Bacterial pathogens require the conserved membrane histidine sensor kinase (QseC) to detect both host-derived adrenergic signals and the bacterial autoinducer-3 (AI-3), thus activating a signaling cascade that induces virulence gene expression. LED209 is a potent QseC inhibitor that blocks both norepinephrine- and epinephrine-triggered QseC-dependent virulence gene expression at 5 pM in vitro. While LED209 inhibits virulence of enterohemorrhagic E. coli, S. typhimurium, and F. tularensis, it does not inhibit pathogen growth, a highly desirable feature of antimicrobial agents to prevent drug resistance.