Enhancement of protective immunity in blue gourami, Trichogaster trichopterus (Pallas), against Aeromonas hydrophila and Vibrio anguillarum by A-hydrophila major adhesin

Blue gourami, Trichogaster trichopterus (Pallas), were intraperitoneally im munized with major adhesin, a 43 kDa OMP protein isolated from fish Aeromon as hydrophila, in the presence of Freund's complete adjuvant (FCA). Three w eeks later, a booster injection of adhesin without FCA was administered Con trol group fish were similarly treated with phosphate-buffered saline (PBS) and FCA. Results showed that anti-adhesin serum obtained from fish after b ooster immunization exhibited very strong ability in agglutinating bacteria l cells. Although this antiserum had no bactericidal effect, it could signi ficantly inhibit serologically different strains of A. hydrophila from inva ding EPC (Epithelioma papillosum of carp) cells in vitro. In addition, the proliferative response of head kidney leucocytes of these immune fish was s ignificantly increased as compared to that of the control. The results also showed that the major adhesin could provide significant protective immunit y to fish against the challenge by homologous and heterologous strains of A . hydrophila and one virulent strain of Vibrio anguillarum.