Retrieval of Microbial Inactivation Kinetic Parameters in Chemical Preservation and Disinfection by the Endpoints Method

Abstract

The response of microorganisms to chemical preservatives and disinfectants can be described by the traditional Chick-Watson-Hom’s (CWH) model or more general Weibullian survival model, of which it is a special case. The chemical agent efficacy and its concentration dependence can be described by either a power-law or log-exponential term. For dynamic inactivation, the unstable or volatile agent’s dissipation can be described by a flexible two-parameter model, which is inserted as an algebraic term into the differential rate equation. In principle, both models can be used to estimate a targeted microbe’s survival parameters from the agent’s concentrations when constant or its initial and final concentrations only if not, and the corresponding final survival ratios reached. This Endpoints Method eliminates the need to determine the entire survival curves, and in the dynamic case the agent’s entire dissipation curves too. Static inactivation requires the numerical solution of simultaneous nonlinear algebraic equations, and dynamic, of simultaneous nonlinear equations whose right-hand side is the numerical solution of differential rate equations in which the agent’s dissipating pattern is incorporated as a term. When the Weibullian survival model’s shape factor is known a priori, the theoretical minimum of experimental final survival ratios needed is two and when unknown three. However, validation of the model and mathematical procedure must come from their ability to predict correctly final survival ratios not used in the parameter magnitudes calculation, which requires at least one additional experimental final survival ratio determination.