The overall aim of this bench-scale study was to quantify differences in the inactivation
kinetics of organisms of the same species obtained from various environments (disinfected and
non-disinfected) versus culture collection strains of the same species. The disinfected
environments included water sampled from four full-scale distribution systems. Microorganisms
from non-disinfected environments included bacterial isolates from raw water (from the same
four participating utilities), pure culture strains of heterotrophic bacteria and E. coli O157:H7
from ATCC, and six environmental strains of E. coli O157:H7 isolated by the Wisconsin Food
Research Institute from cow manure and farm wastewater. Microbial sources from disinfected
environments included isolated heterotrophic bacteria from distributed municipal water from
four different locations across North America. The inactivation kinetics experiments were
conducted at bench-scale at 21oC. The disinfectants tested included free chlorine and
monochloramine.
With monochloramine, all strains of E. coli O157:H7 tested showed approximately 2 to 3
log10 of inactivation with Ct values ranging from 20-30 mg.min/L. The Ct values for 2-3 log<sub>10</sub> of
inactivation of E. coli O157:H7 using chlorine were less than 0.30 mg.min/L. All environmental
strains of E. coli O157:H7 were consistently more resistant to monochloramine than the ATCC
35150 strain and these differences were statistically significant. Several strains of heterotrophic
bacteria have been isolated from distributed water collected from the four participating utilities.
These isolates were identified using API biochemical profiling and included various types of
pseudomonads (P. fluorescens) and pseumonad-related bacteria such Brevundimonas vesicularis
and Sphingomonas paucimobilis. Inactivation kinetics experiments of these isolates as well as
the kinetics of culture collection strains show that there was a wide range of resistance among
heterotrophic bacteria.
If evidence is generated in support of the hypothesis that disinfectant-tolerant
microorganisms can evolve in distribution systems, it could potentially lead to a reassessment of
the practice of maintaining a steady concentration of secondary disinfectant. Strategies such as
periodic changes in disinfectant concentration or type may potentially be considered. Includes 3 references, tables.
| Edition : | Vol. - No. |
| File Size : | 1
file
, 270 KB |
| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 11 |
| Published : | 11/02/2003 |
