The survival responses of Listeria monocytogenes strains in a lactic soft cheese were studied following acid and osmotic stress exposures. Survival data of individual and mixed strains were fitted to 4 inactivation models (log-linear with tail, biphasic, Weibull and Weibull with tail). Lack of fit (LoF) analysis, showed the Weibull and log-linear with tail models provided the best fit of the data and were used to determine kinetic parameters. Analysis of inactivation kinetics showed that the susceptibility of individual strains (P < 0.0001) and the form of stress exposure (P < 0.05) have a significant effect on survival responses. Although both acid and osmotic stress exposures mainly resulted in enhanced survival of the L. monocytogenes strain, in one susceptible strain stress exposure caused inactivation. These findings imply that responses of L. monocytogenes strains in foods are dependent on the differences in the intrinsic susceptibilities of individual strains. Moreover, when introduced into the food as mixed strains, analysis of the diversity of surviving populations revealed that one strain out-lived other and remained as the only survivor after 15 d. These findings underscore the fact that predictions of pathogen responses in foods based on mixed strain cocktails as a way of accommodating strain heterogeneity must be treated with caution. Furthermore, data based on survival kinetics of stress-hardened cells could provide fail-safe models for predicting L. monocytogenes survival in foods.