Resistance to Reinfection in Experimental Brucellosis

Summary and Conclusions

1. The purpose of the present work was to determine if a relationship exists between resistance to superimposed infection and the presence of the organisms of primary inoculation in the body of guinea pigs infected with Br. abortus. The organisms of reinoculation never persisted in the tissues in the presence of the brucellae of primary infection, except in one instance. The exception was a guinea pig reinoculated 11 days after infection. Some animals, from which the organisms of the original infection were not recovered from any of the tissues, were resistant to reinfection. Resistance waned gradually after the organisms of primary inoculation could no longer be recovered from the tissues. 2. A local reaction with abscess formation was produced at the site of subcutaneous inoculation in infected guinea pigs; brucellae were recovered in large numbers from these lesions. The organisms of reinfection penetrated into the deep tissues but disappeared promptly. This suggests that the local reaction was not a major contributing factor in resistance to reinfection. When previously infected animals were injected intracardially the brucellae of reinfection also disappeared rapidly from the tissues. 3. In order to meet the criticism that intracellular brucellae could not be cultivated by routine methods, all tissues were cultivated after disintegration by rapid vibration, under optimal conditions. The results obtained with this technic corroborated the findings obtained with other methods. 4. It is puzzling to see that the Brucella of original infection can persist for months in the tissues from which the organisms of reinoculation disappear rapidly. An explanation for this phenomenon is not apparent and these studies are being extended in an attempt to clarify this point. 5. Cultivation of disintegrated blood on the surface of solid media constituted an improvement over other methods used routinely for the isolation of brucellae from the blood.