Since the revolution that followed the discovery of the importance of gut microbiome, the cosmetics industry is increasingly questioning scientists about the effect of its own products on the skin microbiome.
With a complementary question how evaluating this impact?
It is possible to answer gradually to the other questions, by comparing skin swabs from subjects receiving a cosmetic product or a placebo.
The major species of skin bacteria are known and there is a need for a method which is able to quantify it in a specific way. The quantitative PCR method allows to know the evolution of bacteria quantities between two conditions. For example you can follow Staphylococcus sp. (Firmicutes), Corynebacterium sp. (Actinobacteria), Propionibacterium sp. (Actinobacteria) at the genus level or target the species level. It answers to the question, saying yes, my product impacts or does not impact these species of skin microbiome.
This method benefit is the cost, it is a basic investigation method, but it is limited to the targeted species. However, at this stage, it is difficult to explain if the modifications of species are good or bad.
Bacteria sequencing
Going further, a larger investigation may be done by using the 16S rDNA sequencing for bacteria and ITS sequencing for fungi. This method will provide the semi-quantitative evolutions of the taxonomic composition and evolutions of the microbial diversity index. It is then possible to know if the product broadly modifies or not the microbiome.
This method has the advantage to provide an in-depth investigation of the microbial communities and to avoid the culture which is limited to species which grow on the proposed medium. The disadvantage is thesemi-quantitation, the yield variations of 16S PCR, and the lack of cause-and-effect relationship on skin.
High resolution proteomics
Going deeper, it is possible to know more, particularly by investigating the skin and its microbiota simultaneously, and this at the level of metabolic functions and pathways. This is done with high resolution proteomics(nanoLC-MS/ms mass spectrometry and associated bioinformatics).
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