The Listeria monocytogenes B Regulon and Its Virulence-Associated Functions Are Inhibited by a Small Molecule

ABSTRACT The stress-responsive alternative sigma factorB is conserved across diverse Gram-positive bacterial genera. In Liste-ria monocytogenes,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. monocytogenesB 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) (IC50 3.5M) downregulated the ma-jority of genes previously identified as members of theB regulon in L. monocytogenes 10403S, thus generating a transcriptional profile comparable to that of a 10403SsigB strain. Specifically, of the 208 genes downregulated by FPSS, 75 % had been identi-fied previously as positively regulated byB. 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 in-testinal epithelial cells and bile salt hydrolase activity. The ability of FPSS to inhibitB activity in both L. monocytogenes and Bacillus subtilis indicates its utility as a specific inhibitor ofB across multiple Gram-positive genera. IMPORTANCE TheB transcription factor regulates expression of genes responsible for bacterial survival under changing envi-ronmental conditions and for virulence; therefore, this alternative sigma factor is important for transmission of L. monocyto-genes and other Gram-positive bacteria. Regulation ofB activity is complex and tightly controlled, reflecting the key role of this factor in bacterial metabolism.We present multiple lines of evidence indicating that fluoro-phenyl-styrene-sulfonamide (FPSS