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 × 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 μg, 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 μg 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-μg 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.