Temperature governs the inactivation rate of vegetative bacteria under growth-preventing conditions

Novel studies, in combination with a meta-analysis of available data, were undertaken to explore the kinetics of non-thermal inactivation of Escherichia coli with particular attention to inactivation in fermented meats and including analogous broth-based model systems. The analyses were based on rates of inactivation and specifically investigated the influence of temperature, pH and water activity at levels that alone, or in combination, prevented growth. When independently-derived inactivation data, obtained using different test conditions and diverse E. coli strains, were presented as Arrhenius plots, temperature was found to have a strong effect on the rate of inactivation, explaining 60% of the variance in the data. The slope of the Arrhenius plot changed, however, at temperatures above approximately 47 degrees C, corresponding to the maximum for growth of E. coli. A strong and consistent effect of pH or water activity on inactivation rate was not observed upon meta-analysis of collated data, but the relative effect of both factors was quantified in an analogous broth-based system. We also observed that inactivation rates of three strains of Listeria monocytogenes in the range 5 to 40 degrees C did not differ systematically from those of four strains of E. coli when growth was prevented by low pH and water activity. The observations of a consistent slope of Arrhenius plots for non-thermal inactivation rate of bacteria under diverse environmental conditions and for different strains and species, but which differ from slopes associated with thermal inactivation, raise the intriguing possibility of a mechanism of inactivation at sub-lethal temperatures, distinct from thermal inactivation, that is common to many vegetative bacteria.