Biofilm propensity of Staphylococcus aureus skin isolates is associated with increased atopic dermatitis severity and barrier dysfunction in the MPAACH pediatric cohort

Progressive accumulation of hyperinflammatory NKG2Dlow NK cells in early childhood severe atopic dermatitis

Atopic dermatitis (AD) is a chronic inflammatory skin disease that often precedes the development of food allergy, asthma, and allergic rhinitis. The prevailing paradigm holds that a reduced frequency and function of natural killer (NK) cell contributes to AD pathogenesis, yet the underlying mechanisms and contributions of NK cells to allergic comorbidities remain ill-defined. Here, analysis of circulating NK cells in a longitudinal early life cohort of children with AD revealed a progressive accumulation of NK cells with low expression of the activating receptor NKG2D, which was linked to more severe AD and sensitivity to allergens. This was most notable in children co-sensitized to food and aeroallergens, a risk factor for development of asthma. Individual-level longitudinal analysis in a subset of children revealed coincident reduction of NKG2D on NK cells with acquired or persistent sensitization, and this was associated with impaired skin barrier function assessed by transepidermal water loss. Low expression of NKG2D on NK cells was paradoxically associated with depressed cytolytic function but exaggerated release of the proinflammatory cytokine tumor necrosis factor-α. These observations provide important insights into a potential mechanism underlying the development of allergic comorbidity in early life in children with AD, which involves altered NK cell functional responses, and define an endotype of severe AD.

Synthetic Peptides Capable of Potent Multigroup Staphylococcal Quorum Sensing Activation and Inhibition in Both Cultures and Biofilm Communities

The pathogen Staphylococcus epidermidis uses a chemical signaling process, i.e., quorum sensing (QS), to form robust biofilms and cause human infection. Many questions remain about QS in S. epidermidis, as it uses this intercellular communication pathway to both negatively and positively regulate virulence traits. Herein, we report synthetic multigroup agonists and antagonists of the S. epidermidis accessory gene regulator (agr) QS system capable of potent superactivation and complete inhibition, respectively. These macrocyclic peptides maintain full efficacy across the three major agr specificity groups, and their activity can be "mode-switched" from agonist to antagonist via subtle residue-specific structural changes. We describe the design and synthesis of these non-native peptides and demonstrate that they can appreciably decrease biofilm formation on abiotic surfaces, underscoring the potential for agr agonism as a route to block S. epidermidis virulence. Additionally, we show that both the S. epidermidis agonists and antagonists are active in S. aureus, another common pathogen with a related agr system, yet only as antagonists. This result not only revealed one of the most potent agr inhibitors known in S. aureus but also highlighted differences in the mechanisms of agr agonism and antagonism between these related bacteria. Finally, our investigations reveal unexpected inhibitory behavior for certain S. epidermidis agr agonists at sub-activating concentrations, an observation that can be leveraged for the design of future probes with enhanced potencies. Together, these peptides provide a powerful tool set to interrogate the role of QS in S. epidermidis infections and in Staphylococcal pathogenicity in general.

RNA-sequencing of paired tape-strips and skin biopsies in atopic dermatitis reveals key differences

BACKGROUND

Skin tape-strips and biopsies are widely used methods for investigating the skin in atopic dermatitis (AD). Biopsies are more commonly used but can cause scarring and pain, whereas tape-strips are noninvasive but sample less tissue. The study evaluated the performance of skin tape-strips and biopsies for studying AD.

METHODS

Whole-transcriptome RNA-sequencing was performed on paired tape-strips and biopsies collected from lesional and non-lesional skin from AD patients (n = 7) and non-AD controls (n = 5). RNA yield, mapping efficiency, and differentially expressed genes (DEGs) for the two methods (tape-strip/biopsy) and presence of AD (AD/non-AD) were compared.

RESULTS

Tape-strips demonstrated a lower RNA yield (22 vs. 4596 ng) and mapping efficiency to known genes (28% vs. 93%) than biopsies. Gene-expression profiles of paired tape-strips and biopsies demonstrated a medium correlation (R2 = 0.431). Tape-strips and biopsies demonstrated systematic differences in measured expression levels of 6483 genes across both AD and non-AD samples. Tape-strips preferentially detected many itch (CCL3/CCL4/OSM) and immune-response (CXCL8/IL4/IL5/IL22) genes as well as markers of epidermal dendritic cells (CD1a/CD207), while certain cytokines (IL18/IL37), skin-barrier genes (KRT2/FLG2), and dermal fibroblasts markers (COL1A/COL3A) were preferentially detected by biopsies. Tape-strips identified more DEGs between AD and non-AD (3157 DEGs) then biopsies (44 DEGs). Tape-strips also detected higher levels of bacterial mRNA than biopsies.

CONCLUSIONS

This study concludes that tape-strips and biopsies each demonstrate respective advantages for measuring gene-expression changes in AD. Thus, the specific skin layers and genes of interest should be considered before selecting either method.

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.

Effect of Potassium Permanganate on Staphylococcal Isolates Derived from the Skin of Patients with Atopic Dermatitis

In atopic dermatitis (AD), Staphylococcus aureus frequently colonizes lesions, leading to superinfections that can then lead to exacerbations. The presence of biofilm-producing isolates has been associated with worsening of the disease. Potassium permanganate is used as a topical treatment of infected eczema, blistering conditions, and wounds. Little is known of its effects against microbes in AD skin. The aim of this study was to explore antibacterial and antibiofilm properties of potassium permanganate against staphylococcal isolates derived from AD skin. Viable count and radial diffusion assays were used to investigate antibacterial effects of potassium permanganate against planktonic staphylococcal isolates. The antibiofilm effects were assessed using biofilm assays and scanning electron microscopy. The Staphylococcus aureus isolates were completely killed when exposed to 0.05% of potassium permanganate. In concentrations of 0.01%, potassium permanganate inhibited bacterial biofilm formation. Eradication of established staphylococcal biofilm was observed in concentrations of 1%. Electron microscopy revealed dense formations of coccoidal structures in growth control and looser formations of deformed bacteria when exposed to potassium permanganate. This suggests antibacterial and antibiofilm effects of potassium permanganate against staphylococcal isolates derived from AD skin, when tested in vitro, and a potential role in the treatment of superinfected AD skin.

Filaggrin and beyond: New insights into the skin barrier in atopic dermatitis and allergic diseases, from genetics to therapeutic perspectives

Atopic dermatitis (AD) is the most common inflammatory skin disease worldwide, affecting 20% of children and 5% of adults. One critical component in the pathophysiology of AD is the epidermal skin barrier, with its outermost layer, the stratum corneum (SC), conferring biochemical properties that enable resilience against environmental threats and maintain homeostasis. The skin barrier may be conceptualized as a key facilitator of complex interactions between genetics, host immunity, the cutaneous microbiome, and environmental exposures. The key genetic risk factor for AD development and persistence is a loss-of-function mutation in FLG, with recent advances in genomics focusing on rare variant discovery, establishment of pathogenic mechanisms, and exploration of the role of other epidermal differentiation complex gene variants in AD. Aberrant type 2 inflammatory responses down-regulate the transcription of key epidermal barrier genes, alter the composition of SC lipids, and induce further injury through a neurocutaneous feedback loop and the itch-scratch cycle. The dysbiotic epidermis exhibits reduced bacterial diversity and enhanced colonization with Staphylococcus and Malassezia species, which contribute to both direct barrier injury through the action of bacterial toxins and perpetuation of the inflammatory cascades. Enhanced understanding of each of the pathogenic mechanisms underpinning barrier disruption has led to the development of novel topical and systemic molecules, including interleukin (IL)-4Ra, IL-13, PDE4, and Janus-associated kinase inhibitors, whose clinical effectiveness exceeds conventional treatment modalities. In this narrative review, we aim to summarize the current understanding of the above-mentioned pathophysiological and therapeutic mechanisms, with a focus on the genetic, cellular, and molecular mechanisms underpinning AD development.

The role of human extracellular matrix proteins in defining Staphylococcus aureus biofilm infections

Twenty to forty one percent of the world's population is either transiently or permanently colonized by the Gram-positive bacterium, Staphylococcus aureus. In 2017, the CDC designated methicillin-resistant S. aureus (MRSA) as a serious threat, reporting ∼300 000 cases of MRSA-associated hospitalizations annually, resulting in over 19 000 deaths, surpassing that of HIV in the USA. S. aureus is a proficient biofilm-forming organism that rapidly acquires resistance to antibiotics, most commonly methicillin (MRSA). This review focuses on a large group of (>30) S. aureus adhesins, either surface-associated or secreted that are designed to specifically bind to 15 or more of the proteins that form key components of the human extracellular matrix (hECM). Importantly, this includes hECM proteins that are pivotal to the homeostasis of almost every tissue environment [collagen (skin), proteoglycans (lung), hemoglobin (blood), elastin, laminin, fibrinogen, fibronectin, and fibrin (multiple organs)]. These adhesins offer S. aureus the potential to establish an infection in every sterile tissue niche. These infections often endure repeated immune onslaught, developing into chronic, biofilm-associated conditions that are tolerant to ∼1000 times the clinically prescribed dose of antibiotics. Depending on the infection and the immune response, this allows S. aureus to seamlessly transition from colonizer to pathogen by subtly manipulating the host against itself while providing the time and stealth that it requires to establish and persist as a biofilm. This is a comprehensive discussion of the interaction between S. aureus biofilms and the hECM. We provide particular focus on the role of these interactions in pathogenesis and, consequently, the clinical implications for the prevention and treatment of S. aureus biofilm infections.

Progressive accumulation of hyperinflammatory NKG2D low NK cells in early childhood severe atopic dermatitis

Atopic dermatitis (AD) is a chronic inflammatory skin disease that often precedes the development of food allergy, asthma, and allergic rhinitis. The prevailing paradigm holds that a reduced frequency and function of natural killer (NK) cell contributes to AD pathogenesis, yet the underlying mechanisms and contributions of NK cells to allergic co-morbidities remain ill-defined. Herein, analysis of circulating NK cells in a longitudinal early life cohort of children with AD revealed a progressive accumulation of NK cells with low expression of the activating receptor NKG2D, which was linked to more severe AD and sensitivity to allergens. This was most notable in children co-sensitized to food and aero allergens, a risk factor for development of asthma. Individual-level longitudinal analysis in a subset of children revealed co-incident reduction of NKG2D on NK cells with acquired or persistent sensitization, and this was associated with impaired skin barrier function assessed by transepidermal water loss. Low expression of NKG2D on NK cells was paradoxically associated with depressed cytolytic function but exaggerated release of the proinflammatory cytokine TNF-α. These observations provide important insights into a potential mechanism underlying the development of allergic co-morbidity in early life in children with AD which involves altered NK-cell functional responses, and define an endotype of severe AD.

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.

Combining 16S Sequencing and qPCR Quantification Reveals Staphylococcus aureus Driven Bacterial Overgrowth in the Skin of Severe Atopic Dermatitis Patients

Atopic dermatitis (AD) is an inflammatory skin disease with a microbiome dysbiosis towards a high relative abundance of Staphylococcus aureus. However, information is missing on the actual bacterial load on AD skin, which may affect the cell number driven release of pathogenic factors. Here, we combined the relative abundance results obtained by next-generation sequencing (NGS, 16S V1-V3) with bacterial quantification by targeted qPCR (total bacterial load = 16S, S. aureus = nuc gene). Skin swabs were sampled cross-sectionally (n = 135 AD patients; n = 20 healthy) and longitudinally (n = 6 AD patients; n = 6 healthy). NGS and qPCR yielded highly inter-correlated S. aureus relative abundances and S. aureus cell numbers. Additionally, intra-individual differences between body sides, skin status, and consecutive timepoints were also observed. Interestingly, a significantly higher total bacterial load, in addition to higher S. aureus relative abundance and cell numbers, was observed in AD patients in both lesional and non-lesional skin, as compared to healthy controls. Moreover, in the lesional skin of AD patients, higher S. aureus cell numbers significantly correlated with the higher total bacterial load. Furthermore, significantly more severe AD patients presented with higher S. aureus cell number and total bacterial load compared to patients with mild or moderate AD. Our results indicate that severe AD patients exhibit S. aureus driven increased bacterial skin colonization. Overall, bacterial quantification gives important insights in addition to microbiome composition by sequencing.

Novel insights into atopic dermatitis

Recent research into the pathophysiology and treatment of atopic dermatitis (AD) has shown notable progress. An increasing number of aspects of the immune system are being implicated in AD, including the epithelial barrier, TH2 cytokines, and mast cells. Major advances in therapeutics were made in biologic cytokine and receptor antagonists and among Janus kinase inhibitors. We focus on these areas and address new insights into AD epidemiology, biomarkers, endotypes, prevention, and comorbidities. Going forward, we expect future mechanistic insights and therapeutic advances to broaden physicians' ability to diagnose and manage AD patients, and perhaps to find a cure for this chronic condition.

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.

Mechanistic basis of staphylococcal interspecies competition for skin colonization

Staphylococci, whether beneficial commensals or pathogens, often colonize human skin, potentially leading to competition for the same niche. In this multidisciplinary study we investigate the structure, binding specificity, and mechanism of adhesion of the Aap lectin domain required for Staphylococcus epidermidis skin colonization and compare its characteristics to the lectin domain from the orthologous Staphylococcus aureus adhesin SasG. The Aap structure reveals a legume lectin-like fold with atypical architecture, showing specificity for N-acetyllactosamine and sialyllactosamine. Bacterial adhesion assays using human corneocytes confirmed the biological relevance of these Aap-glycan interactions. Single-cell force spectroscopy experiments measured individual binding events between Aap and corneocytes, revealing an extraordinarily tight adhesion force of nearly 900 nN and a high density of receptors at the corneocyte surface. The SasG lectin domain shares similar structural features, glycan specificity, and corneocyte adhesion behavior. We observe cross-inhibition of Aap-and SasG-mediated staphylococcal adhesion to corneocytes. Together, these data provide insights into staphylococcal interspecies competition for skin colonization and suggest potential avenues for inhibition of S. aureus colonization.

Diabetic Peripheral Neuropathy Associated with Foot Ulcer: One of a Kind

Significance: Diabetic peripheral neuropathy (DPN) associated with a diabetic foot ulcer (DFU) is likely to be complicated with critical factors such as biofilm infection and compromised skin barrier function of the diabetic skin. Repaired skin with a history of biofilm infection is known to be compromised in barrier function. Loss of barrier function is also observed in the oxidative stress affected diabetic and aged skin. Recent Advances: Loss of barrier function makes the skin prone to biofilm infection and cellulitis, which contributes to chronic inflammation and vasculopathy. Hyperglycemia favors biofilm formation as glucose lowering led to reduction in biofilm development. While vasculopathy limits oxygen supply, the O2 cost of inflammation is high increasing hypoxia severity. Critical Issues: The host nervous system can be inhabited by bacteria. Because electrical impulses are a part of microbial physiology, polymicrobial colonization of the host's neural circuit is likely to influence transmission of action potential. The identification of perineural apatite in diabetic patients with peripheral neuropathy suggests bacterial involvement. DPN starts in both feet at the same time. Future Directions: Pair-matched studies of DPN in the foot affected with DFU (i.e., DFU-DPN) compared with DPN in the without ulcer, and intact skin barrier function, are likely to provide critical insight that would help inform effective care strategies. This review characterizes DFU-DPN from a translational science point of view presenting a new paradigm that recognizes the current literature in the context of factors that are unique to DFU-DPN.

Efflux pump inhibitor combined with ofloxacin decreases MRSA biofilm formation by regulating the gene expression of NorA and quorum sensing

Carbonyl cyanide p-nitrophenylhydrazone (2e) displayed a lone or synergistic efficacy against MRSA (RSC Adv., 2020, 10, 17854). In this work, the synergistic mechanism of 2e with ofloxacin was studied. MRSA2858 had potential for biofilm formation, and the value of MBEC of 2e alone was 0.78-1.56 μM, while that of 2e + ofloxacin was 0.39-0.78 μM. 2e combined with ofloxacin showed a synergistic anti-biofilm effect against MRSA. Efflux pump inhibitor 2e can better bind to NorA protein. After MRSA2858 was treated with 2e of 1/2MIC (0.78 μM) and ofloxacin of 1/8MIC (0.097 μM), the transcript levels of efflux genes (norA) and quorum-sensing (QS) regulatory genes (agrA, sarA, icaA, hla) were substantially down-regulated, and alpha-hemolysin (Hla) was inhibited by 99.15%. 2e combined with ofloxacin was more effective than 2e alone in reducing bacterial load in vivo. All in all, efflux pump inhibitor 2e enhanced the bactericidal activities of antibiotics through regulating the gene expression of NorA and QS system.

Antimicrobial resistance and biofilm formation capacity among Acinetobacter baumannii strains isolated from patients with burns and ventilator-associated pneumonia

BACKGROUND

Acinetobacter baumannii is a pathogen responsible for nosocomial infections, especially in patients with burns and ventilator-associated pneumonia (VAP). The aims of this study was to compare the biofilm formation capacity, antimicrobial resistance patterns and molecular typing based on PFGE (Pulsed-Field Gel Electrophoresis) in A. baumannii isolated from burn and VAP patients.

MATERIALS AND METHODS

A total of 50 A. baumannii isolates were obtained from burn and VAP patients. In this study, we assessed antimicrobial susceptibility, biofilm formation capacity, PFGE fingerprinting, and the distribution of biofilm-related genes (csuD, csuE, ptk, ataA, and ompA).

RESULTS

Overall, 74% of the strains were multidrug resistant (MDR), and 26% were extensively drug-resistant (XDR). Regarding biofilm formation capacity, 52%, 36%, and 12% of the isolates were strong, moderate, and weak biofilm producers. Strong biofilm formation capacity significantly correlated with XDR phenotype (12/13, 92.3%). All the isolates harbored at least one biofilm-related gene. The most prevalent gene was csuD (98%), followed by ptk (90%), ataA (88%), ompA (86%), and csuE (86%). Harboring all the biofilm-related genes was significantly associated with XDR phenotype. Finally, PFGE clustering revealed 6 clusters, among which cluster No. 2 showed a significant correlation with strong biofilm formation and XDR phenotype.

CONCLUSION

Our findings revealed the variable distribution of biofilm-related genes among MDR and XDR A. baumannii isolates from burn and VAP patients. A significant correlation was found between strong biofilm formation capacity and XDR phenotype. Finally, our results suggested that XDR phenotype was predominant among strong-biofilm producer A. baumannii in our region.

Knowledge mapping of the links between the microbiota and allergic diseases: A bibliometric analysis (2002-2021)

BACKGROUND

In recent decades, dramatic changes in modern environmental exposures and lifestyles have resulted in a steep rise in the prevalence of allergic diseases such as asthma, allergic rhinitis, atopic dermatitis and food allergies. Evidence is mounting that the microbiota plays a crucial role in allergic disorder development and evolution. Therefore, a better understanding of allergic diseases within the context of the microbiota is urgently needed. This work aimed to comprehensively outline general characteristics, research hotspots, evolution routes, and emerging trends in this area.

METHODS

Relevant publications from January 2002 to December 2021 were obtained from the Web of Science Core Collection on 5 August 2022. Bibliometric and visual analyses were performed using CiteSpace; VOSviewer; an online bibliometric platform; and Microsoft Excel 2019.

RESULTS

In total, 2535 documents met the requirements. The annual number of publications has shown rapid growth in the last two decades. The USA, University of California System, and Isolauri E of the University of Turku were the most productive and influential country, institution, and author, respectively. The Journal of Allergy and Clinical Immunology was the most prolific and most cocited journal. High-frequency keywords included "gut microbiota", "asthma", "atopic dermatitis", "children", and "probiotics". Recent studies have focused on "atopic dermatitis", "skin", "asthma", and "probiotics", according to the cocitation analysis of references. Burst detection analysis of keywords showed that "community", "skin microbiome", "microbiome", "Staphylococcus aureus", and "chain fatty acid" were emerging research frontiers, which currently have ongoing bursts.

CONCLUSION

In the last 20 years, studies of the microbiota in allergic diseases have been flourishing, and the themes have been increasing in depth. These findings provide valuable references on the current research hotspots and gaps and development trends in the link between the microbiota and allergic diseases.

Staphylococcus aureus Biofilm Inhibiting Activity of Advanced Glycation Endproduct Crosslink Breaking and Glycation Inhibiting Compounds

Staphylococcus aureus is a Gram-positive bacterium that plays a role in the pathogenesis of skin lesions in diabetes mellitus, atopic dermatitis, and psoriasis, all of which are associated with elevated non-enzymatic glycation biomarkers. The production of biofilm protects resident bacteria from host immune defenses and antibiotic interventions, prolonging pathogen survival, and risking recurrence after treatment. Glycated proteins formed from keratin and glucose induce biofilm formation in S. aureus, promoting dysbiosis and increasing pathogenicity. In this study, several glycation-inhibiting and advanced glycation endproduct (AGE) crosslink-breaking compounds were assayed for their ability to inhibit glycated keratin-induced biofilm formation as preliminary screening for clinical testing candidates. Ascorbic acid, astaxanthin, clove extract, n-phenacylthiazolium bromide, and rosemary extract were examined in an in vitro static biofilm model with S. aureus strain ATCC 12600. Near complete biofilm inhibition was achieved with astaxanthin (ED₅₀ = 0.060 mg/mL), clove extract (ED₅₀ = 0.0087 mg/mL), n-phenacylthiazolium bromide (ED₅₀ = 5.3 mg/mL), and rosemary extract (ED₅₀ = 1.5 mg/mL). The dosage necessary for biofilm inhibition was not significantly correlated with growth inhibition (R² = 0.055. p = 0.49). Anti-glycation and AGE breaking compounds with biofilm inhibitory activity are ideal candidates for treatment of S. aureus dysbiosis and skin infection that is associated with elevated skin glycation.

Mitochondrial Activity Is Upregulated in Nonlesional Atopic Dermatitis and Amenable to Therapeutic Intervention

Previous work has shown increased expression of genes related to oxidative stress in nonlesional atopic dermatitis (ADNL) skin. Although mitochondria are key regulators of ROS production, their function in AD has never been investigated. Energy metabolism and the oxidative stress response were studied in keratinocytes (KCs) from patients with ADNL or healthy controls. Moreover, ADNL human epidermal equivalents were treated with tigecycline or MitoQ. We found that pyruvate and glucose were used as energy substrates by ADNL KCs. Increased mitochondrial oxidation of (very) long-chain fatty acids, associated with enhanced complexes I and II activities, was observed in ADNL KCs. Metabolomic analysis revealed increased tricarboxylic acid cycle turnover. Increased aerobic metabolism generated oxidative stress in ADNL KCs. ADNL human epidermal equivalents displayed increased mitochondrial function and an enhanced oxidative stress response compared with controls. Treatment of ADNL human epidermal equivalents with tigecycline or MitoQ largely corrected the AD profile, including high p-65 NF-κB, abnormal lamellar bodies, and cellular damage. Furthermore, we found that glycolysis supports but does not supersede mitochondrial metabolism in ADNL KCs. Thus, aerobic metabolism predominates in ADNL but leads to oxidative stress. Therefore, mitochondria could be a reservoir of potential therapeutic targets in atopic dermatitis.

Atopic dermatitis: Is innate or adaptive immunity in control? A clinical perspective

Atopic dermatitis (AD) is a chronic inflammatory skin disease with barrier defects and immune dysregulations. The pathogenesis of AD involves the physical barrier as well as epithelial cells, which are considered a vital part of the innate immunity of the skin. The importance of filaggrin mutations in the pathogenesis of AD has also been well-established with reproducible results around the world in multiple studies and ethnic groups. This protein plays an important role in skin barrier functions and further reaffirms barrier defects as one of the primary causes of AD. The main epithelial cells, keratinocytes, function as a major sentinel for the skin in detecting danger signals or microbial pathogens, and trigger downstream immune responses. In AD, these cells express TSLP, IL-33 and IL-25, which lead to downstream systemic production of type 2 cytokines. In spite of major advances in our understanding of the innate immunity of AD, recent success in the systemic therapeutics of AD have focused on targeting the products of the adaptive immunity, particularly cytokines produced by T cells. In addition to type 2 cytokines, type 17 cytokines have also been implicated in the pathogenesis of AD. The current review examines the implications of these cytokines in AD from clinical perspectives.

Skin and nasal colonization of coagulase-negative staphylococci are associated with atopic dermatitis among South African toddlers

Background

Skin colonization with coagulase-negative staphylococci (CoNS) is generally beneficial, but recent investigations suggest its association with flares and atopic dermatitis (AD) severity. However, this relationship remains unclear.

Objective

To assess patterns of staphylococcal colonization and biofilm formation in toddlers with and without AD from rural and urban South African settings.

Methods

We conducted a cross-sectional study of AD-affected and non-atopic AmaXhosa toddlers from rural Umtata and urban Cape Town, South Africa. CoNS isolates were recovered from lesional, nonlesional skin samples and the anterior nares of participants. Identification of the staphylococci was achieved by MALDI-TOF mass spectrometry. The microtiter plate assay assessed in-vitro biofilm formation.

Results

CoNS and S. aureus commonly co-colonized nonlesional skin among cases (urban: 24% vs. 3%, p = 0.037 and rural 21% vs. 6%, p<0.001), and anterior nares in urban cases (24% vs. 0%, p = 0.002) than the control group. S. capitis colonization on nonlesional skin and anterior nares was positively associated with more severe disease in rural (48.3±10.8 vs. 39.7±11.5, P = 0.045) and urban cases (74.9±10.3 vs. 38.4±13, P = 0.004), respectively. Biofilm formation was similar between cases and controls, independent of rural-urban living.

Conclusion

CoNS colonization is associated with AD and disease severity and may be implicated in AD exacerbations. Studies are needed to understand their underlying pathological contribution in AD pathogenesis.

Skin microbiome of atopic dermatitis

The skin microbiome is a key component of pathogenesis in atopic dermatitis (AD). The skin of AD patients is characterized by microbial dysbiosis, with a reduction of microbial diversity and overrepresentation of pathogenic Staphylococcus aureus (S. aureus). Recent exciting studies have elucidated an importance of establishing an appropriate immune response to microbes in early life and uncovered the new mechanisms of microbial community dynamics in modulating our skin microbiome. Several microbes are associated with AD pathogenesis, with proposed pathogenic effects from S. aureus and Malassezia. The complex relationships between microbes within the skin microbiome consortia includes various species, such as Staphylococcal, Roseomonas and Cutibacterium strains, that can inhibit S. aureus and are potential probiotics for AD skin. Numerous microbes are now also reported to modulate host response via communication with keratinocytes, specialized immune cells and adipocytes to improve skin health and barrier function. This increased understanding of skin microbiota bioactives has led to new biotherapeutic approaches that target the skin surface microenvironment for AD treatment.

Advances and highlights in biomarkers of allergic diseases

During the past years, there has been a global outbreak of allergic diseases, presenting a considerable medical and socioeconomical burden. A large fraction of allergic diseases is characterized by a type 2 immune response involving Th2 cells, type 2 innate lymphoid cells, eosinophils, mast cells, and M2 macrophages. Biomarkers are valuable parameters for precision medicine as they provide information on the disease endotypes, clusters, precision diagnoses, identification of therapeutic targets, and monitoring of treatment efficacies. The availability of powerful omics technologies, together with integrated data analysis and network‐based approaches can help the identification of clinically useful biomarkers. These biomarkers need to be accurately quantified using robust and reproducible methods, such as reliable and point‐of‐care systems. Ideally, samples should be collected using quick, cost‐efficient and noninvasive methods. In recent years, a plethora of research has been directed toward finding novel biomarkers of allergic diseases. Promising biomarkers of type 2 allergic diseases include sputum eosinophils, serum periostin and exhaled nitric oxide. Several other biomarkers, such as pro‐inflammatory mediators, miRNAs, eicosanoid molecules, epithelial barrier integrity, and microbiota changes are useful for diagnosis and monitoring of allergic diseases and can be quantified in serum, body fluids and exhaled air. Herein, we review recent studies on biomarkers for the diagnosis and treatment of asthma, chronic urticaria, atopic dermatitis, allergic rhinitis, chronic rhinosinusitis, food allergies, anaphylaxis, drug hypersensitivity and allergen immunotherapy. In addition, we discuss COVID‐19 and allergic diseases within the perspective of biomarkers and recommendations on the management of allergic and asthmatic patients during the COVID‐19 pandemic.

A new era of atopic eczema research: Advances and highlights

Atopic eczema (AE) is an inflammatory skin disease with involvement of genetic, immunological and environmental factors. One hallmark of AE is a skin barrier disruption on multiple, highly interconnected levels: filaggrin mutations, increased skin pH and a microbiome dysbiosis towards Staphylococcus aureus overgrowth are observed in addition to an abnormal type 2 immune response. Extrinsic factors seem to play a major role in the development of AE. As AE is a first step in the atopic march, its prevention and appropriate treatment are essential. Although standard therapy remains topical treatment, powerful systemic treatment options emerged in the last years. However, thorough endotyping of the individual patients is still required for ideal precision medicine approaches in future. Therefore, novel microbial and immunological biomarkers were described recently for the prediction of disease development and treatment response. This review summarizes the current state of the art in AE research.

The Multitasking Surface Protein of Staphylococcus epidermidis: Accumulation-Associated Protein (Aap)

The stratum corneum is the outermost layer of the epidermis and is thus directly exposed to the environment. It consists mainly of corneocytes, which are keratinocytes in the last stage of differentiation, having neither nuclei nor organelles. However, they retain keratin filaments embedded in filaggrin matrix and possess a lipid envelope which protects the body from desiccation. Despite the desiccated, nutrient-poor, and acidic nature of the skin making it a hostile environment for most microorganisms, this organ is colonized by commensal microbes. Among the classic skin commensals are Propionibacterium acnes and coagulase-negative staphylococci (CoNS) with Staphylococcus epidermidis as a leading species. An as-yet-unanswered question is what enables S. epidermis to colonize skin so successfully. In their recent article, P. D. Fey and his colleagues (P. Roy, A. R. Horswill, and P. D. Fey, mBio 12:e02908-20, 2021, https://doi.org/10.1128/mBio.02908-20) have brought us one step closer to answering this question.

Free human DNA attenuates the activity of antimicrobial peptides in atopic dermatitis

BACKGROUND

The high susceptibility of AD patients to microbial skin infections has been attributed to a deficient antimicrobial peptide (AMP) expression, which is contradicted by a growing amount of recent studies clearly demonstrating that AMP expression is not impaired in lesional skin of AD patients. The reasons for the high susceptibility of AD patients to microbial infections are still unknown.

METHODS

The influence of self-DNA on the antimicrobial activity of RNase 7, LL-37, and hBD2 has been investigated using antibacterial and antiviral assays. The amount of self-DNA on skin has been analyzed by skin rinsings and subsequent quantification using dsDNA assays. DNA source was identified by qPCR.

RESULTS

Complex formation of the AMPs with self-DNA significantly impaired their antibacterial activity against Staphylococcus aureus and their antiviral activity against HSV-1. The inhibition of the antibacterial activity was dependent on the DNA concentration but not on the length of the DNA molecules. Of note, we detected significant higher amounts of cell-free self-DNA in skin rinses taken from lesional AD skin compared to skin rinses from non-lesional skin and from normal skin of healthy donors. Consequently, rinse solution from AD lesional skin prevented antibacterial activity of LL-37.

CONCLUSION

Our study indicates that extracellular self-DNA is released in considerable amounts in AD skin lesions and AMP-self-DNA-complex formation leads to a significant loss of antibacterial and antiviral activity in atopic dermatitis. Studies on strategies to reduce the amount of extracellular DNA in AD are needed to identify possible methods relevant in clinical settings.

Dysregulation of the epithelial barrier by environmental and other exogenous factors

The “epithelial barrier hypothesis” proposes that the exposure to various epithelial barrier–damaging agents linked to industrialization and urbanization underlies the increase in allergic diseases. The epithelial barrier constitutes the first line of physical, chemical, and immunological defense against environmental factors. Recent reports have shown that industrial products disrupt the epithelial barriers. Innate and adaptive immune responses play an important role in epithelial barrier damage. In addition, recent studies suggest that epithelial barrier dysfunction plays an essential role in the pathogenesis of the atopic march by allergen sensitization through the transcutaneous route. It is evident that external factors interact with the immune system, triggering a cascade of complex reactions that damage the epithelial barrier. Epigenetic and microbiome changes modulate the integrity of the epithelial barrier. Robust and simple measurements of the skin barrier dysfunction at the point‐of‐care are of significant value as a biomarker, as recently reported using electrical impedance spectroscopy to directly measure barrier defects. Understanding epithelial barrier dysfunction and its mechanism is key to developing novel strategies for the prevention and treatment of allergic diseases. The aim of this review is to summarize recent studies on the pathophysiological mechanisms triggered by environmental factors that contribute to the dysregulation of epithelial barrier function.

The Influence of Microbiome Dysbiosis and Bacterial Biofilms on Epidermal Barrier Function in Atopic Dermatitis-An Update

Atopic dermatitis (AD) is a common inflammatory dermatosis affecting up to 30% of children and 10% of adults worldwide. AD is primarily driven by an epidermal barrier defect which triggers immune dysregulation within the skin. According to recent research such phenomena are closely related to the microbial dysbiosis of the skin. There is growing evidence that cutaneous microbiota and bacterial biofilms negatively affect skin barrier function, contributing to the onset and exacerbation of AD. This review summarizes the latest data on the mechanisms leading to microbiome dysbiosis and biofilm formation in AD, and the influence of these phenomena on skin barrier function.

Glycan-Dependent Corneocyte Adherence of Staphylococcus epidermidis Mediated by the Lectin Subdomain of Aap

Staphylococcus epidermidis and other coagulase-negative staphylococci (CoNS) that colonize skin are known to promote skin immunity and inhibit colonization of pathogens that cause skin and soft tissue infections, including Staphylococcus aureus. However, S. epidermidis adherence to corneocytes, the cells that constitute the uppermost layer of the skin epidermis, remains poorly understood. Our study documents that S. epidermidis corneocyte adherence is dependent upon the accumulation-associated protein (Aap). Aap is composed of two distinct A and B domains. The A domain is comprised of a repeat region and a conserved L-type lectin domain, whereas the fibrillar B domain, which is comprised of G5 and E repeats, is linked to the cell wall in a sortase-dependent manner. Our studies revealed that adherence to corneocytes is dependent upon the lectin subdomain within the A domain. However, significant adherence was only observed when the lectin domain was expressed with both the A repeat and the B domain, suggesting further interactions between these three domains. Our data also suggest that the A repeat domain is important for stability or expression of Aap. Deglycosylation treatment suggested that glycans expressed in the host stratum corneum serve as potential binding partners for Aap-mediated corneocyte adherence. Last, bioinformatic analyses of the predominant commensal species of CoNS identified open reading frames (ORFs) homologous to aap, thus suggesting that Aap orthologues containing lectin-like domains may provide the basis for staphylococcal colonization of skin. Corroborating these observations, adherence to corneocytes in an S. aureus mgrA mutant was dependent upon SasG, the Aap orthologue in S. aureus. IMPORTANCE Staphylococcus aureus is the most significant cause of skin and soft tissue infections yet it rarely colonizes the skin of healthy individuals. This is believed to be due, in part, to inhibition of colonization via toxic substances produced by normal skin flora, including by S. epidermidis. Furthermore, we surmise that S. aureus colonization inhibition may also be due to competition for binding sites on host corneocytes. To understand these potential interactions between S. aureus and S. epidermidis and, potentially, other coagulase-negative staphylococci, we must first understand how staphylococci adhere to corneocytes. This work documents that S. epidermidis adherence to corneocytes is dependent upon the fibrillar cell wall-associated protein Aap. Our work further documents that Aap binds to glycans exposed on the corneocyte surface, which are commonly exploited by bacteria to facilitate adherence to host cells. Furthermore, we find that Aap orthologues may be responsible for corneocyte adherence in other staphylococci, including in S. aureus.

Skin and Gut Microbiome in Psoriasis: Gaining Insight Into the Pathophysiology of It and Finding Novel Therapeutic Strategies

Psoriasis affects the health of myriad populations around the world. The pathogenesis is multifactorial, and the exact driving factor remains unclear. This condition arises from the interaction between hyperproliferative keratinocytes and infiltrating immune cells, with poor prognosis and high recurrence. Better clinical treatments remain to be explored. There is much evidence that alterations in the skin and intestinal microbiome play an important role in the pathogenesis of psoriasis, and restoration of the microbiome is a promising preventive and therapeutic strategy for psoriasis. Herein, we have reviewed recent studies on the psoriasis-related microbiome in an attempt to confidently identify the “core” microbiome of psoriasis patients, understand the role of microbiome in the pathogenesis of psoriasis, and explore new therapeutic strategies for psoriasis through microbial intervention.