Comparison of bacterial microbiota in skin biopsies from normal and psoriatic skin.

Microorganisms have been implicated in the pathogenesis of psoriasis. Previous studies of psoriasis and normal skin have used swabs from the surface rather than skin biopsies. In this study, biopsies were taken from 10 patients with psoriasis and 12 control subjects from unmatched sites. Samples were analysed with massive parallel pyrosequencing on the 454 platform targeting the 16S rRNA gene and the variable regions V3-V4. The samples grouped into 19 phyla, 265 taxon and 652 operational units (OTUs) at 97% identity. A cut-off abundance level was set at 1%. The three most common phyla in both normal and psoriasis skin were Firmicutes (39% psoriasis, 43% normal skin), Proteobacteria (38% psoriasis, 27% normal skin) and Actinobacteria (5% psoriasis, 16% normal skin, p = 0.034). In trunk skin, Proteobacteria were present at significantly higher levels in psoriasis compared to controls (52 vs. 32%, p = 0.0113). The commonest genera were Streptococci in both psoriasis (32%) and normal skin (26%). Staphylococci were less common in psoriasis (5%) than in controls (16%), as were Propionibacteria (psoriasis 0.0001669%, controls 0.0254%). Both Staphylococci and Propionibacteria were significantly lower in psoriasis versus control limb skin (p = 0.051, 0.046, respectively). This study has shown some differences in microbiota between psoriasis and normal skin. Whether these are of primary aetiological significance, or secondary to the altered skin of psoriasis remains to be determined.