Listeria Monocytogenes Stress Response Systems and Their Significance for Survival in Food Processing Environments

L. monocytogenes is a gram positive bacterial pathogen that can cause severe foodborne disease. Listeriosis is predominantly acquired by consumption of contaminated foods. Therefore, effective control of L. monocytogenes in food processing environments and in foods is important. The ability of L. monocytogenes to survive in a variety of different environments suggests that this organism has evolved effective molecular responses to react to environmental stress conditions through up and down regulation of the synthesis of specific proteins. Efforts to reduce food contamination with L. monocytogenes have primarily focused on strategies to eliminate and reduce cross contamination in food processing plants. However, it is possible that sanitizer treatment may induce expression of stress pathways in Listeria cells, which may confer an enhanced ability to survive sanitizer stress and other environmental stress conditions, thus allowing L. monocytogenes to persist in the food
processing environment. Thus, the goals of this project are to (i) characterize different classes of L. monocytogenes stress response genes as well as interactions among different stress response systems; (ii) identify the stress response pathways induced by different stress conditions/sanitizers; and (iii) characterize stress resistance and stress response pathways in persistent L. monocytogenes strains. To these ends, we propose to: Objective 1. Construct L. monocytogenes strains bearing either inducible ctsR and hrcA genes or null mutations in these genes and use microarray based strategies to define and characterize class I (HrcA dependent), class III (CtsR dependent) and class IV (HrcA, CtsR, and sigma B independent) stress response genes. Objective 2. Characterize stress response gene expression under conditions relevant for survival in the food-processing environment (e.g., nutrient deprivation, sanitizer presence). Objective 3. Compare stress response pathways in persistent
and non-persistent L. monocytogenes isolates already obtained from food processing environments.