Vaccination experiments and studies of the humoral immune responses in cod, Gadus morhua L., to four strains of monoclonal-defined Vibrio anguillarum

Abstract. Vibrio anguillarum isolated from diseased cod, Gadus morhua L., were serotyped by use of a panel of monoclonal antibodies. Four serotypes could be distinguished, having different lipopolysaccharide determinants. These phenotypic differences were also reflected in the genetic map, as revealed by fingerprinting of bacterial DNA. Antisera were raised in cod after immunization with the V. anguillarum serotypes, and Western blot techniques demonstrated production of specific antibodies mainly to LPS-antigens. The immune system in cod discriminates to a eertain degree between the four serotypes as shown by crossreactions of the immune sera in elisa . Moreover, it was also shown that natural antibodies to bacterial antigens are present in non-immune sera, but these specificities are non-LPS in nature. As a consequence of the heterogeneity of the V. anguillarum strains, vaccination experiments were performed under laboratory conditions to compare the effectiveness of bacterins based on either single vaccines or polyvaccines. The results from these experiments were promising since challenge with one strain demonstrated 100% protection both in fish vaccinated with the homologous serotype as well as a mixture of all the four serotypes.