Assessing Energy Regime Effects on Pathogen-Particle Interactions Linking Water Quality to Ecosystems and Public Health

Tirado, Sandra M.
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University of Guelph

Floc-pathogen interactions are important determinants of the fate of pathogens in aquatic systems. The dissociation of bacteria from particles due to shear stress can significantly increase the presence of free-floating pathogenic bacteria in the aqueous phase. This has implications for pathogen transport and water quality. This study evaluated the interactions of water-borne pathogens with particles in selected aquatic ecosystems. Three experimental chapters and one concluding chapter is presented. Chapter 3 assesses the strength of the floc-microorganism association under different energy levels in relation to the physico-chemical properties and the bioorganic content of flocs from six different aquatic environments (SB, CSO, RF, AG, ML, MN); Chapter 4 evaluates how energy dissociates bacteria and affects microbial diversity in free-floating and particle-associated fractions in cohesive bed sediments (BedS) and suspended flocs (SusF) of three sites (SB, CSO, RF). Chapter 5 studies the diversity and succession among free-floating and particle-associated bacteria at different energy levels and the abundance of antibiotic resistance genes and Class 1 integrons (intI1) as a result of ecosystem perturbation in the six initial sites. Different strategies, such as standard laboratory analytical methods, as well as techniques based on analytical chemistry, biochemistry and molecular biology were used to accomplish these objectives. The bioorganic and physico-chemical properties of flocs and sediments, and the energy effects these structures are exposed to, play a role in the assessment of pathogen risk in water systems. Molecular approaches showed a significant difference in the composition of free-floating and particle-associated assemblages after simulated flow conditions and detected earlier differences in the dissociation of bacteria, compared to plating techniques. The analysis of integrons provided evidence for horizontal gene transfer events. Free-floating and particle-associated bacterial assemblages are potential genetic reservoirs for antibiotic resistance genes. This research shows that particles act as reservoirs for microorganisms, providing an early warning for potential indicators of human health risk in water systems and could determine the presence of future clinically relevant antibiotic resistance mechanisms and/or pathogenic microbial gene transfer in sediments, demonstrating the need to improve the existing protocols and methodologies that assess water quality.

energy impact, microbial floc, sediments, water quality, indicator organisms, integron, bacterial dissociation