Evaluation of Prolonged Antibiotic Therapy in Mice with Chronic Brucella Infection Due to Brucella Melitensis

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Abstract
Summary and Conclusions: A chronic, sublethal Brucella melitensis infection was established in mice. Therapy with aureomycin, terramycin, sulfadiazine, or streptomycin, alone and in combinations, was started 4 weeks after establishment of the infection, and continued for 3 or 6 weeks. The results of therapy were evaluated by spleen cultures for brucella at the completion of treatment and 4 weeks after stopping therapy. The experimental results showed that any of the combined types of therapy with streptomycin plus aureomycin, terramycin, or sulfadiazine were definitely superior to any one of the drugs when used alone. Such combined therapy completely eradicated brucella from the spleens of all but 1 of 100 mice treated with any of these combinations. Therapy with aureomycin or terramycin alone in doses of 60 mg per kg per day for 3 weeks resulted in the eradication of brucella from the spleens in only 20 to 30% of the animals, as determined by spleen cultures at the completion of treatment. However, the final result of this therapy, determined by spleen cultures 4 weeks after stopping treatment, was eradication of the organisms in 70 to 80% of the animals. This observation emphasized the significant role of the host's immune mechanisms in the final eradication of brucella infections. Therapy with aureomycin alone in doses of 30 to 60 mg per kg per day for 6 weeks produced, as an immediate result, eradication of brucella from the spleens in 75 to 100% of the animals. However, the final results of this prolonged therapy, as determined 4 weeks after stopping treatment, were no better than the final results with only 3 weeks of treatment.