Metabolite-Resistance and Virulence of Smooth Brucella Variants Isolated after Prolonged Cultivation

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Abstract
Following prolonged incubation of originally smooth B. abortus broth cultures, relatively avirulent non-smooth variants established themselves but were eventually replaced by a smooth type (S[image]) in turn replaced later by still another smooth type (dS). These 3 types were similar in many characteristics, including virulence, but differed significantly in their resistance to alanine, an inhibitory metabolite which accumulates in the culture fluid. These differences in alanine resistance permitted the S[image] and dS mutants to establish themselves at periods when alanine levels of the cultures were high. Therefore, what superficially appeared to be an establishment of reverse mutants actually involved the establishment of novel mutants which simulated the original smooth type in many characteristics.