Yersinia enterocolitica is a pathogen with a global distribution in nature, showing a big diversity in biochemical activity, chemical composition and structure of O-somatic antigen and pathogenic properties. Y. enterocolitica is isolated from animals belonging to different taxonomic groups as well as from food, soil and water, but pigs are considered to be the main reservoir of Y. enterocolitica strains pathogenic to humans. The pathogenicity of Y. enterocolitica rods is determined by several virulence factors encoded by genes located in the chromosome and the virulence plasmid pYV. The chromosomally located virulence determinant is the enterotoxin Yst, which activates the guanylate cyclase that leads to increased cGMP levels in the intestine. The chromosomally encoded adhesin Ail is involved in attachment and tissue invasion. Invasin is a primary invasion factor of Y. enterocolitica and is required for the translocation of Y. enterocolitica across the intestinal epithelium. Probably the surface antigen Myf promotes the colonization of the intestine and enables the secretion of Yst in close vicinity of the enterocyte surface. The virulence plasmid pYV encodes a type III secretion and the outer membrane protein YadA, which has been found to play multiple functions in the pathogenesis. YadA is involved in autoagglutination, serum resistance and adhesion. Adhesion to host cells mediated by YadA supports the injection of Yops into the cytosol of a eukaryotic cell. Yops form two groups of proteins. Yop effector proteins in eukaryotic cells interfere with signaling pathways involved in the regulation of the actin cytoskeleton, resulting in the inhibition of phagocytosis as well as induces apoptosis. The second group of Yops proteins form a channel in the membrane of a eukaryotic cell, which allows the translocation of effectors across the eukaryotic membrane. The secretory apparatus Ysc enables the injection of effector proteins into eukaryotic cells by extracellular Y. enterocolitica adhering to the cell surface.
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