Effect of specific immune mouse serum on the growth of Salmonella enteritidis in mice preimmunized with living or ethyl alcohol-killed vaccines.

The effect of prior opsonization of virulent Salmonella enteritidis on the growth of this organism in blood, liver, spleen, peritoneal cavity, and inguinal lymph node of specific pathogen-free mice prevaccinated with ethyl alcohol-killed S. enteritidis or living S. gallinarum was determined by daily enumeration. Both the vaccines and the challenge inocula were injected by the intravenous, intraperitoneal, or subcutaneous routes to determine the effect of variations in the vaccinating procedure on the level of immunity induced. The survival percentage observed in mice vaccinated with killed organisms varied extensively, depending on the route of challenge. However, simultaneous organ enumeration studies revealed that vaccination with killed organisms failed to prevent the growth of the challenge organism in vivo. On the other hand, virulent S. enteritidis injected into mice vaccinated with living S: gallinarum failed to multiply and was subsequently eliminated. Immunity in these animals was so effective that a subcutaneously injected challenge did not spread beyond the regional node. Immunization with killed organisms slowed but was unable to prevent the spread of such a challenge beyond the draining node involved in the primary immune response. Neither the route of challenge nor the regimen used in the vaccination had any appreciable influence on the level of antibacterial immunity detected in the organs of the reticuloendothelial system at the time of challenge.