Primary Models

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The concept of the primary model is fundamental to the field of predictive microbiology (see the definition of a model in the Preface). A primary model for microbial growth aims to describe the kinetics of the process with as few parameters as possible, while still being able to accurately define the distinct stages of growth. A typical bacterial growth curve is shown in Figure 2.1. When the increase in population density (usually defined as the base 10 logarithm of cell numbers) is plotted against time, the resulting curve usually has four phases, referred to respectively as the lag, exponential, stationary, and death or decline phases.