Antimicrobial Resistance in Wastewater Effluent Streams and in Urban Coastal Waters Influenced by Effluent Discharge

Joshua A Steele1, Rachel Diner1,2, Amy Zimmer-Faust1, Madison L Griffith1, Thomas Harper1,3, Jeffrey Chokry1,4, David Wanless1 and John F Griffith1, (1)Southern California Coastal Water Research Project, Microbiology, Costa Mesa, CA, United States, (2)J. Craig Venter Institute, La Jolla, CA, United States, (3)University of California Los Angeles, Fielding School of Public Health, Los Angeles, CA, United States, (4)California State University Fullerton, Fullerton, CA, United States
Abstract:
Antibiotic resistant infections from community-acquired sources have raised concerns about antimicrobial resistant (AMR) bacteria entering the sewer system, being discharged into the ocean, rivers, and streams, and ultimately making their way to highly populated beaches. Yet, the impact of treatment level and the fate of AMR bacteria and genes after they are discharged into the environment remains understudied. We measured the abundance of AMR bacteria and genes in wastewater from 10 plants in southern California with treatment processes ranging from minimal treatment (primary) to high levels of disinfection (tertiary). Quarterly samples of raw influent and final effluent were collected both for cultivation/isolation and for quantification of resistance genes. Water samples were collected at increasing distances from an ocean outfall and an inland river outfall determine the spatial extent AMR bacteria and genes discharged in the environment. Carbapenem Resistant Enterobacteriaciae (CRE); Vancomycin Resistant Enterococci (VRE), and Methicillin Resistant Staphylococcus aureus (MRSA) were cultivated and quantified in wastewater. AMR genes for carbapenem resistance (e.g. blaKPC), vancomycin resistance (e.g. vanA), and methicillin resistance (e.g. mecA) were assayed in wastewater, river, and ocean water using digital PCR. Viable AMR bacteria were found in the effluent of every plant with CRE and MRSA detected most frequently across treatments. Concentrations of AMR bacteria lower in effluent (0-104 CFU per 100ml) compared to influent (1-105 CFU per 100ml). AMR genes were found at higher concentrations than viable ARB in both influent (105-107 copies per 100ml) and effluent (below detection-106 copies per 100ml). Higher levels of treatment produced greater reduction in AMR bacteria and gene concentrations. Distinct microbial communities and AMR genes were identified in wastewater effluent and a gradient was observed at increasing distance from the outfalls. While the reduction in AMR bacteria and genes following tertiary treatment is encouraging, a large number of AMR bacteria and genes are being discharged into the coastal ocean. This presents both a potential to spread resistance to endemic bacterial populations and unknown consequences for human or environmental health.
Back to: Human Populations and Influences in the Coastal Zone: Effects on Ocean and Human Health (OHH) II