Urban Exposome and Skin Microbiome in Atopic Dermatitis: A Comparative Study Between Two Brazilian Municipalities

INTRODUCTION: Atopic dermatitis (AD) is thought to arise from the interplay of skin barrier dysfunction, type 2 immune dysregulation, and cutaneous dysbiosis, the last of these characterized by reduced bacterial diversity and predominance of Staphylococcus aureus. The urban exposome, including air pollution and reduced environmental microbial diversity, may modulate this dysbiosis. We hypothesized that patients with AD residing in a metropolitan area with a higher pollutant burden would show greater skin dysbiosis, reflected by a higher relative abundance of S. aureus, than patients residing in a municipality with a lower pollutant load and greater environmental biodiversity. METHODS: This cross-sectional, comparative study enrolled ten children (6-12 years) and ten adults (20-31 years) with active AD, without specific treatment in the preceding 30 days, residing in the metropolitan region of São Paulo or in Botucatu, an interior municipality of São Paulo State, Brazil. Skin swabs were collected from eczematous lesions and characterized by 16S ribosomal RNA (rRNA) gene (V3-V4) sequencing. Alpha and beta diversity and the relative abundance of S. aureus, S. epidermidis, and S. hominis were compared between municipalities and age groups using generalized linear models, Bray-Curtis dissimilarity, principal coordinates analysis (PCoA), and permutational multivariate analysis of variance (PERMANOVA). RESULTS: The sample (n = 20) had a predominance of male sex (60%) and moderate AD severity (75%). A total of 658 taxa were identified. Alpha diversity did not differ by municipality or age group, and PERMANOVA revealed no global difference in bacterial community composition (p > 0.1). However, participants residing in the metropolitan municipality showed a significantly higher relative abundance of S. aureus and higher proportions of S. aureus relative to total bacteria and to other staphylococci than those residing in the interior municipality. CONCLUSION: Despite similar overall microbial diversity, patients with AD living in a metropolitan municipality showed selective enrichment of S. aureus compared with those in a less polluted interior municipality. These exploratory findings generate the hypothesis that the urban exposome contributes to cutaneous dysbiosis in AD and warrant confirmation in larger studies with objective exposure measurement.