Salmonella enterica Gallinarum (SG) causes fowl typhoid (FT), a septicemic disease in avian species. We constructed deletion mutants lacking the stress sigma factor RpoS, the nitric oxide (NO)-detoxifying flavohemoglobin Hmp, and the SsrA/SsrB regulator to confirm the functions of these factors in SG. All gene products were fully functional in wild-type (WT) SG whereas mutants harboring single mutations or a combination of rpoS, hmp, and ssrAB mutations showed hypersusceptibility to H2O2, loss of NO metabolism, and absence of Salmonella pathogenicity island (SPI)-2 expression, respectively. A triple-deletion mutant, SGDelta3 (SGDeltarpoSDeltahmpDeltassrAB), was evaluated for attenuated virulence and protection efficacy in two-week-old Lohmann layer chickens. The SGDelta3 mutant did not cause any mortality after inoculation with either 1 x 10(6) or 1 x 10(8) colony-forming units (CFUs) of bacteria. Significantly lower numbers of salmonellae were recovered from the liver and spleen of chickens inoculated with the SGDelta3 mutant compared to chickens inoculated with WT SG. Vaccination with the SGDelta3 mutant conferred complete protection against challenge with virulent SG on the chickens comparable to the group vaccinated with a conventional vaccine strain, SG9R. Overall, these results indicate that SGDelta3 could be a promising candidate for a live Salmonella vaccine against FT.
Administration, Oral ; Animals ; Bacterial Proteins/*genetics/immunology ; *Chickens ; Female ; Poultry Diseases/*immunology/microbiology ; Salmonella Infections, Animal/*immunology/microbiology ; Salmonella Vaccines/administration & dosage/genetics/*immunology ; Salmonella enterica/immunology/*physiology ; Vaccines, Attenuated/administration & dosage/genetics/immunology ; Virulence

The immunologic reactivity of a lipopolysaccharide (LPS)-protein complex isolated from a potassium thiocyanate extract of a Pasteurella multocida (capsular type A and somatic type 3) strain was evaluated in mice. The LPS-protein complex provided 100% protection in mice against a challenge with the homologous strain. However, when the complex was fractionated into LPS and protein moieties by phenol-water treatment, both components lacked immunogenicity. The complex and extracted components were mitogenic for mouse B lymphocytes with the protein moiety the most active. Although immune serum against the LPS-protein complex protected mice against challenge thereby indicating a role for humoral immunity, the LPS-protein complex of P. multocida was also found to induce cell-mediated immunity. This cell-mediated immunity was demonstrated in mice immunized with the complex by: (1). mitogenic responses of T lymphocytes, (2). induction of delayed type hypersensitivity reaction in the hind footpads, and (3). enhanced resistance to challenge infection with Salmonella enteritidis.
Animals ; Antibodies, Bacterial/blood/immunology ; Bacterial Proteins/chemistry/*immunology ; Chemical Fractionation ; Hypersensitivity, Delayed ; Immune Sera/immunology ; Immunity, Cellular ; Immunization, Passive ; Lipopolysaccharides/chemistry/*immunology ; Lymphocyte Activation ; Mice ; Pasteurella Infections/immunology/*prevention & control ; Pasteurella multocida/*chemistry/immunology ; Salmonella Infections, Animal/immunology/prevention & control ; Salmonella enteritidis/growth & development/immunology ; Spleen/cytology/immunology/microbiology