Reduction of Escherichia coli O157:H7 populations in soy sauce, a fermented seasoning

We studied five Escherichia coli O157:H7 strains in soy sauce which was incubated at 4, 18, or 30 degrees C after inoculation. The cell numbers of E. coli O157:H7 decreased to an undetectable level (<20 CFU/ml) within 9 days in all the soy sauce samples at 30 degrees C, but did not decrease in the 0.1 M phosphate-buffered saline (pH 7.0) control solution under the same conditions. Soy sauce reduced the cell, numbers of bacteria at 18 degrees C to a lesser extent than at 30 degrees C, but to a greater extent than at 4 degrees C. Components of soy sauce such as 10% or 16% NaCl, 5%, ethanol, lactic acid, or acetic acid at pH 4.5, sodium benzoate (0.6 g/kg), or p-hydroxybenzoic acid n-butyl ester (0.05 g/liter) caused a reduction of the E. coli O157:H7 population at 30 degrees C, and the anti-h coli O157:H7 effect of each component was less than that of soy sauce. The fate of E. coli O157:H7 cells in a buffered solution containing various components of soy sauce resembled that in soy sauce at 30 degrees C, which demonstrated the importance of the combination of the soy sauce components for its anti-E. coli O157:H7 action.