The Impact of Growth History on Stress Robustness of Listeria Monocytogenes

Environmental factors like oxygen availability have an impact on the stress adaptive behavior and robustness of microorganisms. Adaptation to non-optimal environmental conditions induces molecular changes that help microorganisms developing survival strategies towards more severe stress conditions. Listeria monocytogenes as a food-borne pathogen is regularly exposed to such environmental stresses within its natural habitat, during food processing and throughout its infection cycle. The ability of Listeria to adapt to such changing environment enhances its ability for survival and growth in food and influences its pathogenic potential. In this study, we will investigate the impact of oxygen availability on the growth and robustness induction towards lethal oxidative and acid stresses for three Listeria monocytogenes strains ScottA, EGDe and F2365. Aerobically grown cells showed higher growth rate and were more resistant to oxidative stress than anaerobically and microaerobically grown cells. While for the acid stress, anaerobically and microaerobically grown cells were more resistant than the cells that were cultured aerobically. Catalase activity was measured in the exponential phase Listeria cells, cultured under the different atmospheric conditions i.e. aerobic, microaerobic and anaerobic. Induction of catalase activity was found to be correlated with robustness towards lethal oxidative stress with significant correlation only for F2365 strain. This correlation might be associated with intracellular accumulation of reactive oxygen species (ROS) and subsequent induction of catalase activity. Catalase scavenges the formed H2O2 upon oxidative stress treatment and helps the aerobically grown cells being more resistant towards further oxidative stress. Anaerobically grown cells showed lower level of catalase induction, and hence lower robustness, possibly due to the use of alternative respiration machinery than the aerobically grown cells that results in less ROS formation. That suggests the possibility of using catalase as a biomarker for predicting the robustness of L. monocytogenes towards lethal oxidative stress. However, an inverse correlation was found between catalase activity induction and robustness towards lethal acid stress. Therefore, catalase activity could function as inverse-response biomarker in this condition.The finding of our study might explain also why L. monocytogenes is a target organism in the minimally processed foods. Modified atmosphere packaging is widely used in ready-to-eat foods. The limited oxygen availability of this condition in particular vacuum packaging can have an impact on the robustness of Listeria to further acid stress treatment used in food industry.

 

Author(s): Islam Salih Sharkawy

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