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Metabolism of azo dyes by human skin microbiota

National Center for Toxicological Research

¹ E-mail: huizhong.chen{at}fda.hhs.gov

Received May 4, 2009
Accepted September 1, 2009

Reduction of Methyl Red and Orange II by 26 human skin bacterial species was monitored by a rapid spectrophotometric assay. The analysis indicated that skin bacteria, representing the genera Staphylococcus, Corynebacterium, Micrococcus, Dermacoccus, and Kocuria, were able to reduce Methyl Red by 74-100% in 24 h, with only three species unable to reduce completely the dye in that time. Among the species tested, only C. xerosis was unable to reduce Orange II to any degree by 24 h, and only Staphy. delphini, Staphy. sciuri sciuri, and Pseudomonas aeruginosa were able to reduce completely this dye within 24 h. Methyl Red reduction started with early exponential growth in Staphy. aureus and Staphy. epidermidis, and around late exponential/early stationary growth in P. aeruginosa. Reduction of Orange II, Ponceau S, and Ponceau BS started during late exponential/early stationary growth for all three species. Using LC/ESI-MS/MS analyses, Methyl Red metabolites produced by Staphy. aureus, Staphy. epidermidis, and P. aeruginosa were identified as N,N-dimethyl-p-phenylenediamine and 2-aminobenzoic acid. Searches of available genomic and proteomic data revealed that at least four of the staphylococci in this study, Staphy. haemolyticus, Staphy. epidermidis, Staphy. cohnii, and Staphy. saprophyticus, have hypothetical genes with 77, 76, 75, and 74% sequence identity to azo1 encoding an azoreductase form Staphy. aureus and hypothetical proteins with 82, 80, 72, and 74% identity to Azo1, respectively. In addition, Staphy. capitis has a protein with 79% identity to Azo1. Western analysis detected proteins similar to Azo1 in all the staphylococci tested, except Staphy. delphini, Staphy. sciuri sciuri, and Staphy. auricularis. The data presented in this report will be useful in the risk assessment process for evaluation of public exposure to products containing these dyes.