BACTERIAL PHENOTYPES MEDIATED BY MVIA AND THEIR RELATIONSHIP TO THE MOUSE VIRULENCE OF SALMONELLA-TYPHIMURIUM

The focus of this study was the phenotypic characterization of Salmone lla typhimurium mutants lacking the function of the response regulator mviA. The inactivation of mviA(+) (mviA::kan) is shown to induce a si gnificant change in the growth of most virulent strains, as reflected in the size of the colonies formed on agar plates. The colony phenotyp e observed in these strains has been designated as the small colony mo rphology (Scm(+)) phenotype. Mutants exhibiting the Scm(+) phenotype a re shown to be significantly attenuated for virulence in susceptible ( lty(s)) mice. The Scm(+) phenotype therefore provides an in vitro phen otypic marker for mviA(+) activity. Further examination of Scm(+) muta nts has revealed that they lack expression of a 55 kDa periplasmic pro tein which is detected in isogenic mviA(+) strains. This protein has b een designated mviA(+) related protein A (MrpA) and was expressed in d irect correlation with virulence in all S. typhimurium strains examine d. (C) 1997 Academic Press Limited.