MODULATION OF VIRULENCE FACTOR EXPRESSION BY PATHOGEN TARGET-CELL CONTACT

Upon contact with the eukaryotic cell, Yersinia pseudotuberculosis inc reased the rate of transcription of virulence genes (yop), as determin ed by in situ monitoring of light emission from individual bacteria ex pressing luciferase under the control of the yopE promoter, The microb e-host interaction triggered export of LcrQ, a negative regulator of Y op expression, via the Yop-type III secretion system. The intracellula r concentration of LcrQ was thereby lowered, resulting in increased ex pression of Yops. These results suggest a key role for the type III se cretion system of pathogenic bacteria to coordinate secretion with exp ression of virulence factors after physical contact with the target ce ll.