A model describing microbial inactivation and growth kinetics

Abstract

A model based on the chance of collision between environmental water molecules having appropriate energy and microbial cells, and leading to description of both inactivation and growth kinetics is presented. Functions derived from the model can describe the known shapes of survival curves (concave, convex, sigmoid, linear, on semi-log plot), the tailing-off phenomenon, some prominent behaviour of growing population kinetics, and are provided with fair predictive power. The main features of the model as heat inactivation is concerned are: (1) always the survival curves are expected to be concave on semi-log plot, unless some lag occurs in reaching the treatment temperature; (2) the tailing-off occurs when the concentration of living cells and/or water molecules having lethal energy is low enough; (3) heat inactivation curve at any temperature and whichever is the water content of the medium can easily be predicted, provided a single survivor concentration after time t at temperature T in a medium of defined composition is known; (4) the energy value of molecules leading to inactivation is about half the activation energy expected from classical thermodynamic treatment of reaction rate; (5) the concentration of water molecules having enough energy to drive the process changes exactly Q 10 times each 10 °C or ten times each z degrees. As radiation or chemical inactivation is concerned the model allows the description of known shapes of survival curves, linking the shape of the survival curve to the concentration of specific cellular molecular groups. Appropriate modification of the fundamental equation of the model leads to description of cell growth kinetics as a function of cell concentration, temperature, water content in the environment, the presence of metabolic by-products, antimetabolites, etc., as well as to the formulation of hypotheses about growth, death and senescence regulating structures.