Abstract
INTRODUCTION: Changes in the skin microbiome in atopic dermatitis (AD) include a reduced bacterial diversity and increased abundance of Staphylococcus aureus. Topical antibiotics and antiseptics may decrease bacterial pathogens but lack positive effects on microbiome diversity. METHODS: In this double-blind, intraindividual vehicle-controlled proof-of-concept study, n = 20 patients received a gel containing a defined extract (Spiralin®) of the microalgae Spirulina platensis, previously shown to exert anti-microbial effects, or vehicle on target lesions of similar size and clinical activity. The Shannon index reflecting α-diversity and the abundance of S. aureus were calculated from the analysis of 16s rRNA gene libraries with untreated non-lesional skin serving as control. Clinical activity was determined by the Target Lesion Severity Score (TLSS) and lesion size. RESULTS: Positive effects of the active gel on the microbiome after 4 weeks of treatment were indicated by a significant increase of the Shannon index in areas treated with verum (mean increase 16.7%; p < 0.01 vs. baseline), but not in areas treated with vehicle. This increase in verum-treated lesions was more pronounced in lesions with an at least 50% (26.3%) or an at least 75% reduction of the TLSS (33.3%). There was also a stronger decrease of the abundance of S. aureus in lesions treated with active gel compared to those treated with vehicle (25.5% vs. 9.4%), but significance was not met. There were several trends, indicating clinical effects of the active gel. For example, vehicle-treated areas showed no reduction in area size (77.8 cm2 at week 4 compared to 77.0 cm2 at baseline), while verum-treated lesion area decreased on average by 6.9 cm2. Active and vehicle gel were well tolerated, and very few local side effects were noted. CONCLUSION: These preliminary results indicate a positive effect of a gel-containing Spiralin® on the skin microbiome in patients with active AD lesions combined with reductions in clinical disease activity, supporting further investigations of the active gel alone or in combination with anti-inflammatory treatments in larger AD studies.