The influence of non-lethal temperature on the rate of inactivation of vegetative bacteria in inimical environments may be independent of bacterial species Original Research Article

The influence of non-lethal temperature on the survival of two species of food-borne bacteria under growth-preventing pH and water activity conditions was investigated. Specifically, inactivation rates of four strains of Escherichia coli and three strains of Listeria monocytogenes were determined in culture broth adjusted to pH 3.5 and water activity 0.90, to prevent growth of both species, and for temperatures in the range 5–45 °C at 5 °C intervals. Sixty-three inactivation rates were obtained, plotted on Arrhenius co-ordinates, and lines of best-fit determined by simple linear regression. Differences in the mean inactivation rate of each species at a given temperature were not significant (p < 0.05) with the exception of the rates at 25 °C. The inactivation rate responses of both species were comparable to those reported by McQuestin et al. (Appl. Environ. Microbiol., 75:6963–6972, 2009) for a variety of E. coli strains under a wide range of growth-preventing pH and water activity conditions. The results support the hypothesis that non-lethal temperature is a key factor governing the rate of inactivation of vegetative bacteria in foods when other hurdles prevent their growth and indicate that the temperature effect may also be independent of bacterial species.