Metabolism of azo dyes by human skin microbiota

Abstract

Reduction of Methyl Red (MR) and Orange II (Or II) by 26 human skin bacterial species was monitored by a rapid spectrophotometric assay. The analysis indicated that skin bacteria, representing the generaStaphylococcus,Corynebacterium,Micrococcus,DermacoccusandKocuria, were able to reduce MR by 74–100 % in 24 h, with only three species unable to reduce completely the dye in that time. Among the species tested, onlyCorynebacterium xerosiswas unable to reduce Or II to any degree by 24 h, and onlyStaphylococcus delphini,Staphylococcus sciurisubsp.sciuriandPseudomonas aeruginosawere able to reduce completely this dye within 24 h. MR reduction started with early-exponential growth inStaphylococcus aureusandStaphylococcus epidermidis, and around late-exponential/early-stationary growth inP. aeruginosa. Reduction of Or II, Ponceau S and Ponceau BS started during late-exponential/early-stationary growth for all three species. Using liquid chromatography/electrospray ionization mass spectrometry analyses, MR metabolites produced byStaph. aureus,Staph. epidermidisandP. aeruginosawere identified asN,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,Staphylococcus haemolyticus,Staph. epidermidis,Staphylococcus cohniiandStaphylococcus saprophyticus, have hypothetical genes with 77, 76, 75 and 74 % sequence identity toazo1encoding an azoreductase fromStaph. aureusand hypothetical proteins with 82, 80, 72 and 74 % identity to Azo1, respectively. In addition,Staphylococcus capitishas a protein with 79 % identity to Azo1. Western analysis detected proteins similar to Azo1 in all the staphylococci tested, exceptStaph. delphini,Staph. sciurisubsp.sciuriandStaphylococcus 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.