Influence of stress on individual lag time distributions of Listeria monocytogenes

The effects of nine common food industry stresses on the times to the turbidity (T-d) distribution of Listeria monocytogenes were determined. It was established that the main source of the variability of T-d for stressed cells was the variability of individual lag times. The distributions of T-d revealed that there was a noticeable difference in response to the stresses encountered by the L. monocytogenes cells. The applied stresses led to significant changes of the shape, the mean, and the variance of the distributions. The variance of T-d of wells inoculated with single cells issued from a culture in the exponential growth phase was multiplied by at least 6 and up to 355 for wells inoculated with stressed cells. These results suggest stress-induced variability may be important in determining the reliability of predictive microbiological models.