The role of the microbiome in psoriasis: moving from disease description to treatment selection?

Background With several million microbes per square centimetre of skin, the task of mapping the physiological cutaneous microbiome is enormous. Indeed, the reliance on bacterial culture to identify cutaneous bacterial communities has led to a systematic underappreciation of cutaneous microbial diversity, potentially limiting our understanding of common inflammatory skin diseases, including psoriasis. However, based heavily on developments in molecular biology and bioinformatics, including next-generation sequencing, the last decade has witnessed a marked increase in our understanding of the extent and composition of the cutaneous microbiome. It is already clear that skin-specific (skin site and skin microenvironment), individual-specific (hygiene, sex, age and hormonal status), disease-specific (atopic eczema, acne) and genetic factors can all influence the cutaneous microbiome, albeit to varying and, as yet, ill-defined extents. Objectives To investigate the role of the microbiome in psoriasis and to outline how microbiome studies can be harnessed to provide new insights into disease pathogenesis and treatment selection. Methods This review briefly describes the process of 16S ribosomal RNA sequencing and then charts our current understanding of the cutaneous microbiome in health and the alterations (dysbiosis) associated with chronic inflammatory diseases, with particular reference to psoriasis. Results The possibility and clinical relevance of intraindividual cross-talk between the various microbiomes is discussed and potential mechanisms underpinning the interactions between resident skin flora and the immune system are highlighted. Conclusions Ultimately, in the age of personalized medicine, the integration of cutaneous microbiome signatures and comprehensive disease and drug response endotypes will herald a novel approach in the clinical management of chronic multisystem inflammatory diseases.