Selection for in vivo regulators of bacterial virulence

We devised a noninvasive genetic selection strategy to identify positive re gulators of bacterial virulence genes during actual infection of an intact animal host. This strategy combines random mutagenesis with a switch-like r eporter of transcription that confers antibiotic resistance in the off stat e and sensitivity in the on state. Application of this technology to the hu man intestinal pathogen Vibrio cholerae identified several regulators of ch olera toxin and a central virulence gene regulator that are operative durin g infection. These regulators function in chemotaxis, signaling pathways, t ransport across the cell envelope, biosynthesis. and adherence. We show tha t phenotypes that appear genetically independent in cell culture become int errelated in the host milieu.