Modeling and Validation of the Ecological Behavior of Wild-Type Listeria monocytogenes and Stress-Resistant Variants

Abstract

Listeria monocytogenes exhibits a heterogeneous response upon stress exposure which can be partially attributed to the presence of stable stress-resistant variants. This study aimed to evaluate the impact of the presence of stress-resistant variants of Listeria monocytogenes and their corresponding trade-offs on population composition under different environmental conditions. A set of stress robustness and growth parameters of the wild type (WT) and an rpsU deletion variant was obtained and used to model their growth behavior under combined mild stress conditions and to model their kinetics under single-and mixed-strain conditions in a simulated food chain. Growth predictions for the WT and the rpsU deletion variant matched the experimental data generally well, although some deviations from the predictions were observed. The data highlighted the influence of the environmental conditions on the ratio between the WT and variant. Prediction of performance in the simulated food chain proved to be challenging. The trend of faster growth and lower stress robustness for the WT than for the rpsU variant in the different steps of the chain was confirmed, but especially for the inactivation steps and the time needed to resume growth after an inactivation step, the experimental data deviated from the model predictions. This report provides insights into the conditions which can select for stress-resistant variants in industrial settings and discusses their potential persistence in food processing environments. IMPORTANCEListeria monocytogenes exhibits a heterogeneous stress response which can partially be attributed to the presence of genetic variants. These stress-resistant variants survive better under severe conditions but have, on the other hand, a reduced growth rate. To date, the ecological behavior and potential impact of the presence of stress-resistant variants is not fully understood. In this study, we quantitatively assessed growth and inactivation behavior of wild-type L. monocytogenes and its stress-resistant variants. Predictions were validated under different conditions, as well as along a model food chain. This work illustrates the effects of environmental factors on population dynamics of L. monocytogenes and is a first step in evaluating the impact of population diversity on food safety. D iversity exists within bacterial populations which can, for example, be observed by tailing of inactivation curves upon stress exposure. This tail can be caused by either phenotypic or genotypic heterogeneity. Phenotypic heterogeneity refers to transiently increased resistance with a physiological or epigenetic background. Reasons for phenotypic heterogeneity can include the presence of persisters (1), bistability caused by noise in stochastic gene expression (2-4), or epigenetic phenotype switching (5). Genotypic heterogeneity refers to the presence of stable stressresistant variants with an inheritable stress-resistant phenotype caused by genomic alterations (6). These stable stress-resistant variants have bee...

Towards transparent and consistent exchange of knowledge for improved microbiological food safety

“…In addition, the modelling approach followed in those studies that consider the inter-strain variability of the same microbial species has changed with respect to previous studies [18,19]. Latter developments in predictive modelling approaches have also resulted in new model equations [20], stochastic models [6,21,22] and models considering dynamic conditions [23].…”

Moderate and high intensity pulsed electric fields : Effect on microbial inactivation, shelf life and quality of fruit juices

“…The models presented in this work were evaluated using published data. Inactivation data of proteinase was obtained by digitizing published graphs (Driessen, 1983;Schokker & Van Boekel, 1997) using GraphClick 3.0.3 (Arizona Software 2012), and for L. monocytogenes the original raw data was used (Metselaar et al, 2013 andMetselaar et al, 2016).…”

“…4.7. Highly accurate kinetic inactivation data for Listeria monocytogenes at different temperatures and pH, were provided by Metselaar et al (2013), Metselaar et al (2016). Metselaar et al (2013) have studied the inactivation of L. monocytogenes LO28 wild type (WT) and an acid resistant variant 14, at two different growth stages (late exponential and stationary phase) towards combinations of heat and acidification.…”

“…Parameter estimates of the Gauss-Eyring model for L. monocytogenes when exposed to heat and pH. The estimates are for a global fit to the inactivation data (Metselaar et al, 2013 andMetselaar et al, 2016) for LO28-WT and the variant 14 in the late exponential (LE) and stationary phase (SP). In each isolate two subpopulations were resolved that differ in reference temperature Tr and Z-value.…”

“…The Gauss-Eyring model was fitted as a global model to the inactivation data of Metselaar et al (2013), Metselaar et al (2016) using temperature, pH and time as the independent variables and assuming two Gaussian subpopulations (8 parameters) according to:…”