Metabolism of azo dyes derived from benzidine, 3,3'-dimethylbenzidine and 3,3' -dimethoxybenzidine to potentially carcinogenic aromatic amines by intestinal bacteria

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Abstract
The metabolism of a benzidine-based dye, Direct Black 38, a 3,3''-dimethylbenzidine-based dye, Direct Red 2, and a 3,3''-dimethoxybenzidine-based dye, Direct Blue 15, was studied both in pure cultures of anaerobic bacteria and in bacterial suspensions derived from the intestinal contents of the rat. All of the pure cultures and the rat intestinal bacteria were able to reduce the azo linkages of Direct Black 38, Direct Red 2 and Direct Blue 15 with the subsequent formation of benzidine, 3,3''-dimethylbenzidine and 3,3''-dimethoxybenzidine, respectively. The metabolites of Direct Black 38, Direct Red 2 and Direct Blue 15 were isolated and identified by gas chromatography/mass spectrometry and had similar chromatographic and mass spectral properties with those of authentic standards. In vitro anaerobic incubations of rat intestinal microorganisms were evidently able to reduce and cleave the azo bonds of dyes derived from benzidine, 3,3''-dimethylbenzidine and 3,3''-dimethoxybenzidine to form potentially carcinogenic aromatic amines.