Predictive modelling of Escherichia coli O157:H7: inclusion of carbon dioxide as a fourth factor in a pre-existing model.

Two models for Escherichia coli O157:H7 are compared, one with growth-controlling factors pH (4.5-7.0), temperature (10-30 degrees C) and NaCl concentration (0.5-6.5% w/v) and the other with the same factors and ranges, but with the addition of carbon dioxide (CO2: 10-80% v/v). Validation of the four-factor model, to include food packed in modified atmospheres containing CO2, was not possible due to lack of published data. However, where CO2 concentration was entered as 0%, only minor differences occurred between the predictions from the two models for the same conditions of pH, NaCl and temperature; consequently reliable, safe predictions using the four-factor model, with CO2 concentration recorded as 0%, can be made for foods packed in air. At temperatures from 10 to 30 degrees C, it was found that lower (10 and 20%) concentrations of CO2 had little effect on lag times and growth rates, and higher concentrations still permitted growth of E. coli O157:H7 under a wide range of conditions of NaCl concentration, pH value and temperature, suggesting that the organism is relatively CO2-tolerant.