A HETEROGENEOUS POPULATION-MODEL FOR THE ANALYSIS OF BACTERIAL-GROWTHKINETICS

A two-compartment, heterogeneous population model (HPM) was derived us ing the simulation software SB ModelMaker(C) to describe the growth of Listeria monocytogenes in bacteriological media at 5-35 degrees C. Th e model assumed that, at time t = 0, the inoculum was distributed betw een two distinct compartments, Non-Growing and Growing, and that growt h could be described by four parameters: initial total cell population (N-c), final maximum cell population (N-max), maximum specific growth rate (mu(max)), and initial cell population in the Growing compartmen t (G(0)). The model was fitted to the data by optimizing the four para meters, and lag phase duration (lambda) was calculated. The resulting values of mu(max) and lambda were similar to those determined using th e modified Gompertz equation. A new parameter, w(0), was defined which relates to the proportion of the initial cell population capable of g rowth, and is a measure of the initial physiological stare of the cell s. A modified model in which mu(max) was replaced with a temperature f unction, and w(0) replaced G(0), was used to predict the effect of tem perature on the growth of L. monocytogenes. The results of this study raise questions concerning the current definition of the lag phase. (C ) 1997 Elsevier Science B.V.