relevant genotypes were recovered from 15 WWTPs (30%) of which 13 (50%) serviced large metropolitan areas and 2 (8.3%) represented small rural populations (P < 0.05). Recovery of CPB was lowest among WWTPs that utilized ultraviolet radiation for primary disinfection (12%), and higher (P = 0.11) for WWTPs that used chlorination (42%) or that did not utilize disinfection (50%). We did not detect a difference in CPB recovery by sampling site, although fewer CPB were detected in upstream (8%) compared to effluent (20%) and downstream (18%) samples. Our results indicate that WWTP effluent and nearby surface waters in the US are routinely contaminated with CPB with clinically important genotypes including those producing Klebsiella pneumoniae carbapenemase (KPC) and New Delhi metallo-beta-lactamase (NDM). This is a concern for both public health and animal agriculture because introduction of CPB into intensively managed livestock populations could lead to their amplification and foodborne dissemination.
Highlights
The therapeutic use of carbapenem antimicrobials has been followed by the emergence and dissemination of clinically-relevant carbapenemase-producing Enterobacteriaceae (CPE)
Twenty-six sets of water samples were from wastewater treatment plants (WWTP) servicing large metropolitan cities with a mean population of over 800,000 residents
US WWTP effluent, upstream, and downstream surface water samples yielded a diverse mixture of carbapenemase-producing bacterial species, carbapenem-resistance genotypes, and plasmid replicon types
Summary
The therapeutic use of carbapenem antimicrobials has been followed by the emergence and dissemination of clinically-relevant carbapenemase-producing Enterobacteriaceae (CPE). BlaKPC and other mobile carbapenemase genes, including the metallo β-lactamases, have migrated beyond the healthcare environment and are recovered from both hospital- and community-acquired human infections in multiple bacterial species [5]. These carbapenemase-producing bacteria may be disseminated in waste flows exiting healthcare facilities and have been reported in wastewater effluent and surface water [6]. Real-time PCR (qPCR) quantification of KPC-2 gene copies in hospital effluent from two facilities in the Catalonia region of northeastern Spain was 4.4x107 and 5.4x104 per milliliter of sample [12] These findings highlight the concerning potential for waste-mediated dissemination of CPE originating from hospital settings moving into open public waterways, and demonstrate the potential for CPE to disseminate across large geographic regions. The extent of this environmental expansion of CPE remains unknown
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