The role of water distribution systems in the enrichment of antimicrobial resistance

The drinking-water environment is prone to chemical and biological pollution, and it remains a challenge to achieve contamination-free water for the consumer. Biological contaminants (microorganisms and their genetic traits) can become more difficult to treat, as compared to chemical, as they can escape treatment processes (including disinfection) and replicate. Their presence in the drinking water environment has become considered to be a hotspot for the dissemination of antimicrobial resistance genes (ARG). Moreover, the treatment process may create conditions that may exacerbate the development and dissemination of ARG. The inter-relationship between disinfectant exposure, a common water-treatment process and the development of antibiotic resistance was investigated in this study. Potential human and animal pathogens from municipal drinking water, representing twenty-two genera, were characterized for antibiotic and disinfectant resistances. The co-existence of antibiotic resistant and transferable genes was found in bacteria, and significant but weak correlations were detected between disinfectant and antibiotic resistance (against sulfamethoxazole, tetracycline and amoxicillin).The applicability of a minimum-selectable-concentration model (MSC) for the selection of resistant population was evaluated for the first time in this study. MSCs were found to be lower than minimum inhibitory concentrations (MIC) causing the enrichment of resistant populations at sub-inhibitory concentrations. Both MIC and MSC metrics should be considered when planning treatment against resistant organisms. Finally, the potential roles of dispersal and gene enrichment in a model distribution system were explored. Different pipe surfaces, especially PVC, became colonized with bacteria and enriched the abundances of resistant populations in the presence of free chlorine. Additionally, resistant bacteria were enriched more in biofilm than water. This thesis highlights how water-distribution ecosystems contribute to the emergence of resistance. The water-supply system must be considered for the control of resistant bacteria. Further, we must prevent the presence of microorganisms post-treatment as exposure to sub-inhibitory disinfectant levels causes the greatest risk.The drinking-water environment is prone to chemical and biological pollution, and it remains a challenge to achieve contamination-free water for the consumer. Biological contaminants (microorganisms and their genetic traits) can become more difficult to treat, as compared to chemical, as they can escape treatment processes (including disinfection) and replicate. Their presence in the drinking water environment has become considered to be a hotspot for the dissemination of antimicrobial resistance genes (ARG). Moreover, the treatment process may create conditions that may exacerbate the development and dissemination of ARG. The inter-relationship between disinfectant exposure, a common water-treatment process and the development of antibiotic resistance was investigated in this study. Potential human and animal pathogens from municipal drinking water, representing twenty-two genera, were characterized for antibiotic and disinfectant resistances. The co-existence of antibiotic resistant and transferable genes was found in bacteria, and significant but weak correlations were detected between disinfectant and antibiotic resistance (against sulfamethoxazole, tetracycline and amoxicillin).The applicability of a minimum-selectable-concentration model (MSC) for the selection of resistant population was evaluated for the first time in this study. MSCs were found to be lower than minimum inhibitory concentrations (MIC) causing the enrichment of resistant populations at sub-inhibitory concentrations. Both MIC and MSC metrics should be considered when planning treatment against resistant organisms. Finally, the potential roles of dispersal and gene enrichment in a model distribution system were explored. Different pipe surfaces, especially PVC, became colonized with bacteria and enriched the abundances of resistant populations in the presence of free chlorine. Additionally, resistant bacteria were enriched more in biofilm than water. This thesis highlights how water-distribution ecosystems contribute to the emergence of resistance. The water-supply system must be considered for the control of resistant bacteria. Further, we must prevent the presence of microorganisms post-treatment as exposure to sub-inhibitory disinfectant levels causes the greatest risk