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Research Note: Chlorine Inactivation of
Eschrichia 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, University
of Georgia,
Paul Blake, Georgia State Public Health Laboratory, Georgia State Public Health
Department,
Fone-Mao Wu, Center for Food Safety, University of Georgia
Abstract
Six human isolates of Escherichia coli O157:H7 and E. coli (ATCC 11229) were
used to determine the concentrations of free chlorine and exposure times
required for inactivation. Free chlorine concentrations of 0.25, 0.5, 1.0, and
2.0 ppm at 23°C were evaluated, with sampling times at 0, 0.5, 1.0, and 2.0
min. 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/ml
reduction of each of these strains by 0.25 ppm free chlorine within 1 min.
However, comparatively, one of the seven strains was unusually tolerant to
chlorine at 23°C for 1 min, with a 4-, 5.5-, 5.8-, and >5.8-log CFU/ml
reduction 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 no
unusual tolerance to chlorine; however, one strain was exceptional in being
recovered 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 chlorine
tolerance of E. coli
O157:H7.
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