The treatment of psoriasis has been revolutionised by the development of biologic therapies. However, the pathogenesis of psoriasis, in particular the role of the cutaneous microbiome, remains incompletely understood. Moreover, skin microbiome studies have heavily relied on 16S rRNA sequencing data in the absence of bacterial culture.
To characterise and compare the cutaneous microbiome in 20 healthy controls and 23 patients with psoriasis using metagenomic analyses and to determine changes in the microbiome during treatment.
Swabs from lesional and non-lesional skin from psoriasis patients, and from site- and skin microenvironment matched controls, were analysed using both 16S rRNA sequencing and traditional culture combined with mass spectrometry (MALDI-TOF) in a prospective study.
Psoriasis was associated with an increased abundance of Firmicutes and a corresponding reduction in Actinobacteria, most marked in lesional skin, and at least partially reversed during systemic treatment. Shifts in bacterial community composition in lesional sites were reflected in similar changes in culturable bacteria, although changes in the microbiota over repeated swabbing were only detectable with sequencing. The composition of the microbial communities varied by skin site and microenvironment. Prevotella and Staphylococcus were significantly associated with lesional skin; Anaerococcus and Propionibacterium with non-lesional skin. There were no significant differences in the amount of bacteria cultured from the skin of healthy controls and psoriasis patients.
Shifts in the cutaneous microbiome in psoriasis, particularly during treatment, may shed new light on the pathogenesis of the disease and may be clinically exploited to predict treatment response.