Studies on the pathogenicity of Listeria monocytogenes.

The characterization of mutants of Listeria monocytogenes with reduced virulence properties is described. Reduction in the amount of the extracellular protein p60 (encoded by the ipa gene) leads to cell filaments with impaired invasiveness. Mutants which cannot synthesize listeriolysin are still invasive but unable to survive within phagocytic cells. One type of listeriolysin-negative mutants is defective in the synthesis of a positive regulatory element PrfA which coordinately regulates the listeriolysin gene (lisA) together with several other genes, including those for a phosphatidylinositol-specific phospholipase and a metalloprotease.