Influence of stress and growth conditions on individual lag time distributions of Listeria monocytogenes

The effects of nine common food industry stresses on the individual lag time (lag) distribution of L. monocytogenes were determined. The distributions of lag obtained in a single re-growth condition 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 in the shape, mean and variance of lag distributions (in a single re-growth condition). Then, the influence of re-growth conditions on lag distribution and on the probability to initiate growth were examined for L. monocytogenes cells previously subjected to a representative stress situation of the dairy processing. A linear relation was observed between means of lag and their standard deviation. A decrease in the probability of initiating growth for stressed cells was also observed as growth conditions became unfavourable. These results suggest that stress-induced variability may be important in determining the reliability of predictive microbiological models.