Project Abstract Recent work has concluded that some commensal bacteria residing on human skin are beneficial to immune defense. In contrast, colonization by S. aureus of the skin of patients with atopic dermatitis is detrimental. Through high-throughput screening of the normal human skin microbiome we have identified specific strains of commensal coagulase-negative Staphylococcus that kill pathogenic bacteria and enhance skin innate immune defense. Analysis of the function of the skin microbiome from atopic dermatitis patients has further shown that most atopic patients are deficient in these beneficial commensal strains. We therefore hypothesize that increasing the abundance of such commensal bacteria will benefit patients with atopic dermatitis. To test these hypothesis we propose an interventional clinical trial of the topical application of a defined combination of 4 bacteria from the human skin microbiome. We will confirm that this ?transplant? of beneficial bacteria will kill S. aureus on patient skin. We then determine the stability of this transplant in order to design appropriate dosing over a 28-day trial period and evaluate several elements of the host immune response. This intervention will test if transplant of the skin microbiome will benefit subjects with atopic dermatitis by decreasing S. aureus colonization and/or improve inflammation. Therefore, successful completion of this project will provide answers to key questions about the function of the microbiome on human skin and provide a new approach to treat atopic dermatitis. Our specific aims are: 1: Evaluate the capacity of a microbiome transplant to decrease S. aureus colonization in patients with atopic dermatitis (AD). 2: Determine the stability of the microbiome transplant on lesional and matched non-lesional skin of AD subjects and normal subjects. 3: Evaluate the clinical response to microbiome transplant and identify relevant biomarkers associated with the clinical response.