Identification and disinfection tolerance of coliform bacteria in water treatment

Reoccurring coliform events in drinking water treatment utilities and distribution systems may be characterized using molecular tools to determine the origin of the bacteria and the reason for chronic coliform-positive water samples. Coliform events from three treatment utilities were characterized using Pulsed Field Gel Electrophoresis (PFGE). Genetic relatedness of isolates from distribution systems in Laval, QC and Lexington, KY and a treatment utility in Pinellas County, FL was determined using PFGE. The results showed that isolates from Laval, QC were for the most part unrelated, which indicates that the coliforms originated from different intrusion events. In contrast, some genetic similarity was observed among isolates from the distribution system in Lexington, KY which signifies that coliform events were likely due to the presence of chronic biofilm within the system. Genetic similarity among isolates from the treatment utility in Pinellas County, FL was found to be site dependent. A high number of genetically related isolates from a series of finished water samples indicates that a disinfectant tolerant population of Enterobacter cloacae may exist within the plant. One of the Ent. cloacae isolates from the dominant subpopulation was examined to determine whether it demonstrated tolerance to disinfection in vitro.;Further investigation of the Ent. cloacae isolate from the treatment utility in Pinellas County, FL indicated that the presence of the dominant strain found in multiple samples of treated water was most likely not due to disinfectant tolerance of the bacterial population through acquired genetic changes. Results of inactivation experiments conducted at different temperatures showed an increase in disinfection efficacy at warm temperatures compared to cool temperatures, which indicates that the warm water temperature, while being optimal for cell growth and reproduction, does not allow for survival in the presence of a disinfectant. There are clearly other factors at play that allowed these bacteria to survive in the presence of disinfectant. Biofilm forming potential of the Ent. cloacae isolate was assessed over a short time period and disinfection tolerance of attached cells was examined. Results of inactivation experiments conducted using suspended and attached Ent. cloacae cells showed that attached cells were more easily inactivated compared to suspended cells. This may seem counterintuitive because biofilm cells tend to exhibit resistance to chemical disinfectants compared to planktonic cells. However, the attached cells used in this study were cultured over a short time period and it is unlikely that this time was sufficient to form a biofilm.;Continuous flow experiments were conducted to determine the effect of different water matrices on attachment and growth of Ent. cloacae cells. The results of the continuous flow experiments indicate that the differences in water chemistry between Halifax tap water and water from Pinellas County treatment utility had no effect on growth of Ent. cloacae on a stainless steel surface.;The methods used in the experiments described above used either membrane integrity or culturability as indicators of cell viability, as adenosine triphosphate (ATP) quantification was not an accurate indicator of the number of viable waterborne bacteria evaluated in this study.