Resistance of normal or immunized guinea pigs against a subcutaneous challenge of Brucella abortus

Guinea pigs were inoculated subcutaneously into a hind footpad with Brucella abortus. Unimmunized guinea pigs had little capacity for barring brucella from spreading to their spleens: the inoculum dose needed to infect 50% of the spleens one month after inoculation was about 10 brucella. When the size of the challenge inoculum reached approximately 5 x 10(3) ID50 a previous immunization with killed or virulent brucella: --did not prevent the challenge bacteria from reaching the lymph nodes near the inoculation site, but reduced the level of infection in these, --barred or reduced the spreading of brucella throughout the remainder of the reticuloendothelial system. Immunization with a small number of virulent brucella was more effective than immunization with a higher number of killed bacteria to produce such modifications of the repartition of challenge brucella.