Cultural Separation of Bacteria on the Basis of Triphenyl Methane Co-Efficients

Abstract

The general parallelism between the Gram reaction and normal selective bacteriostasis by the triphenylmethane dyes is well established, as is also the existence of a small number of organisms in each group which do not follow the rule. Reverse extrinsic bacteriostasis has been demonstrated, but only within a very limited field. The discovery of substances possessing reverse selective power, comparable in extent to normal selective power, would be of value. In the absence of such substances, the slight quantitative differences in the behavior toward dyes, of organisms belonging to the same Gram group, may be turned to account. The authors have determined with great accuracy the crystal violet coefficients of five Gram-positive and five Gram-negative organisms. These observations show that all known aerobic organisms could probably, on the basis of their triphenylmethane coefficients, be placed on a curve, which would on the whole, parallel the Gram reaction. The possibilities of separating Gram-negative organisms from Gram-positives by means of the dyes are well understood. The authors cite experiments to show that similar separations may be made within the Gram groups by making use of the quantitative differences in triphenylmethane coefficients.