The effects of ALA-PDT on microbiota in pilosebaceous units of patients with severe acne: A metagenomic study.

BACKGROUND: 5-aminolevulinic acid mediated photodynamic therapy (ALA-PDT) is increasingly used to control severe acne. However, its impact on skin microbiota remains uncertain. OBJECTIVES: We aimed to compare the makeup, diversity, and function of the microbiota in pilosebaceous units of patients with severe acne before and after ALA-PDT. METHODS: A longitudinal cohort study was performed on 11 participants with severe facial acne. All patients were given 5%ALA-PDT every two weeks for three sessions in total. The contents of lesions were sampled for metagenomic sequencing at baseline and two weeks after the first ALA-PDT session. RESULTS: Cutibacterium acnes was the most dominant species followed by Staphylococcus epidermidis and Pseudomonas fluorescens. Treatment with ALA-PDT led to clinical improvements in acne severity concurrent with a significant reduction in the relative abundance of C. acnes, while P. fluorescens increased significantly after ALA-PDT. No significant change was identified in other species. ALA-PDT administration was associated with an increased microbiota diversity and reductions in the relative abundance of the functional genes involved in energy metabolism and DNA replication. CONCLUSIONS: ALA-PDT plays a therapeutic role by killing C. acnes, increasing P. fluorescens and the microbiome diversity, while inhibiting the function of microbiota in pilosebaceous units of severe acne.