P-007. Contributions of Multiple Transcriptional Regulators to Listeria monocytogenes Virulence and Virulence-Associated Phenotypes

M. E. Palmer, S. Chaturongakul, S. Raengpradub, Y. Hu, M. Wiedmann, K. J. Boor;
Cornell Univ., Ithaca, NY.

The foodborne pathogenic bacterium, Listeria monocytogenes, causes listeriosis, a rare, but serious, invasive disease affecting both humans and animals. The ability of L. monocytogenes to survive transmission through food systems and cause disease is attributed to both its environmental stress survival capabilities and its virulence gene repertoire. Stress response, virulence, and virulence-associated functions in L. monocytogenes have been ascribed to the pleiotropic transcriptional regulators SigB and PrfA. Additional transcriptional regulators, including alternative sigma factors and repressors, were hypothesized to contribute to L. monocytogenes pathogenicity. To assess contributions of various regulatory proteins to virulence and associated phenotypes, stationary phase cells of L. monocytogenes laboratory parent strain 10403S and of a collection of isogenic strains each bearing a single in-frame deletion in a gene encoding alternative sigma factors SigL, SigH, or SigC or in repressors CtsR or HrcA were tested in: (i) invasion assays with Caco-2 intestinal epithelial cells; (ii) intracellular growth assays in activated J774 macrophage-like cells; and (iii) intragastric infections in the guinea pig model. Among the regulatory proteins, only SigB was essential for optimal invasion efficiency in Caco-2 cells. In intracellular growth assays, only PrfA was obligatory for wildtype growth in the cytosol. As previous work has shown that a prfA mutant strain is completely avirulent and a sigB mutant strain is virulence-attenuated during intragastric infection in the guinea pig, in this study, virulence capabilities were compared among 10403S and isogenic strains with a single mutation in a gene encoding SigL, SigH, SigC, CtsR or HrcA. Among these, only CtsR was essential for full virulence in the guinea pig model. In summary, no clear virulence-associated phenotypes for L. monocytogenes SigL, SigH, SigC, or HrcA were observed in invasion, intracellular growth or virulence in the guinea pig model. However, it is possible that regulatory networks exist among multiple transcriptional regulators to enable at least partial functional compensation in the absence of a given factor.