Fate and Transport of Determinants of Antimicrobial Resistance in Variably Saturated Terrestrial Environments

Abstract

Antimicrobial resistance (AMR) is a major global public health threat which contributes to reduced effectiveness of antibiotics for treatment of bacterial infections in humans. Residuals of antimicrobial products from anthropogenic uses creates a selective environment and shifts the microbial populations in our municipal wastewater to become resistant. This leads to high concentrations of bacterial resistance or “hot spots.” The link between clinical incidence of AMR infections and the environmental dimension impacted by anthropogenic activities has been demonstrated to be important. Surveillance of AMR hot spots in the environment is conducted by monitoring environmental compartments for determinants of AMR including: antibiotic resistance genes (ARGs), mobile genetic elements, and antibiotic resistant bacteria (ARB). This thesis explores the fate of AMR determinants in variably saturated terrestrial environments that are used for municipal wastewater treatment and disposal. Specific focus was on rural, developing and remote regions, due to the challenges in the provision of adequate wastewater treatment in jurisdictions which are reliant on decentralized wastewater treatment. Often residents in these communities are particularly vulnerable to AMR infections. AMR contamination from municipal wastewater was studied in communities in the Canadian Arctic. Hydrology of wetland receiving environments played an important role in the dissemination of AMR contaminants in the environment. Reference wetlands representative of background conditions with limited anthropogenic impacts had relatively low levels of determinants of AMR indicative of the environmental resistome. Technologies for mitigation of the spread of AMR from sources in rural regions were studied. Removal of contaminants of AMR via physical filtration in lateral flow sand filters—used as a type of domestic on-site wastewater treatment system—was studied. This type of filtration technology was effective in attenuation of AMR contaminants with 2.9 to 5.4 log reductions for ARGs observed. A commercially available computer model (HYDRUS 2D/3D) was used to simulate the attenuation processes within the sand filters. Prediction of ARB was well represented in the modeling but prediction of ARGs and other genetic elements could be improved. This thesis represents one of the first studies to observe and model the fate and transport of determinants of AMR in subsurface environments.