Salmonella typhimurium deletion mutants lacking adenylate cyclase and cyclic AMP receptor protein are avirulent and immunogenic

Salmonella typhimurium SR-11 mutants with cya::Tn10 or crp::Tn10 mutations were found to be avirulent and immunogenic for BALB/c mice. Fusaric acid-resistant derivatives with deletions of the Tn10 and adjacent DNA sequences were constructed in S. typhimurium SR-11 strains with or without the virulence plasmid pStSR100. These Δcya Δcrp strains grew more slowly than wild-type strains. They possessed wild-type ability to attach to, invade, and persist in gut-associated lymphoid tissue for up to a week but exhibited a diminished ability to reach mesenteric lymph nodes and the spleen. Mice 4 to 8 weeks old were resistant to oral infection with 10⁹ cells of several different Δcya and Δcya Δcrp strains (the equivalent to 10⁴ 50% lethal doses of wild-type S. typhimurium SR-11) and 30 days after immunization became resistant to oral challenge with 10³ to 10⁴ 50% lethal doses of wild-type S. typhimurium SR-11.