Assessment of fecal contamination and antimicrobial-resistant Escherichia coli in lakes across Canada and the role of wildlife in their dissemination

Abstract

Fecal contamination of the environment can pose serious health threats. Fecal microbes can enter the environment from a wide variety of sources such as wastewater effluent, wildlife, agricultural drainage, and/or land runoff. Microbes present in the environment cause infections in humans and animals that interact with contaminated areas, with these infections harder to treat if microbes are more virulent or resistant to antimicrobials. Most previous research has investigated this problem with a focus on heavily polluted environments, so there is a current lack of knowledge about this problem in more natural, less overtly impacted environments. In this thesis I applied a One Health perspective on this topic and investigated fecal contamination in aquatic environments and antimicrobial-resistant Escherichia coli in aquatic sediments and wild birds. I first studied this problem from a broad lens, investigating coliform contamination in surface waters of more than 400 lakes from across Canada using custom-built portable incubators to culture bacteria directly in the field. I then shifted my focus deeper and carried out an in-depth investigation of antimicrobial-resistant E. coli present in lake sediments in St. John’s, Newfoundland. I determined that environmental persistence, transmission between sites, most likely mediated by wild birds, and the activities of mobile genetic elements likely contributed significantly to the drug resistance patterns observed in the minimally polluted environments studied. Lastly, I investigated antimicrobial-resistant E. coli carried by wild birds in eastern Newfoundland over a six-year period. Through this work, I identified that wild birds in the region are significant reservoirs of antimicrobial-resistant and potentially pathogenic E. coli. However, there were large differences in carriage of these depending on whether the bacteria were isolated from ducks, gulls, or seabirds. Taken together, these works significantly advance our current understanding of fecal contamination in freshwater lakes in Canada, and antimicrobial-resistant E. coli in environmental and wild bird reservoirs and furthers our understanding of the threats posed by these to human and animal health.