Evaluating the Fate and Behavior of Disinfection-Surviving Bacteria
Authors:Brian Cruz, Alicia Taylor
Mentor:Sharon Walker, Associate Professor of Environmental Engineering, UC Riverside
Waterborne outbreaks of pathogenic bacteria due to insufficient wastewater disinfection are of growing concern. Current research has focused on decreasing bacterial concentrations in treated water; however, there is little understanding about the fate and behavior of disinfection-surviving bacteria, specifically changes in virulence and viability. Recent research has demonstrated that Salmonella typhimurium and Escherichia coli O157:H7 exhibit increased virulence and retained viability when exposed to antibiotic spiked groundwater; bacterial stress and virulence responses to disinfection are suspected to be similar to responses with antibiotics. Escherichia coli O157:H7 and E. coli OP50 were chosen to model the responses of pathogenic and non-pathogenic strains of E. coli to chlorination, titanium dioxide, and ultraviolet light (UV) which are three common types of disinfection for water and may generate reactive oxygen species (ROS) which are important for bacteria elimination. The viability and virulence of E. coli O157:H7 and E. coli OP50 after exposure to UV (280 nm) over a period of 20, 45, 90 and 120 minutes will be evaluated by a BacLight Live/Dead assay and a soil nematode (Caenorhabditis elegans) assay. Disinfection residence times for all three methods will be evaluated and ROS production will be measured. Phenotypic changes in cellular behavior will be analyzed through zeta potential, hydrophobicity and cell size analysis. Initial results of UV disinfection has indicated a significant decrease in viability after 90 minutes of exposure; however, initial phenotypic characterization has shown no significant changes in cell charge, size, or hydrophobicity. Future results are expected to indicate an increase in virulence and decrease in viability after disinfection based on previous work. It is also suspected increases in virulence will coincide with significant changes in phenotypic cellular behavior, such as changes in cell size. These results will help guide the implementation of stricter regulations needed to control potential disease outbreaks.