Modelling the effect of sublethal injury on the distribution of the lag times of individual cells of Lactobacillus plantarum

The effect of heat stress on subsequent duration of the lag time of individual cells of Lactobacillus plantarum was analysed by flow cytometry. The results show clearly that both the mean and the standard deviation of the distribution of the lag time increased after sublethal heat treatment. The distributions of the lag times or the log lag times of untreated and treated cells, respectively, could be described as extreme value distributions. From these distributions, the distribution of the minimum lag times could be calculated and thus the effect of inoculum size on the apparent lag could be deduced. The results show clearly that the apparent lag time is dependent on the size of the inoculum, especially when the inoculum is sublethally injured.