PREDICTING THE GROWTH OF ESCHERICHIA-COLI ON DISPLAYED PORK

Samples of sterile pork fat or muscle tissue were inoculated with loga rithmic phase cultures of Escherichia coli and were incubated in a dis play case at positions where they experienced average temperatures of 3.5, 6.0, 6.9, 8.0, 9.7 or 11.4 degrees C. The temperature history of the tissue at each position was recorded. During incubation for up to 7 days, samples of each tissue were removed daily from each position f or enumeration of E. coli and growth of E. coli at each position at ea ch of those times was estimated by integrating the temperature history of the tissue with respect to a model describing the dependency on te mperature of the aerobic growth of E. coli. When temperatures fluctuat ed above 7 degrees C for periods <1 h, no growth of E. coli occurred o n fat or muscle tissue although growth would be predicted by the model . When temperatures fluctuated above 7 degrees C for periods >1 h, the predicted growth and that observed on fat tissue were similar. Howeve r, growth on muscle tissue occurred only when temperatures fluctuated above 9 degrees C for lengthy periods, and then only after a lag of ab out 4 days when temperatures remained mainly below 12 degrees C. When temperatures fluctuated above 12 degrees for lengthy periods the predi cted growth and that observed on both fat and muscle tissues were simi lar. Accurate prediction of the growth off. coli on meat which experie nces temperatures that fluctuate below 7 degrees C will require the de velopment of models to predict the lag before growth of E. coli on fat or muscle tissues during periods at growth-permitting temperatures.