The adhesive and immunomodulating properties of the multifunctional Staphylococcus aureus protein Eap

Inhibition of staphylothrombin by dabigatran reduces Staphylococcus aureus virulence

BACKGROUND

Staphylocoagulase and von Willebrand binding protein (VWbp) bind to prothrombin to form the staphylothrombin complex that converts fibrinogen into fibrin.

OBJECTIVES

To study the role of staphylothrombin and its inhibition by dabigatran on Staphylococcus aureus virulence.

METHODS

We studied the effect of staphylothrombin inhibition on bacterial attachment to polystyrene surfaces, leukocyte activation and bactericidal activity for S. aureus ATCC 25923, S. aureus Newman, and staphylocoagulase- and VWbp-negative S. aureus Newman mutants in the presence or absence of prothrombin and fibrinogen. We measured the abscess size after subcutaneous (s.c.) injection of S. aureus ATCC 25923 and S. aureus Newman, as well as an S. aureus Newman mutant strain lacking staphylocoagulase and VWbp, in mice treated with either dabigatran or placebo.

RESULTS

Staphylothrombin-mediated fibrin increased the association of S. aureus to polystyrene surfaces and reduced the bactericidal activity of leukocytes. The absence or inhibition of staphylothrombin decreased the bacterial association, enhanced leukocyte activation and reduced bacterial survival in vitro. Abscess size was smaller in mice treated with dabigatran or infected with a coagulase-negative mutant.

CONCLUSION

Inhibition or the absence of staphylothrombin reduced S. aureus virulence in in vitro and in vivo models.

Salicylic acid enhances Staphylococcus aureus extracellular adhesin protein expression

One of the virulence factors required by Staphylococcus aureus at the early stages of infection is Eap, a secreted adhesin that binds many host proteins and is upregulated by the two-component regulatory system saeRS. The S. aureus Newman strain harbors a mutation in saeS that is thought to be responsible for the high level of Eap expression in this strain. This study was designed to ascertain whether salicylic acid (SAL) affects the expression of Eap and the internalization of S. aureus into epithelial cells. The strain Newman treated with SAL exhibited increased levels of eap transcription and protein expression. Furthermore, SAL treatment increased the eap promoter activity. SAL treatment enhanced Eap expression in the Newman and in other S. aureus strains that do not carry the mutation in saeS. Internalization of S. aureus eap and sae mutants into the MAC-T epithelial cells was significantly decreased compared with the wild-type counterparts. In conclusion, we demonstrated that a low concentration of SAL increased S. aureus Eap expression possibly due to enhancement of sae. SAL may create the conditions for S. aureus persistence in the host, not only by decreasing the capsular polysaccharide expression as shown before, but also by enhancing Eap expression.

How does Staphylococcus aureus escape the bloodstream?

Staphylococcus aureus is a major cause of bacteraemia, which frequently leads to infective endocarditis, osteomyelitis, septic arthritis and metastatic abscess formation. The development of these secondary infections is due to bacterial dissemination from the blood into surrounding tissues and is associated with significantly increased morbidity and mortality. Despite the importance of S. aureus extravasation in disease progression, there is relatively little understanding of the molecular mechanisms by which this pathogen crosses the endothelial barrier and establishes new sites of infection. Recent work has identified a number of putative routes by which S. aureus can escape the bloodstream. In this article we review these new developments and set them in the context of strategies used by other established pathogens to traverse cellular barriers.

RNAIII activates map expression by forming an RNA-RNA complex in Staphylococcus aureus

Staphylococcus aureus is a gram-positive pathogen responsible for a wide variety of diseases. RNAIII is the key effector of the accessory gene regulator (agr) system. It is a regulatory RNA (514 nucleotides long) that acts at both transcription and translation level to regulate the production of numerous toxins, enzymes and cell surface proteins. Here, we reveal that map (major histocompatibility complex class II analogous protein) is positively regulated by RNAIII. Our further study indicates that the 108-135nt fragment of RNAIII acts as an antisense RNA and anneals to map mRNA, forming RNA duplexes. The interaction between RNAIII and map mRNA may activate translation initiation. This may be helpful for understanding the regulation of virulence in S. aureus.

Antibody response to the extracellular adherence protein (Eap) of Staphylococcus aureus in healthy and infected individuals

The extracellular adherence protein (Eap) from Staphylococcus aureus has been suggested as a vaccine candidate and for therapeutic use due to its immunomodulating and antiangiogenic properties; however, little is known about anti-Eap antibodies in humans. We determined anti-Eap antibody titers by enzyme-linked immunosorbent assay and Western blot and measured serum samples from 92 patients with proven S. aureus infections and 93 healthy controls. The functionality of antibodies was assessed by a phagocytosis assay using Eap-coated fluorescent microspheres. Antibodies were detected in all human samples, but not in mice. Patients showed significantly higher titers than controls [immunoglobulin M (IgM), P=0.007; IgG, P<0.0001]. Patients with deep or severe infections showed higher titers than those with superficial or mild disease. Eap alone was sufficient to promote phagocytosis by peripheral blood mononuclear cell and granulocytes that was moderately enhanced in the presence of human serum, but no correlation was found with the levels of anti-Eap antibodies. Anti-Eap antibodies are prevalent in all tested humans and correlate with the severity of S. aureus infection; however, they do not seem to provide protection against invasive infections. Before considering Eap for therapy or as a vaccine candidate, further studies are warranted to assess the impact of the interference between Eap and its specific antibodies.

Surfactant protein A (SP-A)-mediated clearance of Staphylococcus aureus involves binding of SP-A to the staphylococcal adhesin eap and the macrophage receptors SP-A receptor 210 and scavenger receptor class A

Staphylococcus aureus causes life-threatening pneumonia in hospitals and deadly superinfection during viral influenza. The current study investigated the role of surfactant protein A (SP-A) in opsonization and clearance of S. aureus. Previous studies showed that SP-A mediates phagocytosis via the SP-A receptor 210 (SP-R210). Here, we show that SP-R210 mediates binding and control of SP-A-opsonized S. aureus by macrophages. We determined that SP-A binds S. aureus through the extracellular adhesin Eap. Consequently, SP-A enhanced macrophage uptake of Eap-expressing (Eap(+)) but not Eap-deficient (Eap(-)) S. aureus. In a reciprocal fashion, SP-A failed to enhance uptake of Eap(+) S. aureus in peritoneal Raw264.7 macrophages with a dominant negative mutation (SP-R210(DN)) blocking surface expression of SP-R210. Accordingly, WT mice cleared infection with Eap(+) but succumbed to sublethal infection with Eap- S. aureus. However, SP-R210(DN) cells compensated by increasing non-opsonic phagocytosis of Eap(+) S. aureus via the scavenger receptor scavenger receptor class A (SR-A), while non-opsonic uptake of Eap(-) S. aureus was impaired. Macrophages express two isoforms: SP-R210(L) and SP-R210(S). The results show that WT alveolar macrophages are distinguished by expression of SP-R210(L), whereas SR-A(-/-) alveolar macrophages are deficient in SP-R210(L) expressing only SP-R210(S). Accordingly, SR-A(-/-) mice were highly susceptible to both Eap(+) and Eap(-) S. aureus. The lungs of susceptible mice generated abnormal inflammatory responses that were associated with impaired killing and persistence of S. aureus infection in the lung. In conclusion, alveolar macrophage SP-R210(L) mediates recognition and killing of SP-A-opsonized S. aureus in vivo, coordinating inflammatory responses and resolution of S. aureus pneumonia through interaction with SR-A.

New insights into the prevention of staphylococcal infections and toxic shock syndrome

Staphylococcus aureus is a major human pathogen capable of causing various diseases, from skin infections to life-threatening pneumonia and toxic shock syndrome. S. aureus exoproteins, including superantigens, contribute significantly to the pathogenesis of this organism. Antibiotics inhibit growth, but often provide no protection from S. aureus exoproteins. With the emergence of antibiotic-resistant S. aureus, new therapeutic options to treat or prevent S. aureus-associated diseases are critical. Most S. aureus infections begin on the skin or mucosal surfaces from direct inflammatory or cytotoxic effects of exotoxins. Therefore, antitoxin therapies that prevent toxin production and prevent their effects on host cells are being researched. Current treatments for staphylococcal diseases and recent developments in antitoxin therapeutic agents and vaccines are reviewed.

Antibody responses in patients with invasive Staphylococcus aureus infections

Correlation between antibody response and clinical outcome in Staphylococcus aureus bacteremia has yielded conflicting results. Immunization schedules have failed in clinical trials. Is the humoral response toward S. aureus of protective nature? A prospective study was performed in patients with invasive S. aureus (ISA) infections during the period 2003-2005. The antibody levels were determined at the beginning and at the end of treatment and one month later (n = 96, n = 71, and n = 51, respectively). As controls, 115 healthy individuals were used. A quantitative enzyme-linked immunosorbent assay (ELISA) against eight purified antigens was performed. Bacterial isolates were grouped as to the production of alpha-toxin, agr type, and pulsed-field gel electrophoresis (PFGE) type. Large variations were seen in the antibody levels. The levels in the second sample were the highest. A correlation between agr group, PFGE group, alpha-toxin production, and initial antibody levels was observed. Patients with fatal outcome displayed lower initial antibody levels to all antigens and significantly so in regard to teichoic acid, lipase, enterotoxin A, and scalded skin syndrome toxin. In episodes with complicated bacteremia, initial significantly low levels to teichoic acid and lipase were registered. Low initial antibody levels against several antigens were associated with increased mortality and complicated bacteremia in invasive S. aureus infections. Bacterial properties, strain, and toxin production affected the antibody response.

Ultrahigh sensitivity made simple: nanoplasmonic label-free biosensing with an extremely low limit-of-detection for bacterial and cancer diagnostics

We present a simple and robust scheme for biosensing with an ultralow limit-of-detection down to several pg cm(-2) (or several tens of attomoles cm(-2)) based on optical label-free biodetection with localized surface plasmon resonances. The scheme utilizes cost-effective optical components and comprises a white light source, a properly functionalized sensor surface enclosed in a simple fluidics chip, and a spectral analyzer. The sensor surface is produced by a bottom-up nanofabrication technique with hole mask colloidal lithography. Despite its simplicity, the method is able to reliably detect protein-protein binding events at low picomolar and femtomolar concentrations, which is exemplified by the label-free detection of the extracellular adherence protein (EAP) found on the outer surface of the bacterium Staphylococcus aureus and of prostate-specific antigen (PSA), which is believed to be a prostate cancer marker. These experiments pave the way towards an ultra-sensitive yet compact biodetection platform for point-of-care diagnostics applications.

The signal peptide of Staphylococcus aureus panton valentine leukocidin LukS component mediates increased adhesion to heparan sulfates

Staphylococcus aureus necrotizing pneumonia is a severe disease caused by S. aureus strains carrying the Panton Valentine leukocidin (PVL) genes (lukS-PV & lukF-PV) encoded on various bacteriophages (such as phiSLT). Clinical PVL+ strains isolated from necrotizing pneumonia display an increased attachment to matrix molecules (type I and IV collagens and laminin), a phenotype that could play a role in bacterial adhesion to damaged airway epithelium during the early stages of necrotizing pneumonia (J Infect Dis 2004; 190: 1506–15). To investigate the basis of the observed adhesion of S. aureus PVL+ strains, we compared the ability of PVL+ and their isogenic PVL− strains to attach to various immobilized matrix molecules. The expression of recombinant fragments of the PVL subunits and the addition of synthetic peptides indicated that the processed LukS-PV signal peptide (LukS-PV SP) was sufficient to significantly enhance the ability of S. aureus to attach to extracellular matrix (ECM) components. Furthermore, we showed that adhesion to ECM components was inhibited by heparin and heparan sulfates (HS) suggesting that in vivo, HS could function as a molecular bridge between the matrix and S. aureus expressing the LukS-PV signal peptide. Site directed mutagenesis, biochemical and structural analyses of the LukS-PV signal peptide indicate that this peptide is present at the S. aureus surface, binds to HS in solid phase assay, and mediates the enhanced S. aureus matrix component adhesion. Our data suggests that after its cleavage by signal peptidase, the signal peptide is released from the membrane and associates to the cell wall through its unique C-terminus sequence, while its highly positively charged N-terminus is exposed on the bacterial surface, allowing its interaction with extracellular matrix-associated HS. This mechanism may provide a molecular bridge that enhances the attachment of the S. aureus PVL+ strains to ECM components exposed at damaged epithelial sites.

The Staphyloccous aureus Eap protein activates expression of proinflammatory cytokines

The extracellular adhesion protein (Eap) secreted by the major human pathogen Staphylococcus aureus is known to have several effects on human immunity. We have recently added to knowledge of these roles by demonstrating that Eap enhances interactions between major histocompatibility complex molecules and human leukocytes. Several studies have indicated that Eap can induce cytokine production by human peripheral blood mononuclear cells (PBMCs). To date, there has been no rigorous attempt to identify the breadth of cytokines produced by Eap stimulation or to identify the cell subsets that respond. Here, we demonstrate that Eap induces the secretion of the proinflammatory cytokines interleukin 6 (IL-6) and tumor necrosis factor alpha (TNF-alpha) by CD14(+) leukocytes (monocytes and macrophages) within direct ex vivo PBMC populations (note that granulocytes are also CD14(+) but are largely depleted from PBMC preparations). Anti-intercellular adhesion molecule 1 (CD54) antibodies inhibited this induction and implicated a role for this known Eap binding protein in cellular activation. IL-6 and TNF-alpha secretion by murine cells exposed to Eap was also observed. The activation of CD14(+) cells by Eap suggests that it could play a significant role in both septic shock and fever, two of the major pathological features of S. aureus infections.

Differential roles of sortase-anchored surface proteins and wall teichoic acid in Staphylococcus aureus nasal colonization

Most of the severe bacterial infections originate from the endogenous microflora of human body surfaces. However, the molecular basis of colonization, e.g. of the human nose by Staphylococcus aureus, has remained incompletely understood. Several surface-exposed proteins and wall teichoic acid (WTA) polymers have previously been implicated in S. aureus attachment to nasal epithelial cells. Here we dissect the role of these molecules in colonization using S. aureus sortase A (srtA) and tagO mutants deficient in surface protein and WTA display, respectively. Although the two mutants were similarly affected in attachment to nasal cells they were abrogated in binding to different types of epithelial ligands. Surface protein sorting, but not WTA, were required for keratin- or fibronectin-mediated interactions while only WTA-mediated binding to nasal cells was effectively inhibited by polyinosinic acid, indicating a possible role of scavenger receptor-like molecules in WTA-dependent epithelial interactions. Both mutants exhibited profound colonization defects in a cotton rat nasal colonization model, albeit at different stages of colonization (>90% reduced bacterial counts at 24h or several days after inoculation with the tagO or srtA mutant, respectively). These data indicate that S. aureus nasal colonization is a multifactorial process with various ligands affecting initial colonization and prolonged persistence in different ways. Our studies should be useful in the development of new preventive and therapeutic strategies.

eap Gene as novel target for specific identification of Staphylococcus aureus

The cell surface-associated extracellular adherence protein (Eap) mediates adherence of Staphylococcus aureus to host extracellular matrix components and inhibits inflammation, wound healing, and angiogenesis. A well-characterized collection of S. aureus and non-S. aureus staphylococcal isolates (n = 813) was tested for the presence of the Eap-encoding gene (eap) by PCR to investigate the use of the eap gene as a specific diagnostic tool for identification of S. aureus. Whereas all 597 S. aureus isolates were eap positive, this gene was not detectable in 216 non-S. aureus staphylococcal isolates comprising 47 different species and subspecies of coagulase-negative staphylococci and non-S. aureus coagulase-positive or coagulase-variable staphylococci. Furthermore, non-S. aureus isolates did not express Eap homologs, as verified on the transcriptional and protein levels. Based on these data, the sensitivity and specificity of the newly developed PCR targeting the eap gene were both 100%. Thus, the unique occurrence of Eap in S. aureus offers a promising tool particularly suitable for molecular diagnostics of this pathogen.

The Staphylococcus aureus extracellular adherence protein (Eap) adopts an elongated but structured conformation in solution

The extracellular adherence protein (Eap) of Staphylococcus aureus participates in a wide range of protein-protein interactions that facilitate the initiation and dissemination of Staphylococcal disease. In this report, we describe the use of a multidisciplinary approach to characterize the solution structure of full-length Eap. In contrast to previous reports suggesting that a six-domain isoform of Eap undergoes multimerization, sedimentation equilibrium analytical ultracentrifugation data revealed that a four-domain isoform of Eap is a monomer in solution. In vitro proteolysis and solution small angle X-ray scattering studies both indicate that Eap adopts an extended conformation in solution, where the linkers connecting sequential EAP modules are solvent exposed. Construction of a low-resolution model of full-length Eap using a combination of ab initio deconvolution of the SAXS data and rigid body modeling of the EAP domain crystal structure suggests that full-length Eap may present several unique concave surfaces capable of participating in ligand binding. These results also raise the possibility that such surfaces may be held together by additional interactions between adjacent EAP modules. This hypothesis is supported by a comparative Raman spectroscopic analysis of full-length Eap and a stoichiometric solution of the individual EAP modules, which indicates the presence of additional secondary structure and a greater extent of hydrogen/deuterium exchange protection in full-length Eap. Our results provide the first insight into the solution structure of full-length Eap and an experimental basis for interpreting the EAP domain crystal structures within the context of the full-length molecule. They also lay a foundation for future studies into the structural and molecular bases of Eap-mediated protein-protein interactions with its many ligands.

Mapping the transcription start points of the Staphylococcus aureus eap, emp, and vwb promoters reveals a conserved octanucleotide sequence that is essential for expression of these genes

Mapping the transcription start points of the eap, emp, and vwb promoters revealed a conserved octanucleotide sequence (COS). Deleting this sequence abolished the expression of eap, emp, and vwb. However, electrophoretic mobility shift assays gave no evidence that this sequence was a binding site for SarA or SaeR, known regulators of eap and emp.

Use of peptide-major histocompatibility complex tetramer technology to study interactions between Staphylococcus aureus proteins and human cells

In this study, we report the use of peptide-major histocompatibility complex tetramer technology to study the interactions that occur between Staphylococcus aureus proteins and human leukocytes. We demonstrated that this technology can be used to study the activity of superantigens such as toxic shock syndrome toxin 1 and also found that despite similarities to known proteins (i.e., major histocompatibility complex [MHC] class II molecules and superantigens), the S. aureus Eap protein does not block MHC-T-cell receptor interactions and is not a superantigen. Instead, it has nonspecific cross-linking activity that is dependent upon having at least two of its six 110-amino-acid repeats.

The anti-inflammatory activities of Staphylococcus aureus

Staphylococcus aureus is a versatile and harmful pathogen in both hospital- and community-associated infections that range from superficial to systemic infections. S. aureus engages a multitude of mechanisms to subvert the innate immune response of the host, including inhibition of complement activation and neutralization of anti-microbial peptides. In addition, inflammatory cell and phagocyte recruitment is an integral part of the innate defense to staphylococcal infection and comprises a well-coordinated multi-step cascade of adhesive events. Recent and rapidly growing experimental evidence indicates the existence of a machinery of anti-adhesive and anti-chemotactic moieties of S. aureus that allow the bacterium to interfere with specific adhesive steps of the homing mechanism of leukocytes. Understanding the functions of these S. aureus-derived anti-inflammatory agents could also provide the platform for designing new therapies in several inflammatory and autoimmune diseases.

Innate immune response of bovine mammary gland to pathogenic bacteria responsible for mastitis

Mastitis (mammary gland inflammation) is one of the most important bovine diseases causing economic losses to dairy producers. Mammary gland inflammation is a consequence of the activity of a number of cell and soluble factors that function together to eliminate invading microorganisms. The factors involved in this inflammatory response differ depending on the infectious agent. This review analyzes the factors involved in the immunologic mechanisms against the main pathogenic bacteria causing mastitis, and emphasizes the innate immune response of the mammary gland. Knowledge, at the molecular level, of the mammary gland immune response during infection by pathogenic bacteria is fundamental to the design of effective therapies to control and eradicate bovine mastitis.

Identification and characterization of a cell surface protein ofPrevotella intermedia 17 with broad-spectrum binding activity for extracellular matrix proteins

Prevotella intermedia binds and invades a variety of host cells. This binding is most probably mediated through cell surface proteins termed adhesins. To identify proteins binding to the host extracellular matrix (ECM) component, fibronectin, and study the molecular mechanism underlying bacterial colonization, we applied proteomic approaches to perform a global investigation of P. intermedia strain 17 outer membrane proteins. 2-DE followed by Far Western Blot analysis using fibronectin as a probe revealed a 29-kDa fibronectin-binding protein, designated here AdpB. The molecular identity of the protein was determined using PMF followed by a search of the P. intermedia 17 protein database. Database searches revealed the similarity of AdpB to multiple bacterial outer membrane proteins including the fibronectin-binding protein from Campylobacter jejuni. A recombinant AdpB protein bound fibronectin as well as other host ECM components, including fibrinogen and laminin, in a saturable, dose-dependent manner. Binding of AdpB to immobilized fibronectin was also inhibited by soluble fibronectin, laminin, and fibrinogen, indicating the binding was specific. Finally, immunoelectron microscopy with anti-AdpB demonstrated the cell surface location of the protein. This is the first cell surface protein with a broad-spectrum ECM-binding abilities identified and characterized in P. intermedia 17.

The anchorless adhesin Eap (extracellular adherence protein) from Staphylococcus aureus selectively recognizes extracellular matrix aggregates but binds promiscuously to monomeric matrix macromolecules

Besides a number of cell wall-anchored adhesins, the majority of Staphylococcus aureus strains produce anchorless, cell wall-associated proteins, such as Eap (extracellular adherence protein). Eap contains four to six tandem repeat (EAP)-domains. Eap mediates diverse biological functions, including adherence and immunomodulation, thus contributing to S. aureus pathogenesis. Eap binding to host macromolecules is unusually promiscuous and includes matrix or matricellular proteins as well as plasma proteins. The structural basis of this promiscuity is poorly understood. Here, we show that in spite of the preferential location of the binding epitopes within triple helical regions in some collagens there is a striking specificity of Eap binding to different collagen types. Collagen I, but not collagen II, is a binding substrate in monomolecular form. However, collagen I is virtually unrecognized by Eap when incorporated into banded fibrils. By contrast, microfibrils containing collagen VI as well as basement membrane-associated networks containing collagen IV, or aggregates containing fibronectin bound Eap as effectively as the monomeric proteins. Therefore, Eap-binding to extracellular matrix ligands is promiscuous at the molecular level but not indiscriminate with respect to supramolecular structures containing the same macromolecules. In addition, Eap bound to banded fibrils after their partial disintegration by matrix-degrading proteinases, including matrix metalloproteinase 1. Therefore, adherence to matrix suprastructures by S. aureus can be supported by inflammatory reactions.

Suppression of experimental autoimmune encephalomyelitis by extracellular adherence protein of Staphylococcus aureus

Multiple sclerosis (MS) is a devastating inflammatory disorder of the central nervous system (CNS). A major hallmark of MS is the infiltration of T cells reactive against myelin components. T cell infiltration is mediated by the interaction of integrins of the beta1 and beta2 family expressed by lymphocytes with their endothelial counter-receptors, vascular cell adhesion molecule 1 and intercellular adhesion molecule (ICAM)-1, respectively. We have reported previously that extracellular adherence protein (Eap) of Staphylococcus aureus exerts antiinflammatory activities by interacting with ICAM-1 and blocking beta2-integrin-dependent neutrophil recruitment. Here, we report that Eap inhibits experimental autoimmune encephalomyelitis (EAE) in mice. In vitro, Eap reduced adhesion of peripheral blood T cells to immobilized ICAM-1 as well as their adhesion and transmigration of TNF-activated human endothelium under static and shear flow conditions. These inhibitory effects were corroborated in two mouse models of inflammation. In a delayed-type hypersensitivity model, both T cell infiltration and the corresponding tissue edema were significantly reduced by Eap. In addition, Eap administration prevented the development of EAE and markedly decreased infiltration of inflammatory cells into the CNS. Strikingly, intervention with Eap after the onset of EAE suppressed the disease. Collectively, our findings indicate that Eap represents an attractive treatment for autoimmune neuroinflammatory disorders such as MS.

The extracellular adherence protein (Eap) of Staphylococcus aureus inhibits wound healing by interfering with host defense and repair mechanisms

Staphylococcus aureus is a major human pathogen interfering with host-cell functions. Impaired wound healing is often observed in S aureus-infected wounds, yet, the underlying mechanisms are poorly defined. Here, we identify the extracellular adherence protein (Eap) of S aureus to be responsible for impaired wound healing. In a mouse wound-healing model wound closure was inhibited in the presence of wild-type S aureus and this effect was reversible when the wounds were incubated with an isogenic Eap-deficient strain. Isolated Eap also delayed wound closure. In the presence of Eap, recruitment of inflammatory cells to the wound site as well as neovascularization of the wound were prevented. In vitro, Eap significantly reduced intercellular adhesion molecule 1 (ICAM-1)-dependent leukocyte-endothelial interactions and diminished the consequent activation of the proinflammatory transcription factor nuclear factor kappaB (NFkappaB) in leukocytes associated with a decrease in expression of tissue factor. Moreover, Eap blocked alphav-integrin-mediated endothelial-cell migration and capillary tube formation, and neovascularization in matrigels in vivo. Collectively, the potent anti-inflammatory and antiangiogenic properties of Eap provide an underlying mechanism that may explain the impaired wound healing in S aureus-infected wounds. Eap may also serve as a lead compound for new anti-inflammatory and antiangiogenic therapies in several pathologies.

Rhinoviruses promote internalisation of Staphylococcus aureus into non-fully permissive cultured pneumocytes

Respiratory viruses, including rhinoviruses, frequently promote bacterial opportunistic infections, through mechanisms that still deserve to be investigated in detail. This work was aimed at understanding how a viral infection mostly affecting the upper respiratory tract, such as the common cold, can repeatedly promote opportunistic infections in the lower airways, a site where viral replication is limited. The adhesivity and invasivity of Staphylococcus aureus were evaluated, in permissive and non-permissive cells, infected with Rhinovirus-1b. The role of inflammatory cytokines, and of ICAM-1 overexpression in the Rhinovirus-S. aureus cooperation was evaluated. Rhinovirus-1b enhanced the efficiency of internalisation of S. aureus irrespective of cellular permissivity, even when very low viral multiplicities of infection were used. Experiments performed with UV inactivated and heat inactivated viral particles suggested that this enhancement does not depend upon viral replication, but requires viral adhesion. Experimental data suggest that Rhinovirus-1b can significantly increase the ability of S. aureus to internalise into pneumocytes with a mechanism that involves the virus induced release of IL-6 and IL-8, and the overexpression of ICAM-1. Overall data disclose a possible mechanism through which rhinoviruses can promote bacterial infections in the lower respiratory tract.

Heparan sulfate proteoglycans mediate Staphylococcus aureus interactions with intestinal epithelium

Staphylococcus aureus can be internalized by non-professional phagocytes, and may colonize the intestine in normal and antibiotic-treated individuals. Intestinal colonization may depend on the interactions of S. aureus with the intestinal epithelium. The best described mechanism of S. aureus binding to eukaryotic cells involves S. aureus fibronectin binding proteins (FnBPs), using fibronectin as a bridging molecule to beta1 integrins on the eukaryotic cell surface. Because S. aureus can be internalized by enterocytes, and because S. aureus is known to bind heparan sulfate (HS), we hypothesized that heparan sulfate proteoglycans (HSPGs) widely expressed on epithelia may mediate S. aureus interactions with intestinal epithelial cells. Internalization of S. aureus RN6390 by cultured intestinal epithelial cells was inhibited in a dose-dependent fashion by the HS mimic heparin, and by HS itself. Internalization of S. aureus DU5883, which lacks expression of staphylococcal FnBPs, was also inhibited by heparin. S. aureus adherence to ARH-77 cells, transfected to express the HSPG syndecan-1, was greatly increased when compared to adherence to plasmid control ARH-77 cells which have little detergent extractable HS. In addition, compared to wild-type HS-expressing Chinese hamster ovary (CHO) cells, internalization of S. aureus was decreased using mutant CHO cells with decreased HS expression. These findings are consistent with a model wherein S. aureus internalization by intestinal epithelial cells (and perhaps other epithelia) is mediated by S. aureus binding to the HS moiety of cell-surface HSPGs, and this interaction appears independent of fibronectin binding.

Clonal distribution and phase-variable expression of a major histocompatibility complex analogue protein in Staphylococcus aureus

The mapW gene of Staphylococcus aureus strain N315 contains a poly(A) tract which truncates translation of the protein. This study demonstrates that mapW is an allelic variant of the map/eap genes found in other strains and that the variation in the length of this poly(A) tract suggests that it is a contingency locus.

The crystal structures of EAP domains from Staphylococcus aureus reveal an unexpected homology to bacterial superantigens

The Eap (extracellular adherence protein) of Staphylococcus aureus functions as a secreted virulence factor by mediating interactions between the bacterial cell surface and several extracellular host proteins. Eap proteins from different Staphylococcal strains consist of four to six tandem repeats of a structurally uncharacterized domain (EAP domain). We have determined the three-dimensional structures of three different EAP domains to 1.8, 2.2, and 1.35 A resolution, respectively. These structures reveal a core fold that is comprised of an alpha-helix lying diagonally across a five-stranded, mixed beta-sheet. Comparison of EAP domains with known structures reveals an unexpected homology with the C-terminal domain of bacterial superantigens. Examination of the structure of the superantigen SEC2 bound to the beta-chain of a T-cell receptor suggests a possible ligand-binding site within the EAP domain (Fields, B. A., Malchiodi, E. L., Li, H., Ysern, X., Stauffacher, C. V., Schlievert, P. M., Karjalainen, K., and Mariuzza, R. (1996) Nature 384, 188-192). These results provide the first structural characterization of EAP domains, relate EAP domains to a large class of bacterial toxins, and will guide the design of future experiments to analyze EAP domain structure/function relationships.