Skin dysbiosis in the microbiome in atopic dermatitis is site-specific and involves bacteria, fungus and virus

Skin and systemic infections in children with atopic dermatitis: review of the current evidence

Atopic dermatitis is a chronic, pruritic inflammatory skin disorder that affects approximately 2%-42% of children worldwide. Its course is frequently complicated by secondary bacterial, viral, and fungal infections, which can exacerbate disease severity and hinder treatment outcomes. These infections are thought to arise due to a disrupted skin barrier, reduced antimicrobial peptide production, alterations in the skin microbiome, and Th2-dominant inflammatory response. Identifying the most prevalent and pathogenic microorganisms in patients with AD is critical for early diagnosis, effective management, and prevention of complications. This review provides an updated synthesis of current knowledge on the infectious agents implicated in AD pathogenesis, summarizing recent findings on the epidemiology, microbial interactions, and immune mechanisms involved. Furthermore, it provides an overview of the latest therapeutic strategies for managing AD and its associated infections. By integrating recent insights into pathogenesis and treatment, this study offers a comprehensive perspective on the evolving landscape of AD management in children.

Skin-associated commensal microorganisms and their metabolites

The skin microbiome is an essential component on our skin and is critical for the maintenance of skin health. It consists of a diverse ecosystem of bacteria, fungi, and viruses. Different body sites in humans exhibit vastly different levels of sebum, temperature, and pH, therefore the microbes that colonize these areas have adapted to create a niche for colonization. Healthy microbial diversity is important in the normal function of the skin, and imbalances in microbial diversity in the skin microbiome have been found to correlate with several skin diseases, such as atopic dermatitis, acne vulgaris, psoriasis, and chronic wound infections. These microorganisms, especially commensal bacteria, produce various metabolites such as short-chain fatty acids, antimicrobial peptides, siderophores, and tryptophan-derived metabolites. These metabolites can interact with and aid the host in processes, such as wound healing and colonization resistance. Metabolites produced by skin commensals have promising therapeutical potential for drug-resistant bacterial infections in place of conventional antibiotics to combat widespread antibiotic resistance. In this review, we will discuss the composition of the skin microbiota and the different classes of metabolites produced by its members, as well as how changes in the skin microbiome impact certain disease conditions.

Advances of the exposome at individual levels and prevention in atopic dermatitis

Atopic dermatitis (AD), or eczema, is an inflammatory skin disease related to environmental factors. As a heterogeneous disease, it presents with complex phenotypes and endotypes. A variety of intrinsic and extrinsic factors can promote the development of AD. While there has been extensive discussion on environmental exposure at the population and community levels, discourse on exposome at individual levels in AD remains insufficient. For example, allergens, microorganisms, parasites, dietary factors, and psychological factors such as stress and anxiety play important roles in AD development. Microorganisms, in particular, exhibit altered composition and diversity on the skin of AD patients, influencing skin barrier integrity and immune responses. The impact of certain microorganisms, such as fungi and viruses, on AD has garnered increasing attention because of their important role in maintaining skin homeostasis. Dietary factors, including sugar intake and histamine-rich foods, may modulate AD risk and severity, although findings are controversial. Allergens, particularly house dust mite allergens, and aeroallergens, exacerbate AD symptoms by promoting inflammation and barrier dysfunction. Since AD is often the first step in the atopic march, its primary prevention measures are crucial. Some preventive measures involving microorganisms, diet, and moisturizers remain controversial. Effective preventive strategies necessitate a clear understanding of the complex mechanisms of AD, especially host-microbe-environment interactions. This review summarizes recent advances in understanding various risk and protective factors, as well as primary prevention measures for AD.

Prurigo nodularis and the microbiome

Prurigo nodularis (PN) is a chronic skin condition that profoundly impacts quality of life. Histopathological studies of itchy hyperkeratotic nodules show dense infiltrates of T lymphocytes, mast cells, and eosinophils. A robust inflammatory response is implicated, coupled with key changes in neuronal plasticity that affect nerve fiber architecture and function. The microbial community in PN lesions exhibits a distinct composition, marked by decreased α-diversity and a prominent increase in Staphylococcus aureus (S aureus). This alteration appears to contribute to the disease's pathophysiology, causing further disruption of the skin barrier, immune dysregulation, and neuronal plasticity. There is ample evidence that virulence factors of S aureus promote Th2, Th17, and Th22 cytokine production, which are key to PN. In addition, S aureus V8 protease (Endoproteinase Glu-C) has recently been identified to trigger robust itch by activating protease-activated receptor 1 (PAR1) on sensory neurons. This review underscores the complex interplay between the altered microbiome and the itch-scratch cycle of PN, providing insights into potential therapeutics targeting the skin microbiome. A multidisciplinary approach is crucial for providing relief to individuals suffering from this skin condition.

The Western Diet and Atopic Dermatitis: The Potential Role of Nutrients, Contaminants, and Additives in Dysbiosis and Epithelial Barrier Dysfunction

Atopic dermatitis (AD) is a chronic inflammatory skin disorder influenced by both genetic and environmental factors, collectively termed the exposome. Among these determinants, diet emerges as a pivotal component, with diverse nutrients, contaminants, and additives shaping immune responses, microbiota composition, and systemic inflammatory status. This literature review aimed to elucidate the interplay between dietary factors and skin dysbiosis in AD, providing insights into how these interactions may impact disease susceptibility and progression. A comprehensive search of PubMed and Scopus was conducted using relevant keywords and medical subject headings (MeSH). Studies published in English within the past 25 years were included, encompassing in vitro, in vivo, and ex vivo research, as well as reviews. Priority was given to frequently cited articles, reflecting significant contributions to current understanding. Findings suggest that dietary habits influence AD by modulating both gut and skin microbiota, immune pathways, and inflammatory processes. These insights underscore the importance of considering diet within a broader exposome framework, paving the way for targeted interventions to improve AD management. Further research is needed to clarify the mechanisms and optimize nutritional strategies, potentially informing preventive and therapeutic approaches for AD.

The Skin Mycobiome of Patients With Atopic Dermatitis and Healthy Volunteers: A Case-Control Study

Atopic dermatitis (AD) is a common inflammatory skin disease, for which dysbiosis of the skin mycobiome is considered a triggering factor. The aim of this study was to explore the skin mycobiome of AD patients and healthy volunteers (HV). The study included 50 AD patients and as many HV. Culture-based species identification involved a battery of conventional phenotypic tests and PCR sequencing of the internal transcribed spacer (ITS) 1 and 2 regions within the rDNA cluster. Culture-independent, metataxonomic sequencing was performed with ITS1 as the target region. The overall culture-positive rate was higher in AD patients than in HV (74% vs 28%). Among the former, Rhodotorula spp. dominated, followed by Candida spp., Malassezia spp. and Naganishia albida. The congruence between PCR sequencing and phenotyping was 68.6%. Upon metataxonomy of AD samples, 33 (66%) demonstrated close clustering with HV samples ('control-like' AD), while 17 (34%) displayed a remarkably different mycobiome composition ('AD-specific'), with Cladosporium, Malassezia, Candida, Diplodia, Saccharomyces, Penicillium and Aspergillus genera showing increased abundance. Patients with 'AD-specific' mycobiomes were more commonly exposed to air-conditioning compared to 'control-like' AD patients (p = 0.030). A subset of patients with AD has a different cutaneous mycobiome make-up dominated by environmental moulds, and Malassezia and Candida yeasts. Anthropogenic factors may affect the cutaneous mycobiome composition in AD and should be taken into account in microbiome studies.

Diversity and Characteristics of the Oral Microbiome Associated with Self-Reported Ancestral/Ethnic Groups

Periodontitis disproportionately affects genetic ancestral/ethnic groups. To characterize the oral microbiome from different genetic ancestral/ethnic groups, we collected 161 dental plaque samples from self-identified African Americans (AAs), Caucasian Americans (CAs), and Hispanic Americans (HAs) with clinical gingival health or biofilm-induced gingivitis on an intact periodontium. DNA was extracted from these samples, and then DNA libraries were prepared and sequenced using an Illumina NovaSeq high-throughput sequencer. We found significant differences in the diversity and abundance of microbial taxa among dental plaque samples of the AA, CA, and HA groups. We also identified unique microbial species in a self-reported ancestral/ethnic group. Moreover, we revealed variations in functional potentials of the oral microbiome among the three ancestral/ethnic groups, with greater diversity and abundance of antibiotic-resistant genes in the oral microbiome and significantly more genes involved in the modification of glycoconjugates and oligo- and polysaccharides in AAs than in CAs and HAs. Our observations suggest that the variations in the oral microbiome associated with ancestral/ethnic backgrounds may directly relate to their virulence potential including their abilities to induce host immune responses and to resist antibiotic treatment. These finding can be a steppingstone for developing precision medicine and personalized periodontal prevention/treatment and for reducing oral health disparities.

The pathogenicity and virulence of the opportunistic pathogen Staphylococcus epidermidis

The pervasive presence of Staphylococcus epidermidis and other coagulase-negative staphylococci on the skin and mucous membranes has long underpinned a casual disregard for the infection risk that these organisms pose to vulnerable patients in healthcare settings. Prior to the recognition of biofilm as an important virulence determinant in S. epidermidis, isolation of this microorganism in diagnostic specimens was often overlooked as clinically insignificant with potential delays in diagnosis and onset of appropriate treatment, contributing to the establishment of chronic infection and increased morbidity or mortality. While impressive progress has been made in our understanding of biofilm mechanisms in this important opportunistic pathogen, research into other virulence determinants has lagged S. aureus. In this review, the broader virulence potential of S. epidermidis including biofilm, toxins, proteases, immune evasion strategies and antibiotic resistance mechanisms is surveyed, together with current and future approaches for improved therapeutic interventions.

Staphylococcus aureus colonizing the skin microbiota of adults with severe atopic dermatitis exhibits genomic diversity and convergence in biofilm traits

Atopic dermatitis (AD) is a chronic inflammatory skin disorder exacerbated by Staphylococcus aureus colonization. The specific factors that drive S. aureus overgrowth and persistence in AD remain poorly understood. This study analyzed skin barrier functions and microbiome diversity in lesional (LE) and non-lesional (NL) forearm sites of individuals with severe AD compared to healthy control subjects (HS). Notable differences were found in transepidermal water loss, stratum corneum hydration, and microbiome composition. Cutibacterium was more prevalent in HS, while S. aureus and S. lugdunensis were predominantly found in AD LE skin. The results highlighted that microbial balance depends on inter-species competition. Specifically, network analysis at the genus level demonstrated that overall bacterial correlations were higher in HS, indicating a more stable microbial community. Notably, network analysis at the species level revealed that S. aureus engaged in competitive interactions in NL and LE but not in HS. Whole-genome sequencing (WGS) showed considerable genetic diversity among S. aureus strains from AD. Despite this variability, the isolates exhibited convergence in key phenotypic traits such as adhesion and biofilm formation, which are crucial for microbial persistence. These common phenotypes suggest an adaptive evolution, driven by competition in the AD skin microenvironment, of S. aureus and underscoring the interplay between genetic diversity and phenotypic convergence in microbial adaptation.

Silver Nanoparticles in 3D Printing: A New Frontier in Wound Healing

This review examines the convergence of silver nanoparticles (AgNPs), three-dimensional (3D) printing, and wound healing, focusing on significant advancements in these fields. We explore the unique properties of AgNPs, notably their strong antibacterial efficacy and their potential applications in enhancing wound recovery. Furthermore, the review delves into 3D printing technology, discussing its core principles, various materials employed, and recent innovations. The integration of AgNPs into 3D-printed structures for regenerative medicine is analyzed, emphasizing the benefits of this combined approach and identifying the challenges that must be addressed. This comprehensive overview aims to elucidate the current state of the field and to direct future research toward developing more effective solutions for wound healing.

Diversity and characteristics of the oral microbiome influenced by race and ethnicity

Periodontitis disproportionately affects racial/ethnic populations. Besides social determinants contributing to disparities in periodontal health, variations of oral microbial communities may also be a key factor influencing oral immune responses. To characterize the oral microbiome from different racial/ethnic populations, we collected 161 dental plaque samples from African Americans (AAs), Caucasian Americans (CAs), and Hispanic Americans (HAs) with clinical gingival health or biofilm-induced gingivitis on an intact periodontium. Using metagenomic sequencing, we found significant difference in diversity and abundance of microbial taxa in the dental plaque samples from AA, CA, and HA groups and unique microbial species that can only be detected in a particular racial/ethnic group. Moreover, we revealed racial/ethnic associated variations in functional potential of the oral microbiome, showing that diversity and abundance of antibiotic resistant genes were greater in the oral microbiome of the AAs than those in CAs or HAs, and that the AAs exhibited higher levels of genes involving in modification of glycoconjugates, oligo- and polysaccharides. These findings indicate more complex and higher virulence potential oral microbiome in AA and HA populations, which likely contributes to higher prevalence of periodontitis in AAs and HAs.

Atopic dermatitis and food allergy: More than sensitization

The increased risk of food allergy in infants with atopic dermatitis (AD) has long been recognized; an epidemiologic phenomenon termed "the atopic march." Current literature supports the hypothesis that food antigen exposure through the disrupted skin barrier in AD leads to food antigen-specific immunoglobulin E production and food sensitization. However, there is growing evidence that inflammation in the skin drives intestinal remodeling via circulating inflammatory signals, microbiome alterations, metabolites, and the nervous system. We explore how this skin-gut axis helps to explain the link between AD and food allergy beyond sensitization.

Decoding the diagnostic and therapeutic potential of microbiota using pan-body pan-disease microbiomics

The human microbiome emerges as a promising reservoir for diagnostic markers and therapeutics. Since host-associated microbiomes at various body sites differ and diseases do not occur in isolation, a comprehensive analysis strategy highlighting the full potential of microbiomes should include diverse specimen types and various diseases. To ensure robust data quality and comparability across specimen types and diseases, we employ standardized protocols to generate sequencing data from 1931 prospectively collected specimens, including from saliva, plaque, skin, throat, eye, and stool, with an average sequencing depth of 5.3 gigabases. Collected from 515 patients, these samples yield an average of 3.7 metagenomes per patient. Our results suggest significant microbial variations across diseases and specimen types, including unexpected anatomical sites. We identify 583 unexplored species-level genome bins (SGBs) of which 189 are significantly disease-associated. Of note, the existence of microbial resistance genes in one specimen was indicative of the same resistance genes in other specimens of the same patient. Annotated and previously undescribed SGBs collectively harbor 28,315 potential biosynthetic gene clusters (BGCs), with 1050 significant correlations to diseases. Our combinatorial approach identifies distinct SGBs and BGCs, emphasizing the value of pan-body pan-disease microbiomics as a source for diagnostic and therapeutic strategies.

Microbial Dysbiosis in the Skin Microbiome and Its Psychological Consequences

The homeostasis of the skin microbiome can be disrupted by both extrinsic and intrinsic factors, leading to a state of dysbiosis. This imbalance has been observed at the onset of persistent skin diseases that are closely linked to mental health conditions like anxiety and depression. This narrative review explores recent findings on the relationship between the skin microbiome and the pathophysiology of specific skin disorders, including acne vulgaris, atopic dermatitis, psoriasis, and wound infections. Additionally, it examines the psychological impact of these skin disorders, emphasizing their effect on patients' quality of life and their association with significant psychological consequences, such as anxiety, depression, stress, and suicidal ideation in the most severe cases.

Comparison of the Skin Microbiota in the Periocular Region between Patients with Inflammatory Skin Diseases and Healthy Participants: A Preliminary Study

(1) Background: Periocular or periorbital dermatitis is a common term for all inflammatory skin diseases affecting the area of skin around the eyes. The clear etiopathogenesis of periocular dermatitis is still not fully understood. Advances in molecular techniques for studying microorganisms living in and on our bodies have highlighted the microbiome as a possible contributor to disease, as well as a promising diagnostic marker and target for innovative treatments. The aim of this study was to compare the composition and diversity of the skin microbiota in the periocular region between healthy individuals and individuals affected by the specific entity of periocular dermatitis. (2) Methods: A total of 35 patients with periocular dermatitis and 39 healthy controls were enrolled in the study. After a skin swab from the periocular region was taken from all participants, DNA extraction and 16S rRNA gene amplicon sequencing using Illumina NovaSeq technology were performed. (3) Results: Staphylococcus and Corynebacterium were the most abundant bacterial genera in the microbiota of healthy skin. Analysis of alpha diversity revealed a statistically significant change (p < 0.05) in biodiversity based on the Faith's PD index between patients and healthy individuals. We did not observe changes in beta diversity. The linear discriminant analysis effect size (LEfSe) revealed that Rothia, Corynebacterium, Bartonella, and Paracoccus were enriched in patients, and Anaerococcus, Bacteroides, Porphyromonas, and Enhydrobacter were enriched in healthy controls. (4) Conclusions: According to the results obtained, we assume that the observed changes in the bacterial microbiota on the skin, particularly Gram-positive anaerobic cocci and skin commensals of the genus Corynebacterium, could be one of the factors in the pathogenesis of the investigated inflammatory diseases. The identified differences in the microbiota between healthy individuals and patients with periocular dermatitis should be further investigated.

Exploring the skin microbiome in atopic dermatitis pathogenesis and disease modification

Inflammatory skin diseases such as atopic eczema (atopic dermatitis [AD]) affect children and adults globally. In AD, the skin barrier is impaired on multiple levels. Underlying factors include genetic, chemical, immunologic, and microbial components. Increased skin pH in AD is part of the altered microbial microenvironment that promotes overgrowth of the skin microbiome with Staphylococcus aureus. The secretion of virulence factors, such as toxins and proteases, by S aureus further aggravates the skin barrier deficiency and additionally disrupts the balance of an already skewed immune response. Skin commensal bacteria, however, can inhibit the growth and pathogenicity of S aureus through quorum sensing. Therefore, restoring a healthy skin microbiome could contribute to remission induction in AD. This review discusses direct and indirect approaches to targeting the skin microbiome through modulation of the skin pH; UV treatment; and use of prebiotics, probiotics, and postbiotics. Furthermore, exploratory techniques such as skin microbiome transplantation, ozone therapy, and phage therapy are discussed. Finally, we summarize the latest findings on disease and microbiome modification through targeted immunomodulatory systemic treatments and biologics. We believe that targeting the skin microbiome should be considered a crucial component of successful AD treatment in the future.

The Role of the Microbiota in the Pathogenesis and Treatment of Atopic Dermatitis-A Literature Review

Atopic dermatitis (AD) is a chronic inflammatory skin condition with a high prevalence worldwide. AD pathogenesis is complex and consists of immune system dysregulation and impaired skin barrier, influenced by genetic and environmental factors. The purpose of the review is to show the complex interplay between atopic dermatitis and the microbiota. Human microbiota plays an important role in AD pathogenesis and the course of the disease. Dysbiosis is an important factor contributing to the development of atopic diseases, including atopic dermatitis. The gut microbiota can influence the composition of the skin microbiota, strengthening the skin barrier and regulating the immune response via the involvement of bacterial metabolites, particularly short-chain fatty acids, in signaling pathways of the gut-skin axis. AD can be modulated by antibiotic intake, dietary adjustments, hygiene, and living conditions. One of the promising strategies for modulating the course of AD is probiotics. This review offers a summary of how the microbiota influences the development and treatment of AD, highlighting aspects that warrant additional investigation.

Atopic Dermatitis and Psoriasis: Similarities and Differences in Metabolism and Microbiome

Atopic dermatitis and psoriasis are common chronic inflammatory diseases of high incidence that share some clinical features, including symptoms of pruritus and pain, scaly lesions, and histologically, acanthosis and hyperkeratosis. Meanwhile, they are both commonly comorbid with metabolic disorders such as obesity and diabetes, indicating that both diseases may exist with significant metabolic disturbances. Metabolomics reveals that both atopic dermatitis and psoriasis have abnormalities in a variety of metabolites, including lipids, amino acids, and glucose. Meanwhile, recent studies have highlighted the importance of the microbiome and its metabolites in the pathogenesis of atopic dermatitis and psoriasis. Metabolic alterations and microbiome dysbiosis can also affect the immune, inflammatory, and epidermal barrier, thereby influencing the development of atopic dermatitis and psoriasis. Focusing on the metabolic and microbiome levels, this review is devoted to elaborating the similarities and differences between atopic dermatitis and psoriasis, thus providing insights into the intricate relationship between both conditions.

In Silico Elucidation of Key Drivers of Staphyloccocus aureus-Staphyloccocus epidermidis-Induced Skin Damage in Atopic Dermatitis Lesions

Staphylococcus aureus (SA) colonizes and can damage skin in atopic dermatitis lesions, despite being commonly found with Staphylococcus epidermidis (SE), a commensal that can inhibit SA's virulence and kill SA. In this study, we developed an in silico model, termed a virtual skin site, describing the dynamic interplay between SA, SE, and the skin barrier in atopic dermatitis lesions to investigate the mechanisms driving skin damage by SA and SE. We generated 106 virtual skin sites by varying model parameters to represent different skin physiologies and bacterial properties. In silico analysis revealed that virtual skin sites with no skin damage in the model were characterized by parameters representing stronger SA and SE growth attenuation than those with skin damage. This inspired an in silico treatment strategy combining SA-killing with an enhanced SA-SE growth attenuation, which was found through simulations to recover many more damaged virtual skin sites to a non-damaged state, compared with SA-killing alone. This study demonstrates that in silico modelling can help elucidate the key factors driving skin damage caused by SA-SE colonization in atopic dermatitis lesions and help propose strategies to control it, which we envision will contribute to the design of promising treatments for clinical studies.

Dupilumab-associated head and neck dermatitis shows a pronounced type 22 immune signature mediated by oligoclonally expanded T cells

Dupilumab, an IL4R-blocking antibody, has shown clinical efficacy for atopic dermatitis (AD) treatment. In addition to conjunctivitis/blepharitis, the de novo appearance of head/neck dermatitis is now recognized as a distinct side effect, occurring in up to 10% of patients. Histopathological features distinct from AD suggest a drug effect, but exact underlying mechanisms remain unknown. We profiled punch biopsies from dupilumab-associated head and neck dermatitis (DAHND) by using single-cell RNA sequencing and compared data with untreated AD and healthy control skin. We show that dupilumab treatment was accompanied by normalization of IL-4/IL-13 downstream activity markers such as CCL13, CCL17, CCL18 and CCL26. By contrast, we found strong increases in type 22-associated markers (IL22, AHR) especially in oligoclonally expanded T cells, accompanied by enhanced keratinocyte activation and IL-22 receptor upregulation. Taken together, we demonstrate that dupilumab effectively dampens conventional type 2 inflammation in DAHND lesions, with concomitant hyperactivation of IL22-associated responses.

Atopic dermatitis: Pathophysiology, microbiota, and metabolome - A comprehensive review

Atopic dermatitis (AD) is a prevalent inflammatory skin condition that commonly occurs in children. Genetics, environment, and defects in the skin barrier are only a few of the factors that influence how the disease develops. As human microbiota research has advanced, more scientific evidence has shown the critical involvement of the gut and skin bacteria in the pathogenesis of atopic dermatitis. Microbiome dysbiosis, defined by changed diversity and composition, as well as the development of pathobionts, has been identified as a potential cause for recurring episodes of atopic dermatitis. Gut dysbiosis causes "leaky gut syndrome" by disrupting the epithelial lining of the gut, which allows bacteria and other endotoxins to enter the bloodstream and cause inflammation. The same is true for the disruption of cutaneous homeostasis caused by skin dysbiosis, which enables bacteria and other pathogens to reach deeper skin layers or even systemic circulation, resulting in inflammation. Furthermore, it is now recognized that the gut and skin microbiota releases both beneficial and toxic metabolites. Here, this review covers a range of topics related to AD, including its pathophysiology, the microbiota-AD connection, commonly used treatments, and the significance of metabolomics in AD prevention, treatment, and management, recognizing its potential in providing valuable insights into the disease.

Multi-omics analyses reveal interactions between the skin microbiota and skin metabolites in atopic dermatitis

Introduction

Atopic dermatitis (AD) is one of the most common inflammatory skin diseases. Skin microecological imbalance is an important factor in the pathogenesis of AD, but the underlying mechanism of its interaction with humans remains unclear.

Methods

16S rRNA gene sequencing was conducted to reveal the skin microbiota dynamics. Changes in skin metabolites were tracked by LC-MS metabolomics. We then explored the potential mechanism of interaction by analyzing the correlation between skin bacterial communities and metabolites in corresponding skin-associated samples.

Results

Samples from 18 AD patients and 18 healthy volunteers (HVs) were subjected to 16S rRNA gene sequencing and LC-MS metabolomics. AD patients had dysbiosis of the skin bacterial community with decreased species richness and evenness. The relative abundance of the genus Staphylococcus increased significantly in AD, while the abundances of the genera Propionibacterium and Brevundimonas decreased significantly. The relative abundance of the genera Staphylococcus in healthy females was significantly higher than those in healthy males, while it showed no difference in AD patients with or without lesions. The effects of AD status, sex and the presence or absence of rashes on the number of differentially abundant metabolites per capita were successively reduced. Multiple metabolites involved in purine metabolism and phenylalanine metabolism pathways (such as xanthosine/xanthine and L-phenylalanine/trans-cinnamate) were increased in AD patients. These trends were much more obvious between female AD patients and female HVs. Spearman correlation analysis revealed that the genus Staphylococcus was positively correlated with various compounds involved in phenylalanine metabolism and purine metabolic pathways. The genera Brevundimonas and Lactobacillus were negatively correlated with various compounds involved in purine metabolism, phenylalanine metabolism and sphingolipid signaling pathways.

Discussion

We suggest that purine metabolism and phenylalanine metabolism pathway disorders may play a certain role in the pathogenic mechanism of Staphylococcus aureus in AD. We also found that females are more likely to be colonized by the genus Staphylococcus than males. Differentially abundant metabolites involved in purine metabolism and phenylalanine metabolism pathways were more obvious in female. However, we should notice that the metabolites we detected do not necessarily derived from microbes, they may also origin from the host.

The virome in allergy and asthma: A nascent, ineffable player

Allergic diseases can be affected by virus-host interactions and are increasingly linked with the tissue-specific microbiome. High-throughput metagenomic sequencing has offered the opportunity to study the presence of viruses as an ecologic system, namely, the virome. Even though virome studies are technically challenging conceptually and analytically, they are already producing novel data expanding our understanding of the pathophysiologic mechanisms related to chronic inflammation and allergy. The importance of interspecies and intraspecies interactions is becoming apparent, as they can significantly, directly or indirectly, affect the host's response and antigenic state. Here, we emphasize the challenges and potential insights related to study of the virome in the context of allergy and asthma. We review the limited number of studies that have investigated the virome in these conditions, underlining the need for prospective, repeated sampling designs to unravel the virome's impact on disease development and its interplay with microbiota and immunity. The potential therapeutic use of bacteriophages, which are highly complex components of the virome, is discussed. There is clearly a need for further in-depth investigation of the virome as a system in allergic diseases.

The epithelial barrier: The gateway to allergic, autoimmune, and metabolic diseases and chronic neuropsychiatric conditions

Since the 1960 s, our health has been compromised by exposure to over 350,000 newly introduced toxic substances, contributing to the current pandemic in allergic, autoimmune and metabolic diseases. The "Epithelial Barrier Theory" postulates that these diseases are exacerbated by persistent periepithelial inflammation (epithelitis) triggered by exposure to a wide range of epithelial barrier-damaging substances as well as genetic susceptibility. The epithelial barrier serves as the body's primary physical, chemical, and immunological barrier against external stimuli. A leaky epithelial barrier facilitates the translocation of the microbiome from the surface of the afflicted tissues to interepithelial and even deeper subepithelial locations. In turn, opportunistic bacterial colonization, microbiota dysbiosis, local inflammation and impaired tissue regeneration and remodelling follow. Migration of inflammatory cells to susceptible tissues contributes to damage and inflammation, initiating and aggravating many chronic inflammatory diseases. The objective of this review is to highlight and evaluate recent studies on epithelial physiology and its role in the pathogenesis of chronic diseases in light of the epithelial barrier theory.

Limosilactobacillus reuteri in immunomodulation: molecular mechanisms and potential applications

Frequent use of hormones and drugs may be associated with side-effects. Recent studies have shown that probiotics have effects on the prevention and treatment of immune-related diseases. Limosilactobacillus reuteri (L. reuteri) had regulatory effects on intestinal microbiota, host epithelial cells, immune cells, cytokines, antibodies (Ab), toll-like receptors (TLRs), tryptophan (Try) metabolism, antioxidant enzymes, and expression of related genes, and exhibits antibacterial and anti-inflammatory effects, leading to alleviation of disease symptoms. Although the specific composition of the cell-free supernatant (CFS) of L. reuteri has not been clarified, its efficacy in animal models has drawn increased attention to its potential use. This review summarizes the effects of L. reuteri on intestinal flora and immune regulation, and discusses the feasibility of its application in atopic dermatitis (AD), asthma, necrotizing enterocolitis (NEC), systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), and multiple sclerosis (MS), and provides insights for the prevention and treatment of immune-related diseases.

Bioprospecting the Skin Microbiome: Advances in Therapeutics and Personal Care Products

Bioprospecting is the discovery and exploration of biological diversity found within organisms, genetic elements or produced compounds with prospective commercial or therapeutic applications. The human skin is an ecological niche which harbours a rich and compositional diversity microbiome stemming from the multifactorial interactions between the host and microbiota facilitated by exploitable effector compounds. Advances in the understanding of microbial colonisation mechanisms alongside species and strain interactions have revealed a novel chemical and biological understanding which displays applicative potential. Studies elucidating the organismal interfaces and concomitant understanding of the central processes of skin biology have begun to unravel a potential wealth of molecules which can exploited for their proposed functions. A variety of skin-microbiome-derived compounds display prospective therapeutic applications, ranging from antioncogenic agents relevant in skin cancer therapy to treatment strategies for antimicrobial-resistant bacterial and fungal infections. Considerable opportunities have emerged for the translation to personal care products, such as topical agents to mitigate various skin conditions such as acne and eczema. Adjacent compound developments have focused on cosmetic applications such as reducing skin ageing and its associated changes to skin properties and the microbiome. The skin microbiome contains a wealth of prospective compounds with therapeutic and commercial applications; however, considerable work is required for the translation of in vitro findings to relevant in vivo models to ensure translatability.

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.

Competition between skin antimicrobial peptides and commensal bacteria in type 2 inflammation enables survival of S. aureus

During inflammation, the skin deploys antimicrobial peptides (AMPs) yet during allergic inflammation it becomes more susceptible to Staphylococcus aureus. To understand this contradiction, single-cell sequencing of Il4ra^-/- mice combined with skin microbiome analysis reveals that lower production of AMPs from interleukin-4 receptor α (IL-4Rα) activation selectively inhibits survival of antibiotic-producing strains of coagulase-negative Staphylococcus (CoNS). Diminished AMPs under conditions of T helper type 2 (Th2) inflammation enable expansion of CoNS strains without antibiotic activity and increase Staphylococcus aureus (S. aureus), recapitulating the microbiome on humans with atopic dermatitis. This response is rescued in Camp^-/- mice or after topical steroids, since further inhibition of AMPs enables survival of antibiotic-producing CoNS strains. In conditions of Th17 inflammation, a higher expression of host AMPs is sufficient to directly inhibit S. aureus survival. These results show that antimicrobials produced by the host and commensal bacteria each act to control S. aureus on the skin.

Chitosan-based drug delivery systems for skin atopic dermatitis: recent advancements and patent trends

Atopic dermatitis (AD) is a complex, relapsing inflammatory skin disease with a considerable social and economic burden globally. AD is primarily characterized by its chronic pattern and it can have important modifications in the quality of life of the patients and caretakers. One of the fastest-growing topics in translational medicine today is the exploration of new or repurposed functional biomaterials into drug delivery therapeutic applications. This area has gained a considerable amount of research which produced many innovative drug delivery systems for inflammatory skin diseases like AD. Chitosan, a polysaccharide, has attracted attention as a functional biopolymer for diverse applications, especially in pharmaceutics and medicine, and has been considered a promising candidate for AD treatment due to its antimicrobial, antioxidative, and inflammatory response modulation properties. The current pharmacological treatment for AD involves prescribing topical corticosteroid and calcineurin inhibitors. However, the adverse reactions associated with the long-term usage of these drugs such as itching, burning, or stinging sensation are also well documented. Innovative formulation strategies, including the use of micro- and nanoparticulate systems, biopolymer hydrogel composites, nanofibers, and textile fabrication are being extensively researched with an aim to produce a safe and effective delivery system for AD treatment with minimal side effects. This review outlines the recent development of various chitosan-based drug delivery systems for the treatment of AD published in the past 10 years (2012-2022). These chitosan-based delivery systems include hydrogels, films, micro-, and nanoparticulate systems as well as chitosan textile. The global patent trends on chitosan-based formulations for the AD are also discussed.

Evolving approaches to profiling the microbiome in skin disease

Despite its harsh and dry environment, human skin is home to diverse microbes, including bacteria, fungi, viruses, and microscopic mites. These microbes form communities that may exist at the skin surface, deeper skin layers, and within microhabitats such as the hair follicle and sweat glands, allowing complex interactions with the host immune system. Imbalances in the skin microbiome, known as dysbiosis, have been linked to various inflammatory skin disorders, including atopic dermatitis, acne, and psoriasis. The roles of abundant commensal bacteria belonging to Staphylococcus and Cutibacterium taxa and the fungi Malassezia, where particular species or strains can benefit the host or cause disease, are increasingly appreciated in skin disorders. Furthermore, recent research suggests that the interactions between microorganisms and the host's immune system on the skin can have distant and systemic effects on the body, such as on the gut and brain, known as the "skin-gut" or "skin-brain" axes. Studies on the microbiome in skin disease have typically relied on 16S rRNA gene sequencing methods, which cannot provide accurate information about species or strains of microorganisms on the skin. However, advancing technologies, including metagenomics and other functional 'omic' approaches, have great potential to provide more comprehensive and detailed information about the skin microbiome in health and disease. Additionally, inter-species and multi-kingdom interactions can cause cascading shifts towards dysbiosis and are crucial but yet-to-be-explored aspects of many skin disorders. Better understanding these complex dynamics will require meta-omic studies complemented with experiments and clinical trials to confirm function. Evolving how we profile the skin microbiome alongside technological advances is essential to exploring such relationships. This review presents the current and emerging methods and their findings for profiling skin microbes to advance our understanding of the microbiome in skin disease.

The Imprint of Exposome on the Development of Atopic Dermatitis across the Lifespan: A Narrative Review

Atopic dermatitis (AD) is a chronic inflammatory skin condition that affects more than 200 million people worldwide, including up to 20% of children and 10% of the adult population. Although AD appears frequently in childhood and often continues into adulthood, about 1 in 4 adults develop the adult-onset disease. The prenatal period, early childhood, and adolescence are considered critical timepoints for the development of AD when the exposome results in long-lasting effects on the immune system. The exposome can be defined as the measure of all the exposures of an individual during their lifetime and how these exposures relate to well-being. While genetic factors could partially explain AD onset, multiple external environmental exposures (external exposome) in early life are implicated and are equally important for understanding AD manifestation. In this review, we describe the conceptual framework of the exposome and its relevance to AD from conception and across the lifespan. Through a spatiotemporal lens that focuses on the multi-level phenotyping of the environment, we highlight a framework that embraces the dynamic complex nature of exposome and recognizes the influence of additive and interactive environmental exposures. Moreover, we highlight the need to understand the developmental origins of AD from an age-related perspective when studying the effects of the exposome on AD, shifting the research paradigm away from the per se categorized exposome factors and beyond clinical contexts to explore the trajectory of age-related exposome risks and hence future preventive interventions.

The dynamic balance of the skin microbiome across the lifespan

For decades research has centered on identifying the ideal balanced skin microbiome that prevents disease and on developing therapeutics to foster this balance. However, this single idealized balance may not exist. The skin microbiome changes across the lifespan. This is reflected in the dynamic shifts of the skin microbiome's diverse, inter-connected community of microorganisms with age. While there are core skin microbial taxa, the precise community composition for any individual person is determined by local skin physiology, genetics, microbe-host interactions, and microbe-microbe interactions. As a key interface with the environment, the skin surface and its appendages are also constantly exchanging microbes with close personal contacts and the environment. Hormone fluctuations and immune system maturation also drive age-dependent changes in skin physiology that support different microbial community structures over time. Here, we review recent insights into the factors that shape the skin microbiome throughout life. Collectively, the works summarized within this review highlight how, depending on where we are in lifespan, our skin supports robust microbial communities, while still maintaining microbial features unique to us. This review will also highlight how disruptions to this dynamic microbial balance can influence risk for dermatological diseases as well as impact lifelong health.

The Role of the Cutaneous Mycobiome in Atopic Dermatitis

Atopic dermatitis is a chronic inflammatory skin disorder characterized by eczematous lesions, itch, and a significant deterioration in the quality of life. Recently, microbiome dysbiosis has been implicated in the pathogenesis of atopic dermatitis. Changes in the fungal microbiome (also termed mycobiome) appear to be an important factor influencing the clinical picture of this entity. This review summarizes the available insights into the role of the cutaneous mycobiome in atopic dermatitis and the new research possibilities in this field. The prevalence and characteristics of key fungal species, the most important pathogenesis pathways, as well as classic and emerging therapies of fungal dysbiosis and infections complicating atopic dermatitis, are presented.

Potential of Tamanu (Calophyllum inophyllum) Oil for Atopic Dermatitis Treatment

Tamanu oil, derived from the nut of Calophyllum inophyllum L., has been traditionally used to treat various skin-related ailments. In recent years, this oil is increasingly gaining popularity as researchers continue to search for novel natural alternative therapies for various skin diseases. There have been a number of in vitro and in vivo studies investigating various skin-active properties of tamanu oil, and it has been proven to have potent anti-inflammatory, antioxidant, antimicrobial, analgesic, and even wound-healing abilities. These properties make tamanu oil an especially interesting candidate for the treatment of atopic dermatitis (AD). This multifaceted disease is marked by the disruption of the skin barrier function, chronic inflammation, and skin microbiome dysbiosis with limited treatment options, which is free from adverse events and inexpensive, making it desperate for a new treatment option. In this review, we examine previous in vitro and in vivo studies on AD-relevant pharmacological properties of tamanu oil in order to evaluate the potential of tamanu oil as a novel treatment option for AD.