Comparison of the Disinfection Kinetics of Wastewater-Sourced and Laboratory-Cultured E. coli and Enterococcus spp. (E. faecalis, E. faecium, E. casseliflavus) with Exposure to Free Chlorine, Monochloramine, UVC, and Simulated Sunlight

Most data on laboratory-scale experiments evaluating E. coli and enterococci disinfection are from experiments conducted using laboratory-cultured bacteria. However, environmental bacteria, such as those in wastewater, have potential to be more resistant to disinfection than their laboratory-cultured counterparts. Additionally, most Enterococcus disinfection studies have only evaluated E. faecalis despite the diversity of Enterococcus species in the environment. In this study, we evaluated inactivation kinetics of wastewater-sourced E. coli and enterococci, laboratory-cultured E. coli, and three species of laboratory-cultured Enterococcus with exposure to free chlorine, monochloramine, UVC, and simulated sunlight. All bacteria were purified and suspended in a chlorine-demand-free buffer with minimal light attenuation to allow comparison between populations without confounding matrix effects. Laboratory-cultured bacteria were more susceptible to the oxidants than the wastewater-sourced bacteria, highlighting that research using reference-strain bacteria in the laboratory may not reflect inactivation kinetics in the environment. When exposed to the light-based disinfectants, only laboratory-cultured E. coli and E. faecalis were more susceptible than the wastewater-sourced bacteria. Notably, different laboratory-cultured Enterococcus species had different inactivation rates, with E. faecalis being the most susceptible. These findings highlight the importance of incorporating indigenous environmental bacteria in laboratory studies and assessing a variety of Enterococcus species in disinfection research.

Environmental bacteria in wastewater can have slower disinfection kinetics than bacteria grown in the laboratory and should be included in laboratory-based experiments evaluating the mechanisms and kinetics of disinfection.