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.

Growth of bacteria in blood: use of cation exchange resins for enhancing or suppressing growth.

It has been demonstrated experimentally that small numbers of a variety of different bacteria fail to survive or multiply in normal cow or human blood or in a mixture of blood and a suitable culture medium, owing to the binding of the magnesium ion and a protein component of the antimicrobial system. However, a satisfactory and simple method has now been evolved for the rapid multiplication of Gram-negative and Gram-positive bacteria in blood without the addition of a liquid culture medium. This method involves the addition to blood of optimum amounts of hydrogen and magnesium ion exchange resins and sodium citrate.