Abstract
Human skin is a complex ecosystem and is host to a large number of microorganisms. When the bacterial ecosystem is balanced and differentiated, skin remains healthy. However, the use of cosmetics can change this balance and promote the appearance of skin diseases. The skin’s microorganisms can utilize some cosmetic components, which either promote their growth, or produce metabolites that influence the skin environment. In this study, we tested the ability of the Malassezia species and some bacterial strains to assimilate substances frequently used in dermal formulations. The growth capability of microorganisms was determined and their lipase activity was analyzed. The growth of all Malassezia spp. in the presence of free acids, free acid esters, and fatty alcohols with a fatty chain length above 12 carbon atoms was observed. No growth was observed in the presence of fatty alcohol ethers, secondary fatty alcohols, paraffin- and silicon-based substances, polymers, polyethylene glycols, quaternary ammonium salts, hydroxy fatty acid esters, or fatty acids and fatty acid esters with a fatty chain length shorter than 12 carbon atoms. The hydrolysis of esters by Malassezia lipases was detected using High Performance Thin Layer Chromatography (HPTLC). The production of free fatty acids as well as fatty alcohols was observed. The growth promotion or inhibition of bacterial strains was only found in the presence of a few ingredients. Based on these results, formulations containing microbiome inert ingredients were developed.
Highlights
The skin provides a diversity of habitats for bacteria, yeasts, and mold, with different microbiota associated with different regions of the skin
All tested strains of Malassezia species grown on plates of agar selective for pathogenic fungi in the presence of olive oil resulted in growth of white colonies on the plates (Figure 1a)
Our results show that the use of cosmetic products strongly influences natural skin microbiota
Summary
The skin provides a diversity of habitats for bacteria, yeasts, and mold, with different microbiota associated with different regions of the skin. Fungal diversity is dominated by the genus Malassezia [1]. Several of these skin microorganisms are involved in dermatological diseases, such as seborrheic dermatitis, atopic dermatitis, and acne vulgaris [2,3,4]. Malassezia and bacteria such as Staphylococcus spp., Propionibacterium spp., and Corynebacteria spp. secrete multiple lipases with a broad spectrum of activity that hydrolyzes almost all triglycerides in the sebum into fatty acids [5,6,7]. With the exception of M. pachydermatis, all Malassezia species known so far require an external lipid source for growth, i.e., they are inevitably lipid dependent [6]
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