Identification of staphylococcal protein A in infected atopic dermatitis lesions

Pathogenesis of allergic diseases and implications for therapeutic interventions

Allergic diseases such as allergic rhinitis (AR), allergic asthma (AAS), atopic dermatitis (AD), food allergy (FA), and eczema are systemic diseases caused by an impaired immune system. Accompanied by high recurrence rates, the steadily rising incidence rates of these diseases are attracting increasing attention. The pathogenesis of allergic diseases is complex and involves many factors, including maternal-fetal environment, living environment, genetics, epigenetics, and the body's immune status. The pathogenesis of allergic diseases exhibits a marked heterogeneity, with phenotype and endotype defining visible features and associated molecular mechanisms, respectively. With the rapid development of immunology, molecular biology, and biotechnology, many new biological drugs have been designed for the treatment of allergic diseases, including anti-immunoglobulin E (IgE), anti-interleukin (IL)-5, and anti-thymic stromal lymphopoietin (TSLP)/IL-4, to control symptoms. For doctors and scientists, it is becoming more and more important to understand the influencing factors, pathogenesis, and treatment progress of allergic diseases. This review aimed to assess the epidemiology, pathogenesis, and therapeutic interventions of allergic diseases, including AR, AAS, AD, and FA. We hope to help doctors and scientists understand allergic diseases systematically.

Bacterial membrane vesicles shape Staphylococcus aureus skin colonization and induction of innate immune responses

Staphylococcus aureus colonization is abundant on the skin of atopic dermatitis (AD) patients where it contributes to skin inflammation. S. aureus produces virulence factors that distinguish it from commensal skin bacteria such as S. epidermidis and S. lugdunensis. However, it has remained unclear, which of these virulence factors have the strongest impact on AD. Membrane vesicles (MVs) are released by pathogenic bacteria and might play an essential role in the long-distance delivery of bacterial effectors such as virulence factors. We show that MVs are also released by skin commensals in a similar quantity and membrane lipid amount as those from pathogenic S. aureus. Interestingly, MVs from skin commensals can protect against S. aureus skin colonization by conditioning human skin for enhanced defence. In contrast, MVs released by S. aureus are able to induce CXCL8 and TNF-α in primary human keratinocytes, recruit neutrophils and induce neutrophil extracellular traps, which enhance S. aureus skin colonization. CXCL8 induction is TLR2- and NFkB-dependent and the induction level correlates with the membrane lipid and protein A content of the MVs. Interestingly, MVs of S. aureus strains from the lesional skin of AD patients show an enhanced membrane lipid and protein A content compared to the strains from the non-lesional sites and have an enhanced proinflammatory potential. Our data underline the complex interplay in host- and bacterial derived factors in S. aureus skin colonization and the important role of bacterial derived MVs and their membrane lipid and protein A content in skin inflammatory disorders.

First Description of the Composition and the Functional Capabilities of the Skin Microbial Community Accompanying Severe Scabies Infestation in Humans

Epidemiological studies link Sarcoptes scabiei infection and impetigo. Scabies mites can promote Streptococcus pyogenes (Group A Streptococcus) and Staphylococcus aureus infections by breaching the skin barrier and excreting molecules that inhibit host innate immune responses. However, little is known about the composition and the function of the scabies-associated microbiota. Here, high-throughput whole-metagenome sequencing was used to explore the scabies-associated microbiome. Scabies mites including their immediate microenvironments were isolated from two patients with severe scabies in Northern Australia. Two ~45–50 million paired-end reads Illumina libraries were generated of which ~2 (5.1%) and 0.7 million (1.3%) microbial reads were filtered out by mapping to human (hg19) and mite draft genomes. Taxonomic profiling revealed a microbial community dominated by the phylum Firmicutes (A: 79% and B: 59%) and genera that comprise Streptococcus, Staphylococcus, Acinetobacter, and Corynebacterium. Assembly of the metagenome reads resulted in genome bins representing reference genomes of Acinetobacter baumannii, Streptococcus dysgalactiae (Group C/G), Proteus mirablis and Staphylococcus aureus. The contigs contained genes relevant to pathogenicity and antibiotics resistance. Confocal microscopy of a patient skin sample confirmed A. baumannii, Streptococci and S. aureus in scabies mite gut and faeces and the surrounding skin. The study provides fundamental evidence for the association of opportunistic pathogens with scabies infection.

Staphylococcus aureus-derived extracellular vesicles induce monocyte recruitment by activating human dermal microvascular endothelial cells in vitro

BACKGROUND

Atopic dermatitis (AD) represents the most common inflammatory skin disorder in children showing massive infiltration of immune cells. The colonization of AD-afflicted skin by Staphylococcus aureus and S. aureus-derived extracellular vesicles (SEVs) has been associated with AD pathogenesis; however, the molecular mechanism underlying SEV-mediated inflammatory responses remains unclear.

OBJECTIVE

We investigated how SEVs can mediate inflammatory responses in AD pathogenesis by examining the effect of SEVs on human dermal microvascular endothelia cells (HDMECs).

METHODS

HDMECs were treated with SEVs, and the expression of cell adhesion molecules or cytokines was assessed using RT-qPCR, Western blot or cytokine array analyses. The receptor for SEVs and related signalling molecules in HDMECs were addressed and verified via gene knockdown or inhibitor experiments. The recruitment assay of human THP-1 monocytic cells on HDMECs was performed after SEV treatment in the presence or absence of the verified receptor or signalling molecule.

RESULTS

SEVs, but not other gram-positive bacteria-derived extracellular vesicles, directly activated HDMECs by increasing the expression of cell adhesion molecules (E-selectin, VCAM1 and ICAM1) and that of IL-6, the inflammatory cytokine; consequently, they enhanced the recruitment of THP-1 monocytic cells to HDMECs. The SEV-induced HDMEC activation was dependent on Toll-like receptor 4 and the NF-κB signalling pathway, which was rapidly activated within 1 hour post-treatment and followed by an upregulation of cell adhesion molecules and IL-6 at later time-points. Moreover, SEV-mediated HDMEC responses were more rapid and intense than those induced by the same protein concentrations of S. aureus extracts.

CONCLUSIONS & CLINICAL RELEVANCE

SEVs as proinflammatory factors could mediate immune cell infiltration in AD by efficiently inducing endothelial cell activation and monocyte recruitment, which may provide insights into alleviating the S. aureus-mediated onset or progression of AD and its phenotypes.

Thymol attenuates the worsening of atopic dermatitis induced by Staphylococcus aureus membrane vesicles

Staphylococcus aureus membrane vesicles (MVs) aggravate atopic dermatitis (AD) through the delivery of bacterial effector molecules to host cells and the stimulation of inflammatory responses. This study investigated the inhibitory effect of thymol, a phenolic monoterpene found in essential oils derived from plants, on the worsening of AD induced by S. aureus MVs both in vitro and in vivo. The sub-minimal inhibitory concentrations of thymol disrupted S. aureus MVs. Intact S. aureus MVs induced the expression of pro-inflammatory cytokine (interleukin (IL)-1β, IL-6, and tumor necrosis factor-α) and chemokine (IL-8 and monocyte chemoattractant protein-1) genes in cultured keratinocytes, whereas thymol-treated S. aureus MVs did not stimulate the expression of these genes. Topical application of thymol-treated S. aureus MVs or treatment with thymol after intact S. aureus MVs to AD-like skin lesions diminished the pathology of AD. This included decreases in epidermal/dermal thickness and infiltration of eosinophils/mast cells, and inhibited expression of pro-inflammatory cytokine and chemokine genes in mouse AD model. Moreover, thymol significantly suppressed the Th1, Th2, and Th17-mediated inflammatory responses in AD-like skin lesions induced by S. aureus MVs, and reduced the serum levels of immunoglobulin (Ig) G2a, mite-specific IgE, and total IgE. In summary, thymol disrupts S. aureus MVs and suppresses inflammatory responses in AD-like skin lesions aggravated by S. aureus MVs. Our results suggest that thymol is a possible candidate for the management of AD aggravation induced by S. aureus colonization or infection in the lesions.

Beyond Hygiene: Commensal Microbiota and Allergic Diseases

Complex communities of microorganisms, termed commensal microbiota, inhabit mucosal surfaces and profoundly influence host physiology as well as occurrence of allergic diseases. Perturbing factors such as the mode of delivery, dietary fibers and antibiotics can influence allergic diseases by altering commensal microbiota in affected tissues as well as in intestine. Here, we review current findings on the relationship between commensal microbiota and allergic diseases, and discuss the underlying mechanisms that contribute to the regulation of allergic responses by commensal microbiota.

Staphlyococcus aureus phenol-soluble modulins stimulate the release of proinflammatory cytokines from keratinocytes and are required for induction of skin inflammation

Staphylococcus aureus is a human commensal that colonizes the skin. While it is normally innocuous, it has strong associations with atopic dermatitis pathogenesis and has become the leading cause of skin and soft tissue infections in the United States. The factors that dictate the role of S. aureus in disease are still being determined. In this work, we utilized primary keratinocyte culture and an epidermal murine colonization model to investigate the role of S. aureus phenol-soluble modulins (PSMs) in proinflammatory cytokine release and inflammation induction. We demonstrated that many species of Staphylococcus are capable of causing release of interleukin 18 (IL-18) from keratinocytes and that S. aureus PSMs are necessary and sufficient to stimulate IL-18 release from keratinocytes independently of caspase 1. Further, after 7 days of epicutaneous exposure to wild-type S. aureus, but not S. aureus Δpsm, we saw dramatic changes in gross pathology, as well as systemic release of proinflammatory cytokines. This work demonstrates the importance of PSM peptides in S. aureus-mediated inflammatory cytokine release from keratinocytes in vitro and in vivo and further implicates PSMs as important contributors to pathogenesis.

Microbial ecology of the skin in the era of metagenomics and molecular microbiology

The skin is the primary physical barrier between the body and the external environment and is also a substrate for the colonization of numerous microbes. Previously, dermatological microbiology research was dominated by culture-based techniques, but significant advances in genomic technologies have enabled the development of less-biased, culture-independent approaches to characterize skin microbial communities. These molecular microbiology approaches illustrate the great diversity of microbiota colonizing the skin and highlight unique features such as site specificity, temporal dynamics, and interpersonal variation. Disruptions in skin commensal microbiota are associated with the progression of many dermatological diseases. A greater understanding of how skin microbes interact with each other and with their host, and how we can therapeutically manipulate those interactions, will provide powerful tools for treating and preventing dermatological disease.

Treatment outcomes of secondarily impetiginized pediatric atopic dermatitis lesions and the role of oral antibiotics

Patients with atopic dermatitis (AD) are predisposed to infection with Staphylococcus aureus, which worsens their skin disease; it has been postulated that the lack of antimicrobial peptides due to aberrant allergic inflammation in skin with AD could mediate this enhanced bacterial susceptibility. We sought to characterize the amounts of S. aureus and biological products found in infected AD lesions and whether treatment with topical corticosteroids and oral cephalexin as the only antimicrobial improved outcomes. Fifty-nine children with clinically and S. aureus-positive impetiginized lesions of AD were enrolled in this study. A lesion was graded clinically using the Eczema Area and Severity Index, and wash fluid was obtained from the lesion for quantitative bacterial culture and antibiotic sensitivities and measurement of bacterial products and cytokines. Subjects were re-evaluated 2 weeks after treatment. Improvement in the clinical and inflammatory characteristics of impetiginized lesions were noted, even in the 15% of lesions infected with Methicillin-resistant S. aureus (MRSA). In a subgroup of subjects whose lesions did not contain S. aureus 2 weeks after initiating treatment, beta-defensin levels were higher at both visits than in normal skin. Treatment of uncomplicated impetiginized pediatric AD with topical corticosteroids and cephalexin results in significant clinical improvement, even in subjects infected with MRSA. We propose that the inhibition of abnormal inflammation by the treatment regimen, resulting in the high levels of defensins, is involved in the improvement of AD and that systemic antibiotics do not appear to be necessary in secondary impetiginized AD.