Skin pH-dependent Staphylococcus aureus abundance as predictor for increasing atopic dermatitis severity.

Abstract

Atopic eczema (atopic dermatitis, AD) is characterized by disrupted skin barrier associated with elevated skin pH and skin microbiome dysbiosis, due to high Staphylococcus aureus loads, especially during flares. Since Saureus shows optimal growth at neutral pH, we investigated the longitudinal interplay between these factors and AD severity in a pilot study. Emollient (with either basic pH 8.5 or pH 5.5) was applied double-blinded twice daily to 6 AD patients and 6 healthy (HE) controls for 8weeks. Weekly, skin swabs for microbiome analysis (deep sequencing) were taken, AD severity was assessed, and skin physiology (pH, hydration, transepidermal water loss) was measured. Physiological, microbiome, and clinical results were not robustly related to the pH of applied emollient. In contrast to longitudinally stable microbiome in HE, Saureus frequency significantly increased in AD over 8weeks. High Saureus abundance was associated with skin pH 5.7-6.2. High baseline Saureus frequency predicted both increase in Saureus and in AD severity (EASI and local SCORAD) after 8weeks. Skin pH is tightly regulated by intrinsic factors and limits the abundance of Saureus. High baseline Saureus abundance in turn predicts an increase in AD severity over the study period. This underlines the importance and potential of sustained intervention regarding the skin pH and urges for larger studies linking skin pH and skin Saureus abundance to understand driving factors of disease progression.