Modelling the bacterial growth/no growth interface

A logistic regression model is proposed which enables one to model the boundary between growth and no growth for bacterial strains in the presence of one or more growth controlling factors such as temperature, pH and additives such as salt and sodium nitrite. The form of the expression containing the growth limiting factors may be suggested by a kinetic model, while the response at a given combination of factors may either be presence/absence (i.e. growth/no growth) or probabilistic (i.e. r successes in n trials). The approach described represents an integration of the probability and kinetic aspects of predictive microbiology, and a unification of predictive microbiology and the hurdle concept. The model is illustrated using data for Shigella flexneri.