Emergence during growth of Brucella strains on dye-agar media of cells that show changes in sulfur metabolism.

Division of Brucella strains into three species has long been based on differences in growth characteristics on certain dye-agar media and on variations in H(2)S production on liver agar slants. But certain workers believe these differences to be merely quantitative, such as are found between varieties of one species. Moreover, certain strains show characteristics that do not allow them to be classified with certainty in any one of the three species. If all characteristics of one "species" could be changed in the laboratory so as no longer to be capable of differentiation from those of another, that might be proof that all Brucella strains are in fact varieties of a single species.The study reported in this paper represents an attempt to determine whether the biochemical and antigenic characteristics used to identify Brucella species can be changed by laboratory procedures exclusive of animal inoculation, and whether, if such changes occur, they are of a nature to substantiate the hypothesis that mutations occur in Brucella cells and that one species can be changed into another.The results do not provide evidence to confirm the mutation hypothesis. Although cells of the different species could be adapted to grow on media which ordinarily inhibit their growth, it is considered questionable whether the change can be taken as a mutation. Alterations in the activity of only one enzyme system were demonstrated in cells of certain colonies of particular strains of Br. abortus, Br. melitensis and Br. suis. The enzyme is one that decomposes a sulfur-containing compound into H(2)S and is found in most peptones and animal tissue extracts. The other biochemical and antigenic properties studied showed no measurable changes.