Application of Probabilistic Model to Calculate Probabilities of Escherichia coli O157:H7 Growth on Polyethylene Cutting Board

Abstract

This study calculated kinetic parameters of Escherichia coli O157:H7 and developed a probabilistic model to estimate growth probabilities of E. coli O157:H7 on polyethylene cutting boards as a function of temperature and time. The surfaces of polyethylene coupons (3x5 cm) were inoculated with E. coli O157:H7 NCCP11142 at 4 Log CFU/cm(2). The coupons were stored at 13 to 35 degrees C for 12 h, and cell counts of E. coli O157:H7 were enumerated on McConkey II with sorbitol agar every 2 h. Kinetic parameters (maximum specific growth rate, Log CFU/cm(2)/h; lag phase duration, h; lower asymptote, Log CFU/cm(2); upper asymptote, Log CFU/cm(2)) were calculated with the modified Gompertz model. Of 56 combinations (temperature x time), the combinations that had >= 0.5 Log CFU/cm(2) of bacterial growth were designated with the value of 1, and the combinations that had increases of <0.5 Log CFU/cm(2) were given the value 0. These growth response data were fitted to the logistic regression to develop the model predicting probabilities of E. coli O157:H7 growth. Specific growth rate and growth data showed that E. coli O157:H7 cells were grown at 28-35 degrees C, but there were no obvious growth of the pathogen below 25 degrees C. Moreover, the developed probabilistic model showed acceptable performance to calculate growth probability of E. coli O157:H7. Therefore, the results should be useful in determining upper limits of working temperature and time, inhibiting E. coli O157:H7 growth on polyethylene cutting board.