Interaction of virulent and non-virulent Yersinia enterocolitica strains and an epithelial and a phagocytic cell lines.

Morphological alterations of HEp-2 and P338D1 cells were detected as result of Yersinia virulent strains action only. A non-virulent strain caused none of these alterations even 24 h post infection (p.i.). The internalization of the bacteria was demonstrated by double fluorescence staining. Adherence and beginning of cell invasion of virulent strains was detected 30 min p.i. already. Two hours p.i. these bacteria were in great numbers inside the cells of both lines. The non-virulent Yersinia strain was found only in the P338D1 macrophages at 2 and 24 h p.i. but in smaller numbers than virulent strains. Electron microscopy confirmed that internalization of virulent strains Y526 and Y527 was done by the phagocytosis of both cell lines. Even intracellular replication of these virulent strains was observed in both cell lines at 2 and 24 h p.i. Both bacterial strains were disintegrated as well as they multiplied inside the cells. In strain Y526 disintegration of bacteria prevailed, whereas their replication predominated in the strain Y527. At 24 h p.i. cells infected with strain Y527 were sac-like, with rudiments of the cytoplasm and organelles, packed with bacteria that were released after cell membrane rupture. Cells infected with strain Y526 were metabolically active and even at 24 h p.i. predominately contained disintegrated bacteria, but even in this case replication and release of bacteria was observed.