Chlorine Inactivation of Eschrichia Coli O157 H7 in Water

Research Note: Chlorine Inactivation ofEschrichia Coli O157:H7 in Water
October 2001
Journal of Food Protection: Vol. 64, No. 10, pp. 16071609.
Tong Zhao, Michael P. Doyle, and Ping Zhao, Center for Food Safety, Universityof Georgia,
Paul Blake, Georgia State Public Health Laboratory, Georgia State Public HealthDepartment,
Fone-Mao Wu, Center for Food Safety, University of Georgia

Six human isolates of Escherichia coli O157:H7 and E. coli (ATCC 11229) wereused to determine the concentrations of free chlorine and exposure timesrequired for inactivation. Free chlorine concentrations of 0.25, 0.5, 1.0, and2.0 ppm at 23°C were evaluated, with sampling times at 0, 0.5, 1.0, and 2.0min. Results revealed that five of six E. coli O157:H7 isolates and the E.coli control strain were highly susceptible to chlorine, with >7 log10 CFU/mlreduction of each of these strains by 0.25 ppm free chlorine within 1 min.However, comparatively, one of the seven strains was unusually tolerant tochlorine at 23°C for 1 min, with a 4-, 5.5-, 5.8-, and >5.8-log CFU/mlreduction at free chlorine concentrations (ppm) of 0.25, 0.5, 1.0, and 2.0,respectively. Based on these studies most isolates of E. coli O157:H7 have nounusual tolerance to chlorine; however, one strain was exceptional in beingrecovered after 1-min of exposure of 107 CFU/ml to 2.0 ppm of free chlorine.This isolate may be a useful reference strain for future studies on chlorinetolerance of E. coli