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.

The rates of metabolism of Sudan I and II and Para Red by human intestinal microflora were high compared to those of Sudan III and IV under anaerobic conditions. Metabolites of the dyes were identified as aniline, 2,4-dimethylaniline, o -toluidine, and 4-nitroaniline through high-performance liquid chromatography and liquid chromatography electrospray ionization tandem mass spectrometry analyses. These data indicate that human intestinal bacteria are able to reduce Sudan dyes to form potentially carcinogenic aromatic amines.

Due to potential interference of nanoparticles on bacterial quantification, there is a challenge to develop a fast, accurate and reproducible method for bacterial quantification. Currently various bacterial quantification methods are used by researchers performing nanoparticles study, but there has been no efficacy evaluation of these methods. Here we study interference of nanoparticles on three most commonly used conventional bacterial quantification methods, including colony counting to determine the colony-forming units (CFU), spectrophotometer method of optical density (OD) measurement, and flow cytometry (FCM).

The capability of Lactobacillus acidophilus and Lactobacillus fermentum to degrade azo dyes was investigated. The bacteria were incubated under anaerobic conditions in the presence of 6 µg/ml Methyl Red, Ponceau BS, Orange G, Amaranth, Orange II, and Direct Blue 15; 5 µg/ml Sudan I and II; or 1.5 µg/ml Sudan III and IV in deMann–Rogosa–Sharpe broth at 37°C for 36 h, and reduction of the dyes was monitored. Both bacteria were capable of degrading all of the water-soluble azo dyes to some extent. They were also able to completely reduce the oil-soluble diazo dyes Sudan III and IV but were unable to reduce the oil-soluble monoazo dyes Sudan I and II to any significant degree in the concentrations studied. Growth of the bacteria was not significantly affected by the presence of the Sudan azo dyes. Metabolites of the bacterial degradation of Sudan III and IV were isolated and identified by liquid chromatography electrospray ionization tandem mass spectrometry analyses and compared with authentic standards. Aniline and o-toluidine (2-methylaniline), both potentially carcinogenic aromatic amines, were metabolites of Sudan III and IV, respectively.