🔍 Key Finding

Atopic dermatitis skin shows distinctive dysbiosis characterized by low bacterial diversity, high non-Malassezia fungal diversity, elevated Staphylococcus aureus and S. epidermidis, and reduced abundance of other genera including Propionibacterium.

🔬 Methodology Overview

• Systematic review registered in PROSPERO (CRD42016035813)

• Literature search in PubMed, Embase, Scopus, and ClinicalTrials.gov for primary research studies using culture-independent microbiome analysis

• Included 32 studies meeting criteria (17 published: 11 human, 6 animal)

• Human studies included 355 AD patients aged 2 months to 62 years with mild to severe disease

• Disease severity primarily measured using SCORAD in 8/11 human studies

• Most studies used 16S rRNA sequencing for bacterial analysis; 2 studies analyzed fungal microbiome

📊 Evidence

• AD skin had lower bacterial diversity compared to controls, especially at lesional sites

• S. aureus abundance was elevated in AD skin and correlated positively with disease severity

• Three studies showed depletion of Malassezia species but high non-Malassezia fungal diversity

• Reduced abundances of Propionibacterium, Streptococcus, Acinetobacter, Corynebacterium and Prevotella were observed

• Two-month-old infants who later developed AD showed significantly lower commensal Staphylococcus species

• A mouse study demonstrated that dysbiosis drives eczema pathogenesis and that targeted antibiotics relieved symptoms

💡 Clinical Impact

The findings suggest that AD treatment should consider the broader microbiome beyond just targeting S. aureus, as dysbiosis involves multiple microbial species. Early colonization with commensal staphylococci may be protective, and therapeutic approaches targeting microbiome restoration show promise.

🤔 Limitations

• Heterogeneity in study populations, designs, and methodologies prevented quantitative synthesis

• Data insufficient for robust microbiome characterization in AD

• Various DNA extraction protocols and sequencing methods across studies

• Studies varied in quality and most used 16S rRNA sequencing rather than more comprehensive whole metagenome sequencing

• Limited data on temporal dynamics and clinical correlations