The Role of the Microbiome in Psoriasis: Moving from Disease Description to Treatment Prediction?

Human skin is awash with microbes. It has been estimated that there are up to 2 million organisms, mainly bacteria, in each square centimetre of skin. Until now our understanding of the complexity of this cutaneous (skin) “microbiome” has been limited by traditional laboratory culture methods. Recent advances in molecular techniques have revealed that these older methods may have only detected about 10% of organisms living on the skin. The true state of affairs is vastly more complex. This collaborative paper between scientists in Germany and the UK reviews recent literature in this area of research. Much of the work has been done using a molecular technique called 16S ribosomal RNA sequencing. This permits the detection of the molecular signature of a bacterium, undetectable using traditional culture techniques. It is clear that the pattern of bacteria resident in the skin is influenced by many factors such as anatomical site, patient factors such as age and sex, the presence of skin disease and genetic factors. The role of the “microbiome” in psoriasis is now under scrutiny. Some organisms are prevalent in uninvolved (i.e. symptom‐free) skin but reduced in psoriasis lesions (patches that are affected by psoriasis), whereas Streptococci are more numerous in psoriasis plaques. The role of Streptococcal throat infections in exacerbating psoriasis has long been recognised. It is reasonable to speculate that the interaction between this organism and the host immune system is playing a role in affecting disease activity. It is also possible that studying a patient's “psoriatic microbiome” signature may help scientists to predict their response to treatment.