P-009. Transcriptomic and Phenotypic Analyses Suggest Differences in Sigma B Contributions to Stress Response and Virulence in Listeria monocytogenes Strains Representing Lineages I, II, IIIA, and IIIB

H. F. Oliver, M. Wiedmann, K. J. Boor;
Cornell Univ., Ithaca, NY.

Background: Phylogenetic analysis of L. monocytogenes strains has identified three distinct lineages. While lineages I and II are both common among human clinical and food isolates, lineage I strains are overrepresented among clinical isolates, and lineage II strains are overrepresented among food and environmental isolates. Lineage III, which includes subgroups IIIA and IIIB, is rare and predominantly associated with animal disease. Sigma B, encoded by sigB, is a sigma factor previously demonstrated to critically contribute to stress response and virulence in lineage II strains. Thus, we used phenotypic and transcriptomic analyses to characterize the role of sigma B in L. monocytogenes strains representing lineages I, II, IIIA, and IIIB. Methods: Whole-genome microarrays were employed in competitive hybridization experiments using RNA isolated from stationary phase wildtype and sigB null mutant cells in four different strains (lineages I, II, IIA, and IIIB). In addition, mutant and wildtype strains were tested for acid stress survival (pH 2.5, 60 min), oxidative stress survival (13 mM CHP, 15 min), and ability to invade Caco-2 human intestinal epithelial cells. Results: A total of 57 genes were positively regulated by sigma B in all four strains evaluated. In addition, a number of genes were found to be positively regulated by sigma B only in specific strains. For example, 83 genes appear to be positively regulated by sigma B only in the lineage I strain. While sigma B contributed significantly to acid and oxidative stress survival and Caco-2 cell invasion in lineage I, II, and IIIB strains, sigma B contributions to stress survival and invasion in the lineage IIIA strain were not significant under the conditions tested. Conclusions: Our results indicate that the role of sigma B in stress response and virulence differs among L. monocytogenes strains, which may contribute to the differences in the distribution of L. monocytogenes lineages among different sources (e.g., humans and foods).