Expression in vivo of additional plasmid-mediated proteins during intestinal infection with Yersinia enterocolitica serotype O8.

The decisive aspect of Yersinia enterocolitica virulence in vivo is the ability of the plasmid-bearing bacteria to resist the immune response within the host tissue. The expression of plasmid-mediated virulence proteins was investigated in the intestinal lumen and in the Peyer's patches of infected mice. Three novel plasmid-mediated outer-membrane proteins have been identified with antisera raised against bacteria grown in vivo. When the bacteria were grown in the intestinal lumen, all plasmid-coded proteins known to be expressed in vitro, except the 26-Kda protein were expressed. Additionally, a novel outer-membrane protein of 23 Kda was synthesised. After penetration into the Peyer's patches, two further proteins of 240 and 210 Kda were expressed. None of these three proteins was detected in the outer membrane of bacteria grown in vitro. By contrast, plasmid-coded released proteins, which are abundantly synthesised in Ca(2+)-deficient media in vitro, were not detectable in the ileal lumen nor in the tissue of infected Peyer's patches, which suggests that they are not required for Y. enterocolitica pathogenesis.