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Immunogenicity of living and heat-killed Salmonella pullorum vaccines
Abstract:
Specific pathogen-free CD-1 and C57Bl mice were infected in a hind footpad with 5 x 10(4) viable Salmonella enteritidis cells or 10(7) viable S. pullorum cells. The resulting bacterial growth within the footpad, the draining lymph nodes, and the liver and spleen was followed for 14 days. Mice vaccinated with live S. enteritidis rapidly developed an effective antibacterial resistance to both intravenous and intragastric challenge with S. enteritidis SM(R). The viable inoculum of S. pullorum was rapidly eliminated from the normal mouse tissues and failed to induce a detectable anti-Salmonella resistance to parenteral or oral challenge with S. enteritidis. Heat-killed saline suspensions (200 mug, dry wt) of S. enteritidis or S. pullorum were unable to induce an effective antimicrobial resistance against a subsequent virulent Salmonella challenge. However, when the organisms were suspended in Freund complete adjuvant, both vaccines induced an antibacterial resistance to intravenous and intragastric challenge. Reduction of the antigenic dose from 200 to 40 mug did not greatly affect the protective value of the two killed vaccines against an intravenous challenge, but the level of protection observed with two 40-mug doses of S. pullorum was considerably reduced when the animals were infected intragastrically, suggesting that some quantitative differences existed between the sensitizing antigenic contents of the two test organisms.
Insights
Live Salmonella enteritidis vaccination effectively protects mice against challenge. However, Salmonella pullorum vaccination, whether live or killed, does not induce significant Salmonella enteritidis resistance, indicating strain-specific immunity.
Area of Science:
- Immunology
- Microbiology
- Vaccinology
Background:
- Salmonella infections pose a significant public health threat.
- Developing effective vaccines against Salmonella is crucial for disease prevention.
- Understanding the immune response to different Salmonella strains is key to vaccine development.
Purpose of the Study:
- To evaluate the immunogenicity and protective efficacy of live and killed Salmonella enteritidis and Salmonella pullorum vaccines in mice.
- To compare the immune responses induced by different vaccine preparations and administration routes.
- To investigate the potential for cross-protection between S. enteritidis and S. pullorum.
Main Methods:
- Mice were infected with S. enteritidis or S. pullorum in the hind footpad.
- Bacterial growth was monitored in tissues (footpad, lymph nodes, liver, spleen) for 14 days.
- Vaccination strategies included live attenuated bacteria, heat-killed bacteria in saline, and heat-killed bacteria in Freund complete adjuvant.
- Mice were subsequently challenged with virulent S. enteritidis via intravenous or intragastric routes.
- Antibacterial resistance was assessed by monitoring bacterial loads post-challenge.
Main Results:
- Live S. enteritidis vaccination conferred significant resistance to subsequent S. enteritidis challenge via both intravenous and intragastric routes.
- Live S. pullorum was rapidly cleared and did not induce detectable resistance to S. enteritidis challenge.
- Heat-killed S. enteritidis and S. pullorum in saline failed to induce protective immunity.
- Both heat-killed vaccines formulated with Freund complete adjuvant induced antibacterial resistance to S. enteritidis challenge.
- Reducing the antigen dose of killed vaccines affected protection, particularly for S. pullorum against intragastric challenge, suggesting quantitative differences in antigenicity.
Conclusions:
- Live S. enteritidis vaccination is effective in inducing protective immunity against homologous challenge.
- S. pullorum, in the forms tested, is not an effective vaccine candidate for protection against S. enteritidis.
- Freund complete adjuvant enhances the immunogenicity of killed Salmonella vaccines.
- Quantitative differences in antigenic content may exist between S. enteritidis and S. pullorum, influencing vaccine efficacy.