The microbiome extends to subepidermal compartments of normal skin

The gut-skin axis: a bi-directional, microbiota-driven relationship with therapeutic potential

This review explores the emerging term "gut-skin axis" (GSA), describing the bidirectional signaling that occurs between the skin and the gastrointestinal tract under both homeostatic and disease conditions. Central to GSA communication are the gut and skin microbiota, the microbial communities that colonize these barrier surfaces. By influencing diverse host pathways, including innate immune, vitamin D receptor, and Aryl hydrocarbon receptor signaling, a balanced microbiota contributes to both tissue homeostasis and host defense. In contrast, microbiota imbalance, or dysbiosis at one site, can lead to local barrier dysfunction, resulting in the activation of signaling pathways that can disrupt tissue homeostasis at the other site, potentially leading to inflammatory skin conditions such as atopic dermatitis and psoriasis, or gut diseases like Inflammatory Bowel Disease. To date, most research on the GSA has examined the impact of the gut microbiota and diet on skin health, but recent studies show that exposing the skin to ultraviolet B-light can beneficially modulate both the gut microbiome and intestinal health. Thus, despite the traditional focus of clinicians and researchers on these organ systems as distinct, the GSA offers new opportunities to better understand the pathogenesis of cutaneous and gastrointestinal diseases and promote health at both sites.

Transcatheter aortic valve implantation: Association between skin flora and infective endocarditis?

BACKGROUND

Infective endocarditis is a rare but severe complication that may arise following transcatheter aortic valve implantation. Recent advances in microbiological epidemiology have highlighted staphylococci and enterococci as the primary pathogens involved.

AIM

To investigate the prevalence of these bacteria in patients' cutaneous flora before and after transcatheter aortic valve implantation procedures, and to assess the implications for antibiotic prophylaxis recommendations.

METHODS

A single-centre prospective epidemiological study was conducted, enrolling patients admitted consecutively for transcatheter aortic valve implantation procedures between June 2021 and February 2022. Cutaneous samples were obtained from each patient at the puncture site of the transcatheter aortic valve implantation procedure, before and after skin detersion, and from operator hands after skin detersion.

RESULTS

One hundred patients were included, with a mean age of 82±6.1years, a male-to-female ratio of 0.48 and a mean body mass index of 29±4.4kg/m2. Before skin detersion, cutaneous samples were positive in 58 patients; among them were coagulase-negative staphylococci (n=48, 82%, 95% confidence interval 71-91%), enterococci (n=12, 21%, 95% confidence interval: 11-33%), Staphylococcus aureus (n=2, 3%, 95% confidence interval 0-12%) and Enterobacteriaceae (n=4, 7%, 95% confidence interval: 2-17%).

CONCLUSIONS

Enterococci are frequently present in patients' cutaneous flora at the puncture site before skin detersion, suggesting a potential source for infective endocarditis after transcatheter aortic valve implantation. These findings support considering amoxicillin-clavulanate as antibiotic prophylaxis before transcatheter aortic valve implantation procedures to mitigate the risk of infective endocarditis associated with enterococcal colonization.

Pathophysiology and Prevention of Ventriculostomy-Related Infections: A Review

This qualitative review aims to summarize current knowledge on ventriculostomy-related infection (VRI) pathophysiology and its prevention. VRI generally occurs at day 10, mainly because of Gram-positive cocci , after a cerebrospinal fluid leak. Skin microbiota and biofilm seem to play a major role in VRI pathogenesis. Colonization of external ventricular drain by biofilm is universal and occurs quickly after catheter insertion. However, pathogens from the skin are more often associated with VRI than commensal bacteria. A review of proposed preventive measures shows that none has proven to be fully efficient. Periprocedural and prolonged systemic prophylactic antimicrobials have not shown to prevent VRIs and may promote the emergence of more resistant or pathogenic strains. Antimicrobial and silver-impregnated external ventricular drains, although promising, have not demonstrated preventive effects and may modify bacterial ecology. These results are consistent with the proposed pathophysiology. Finally, we will present a few propositions for future research that may help in improving our knowledge and thus better prevent VRIs. Until then, given the available data, limiting the duration of ventricular drainage may be the most attainable option to prevent VRIs.

Allergens in Atopic Dermatitis

Atopic dermatitis (AD) is a chronic inflammatory skin disease with a complex relationship to allergens. While AD itself is not an allergic reaction and does not necessarily involve allergen sensitization, AD patients show higher rates of sensitization to food and inhalant allergens compared to the general population. Recent evidence refining the "dual allergen exposure hypothesis" demonstrates that early oral exposure to allergens through an intact gastrointestinal barrier typically promotes tolerance, while exposure through compromised skin or respiratory barriers often leads to sensitization. Therefore, the impaired skin barrier function in AD patients increases the risk of transcutaneous sensitization and may interfere with oral tolerance development. Interestingly, AD patients' sensitivity to contact allergens (such as metals and fragrances) is not necessarily higher than that of the general population, which may be related to the inherent properties of these allergens. Personalized allergen testing can help guide appropriate allergen avoidance and reintroduction strategies in AD management. The insights into optimal allergen exposure conditions have also expanded the potential applications of allergen-specific immunotherapy in preventing AD onset in high-risk populations and halting the atopic march.

Skin Microbiota and Pathological Scars: A Bidirectional Two-Sample Mendelian Randomization Study

BACKGROUND

Pathological scars (PSs), resulting from abnormal skin repair, chronic inflammation, and fibrosis, affect millions of people. Previous studies have demonstrated that skin microbiota (SM) plays a role in cutaneous inflammation and healing, but the interplay between PSs and SM remains unclear yet.

OBJECTIVE

To investigate the causal associations between SM and two specific PSs: hypertrophic scars (HSs) and keloids.

METHODS

A bidirectional two-sample mendelian randomization (MR) analysis using genetic data for SM, HS, and keloids was conducted. The random-effects inverse variance weighted (IVW) method was used as the primary approach, along with multiple MR methods. False discovery rate (FDR) correction was employed to address multiple testing.

RESULTS

In forward analysis, the family Moraxellaceae and order Pseudomonadales exhibited the same significant protective effects on keloids (odds ratio [OR]: 0.849, 95% confidence interval [CI]: 0.770-0.935, q2 = 0.03626). The class Betaproteobacteria (OR: 0.938, 95% CI: 0.894-0.985, q1 = 0.01965) and genus Bacteroides (OR: 0.928, 95% CI: 0.884-0.973, q1 = 0.00889) each demonstrated a suggestive protective effect on HSs and keloids, respectively. Some limited evidence suggested that order Actinomycetales contributes to an increased risk of keloids. In reverse analysis, keloids were found to have negative effects on the class Gammaproteobacteria with limited evidence. There was no detectable evidence of horizontal pleiotropy or heterogeneity.

CONCLUSION

This study provided evidence for the causalities between SM and PSs, which laid foundation for furthering clinical practice and research of microorganism-skin interaction.

Bidirectional Mendelian Randomization Analysis to Study the Relationship Between Human Skin Microbiota and Radiation-Induced Skin Toxicity

Radiation-induced skin toxicity, resulting from ionizing or nonionizing radiation, is a common skin disorder. However, the underlying relationship between skin microbiota and radiation-induced skin toxicity remains largely unexplored. Herein, we uncover the microbiota-skin interaction based on a genome-wide association study (GWAS) featuring 150 skin microbiota and three types of skin microenvironment. Summary datasets of human skin microbiota were extracted from the GWAS catalog database, and summary datasets of radiation-induced skin toxicity from the FinnGen biobank. Mendelian Randomization (MR) analysis was leveraged to sort out the causal link between skin microbiota and radiation-induced skin toxicity. We identified 33 causal connections between human skin microbiota and radiation-induced skin toxicity, including 19 positive and 14 negative causative directions. Among these potential associations, the genus Staphylococcus could serve as a common risk factor for radiation-induced skin toxicity, especially for radiodermatitis. And Streptococcus salivarius was identified as a potential protective factor against radiation-induced skin toxicity. Additional analysis indicated no pleiotropy, heterogeneity, or reverse causal relationship in the results. We comprehensively assessed potential associations of skin microbiota with radiation-induced skin toxicity and identified several suggestive links. Our results provide promising targets for the prevention and treatment of radiation-induced skin toxicity.

Genetic Causal Association Between Skin Microbiota and Biological Aging: Evidence From a Mendelian Randomization Analysis

BACKGROUND

The skin microbiota, a complex community of microorganisms residing on the skin, plays a crucial role in maintaining skin health and overall homeostasis. Recent research has suggested that alterations in the composition and function of the skin microbiota may influence the aging process. However, the causal relationships between specific skin microbiota and biological aging remain unclear. Mendelian randomization (MR) analysis provides a powerful tool to explore these causal links by utilizing genetic variants as instrumental variables, thereby minimizing confounding factors and reverse causality that often complicate observational studies.

METHODS

We utilized a two-sample MR approach with population-based cross-sectional data from two German cohorts, KORA FF4 (n = 324) and PopGen (n = 273). In total, GWAS summary data from 1656 skin samples and datasets on accelerated biological age were analyzed to investigate the causal relationship between skin microbiota and accelerated biological aging. The primary analysis was performed using the inverse variance weighted (IVW) method with random effects and was further supported by MR-Egger regression, Cochran's Q test, and a range of sensitivity analyses.

RESULTS

The MR analysis revealed that for biological age acceleration (BioageAccel), the IVW analysis identified protective effects from certain skin microbiota, including Alphaproteobacteria_Dry (p = 0.046), Asv033_sebaceous (p = 0.043), Burkholderiales_Moist (p = 0.008), and Proteobacteria_Moist (p = 0.042). Similar protective effects were observed for Burkholderiales_Moist (p = 0.045) and Proteobacteria_Moist (p = 0.012) in the weighted median analysis. In contrast, Paracoccus_Moist (p = 0.013) and Proteobacteria_Sebaceous (p = 0.005) were associated with accelerated aging. When using PhenoAge acceleration as the outcome, the IVW analysis linked skin microbiota like Asv005_Dry (p = 0.026), ASV039_Dry (p = 0.003), Betaproteobacteria_Sebaceous (p = 0.038), and Chryseobacterium_Moist (p = 0.013) with accelerated aging. The weighted median analysis supported these findings and also identified protective effects from ASV011_Dry (p = 0.021), ASV023_Dry (p = 0.040), Bacteroidales_Dry (p = 0.022), Enhydrobacter_Moist (p = 0.038), Proteobacteria_Moist (p = 0.002), and Rothia_Moist (p = 0.038).

CONCLUSIONS

This two-sample MR study reveals potential causal relationships between skin microbiota and aging. However, to confirm these findings, further randomized controlled trials (RCTs) are necessary.

Topical Mupirocin Treatment Reduces Interferon and Myeloid Signatures in Cutaneous Lupus Erythematous Lesions Through Targeting of Staphyloccal Species

OBJECTIVE

Cutaneous lupus erythematosus (CLE) is an inflammatory skin manifestation of systemic lupus erythematosus. Type I interferons (IFNs) promote inflammatory responses and are elevated in CLE lesions. We recently reported that CLE lesions are frequently colonized with Staphylococcus aureus. Here, we follow up via a proof-of-concept study to investigate whether type I IFN and inflammatory gene signatures in CLE lesions can be modulated with mupirocin, a topical antibiotic treatment against S aureus-mediated skin infections.

METHODS

Participants with active CLE lesions (n = 12) were recruited and randomized into a week of topical treatment with either 2% mupirocin or petroleum jelly vehicle. Paired samples were collected before and after seven days of treatment to assess microbial lesional skin responses. Microbial samples from nares and lesional skin were used to determine baseline and posttreatment Staphylococcus abundance and microbial community profiles by 16S ribosomal RNA gene sequencing. Inflammatory responses were evaluated by bulk RNA sequencing of lesional skin biopsies.

RESULTS

We identified 173 differentially expressed genes in CLE lesions after topical mupirocin treatment. Decreased lesional Staphylococcus burden correlated with decreased IFN pathway signaling and inflammatory gene expression and barrier dysfunction. Interestingly, mupirocin treatment lowered skin monocyte levels, and this mupirocin-associated depletion of monocytes correlated with decreased inflammatory gene expression.

CONCLUSION

Mupirocin treatment decreased lesional Staphylococcus, and this correlated with decreased IFN signaling and inflammatory gene expression. This study suggests a topical antibiotic could be employed to decrease lupus skin inflammation and type I IFN responses by reducing Staphylococcus colonization.

Microenvironmental host-microbe interactions in chronic inflammatory skin diseases

Several microbiome studies have recently demonstrated microbial dysbiosis in various chronic inflammatory skin diseases, and it is considered an important role in the pathogenesis. Although the role of skin dysbiosis in inflammatory skin diseases is debatable, the local microenvironment is considered essential concerning compositional changes and functional alterations of the skin microbiota. Indeed, various local nutrients (e.g., lipids), pH values, water, oxygen, and antimicrobial peptides may affect the level of skin dysbiosis in these skin diseases. In particular, in atopic dermatitis and hidradenitis suppurativa, significant changes in skin dysbiosis have been associated with local aberrant host immune changes. In this review, the potential pathogenic crosstalk between the host and the microbiota is reviewed in relation to the physical, chemical, and biological microenvironments of various chronic inflammatory skin diseases.

Regulatory Standard for Determining Preoperative Skin Preparation Efficacy Underreports True Dermal Bioburden in a Porcine Model

Medical device companies and regulatory bodies rely on a nondestructive bacterial sampling technique specified by the American Society for Testing and Materials (ASTM E1173-15) to test preoperative skin preparations (PSPs). Despite the widespread use of PSPs, opportunistic skin-flora pathogens remain the most significant contributor to surgical site infections, suggesting that the ASTM testing standard may be underreporting true dermal bioburden. We hypothesized that ASTM E1173-15 may fail to capture deep skin-dwelling flora. To test this hypothesis, we applied ASTM E1173-15 and a full-thickness skin sampling technique, which we established previously through application to the backs of seven pigs (Yorkshire/Landrace hybrid) following a clinically used PSP (4% chlorhexidine gluconate). The results showed that samples quantified using the full-thickness skin method consistently cultured more bacteria than the ASTM standard, which principally targeted surface-dwelling bacteria. Following PSP, the ASTM standard yielded 1.05 ± 0.24 log10 CFU/cm2, while the full-thickness tissue method resulted in 3.24 ± 0.24 log10 CFU/cm2, more than a 2 log10 difference (p < 0.001). Immunofluorescence images corroborated the data, showing that Staphylococcus epidermidis was present in deep skin regions with or without PSP treatment. Outcomes suggested that a full-thickness sampling technique may better evaluate PSP technologies as it resolves bioburdens dwelling in deeper skin regions.

The Central Roles of Keratinocytes in Coordinating Skin Immunity

The function of keratinocytes (KCs) to form a barrier and produce cytokines is well-known, but recent progress has revealed many different roles for KCs in regulation of skin immunity. In this review, we provide an update on the current understanding of how KCs communicate with microbes, immunocytes, neurons, and other cells to form an effective immune barrier. We catalog the large list of genes and metabolites of KCs that participate in host defense and discuss the mechanisms of immune crosstalk, addressing how KCs simultaneously form a physical barrier, communicate with fibroblasts, and control immune signals. Overall, the signals sent and received by KCs are an exciting group of therapeutic targets to explore in the treatment of dermatologic disorders.

Microbial imbalance in Darier disease: Dominance of various staphylococcal species and absence of Cutibacteria

Darier disease (DD) is a rare autosomal dominant genodermatosis characterized by erythematous papules and plaques mainly involving sebaceous areas, such as the face, chest and back. Skin microbiome plays an essential role in maintaining skin homeostasis. A disturbed skin microbiome may contribute to the exacerbation of DD. We investigated the bacterial composition of two predilectional sites in DD patients and healthy individuals. We also measured the microbiome composition of deeper skin layers, where diversity was significantly reduced compared to the superficial layer of the skin from the same area. The microbiome of DD patients at lesional sites differed from that of non-lesional skin areas; moreover, non-lesional sites were different from those of the controls. Lesional areas were dominated by Staphylococcus species, such as S. aureus, S. epidermidis, S. hominis, S. sciuri, and S. equorum. However, levels of Cutibacterium acnes (formerly Propionibacterium acnes) and C. acnes subspecies defendens were significantly lower in lesional sites than in non-lesional sites. A significant decrease was measured in the levels of these two bacteria between non-lesional and control samples. Our findings may indicate that alterations in the skin microbiome could contribute to the inflammation of skin lesions in DD.

Decoding skin mysteries: Unveiling the link between microbiota and keloid scars through a Mendelian randomization study

The cause of keloids remains unclear, but studies suggest a link between skin microbiota and keloid formation. However, the causal relationship has not been confirmed. This study utilized Genome-Wide Association Studies (GWAS) data from 2 population-based German cohorts, comprising a total of 1656 skin samples. To bolster the reliability of our results, we incorporated GWAS data from 3 keloid cohorts, encompassing 2555 patients and 870,556 controls (GWAS ID: keloid1, ebi-a-GCST90018874; keloid2, bbj-a-131; keloid3, ebi-a-GCST90018654). Subsequently, we employed bidirectional 2-sample Mendelian randomization (MR) analysis to probe the causal relationship between the variables. The primary method employed was the inverse-variance weighted (IVW) method, supported by heterogeneity analysis, horizontal pleiotropy testing, outlier detection, and "leave-one-out" sensitivity analysis. By synthesizing the results from 3 groups of MR analyses, we discovered a negative causal association between a.ASV063 [Finegoldia (unc.)] located on the volar forearm and keloid disease (IVW (keloid1) odds ratio (OR): 0.939, 95% confidence interval (CI): 0.886-0.994, P = .032; IVW (keloid2) OR: 0.897, 95% CI: 0.813-0.990, P = .031; IVW (keloid3) OR: 0.900, 95% CI: 0.825-0.981, P = .017). Similarly, a negative causal relationship may also exist between the genus: Bacteroides from the antecubital fossa and keloid disease (IVW (keloid1) OR: 0.928, 95% CI: 0.884-0.973, P = .002; IVW (keloid2) OR: 0.891, 95% CI: 0.820-0.968, P = .007; IVW (keloid3) OR: 0.918, 95% CI: 0.849-0.992, P = .030). Additionally, no reverse causation was found, with all analyses showing no signs of horizontal pleiotropy or heterogeneity. This study offers new insights for the prevention and treatment of keloids.

Sample collecting methods for bacterial community structure analysis of scalp hair: non-invasive swabbing versus intrusive hair shaft cutting

Human skin samples for microbiome analysis are traditionally collected using a non-invasive swabbing method. Here, we compared the differences in bacterial community structures on scalp hair and scalps with samples collected using non-invasive swabbing and cutting/removal of scalp hair in 12 individuals. Hair-related samples, such as hair shafts and hair swabs, had significantly higher alpha diversity than scalp swab samples, whereas there were no significant differences between hair shafts and hair swabs. The relative abundances of the three major phyla and five major operational taxonomic units were not significantly different between the hair shaft and hair swab samples. The principal coordinate analysis plots based on weighted UniFrac distances were grouped into two clusters: samples from hair-related areas and scalp swabs, and there were significant differences only between samples from hair-related areas and scalp swabs. In addition, a weighted UniFrac analysis revealed that the sampling site-based category was a statistical category but not a hair sampling method-based category. These results suggest that scalp hair bacteria collected using non-invasive swab sampling were comparable to those collected cutting/removal of scalp hair.

SkinCom, a synthetic skin microbial community, enables reproducible investigations of the human skin microbiome

Existing models of the human skin have aided our understanding of skin health and disease. However, they currently lack a microbial component, despite microbes' demonstrated connections to various skin diseases. Here, we present a robust, standardized model of the skin microbial community (SkinCom) to support in vitro and in vivo investigations. Our methods lead to the formation of an accurate, reproducible, and diverse community of aerobic and anaerobic bacteria. Subsequent testing of SkinCom on the dorsal skin of mice allowed for DNA and RNA recovery from both the applied SkinCom and the dorsal skin, highlighting its practicality for in vivo studies and -omics analyses. Furthermore, 66% of the responses to common cosmetic chemicals in vitro were in agreement with a human trial. Therefore, SkinCom represents a valuable, standardized tool for investigating microbe-metabolite interactions and facilitates the experimental design of in vivo studies targeting host-microbe relationships.

Microbiological insights and dermatological applications of live biotherapeutic products

As our understanding of dermatological conditions advances, it becomes increasingly evident that traditional pharmaceutical interventions are not universally effective. The intricate balance of the skin microbiota plays a pivotal role in the development of various skin conditions, prompting a growing interest in probiotics, or live biotherapeutic products (LBPs), as potential remedies. Specifically, the topical application of LBPs to modulate bacterial populations on the skin has emerged as a promising approach to alleviate symptoms associated with common skin conditions. This review considers LBPs and their application in addressing a wide spectrum of dermatological conditions with particular emphasis on three key areas: acne, atopic dermatitis, and wound healing. Within this context, the critical role of strain selection is presented as a pivotal factor in effectively managing these dermatological concerns. Additionally, the review considers formulation challenges associated with probiotic viability and proposes a personalised approach to facilitate compatibility with the skin's unique microenvironment. This analysis offers valuable insights into the potential of LBPs in dermatological applications, underlining their promise in reshaping the landscape of dermatological treatments while acknowledging the hurdles that must be overcome to unlock their full potential.

Genome-wide transcription response of Staphylococcus epidermidis to heat shock and medically relevant glucose levels

Skin serves as both barrier and interface between body and environment. Skin microbes are intermediaries evolved to respond, transduce, or act in response to changing environmental or physiological conditions. We quantified genome-wide changes in gene expression levels for one abundant skin commensal, Staphylococcus epidermidis, in response to an internal physiological signal, glucose levels, and an external environmental signal, temperature. We found 85 of 2,354 genes change up to ~34-fold in response to medically relevant changes in glucose concentration (0-17 mM; adj p ≤0.05). We observed carbon catabolite repression in response to a range of glucose spikes, as well as upregulation of genes involved in glucose utilization in response to persistent glucose. We observed 366 differentially expressed genes in response to a physiologically relevant change in temperature (37-45°C; adj p ≤ 0.05) and an S. epidermidis heat-shock response that mostly resembles the heat-shock response of related staphylococcal species. DNA motif analysis revealed CtsR and CIRCE operator sequences arranged in tandem upstream of dnaK and groESL operons. We identified and curated 38 glucose-responsive genes as candidate ON or OFF switches for use in controlling synthetic genetic systems. Such systems might be used to instrument the in-situ skin microbiome or help control microbes bioengineered to serve as embedded diagnostics, monitoring, or treatment platforms.

The extracellular serine protease from Staphylococcus epidermidis elicits a type 2-biased immune response in atopic dermatitis patients

Background

Atopic dermatitis (AD) is a chronic, relapsing inflammatory skin disease with skin barrier defects and a misdirected type 2 immune response against harmless antigens. The skin microbiome in AD is characterized by a reduction in microbial diversity with a dominance of staphylococci, including Staphylococcus epidermidis (S. epidermidis).

Objective

To assess whether S. epidermidis antigens play a role in AD, we screened for candidate allergens and studied the T cell and humoral immune response against the extracellular serine protease (Esp).

Methods

To identify candidate allergens, we analyzed the binding of human serum IgG4, as a surrogate of IgE, to S. epidermidis extracellular proteins using 2-dimensional immunoblotting and mass spectrometry. We then measured serum IgE and IgG1 binding to recombinant Esp by ELISA in healthy and AD individuals. We also stimulated T cells from AD patients and control subjects with Esp and measured the secreted cytokines. Finally, we analyzed the proteolytic activity of Esp against IL-33 and determined the cleavage sites by mass spectrometry.

Results

We identified Esp as the dominant candidate allergen of S. epidermidis. Esp-specific IgE was present in human serum; AD patients had higher concentrations than controls. T cells reacting to Esp were detectable in both AD patients and healthy controls. The T cell response in healthy adults was characterized by IL-17, IL-22, IFN-γ, and IL-10, whereas the AD patients' T cells lacked IL-17 production and released only low amounts of IL-22, IFN-γ, and IL-10. In contrast, Th2 cytokine release was higher in T cells from AD patients than from healthy controls. Mature Esp cleaved and activated the alarmin IL-33.

Conclusion

The extracellular serine protease Esp of S. epidermidis can activate IL-33. As an antigen, Esp elicits a type 2-biased antibody and T cell response in AD patients. This suggests that S. epidermidis can aggravate AD through the allergenic properties of Esp.

Human neutrophils drive skin autoinflammation by releasing interleukin (IL)-26

Autoinflammation is a sterile inflammatory process resulting from increased neutrophil infiltration and overexpression of IL-1 cytokines. The factors that trigger these events are, however, poorly understood. By investigating pustular forms of psoriasis, we show that human neutrophils constitutively express IL-26 and abundantly release it from granular stores upon activation. In pustular psoriasis, neutrophil-derived IL-26 drives the pathogenic autoinflammation process by inducing the expression of IL-1 cytokines and chemokines that further recruit neutrophils. This occurs via activation of IL-26R in keratinocytes and via the formation of complexes between IL-26 and microbiota DNA, which trigger TLR9 activation of neutrophils. Thus our findings identify neutrophils as an important source of IL-26 and point to IL-26 as the key link between neutrophils and a self-sustaining autoinflammation loop in pustular psoriasis.

The role of the skin microbiome in wound healing

The efficient management of skin wounds for rapid and scarless healing represents a major clinical unmet need. Nonhealing skin wounds and undesired scar formation impair quality of life and result in high healthcare expenditure worldwide. The skin-colonizing microbiota contributes to maintaining an intact skin barrier in homeostasis, but it also participates in the pathogenesis of many skin disorders, including aberrant wound healing, in many respects. This review focuses on the composition of the skin microbiome in cutaneous wounds of different types (i.e. acute and chronic) and with different outcomes (i.e. nonhealing and hypertrophic scarring), mainly based on next-generation sequencing analyses; furthermore, we discuss the mechanistic insights into host-microbe and microbe-microbe interactions during wound healing. Finally, we highlight potential therapeutic strategies that target the skin microbiome to improve healing outcomes.

Eradication of skin microbiota restores cytokine production and release in polymorphic light eruption

Polymorphic light eruption (PLE) has been mechanistically linked to cytokine abnormalities. Emerging preclinical evidence posits the skin microbiome as a critical modulator of ultraviolet (UV)-induced cytokine expression, thereby influencing subsequent immune responses. This intricate relationship remains underexplored in the context of PLE. Hence, we investigated the differential responses between disinfected and non-disinfected skin following both single and repetitive exposures to solar-simulated UV radiation in patients with PLE. An experimental, half-body pilot study was conducted involving six PLE patients and 15 healthy controls. Participants' skin was exposed to single and multiple doses of solar-simulated UV radiation, both in disinfected and in non-disinfected skin areas. The co-primary outcomes were PLE score and cytokine expression in blister fluid analysed through OLINK proteomic profiling. Secondary outcomes were erythema, pigmentation, induction of apoptotic cells in vacuum-generated suction blisters, and density of infiltrate in skin biopsies of PLE patients. Among the 71 cytokines analysed, baseline expression levels of 20 specific cytokines-integral to processes such as apoptosis, inflammation, immune cell recruitment, cellular growth, and differentiation-were significantly impaired in PLE patients compared with healthy controls. Notably, skin disinfection reversed the observed cytokine imbalances following a single UV exposure at the minimal erythema dose (MED) level and exhibited even more pronounced effects after multiple UV exposures. However, no significant differences were evident in PLE score, erythema, pigmentation, or rates of apoptotic cell induction upon UV radiation. These findings provide evidence for UV-driven cytokine regulation by the skin microbiota and imply microbiome involvement in the PLE immune response.

A Staphylococcus epidermidis strain inhibits the uptake of Staphylococcus aureus derived from atopic dermatitis skin into the keratinocytes

BACKGROUND

Various bacterial species form a microbiome in the skin. In the past, dead Staphylococcus aureus derived from atopic dermatitis (AD) are taken up by keratinocytes; however, whether live S. aureus can be taken up by keratinocytes is unknown.

OBJECTIVE

This study aimed to examine whether live AD strains of S. aureus internalize into the keratinocytes and how the internalization changes under conditions in which other bacterial species including S. epidermidis are present.

METHODS

HaCaT cells were cultured with live S. aureus and S. epidermidis (live or heat-treated) or their culture supernatants. After coculture, the change in the amount of S. aureus in the cytoplasm of HaCaT cells was analyzed using, a high-throughput imaging system, Opera Phenix™.

RESULTS

Live S. aureus were taken up in the cytoplasm of HaCaT cells. Coculturing live S. aureus with live S. epidermidis or the culture supernatants decreased the abundance of S. aureus in the cytoplasm. The heat-treated culture supernatants of live S. epidermidis or culture supernatants of other S. strains did not decrease the abundance of S. aureus in the cytoplasm.

CONCLUSION

Live S. aureus was internalized into the cytoplasm of HaCaT cells as does heat-treated S. aureus. In addition, the heat-sensitive substances secreted by coculture with S. epidermidis and keratinocytes inhibited the uptake of S. aureus by keratinocytes.

Microbiome: Role in Inflammatory Skin Diseases

As the body's largest organ, the skin harbors a highly diverse microbiota, playing a crucial role in resisting foreign pathogens, nurturing the immune system, and metabolizing natural products. The dysregulation of human skin microbiota is implicated in immune dysregulation and inflammatory responses. This review delineates the microbial alterations and immune dysregulation features in common Inflammatory Skin Diseases (ISDs) such as psoriasis, rosacea, atopic dermatitis(AD), seborrheic dermatitis(SD), diaper dermatitis(DD), and Malassezia folliculitis(MF).The skin microbiota, a complex and evolving community, undergoes changes in composition and function that can compromise the skin microbial barrier. These alterations induce water loss and abnormal lipid metabolism, contributing to the onset of ISDs. Additionally, microorganisms release toxins, like Staphylococcus aureus secreted α toxins and proteases, which may dissolve the stratum corneum, impairing skin barrier function and allowing entry into the bloodstream. Microbes entering the bloodstream activate molecular signals, leading to immune disorders and subsequent skin inflammatory responses. For instance, Malassezia stimulates dendritic cells(DCs) to release IL-12 and IL-23, differentiating into a Th17 cell population and producing proinflammatory mediators such as IL-17, IL-22, TNF-α, and IFN-α.This review offers new insights into the role of the human skin microbiota in ISDs, paving the way for future skin microbiome-specific targeted therapies.

A multi-study analysis enables identification of potential microbial features associated with skin aging signs

Introduction: During adulthood, the skin microbiota can be relatively stable if environmental conditions are also stable, yet physiological changes of the skin with age may affect the skin microbiome and its function. The microbiome is an important factor to consider in aging since it constitutes most of the genes that are expressed on the human body. However, severity of specific aging signs (one of the parameters used to measure "apparent" age) and skin surface quality (e.g., texture, hydration, pH, sebum, etc.) may not be indicative of chronological age. For example, older individuals can have young looking skin (young apparent age) and young individuals can be of older apparent age. Methods: Here we aim to identify microbial taxa of interest associated to skin quality/aging signs using a multi-study analysis of 13 microbiome datasets consisting of 16S rRNA amplicon sequence data and paired skin clinical data from the face. Results: We show that there is a negative relationship between microbiome diversity and transepidermal water loss, and a positive association between microbiome diversity and age. Aligned with a tight link between age and wrinkles, we report a global positive association between microbiome diversity and Crow's feet wrinkles, but with this relationship varying significantly by sub-study. Finally, we identify taxa potentially associated with wrinkles, TEWL and corneometer measures. Discussion: These findings represent a key step towards understanding the implication of the skin microbiota in skin aging signs.

Suppression of UVB-Induced MMP-1 Expression in Human Skin Fibroblasts Using Lysate of Lactobacillus iners Derived from Korean Women's Skin in Their Twenties

The process of skin aging is intricate, involving intrinsic aging, influenced by internal factors, and extrinsic aging, mainly caused by exposure to UV radiation, resulting in photoaging. Photoaging manifests as skin issues such as wrinkles and discoloration. The skin microbiome, a diverse community of microorganisms on the skin's surface, plays a crucial role in skin protection and can be affected by factors like humidity and pH. Probiotics, beneficial microorganisms, have been investigated for their potential to enhance skin health by regulating the skin microbiome. This can be accomplished through oral probiotics, impacting the gut-skin axis, or topical applications introducing live bacteria to the skin. Probiotics mitigate oxidative stress, suppress inflammation, and maintain the skin's extracellular matrix, ultimately averting skin aging. However, research on probiotics derived from human skin is limited, and there is no established product for preventing photoaging. The mechanism by which probiotics shield the skin microbiome and skin layers from UV radiation remains unclear. Recently, researchers have discovered Lactobacillus in the skin, with reports indicating a decrease in this microorganism with age. In a recent study, scientists isolated Lactobacillus iners KOLBM20 from the skin of individuals in their twenties and confirmed its effectiveness. A comparative analysis of genetic sequences revealed that strain KOLBM20 belongs to the Lactobacillus genus and closely relates to L. iners DSM13335(T) with a 99.20% similarity. Importantly, Lactobacillus iners KOLBM20 displayed anti-wrinkle properties by inhibiting MMP-1. This investigation demonstrated the inhibitory effect of KOLBM20 strain lysate on MMP-1 expression. Moreover, the data suggest that KOLBM20 strain lysate may prevent UVB-induced MMP-1 expression by inhibiting the activation of the ERK, JNK, and p38 signaling pathways induced by UVB. Consequently, KOLBM20 strain lysate holds promise as a potential therapeutic agent for preventing and treating skin photoaging.

A Comparison of Chlorhexidine-Alcohol and Povidone-Iodine-Alcohol on the Incidence of Surgical Site Infection

BACKGROUND

Surgical site infection (SSI) persists as a global challenge, accounting for 20%-25% of all healthcare-associated infections. The SSI rate has been reported to range from 2.5% to 41.9%. Skin preparation with acceptable antiseptic preparations has a high recommendation from the Centers for Disease Control as an SSI preventive measure.

AIM

The aim was to compare the efficacy of 10% povidone-iodine in 70% isopropyl alcohol with 2% chlorhexidine in 70% isopropyl alcohol in preventing SSI.

METHOD

This prospective randomized study included patients who were followed up for 30 days looking for SSI. Swabs were taken from wounds that developed SSI. A culture of all swabs was done.

RESULT

One hundred and fifty-three patients were recruited into the study. Overall, eight (5.23%) of the 153 patients developed SSI. The SSI rate in clean wounds was 2.6%, while the SSI rate in clean-contaminated wounds was 7.9%. No statistically significant difference was found (p=0.141) between the two groups.

A review of skin immune processes in acne

Acne vulgaris is one of the most prevalent skin conditions, affecting almost all teenagers worldwide. Multiple factors, including the excessive production of sebum, dysbiosis of the skin microbiome, disruption of keratinization within hair follicles, and local inflammation, are believed to trigger or aggravate acne. Immune activity plays a crucial role in the pathogenesis of acne. Recent research has improved our understanding of the immunostimulatory functions of microorganisms, lipid mediators, and neuropeptides. Additionally, significant advances have been made in elucidating the intricate mechanisms through which cutaneous innate and adaptive immune cells perceive and transmit stimulatory signals and initiate immune responses. However, our understanding of precise temporal and spatial patterns of immune activity throughout various stages of acne development remains limited. This review provides a comprehensive overview of the current knowledge concerning the immune processes involved in the initiation and progression of acne. Furthermore, we highlight the significance of detailed spatiotemporal analyses, including analyses of temporal dynamics of immune cell populations as well as single-cell and spatial RNA sequencing, for the development of targeted therapeutic and prevention strategies.

Emerging Role of the Mast Cell-Microbiota Crosstalk in Cutaneous Homeostasis and Immunity

The skin presents a multifaceted microbiome, a balanced coexistence of bacteria, fungi, and viruses. These resident microorganisms are fundamental in upholding skin health by both countering detrimental pathogens and working in tandem with the skin's immunity. Disruptions in this balance, known as dysbiosis, can lead to disorders like psoriasis and atopic dermatitis. Central to the skin's defense system are mast cells. These are strategically positioned within the skin layers, primed for rapid response to any potential foreign threats. Recent investigations have started to unravel the complex interplay between these mast cells and the diverse entities within the skin's microbiome. This relationship, especially during times of both balance and imbalance, is proving to be more integral to skin health than previously recognized. In this review, we illuminate the latest findings on the ties between mast cells and commensal skin microorganisms, shedding light on their combined effects on skin health and maladies.

Staphylococcus aureus Adaptation to the Skin in Health and Persistent/Recurrent Infections

Staphylococcus aureus is a microorganism with an incredible capability to adapt to different niches within the human body. Approximately between 20 and 30% of the population is permanently but asymptomatically colonized with S. aureus in the nose, and another 30% may carry S. aureus intermittently. It has been established that nasal colonization is a risk factor for infection in other body sites, including mild to severe skin and soft tissue infections. The skin has distinct features that make it a hostile niche for many bacteria, therefore acting as a strong barrier against invading microorganisms. Healthy skin is desiccated; it has a low pH at the surface; the upper layer is constantly shed to remove attached bacteria; and several host antimicrobial peptides are produced. However, S. aureus is able to overcome these defenses and colonize this microenvironment. Moreover, this bacterium can very efficiently adapt to the stressors present in the skin under pathological conditions, as it occurs in patients with atopic dermatitis or suffering chronic wounds associated with diabetes. The focus of this manuscript is to revise the current knowledge concerning how S. aureus adapts to such diverse skin conditions causing persistent and recurrent infections.

Size-dependent promotion of micro(nano)plastics on the horizontal gene transfer of antibiotic resistance genes in constructed wetlands

Constructed wetlands (CWs) have been identified as significant sources of micro(nano)plastics (MPs/NPs) and antibiotic resistance genes (ARGs) in aquatic environments. However, little is known about the impact of MPs/NPs exposure on horizontal gene transfer (HGT) of ARGs and shaping the corresponding ARG hosts' community. Herein, the contribution of polystyrene (PS) particles (control, 4 mm, 100 μm, and 100 nm) to ARG transfer was investigated by adding an engineered fluorescent Escherichia coli harboring RP4 plasmid-encoded ARGs into CWs. It was found MPs/NPs significantly promoted ARG transfer in a size-dependent manner in each CW medium (p < 0.05). The 100 μm-sized PS exhibited the most significant promotion of ARG transfer (p < 0.05), whereas 100 nm-sized PS induced limited promotion due to its inhibitory activity on microbes. The altered RP4-carrying bacterial communities suggested that MPs/NPs, especially 100 µm-PS, could recruit pathogenic and nitrifying bacteria to acquire ARGs. The increased sharing of RP4-carrying core bacteria in CW medium further suggested that ARGs can spread into CW microbiome using MPs/NPs as carriers. Overall, our results highlight the high risks of ARG dissemination induced by MPs/NPs exposure and emphasize the need for better control of plastic disposal to prevent the potential health threats.

The Gut and Skin Microbiome in Alopecia: Associations and Interventions

Objective

This review examines the current literature on the gut-skin connection in alopecia and summarizes interventions that impact hair growth by modulation of the gut or skin microbiome.

Methods

PubMed searches were done to assess studies of the gut and skin microbiome and forms of alopecia including, alopecia areata (AA), androgenic alopecia (AGA), alopecia universalis (AU), central centrifugal cicatricial alopecia (CCCA) and lichen planopilaris (LPP). Filters were applied for human and animal studies. Articles not translated to English and studies assessing supplemental therapies on alopecia were excluded.

Results

There is evidence that scalp, hair follicle, and gut microbiome alterations are associated with various types of alopecia. There is potential in the use of interventions targeting microbiome dysbiosis, including fecal transplants and probiotics.

Limitations

This field of study still requires more high-quality research and studies with larger participant populations.

Conclusion

Dysbiosis on the scalp, within the hair follicle and the gut seem to have a role in the pathophysiology of various forms of alopecia. There is evidence that interventions targeting dysbiosis may have potential in the treatment and management of hair loss. Further studies are needed to establish a direct connection and to clarify specific effects of these interventions.

Fabrication and characterisation of poly(sulfonated) and poly(sulfonic acid) dissolving microneedles for delivery of antibiotic and antifungal agents

Skin and soft tissue infections (SSTIs) arise from microbial ingress into the skin. In this study, poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (polyAMPS), which has been reported to exhibit antimicrobial properties was synthesised for the manufacture of microarray patches (MAPs). The free acid and sodium salt of polyAMPS with controlled molar masses and narrow dispersity were synthesised via reversible addition - fragmentation chain-transfer (RAFT) polymerisation reaction with a monomer conversion of over 99%, as determined by 1H NMR. The polymers were shown to be biocompatible when evaluated using a fibroblast dermal cell line while agar plating assay using cultures of C. albican demonstrated that the acid form of polyAMPS exhibited antimicrobial inhibition, which is potentiated in the presence of antimicrobial agents. The synthesised polymers were then used to fabricate dissolving MAPs, which were loaded with either ITRA or levofloxacin (LEV). The MAPs displayed acceptable mechanical resistance and punctured ex vivo skin to a depth of 600 µm. Skin deposition studies revealed that the MAPs were able to administer up to ∼ 1.9 mg of LEV (delivery efficiency: 94.7%) and ∼ 0.2 mg of ITRA (delivery efficiency: 45.9%), respectively. Collectively, the synthesis and development of this novel pharmaceutical system may offer a strategy to manage SSTIs.

S. aureus virulence factors decrease epithelial barrier function and increase susceptibility to viral infection

Individuals with atopic dermatitis (AD) are highly colonized by Staphylococcus aureus and are more susceptible to severe viral complications. We hypothesized that S. aureus secreted virulence factors may alter keratinocyte biology to enhance viral susceptibility through disruption of the skin barrier, impaired keratinocyte differentiation, and/or inflammation. To address this hypothesis, human keratinocytes were exposed to conditioned media from multiple S. aureus strains that vary in virulence factor production (USA300, HG003, and RN4220) or select purified virulence factors. We have identified the S. aureus enterotoxin-like superantigen SElQ, as a virulence factor of interest, since it is highly produced by USA300 and was detected on the skin of 53% of AD subjects (n = 72) in a study conducted by our group. Treatment with USA300 conditioned media or purified SElQ resulted in a significant increase in keratinocyte susceptibility to infection with vaccinia virus, and also significantly decreased barrier function. Importantly, we have previously demonstrated that keratinocyte differentiation influences susceptibility to viral infection, and our qPCR observations indicated that USA300 S. aureus and SElQ alter differentiation in keratinocytes. CRISPR/Cas9 was used to knock out CD40, a potential enterotoxin receptor on epithelial cells. We found that CD40 expression on keratinocytes was not completely necessary for SElQ-mediated responses, as measured by proinflammatory cytokine expression and barrier function. Together, these findings support that select S. aureus virulence factors, particularly SElQ, enhance the susceptibility of epidermal cells to viral infection, which may contribute to the increased cutaneous infections observed in individuals with AD. IMPORTANCE Staphylococcus aureus skin colonization and infection are frequently observed in individuals with atopic dermatitis. Many S. aureus strains belong to the clonal group USA300, and these strains produce superantigens including the staphylococcal enterotoxin-like Q (SElQ). Our studies highlight that SElQ may play a key role by altering keratinocyte differentiation and reducing barrier function; collectively, this may explain the AD-specific enhanced infection risk to cutaneous viruses. It is unclear what receptor mediates SElQ's effects on keratinocytes. We have shown that one putative surface receptor, CD40, was not critical for its effects on proinflammatory cytokine production or barrier function.

Microbiome dysbiosis occurred in hypertrophic scars is dominated by S. aureus colonization

Background

The mechanisms of hypertrophic scar formation and its tissue inflammation remain unknown.

Methods

We collected 33 hypertrophic scar (HS) and 36 normal skin (NS) tissues, and detected the tissue inflammation and bacteria using HE staining, Gram staining, and transmission electronic microscopy (TEM), in situ hybridization and immunohistochemistry for MCP-1, TNF-α, IL-6 and IL-8. In addition, the samples were assayed by 16S rRNA sequencing to investigate the microbiota diversity in HS, and the correlation between the microbiota and the indices of Vancouver Scar Scale(VSS)score.

Results

HE staining showed that a dramatically increased number of inflammatory cells accumulated in HS compared with NS, and an enhanced number of bacteria colonies was found in HS by Gram staining, even individual bacteria could be clearly observed by TEM. In situ hybridization demonstrated that the bacteria and inflammation cells co-localized in the HS tissues, and immunohistochemistry indicated the expression of MCP-1, TNF-α, IL-6, and IL-8 were significantly upregulated in HS than that in NS. In addition, there was a significantly different microbiota composition between HS and NS. At the phylum level, Firmicutes was significantly higher in HS than NS. At the genus level, S. aureus was the dominant species, which was significantly higher in HS than NS, and was strongly correlated with VSS indices.

Conclusion

Microbiome dysbiosis, dominated by S. aureus, occurred in HS formation, which is correlated with chronic inflammation and scar formation, targeting the microbiome dysbiosis is perhaps a supplementary way for future scar management.

Emerging Trends and Focus in Human Skin Microbiome Over the Last Decade: A Bibliometric Analysis and Literature Review

Background

Human skin microbiome is the first barrier against exogenous attack and is associated with various skin disease pathogenesis and progression. Advancements in high-throughput sequencing technologies have paved the way for a deeper understanding of this field. Based on the bibliometric analysis, this investigation aimed to identify the hotspots and future research trends associated with human skin microbiomes studied over the past decade.

Methods

The published research on skin microbiome from January 2013 to January 2023 was retrieved from the Web of Science Core Collection. Data cleaning processes to ensure robust data and the bibliometrix packages R, CiteSpace, VOSviewer, Origin, and Scimago Graphica for bibliometric and visual analyses were utilized.

Results

A total of 1629 published documents were analyzed. The overall publication trend steadily increased, with relatively fast growth in 2017 and 2020. The United States of America has the highest number of publications and citations and shows close collaborations with China and Germany. The University of California, San Diego, indicated a higher number of publications than other institutions and the fastest growth rate. The top three most publishing journals on this topic are Microorganisms, Frontiers in Microbiology, and Experimental dermatology. Gallo RL is the most influential author with the highest h- and g-index and most publications in skin microecology, followed by Grice EA and Kong HH. The top 10 most frequently used keywords in recent years included skin microbiome, microbiome, staphylococcus aureus, diversity, atopic dermatitis, skin, bacteria, infections, gut microbiota, and disease.

Conclusion

The skin microbiome is an area of research that requires continuous analysis, and even with much-achieved progress, future research will further be aided as technology develops.

Synthase-selected sorting approach identifies a beta-lactone synthase in a nudibranch symbiotic bacterium

BACKGROUND

Nudibranchs comprise a group of > 6000 marine soft-bodied mollusk species known to use secondary metabolites (natural products) for chemical defense. The full diversity of these metabolites and whether symbiotic microbes are responsible for their synthesis remains unexplored. Another issue in searching for undiscovered natural products is that computational analysis of genomes of uncultured microbes can result in detection of novel biosynthetic gene clusters; however, their in vivo functionality is not guaranteed which limits further exploration of their pharmaceutical or industrial potential. To overcome these challenges, we used a fluorescent pantetheine probe, which produces a fluorescent CoA-analog employed in biosynthesis of secondary metabolites, to label and capture bacterial symbionts actively producing these compounds in the mantle of the nudibranch Doriopsilla fulva.

RESULTS

We recovered the genome of Candidatus Doriopsillibacter californiensis from the Ca. Tethybacterales order, an uncultured lineage of sponge symbionts not found in nudibranchs previously. It forms part of the core skin microbiome of D. fulva and is nearly absent in its internal organs. We showed that crude extracts of D. fulva contained secondary metabolites that were consistent with the presence of a beta-lactone encoded in Ca. D. californiensis genome. Beta-lactones represent an underexplored group of secondary metabolites with pharmaceutical potential that have not been reported in nudibranchs previously.

CONCLUSIONS

Altogether, this study shows how probe-based, targeted sorting approaches can capture bacterial symbionts producing secondary metabolites in vivo. Video Abstract.

Oral and Topical Probiotics and Postbiotics in Skincare and Dermatological Therapy: A Concise Review

The skin microbiota is a pivotal contributor to the maintenance of skin homeostasis by protecting it from harmful pathogens and regulating the immune system. An imbalance in the skin microbiota can lead to pathological conditions such as eczema, psoriasis, and acne. The balance of the skin microbiota components can be disrupted by different elements and dynamics such as changes in pH levels, exposure to environmental toxins, and the use of certain skincare products. Some research suggests that certain probiotic strains and their metabolites (postbiotics) may provide benefits such as improving the skin barrier function, reducing inflammation, and improving the appearance of acne-prone or eczema-prone skin. Consequently, in recent years probiotics and postbiotics have become a popular ingredient in skincare products. Moreover, it was demonstrated that skin health can be influenced by the skin-gut axis, and imbalances in the gut microbiome caused by poor diet, stress, or the use of antibiotics can lead to skin conditions. In this way, products that improve gut microbiota balance have been gaining attention from cosmetic and pharmaceutical companies. The present review will focus on the crosstalk between the SM and the host, and its effects on health and diseases.

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.

Dissecting skin microbiota and microenvironment for the development of therapeutic strategies

The skin is a pivotal barrier between the human body and the environment, and is a habitat for numerous microorganisms. While host-microbiota interactions in the skin are essential for homeostasis, disturbances in microbial composition and the abnormal growth of certain bacteria are associated with various diseases. Here, we identify strains and communities of skin commensals that contribute to or impair skin barrier function. Furthermore, we discuss the skin microenvironments suitable for specific microbiota that exert therapeutic effects and suggest focus areas for the prospective development of therapeutic strategies using bacterial agents. Finally, we highlight recent efforts to treat skin diseases associated with live bacteria.

Tralokinumab treatment improves the skin microbiota by increasing the microbial diversity in adults with moderate-to-severe atopic dermatitis: Analysis of microbial diversity in ECZTRA 1, a randomized controlled trial

BACKGROUND

Atopic dermatitis (AD) is characterized by microbial dysbiosis, immune dysregulation, and an impaired skin barrier. Microbial dysbiosis in AD involves a reduction in diversity primarily driven by an increased abundance of Staphylococcus aureus. Tralokinumab, an approved treatment for adults with moderate-to-severe AD, improves the skin barrier and immune abnormalities by specifically targeting the interleukin 13 cytokine, but its impact on the skin microbiome is unknown.

OBJECTIVE

To investigate how tralokinumab affects the skin microbiome by examining the lesional skin of adults with moderate-to-severe AD from the phase 3 ECZTRA 1 trial (NCT03131648).

METHODS

Microbiome profiling, S aureus abundance, and biomarker data were assessed in a subset of ECZTRA 1 participants (S aureus abundance at baseline and week 16; microbiome profiling at baseline, and week 8/16; and serum sampling before dose and week 4/8/16/28/52).

RESULTS

Tralokinumab treatment led to increased microbial diversity, reduced S aureus abundance, and increased abundance of the commensal coagulase-negative Staphylococci.

LIMITATIONS

Limitations include a lack of S aureus abundance data at week 8, sampling site variation between participants, and possible influence from concomitant systemic antiinfectives.

CONCLUSION

Our findings indicate specific targeting of the interleukin 13 cytokine with tralokinumab can directly and/or indirectly improve microbial dysbiosis seen in AD skin.

Laser capture microdissection as a method for investigating the human hair follicle microbiome reveals region-specific differences in the bacteriome profile

OBJECTIVE

Human hair follicles (HFs) are populated by a rich and diverse microbiome, traditionally evaluated by methods that inadvertently sample the skin microbiome and/or miss microbiota located in deeper HF regions. Thereby, these methods capture the human HF microbiome in a skewed and incomplete manner. This pilot study aimed to use laser-capture microdissection of human scalp HFs, coupled with 16S rRNA gene sequencing to sample the HF microbiome and overcome these methodological limitations.

RESULTS

HFs were laser-capture microdissected (LCM) into three anatomically distinct regions. All main known core HF bacterial colonisers, including Cutibacterium, Corynebacterium and Staphylococcus, were identified, in all three HF regions. Interestingly, region-specific variations in α-diversity and microbial abundance of the core microbiome genera and Reyranella were identified, suggestive of variations in microbiologically relevant microenvironment characteristics. This pilot study therefore shows that LCM-coupled with metagenomics is a powerful tool for analysing the microbiome of defined biological niches. Refining and complementing this method with broader metagenomic techniques will facilitate the mapping of dysbiotic events associated with HF diseases and targeted therapeutic interventions.

A microbiology study on the wounds of pediatric patients undergoing spinal fusion for scoliosis

PURPOSE

Surgical site infection is a significant complication in posterior spinal fusion for scoliosis in pediatric and adolescent patients. Current literature demonstrates a lack of consensus regarding best prophylactic systemic and topical antibiotic regimens for reducing infection rates. This study aims to identify which common microbes are present at particular locations in the spine, and whether these are covered by our current systemic and topical antibiotic prophylaxis regimens.

METHODS

A prospective observational study at a National Children's Hospital was conducted on 21 consecutive patients who underwent elective surgery for spinal deformity. Swabs were taken from four layers of the spine, including the superficial skin surface at the start of the case (after surgical site preparation with povidone-iodine), the deep dermis, and the deep surgical bed at the end of exposure and again after the corrective maneuver prior to closure. At each layer, swabs were taken from the proximal, middle, and distal portion of the wound. Swabs were sent to the laboratory for culture and susceptibility testing.

RESULTS

Thirteen (62%) of patients had positive microbial growth. Two microbes were identified, Staphylococcus epidermidis (9.5% of patients) and Cutibacterium acnes (Propionibacterium acnes) (52% of patients). 100% of these microbes were sensitive to cefazolin and vancomycin. 3% of patients had positive growth at the skin layer, 32% positive at the dermal layer, 17% positive after exposure, and 40% positive at the conclusion of the case (p = 0.006). No difference was observed in microbial presence in the upper thoracic, lower thoracic and lumbar spine.

CONCLUSION

Despite adequate surgical site preparation and sterile procedure, microbial contamination remains abundant in the dermal layer and deeper in the spinal wound throughout the case.

Alterations of Epidermal Lipid Profiles and Skin Microbiome in Children With Atopic Dermatitis

PURPOSE

We aimed to investigate epidermal lipid profiles and their association with skin microbiome compositions in children with atopic dermatitis (AD).

METHODS

Specimens were obtained by skin tape stripping from 27 children with AD and 18 healthy subjects matched for age and sex. Proteins and lipids of stratum corneum samples from nonlesional and lesional skin of AD patients and normal subjects were quantified by liquid chromatography tandem mass spectrometry. Skin microbiome profiles were analyzed using bacterial 16S rRNA sequencing.

RESULTS

Ceramides with nonhydroxy fatty acids (FAs) and C18 sphingosine as their sphingoid base (C18-NS-CERs) N-acylated with C16, C18 and C22 FAs, sphingomyelin (SM) N-acylated with C18 FAs, and lysophosphatidylcholine (LPC) with C16 FAs were increased in AD lesional skin compared to those in AD nonlesional skin and that of control subjects (all P < 0.01). SMs N-acylated with C16 FAs were increased in AD lesional skin compared to control subjects (P < 0.05). The ratio of NS-CERs with long-chain fatty acids (LCFAs) to short-chain fatty acids (SCFAs) (C24-32:C14-22), the ratio of LPC with LCFAs to SCFAs (C24-30:C16-22) as well as the ratio of total esterified omega-hydroxy ceramides to total NS-CERs were negatively correlated with transepidermal water loss (rho coefficients = -0.738, -0.528, and -0.489, respectively; all P < 0.001). The proportions of Firmicutes and Staphylococcus were positively correlated to SCFAs including NS ceramides (C14-22), SMs (C17-18), and LPCs (C16), while the proportions of Actinobacteria, Proteobacteria, Bacteroidetes, Corynebacterium, Enhydrobacteria, and Micrococcus were negatively correlated to these SCFAs.

CONCLUSIONS

Our results suggest that pediatric AD skin shows aberrant lipid profiles, and these alterations are associated with skin microbial dysbiosis and cutaneous barrier dysfunction.

Realizing Highly Efficient Sonodynamic Bactericidal Capability through the Phonon-Electron Coupling Effect Using Two-Dimensional Catalytic Planar Defects

Conferring catalytic defects in sonosensitizers is of paramount importance in reinforcing sonodynamic therapy. However, the formation of such 0D defects is governed by the Schottky defect principle. Herein, 2D catalytic planar defects are designed within Ti₃ C₂  sheets to address this challenge. These specific planar slip dislocations with abundant Ti³⁺ species (Ti₃ C₂ -SD(Ti³⁺ )) can yield surface-bound O due to the effective activation of O₂ , thus resulting in a substantial amount of ¹ O₂  generation and the 99.72% ± 0.03% bactericidal capability subject to ultrasound (US) stimulation. It is discovered that the 2D catalytic planar defects can intervene in electron transfer through the phonon drag effect-a coupling effect between surface electrons and US-triggered phonons-that simultaneously contributes to a dramatic decrease in O₂  activation energy from 1.65 to 0.06 eV. This design has achieved a qualitative leap in which the US catalytic site has transformed from 0D to 2D. Moreover, it is revealed that the electron origin, electron transfer, and visible O₂  activation pathway triggered by US can be attributed to the phonon-electron coupling effect. After coating with neutrophil membrane (NM) proteins, the NM-Ti₃ C₂ -SD(Ti³⁺ ) sheets further demonstrate a 6-log₁₀  reduction in methicillin-resistant Staphylococcus aureus burden in the infected bony tissue.

Staphylococcus epidermidis and its dual lifestyle in skin health and infection

The coagulase-negative bacterium Staphylococcus epidermidis is a member of the human skin microbiota. S. epidermidis is not merely a passive resident on skin but actively primes the cutaneous immune response, maintains skin homeostasis and prevents opportunistic pathogens from causing disease via colonization resistance. However, it is now appreciated that S. epidermidis and its interactions with the host exist on a spectrum of potential pathogenicity derived from its high strain-level heterogeneity. S. epidermidis is the most common cause of implant-associated infections and is a canonical opportunistic biofilm former. Additional emerging evidence suggests that some strains of S. epidermidis may contribute to the pathogenesis of common skin diseases. Here, we highlight new developments in our understanding of S. epidermidis strain diversity, skin colonization dynamics and its multifaceted interactions with the host and other members of the skin microbiota.

Innovations in Therapeutic Improvement of the Cutaneous Microbiome in Children with Atopic Dermatitis

Biofilm is the dominant form of skin microbiota organization that provides adhesion and preservation of microorganisms in the skin micro-environment. It is necessary to ensure epidermal barrier function and local immunomodulation. Staphylococcus aureus becomes the major colonizer of skin lesions in case of atopic dermatitis exacerbation, and it also can form the biofilms. S. aureus growth and biofilm formation due to other microbial commensals on the skin of patients with atopic dermatitis leads to chronic output of pro-inflammatory cytokines and later to abnormalities in healthy skin microbiome. The role of microbial biofilm in human’s health makes the skin microbiota an attractive target for therapeutic intervention in various skin diseases.

How Our Microbiome Influences the Pathogenesis of Alopecia Areata

Alopecia areata is a multifactorial autoimmune-based disease with a complex pathogenesis. As in all autoimmune diseases, genetic predisposition is key. The collapse of the immune privilege of the hair follicle leading to scalp loss is a major pathogenic event in alopecia areata. The microbiota considered a bacterial ecosystem located in a specific area of the human body could somehow influence the pathogenesis of alopecia areata, as it occurs in other autoimmune diseases. Moreover, the Next Generation Sequencing of the 16S rRNA bacterial gene and the metagenomic methodology have provided an excellent characterization of the microbiota. The aim of this narrative review is to examine the published literature on the cutaneous and intestinal microbiota in alopecia areata to be able to establish a pathogenic link. In this review, we summarize the influence of the microbiota on the development of alopecia areata. We first introduce the general pathogenic mechanisms that cause alopecia areata to understand the influence that the microbiota may exert and then we summarize the studies that have been carried out on what type of gut and skin microbiota is found in patients with this disease.

Skin microbiota analysis in patients with anorexia nervosa and healthy-weight controls reveals microbial indicators of healthy weight and associations with the antimicrobial peptide psoriasin

Anorexia nervosa (AN), a psychiatric condition defined by low body weight for age and height, is associated with numerous dermatological conditions. Yet, clinical observations report that patients with AN do not suffer from infectious skin diseases like those associated with primary malnutrition. Cell-mediated immunity appears to be amplified in AN; however, this proinflammatory state does not sufficiently explain the lower incidence of infections. Antimicrobial peptides (AMPs) are important components of the innate immune system protecting from pathogens and shaping the microbiota. In Drosophila melanogaster starvation precedes increased AMP gene expression. Here, we analyzed skin microbiota in patients with AN and age-matched, healthy-weight controls and investigated the influence of weight gain on microbial community structure. We then correlated features of the skin microbial community with psoriasin and RNase 7, two highly abundant AMPs in human skin, to clarify whether an association between AMPs and skin microbiota exists and whether such a relationship might contribute to the resistance to cutaneous infections observed in AN. We find significant statistical correlations between Shannon diversity and the highly abundant skin AMP psoriasin and bacterial load, respectively. Moreover, we reveal psoriasin significantly associates with Abiotrophia, an indicator for the healthy-weight control group. Additionally, we observe a significant correlation between an individual's body mass index and Lactobacillus, a microbial indicator of health. Future investigation may help clarify physiological mechanisms that link nutritional intake with skin physiology.