Conventional wastewater treatment plants are able to reduce contaminant loads within regulations but do not take into account emerging contaminants. Antibiotic resistance genes and antibiotic resistant bacteria have been shown to survive wastewater treatment and remain detectable in effluents. The safety of treated wastewaters is crucial, otherwise unregulated and unmitigated emerging contaminants pose risks to public health and impede wastewater reuse.
This dissertation aimed to further understanding of emerging microbial threats, and tested two natural and low-cost tools for their mitigation: sunlight, and bacteriophages. A wastewater bacterial isolate, named E. coli PI-7, which is highly antibiotic resistant, carries the novel antibiotic resistance gene New Delhi metallo-beta-lactamase NDM-1 gene, and displays pathogenic traits, was chosen to model responses to the treatments.
Results found that solar irradiation was able to achieve a 5-log reduction in E. coli PI-7 numbers within 12 hours of exposure. However, the results also emphasized the risks from emerging microbial contaminants since E. coli PI-7, when compared with a non-pathogenic strain E. coli DSM1103 that has less antibiotic resistance, showed longer survival under solar irradiation. In certain instances, E. coli PI-7 persisted for over 6 hours before starting to inactivate, exhibited complex stress resistance gene responses, and activated many of its concerning pathogenicity and antibiotic resistance traits.
However, upon solar irradiation, gene expression results obtained from both E. coli strains also showed increased susceptibility to bacteriophages. Hence, bacteriophages were coupled with solar irradiation as an additional mitigation strategy. Results using the coupled treatment found reduced cell-wall and extracellular matrix production in E. coli PI-7. DNA repair and other cellular defense functions like oxidative stress responses were also impeded, rendering E. coli PI-7 more susceptible to both stressors and successfully hastening the onset of its inactivation.
Overall, the dissertation is built upon the need to develop strategies to further mitigate risks associated with emerging microbial contaminants. Solar irradiation and bacteriophages demonstrate potential as natural and low-cost mitigation strategies. Sunlight was able to achieve significant log-reductions in tested E. coli numbers within a day’s exposure. Bacteriophages were able to overwhelm E. coli PI-7’s capacity to resist solar inactivation while not affecting the indigenous microbiota.
|Date of Award||Jul 2018|
- Biological, Environmental Science and Engineering
|Supervisor||Peiying Hong (Supervisor)|