Killed vaccine in adjuvant and protection of mice against an intraperitoneal challenge of Brucella: kinetic studies.

CD-I female mice were immunized with a subcutaneous injection of heat-inactivated Brucella melitensis (strain 53 H 38) incorporated into a water-in-oil emulsion. One month later, the effectiveness of this immunization was investigated by studying quantitatively in the spleen the fate of an intraperitoneal challenge inoculum of approximately I X 10(6) viable B. abortus strain 544. In unvaccinated mice, the number of viable challenge bacteria increased until about the 10th day, decreased and then remained at a nearly constant level. In animals vaccinated with a suitable dose of inactivated Brucella in adjuvant, the number of challenge organisms decreased on the first two days, then increased, but remained at a lower level than that found in control animals; the spleens of control animals reached higher weights than those of vaccinated ones. The effect of graduated doses of challenge on immunized mice was investigated: the splenic infection diminished sooner when the challenge dose was weaker. The findings are discussed in relation to the methods used to test the potency of Brucella vaccines.