Crystal Violet Agar as a Differential Medium for Staphylococci

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Abstract
A hemolytic, coagulating strain of staphylococcus was more resistant to a number of chemical substances than a non-hemolytic, non-coagulating strain. The best differentiation was obtained with crystal violet. The dye was then added to proteose lactose agar (1:300,000). On this medium, strains which reacted positively to hemolysis and coagulase tests [see B. A. 9(5) : entry 9709] produced violet growths or golden growths tinged with violet. Strains which reacted negatively to hemolysis and coagulase tests produced white or pale growths. Exposure of strains to solutions of crystal violet indicated that the mechanism of the reaction depended upon reduction of the dye to its leuco base by non-hemolytic, non-coagulating strains. There was an agreement of the violet agar reaction with hemolysis and coagulase tests in 93% of 1034 strains. Using death of rabbits within 4 days as a criterion of the toxicity of killed (Merthiolated) suspensions, there was an agreement between toxicity for rabbits and the violet agar reaction in 96.4% on the basis of tests on 28 strains.