The biocidal properties of anthraquininoid dyes

A modified minimum inhibitory concentration test method was employed to determine the antimicrobial properties against both Gram-positive and Gram-negative bacteria of two series of cationic anthraquininoid dyes. The antimicrobial strength of the colorants increased with increasing carbon chain length up to C16; the activities of the colorants were improved by the use of elevated temperature as well as either high or low pH. However, the colorants were deactivated in the presence of both anionic surfactants and divalent cations.