Growth of Listeria monocytogenes is promoted at low temperature when exogenous unsaturated fatty acids are incorporated in its membrane

Listeria monocytogenes is a psychrotrophic food-borne pathogen mostly associated with consumption of ready-to eat foods. Due to its high prevalence in raw materials, it is fundamental to control its growth at low temperature. In lipid-rich products, fatty acids can be heterogeneously distributed in the food matrix and can be present in the environment immediately surrounding the pathogen. In this study, we sought to understand the impact of exogenous fatty acids on the growth and membrane physiology of L. monocytogenes according to the temperature and strain. We demonstrate that exogenous unsaturated fatty acids promote the growth of L. monocytogenes at 5 °C but not at 37 °C. The level of growth modifications is dependent upon the strain. At 5 °C, there is high incorporation of unsaturated fatty acids, which decreases the weighted-average melting temperature of membrane fatty acids allowing L. monocytogenes to compensate for the decrease in fluidity caused by the temperature, thus leading to increased growth. In contrast, the incorporation of saturated fatty acids decreases membrane fluidity and prevents growth at 5 °C. This study underlines the absolute necessity to understand better the cold adaptation of L. monocytogenes in lipid-rich foods in order to adjust their shelf-life and guarantee their microbiological safety.