Characteristics of the Skin Microbiome in Selected Dermatological Conditions: A Narrative Review

Characteristics of skin microbiome associated with disease severity in systemic sclerosis

Systemic sclerosis (SSc) is a chronic autoimmune disorder characterised by skin fibrosis and internal organ involvement. Disruptions in the microbial communities on the skin may contribute to the onset of autoimmune diseases that affect the skin. However, current research on the skin microbiome in SSc is lacking. This study aimed to investigate skin microbiome associated with disease severity in SSc. Skin swabs were collected from the upper limbs of 46 healthy controls (HCs) and 36 patients with SSc. Metagenomic analysis based on the 16S rRNA gene was conducted and stratified by cutaneous subtype and modified Rodnan skin score (mRSS) severity. Significant differences in skin bacterial communities were observed between the HCs and patients with SSc, with further significant variations based on subtype and mRSS severity. The identified biomarkers were Bacteroides and Faecalibacterium for patients with diffuse cutaneous SSc with high mRSS (≥ 10) and Mycobacterium and Parabacteroides for those with low mRSS (< 10). Gardnerella, Abies, Lactobacillus, and Roseburia were the biomarkers in patients with limited cutaneous SSc (lcSS) and high mRSS, whereas Coprococcus predominated in patients with lcSS and low mRSS. Cutaneous subtype analysis identified Pediococcus as a biomarker in the HCs, whereas mRSS analysis revealed the presence of Pseudomonas in conjunction with Pediococcus. In conclusion, patients with SSc exhibit distinct skin microbiota compared with healthy controls. Bacterial composition varies by systemic sclerosis cutaneous subtype and skin thickness.

Cutaneous Dysbiosis and Dermatophytosis: The Unexplored Link

The skin, besides being the largest interface between the body and the external environment, also forms an ecological niche which is populated by almost a trillion microorganisms. These, collectively known as the cutaneous microbiome, form a dynamic yet well-controlled system that resists invasion by pathogenic microorganisms, functioning as the so-called 'microbiological barrier', modulating the body's immune response, indirectly playing a crucial role in the pathogenesis of several inflammatory diseases. The composition and complexity of the microbiome are yet to be fully understood. The term 'dysbiosis' originally was coined in 1908 for a change in the gut microbiome. The potential role of 'cutaneous dysbiosis' in human dermatophytic infections, especially in the backdrop of the current epidemic of chronic, recurrent and treatment-resistant dermatophytosis, is understandably a topic of interest. The purpose of this review was to assess all studies using culture-independent methods for analysing the skin microbiome in various dermatophyte infections. The PubMed and Google Scholar databases were searched using the terms 'microbiome', 'dysbiosis', 'dermatophytes', 'dermatophytosis' and 'tinea'. All studies involving the use of standard sequencing methods for the study of the microbiome in various dermatophytoses were included. A total of four studies assessing the local skin microbiome associated with dermatophytic infections were found-one for tinea capitis, one for onychomycosis (in both psoriatic and nonpsoriatic nails) and two studying patients of tinea pedis. The studies determined the microbiological patterns in patients and compared them with healthy individuals using sequencing methods. Significant differences in the species diversity and counts of the various microorganisms between patient and control groups were demonstrated in all. However, cross-sectional design and the absence of pre- and post-treatment data along with a limited sample size were the major limitations in all of them. No data regarding other forms of tinea, most importantly, tinea cruris, corporis, faciei, etc. were found. The existing studies demonstrate a change in the microbiome or dysbiosis associated with cases of dermatophytosis, but are inadequate to determine a causal association. The changes may also be wholly or partly attributed to the effect of the infection. Further longitudinal studies from different regions of the world, also involving other forms of dermatophytosis, are required to provide a clearer insight and a more representative picture.

Bio-Inspired Antioxidant Heparin-Mimetic Peptide Hydrogel for Radiation-Induced Skin Injury Repair

Radiotherapy is one of the most important means of cancer treatment, however, radiation can also cause adverse reactions and even serious injuries to the skin. Radiation-induced excess reactive oxygen species (ROS) production and inflammatory infiltration make skin wounds difficult to heal compared to normal skin injuries. Herein, an antioxidant heparin-mimetic peptide hydrogel (K16, KYKYEYEYAGEGDSS-4Sa) is designed for radiation-induced skin injury (RISI) repair. First, the K16 peptide can self-assemble into a hydrogel with a 3D mesh-like porous nanofiber structure, which can provide certain physical support for skin repair like extracellular matrix (ECM). Then, K16 hydrogel not only scavenges ROS and prevents radiation damage to cellular DNA, but also promotes cell proliferation, migration, and angiogenesis. Meanwhile, 4-sulfobenzoic acid (4Sa) modified at the N-terminal end of the K16 peptide can adsorb inflammatory cytokines, thus acting to eliminate inflammation at the wound site. In vivo experiments showed that K16 hydrogel can inhibit early wound degradation, reduce inflammatory infiltration, and promote angiogenesis and collagen deposition, thus promoting wound healing. Therefore, the K16 hydrogel designed in this study has good potential for application in the field of radiation-induced skin injury repair.

Microbiota and IL-33/31 Axis Linkage: Implications and Therapeutic Perspectives in Atopic Dermatitis and Psoriasis

Microbiome dysbiosis and cytokine alternations are key features of atopic dermatitis (AD) and psoriasis (PsO), two of the most prevalent and burdensome pruritic skin conditions worldwide. Interleukin (IL)-33 and IL-31 have been recognized to be major players who act synergistically in the pathogenesis and maintenance of different chronic inflammatory conditions and pruritic skin disorders, including AD and PsO, and their potential role as therapeutic targets is being thoroughly investigated. The bidirectional interplay between dysbiosis and immunological changes has been extensively studied, but there is still debate regarding which of these two factors is the actual causative culprit behind the aetiopathological process that ultimately leads to AD and PsO. We conducted a literature review on the Pubmed database assessing articles of immunology, dermatology, microbiology and allergology with the aim to strengthen the hypothesis that dysbiosis is at the origin of the IL-33/IL-31 dysregulation that contributes to the pathogenesis of AD and PsO. Finally, we discussed the therapeutic options currently in development for the treatment of these skin conditions targeting IL-31, IL-33 and/or the microbiome.

Healthy microbiome – a mere idea or a sound concept?

Hundreds of studies in last decades have aimed to compare the microbiome of patients suffering from diverse diseases with that of healthy controls. The microbiome-related component was additionally identified in pathophysiology of many diseases formerly considered to depend only on the host physiology. This, however, opens important questions like: “What is the healthy microbiome?” or “Is it possible to define it unequivocally?”. In this review, we describe the main hindrances complicating the definition of “healthy microbiome” in terms of microbiota composition. We discuss the human microbiome from the perspective of classical ecology and we advocate for the shift from the stress on microbiota composition to the functions that microbiome ensures for the host. Finally, we propose to leave the concept of ideal healthy microbiome and replace it by focus on microbiome advantageous for the host, which always depends on the specific context like the age, genetics, dietary habits, body site or physiological state.