Background/Purpose:   Psoriasis (PsO) is a chronic immune-mediated skin condition affecting ~3% of adults worldwide. Up to a third of PsO patients go on to develop psoriatic arthritis (PsA), a heterogeneous inflammatory arthritis characterized by concomitant bone erosion and osteoproliferation. Although multiple advances have been made in the pathogenesis and therapeutics of these disorders, it is currently not possible to predict which individuals will progress from PsO to PsA. The role of the microbiome as a potential trigger for autoimmunity and rheumatic disease has recently been implicated. The goal of this study was to characterize the cutaneous microbiota of patients with PsO and PsA (in both psoriatic plaques and unaffected skin) to determine if there are characteristic features related to disease phenotype.

Methods:   Skin swabs from subjects with PsO (n=29) and PsA (n=62) were collected from both psoriatic plaque lesions and contralateral unaffected skin. 16S rDNA was extracted per protocol (MoBio, USA) and amplicons targeting the hypervariable V4 region were sequenced using MiSeq (Illumina) to define the microbiota composition. The obtained 16S rRNA sequences were analyzed using the Quantitative Insights into Microbial Ecology (QIIME) pipeline. Taxonomic relative abundance was determined to compare their prevalence among different phenotypes using Kruskal-Wallis statistical analysis. Alpha diversity plots and weighted Unifrac analysis (beta diversity) of cutaneous bacterial communities were generated. False discovery rate analysis was applied to identify unique differentiating taxa.

Results:   Baseline characteristics were comparable in both groups. PsO samples had, on average, a similar number of operational taxonomic units as compared to PsA samples. Beta diversity plots did not demonstrate statistically distinct clustering of microbial communities between PsO and PsA subjects, PsO and PsA nonlesional skin, or PsO and PsA lesional skin. Staphylococcus and Corynebacterium were the most abundant genera across all samples. However, several genera were statistically more abundant in PsO compared to PsA lesions, including unclassified Bradyrhizobiaceae (p<0.0006), Rahnella (p<0.0006), unclassified Prevotellaceae (p<0.001), and Parvibaculum (p<0.002). Rothia was more abundant in PsA (p<0.02).

Conclusion:   Our results characterize, for the first time, the cutaneous microbial composition of individuals with PsO compared to those with PsA both in psoriatic lesions and unaffected skin. Although we did not find overall community differences among the various phenotypes, our preliminary observations point towards differences in specific genera, which are characteristically more abundant in PsO. Further in-depth analysis is required to better understand the significance of this dysbiotic process in PsA and whether it contributes to the pathogenesis of the psoriatic disease spectrum. Current efforts are devoted to incorporating healthy controls into our analysis, and analyzing the cutaneous microbiome (and metagenome) across multiple body sites, multiple visits, as well as pre- and post-immunosuppressive/biologic therapy.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/cutaneous-microbiota-features-distinguish-psoriasis-from-psoriatic-arthritis/