IN-VIVO EXPRESSION OF VIRULENCE GENES OF YERSINIA-PSEUDOTUBERCULOSIS

The common virulence plasmid of pathogenic Yersinia species encodes a number of secreted proteins denoted Yops. YopE and YopH are indispensa ble for virulence acid act in concert to mediate resistance to phagocy tosis. In vitro all yop genes are coordinately regulated, with maximal expression and secretion at 37 degrees C in medium lacking Ca2+. In o rder to facilitate studies of in vivo expression of yopE and yopH we c onstructed operon fusions between these two genes and a promoterless l uxAB operon from Vibrio harveyi in Y. pseudotuberculosis. Groups of 10 mice were infected with each fusion strain, and colonization and luci ferase expression in Peyer's patches and spleen were followed by sacri ficing two mice from each group daily. Peyer's patches were found to b e colonized from the first day of infection, whereas the spleen was no t colonized until the third day of infection. Luciferase expression co uld easily be monitored if the sample contained greater than or equal to 10(4) bacteria. Expression levels tended to be highest at the early stages of colonization for the respective organ (day 1 for Peyer's pa tches and day 3 or 4 for spleen). When in vivo expression was compared with in vitro expression, it was found that during infection the expr ession levels were as high or even higher than the in vitro expression observed for strains grown at 37 degrees C in Ca2+-depleted media.