On the Mechanism of Bacteriostasis with Triphenylmethane Dyes.

The selective bacteriostatic effect of triphenylmethane dyes has long been known. It has been found by several authors (Churchman, 1928, and others) that these dyes used in gram staining also inhibit the growth of the grampositive microorganisms. The relations between bacteriostatic power and chemical structure of these dyes were studied by Browning and Gilmour (1913), Kligler (1918), Fairbrother and Renshaw (1922), and other authors. It has been established, for instance, that methylation or ethylation of the amine groups increases efficacy, whereas more complex radicles have a contrary effect. About the mechanism of the selective bacteriostatic effect of the above mentioned dyes, different theories have been elaborated. These were extensively discussed by Churchman (1928), Stearn and Steam (1930), Ingraham (1933), and others (cf. Fischer, Hoffmann, and Prado, 1944). It is generally acknowledged that leucobases of bacteriostatically active dyes are relatively inactive. The special structure of the triphenylmethane dyes permits, however, the formation of numerous other leuco-derivatives besides the proper leucobases. This fact was seldom considered in work on those dyes. The general structure of the best known leuco-derivatives of triphenylmethane dyes is shown below: