Purpose: The skin has evolved a system to prevent pathogenic microorganism colonization and infection. This study examined the role of natural moisturizing factors (NMFs) and skin pH on Staphylococcus aureus (S. aureus) growth and colonization on the human stratum corneum (SC).
Study population and methods: A survey study with 82 female participants was performed. Participants maintained their daily hygiene routine, except for refraining from using leave-on products on their forearms on the day of the test. Skin sampling was performed using adhesive tapes. An ex vivo method was developed to study the viability and growth of S. aureus on human SC sampled from normal skin. NMFs, including pyrrolidone carboxylic acid (PCA), urocanic acid (UCA), histidine, and proline in SC samples, were measured by liquid chromatography with tandem mass spectrometry. The impact of PCA and UCA on S. aureus growth and metabolic activity was measured by optical density and isothermal microcalorimetry, respectively.
Results: Heterogeneity of S. aureus viability on human SC samples was observed. Skin pH showed a significant negative association (p<0.05) with SC antibacterial activity in the ex vivo assay. One unit of skin pH decrease corresponded to 68.1% of S. aureus cell death. The levels of PCA and histidine were significantly negatively associated (p<0.05) with skin pH. The addition of 5 mM and 10 mM PCA significantly inhibited S. aureus growth by approximately 25% at 20 hours and reduced its metabolic activity in vitro.
Conclusion: The results indicate that PCA, one of the NMFs in human skin, plays an important role in regulating the human skin acid mantle in vivo and contributes to antibacterial activity against S. aureus.
Keywords: 2-pyrrolidone-5-carboxylic acid; Staphylococcus aureus; skin acid mantle; skin barrier function; skin moisturizer; skin pH.
© 2023 Li et al.