Nasal colonisation by Staphylococcus aureus depends upon clumping factor B binding to the squamous epithelial cell envelope protein loricrin

TEAL-Seq: targeted expression analysis sequencing

Metagenome sequencing enables the genetic characterization of complex microbial communities. However, determining the activity of isolates within a community presents several challenges, including the wide range of organismal and gene expression abundances, the presence of host RNA, and low microbial biomass at many sites. To address these limitations, we developed "targeted expression analysis sequencing" or TEAL-seq, enabling sensitive species-specific analyses of gene expression using highly multiplexed custom probe pools. For proof of concept, we targeted about 1,700 core and accessory genes of Staphylococcus aureus and S. epidermidis, two key species of the skin microbiome. Two targeting methods were applied to laboratory cultures and human nasal swab specimens. Both methods showed a high degree of specificity, with >90% reads on target, even in the presence of complex microbial or human background DNA/RNA. Targeting using molecular inversion probes demonstrated excellent correlation in inferred expression levels with bulk RNA-seq. Furthermore, we show that a linear pre-amplification step to increase the number of nucleic acids for analysis yielded consistent and predictable results when applied to complex samples and enabled profiling of expression from as little as 1 ng of total RNA. TEAL-seq is much less expensive than bulk metatranscriptomic profiling, enables detection across a greater dynamic range, and uses a strategy that is readily configurable for determining the transcriptional status of organisms in any microbial community.IMPORTANCEThe gene expression patterns of bacteria in microbial communities reflect their activity and interactions with other community members. Measuring gene expression in complex microbiome contexts is challenging, however, due to the large dynamic range of microbial abundances and transcript levels. Here we describe an approach to assessing gene expression for specific species of interest using highly multiplexed pools of targeting probes. We show that an isothermal amplification step enables the profiling of low biomass samples. TEAL-seq should be widely adaptable to the study of microbial activity in natural environments.

The endothelium at the interface between tissues and Staphylococcus aureus in the bloodstream

SUMMARYStaphylococcus aureus is a major human pathogen. It can cause many types of infections, in particular bacteremia, which frequently leads to infective endocarditis, osteomyelitis, sepsis, and other debilitating diseases. The development of secondary infections is based on the bacterium's ability to associate with endothelial cells lining blood vessels. The success of endothelial colonization and infection by S. aureus relies on its ability to express a wide array of cell wall-anchored and secreted virulence factors. Establishment of endothelial infection by the pathogen is a multistep process involving adhesion, invasion, extravasation, and dissemination of the bacterium into surrounding tissues. The process is dependent on the type of endothelium in different organs (tissues) and pathogenetic potential of the individual strains. In this review, we report an update on the organization of the endothelium in the vessels, the structure and function of the virulence factors of S. aureus, and the several aspects of bacteria-endothelial cell interactions. After these sections, we will discuss recent advances in understanding the specific mechanisms of infections that develop in the heart, bone and joints, lung, and brain. Finally, we describe how neutrophils bind to endothelial cells, migrate to the site of infection to kill bacteria in the tissues, and how staphylococci counteract neutrophils' actions. Knowledge of the molecular details of S. aureus-endothelial cell interactions will promote the development of new therapeutic strategies and tools to combat this formidable pathogen.

The mutational landscape of Staphylococcus aureus during colonisation

Staphylococcus aureus is an important human pathogen and a commensal of the human nose and skin. Survival and persistence during colonisation are likely major drivers of S. aureus evolution. Here we applied a genome-wide mutation enrichment approach to a genomic dataset of 3060 S. aureus colonization isolates from 791 individuals. Despite limited within-host genetic diversity, we observed an excess of protein-altering mutations in metabolic genes, in regulators of quorum-sensing (agrA and agrC) and in known antibiotic targets (fusA, pbp2, dfrA and ileS). We demonstrated the phenotypic effect of multiple adaptive mutations in vitro, including changes in haemolytic activity, antibiotic susceptibility, and metabolite utilisation. Nitrogen metabolism showed the strongest evidence of adaptation, with the assimilatory nitrite reductase (nasD) and urease (ureG) showing the highest mutational enrichment. We identified a nasD natural mutant with enhanced growth under urea as the sole nitrogen source. Inclusion of 4090 additional isolate genomes from 731 individuals revealed eight more genes including sasA/sraP, darA/pstA, and rsbU with signals of adaptive variation that warrant further characterisation. Our study provides a comprehensive picture of the heterogeneity of S. aureus adaptive changes during colonisation, and a robust methodological approach applicable to study in host adaptive evolution in other bacterial pathogens.

In silico testing to identify compounds that inhibit ClfA and ClfB binding to the host for the formulation of future drugs against Staphylococcus aureus colonization and infection

Introduction

Staphylococcus aureus is a highly resistant pathogen. It has multiple virulence factors, which makes it one of the most pathogenic bacteria for humankind. The vast increase in antibiotic resistance in these bacteria is a warning of existing healthcare policies. Most of the available antibiotics are ineffective due to resistance; this situation requires the development of drugs that target specific proteins and are not susceptible to resistance.

Methods

In this study, we identified a compound that acts as an antagonist of ClfA and ClfB by inhibiting their binding to host cells.

Results

The shortlisted compound's binding activity was tested by docking and molecular dynamics during its interaction with proteins. The identified compound has excellent binding energy with both ClfA (-10.11 kcal/mol) and ClfB (-11.11 kcal/mol).

Discussion

The molecular dynamics of the protein and compound were stable and promising for further in vitro and in vivo tests. The performance of our compound was tested and compared with that of the control molecule allantodapsone, which was reported in a previous study as a pan inhibitor of the clumping factor. An ADMET study of our selected compound revealed its reliable drug likeliness. This compound is an ideal candidate for in vitro studies.

Type 1 interferons promote Staphylococcus aureus nasal colonization by inducing phagocyte apoptosis

Staphylococcus aureus is an important human commensal which persistently colonizes up to 30% of the human population, predominantly within the nasal cavity. The commensal lifestyle of S. aureus is complex, and the mechanisms underpinning colonization are not fully understood. S. aureus can induce an immunosuppressive environment in the nasal tissue (NT) by driving IL-10 and IL-27 to facilitate nasal colonization, indicating that S. aureus has the capacity to modulate the local immune environment for its commensal habitation. Mounting evidence suggests commensal bacteria drive type 1 interferons (IFN-I) to establish an immunosuppressive environment and whilst S. aureus can induce IFN-I during infection, its role in colonization has not yet been examined. Here, we show that S. aureus preferentially induces IFN signaling in macrophages. This IFN-I in turn upregulates expression of proapoptotic genes within macrophages culminating in caspase-3 cleavage. Importantly, S. aureus was found to drive phagocytic cell apoptosis in the nasal tissue during nasal colonization in an IFN-I dependent manner with colonization significantly reduced under caspase-3 inhibition. Overall, loss of IFN-I signaling significantly diminished S. aureus nasal colonization implicating a pivotal role for IFN-I in controlling S. aureus persistence during colonization through its ability to induce phagocyte apoptosis. Together, this study reveals a novel strategy utilized by S. aureus to circumvent host immunity in the nasal mucosa to facilitate nasal colonization.

Cell-wall-anchored proteins affect invasive host colonization and biofilm formation in Staphylococcus aureus

As a major human and animal pathogen, Staphylococcus aureus can attach to medical implants (abiotic surface) or host tissues (biotic surface), and further establish robust biofilms which enhances resistance and persistence to host immune system and antibiotics. Cell-wall-anchored proteins (CWAPs) covalently link to peptidoglycan, and largely facilitate the colonization of S. aureus on various surfaces (including adhesion and biofilm formation) and invasion into host cells (including adhesion, immune evasion, iron acquisition and biofilm formation). During biofilm formation, CWAPs function in adhesion, aggregation, collagen-like fiber network formation, and consortia formation. In this review, we firstly focus on the structural features of CWAPs, including their intracellular function and interactions with host cells, as well as the functions and ligand binding of CWAPs in different stages of S. aureus biofilm formation. Then, the roles of CWAPs in different biofilm processes with regards in development of therapeutic approaches are clarified, followed by the association between CWAPs genes and clonal lineages. By touching upon these aspects, we hope to provide comprehensive knowledge and clearer understanding on the CWAPs of S. aureus and their roles in biofilm formation, which may further aid in prevention and treatment infection and vaccine development.

IL-10 inhibition during immunization improves vaccine-induced protection against Staphylococcus aureus infection

Staphylococcus aureus is a major human pathogen. An effective anti-S. aureus vaccine remains elusive as the correlates of protection are ill-defined. Targeting specific T cell populations is an important strategy for improving anti-S. aureus vaccine efficacy. Potential bottlenecks that remain are S. aureus-induced immunosuppression and the impact this might have on vaccine-induced immunity. S. aureus induces IL-10, which impedes effector T cell responses, facilitating persistence during both colonization and infection. Thus, it was hypothesized that transient targeting of IL-10 might represent an innovative way to improve vaccine efficacy. In this study, IL-10 expression was elevated in the nares of persistent carriers of S. aureus, and this was associated with reduced systemic S. aureus-specific Th1 responses. This suggests that systemic responses are remodeled because of commensal exposure to S. aureus, which negatively implicates vaccine function. To provide proof of concept that targeting immunosuppressive responses during immunization may be a useful approach to improve vaccine efficacy, we immunized mice with T cell-activating vaccines in combination with IL-10-neutralizing antibodies. Blocking IL-10 during vaccination enhanced effector T cell responses and improved bacterial clearance during subsequent systemic and subcutaneous infection. Taken together, these results reveal a potentially novel strategy for improving anti-S. aureus vaccine efficacy.

Antivirulence Effects of Trans-Resveratrol and Curcumin on Methicillin-Resistant Staphylococcus aureus (MRSA) from Saudi Arabia

Methicillin-resistant Staphylococcus aureus (MRSA) is a common resistant bacterium, whose resistance has expanded to commonly used antibiotics. It is crucial to create novel treatments to tackle bacterial resistance. Trans-resveratrol and curcumin are naturally occurring phenolic compounds, whose effects on MRSA virulence are the subject of this investigation. Sub-MICs of trans-resveratrol and curcumin were tested on the virulence factors of 50 MRSA clinical isolates (CIs), including biofilm, hemolysin, hemagglutination, protease, and lecithinase. The distribution of the virulence factors of the CIs was as follows: hemolysin: 98%, hemagglutination: 70%, protease: 62%, biofilm: 56%, and lecithinase: 52%. The sub-MIC that could reduce the effect of the tested virulence factors by 50% or more (IC50) was observed in the strains that showed susceptibility to the individual administration of trans-resveratrol at 50 µg/mL and curcumin at 20 µg/mL. Hemagglutination and hemolysin activity were inhibited by at least 50% in the majority of CIs (57-94%). Meanwhile, the IC50 for protease and biofilm was observed in 6.5-17.8% of the CIs. A few of the CIs were susceptible to lecithinase inhibition, but all showed a full inhibition. This research supports the possibility of the use of these compounds to reduce the bacterial virulence that can reduce antibiotic utilization, and eventually, they can become a potential alternative treatment in combating bacterial resistance.

Development of nanobodies specific to clumping factors A of Staphylococcus aureus by yeast surface display

The Staphylococcus aureus clumping factor A (ClfA) is a fibrinogen (Fg) binding protein that plays an important role in the clumping of S. aureus in blood plasma. The current anti-infective approaches targeting ClfA are mainly based on monoclonal antibodies but showed less impressive efficacy for clinical applications. Nanobodies offer advantages in enhanced tissue penetration and a propensity to bind small epitopes. However, there is no report on generating specific nanobodies for ClfA. Here, we constructed a synthetic nanobody library based on yeast surface display to isolate nanobodies against the Fg binding domain ClfA221-550. We firstly obtained a primary nanobody directed to ClfA221-550, and then employed error-prone mutagenesis to enhance its binding affinity. Finally, 18 variants were isolated with high affinities (EC50, 1.1 ± 0.1 nM to 4.8 ± 0.3 nM), in which CNb1 presented the highest inhibition efficiency in the adhesion of S. aureus to fibrinogen. Moreover, structural simulation analysis indicated that the epitope for CNb1 partially overlapped with the binding sites for fibrinogen, thus inhibiting ClfA binding to Fg. Overall, these results indicated that the specific nanobodies generated here could prevent the adhesion of S. aureus to fibrinogen, suggesting their potential capacities in the control of S. aureus infections.

Comparative proteomic analysis of vancomycin-sensitive and vancomycin-intermediate resistant Staphylococcus aureus

PURPOSE

The extensive use of vancomycin has led to the development of Staphylococcus aureus strains with varying degrees of resistance to vancomycin. The present study aimed to explore the molecular causes of vancomycin resistance by conducting a proteomics analysis of subcellular fractions isolated from vancomycin-intermediate resistant S. aureus (VISA) and vancomycin-sensitive S. aureus (VSSA) strains.

METHODS

We conducted proteomics analysis of subcellular fractions isolated from 2 isogenic S. aureus strains: strain 11 (VSSA) and strain 11Y (VISA). We used an integrated quantitative proteomics approach assisted by bioinformatics analysis, and comprehensively investigated the proteome profile. Intensive bioinformatics analysis, including protein annotation, functional classification, functional enrichment, and functional enrichment-based cluster analysis, was used to annotate quantifiable targets.

RESULTS

We identified 128 upregulated proteins and 21 downregulated proteins in strain 11Y as compared to strain 11. The largest group of differentially expressed proteins was composed of enzymatic proteins associated with metabolic and catalytic activity, which accounted for 32.1% and 50% of the total proteins, respectively. Some proteins were indispensable parts of the regulatory networks of S. aureus that were altered with vancomycin treatment, and these proteins were related to cell wall metabolism, cell adhesion, proteolysis, and pressure response.

CONCLUSION

Our proteomics study revealed regulatory proteins associated with vancomycin resistance in S. aureus. Some of these proteins were involved in the regulation of cell metabolism and function, which provides potential targets for the development of strategies to manage vancomycin resistance in S. aureus.

Whole-Genome Investigation of Zoonotic Transmission of Livestock-Associated Methicillin-Resistant Staphylococcus aureus Clonal Complex 398 Isolated from Pigs and Humans in Thailand

Livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) has been widespread globally in pigs and humans for decades. Nasal colonization of LA-MRSA is regarded as an occupational hazard to people who are regularly involved in livestock production. Our previous study suggested pig-to-human transmission caused by LA-MRSA clonal complex (CC) 398, using traditional molecular typing methods. Instead, this study aimed to investigate the zoonotic transmission of LA-MRSA CC398 using whole genome sequencing (WGS) technologies. A total of 63 LA-MRSA isolates were identified and characterized in Thailand. Further, the 16 representatives of LA-MRSA CC9 and CC398, including porcine and worker isolates, were subjected to WGS on the Illumina Miseq platform. Core-genome single nucleotide polymorphism (SNP)-based analyses verify the zoonotic transmission caused by LA-MRSA CC398 in two farms. WGS-based characterization suggests the emergence of a novel staphylococcal cassette chromosome (SCC) mec type, consisting of multiple cassette chromosome recombinase (ccr) gene complexes via genetic recombination. Additionally, the WGS analyses revealed putative multi-resistant plasmids and several cross-resistance genes, conferring resistance against drugs of last resort used in humans such as quinupristin/dalfopristin and linezolid. Significantly, LA-MRSA isolates, in this study, harbored multiple virulence genes that may become a serious threat to an immunosuppressive population, particularly for persons who are in close contact with LA-MRSA carriers.

The A domain of clonal complex 1-type fibronectin binding protein B promotes adherence and biofilm formation in Staphylococcus aureus

Adhesive interactions between Staphylococcus aureus and the host rely on cell-wall-anchored proteins such as fibronectin-binding protein B (FnBPB). Recently we showed that the FnBPB protein expressed by clonal complex (CC) 1 isolates of S. aureus mediates bacterial adhesion to corneodesmosin. The proposed ligand-binding region of CC1-type FnBPB shares just 60 % amino acid identity with the archetypal FnBPB protein from CC8. Here we investigated ligand binding and biofilm formation by CC1-type FnBPB. We found that the A domain of FnBPB binds to fibrinogen and corneodesmosin and identified residues within the hydrophobic ligand trench in the A domain that are essential for the binding of CC1-type FnBPB to ligands and during biofilm formation. We further investigated the interplay between different ligands and the influence of ligand binding on biofilm formation. Overall, our study provides new insights into the requirements for CC1-type FnBPB-mediated adhesion to host proteins and FnBPB-mediated biofilm formation in S. aureus.

Functional diversity of staphylococcal surface proteins at the host-microbe interface

Surface proteins of Gram-positive pathogens are key determinants of virulence that substantially shape host-microbe interactions. Specifically, these proteins mediate host invasion and pathogen transmission, drive the acquisition of heme-iron from hemoproteins, and subvert innate and adaptive immune cell responses to push bacterial survival and pathogenesis in a hostile environment. Herein, we briefly review and highlight the multi-facetted roles of cell wall-anchored proteins of multidrug-resistant Staphylococcus aureus, a common etiological agent of purulent skin and soft tissue infections as well as severe systemic diseases in humans. In particular, we focus on the functional diversity of staphylococcal surface proteins and discuss their impact on the variety of clinical manifestations of S. aureus infections. We also describe mechanistic and underlying principles of staphylococcal surface protein-mediated immune evasion and coupled strategies S. aureus utilizes to paralyze patrolling neutrophils, macrophages, and other immune cells. Ultimately, we provide a systematic overview of novel therapeutic concepts and anti-infective strategies that aim at neutralizing S. aureus surface proteins or sortases, the molecular catalysts of protein anchoring in Gram-positive bacteria.

MRSA lineage USA300 isolated from bloodstream infections exhibit altered virulence regulation

The epidemic community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) USA300 lineage has recently become a leading cause of hospital-associated bloodstream infections (BSIs). Here, we leveraged this recent introduction into hospitals and the limited genetic variation across USA300 isolates to identify mutations that contribute to its success in a new environment. We found that USA300 BSI isolates exhibit altered virulence regulation. Using comparative genomics to delineate the genes involved in this phenotype, we discovered repeated and independent mutations in the transcriptional regulator sarZ. Mutations in sarZ resulted in increased virulence of USA300 BSI isolates in a murine model of BSI. The sarZ mutations derepressed the expression and production of the surface protein ClfB, which was critical for the pathogenesis of USA300 BSI isolates. Altogether, these findings highlight ongoing evolution of a major MRSA lineage and suggest USA300 strains can optimize their fitness through altered regulation of virulence.

Staphylococcal Corneocyte Adhesion: Assay Optimization and Roles of Aap and SasG Adhesins in the Establishment of Healthy Skin Colonization

Staphylococcus aureus is an opportunistic pathogen that causes the majority of wound and soft tissue infections. The accumulation-associated protein (Aap) from S. epidermidis and surface protein G (SasG) from S. aureus are cell wall-anchored (CWA) proteins known to be important in adhesion to healthy corneocytes from human skin. We investigated the mechanisms by which S. aureus colonizes healthy human skin by developing an optimized corneocyte adhesion assay. Trypan blue was used for enhanced red autofluorescent visualization of corneocytes with an overlay of green-fluorescent bacteria. The percent area of bacterial adhesion for images acquired by a fluorescence microscope was quantified using Fiji ImageJ. Using this optimized imaging procedure, differences in adhesion between various species and strains of staphylococci were measured. The ability of purified SasG to reduce Staphylococcus epidermidis adhesion was investigated in order to determine if these CWA proteins can compete for binding sites. To further test CWA-mediated adhesion, we engineered a nonadhering S. carnosus strain to express full-length SasG from two methicillin-resistant S. aureus (MRSA) strains. Finally, we demonstrated that the SasG A domain was a critical region of this surface protein for adherence to healthy human corneocytes. The developed imaging and expression methods are useful for studying staphylococcal adhesion to healthy human skin and have the potential to be used with a wide variety of fluorescently labeled organisms on both healthy and disease-state (such as atopic dermatitis) corneocytes. IMPORTANCE The skin is the largest organ of the human body and acts as a shield against hazards such as harmful bacteria like Staphylococcus aureus. A diverse skin microbiota and immune cross talk control S. aureus numbers. S. aureus can bind to healthy skin and subsequently proliferate when the skin barrier is compromised, such as in a wound or in patients with atopic dermatitis (AD). It is important to understand these mechanisms in an effort to prevent pathogenic bacteria from causing infection. We describe an augmented corneocyte adhesion assay using fluorescence microscopy to study binding of various staphylococcal species to healthy human skin cells. In addition, we tested the ability of homologous proteins from different staphylococcal species to reduce binding, and developed a new S. carnosus expression system to test individual protein binding properties. Our newly developed methods and findings will enhance the understanding of how staphylococci bind to healthy human skin.

Adhesive Virulence Factors of Staphylococcus aureus Resist Digestion by Coagulation Proteases Thrombin and Plasmin

Staphylococcus aureus (S. aureus) is an invasive and life-threatening pathogen that has undergone extensive coevolution with its mammalian hosts. Its molecular adaptations include elaborate mechanisms for immune escape and hijacking of the coagulation and fibrinolytic pathways. These capabilities are enacted by virulence factors including microbial surface components recognizing adhesive matrix molecules (MSCRAMMs) and the plasminogen-activating enzyme staphylokinase (SAK). Despite the ability of S. aureus to modulate coagulation, until now the sensitivity of S. aureus virulence factors to digestion by proteases of the coagulation system was unknown. Here, we used protein engineering, biophysical assays, and mass spectrometry to study the susceptibility of S. aureus MSCRAMMs to proteolytic digestion by human thrombin, plasmin, and plasmin/SAK complexes. We found that MSCRAMMs were highly resistant to proteolysis, and that SAK binding to plasmin enhanced this resistance. We mapped thrombin, plasmin, and plasmin/SAK cleavage sites of nine MSCRAMMs and performed biophysical, bioinformatic, and stability analysis to understand structural and sequence features common to protease-susceptible sites. Overall, our study offers comprehensive digestion patterns of S. aureus MSCRAMMs by thrombin, plasmin, and plasmin/SAK complexes and paves the way for new studies into this resistance and virulence mechanism.

Novel Requirement for Staphylococcal Cell Wall-Anchored Protein SasD in Pulmonary Infection

Staphylococcus aureus can complicate preceding viral infections, including influenza virus. A bacterial infection combined with a preceding viral infection, known as superinfection, leads to worse outcomes than a single infection. Most of the pulmonary infection literature focuses on the changes in immune responses to bacteria between homeostatic and virally infected lungs. However, it is unclear how much of an influence bacterial virulence factors have in single or superinfection. Staphylococcal species express a broad range of cell wall-anchored proteins (CWAs) that have roles in host adhesion, nutrient acquisition, and immune evasion. We screened the importance of these CWAs using mutants lacking individual CWAs in vivo in both bacterial pneumonia and influenza superinfection. In bacterial pneumonia, the lack of individual CWAs leads to various decreases in bacterial burden, lung damage, and immune infiltration into the lung. However, the presence of a preceding influenza infection partially abrogates the requirement for CWAs. In the screen, we found that the uncharacterized CWA S. aureus surface protein D (SasD) induced changes in both inflammatory and homeostatic lung markers. We further characterized a SasD mutant (sasD A50.1) in the context of pneumonia. Mice infected with sasD A50.1 have decreased bacterial burden, inflammatory responses, and mortality compared to wild-type S. aureus. Mice also have reduced levels of interleukin-1β (IL-1β), likely derived from macrophages. Reductions in IL-1β transcript levels as well as increased macrophage viability point at differences in cell death pathways. These data identify a novel virulence factor for S. aureus that influences inflammatory signaling within the lung. IMPORTANCE Staphylococcus aureus is a common commensal bacterium that can cause severe infections, such as pneumonia. In the lung, viral infections increase the risk of staphylococcal pneumonia, leading to combined infections known as superinfections. The most common virus associated with S. aureus pneumonia is influenza, and superinfections lead to worse patient outcomes than either infection alone. While there is much known about how the immune system differs between healthy and virally infected lungs, the role of bacterial virulence factors in single and superinfection is less understood. The significance of our research is identifying bacterial components that play a role in the initiation of lung injury, which could lead to future therapies to prevent pulmonary single or superinfection with S. aureus.

Staphylococcus aureus-induced immunosuppression mediated by IL-10 and IL-27 facilitates nasal colonisation

Staphylococcus aureus persistently colonises the anterior nares of a significant proportion of the healthy population, however the local immune response elicited during S. aureus nasal colonisation remains ill-defined. Local activation of IL-17/IL-22 producing T cells are critical for controlling bacterial clearance from the nasal cavity. However, recurrent and long-term colonisation is commonplace indicating efficient clearance does not invariably occur. Here we identify a central role for the regulatory cytokine IL-10 in facilitating bacterial persistence during S. aureus nasal colonisation in a murine model. IL-10 is produced rapidly within the nasal cavity following S. aureus colonisation, primarily by myeloid cells. Colonised IL-10^-/- mice demonstrate enhanced IL-17+ and IL-22+ T cell responses and more rapidly clear bacteria from the nasal tissues as compared with wild-type mice. S. aureus also induces the regulatory cytokine IL-27 within the nasal tissue, which acts upstream of IL-10 promoting its production. IL-27 blockade reduces IL-10 production within the nasal cavity and improves bacterial clearance. TLR2 signalling was confirmed to be central to controlling the IL-10 response. Our findings conclude that during nasal colonisation S. aureus creates an immunosuppressive microenvironment through the local induction of IL-27 and IL-10, to dampen protective T cell responses and facilitate its persistence.

Nasal colonisation by the bacterium Staphylococcus aureus is a very common occurrence in the human population. However there is a lack of knowledge on the immune response that controls nasal colonisation. It is known that a local pro-inflammatory immune response is important for bacterial clearance, however sustained colonisation is commonplace suggesting efficient clearance may not be occurring. Here we demonstrate for the first time that S. aureus is manipulating the host immune response by promoting immunosuppression in the nasal cavity which enables bacterial survival. We found that the regulatory proteins IL-10 and IL-27 are central to this suppressive response and result in reduced protective T cell responses. We also demonstrate that S. aureus is inducing IL-27 production to enhance IL-10 production in order to prolong bacterial colonisation. Our findings show that the host-pathogen interaction during nasal colonisation is more complex than previously described and that S. aureus is capable of manipulating the regulatory immune response of the host for its’ own benefit.

Allantodapsone is a Pan-Inhibitor of Staphylococcus aureus Adhesion to Fibrinogen, Loricrin, and Cytokeratin 10

Staphylococcus aureus infections have become a major challenge in health care due to increasing antibiotic resistance. We aimed to design small molecule inhibitors of S. aureus surface proteins to be developed as colonization inhibitors. We identified allantodapsone in an initial screen searching for inhibitors of clumping factors A and B (ClfA and ClfB). We used microbial adhesion assays to investigate the effect of allantodapsone on extracellular matrix protein interactions. Allantodapsone inhibited S. aureus Newman adhesion to fibrinogen with an IC50 of 21.3 μM (95% CI 4.5-102 μM), minimum adhesion inhibitory concentration (MAIC) of 100 μM (40.2 μg/mL). Additionally, allantodapsone inhibited adhesion of Lactococcus lactis strains exogenously expressing the clumping factors to fibrinogen (L. lactis ClfA, IC50 of 3.8 μM [95% CI 1.0-14.3 μM], MAIC 10 μM, 4.0 μg/mL; and L. lactis ClfB, IC50 of 11.0 μM [95% CI 0.9-13.6 μM], MAIC 33 μM, 13.3 μg/mL), indicating specific inhibition. Furthermore, the dapsone and alloxan fragments of allantodapsone did not have any inhibitory effect. Adhesion of S. aureus Newman to L2v loricrin is dependent on the expression of ClfB. Allantodapsone caused a dose dependent inhibition of S. aureus adhesion to the L2v loricrin fragment, with full inhibition at 40 μM (OD600 0.11 ± 0.01). Furthermore, recombinant ClfB protein binding to L2v loricrin was inhibited by allantodapsone (P < 0.0001). Allantodapsone also demonstrated dose dependent inhibition of S. aureus Newman adhesion to cytokeratin 10 (CK10). Allantodapsone is the first small molecule inhibitor of the S. aureus clumping factors with potential for development as a colonization inhibitor. IMPORTANCE S. aureus colonization of the nares and the skin provide a reservoir of bacteria that can be transferred to wounds that can ultimately result in systemic infections. Antibiotic resistance can make these infections difficult to treat with significant associated morbidity and mortality. We have identified and characterized a first-in-class small molecule inhibitor of the S. aureus clumping factors A and B, which has the potential to be developed further as a colonization inhibitor.

Staphylococcus aureus adhesion to the host

Staphylococcus aureus is a pathobiont capable of colonizing and infecting most tissues within the human body, resulting in a multitude of different clinical outcomes. Adhesion of S. aureus to the host is crucial for both host colonization and the establishment of infections. Underlying the pathogen's success is a complex and diverse arsenal of adhesins. In this review, we discuss the different classes of adhesins, including a consideration of the various adhesion sites throughout the body and the clinical outcomes of each infection type. The development of therapeutics targeting the S. aureus host-pathogen interaction is a relatively understudied area. Due to the increasing global threat of antimicrobial resistance, it is crucial that innovative and alternative approaches are considered. Neutralizing virulence factors, through the development of antivirulence agents, could reduce bacterial pathogenicity and the ever-increasing burden of S. aureus infections. This review provides insight into potentially efficacious adhesion-associated targets for the development of novel decolonizing and antivirulence strategies.

Fibronectin binding protein B binds to loricrin and promotes corneocyte adhesion by Staphylococcus aureus

Colonisation of humans by Staphylococcus aureus is a major risk factor for infection, yet the bacterial and host factors involved are not fully understood. The first step during skin colonisation is adhesion of the bacteria to corneocytes in the stratum corneum where the cornified envelope protein loricrin is the main ligand for S. aureus. Here we report a novel loricrin-binding protein of S. aureus, the cell wall-anchored fibronectin binding protein B (FnBPB). Single-molecule force spectroscopy revealed both weak and ultra-strong (2 nN) binding of FnBPB to loricrin and that mechanical stress enhanced the strength of these bonds. Treatment with a peptide derived from fibrinogen decreased the frequency of strong interactions, suggesting that both ligands bind to overlapping sites within FnBPB. Finally, we show that FnBPB promotes adhesion to human corneocytes by binding strongly to loricrin, highlighting the relevance of this interaction to skin colonisation.

The first step during skin colonization by is its adhesion to corneocytes. Da Costa et al. show that the cell wall-anchored fibronectin binding protein B (FnBPB) of S. aureus binds to loricrin. Applying single cell force spectroscopy, they demonstrate that this interaction promotes adhesion of S. aureus to human corneocytes.

Non-Canonical Host Intracellular Niche Links to New Antimicrobial Resistance Mechanism

Globally, infectious diseases are one of the leading causes of death among people of all ages. The development of antimicrobials to treat infectious diseases has been one of the most significant advances in medical history. Alarmingly, antimicrobial resistance is a widespread phenomenon that will, without intervention, make currently treatable infections once again deadly. In an era of widespread antimicrobial resistance, there is a constant and pressing need to develop new antibacterial drugs. Unraveling the underlying resistance mechanisms is critical to fight this crisis. In this review, we summarize some emerging evidence of the non-canonical intracellular life cycle of two priority antimicrobial-resistant bacterial pathogens: Pseudomonas aeruginosa and Staphylococcus aureus. The bacterial factors that modulate this unique intracellular niche and its implications in contributing to resistance are discussed. We then briefly discuss some recent research that focused on the promises of boosting host immunity as a combination therapy with antimicrobials to eradicate these two particular pathogens. Finally, we summarize the importance of various strategies, including surveillance and vaccines, in mitigating the impacts of antimicrobial resistance in general.

Selection of Staphylococcus aureus in a murine nasopharyngeal colonization model

Staphylococcus aureus nasal colonization is a risk factor for infection. A large proportion of the population are identified as potential S. aureus carriers yet we only partially understand the repertoire of genetic factors that promote long-term nasal colonization. Here we present a murine model of nasopharyngeal colonization that requires a low S. aureus inoculum and is amenable to experimental evolution approaches. We used this model to experimentally evolve S. aureus using successive passages in the nasopharynx to identify those genetic loci under selection. After 3 cycles of colonization, mutations were identified in mannitol, sorbitol, arginine, nitrite and lactate metabolism genes promoting key pathways in nasal colonization. Stress responses were identified as being under selective pressure, with mutations in DNA repair genes including dnaJ and recF and key stress response genes clpL, rpoB and ahpF. Peptidoglycan synthesis pathway genes also revealed mutations indicating potential selection for alteration of the cell surface. The murine model used here is versatile to question colonization, persistence and evolution studies. We studied the human pathogen Staphylococcus aureus in our search to determine factors that contribute to its ability to live in the human nose and throat. The anterior nares and nasopharynx are considered primary habitats but we do not understand how the pathogen adapts as it moves from one person to the next. We first determined sustained survival of the pathogen over multiple days in the nasopharynx that might act as a good model for human persistence due to the low numbers of bacteria needed for it to establish. By using successive rounds of colonization of the nasopharynx across different mice we revealed that multiple genetic changes in the S. aureus occurred. These changes were found in genes associated with the cell surface and metabolism and might indicate adaptation to the niche. One gene showed an accumulation of multiple mutations supporting a key contribution in adaptation but the role of the protein it encodes is not yet known. The contribution of these genes and genetic changes are unclear but indicate an area for future research to better understand how this common human pathogen is so successful at human colonization and survival.

Is decolonisation to prevent PVL-positive Staphylococcus aureus infection in the population effective? A systematic review

INTRODUCTION

Panton-Valentine Leukocidin (PVL) producing Staphylococcus aureus is associated with recurrent skin and soft tissue infections and occasionally invasive infections. There is limited evidence to support current public health guidance on decolonisation of cases and household contacts.

METHODS

This systematic review (CRD42020189906) investigated the efficacy of decolonisation against PVL-positive S. aureus to inform future public health practice. It included studies of cases with PVL-positive infections providing information on the efficacy of decolonisation of cases, carriers, or contacts of cases. Studies were assessed for the risk of bias using the GRADE approach and summarised to inform a narrative synthesis.

RESULTS

The search identified 20, mostly observational, studies with small samples and lacking control groups. Studies with longer follow-ups found that, while early post-decolonisation screening was negative for most individuals, testing over subsequent months identified re-colonisation in some. There is no high quality evidence to show whether decolonisation is effective in reducing (re)infection or long-term carriage of PVL-positive S. aureus and the low quality evidence available indicates it may not be effective in eradicating carriage or reducing future disease. Furthermore, there may be risks associated with decolonisation, for example, potentially increased risk of infection from other microbes, opportunity costs and negative impacts of repeated testing for asymptomatic carriage.

CONCLUSIONS

Further research is required to better understand what affects the ability of decolonisation efforts to reduce risk to cases and their contacts, including strain, host and environmental factors.

The Epidermis: Redox Governor of Health and Diseases

A functional epithelial barrier necessitates protection against dehydration, and ichthyoses are caused by defects in maintaining the permeability barrier in the stratum corneum (SC), the uppermost protective layer composed of dead cells and secretory materials from the living layer stratum granulosum (SG). We have found that loricrin (LOR) is an essential effector of cornification that occurs in the uppermost layer of SG (SG1). LOR promotes the maturation of corneocytes and extracellular adhesion structure through organizing disulfide cross-linkages, albeit being dispensable for the SC permeability barrier. This review takes psoriasis and AD as the prototype of impaired cornification. Despite exhibiting immunological traits that oppose each other, both conditions share the epidermal differentiation complex as a susceptible locus. We also review recent mechanistic insights on skin diseases, focusing on the Kelch-like erythroid cell-derived protein with the cap "n" collar homology-associated protein 1/NFE2-related factor 2 signaling pathway, as they coordinate the epidermis-intrinsic xenobiotic metabolism. Finally, we refine the theoretical framework of thiol-mediated crosstalk between keratinocytes and leukocytes in the epidermis that was put forward earlier.

Staphylococcus aureus iron-regulated surface determinant B (IsdB) protein interacts with von Willebrand factor and promotes adherence to endothelial cells

Staphylococcus aureus is the cause of a spectrum of diseases in humans and animals. The molecular basis of this pathogenicity lies in the expression of a variety of virulence factors, including proteins that mediate adherence to the host plasma and extracellular matrix proteins. In this study, we discovered that the iron-regulated surface determinant B (IsdB) protein, besides being involved in iron transport and vitronectin binding, interacts with von Willebrand Factor (vWF). IsdB-expressing bacteria bound to both soluble and immobilized vWF. The binding of recombinant IsdB to vWF was blocked by heparin and reduced at high ionic strength. Furthermore, treatment with ristocetin, an allosteric agent that promotes the exposure of the A1 domain of vWF, potentiates the binding of IsdB to vWF. Both near-iron transporter motifs NEAT1 and NEAT2 of IsdB individually bound recombinant A1 domain with K_D values in the micromolar range. The binding of IsdB and adhesion of S. aureus expressing IsdB to monolayers of activated endothelial cells was significantly inhibited by a monoclonal antibody against the A1 domain and by IsdB reactive IgG from patients with staphylococcal endocarditis. This suggests the importance of IsdB in adherence of S. aureus to the endothelium colonization and as potential therapeutic target.

Molecular studies of immunological enzyme clumping factor B for the inhibition of Staphylococcus aureus with essential oils of Nigella sativa

Essential oils from black cumin seeds (Nigella sativa) have largely been used in the manufacturing of nutraceuticals and functional food products due to the presence of a wide variety of bioactive compounds. However, their applications in the pharmaceutical sector have recently attracted interest and started blooming. The present research elucidates the in silico and in vitro efficacies of active leads from essential oil of N sativa against the human pathogenic bacterium Staphylococcus aureus. Biofilm development has become an inevitable situation in the health care sector. Lowering the efficacies of antimicrobial drugs is one of the vital ramifications that resulted in the emergence of multidrug resistance. Clumping factor B (clfB) of S aureus plays a key role in the human immune functions during pathogenesis. Through STRING analysis, the interacting protein partners of clfB were found to regulate biofilm pathway. Therefore, eight ligands from essential oil are docked with the critical clfB protein, which revealed p-cymene, thymoquinone and carvacrol as the robust ligands with highest binding affinity. Therefore, antibiofilm potential of N sativa essential oil at in vitro states was evaluated against S aureus. Further, real time PCR analysis showed that the expression of clfB and intercellular adhesion gene (icaA and icaD) was significantly altered upon treatment with essential oil. Altogether, the findings confirmed the antibiofilm efficacy of N sativa essential oil against S aureus. Hence, the essential oil from N. sativa was envisaged to be promising candidate to treat S aureus biofilm mediated infection.

Annexin A2-Mediated Internalization of Staphylococcus aureus into Bovine Mammary Epithelial Cells Requires Its Interaction with Clumping Factor B

BACKGROUND

Staphylococcus aureus is a leading cause of contagious mastitis in dairy cattle. Internalization of S. aureus by bovine mammary gland epithelial cells is thought to be responsible for persistent and chronic intramammary infection, but the underlying mechanisms are not fully understood.

METHODS

In the present study, we evaluated the role of Annexin A2 (AnxA2), a membrane-binding protein, in S. aureus invasion into bovine mammary epithelial cell line (MAC-T). In vitro binding assays were performed to co-immunoprecipitate the binding proteins of AnxA2 in the lysates of S. aureus.

RESULTS

AnxA2 mediated the internalization but not adherence of S. aureus. Engagement of AnxA2 stimulated an integrin-linked protein kinase (ILK)/p38 MAPK cascade to induce S. aureus invasion. One of the AnxA2-precipitated proteins was identified as S. aureus clumping factor B (ClfB) through use of mass spectrometry. Direct binding of ClfB to AnxA2 was further confirmed by using a pull-down assay. Pre-incubation with recombinant ClfB protein enhanced S. aureus internalization, an effect that was specially blocked by anti-AnxA2 antibody.

CONCLUSION

Our results demonstrate that binding of ClfB to AnxA2 has a function in promoting S. aureus internalization. Targeting the interaction of ClfB and AnxA2 may confer protection against S. aureus mastitis.

B and T cell epitope-based peptides predicted from clumping factor protein of Staphylococcus aureus as vaccine targets

Staphylococcus aureus infection is emerging as a global threat because of the highly debilitating nature of the associated disease's unprecedented magnitude of its spread and growing global resistance to antimicrobial medicines. Recently WHO has categorized these bacteria under the high global priority pathogen list and is one of the six nosocomial pathogens termed as ESKAPE pathogens which have emerged as a serious threat to public health worldwide. The development of a specific vaccine can stimulate an optimal antibody response, thus providing immunity against it. Therefore, in the present study efforts have been made to identify potential vaccine candidates from the Clumping factor surface proteins (ClfA and ClfB) of S. aureus. Employing the immunoinformatics approach, fourteen antigenic peptides including T-cell, B-cell epitopes were identified which were non-toxic, non-allergenic, high antigenicity, strong binding efficiency with commonly occurring MHC alleles. Consequently, a multi-epitope vaccine chimera was designed by connecting these epitopes with suitable linkers an adjuvant to enhance immunogenicity. Further, homology modeling and molecular docking were performed to construct the three-dimensional structure of the vaccine and study the interaction between the modeled structure and immune receptor (TLR-2) present on lymphocyte cells. Consequently, molecular dynamics simulation for 100 ns period confirmed the stability of the interaction and reliability of the structure for further analysis. Finally, codon optimization and in silico cloning were employed to ensure the successful expression of the vaccine candidate. As the targeted protein is highly antigenic and conserved, hence the designed novel vaccine construct holds potential against emerging multi-drug-resistant organisms.

Staphylococcus aureus Arsenal To Conquer the Lower Respiratory Tract

Staphylococcus aureus is both a commensal and a pathogenic bacterium for humans. Its ability to induce severe infections is based on a wide range of virulence factors. S. aureus community-acquired pneumonia (SA-CAP) is rare and severe, and the contribution of certain virulence factors in this disease has been recognized over the past 2 decades. First, the factors involved in metabolism adaptation are crucial for S. aureus survival in the lower respiratory tract, and toxins and enzymes are required for it to cross the pulmonary epithelial barrier. S. aureus subsequently faces host defense mechanisms, including the epithelial barrier, but most importantly the immune system. Here, again, S. aureus uses myriad virulence factors to successfully escape from the host's defenses and takes advantage of them. The impact of S. aureus virulence, combined with the collateral damage caused by an overwhelming immune response, leads to severe tissue damage and adverse clinical outcomes. In this review, we summarize step by step all of the S. aureus factors implicated in CAP and described to date, and we provide an outlook for future research.

Monoclonal Antibodies Targeting Surface-Exposed and Secreted Proteins from Staphylococci

Staphylococci (specifically Staphylococcus aureus and Staphylococcus epidermidis) are the causative agents of diseases ranging from superficial skin and soft tissue infections to severe conditions such as fatal pneumonia, bacteremia, sepsis and endocarditis. The widespread and indiscriminate use of antibiotics has led to serious problems of resistance to staphylococcal disease and has generated a renewed interest in alternative therapeutic agents such as vaccines and antibodies. Staphylococci express a large repertoire of surface and secreted virulence factors, which provide mechanisms (adhesion, invasion and biofilm development among others) for both bacterial survival in the host and evasion from innate and adaptive immunity. Consequently, the development of antibodies that target specific antigens would provide an effective protective strategy against staphylococcal infections. In this review, we report an update on efforts to develop anti-staphylococci monoclonal antibodies (and their derivatives: minibodies, antibody–antibiotic conjugates) and the mechanism by which such antibodies can help fight infections. We also provide an overview of mAbs used in clinical trials and highlight their therapeutic potential in various infectious contexts.

Staphylococcus aureus binds to the N-terminal region of corneodesmosin to adhere to the stratum corneum in atopic dermatitis

Staphylococcus aureus colonizes the skin of the majority of patients with atopic dermatitis (AD), and its presence increases disease severity. Adhesion of S. aureus to corneocytes in the stratum corneum is a key initial event in colonization, but the bacterial and host factors contributing to this process have not been defined. Here, we show that S. aureus interacts with the host protein corneodesmosin. Corneodesmosin is aberrantly displayed on the tips of villus-like projections that occur on the surface of AD corneocytes as a result of low levels of skin humectants known as natural moisturizing factor (NMF). An S. aureus mutant deficient in fibronectin binding protein B (FnBPB) and clumping factor B (ClfB) did not bind to corneodesmosin in vitro. Using surface plasmon resonance, we found that FnBPB and ClfB proteins bound with similar affinities. The S. aureus binding site was localized to the N-terminal glycine-serine-rich region of corneodesmosin. Atomic force microscopy showed that the N-terminal region was present on corneocytes containing low levels of NMF and that blocking it with an antibody inhibited binding of individual S. aureus cells to corneocytes. Finally, we found that S. aureus mutants deficient in FnBPB or ClfB have a reduced ability to adhere to low-NMF corneocytes from patients. In summary, we show that FnBPB and ClfB interact with the accessible N-terminal region of corneodesmosin on AD corneocytes, allowing S. aureus to take advantage of the aberrant display of corneodesmosin that accompanies low NMF in AD. This interaction facilitates the characteristic strong binding of S. aureus to AD corneocytes.

Development and validation of a high-throughput whole cell assay to investigate Staphylococcus aureus adhesion to host ligands

Staphylococcus aureus adhesion to the host's skin and mucosae enables asymptomatic colonization and the establishment of infection. This process is facilitated by cell wall-anchored adhesins that bind to host ligands. Therapeutics targeting this process could provide significant clinical benefits; however, the development of anti-adhesives requires an in-depth knowledge of adhesion-associated factors and an assay amenable to high-throughput applications. Here, we describe the development of a sensitive and robust whole cell assay to enable the large-scale profiling of S. aureus adhesion to host ligands. To validate the assay, and to gain insight into cellular factors contributing to adhesion, we profiled a sequence-defined S. aureus transposon mutant library, identifying mutants with attenuated adhesion to human-derived fibronectin, keratin, and fibrinogen. Our screening approach was validated by the identification of known adhesion-related proteins, such as the housekeeping sortase responsible for covalently linking adhesins to the cell wall. In addition, we also identified genetic loci that could represent undescribed anti-adhesive targets. To compare and contrast the genetic requirements of adhesion to each host ligand, we generated a S. aureus Genetic Adhesion Network, which identified a core gene set involved in adhesion to all three host ligands, and unique genetic signatures. In summary, this assay will enable high-throughput chemical screens to identify anti-adhesives and our findings provide insight into the target space of such an approach.

Staphylococcus aureus and its Effects on the Prognosis of Bronchiectasis

Bronchiectasis, which is an abnormal and irreversible dilation of one or several bronchial segments, causes significant morbidity and impaired quality of life to patients, mainly as the result of recurrent and chronic respiratory infections. Staphylococcus aureus is a microorganism known for its high infectious potential related to the production of molecules with great pathogenic power, such as enzymes, toxins, adhesins, and biofilm, which determine the degree of severity of systemic symptoms and can induce exacerbated immune response. This review highlighted the clinical significance of S. aureus colonization/infection in bronchiectasis patients, since little is known about it, despite its increasing frequency of isolation and potential serious morbidity.

Unresponsiveness to inhaled antigen is governed by conventional dendritic cells and overridden during infection by monocytes

The nasal-associated lymphoid tissues (NALTs) are mucosal-associated lymphoid organs embedded in the submucosa of the nasal passage. NALTs represent a known site for the deposition of inhaled antigens, but little is known of the mechanisms involved in the induction of immunity within this lymphoid tissue. We find that during the steady state, conventional dendritic cells (cDCs) within the NALTs suppress T cell responses. These cDCs, which are also prevalent within human NALTs (tonsils/adenoids), express a unique transcriptional profile and inhibit T cell proliferation via contact-independent mechanisms that can be diminished by blocking the actions of reactive oxygen species and prostaglandin E2. Although the prevention of unrestrained immune activation to inhaled antigens appears to be the default function of NALT cDCs, inflammation after localized virus infection recruited monocyte-derived DCs (moDCs) to this region, which diluted out the suppressive DC pool, and permitted local T cell priming. Accommodating for inflammation-induced temporal changes in NALT DC composition and function, we developed an intranasal vaccine delivery system that coupled the recruitment of moDCs with the sustained release of antigen into the NALTs, and we were able to substantially improve T cell responses after intranasal immunization. Thus, homeostasis and immunity to inhaled antigens is tuned by inflammatory signals that regulate the balance between conventional and moDC populations within the NALTs.

Does fibrinogen serve the host or the microbe in Staphylococcus infection?

PURPOSE OF REVIEW

Fibrin(ogen) is a multifunctional clotting protein that not only has critical roles in hemostasis but is also important in inflammatory processes that control bacterial infection. As a provisional extracellular matrix protein, fibrin(ogen) functions as a physical barrier, a scaffold for immune cell migration, or as a spatially-defined cue to drive inflammatory cell activation. These mechanisms contribute to overall host antimicrobial defense against infection. However, numerous bacterial species have evolved mechanisms to manipulate host fibrin(ogen) to promote microbial virulence and survival. Staphylococcal species, in particular, express numerous virulence factors capable of engaging fibrin(ogen), promoting fibrin formation, and driving the dissolution of fibrin matrices.

RECENT FINDINGS

Recent studies have highlighted both new insights into the molecular mechanisms involved in fibrin(ogen)-mediated host defense and pathogen-driven virulence. Of particular interest is the role of fibrin(ogen) in forming host protective biofilms versus pathogen protective barriers and biofilms as well as the role of fibrin(ogen) in mediating direct host antimicrobial responses.

SUMMARY

Current data suggest that the role of fibrin(ogen) in staphylococcal infection is highly context-dependent and that better defining the precise cellular and molecular pathways activated will provide unique opportunities of therapeutic intervention to better treat Staphylococcal disease.

Controlling the Growth of the Skin Commensal Staphylococcus epidermidis Using d-Alanine Auxotrophy

The skin microbiome is rich in opportunities for novel therapeutics for skin diseases, and synthetic biology offers the advantage of providing novel functionality or therapeutic benefit to live biotherapeutic products. The development of novel bacterial strains whose growth can be controlled without the use of antibiotics or genetic elements conferring antibiotic resistance enables modulation of therapeutic exposure and improves safety. This study presents the design and in vitro evidence of a skin commensal whose growth can be controlled through d-alanine. The basis of this strain will support future clinical studies of this strain in humans.

Using live microbes as therapeutic candidates is a strategy that has gained traction across multiple therapeutic areas. In the skin, commensal microorganisms play a crucial role in maintaining skin barrier function, homeostasis, and cutaneous immunity. Alterations of the homeostatic skin microbiome are associated with a number of skin diseases. Here, we present the design of an engineered commensal organism, Staphylococcus epidermidis, for use as a live biotherapeutic product (LBP) candidate for skin diseases. The development of novel bacterial strains whose growth can be controlled without the use of antibiotics or genetic elements conferring antibiotic resistance enables modulation of therapeutic exposure and improves safety. We therefore constructed an auxotrophic strain of S. epidermidis that requires exogenously supplied d-alanine. The S. epidermidis NRRL B-4268 Δalr1 Δalr2 Δdat strain (SE_ΔΔΔ) contains deletions of three biosynthetic genes: two alanine racemase genes, alr1 and alr2 (SE1674 and SE1079), and the d-alanine aminotransferase gene, dat (SE1423). These three deletions restricted growth in d-alanine-deficient medium, pooled human blood, and skin. In the presence of d-alanine, SE_ΔΔΔ colonized and increased expression of human β-defensin 2 in cultured human skin models in vitro. SE_ΔΔΔ showed a low propensity to revert to d-alanine prototrophy and did not form biofilms on plastic in vitro. These studies support the potential safety and utility of SE_ΔΔΔ as a live biotherapeutic strain whose growth can be controlled by d-alanine.

IMPORTANCE The skin microbiome is rich in opportunities for novel therapeutics for skin diseases, and synthetic biology offers the advantage of providing novel functionality or therapeutic benefit to live biotherapeutic products. The development of novel bacterial strains whose growth can be controlled without the use of antibiotics or genetic elements conferring antibiotic resistance enables modulation of therapeutic exposure and improves safety. This study presents the design and in vitro evidence of a skin commensal whose growth can be controlled through d-alanine. The basis of this strain will support future clinical studies of this strain in humans.

The iron-regulated surface determinant B (IsdB) protein from Staphylococcus aureus acts as a receptor for the host protein vitronectin

Staphylococcus aureus is an important bacterial pathogen that can cause a wide spectrum of diseases in humans and other animals. S. aureus expresses a variety of virulence factors that promote infection with this pathogen. These include cell-surface proteins that mediate adherence of the bacterial cells to host extracellular matrix components, such as fibronectin and fibrinogen. Here, using immunoblotting, ELISA, and surface plasmon resonance analysis, we report that the iron-regulated surface determinant B (IsdB) protein, besides being involved in heme transport, plays a novel role as a receptor for the plasma and extracellular matrix protein vitronectin (Vn). Vn-binding activity was expressed by staphylococcal strains grown under iron starvation conditions when Isd proteins are expressed. Recombinant IsdB bound Vn dose dependently and specifically. Both near-iron transporter motifs NEAT₁ and NEAT₂ of IsdB individually bound Vn in a saturable manner, with K_D values in the range of 16-18 nm Binding of Vn to IsdB was specifically blocked by heparin and reduced at high ionic strength. Furthermore, IsdB-expressing bacterial cells bound significantly higher amounts of Vn from human plasma than did an isdB mutant. Adherence to and invasion of epithelial and endothelial cells by IsdB-expressing S. aureus cells was promoted by Vn, and an α_vβ₃ integrin-blocking mAb or cilengitide inhibited adherence and invasion by staphylococci, suggesting that Vn acts as a bridge between IsdB and host α_vβ₃ integrin.

PilVax, a novel Lactococcus lactis-based mucosal vaccine platform, stimulates systemic and mucosal immune responses to Staphylococcus aureus

Most pathogens initiate infection via the mucosa, therefore delivery of vaccines directly to the mucosa is likely to be advantageous for stimulating protective immunity at the site of entry. PilVax is a novel mucosal vaccine platform that harnesses Lactococcus lactis bacteria engineered to stably express multiple copies of vaccine peptide antigens within pili, hair-like structures which extend from the cell wall. This strategy elicited systemic and mucosal antibody responses to a model antigen after intranasal immunization, but has not been tested for its capacity to stimulate protective mucosal immunity. A well-characterized linear B-cell epitope, D3_(22-33) , from the fibronectin-binding protein A of Staphylococcus aureus was successfully introduced into PilVax and delivered intranasally to mice. Specific antipeptide immunoglobulin (Ig) G and IgA antibodies were detected in the serum and respiratory mucosa of vaccinated mice. Responses to the major pilus backbone protein Spy0128 were also assessed; robust antibody responses to this antigen were generated both systemically and in the respiratory and intestinal mucosa. Mice were challenged intranasally with the mouse-adapted S. aureus JSNZ strain and the S. aureus load quantified 7 days after challenge. Unexpectedly, exposure to PilVax, irrespective of the presence of the peptide, resulted in a significant reduction in S. aureus load in both the intestine and nasal mucosa (both P < 0.05) when compared with unvaccinated control mice. The mechanism(s) of protection are unclear, but merit further investigation to determine whether PilVax is a suitable platform for delivery of vaccine candidate antigens to the mucosa.

Differences in virulence between the two more prevalent Staphylococcus aureus clonal complexes in rabbitries (CC121 and CC96) using an experimental model of mammary gland infection

Staphylococcal mastitis is a major health problem in humans and livestock that leads to economic loss running in millions. This process is currently one of the main reasons for culling adult rabbit does. Surprisingly, the two most prevalent S. aureus lineages isolated from non-differentiable natural clinical mastitis in rabbits (ST121 and ST96) generate different immune responses. This study aimed to genetically compare both types of strains to search for possible dissimilarities to explain differences in immune response, and to check whether they showed similar virulence in in vitro tests as in experimental intramammary in vivo infection. The main differences were observed in the enterotoxin gene cluster (egc) and the immune-evasion-cluster (IEC) genes. While isolate ST121 harboured all six egc cluster members (seg, sei, selm, seln, selo, selu), isolate ST96 lacked the egc cluster. Strain ST96 carried a phage integrase Sa3 (Sa3int), compatible with a phage integrated into the hlb gene (β-haemolysin-converting bacteriophages) with IEC type F, while isolate ST121 lacked IEC genes and the hlb gene was intact. Moreover, the in vitro tests confirmed a different virulence capacity between strains as ST121 showed greater cytotoxicity for erythrocytes, polymorphonuclear leukocytes and macrophages than strain ST96. Differences were also found 7 days after experimental intramammary infection with 100 colony-forming units. The animals inoculated with strain ST121 developed more severe gross and histological mastitis, higher counts of macrophages in tissue and of all the cell populations in peripheral blood, and a significantly larger total number of bacteria than those infected by strain ST96.

Bacterial Anti-adhesives: Inhibition of Staphylococcus aureus Nasal Colonization

Bacterial adhesion to the skin and mucosa is often a fundamental and early step in host colonization, the establishment of bacterial infections, and pathology. This process is facilitated by adhesins on the surface of the bacterial cell that recognize host cell molecules. Interfering with bacterial host cell adhesion, so-called anti-adhesive therapeutics, offers promise for the development of novel approaches to control bacterial infections. In this review, we focus on the discovery of anti-adhesives targeting the high priority pathogen Staphylococcus aureus. This organism remains a major clinical burden, and S. aureus nasal colonization is associated with poor clinical outcomes. We describe the molecular basis of nasal colonization and highlight potentially efficacious targets for the development of novel nasal decolonization strategies.

Detection and quantification of Staphylococcus in chronic rhinosinusitis

BACKGROUND

The sinonasal microbiota has been implicated in chronic rhinosinusitis (CRS) pathogenesis, particularly related to the presence of Staphylococcus aureus. Staphylococcus epidermidis is also prevalent within the sinonasal microbiota and may inhibit S. aureus colonization. We investigated polymerase chain reaction (PCR) primer pairs for measuring absolute abundances of S. aureus and S. epidermidis, then compared bacterial community composition and absolute abundances of these species between CRS patients and controls.

METHODS

Six candidate Staphylococcus species-specific primer pairs were tested in silico and in vitro against pure bacterial isolates. Quantitative PCR (qPCR) for absolute quantification of S. aureus, S. epidermidis, and overall bacterial load were assessed in 40 CRS (CRS without nasal polyposis [CRSsNP] = 22, CRS with nasal polyposis [CRSwNP] = 18) patients and 14 controls. Amplicon sequencing of the V3-V4 hypervariable regions of the 16S ribosomal RNA (rRNA) bacterial gene were conducted to investigate community composition.

RESULTS

Primer pairs targeting the gmk gene of S. aureus and nrd gene from S. epidermidis were the most specific and sensitive primers. S. aureus (CRSsNP = 81.8% occurrence, CRSwNP = 83%, control = 92.9%) and S. epidermidis (CRSsNP = 95.5%, CRSwNP = 100%, control = 92.9%) were very prevalent, as indicated by qPCR results. Both CRSsNP and CRSwNP had significantly (p < 0.05) higher bacterial load when compared with controls (p < 0.05 for both). No significant correlation was observed between S. aureus and S. epidermidis abundances (p > 0.05).

CONCLUSION

Bacterial community sequencing detected Staphylococcus-assigned sequences in nearly all patients; however, it could not differentiate between S. aureus and S. epidermidis. Here, we present primer pairs that can distinguish between these species. We report a very high prevalence of S. aureus in both CRS patients and controls.

The MSCRAMM Family of Cell-Wall-Anchored Surface Proteins of Gram-Positive Cocci

The microbial surface components recognizing adhesive matrix molecules (MSCRAMMs) are a family of proteins that are defined by the presence of two adjacent IgG-like folded subdomains. These promote binding to ligands by mechanisms that involve major conformational changes exemplified by the binding to fibrinogen by the 'dock-lock-latch' mechanism or to collagen by the 'collagen hug'. Clumping factors A and B are two such MSCRAMMs that have several important roles in the pathogenesis of Staphylococcus aureus infections. MSCRAMM architecture, ligand binding, and roles in infection and colonization are examined with a focus on recent developments with clumping factors.

Surface Proteins of Staphylococcus aureus

The surface of Staphylococcus aureus is decorated with over 20 proteins that are covalently anchored to peptidoglycan by the action of sortase A. These cell wall-anchored (CWA) proteins can be classified into several structural and functional groups. The largest is the MSCRAMM family, which is characterized by tandemly repeated IgG-like folded domains that bind peptide ligands by the dock lock latch mechanism or the collagen triple helix by the collagen hug. Several CWA proteins comprise modules that have different functions, and some individual domains can bind different ligands, sometimes by different mechanisms. For example, the N-terminus of the fibronectin binding proteins comprises an MSCRAMM domain which binds several ligands, while the C-terminus is composed of tandem fibronectin binding repeats. Surface proteins promote adhesion to host cells and tissue, including components of the extracellular matrix, contribute to biofilm formation by stimulating attachment to the host or indwelling medical devices followed by cell-cell accumulation via homophilic interactions between proteins on neighboring cells, help bacteria evade host innate immune responses, participate in iron acquisition from host hemoglobin, and trigger invasion of bacteria into cells that are not normally phagocytic. The study of genetically manipulated strains using animal infection models has shown that many CWA proteins contribute to pathogenesis. Fragments of CWA proteins have the potential to be used in multicomponent vaccines to prevent S. aureus infections.

Clumping factor B is an important virulence factor during Staphylococcus aureus skin infection and a promising vaccine target

Staphylococcus aureus expresses a number of cell wall-anchored proteins that mediate adhesion and invasion of host cells and tissues and promote immune evasion, consequently contributing to the virulence of this organism. The cell wall-anchored protein clumping factor B (ClfB) has previously been shown to facilitate S. aureus nasal colonization through high affinity interactions with the cornified envelope in the anterior nares. However, the role of ClfB during skin and soft tissue infection (SSTI) has never been investigated. This study reveals a novel role for ClfB during SSTIs. ClfB is crucial in determining the abscess structure and bacterial burden early in infection and this is dependent upon a specific interaction with the ligand loricrin which is expressed within the abscess tissue. Targeting ClfB using a model vaccine that induced both protective humoral and cellular responses, leads to protection during S. aureus skin infection. This study therefore identifies ClfB as an important antigen for future SSTI vaccines.

Staphylococcus aureus is the leading cause of skin and soft tissue infections (SSTIs), the treatment of which is becoming increasingly difficult due to antibiotic resistance. An anti-S. aureus vaccine offers a potential solution, but a better understanding of how S. aureus causes pathology during SSTI is required to identify effective vaccine targets. Here, we identify an important virulence determinant during S. aureus SSTI. Clumping factor B (ClfB), a surface protein expressed by S. aureus is shown to promote skin abscess formation by binding to the host protein loricrin. Targeting ClfB using a model vaccine conferred significant protection during S. aureus SSTI. In this study, we uncover an entirely novel mechanism by which S. aureus forms abscesses during skin infection, identifying an important therapeutic target for treating S. aureus SSTI.