The skin surface is composed of molecules derived from our skin cells, our environment and from the microorganisms living on our skin. The composition and the diversity of skin microorganisms are directly linked to parameters such as temperature, pH, humidity, lipid content and oxygen gradient. The characterization based on Omics tools (metagenomic, transcriptomic, proteomic…) has highlighted the microbiota as a unique ecosystem for each individual whose role in metabolic, immune and neurological functions is now well established.
Role of commensal species
One of the next challenges will be to understand more precisely the role of commensal species composing the skin microbiota. Multiple researches have shown that Propionibacterium acnes, newly called Cutibacterium acnes, comprised different phylotypes, some of them linked to acne pathogenicity. Recently, Nakatsuji et al. (2017) reports evidence that the community of bacteria residing on normal human skin provides protection against S. aureus. Subsequently, isolated S. hominis A9 strain from normal skin was used to produce a Sh-lantibiotics with selective and efficient activity against S. aureus.
Diversity and balance matter
The diversity of skin microbiota is associated to healthy skin when its value is high. In the case of psoriasis, a high-resolution shotgun metagenomics method was used to characterise the microbiome of psoriatic patients. Results showed decrease diversity and increase in Staphylococcus with potential strain-level variations as key determinants of the psoriatic microbiome . An interesting comparative study between the microbiota of Yanomami indians and US citizens led to the conclusion that the Yanomami indians exhibited highest bacterial diversity and westernisation severely seems to affect human skin micro biome diversity.