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 wa s incubated at 4, 18, or 30 degrees C after inoculation. The cell numb ers of E. coli 0157.H7 decreased to an undetectable level (<20 CFU/ml) within 9 days in all the soy sauce samples at 30 degrees C, but did n ot decrease in the 0.1 M phosphate-buffered saline (pH 7.0) control so lution 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, b ut to a greater extent than at 4 degrees C. Components of soy sauce su ch 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 este r (0.05 g/liter) caused a reduction of the E. coli 0157:H7 population at 30 degrees C, and the anti-h coli 0157.H7 effect of each component was less than that of soy sauce. The fate of E. coli 0157:H7 cells in a buffered solution containing various components of soy sauce resembl ed that in soy sauce at 30 degrees C, which demonstrated the importanc e of the combination of the soy sauce components for its anti-E. coli 0157:H7 action.