Characterisation of the effects of ultraviolet radiation on host-microbiota interactions in skin

Abstract

The elegant structure of the skin renders it an appropriate habitat which harbours numerous commensal microorganisms. These live mutualistically on and in skin and are collectively defined as the skin microbiota. Ultraviolet radiation (UVR) is an important environmental factor that influences the skin and skin microbiota potentially throughout life. Whilst the effect of UVR on skin has been studied for decades, its effect on the skin microorganisms is a new topic in dermatology and microbiology. This thesis aims to investigate the effects of UVR on skin commensal bacteria and how the UVR-irradiated organisms might influence the skin response to UVR. The sensitivity of eight skin resident bacteria (Staphylococcus. epidermidis-three strains, Staphylococcus hominis, Staphylococcus capitis, Cutibacterium acnes, Micrococcus luteus and Corynebacterium jeikeium) to a single dose of simulated solar radiation (SSR) was investigated. Data indicate that C. jeikeium and M. luteus are relatively resistant to SSR while S. capitis and C. acnes are more sensitive, among the microbes tested. The mechanisms behind the different SSR sensitivity between species were explored by comparing expression of the RecA protein pre/post SSR treatment. However, a clear conclusion of how RecA regulates the survival of skin bacteria upon SSR exposure cannot be drawn based on current data. The presence of an individual strain of S. epidermidis reduces the viability of keratinocytes following a single dose of SSR because irradiated S. epidermidis can release substance(s) that induce(s) keratinocyte necrosis. The active factor(s) is(are) susceptible to heat and trypsin, indicating that it(they) could be proteinaceous. This hypothesis was investigated using fractionation, from which data suggests that the molecular weights of protein(s) that induce(s) necrosis is(are) between 50-100kDa. Based on these results, a clinical study was designed to investigate the effect of skin microbiota on the minimal erythemal dose response in healthy humans. This study was not completed due to the pandemic. In conclusion, the data in this doctoral thesis broaden the knowledge of the effects of UVR on skin commensals and may lead to a better understanding of the relationship between the skin microbiota and skin health.

Date of Award	1 Aug 2022
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Rachel Watson (Supervisor), Catherine O'Neill (Supervisor) & Andrew Mcbain (Supervisor)