Effect of heat on the antimicrobial activity of brillant green dye

Antimicrobial activity of brilliant green dye in Trypticase soy broth (BBL) is reduced and ultimately destroyed by prolonged autoclaving at 121 C. Loss of antimicrobial activity is accompanied by decolorization of the dye. This is consistent with other evidence that antimicrobial activity of brilliant green resides in the colored dye ion. The dye is not decolorized when heated in distilled water or peptone, but is decolorized by heating in glucose, glycine, or sodium dodecyl sulfate, showing that decolorization results from reaction with components of the medium. To ensure optimal results, it is recommended that bacteriological media be sterilized by heat prior to addition of brilliant green dye.