Selective antimicrobial action is provided by phenol-soluble modulins derived from Staphylococcus epidermidis, a normal resident of the skin

The role of the skin microbiome in atopic dermatitis

Atopic dermatitis (AD) is a common skin disease that affects a large proportion of the population worldwide. The incidence of AD has increased over the last several decades along with AD's burden on the physical and psychological health of the patient and family. However, current advances in understanding the mechanisms behind the pathophysiology of AD are leading to a hopeful outlook for the future. Staphylococcus aureus (S. aureus) colonization on AD skin has been directly correlated to disease severity but the functions of other members of the skin bacterial community may be equally important. Applying knowledge gained from understanding the role of the skin microbiome in maintaining normal skin immune function, and addressing the detrimental consequences of microbial dysbiosis in driving inflammation, is a promising direction for development of new treatments. This review discusses current preclinical and clinical research focused on determining how the skin microbiome may influence the development of AD.

The Innate Immune System in Acute and Chronic Wounds

Significance: This review article provides an overview of the critical roles of the innate immune system to wound healing. It explores aspects of dysregulation of individual innate immune elements known to compromise wound repair and promote nonhealing wounds. Understanding the key mechanisms whereby wound healing fails will provide seed concepts for the development of new therapeutic approaches.

Recent Advances: Our understanding of the complex interactions of the innate immune system in wound healing has significantly improved, particularly in our understanding of the role of antimicrobials and peptides and the nature of the switch from inflammatory to reparative processes. This takes place against an emerging understanding of the relationship between human cells and commensal bacteria in the skin.

Critical Issues: It is well established and accepted that early local inflammatory mediators in the wound bed function as an immunological vehicle to facilitate immune cell infiltration and microbial clearance upon injury to the skin barrier. Both impaired and excessive innate immune responses can promote nonhealing wounds. It appears that the switch from the inflammatory to the proliferative phase is tightly regulated and mediated, at least in part, by a change in macrophages. Defining the factors that initiate the switch in such macrophage phenotypes and functions is the subject of multiple investigations.

Future Directions: The review highlights processes that may be useful targets for further investigation, particularly the switch from M1 to M2 macrophages that appears to be critical as dysregulation of this switch occurs during defective wound healing.

The Microbiota of the Human Skin

The aim of this chapter is to sum up important progress in the field of human skin microbiota research that was achieved over the last years.The human skin is one of the largest and most versatile organs of the human body. Owing to its function as a protective interface between the largely sterile interior of the human body and the highly microbially contaminated outer environment, it is densely colonized with a diverse and active microbiota. This skin microbiota is of high importance for human health and well-being. It is implicated in several severe skin diseases and plays a major role in wound infections. Many less severe, but negatively perceived cosmetic skin phenomena are linked with skin microbes, too. In addition, skin microorganisms, in particular on the human hands, are crucial for the field of hygiene research. Notably, apart from being only a potential source of disease and contamination, the skin microbiota also contributes to the protective functions of the human skin in many ways. Finally, the analysis of structure and function of the human skin microbiota is interesting from a basic, evolutionary perspective on human microbe interactions.Key questions in the field of skin microbiota research deal with (a) a deeper understanding of the structure (species inventory) and function (physiology) of the healthy human skin microbiota in space and time, (b) the distinction of resident and transient skin microbiota members,

Functional characteristics of the Staphylococcus aureus δ-toxin allelic variant G10S

Staphylococcus aureus δ-toxin is a member of the phenol-soluble modulin (PSM) peptide family. PSMs have multiple functions in staphylococcal pathogenesis; for example, they lyse red and white blood cells and trigger inflammatory responses. Compared to other PSMs, δ-toxin is usually more strongly expressed but has only moderate cytolytic capacities. The amino acid sequences of S. aureus PSMs are well conserved with two exceptions, one of which is the δ-toxin allelic variant G10S. This variant is a characteristic of the subspecies S. argenteus and S. aureus sequence types ST1 and ST59, the latter representing the most frequent cause of community-associated infections in Asia. δ-toxin G10S and strains expressing that variant from plasmids or the genome had significantly reduced cytolytic and pro-inflammatory capacities, including in a strain background with pronounced production of other PSMs. However, in murine infection models, isogenic strains expressing the two δ-toxin variants did not cause measurable differences in disease severity. Our findings indicate that the widespread G10S allelic variation of the δ-toxin locus has a significant impact on key pathogenesis mechanisms, but more potent members of the PSM peptide family may overshadow that impact in vivo.

Staphylococcus epidermidis: metabolic adaptation and biofilm formation in response to different oxygen concentrations

Staphylococcus epidermidis has become a major health hazard. It is necessary to study its metabolism and hopefully uncover therapeutic targets. Cultivating S. epidermidis at increasing oxygen concentration [O2] enhanced growth, while inhibiting biofilm formation. Respiratory oxidoreductases were differentially expressed, probably to prevent reactive oxygen species formation. Under aerobiosis, S. epidermidis expressed high oxidoreductase activities, including glycerol-3-phosphate dehydrogenase, pyruvate dehydrogenase, ethanol dehydrogenase and succinate dehydrogenase, as well as cytochromes bo and aa3; while little tendency to form biofilms was observed. Under microaerobiosis, pyruvate dehydrogenase and ethanol dehydrogenase decreased while glycerol-3-phosphate dehydrogenase and succinate dehydrogenase nearly disappeared; cytochrome bo was present; anaerobic nitrate reductase activity was observed; biofilm formation increased slightly. Under anaerobiosis, biofilms grew; low ethanol dehydrogenase, pyruvate dehydrogenase and cytochrome bo were still present; nitrate dehydrogenase was the main terminal electron acceptor. KCN inhibited the aerobic respiratory chain and increased biofilm formation. In contrast, methylamine inhibited both nitrate reductase and biofilm formation. The correlation between the expression and/or activity or redox enzymes and biofilm-formation activities suggests that these are possible therapeutic targets to erradicate S. epidermidis.

The Skin Microbiome in Atopic Dermatitis and Its Relationship to Emollients

BACKGROUND

Human-associated bacterial communities on the skin, skin microbiome, likely play a central role in development of immunity and protection from pathogens. In atopic patients, the skin bacterial diversity is smaller than in healthy subjects.

OBJECTIVE

To review treatment strategies for atopic dermatitis in Canada, taking the skin microbiome concept into account.

METHODS

An expert panel of 8 Canadian dermatologists explored the role of skin microbiome in clinical dermatology, specifically looking at atopic dermatitis.

RESULTS

The panel reached consensus on the following: (1) In atopic patients, the skin microbiome of lesional atopic skin is different from nonlesional skin in adjacent areas. (2) Worsening atopic dermatitis and smaller bacterial diversity are strongly associated. (3) Application of emollients containing antioxidant and antibacterial components may increase microbiome diversity in atopic skin.

CONCLUSION

The skin microbiome may be the next frontier in preventive health and may impact the approach to atopic dermatitis treatment.

Localization-triggered bacterial pathogenesis

Bacterial infections are becoming an increasing problem worldwide and there is a need for a deeper understanding of how bacteria turn pathogenic. Here, we suggest that one answer may be found by taking into account the localization of the bacteria, both at an anatomical level and at a microenvironment level. Both commensals and traditional pathogens alter their interaction with the human host depending on the local surroundings--turning either more or less virulent. These localization effects could derive from the characteristics of different anatomical sites but also from local differences within a microenvironment. In order to understand the adaptive functions of bacterial virulence factors, we need to study the bacteria in the environments where they have evolved.

Insights on virulence from the complete genome of Staphylococcus capitis

Staphylococcus capitis is an opportunistic pathogen of the coagulase negative staphylococci (CoNS). Functional genomic studies of S. capitis have thus far been limited by a lack of available complete genome sequences. Here, we determined the closed S. capitis genome and methylome using Single Molecule Real Time (SMRT) sequencing. The strain, AYP1020, harbors a single circular chromosome of 2.44 Mb encoding 2304 predicted proteins, which is the smallest of all complete staphylococcal genomes sequenced to date. AYP1020 harbors two large mobile genetic elements; a plasmid designated pAYP1020 (59.6 Kb) and a prophage, ΦAYP1020 (48.5 Kb). Methylome analysis identified significant adenine methylation across the genome involving two distinct methylation motifs (1972 putative 6-methyladenine (m6A) residues identified). Putative adenine methyltransferases were also identified. Comparative analysis of AYP1020 and the closely related CoNS, S. epidermidis RP62a, revealed a host of virulence factors that likely contribute to S. capitis pathogenicity, most notably genes important for biofilm formation and a suite of phenol soluble modulins (PSMs); the expression/production of these factors were corroborated by functional assays. The complete S. capitis genome will aid future studies on the evolution and pathogenesis of the coagulase negative staphylococci.

Pilot study on novel skin care method by augmentation with Staphylococcus epidermidis, an autologous skin microbe--A blinded randomized clinical trial

BACKGROUND AND OBJECTIVE

Staphylococcus epidermidis is an autologous bacterium that is beneficial to skin health. Our goal was to develop a novel, personalized basic cosmetic that exploits this characteristic.

METHODS

We conducted a double-blinded, randomized clinical trial on augmentation with S. epidermidis as a pilot study, in which S. epidermidis was collected from the subject, cultured for proliferation, and then continuously applied to the subject's own face before sleep twice per week for four weeks in order to increase colonization levels.

RESULTS

The results showed that this treatment increased the lipid content of the skin and suppressed water evaporation, thereby markedly improving skin moisture retention. Moreover, augmentation with S. epidermidis maintained a low acidic condition on the skin surface. The low risk of undesirable effects induced by augmentation with S. epidermidis was also confirmed by measuring erythema and melanin levels.

CONCLUSIONS

These results may serve as a driving force to accelerate the development of novel, personalized basic cosmetics.

Rosacea: part I. Introduction, categorization, histology, pathogenesis, and risk factors

Rosacea is a chronic inflammatory skin condition that affects approximately 16 million Americans. Four distinct subtypes of rosacea have been recognized, with transient and nontransient facial flushing, telangiectasia, and inflammatory papules and pustules being among the more commonly recognized features. Although the exact pathogenesis of rosacea is unknown, dysregulation of the innate immune system, overgrowth of commensal skin organisms, and aberrant neurovascular signaling may all have a role in promoting the clinical features of rosacea.

Multidrug-Resistance Transporter AbcA Secretes Staphylococcus aureus Cytolytic Toxins

Phenol-soluble modulins (PSMs) are Staphylococcus aureus cytolytic toxins that lyse erythrocytes and neutrophils and have important functions in the S. aureus infectious process. The molecular mechanisms of PSM secretion, however, are not well understood. Here we report that knockout of the multidrug-resistance ABC transporter AbcA, which contributes to S. aureus resistance against antibiotics and chemicals, diminished the secreted amount of PSM, leading to the accumulation of PSM in the intracellular fraction. The amount of PSM in the culture supernatants of the abcA knockout mutants was restored by introduction of the wild-type abcA gene, whereas it was not completely restored by introduction of mutant abcA genes encoding AbcA mutant proteins carrying amino acid substitutions in the adenosine triphosphate binding motifs. The abcA knockout mutant exhibited attenuated virulence in a mouse systemic infection model. These findings suggest that the multidrug resistance transporter AbcA secretes PSMs and contributes to S. aureus virulence.

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.

S. epidermidis influence on host immunity: more than skin deep

The mammalian immune system communicates with skin-resident microbes, and some of these microbes provide benefits to the host. In a recent paper in Nature, Naik et al. (2015) provide evidence that the murine epidermis permits S. epidermidis, a skin-specific bacterium, to shape the immune response.

RNA-Seq Analysis of the Host Response to Staphylococcus aureus Skin and Soft Tissue Infection in a Mouse Model

Staphylococcus aureus is a leading cause of skin and soft tissue infections (SSTI), which are primarily self-limiting. We conducted a comprehensive analysis of the host transcriptome during a S. aureus SSTI to provide insight on the protective mechanisms that thwart these infections. We utilized a murine SSTI model in which one ear is epicutaneously challenged while the other is not. We then harvested these infected and uninfected ears, as well as ears from naïve mice, at one, four, and seven days post-challenge, and performed RNA sequencing (RNA-seq) using the Illumina platform. RNA-seq data demonstrated a robust response at the site of infection. Comparison of gene expression profiles between infected ears and the non-infected ears of challenged mice defined the local response to infection, while comparisons of expression profiles of non-infected ears from challenged mice to ears of naïve mice revealed changes in gene expression levels away from the site indicative of a systemic response. Over 1000 genes exhibited increased expression locally at all tested time points. The local response was more robust than the systemic response. Through evaluation of the RNA-seq data using the Upstream Regulator Analytic as part of the Ingenuity Pathway Analysis software package, we found that changes in the activation and inhibition of regulatory pathways happen first locally, and lag behind systemically. The activated pathways are highly similar at all three time points during SSTI, suggesting a stable global response over time. Transcript increases and pathway activation involve pro- and anti-inflammatory mediators, chemotaxis, cell signaling, keratins, and TH1/TH17 cytokines. Transcript decreases and pathway inhibition demonstrate that metabolic genes and anti-inflammatory pathways are repressed. These data provide insight on the host responses that may aid in resolution of this self-limited S. aureus infection, and may shed light on potential immune correlates of protection for staphylococcal SSTI.

Interstrain interactions between bacteria isolated from vacuum-packaged refrigerated beef

The formation of bacterial spoilage communities in food is influenced by both extrinsic and intrinsic environmental factors. Although many reports describe how these factors affect bacterial growth, much less is known about interactions among bacteria, which may influence community structure. This study investigated interactions among representative species of bacteria isolated from vacuum-packaged (VP) beef. Thirty-nine effectors and 20 target isolates were selected, representing 10 bacterial genera: Carnobacterium, Pseudomonas, Hafnia, Serratia, Yersinia, Rahnella, Brochothrix, Bacillus, Leuconostoc, and Staphylococcus. The influence of live effectors on growth of target isolates was measured by spot-lawn agar assay and also in liquid culture medium broth using live targets and effector cell-free supernatants. Inhibition on agar was quantified by diameter of inhibition zone and in broth by measuring detection time, growth rate, and maximum population density. A number of interactions were observed, with 28.6% of isolates inhibiting and 4.2% promoting growth. The majority of Pseudomonas isolates antagonized growth of approximately one-half of target isolates. Two Bacillus spp. each inhibited 16 targets. Among lactic acid bacteria (LAB), Carnobacterium maltaromaticum inhibited a wider range of isolates compared to other LAB. The majority of effector isolates enhancing target isolate growth were Gram-negative, including Pseudomonas spp. and Enterobacteriaceae. These findings markedly improve the understanding of potential interactions among spoilage bacteria, possibly leading to more mechanistic descriptions of bacterial community formation in VP beef and other foods.

Defensive symbioses of animals with prokaryotic and eukaryotic microorganisms

Many organisms team up with symbiotic microbes for defense against predators, parasites, parasitoids, or pathogens. Here we review the known defensive symbioses in animals and the microbial secondary metabolites responsible for providing protection to the host.

Enemy attraction: bacterial agonists for leukocyte chemotaxis receptors

The innate immune system recognizes conserved microorganism-associated molecular patterns (MAMPs), some of which are sensed by G protein-coupled receptors (GPCRs), and this leads to chemotactic leukocyte influx. Recent studies have indicated that these processes are crucial for host defence and rely on a larger set of chemotactic MAMPs and corresponding GPCRs than was previously thought. Agonists, such as bacterial formyl peptides, enterococcal pheromone peptides, staphylococcal peptide toxins, bacterial fermentation products and the Helicobacter pylori peptide HP(2-20), stimulate specific GPCRs. The importance of leukocyte chemotaxis in host defence is highlighted by the fact that some bacterial pathogens produce chemotaxis inhibitors. How the various chemoattractants, receptors and antagonists shape antibacterial host defence represents an important topic for future research.

Bacterial skin commensals and their role as host guardians

Recent years' investigations of the co-evolution and functional integration of the human body and its commensal microbiota have disclosed that the microbiome has a major impact on physiological functions including protection against infections, reaction patterns in the immune system, and disposition for inflammation-mediated diseases. Two ubiquitous members of the skin microbiota, the Gram-positive bacteria Staphylococcus epidermidis and Propionibacterium acnes, are predominant on human epithelia and in sebaceous follicles, respectively. Their successful colonisation is a result of a commensal or even mutualistic lifestyle, favouring traits conferring persistency over aggressive host-damaging properties. Some bacterial properties suggest an alliance with the host to keep transient, potential pathogens at bay, such as the ability of S. epidermidis to produce antimicrobials, or the production of short-chain fatty acids by P. acnes. These features can function together with host-derived components of the innate host defence to establish and maintain the composition of a health-associated skin microbiota. However, depending largely on the host status, the relationship between the human host and S. epidermidis/P. acnes can also have parasitic features. Both microorganisms are frequently isolated from opportunistic infections. S. epidermidis is a causative agent of hospital-acquired infections, mostly associated with the use of medical devices. P. acnes is suspected to be of major importance in the pathogenesis of acne and also in a number of other opportunistic infections. In this review we will present bacterial factors and traits of these two key members of our skin microbiota and discuss how they contribute to mutualistic and parasitic properties. The elucidation of their roles in health-promoting or disease-causing processes could lead to new prophylactic and therapeutic strategies against skin disorders and other S. epidermidis/P. acnes-associated diseases, and increase our understanding of the delicate interplay of the skin microbiota with the human host.

Impact of prebiotics and probiotics on skin health

This review discusses the role of pre- and probiotics with respect to improving skin health by modulating the cutaneous microbiota. The skin ecosystem is a complex environment covered with a diverse microbiota community. These are classified as either transient or resident, where some are considered as beneficial, some essentially neutral and others pathogenic or at least have the capacity to be pathogenic. Colonisation varies between different parts of the body due to different environmental factors. Pre- and probiotic beneficial effects can be delivered topically or systemically (by ingestion). The pre- and probiotics have the capacity to optimise, maintain and restore the microbiota of the skin in different ways. Topical applications of probiotic bacteria have a direct effect at the site of application by enhancing the skin natural defence barriers. Probiotics as well as resident bacteria can produce antimicrobial peptides that benefit cutaneous immune responses and eliminate pathogens. In cosmetic formulations, prebiotics can be applied to the skin microbiota directly and increase selectively the activity and growth of beneficial 'normal' skin microbiota. Little is known about the efficacy of topically applied prebiotics. Nutritional products containing prebiotics and/or probiotics have a positive effect on skin by modulating the immune system and by providing therapeutic benefits for atopic diseases. This review underlines the potential use of pre- and probiotics for skin health.

Fold modulating function: bacterial toxins to functional amyloids

Many bacteria produce cytolytic toxins that target host cells or other competing microbes. It is well known that environmental factors control toxin expression, however, recent work suggests that some bacteria manipulate the fold of these protein toxins to control their function. The β-sheet rich amyloid fold is a highly stable ordered aggregate that many toxins form in response to specific environmental conditions. When in the amyloid state, toxins become inert, losing the cytolytic activity they display in the soluble form. Emerging evidence suggest that some amyloids function as toxin storage systems until they are again needed, while other bacteria utilize amyloids as a structural matrix component of biofilms. This amyloid matrix component facilitates resistance to biofilm disruptive challenges. The bacterial amyloids discussed in this review reveal an elegant system where changes in protein fold and solubility dictate the function of proteins in response to the environment.

Staphylococci: colonizers and pathogens of human skin

 Staphylococci are abundant bacteria of the human skin microbiome. Several species, particularly Staphylococcus aureus and Staphylococcus epidermidis, are opportunistic pathogens and cause significant disease. The human skin serves many functions and here we review its role as an antimicrobial barrier and the staphylococcal mechanisms to colonize and counteract the various stresses present in this niche. Successful colonization is achieved using a diversity of adhesins, surface proteins and secreted enzymes to counteract the antimicrobial peptides, enzymes and lipid matrix components present in the acid mantle. Further mechanisms enable these bacteria to overcome osmotic and acid stresses and desiccation in order to survive the exacting demands of an ever-changing landscape.

Microbiota in healthy skin and in atopic eczema

The Italian interest group (IG) on atopic eczema and urticaria is member of the Italian Society of Allergology and Immunology. The aim of our IG is to provide a platform for scientists, clinicians, and experts. In this review we discuss the role of skin microbiota not only in healthy skin but also in skin suffering from atopic dermatitis (AD). A Medline and Embase search was conducted for studies evaluating the role of skin microbiota. We examine microbiota composition and its development within days after birth; we describe the role of specific groups of microorganisms that colonize distinct anatomical niches and the biology and clinical relevance of antimicrobial peptides expressed in the skin. Specific AD disease states are characterized by concurrent and anticorrelated shifts in microbial diversity and proportion of Staphylococcus. These organisms may protect the host, defining them not as simple symbiotic microbes but rather as mutualistic microbes. These findings reveal links between microbial communities and inflammatory diseases such as AD and provide novel insights into global shifts of bacteria relevant to disease progression and treatment. This review also highlights recent observations on the importance of innate immune systems and the relationship with normal skin microflora for the maintenance of healthy skin.

The AgrD N-terminal leader peptide of Staphylococcus aureus has cytolytic and amyloidogenic properties

Staphylococcus aureus virulence is coordinated through the Agr quorum-sensing system to produce an array of secreted molecules. One important class of secreted virulence factors is the phenol-soluble modulins (PSMs). PSMs are small-peptide toxins that have recently been characterized for their roles in infection, biofilm development, and subversion of the host immune system. In this work, we demonstrate that the signal peptide of the S. aureus quorum-sensing signal, AgrD, shares structural and functional similarities with the PSM family of toxins. The efficacy of this peptide (termed N-AgrD) beyond AgrD propeptide trafficking has never been described before. We observe that N-AgrD, like the PSMs, is found in the amyloid fibrils of S. aureus biofilms and is capable of forming and seeding amyloid fibrils in vitro. N-AgrD displays cytolytic and proinflammatory properties that are abrogated after fibril formation. These data suggest that the N-AgrD leader peptide affects S. aureus biology in a manner similar to that described previously for the PSM peptide toxins. Taken together, our findings suggest that peptide cleavage products can affect cellular function beyond their canonical roles and may represent a class of virulence factors warranting further exploration.

Colonization and infection of the skin by S. aureus: immune system evasion and the response to cationic antimicrobial peptides

Staphylococcus aureus (S. aureus) is a widespread cutaneous pathogen responsible for the great majority of bacterial skin infections in humans. The incidence of skin infections by S. aureus reflects in part the competition between host cutaneous immune defenses and S. aureus virulence factors. As part of the innate immune system in the skin, cationic antimicrobial peptides (CAMPs) such as the β-defensins and cathelicidin contribute to host cutaneous defense, which prevents harmful microorganisms, like S. aureus, from crossing epithelial barriers. Conversely, S. aureus utilizes evasive mechanisms against host defenses to promote its colonization and infection of the skin. In this review, we focus on host-pathogen interactions during colonization and infection of the skin by S. aureus and methicillin-resistant Staphylococcus aureus (MRSA). We will discuss the peptides (defensins, cathelicidins, RNase7, dermcidin) and other mediators (toll-like receptor, IL-1 and IL-17) that comprise the host defense against S. aureus skin infection, as well as the various mechanisms by which S. aureus evades host defenses. It is anticipated that greater understanding of these mechanisms will enable development of more sustainable antimicrobial compounds and new therapeutic approaches to the treatment of S. aureus skin infection and colonization.

Impact of Staphylococcus aureus on pathogenesis in polymicrobial infections

Polymicrobial infections involving Staphylococcus aureus exhibit enhanced disease severity and morbidity. We reviewed the nature of polymicrobial interactions between S. aureus and other bacterial, fungal, and viral cocolonizers. Microbes that were frequently recovered from the infection site with S. aureus are Haemophilus influenzae, Enterococcus faecalis, Pseudomonas aeruginosa, Streptococcus pneumoniae, Corynebacterium sp., Lactobacillus sp., Candida albicans, and influenza virus. Detailed analyses of several in vitro and in vivo observations demonstrate that S. aureus exhibits cooperative relations with C. albicans, E. faecalis, H. influenzae, and influenza virus and competitive relations with P. aeruginosa, Streptococcus pneumoniae, Lactobacillus sp., and Corynebacterium sp. Interactions of both types influence changes in S. aureus that alter its characteristics in terms of colony formation, protein expression, pathogenicity, and antibiotic susceptibility.

Dermatological therapy by topical application of non-pathogenic bacteria

The microbial community inhabiting skin is an important part of its defense, acting to control immune responses and to influence susceptibility to pathogens. In this issue, Volz et al. report that Vitreoscilla filiformis extracts modulate mouse cutaneous inflammatory responses induces of interleukin-10 production in dendritic cells and priming of regulatory T cells. These findings in a mouse model of atopic dermatitis advance observations of links between bacteria and host immunity, and they provide further evidence for novel therapeutic strategies to treat inflammation in skin.

Phenol-soluble modulins--critical determinants of staphylococcal virulence

Phenol-soluble modulins (PSMs) are a recently discovered family of amphipathic, alpha-helical peptides that have multiple roles in staphylococcal pathogenesis and contribute to a large extent to the pathogenic success of virulent staphylococci, such as Staphylococcus aureus. PSMs may cause lysis of many human cell types including leukocytes and erythrocytes, stimulate inflammatory responses, and contribute to biofilm development. PSMs appear to have an original role in the commensal lifestyle of staphylococci, where they facilitate growth and spreading on epithelial surfaces. Aggressive, cytolytic PSMs seem to have evolved from that original role and are mainly expressed in highly virulent S. aureus. Here, we will review the biochemistry, genetics, and role of PSMs in the commensal and pathogenic lifestyles of staphylococci, discuss how diversification of PSMs defines the aggressiveness of staphylococcal species, and evaluate potential avenues to target PSMs for drug development against staphylococcal infections.

Clinical characteristics of infections in humans due to Staphylococcus epidermidis

Staphylococcus epidermidis is the most common cause of primary bacteremia and infections of indwelling medical devices. The ability to cause disease is linked to its natural niche on human skin and ability to attach and form biofilm on foreign bodies. This review focuses on the S. epidermidis clinical syndromes most commonly encountered by clinicians and future potential treatment modalities.

The isolation and analysis of phenol-soluble modulins of Staphylococcus epidermidis

Phenol-soluble modulins (PSMs) are multifunctional peptide toxins produced by many staphylococcal strains. PSMs have received much recent attention, owing to multiple reports underscoring their importance for staphylococcal pathogenesis. Members of the PSM family may be strongly cytolytic to neutrophils and other cell types; promote inflammatory, receptor-mediated responses in several human cell types; and contribute to biofilm structuring and detachment. Here we describe biochemical methods to isolate, purify, and quantitatively analyze Staphylococcus epidermidis PSMs.

Phenol-soluble modulins: novel virulence-associated peptides of staphylococci

 Phenol-soluble modulins (PSMs), a novel class of small peptides with an amphipathic α-helical structure and strong surfactant-like properties, are produced by most staphylococci, especially pathogenic Staphylococcus aureus and Staphylococcus epidermidis. PSMs can: induce the production of proinflammatory cytokines; recruit, activate and lyse neutrophils to help staphylococci evade immune damage; lyse erythrocytes and are associated with the hemolysis of staphylococcal disease; facilitate the structuring and detachment of staphylococcal biofilms and disseminate biofilm-associated infection; and kill competing microbes and act as weapons in interbacterial warfare. Therefore, PSMs are considered to be critical virulence-associated factors and to play important roles in the pathogenesis of staphylococci. This review summarizes the classification, structure, expression regulation and biological functions of PSMs. The possible means to prevent PSM-associated diseases are also outlined in order to emphasize the need to investigate PSMs as potential targets for drug and vaccine design against staphylococcal infections.

What Lives On Our Skin: Ecology, Genomics and Therapeutic Opportunities Of the Skin Microbiome

Our skin is home to a rich community of microorganisms. Recent advances in sequencing technology have allowed more accurate enumeration of these human-associated microbiota and investigation of their genomic content. Staphylococcus, Corynebacterium and Propionibacterium represent the dominant bacterial genera on skin and illustrate how bacteria adapt to life in this harsh environment and also provide us with unique benefits. In healthy states, our skin peacefully co-exists with commensal bacteria while fending off potentially dangerous invaders. Disruption of this equilibrium, termed "dysbiosis", can result from changes in the composition of our skin bacteria, an altered immune response to them, or both and may be a driving factor in certain types of inflammatory skin disease. Engineering topical therapeutics to favourably influence the composition of our skin flora and optimize interactions with them represents a real therapeutic opportunity for the field of dermatology and warrants additional investigation into skin microbial ecology and disease mechanisms related to host-microbe dysbiosis.

Phenol-soluble modulins

PSMs are a recently discovered family of short, amphipathic, α-helical peptides in staphylococci. Several PSMs are key virulence determinants, particularly in highly virulent Staphylococcus aureus strains. PSMα peptides of S. aureus facilitate neutrophil lysis after phagocytosis, and are key contributors to several infection types, including skin infection and bacteremia. Furthermore, all PSMs contribute to biofilm structuring and the dissemination of biofilm-associated infection. Cytolytic PSMs as produced by S. aureus appear to have evolved from original functions in the non-infectious lifestyle of staphylococci. The surfactant properties of PSMs, which they all share, are believed to facilitate growth on epithelial surfaces. The basic role of PSMs in staphylococcal physiology is underscored, for example, by their exceptionally strict and direct control by quorum-sensing and the presence of a dedicated secretion system. Targeting PSMs for anti-staphylococcal drug development may be a promising approach to overcome the problems associated with widespread antibiotic resistance in staphylococci.

Staphylococcus epidermidis in the human skin microbiome mediates fermentation to inhibit the growth of Propionibacterium acnes: implications of probiotics in acne vulgaris

Increasing evidence demonstrates that commensal microorganisms in the human skin microbiome help fight pathogens and maintain homeostasis of the microbiome. However, it is unclear how these microorganisms maintain biological balance when one of them overgrows. The overgrowth of Propionibacterium acnes (P. acnes), a commensal skin bacterium, has been associated with the progression of acne vulgaris. Our results demonstrate that skin microorganisms can mediate fermentation of glycerol, which is naturally produced in skin, to enhance their inhibitory effects on P. acnes growth. The skin microorganisms, most of which have been identified as Staphylococcus epidermidis (S. epidermidis), in the microbiome of human fingerprints can ferment glycerol and create inhibition zones to repel a colony of overgrown P. acnes. Succinic acid, one of four short-chain fatty acids (SCFAs) detected in fermented media by nuclear magnetic resonance (NMR) analysis, effectively inhibits the growth of P. acnes in vitro and in vivo. Both intralesional injection and topical application of succinic acid to P. acnes-induced lesions markedly suppress the P. acnes-induced inflammation in mice. We demonstrate for the first time that bacterial members in the skin microbiome can undergo fermentation to rein in the overgrowth of P. acnes. The concept of bacterial interference between P. acnes and S. epidermidis via fermentation can be applied to develop probiotics against acne vulgaris and other skin diseases. In addition, it will open up an entirely new area of study for the biological function of the skin microbiome in promoting human health.

Functions of the skin microbiota in health and disease

The skin, the human body's largest organ, is home to a diverse and complex variety of innate and adaptive immune functions. Despite this potent immune system present at the cutaneous barrier, the skin encourages colonization by microorganisms. Characterization these microbial communities has enhanced our knowledge of the ecology of organisms present in normal skin; furthermore, studies have begun to bring to light the intimate relationships shared between host and resident microbes. In particular, it is apparent that just as host immunological factors and behaviors shape the composition of these communities, microbes present on the skin greatly impact the functions of human immunity. Thus, today the skin immune system should be considered a collective mixture of elements from the host and microbes acting in a mutualistic relationship. In this article we will review recent findings of the interactions of skin microbial communities with host immunity, and discuss the role that dysbiosis of these communities plays in diseases of the skin.

The role of the skin barrier in modulating the effects of common skin microbial species on the inflammation, differentiation and proliferation status of epidermal keratinocytes

Background

Skin resident microbial species are often thought of either as pathogenic or commensal. However, little is known about the role of the skin barrier in modulating their potential for causing disease. To investigate this question we measured the effects of three microbial species commonly found on the skin (Staphylococcus epidermidis, Staphylococcus aureus, and Propionibacterium acnes) on a reconstructed human epidermal model by either applying the bacteria on the model surface (intact barrier) or adding them to the culture medium (simulating barrier breach).

Results

When added to the medium, all of the tested species induced inflammatory responses and keratinocyte cell death with species-specific potency. P. acnes and S. epidermidis induced specific alterations in the expression of keratinocyte differentiation and proliferation markers, suggesting a barrier reparation response. S. aureus induced complete keratinocyte cell death. On the contrary, topically applied S. epidermidis and P. acnes caused no inflammatory response even when tested at high concentrations, while topical S. aureus induced a weak reaction. None of the tested species were able to alter the expression of keratinocyte differentiation or expression markers, when applied topically.

Conclusions

We show that the skin barrier prevents the effects of common skin bacteria on epidermal keratinocyte inflammation, differentiation and proliferation and highlight the importance of skin barrier in defending against the pathogenic effects of common skin bacteria.

Structure and function of the human skin microbiome

An abundant and diverse collection of bacteria, fungi, and viruses inhabits the human skin. These microorganisms vary between individuals and between different sites on the skin. The factors responsible for the unique variability of the skin microbiome are only partly understood, but results suggest that host genetic and environmental influences play a major role. Today, the steady accumulation of data describing the skin microbiome, combined with experiments designed to test the biological functions of surface microbes, has provided new insights into links between human physiology and skin microbiota. This review describes some of the current information regarding the skin microbiome and its impact on human health. Specifically, we summarize the present understanding of the function of microbe-host interactions on the skin and highlight some unique features that distinguish skin commensal organisms from pathogenic microbes.

Staphylococcus δ-toxin induces allergic skin disease by activating mast cells

Atopic dermatitis (AD) is a chronic inflammatory skin disease that affects 15 to 30% of children and ~5% of adults in industrialized countries¹. Although the pathogenesis of AD is not fully understood, the disease is mediated by an abnormal immunoglobulin E (IgE) immune response in the setting of skin barrier dysfunction². Mast cells (MCs) contribute to IgE-mediated allergic disorders including AD³. Upon activation, MCs release their membrane-bound cytosolic granules leading to the release of multiple molecules that are important in the pathogenesis of AD and host defense⁴. More than 90% of AD patients are colonized with Staphylococcus aureus in the lesional skin whereas most healthy individuals do not harbor the pathogen⁵. Several Staphylococcal exotoxins (SEs) can act as superantigens and/or antigens in models of AD⁶. However, the role of these SEs in disease pathogenesis remains unclear. Here, we report that culture supernatants of S. aureus contain potent MC degranulation activity. Biochemical analysis identified δ-toxin as the MC degranulation-inducing factor produced by S. aureus. MC degranulation induced by δ-toxin depended on phosphoinositide 3-kinase (PI3K) and calcium (Ca²⁺) influx, but unlike that mediated by IgE crosslinking, it did not require the spleen tyrosine kinase (Syk). In addition, IgE enhanced δ-toxin-induced MC degranulation in the absence of antigen. Furthermore, S. aureus isolates recovered from AD patients produced high levels of δ-toxin. Importantly, skin colonization with S. aureus, but not a mutant deficient in δ-toxin, promoted IgE and IL-4 production, as well as inflammatory skin disease. Furthermore, enhancement of IgE production and dermatitis by δ-toxin was abrogated in Kit^W-sh/W-sh MC-deficient mice and restored by MC reconstitution. These studies identify δ-toxin as a potent inducer of MC degranulation and suggest a mechanistic link between S. aureus colonization and allergic skin disease.

Phenol-soluble modulins and staphylococcal infection

Staphylococcus aureus is an important human pathogen and a leading cause of death worldwide. Phenol-soluble modulins (PSMs) have recently emerged as a novel toxin family defining the virulence potential of highly aggressive S. aureus isolates. PSMs have multiple roles in staphylococcal pathogenesis, causing lysis of red and white blood cells, stimulating inflammatory responses and contributing to biofilm development and the dissemination of biofilm-associated infections. Moreover, the pronounced capacity of PSMs to kill human neutrophils after phagocytosis might explain failures in the development of anti-staphylococcal vaccines. Here, we discuss recent progress made in our understanding of the biochemical and genetic properties of PSMs and their role in S. aureus pathogenesis, and suggest potential avenues to target PSMs for the development of anti-staphylococcal drugs.

Potential role of microorganisms in the pathogenesis of rosacea

Rosacea is a skin condition of abnormal inflammation and vascular dysfunction. The active contribution of a microbial agent in the development or progression of rosacea continues to be debated. Research supports the presence of commensal Demodex folliculorum mites at increased density in the skin and associates Helicobacter pylori infection of the gut with rosacea. Fewer studies implicate Staphylococcus epidermidis, Chlamydophila pneumoniae, and the Demodex-associated bacteria Bacillus oleronius. No research, however, provides a mechanism by which colonization by a microorganism translates to manifestation of the condition. Prevailing and emerging principles in the biology of the microbiome and the pathophysiology of rosacea may help to reconcile these lingering questions. Here the microorganisms implicated in rosacea are reviewed and the reaction of the microbiome to inflammation and to changes in microenvironments and macroenvironments are discussed to explain potential roles for microorganisms in rosacea pathophysiology.

Insight into structure-function relationship in phenol-soluble modulins using an alanine screen of the phenol-soluble modulin (PSM) α3 peptide

Phenol-soluble modulins (PSMs) are a family of peptides with multiple functions in staphylococcal pathogenesis. To gain insight into the structural features affecting PSM functions, we analyzed an alanine substitution library of PSMα3, a strongly cytolytic and proinflammatory PSM of Staphylococcus aureus with a significant contribution to S. aureus virulence. Lysine residues were essential for both receptor-dependent proinflammatory and receptor-independent cytolytic activities. Both phenotypes also required additional structural features, with the C terminus being crucial for receptor activation. Biofilm formation was affected mostly by hydrophobic amino acid positions, suggesting that the capacity to disrupt hydrophobic interactions is responsible for the effect of PSMs on biofilm structure. Antimicrobial activity, absent from natural PSMα3, could be created by the exchange of large hydrophobic side chains, indicating that PSMα3 has evolved to exhibit cytolytic rather than antimicrobial activity. In addition to gaining insight into the structure-function relationship in PSMs, our study identifies nontoxic PSMα3 derivatives for active vaccination strategies and lays the foundation for future efforts aimed to understand the biological role of PSM recognition by innate host defense.

Microbial biosurfactants as additives for food industries

Microbial biosurfactants with high ability to reduce surface and interfacial surface tension and conferring important properties such as emulsification, detergency, solubilization, lubrication and phase dispersion have a wide range of potential applications in many industries. Significant interest in these compounds has been demonstrated by environmental, bioremediation, oil, petroleum, food, beverage, cosmetic and pharmaceutical industries attracted by their low toxicity, biodegradability and sustainable production technologies. Despite having significant potentials associated with emulsion formation, stabilization, antiadhesive and antimicrobial activities, significantly less output and applications have been reported in food industry. This has been exacerbated by uneconomical or uncompetitive costing issues for their production when compared to plant or chemical counterparts. In this review, biosurfactants properties, present uses and potential future applications as food additives acting as thickening, emulsifying, dispersing or stabilising agents in addition to the use of sustainable economic processes utilising agro-industrial wastes as alternative substrates for their production are discussed.

Staphylococcal alpha-phenol soluble modulins contribute to neutrophil lysis after phagocytosis

Staphylococcus aureus community-acquired (CA) MRSA strains are highly virulent and can cause infections in otherwise healthy individuals. The most important mechanism of the host for clearing S. aureus is phagocytosis by neutrophils and subsequent killing of the pathogen. Especially CA-MRSA strains are very efficient in circumventing this neutrophil killing. Interestingly, only a relative small number of virulence factors have been associated with CA-MRSA, one of which are the phenol soluble modulins (PSMs). We have recently shown that the PSMs are functionally inhibited by serum lipoproteins, indicating that PSMs may exert their cytolytic function primarily in the intracellular environment. To further investigate the intracellular role of the PSMs we measured the effect of the α-type and β-type PSMs on neutrophil killing after phagocytosis. Using fluorescently labelled S. aureus, we measured bacterial survival after phagocytosis in a plate reader, which was employed next to flow cytometry and time-lapse microscopy. Phagocytosis of the CA-MRSA strain MW2 by human neutrophils resulted in rapid host cell death. Using mutant strains of MW2, we demonstrated that in the presence of serum, the intracellular expression of only the psmα operon is both necessary and sufficient for both increased neutrophil cell death and increased survival of S. aureus. Our results identify PSMα peptides as prominent contributors to killing of neutrophils after phagocytosis, a finding with major implications for our understanding of S. aureus pathogenesis and strategies for S. aureus vaccine development.

The cutaneous innate immune response in patients with atopic dermatitis

Orchestrating when and how the cutaneous innate immune system should respond to commensal or pathogenic microbes is a critical function of the epithelium. The cutaneous innate immune system is a key determinant of the physical, chemical, microbial, and immunologic barrier functions of the epidermis. A malfunction in this system can lead to an inadequate host response to a pathogen or a persistent inflammatory state. Atopic dermatitis is the most common inflammatory skin disorder and characterized by abnormalities in both skin barrier structures (stratum corneum and tight junctions), a robust T(H)2 response to environmental antigens, defects in innate immunity, and an altered microbiome. Many of these abnormalities may occur as the consequence of epidermal dysfunction. The epidermis directly interfaces with the environment and, not surprisingly, expresses many pattern recognition receptors that make it a key player in cutaneous innate immune responses to skin infections and injury. This review will discuss the role epidermal innate receptors play in regulation of skin barriers and, where possible, discuss the relevance of these findings for patients with atopic dermatitis.

Solution structures of the linear leaderless bacteriocins enterocin 7A and 7B resemble carnocyclin A, a circular antimicrobial peptide

Leaderless bacteriocins are a class of ribosomally synthesized antimicrobial peptides that are produced by certain Gram-positive bacteria without an N-terminal leader section. These bacteriocins are of great interest due to their potent inhibition of many Gram-positive organisms, including food-borne pathogens such as Listeria and Clostridium spp. We now report the NMR solution structures of enterocins 7A and 7B, leaderless bacteriocins recently isolated from Enterococcus faecalis 710C. These are the first three-dimensional structures to be reported for bacteriocins of this class. Unlike most other linear Gram-positive bacteriocins, enterocins 7A and 7B are highly structured in aqueous conditions. Both peptides are primarily α-helical, adopting a similar overall fold. The structures can be divided into three separate α-helical regions: the N- and C-termini are both α-helical, separated by a central kinked α-helix. The overall structures bear an unexpected resemblance to carnocyclin A, a 60-residue peptide that is cyclized via an amide bond between the C- and N-termini and has a saposin fold. Because of synergism observed for other two-peptide leaderless bacteriocins, it was of interest to probe possible binding interactions between enterocins 7A and 7B. However, despite synergistic activity observed between these peptides, no significant binding interaction was observed based on NMR and isothermal calorimetry.