Abstract：As a safety microorganism, Lactococcus lactis is an ideal live vector vaccine candidate for carrying antigen. Aeromonas hydrophila cause hemorrhagic septicemia in many kinds of animals including fish. It is important to find the common protective antigens in vaccine research work, because of the numerous serotype. To explore how the outer membrane protein (OMP) from Aeromonas hydrophila (Ah) AS1.927 strain expressed in the L. lactis and its immunological protection of the expressed OMP, a cloned ompA gene was inserted into pNZ8048 vector and expressed in the L. lactis NZ9000 using nisin induction in this study . The expressed OMP was estimated by migration in 10% sodium dodecyl sulphate-polyarylamide gel electrophoresis (SDS-PAGE). Results showed that the size of the fusion protein was about 36.2 kD, and the mature protein was about 33.7 kD. BALB/c mice (Mus musculus) were orally inoculated with the engineering bacteria L.lactis [pNZ-ompA]. Intestinal secretory immunoglobulin A (sIgA) was determined by double antibody radioimmunoassay and serum IgG was detected by enzymelinked immunosorbent assay (ELISA) at one week post-vaccination,the results indicated that mice vaccinated with L.lactis [pNZ-ompA] significantly increased sIgA level and antigen-specific IgG level in the serum (P<0.05) than that of untreated control group . Besides, on the 14th day after the last immunization, the mice were challenged with 3.3×105 cfu/mL of live Ah AS1.927 (100 LD50), showing that the immunized group had 87.5% relative percent survival (RPS). This indicated that oral immunization of L.lactis [pNZ-ompA] can protectively initiate an immune response upon. It provides a technical basis for developing efficient oral gene engineering vaccine against fish Ah.
