Avirulent Salmonella typhimurium Δcya Δcrp oral vaccine strains expressing a streptococcal colonization and virulence antigen

Salmonella typhimurium SR-11 strains lacking adenylate cyclase and the cyclic AMP receptor protein (CRP) due to deletion (Δ) mutations in the cya and crp genes, respectively, are avirulent for mice and induce high level protective immunity against subsequent challenge with wild-type virulent S. typhimurium SR-11 cells. The avirulence of these Δcya Δcrp mutants has been enhanced by elimination of the 100 kb virulence plasmid pStSR100 without impairing immunogenicity. The present report confirms the avirulence and immunogenicity of these mutant strains, demonstrates that immunization of both four- and eight-week-old mice has no adverse effect on weight gain, and that immunity lasts at least ninety days following initial immunization. Avirulent S. typhimurium strains have been endowed with the ability to produce several streptococcal colonization and virulence antigens for the purpose of constructing recombinant bivalent oral vaccine strains. Important antigenic determinants of the Streptococcus sobrinus surface protein antigen A (SpaA), presumed to be a critical colonization antigen of S. sobrinus, are expressed at high level by the Δcya Δcrp S. typhimurium strains. The recombinant vaccine strains are stable in vitro and in animals (for a period of at least eight days) where they localize to the gut-associated lymphoid tissue (GALT).