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

NON-TECHNICAL SUMMARY: L. monocytogenes has been responsible for the majority of food product recalls due to the presence of contaminating bacteria. Thus, control of L. monocytogenes in food-processing environments appears to be a critical prerequisite for reducing the frequency of food contamination.
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APPROACH: To identify genes under the regulation of HrcA and CtsR, we will create 2 null mutant strains and 2 strains each bearing either hrcA or ctsR fused to a strong inducible promoter. In addition, we will identify class IV stress response genes through comparative expression analyses using microarrays of unstressed and stressed wild-type L. monocytogenes cells. We will further characterize the expression of class I through IV stress response genes in response to different stress conditions that L. monocytogenes is likely to encounter in the food processing environment. Global gene expression patterns upon stress exposure will initially be characterized using microarray analyses. Expression patterns of selected genes will subsequently be verified and quantitative gene expression data will be generated by using quantitative real time RT-PCR. Finally, the expression of class I to IV stress response genes in persistent strains, as well as in nonpersistent strains, after exposure to stress conditions likely encountered in food processing plants (e.g., sanitizer stress and nutrient stress) will be compared using real time RT-PCR. The data will then be used to generate combinations of sanitizers such that they down and/or up regulate stress response genes resulting in inactivation of L. monocytogenes.