[Construction of a recombinant <i>Bacillus subtilis</i> strain expressing SpaA and CbpB of <i>Erysipelothrix rhusiopathiae</i> and evaluation of the strain immunogenicity in a mouse model].

To construct a recombinant <i>Bacillus subtilis</i> strain expressing SpaA and CbpB of <i>Erysipelothrix rhusiopathiae</i> for oral administration, we constructed the recombinant plasmid pDG1730-CBJA by fusion PCR and seamless cloning. The plasmid was introduced into <i>B</i>. <i>subtilis</i> KC strain by natural transformation, and the recombinant strain KC-<i>spaA</i>-<i>cbpB</i> was screened out on the plate containing spectinomycin (<i>spe</i>^<i>r</i>) and confirmed by PCR and starch degradation test. The SpaA and CbpB expressed by KC-<i>spaA</i>-<i>cbpB</i> were detected by Western blotting and indirect immunofluorescence assay, and the genetic stability of the recombinant strain in mice was determined. The plasmid pMAD-∆<i>spe</i>^r with knockout of <i>spe</i>^<i>r</i> was constructed and transformed into KC-<i>spaA-cbpB</i>. The <i>spe</i>^<i>r</i>-deleted mutant strain KC-<i>spaA</i>-<i>cbpB</i>: : ∆<i>spe</i>^r was screened and identified, and its immunogenicity in a mouse model was evaluated by oral immunization. The results showed that the recombinant strain KC-<i>spaA</i>-<i>cbpB</i> was stable in mice, expressing SpaA on the cell surface and CbpB on the spore surface. KC-<i>spaA</i>-<i>cbpB</i>: : ∆<i>spe</i>^r expressed SpaA and CbpB. The mice vaccinated with the spores of KC-<i>spaA</i>-<i>cbpB</i>: : ∆<i>spe</i>^r had higher levels of SpaA and CbpB-specific IgG in the serum that those vaccinated with the wild-type spores 42 days after vaccination by gavage (<i>P</i> < 0.01). The protective rate of mice immunized with the recombinant spores was 67.5%. The results indicated that a recombinant <i>B</i>. <i>subtilis</i> strain expressing SpaA and CbpB of <i>E</i>. <i>rhusiopathiae</i> was successfully constructed, and the recombinant strain laid a foundation for the development of oral live vector vaccines for swine erysipelas.