Background: Atopic dermatitis (AD) is associated with reduced skin microbial diversity and overgrowth of Staphylococcus (S.) aureus. However, the importance of S. aureus colonisation in the complex pathogenesis remains unclear and studies on the effect of anti-staphylococcal therapy in non-infected AD show contradictory results. Long-term interventions against S. aureus might be needed to restore the microbial balance, but carry the risk of bacterial resistance induction. Staphefekt, an engineered bacteriophage endolysin, specifically kills S. aureus leaving other skin commensals unharmed. Bacterial resistance towards endolysins has not been reported, nor is it expected, which allows us to study its effect as long-term anti-staphylococcal treatment in non-infected AD. Methods: This is a multi-centre, placebo-controlled, double-blinded and randomized superiority trial with a parallel group design. A total of 100 participants, aged 18 years or older, diagnosed with moderate to severe AD and using a topical corticosteroid in the weeks before enrolment are included in the study. The study is executed in the Erasmus MC University Medical Centre Rotterdam in collaboration with the Havenziekenhuis Rotterdam. After a 2-week run-in period to standardize the corticosteroid use with triamcinolone acetonide 0.1% cream, participants will be randomized to either treatment with Staphefekt in a cetomacrogol-based cream or a placebo for 12 weeks, followed by an 8-week follow-up period. The primary objective is to assess the difference in the need for corticosteroid co-therapy between the Staphefekt and the placebo group, measuring the number of days per week of corticosteroid cream (triamcinolone) use. Secondary outcomes include the difference in use of corticosteroid cream measured in grams, differences in clinical efficacy, quality of life (QoL), microbial composition (includi23ng S. aureus) between the Staphefekt and the placebo group, and the safety and tolerability. Discussion: The results of this trial will provide data about the effect of long-term anti-staphylococcal therapy with Staphefekt on corticosteroid use, clinical symptoms and QoL in patients with moderate to severe AD. Additional data about growth characteristics of the skin microbiome, including S. aureus, will give insight into the role of the microbiome as a factor in the pathophysiology of AD. Trial registration:, NCT02840955. Registered on 11 July 2016.

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Keywords Atopic dermatitis, Eczema, Endolysins, Lysins, Microbiome, Staphefekt, Staphylococcus aureus
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Journal Trials
Totté, J, de Wit, J. (Jill), Pardo, L. (Luba), Schuren, F. (Frank), van Doorn, M. (Martijn), & Pasmans, S.G.M.A. (2017). Targeted anti-staphylococcal therapy with endolysins in atopic dermatitis and the effect on steroid use, disease severity and the microbiome: Study protocol for a randomized controlled trial (MAAS trial). Trials, 18(1). doi:10.1186/s13063-017-2118-x