Association Between Skin Acid Mantle, Natural Moisturizing Factors, and Antibacterial Activity Against S. aureus in the Stratum Corneum

Abstract

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:

• skin barrier function
• skin moisturizer
• skin pH
• Staphylococcus aureus
• skin acid mantle
• 2-pyrrolidone-5-carboxylic acid

Abbreviations

AD, atopic dermatitis; BCA, bicinchoninic acid; CFU, colony-forming unit; CIDAMP, Cationic Intrinsically Disordered Antimicrobial Peptide; DI, deionized; DT, detection time; FFA, free fatty acid; IMC, isothermal microcalorimetry; NF-TVC, Non-fermenting-Total Viable Count; MRM, multiple reaction monitoring; NMFs, natural moisturizing factors; P&G, Procter & Gamble; PCA, pyrrolidone carboxylic acid; RHE, reconstructed human epidermis; rpm, revolutions per minute; SC, stratum corneum; SEM, scanning electron microscopy; UCA, urocanic acid.

Data Sharing Statement

The data that support the findings of this study are available from the corresponding authors upon reasonable request.

Ethics Approval and Informed Consent

The study protocol was approved by the Human Research Committee of the P&G Singapore Innovation Center (SGIC PRT ID: 965). Informed written consent was obtained from all participants after the procedures were explained with documentation. All experiments were conducted in accordance with the principles of the Declaration of Helsinki.

Acknowledgments

We thank Feng Yue, Miranda Farage, Jamie Fitzgerald, Kunal Gujraty, Angelica Caranza, Pius Parakattil, HiuFung Lau, and Pradipta Sarkar for their useful comments and contributions regarding this research. We also thank Ganna Oliynyk (Symcel AB) for her technical support and guidance on IMC experiments. The clinical study was performed in collaboration with Sara Holloway (P & G International Operations SA SG Branch).

Editorial support for this manuscript was provided by Cactus Life Sciences (part of Cactus Communications), funded by P&G International Operations.

Author Contributions

All authors made a significant contribution to the work reported, whether that is in the conception, study design, execution, acquisition of data, analysis and interpretation, or in all these areas; took part in drafting, revising or critically reviewing the article; gave final approval of the version to be published; have agreed on the journal to which the article has been submitted; and agree to be accountable for all aspects of the work.

Disclosure

All authors are employees of the study sponsor, P&G International Operations. The authors report no other conflicts of interest in this work.

Additional information

Funding

The funding for this study was provided by P&G International Operations.