MODELING THE EFFECT OF PH, ACIDULANT AND TEMPERATURE ON THE GROWTH-RATE OF YERSINIA-ENTEROCOLITICA

Growth of two pathogenic and one environmental serotype of Yersinia enterocolitica under acidic conditions and at 4 and 25-degrees-C was investigated. At both temperatures the maximum growth inhibitory pH depended on the acidulant used and was in the order acetic > lactic > citric > sulphuric. At the lower temperature the maximum growth inhibitory pH was 0.3-0.5 pH units higher than at 25-degrees-C. No difference was observed between the behaviour of pathogenic and environmental serotypes in this respect. Measurement of growth at a number of sub-optimal temperatures and pH values showed that the variation of growth rate with temperature could be represented by a square root plot. The effect of different pH values could be incorporated into the model by replacing the regression coefficient b by its relationship with pH. Values of maximum growth inhibitory pH derived from the model were in good agreement with experimental values with the exception of acetic acid.