Ethyl Violet. A Selective Dye for the Isolation of Gram-Negative Bacteria

Minimal inocula of Gram-negative and positive bacteria were seeded into tryptose broth containing varying concentrations of dyes. Three dyes were used, namely crystal violet, brilliant green and ethyl violet. Growth rates were determined for 2, 4 and 6 hours incubation. All three dyes were equally effective in inhibiting Gram positive bacteria. Ethyl violet showed markedly less toxicity toward Gram negative bacteria than did either crystal violet or brilliant green.