Bacterial phenotypes mediated bymviAand their relationship to the mouse virulence ofSalmonella typhimurium

The focus of this study was the phenotypic characterization ofSalmonella typhimuriummutants lacking the function of the response regulatormviA. The inactivation ofmviA⁺(mviA: :kan) is shown to induce a significant change in the growth of most virulent strains, as reflected in the size of the colonies formed on agar plates. The colony phenotype observed in these strains has been designated as the small colony morphology (Scm⁺) phenotype. Mutants exhibiting the Scm⁺phenotype are shown to be significantly attenuated for virulence in susceptible (Ity^s) mice. The Scm⁺phenotype therefore provides anin vitrophenotypic marker formviA⁺activity. Further examination of Scm⁺mutants has revealed that they lack expression of a 55 kDa periplasmic protein which is detected in isogenicmviA⁺strains. This protein has been designatedmviA⁺relatedprotein A (MrpA) and was expressed in direct correlation with virulence in allS. typhimuriumstrains examined.