RESUMEN
The roles of yadA, invA, and psaA genes introduced into the genetic background of the Y. pseudotuberculosis strain possessing the large p VM82 plasmid in virulence and invasion capacity were studied. Isogenic single mutants as well as double and multiple mutants of these genes were constructed and used. LD50 was used as a measure of virulence and the estimation of the ability to invade mammalian cells and the effect of infection on the weight changes of infected mice were used as additional indicators of pathogenicity. It was shown that the YadA had a major effect on the bacterial virulence when compared with the effects of PsaA and InvA. InvA appears to mediate the main pathway of the cellular invasion. YadA is responsible for the weight loss after infection of mice with sublethal doses of Y. pseudotuberculosis. The effects of YadA on virulence and of InvA on bacterial invasion were independent of the expression of the other genes studied. To our knowledge, this study showed for the first time the direct involvement of YadA in the virulence of Y. pseudotuberculosis in mice. Further pathomorphological studies are required to reveal the differences in the pathogenesis of pseudotuberculosis caused by yadA mutants or yadA+ bacteria of Y. pseudotuberculosis.