A heterogeneous population model for the analysis of bacterial growth kinetics.

A two-compartment, heterogeneous population model (HPM) was derived using the simulation software SB ModelMaker to describe the growth of Listeria monocytogenes in bacteriological media at 5-35 degrees C. The model assumed that, at time t = 0, the inoculum was distributed between two distinct compartments, Non-Growing and Growing, and that growth could be described by four parameters: initial total cell population (N0), final maximum cell population (Nmax), maximum specific growth rate (mu(max)), and initial cell population in the Growing compartment (G0). The model was fitted to the data by optimizing the four parameters, and lag phase duration (lambda) was calculated. The resulting values of mu(max) and lambda were similar to those determined using the modified Gompertz equation. A new parameter, w0, was defined which relates to the proportion of the initial cell population capable of growth, and is a measure of the initial physiological state of the cells. A modified model in which mu(max) was replaced with a temperature function, and w0 replaced G0, was used to predict the effect of temperature on the growth of L. monocytogenes. The results of this study raise questions concerning the current definition of the lag phase.