| Summary: | University of Minnesota Ph.D. dissertation. December 2020. Major: Veterinary Medicine. Advisors: Meggan Craft, Timothy Johnson. 1 computer file (PDF); xvii, 144 pages. Use of antibiotics in human and animal medicine has led to the emergence of many forms of antimicrobial resistant bacteria (ARB). As well as undermining the successful treatment of bacterial infections, intensive use has led to the dissemination of ARB in the community and the environment. While extensive progress has been made in understanding the spread and fate of ARB in the community, the environment has had far less attention. Yet, detection of clinically relevant ARB and associated antimicrobial resistance genes (ARG) in water and soil indicates that the environment could act as an additional exposure pathway for people and domestic animals. ARB have also been isolated from wildlife present in these contaminated environments. Because of this, wildlife are considered to be good candidates for understanding environmental antimicrobial resistance (AMR). While ARB and ARG have been detected in numerous wildlife species across the globe, several questions remain unanswered regarding exposure pathways and what the consequences might be for human and domestic animal health. The goal of this thesis was to assess the contribution of several anthropogenic sources in shaping the AMR profile of wildlife. To do this, we investigated the ecology of AMR in an urban-suburban context, specifically in the city of Chicago. The wildlife species of focus was the raccoon (Procyon lotor) and the ARB were clinically relevant extended-spectrum cephalosporin resistant (ESC-R) Escherichia coli. We first investigated the importance of two known anthropogenic sources of AMR in shaping the ESC-R E. coli profile of raccoons: 1) the presence of rivers that were downstream of a wastewater treatment plant and 2) urban context (urban vs. suburban). We found that the risk of isolating ESC-R E. coli from raccoons was higher when raccoons were sampled at urban sites than at suburban sites. Importantly, we also found that raccoons were more likely to have ESC-R E. coli with transferable ARG when present at sites that were downstream from a WWTP, suggesting that WWTPs may increase the risk for AMR to spread widely in wildlife bacterial communities. We then explored the importance of various landscape factors at predicting isolation of ESC-R E. coli. Landscape factors were examined within estimated raccoon home ranges and we found residential areas and wetlands to increase the risk of isolating ESC-R E. coli from raccoons. This finding is important because most wildlife and environmental AMR research tend to ignore these types of landscape features, and our work highlights that more attention may be warranted. Next, we explored the interface with domestic animals. For this, we first compared the prevalence and phylogenetic relatedness of ESC-R E. coli of raccoons to that of local domestic dogs (Canis lupus familiaris) and asked whether shared space was important for predicting the sharing of ESC-R E. coli. ESC-R E. coli prevalence in raccoons was three times greater than in dogs, but isolated ESC-R E. coli were phylogenetically similar. Shared space was important for predicting isolation of ESC-R E. coli from raccoons but not from dogs, and was not important for predicting phylogenetic associations of ESC-R E. coli. Finally, we compared the AMR profile of raccoons to that of coyotes (Canis latrans), Virginia opossums (Didelphis virginiana), and locally owned and stray dogs. This final step did not focus on ESC-R E. coli, but rather took a broader look at the AMR profile of the four species by examining the presence of multiple ARG in samples that were pooled by animal species and dog type. The three mesocarnivore pooled samples had similar numbers and types of ARGs as the stray dog pooled sample, but not the owned dog pooled sample. Collectively, this thesis provides a concrete example for the need to account for the environment when generating surveillance and control strategies for AMR, and identifies several environmental components that could be targeted for surveillance.
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