Abstract
Summary
A streptomycin-dependent mutant (D) of B. abortus (strain 19) showed the following properties: 1. Its toxicity for mice was almost equal to that of the streptomycin-resistant (R) and non-resistant (NR) parent strains. It produced infections of limited duration with relatively low concentrations of microorganisms in the spleens of white mice, and disappeared from the spleen within 45 to 60 days. Spleen enlargements were observed when 5 × 107 or more microorganisms were injected. Subcutaneous injection in man did not result in serious reactions. 2. The agglu-tinogenic power of the acetone killed D-bacteria in rabbits and guinea pigs was equal to that of NR-bacteria. As living antigens D-and NR-bacteria produced high initial titers, but those produced by the D-bacteria decreased more quickly. Three injections of living D-bacteria prevented completely the appearance of virulent NR-bacteria given as challenge dose in the spleen or lowered their number markedly as compared with the non-immunized controls. Killed vaccines prepared from NR- and D-strains did not exert such marked effects.
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