The Listeria monocytogenes σ^Bregulon and its virulence-associated functions are inhibited by a small molecule

Abstract

The stress-responsive alternative sigma factor σ B is conserved across diverse Gram-positive bacterial genera. In Listeria monocytogenes, σ B regulates transcription of > 150 genes, including genes contributing to virulence and to bacterial survival under host-associated stress conditions, such as those encountered in the human gastrointestinal lumen. An inhibitor of L. monocytogenes σ B activity was identified by screening ~57,000 natural and synthesized small molecules using a high-throughput cell-based assay. The compound fluoro-phenyl-styrene-sulfonamide (FPSS) (IC 50 = 3.5 μM) downregulated the majority of genes previously identified as members of the σ B regulon in L. monocytogenes 10403S, thus generating a transcriptional profile comparable to that of a 10403S ΔsigB strain. Specifically, of the 208 genes downregulated by FPSS, 75% had been identified previously as positively regulated by σ B . Downregulated genes included key virulence and stress response genes, such as inlA, inlB, bsh, hfq, opuC, and bilE. From a functional perspective, FPSS also inhibited L. monocytogenes invasion of human intestinal epithelial cells and bile salt hydrolase activity. The ability of FPSS to inhibit σ B activity in both L. monocytogenes and Bacillus subtilis indicates its utility as a specific inhibitor of σ B across multiple Gram-positive genera. © 2011 Palmer et al.