Characterization of a predominant immunogenic outer membrane protein of Riemerella anatipestifer

The ompA gene, encoding the 42-kDa major antigenic outer membrane protein O mpA of Rimerella anatipestifer, the etiololgical agent of septicemia anseru m exsudativa, was cloned and expressed in Escherichia coli, Recombinant Omp A displayed a molecular mass similar to that predicted from the nucleotide sequence of the ompA gene but lower than that observed in total cell lysate s of R, anatipestifer, The ompA gene showed a conserved C-terminal region c omprising the OmpA-like domain and a variable N-terminal region. This struc ture is similar to those of the analogous outer membrane proteins of severa l gram-negative bacteria. However, OmpA of R, anatipestifer contains six EF -hand calcium-binding domains and two PEST regions, which distinguish it fr om other outer membrane proteins. The occurrence of these motifs in OmpA su ggests a possible role in virulence for this protein. The ompA gene is pres ent in the R. anatipestifer type strain and in all serotype reference strai ns. However, it exhibits some minor genetic heterogeneity among different s erotypes, which seems not to affect the strong antigenic characteristics of the protein, OmpA is a conserved and strong antigenic determinant of R, an atipestifer and hence is suggested to be a valuable protein for the serodet ection of R, anatipestifer infections, independent of their serotype.