Inactivation of Brazilian wild type and enterotoxigenic Escherichia coli by chlorine.

The kinetic inactivation parameters of four wild strains and two enterotoxigenic strains of Escherichia coli exposed to commercial calcium hypochlorite were determined. The four wild strains (1A, 3C, 4D and 8H) were isolated from lettuce bought in Sao Paulo (Brazil), and the two enterotoxigenic strains (TR69 and TR101) were originally isolated from human patients. Decimal reduction time 'D', for 10 mg L-1 available chlorine at pH 6.8, varied between 71.4 s for the wild strain 4D and 31.3 s for the toxigenic strain. The 'D' values obtained for wild strain 1A exposed to 5.0 mg L-1 available chlorine at pH 6.8 varied between 111.1 s and 41.7 s. The 'D' values obtained for E. coli strain TR69 exposed to 10 mg L-1 available chlorine varied from 15.2 s at pH 5.4 up to 83.3 s at pH 8.2. The use of the most resistant wild strain of E. coli as a biological standard assures maximal effectiveness in controlling water contamination by chlorination.