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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.
Document Type: Research Article
Center for Food Safety, University of Georgia, Griffin, Georgia 30223-1797, USA 2:
Georgia State Public Health Laboratory, Georgia State Public Health Department, Decatur, Georgia 30033-4050, USA
Publication date: October 1, 2001
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