Growth of Staphylococcus aureus 2064 described by predictive microbiology: From primary to secondary models

The growth of Staphylococcus aureus 2064 isolate in model nutrient broth was studied as affected by temperature and water activity using principles and models of predictive microbiology. Specific rates resulting from growth curves fitted by the Baranyi model were modelled by the secondary Ratkowsky model for suboptimal temperature range (RTKsub) as well as the Ratkowsky extended model (RTKext) and cardinal model (CM) in the whole temperature range. With the biological background of the RTKext model, cardinal values of temperature T_min = 6.06 °C and T_max = 47.9 °C and water activity a_{w min} = 0.859 were calculated and validated with cardinal values estimated by CM (T_min = 7.72 °C, T_max = 46.73 °C, a_{w min} = 0.808). CM also provided other cardinal values, T_opt = 40.63 °C, a_wopt = 0.994, as well as optimal specific growth rate of 1.97 h^–1 (at T_opt and a_wopt). To evaluate the goodness of fit of all models, mathematical and graphical validation was performed and the statistical indices proved appropriateness of all the secondary models used.