Determinants for thermoinducible cell binding and plasmid-encoded cellular penetration detected in the absence of the Yersinia pseudotuberculosis invasin protein.

Yersinia pseudotuberculosis inv mutants were analyzed for their ability to bind and penetrate mammalian cell lines. Strains defective for the production of invasin and cured of the Yersinia virulence plasmid pIB1 were extremely defective for entry into the HEp-2 cell line. inv strains harboring the virulence plasmid partially overcame this defect, indicating that the virulence plasmid mediates an invasin-independent pathway for low-level entry into cultured cells. Plasmid-cured inv mutants were able to attach efficiently to mammalian cells after bacterial culture at 37 degrees C but not after culture at a lower temperature. The enhanced cellular binding of inv mutants grown at 37 degrees C did not result in efficient cellular penetration, indicating that invasin-mediated entry is the primary chromosomally encoded pathway responsible for Y. pseudotuberculosis penetration into both HEp-2 and Chinese hamster ovary cells under the assay conditions described here.