Oral immunization of mice and swine with an attenuated Salmonella choleraesuis [delta cya-12 delta(crp-cdt)19] mutant containing a recombinant plasmid.

Salmonella choleraesuis chi 3781, an attenuated [delta cya-12 delta(crp-cdt)19] mutant, was electroporated with the plasmid pBA31-R7, which codes for the expression of a 31-kDa protein from Brucella abortus (BCSP31). Recombinant S. choleraesuis chi 3781 stably maintained the pBA31-R7 plasmid and continued to express the cloned protein following recovery of the organism from orally inoculated animals. Unlike previous studies using S. typhimurium chi 4064(pBA31-R7), S. choleraesuis chi 3781(pBA31-R7) was able to colonize both the gut mucosa and deep tissues of both BALB/cByJ mice and crossbred swine. Orally inoculated mice developed serum antibodies to both the cloned 31-kDa protein (rBCSP31) and to S. choleraesuis chi 3781 endotoxin. These mice also developed a local intestinal antibody response to Salmonella endotoxin but not to rBCSP31. Similarly, mice inoculated with recombinant S. choleraesuis chi 3781 did not develop a delayed-type hypersensitivity (DTH) footpad response following injection with rBCSP31; however, these mice did respond to S. choleraesuis chi 3781 soluble antigen. Conversely, orally inoculated swine did not develop significant serum or intestinal antibody responses to cloned protein or Salmonella endotoxin, but DTH responses to both cloned protein and S. choleraesuis chi 3781 soluble antigen were strongly positive. The cell-mediated nature of these DTH responses was confirmed by histological examination. Results suggest that S. choleraesuis chi 3781 may be a suitable choice for further studies of vaccine efficacy in swine, especially for diseases which require cell-mediated immunity for resolution.