Abstract：To define whether the expressed ompA of Aeromonas hydrophila (Ah) AS1.927 strain has antigenicity and determine the relative percentage survival (RPS) for the mice, the 1020 bp fragment encoding ompA was cloned from the Ah AS1.927 genome with a pair of primers designed according to the sequence of omp in GenBank (AF146597)., After digesting the fragment with Sal I ＋Xhol I, the gene was inserted into pET-30a(+) vector. The recombinant pET-30a-ompA plasmid was transformed into the expressing strain BL21 and induced expression by IPTG. The recombinant protein ompA was analyzed by SDS-PAGE and Western blot, and results showed that the ompA fusion protein was about 40.7kD and could react with sera from mice infected with A. hydrophila. BALB/c mice were orally immunized at 1st, 2nd, 3rd, 20th, 21th, and 22th day with the engineering bacteria E.coli [pET-30a-ompA]. The serum IgG was detected by ELISA at 7days post-vaccination. On the 14th day after last immunization, the mice were challenged with 3.3 × 105 cfu of live Ah AS1.927 (100LD50). The results showed that mice vaccinated with E.coli [pET-30a-ompA] showed significantly increased antigen-specific IgG level in the serum (P<0.05) and SIgA level in the intestinal mucosa compared with the control and 75% relative percent survivals (RPS). This indicated that oral immunization of E.coli [pET-30a-ompA] could induce an immune response protective upon challenge with live Ah AS1.927 in BALB/c mice. The present study will provide technical support for developing of efficient gene engineering vaccine against A. hydrophila.
