Crystal Violet Agar as a Differential Medium for Staphylococci.

In a previous paper Chapman, Berens, Peters and Curcio (1934) showed that staphylococci could be differentiated on the basis of their hemolysis and coagulase reactions. It was further shown that a critical interpretation of the hemolysis test depended upon an accurate knowledge of the pigment production of the strain. The existence of intermediate-colored strains or of dissociants showing wide variations in color from the parent strain makes it difficult to interpret hemolysin tests of certain strains. If some correlative reaction were available, it should be useful for comparative purposes. The search for such a reaction is described in the present paper. There was also demonstrated a correlation between the response of a strain to the reactions described and its pathogenicity for rabbits. The animal experiments were not entirely satisfactory because, in those rabbits which died, the interval between the time of inoculation and death varied considerably, suggesting that factors other than toxicity might have been responsible for some of the lethal effects. In the present study attempts were made to eliminate some of these other factors. It was hoped that this vould simplify the interpretation of the animal experiments and result in an improved correlation. Stimulated by the observation of Burbank (1929) on the effect of sodium carbonate on Escherichia coli and streptococci in feces, the effect of sodium carbonate on staphylococci was studied. Strains of staphylococci were treated with varying concentrations