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The overall aim of this bench-scale study was to quantify differences in the inactivationkinetics of organisms of the same species obtained from various environments (disinfected andnon-disinfected) versus culture collection strains of the same species. The disinfectedenvironments included water sampled from four full-scale distribution systems. Microorganismsfrom non-disinfected environments included bacterial isolates from raw water (from the samefour participating utilities), pure culture strains of heterotrophic bacteria and E. coli O157:H7from ATCC, and six environmental strains of E. coli O157:H7 isolated by the Wisconsin FoodResearch Institute from cow manure and farm wastewater. Microbial sources from disinfectedenvironments included isolated heterotrophic bacteria from distributed municipal water fromfour different locations across North America. The inactivation kinetics experiments wereconducted at bench-scale at 21oC. The disinfectants tested included free chlorine andmonochloramine.With monochloramine, all strains of E. coli O157:H7 tested showed approximately 2 to 3log10 of inactivation with Ct values ranging from 20-30 mg.min/L. The Ct values for 2-3 logsub10/sub ofinactivation of E. coli O157:H7 using chlorine were less than 0.30 mg.min/L. All environmentalstrains of E. coli O157:H7 were consistently more resistant to monochloramine than the ATCC35150 strain and these differences were statistically significant. Several strains of heterotrophicbacteria have been isolated from distributed water collected from the four participating utilities.These isolates were identified using API biochemical profiling and included various types ofpseudomonads (P. fluorescens) and pseumonad-related bacteria such Brevundimonas vesicularisand Sphingomonas paucimobilis. Inactivation kinetics experiments of these isolates as well asthe kinetics of culture collection strains show that there was a wide range of resistance amongheterotrophic bacteria.If evidence is generated in support of the hypothesis that disinfectant-tolerantmicroorganisms can evolve in distribution systems, it could potentially lead to a reassessment ofthe practice of maintaining a steady concentration of secondary disinfectant. Strategies such asperiodic changes in disinfectant concentration or type may potentially be considered. Includes 3 references, tables.

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Edition: Vol. - No. Published: 11/02/2003 Number of Pages: 11File Size: 1 file , 270 KB