The Staphyloccous aureus Eap protein activates expression of proinflammatory cytokines

Pediatric Musculoskeletal Infection: Hijacking the Acute-Phase Response

Tissue injury activates the acute-phase response mediated by the liver, which promotes coagulation, immunity, and tissue regeneration. To survive and disseminate, musculoskeletal pathogens express virulence factors that modulate and hijack this response. As the acute-phase reactants required by these pathogens are most abundant in damaged tissue, these infections are predisposed to occur in tissues following traumatic or surgical injury. Staphylococcus aureus expresses the virulence factors coagulase and von Willebrand binding protein to stimulate coagulation and to form a fibrin abscess that protects it from host immune-cell phagocytosis. After the staphylococcal abscess community reaches quorum, which is the colony density that enables cell-to-cell communication and coordinated gene expression, subsequent expression of staphylokinase stimulates activation of fibrinolysis, which ruptures the abscess wall and results in bacterial dissemination. Unlike Staphylococcus aureus, Streptococcus pyogenes expresses streptokinase and other virulence factors to activate fibrinolysis and to rapidly disseminate throughout the body, causing diseases such as necrotizing fasciitis. Understanding the virulence strategies of musculoskeletal pathogens will help to guide clinical diagnosis and decision-making through monitoring of acute-phase markers such as C-reactive protein, erythrocyte sedimentation rate, and fibrinogen.

Characterization of Foodborne Strains of Staphylococcus aureus by Shotgun Proteomics: Functional Networks, Virulence Factors and Species-Specific Peptide Biomarkers

In the present work, we applied a shotgun proteomics approach for the fast and easy characterization of 20 different foodborne strains of Staphylococcus aureus (S. aureus), one of the most recognized foodborne pathogenic bacteria. A total of 644 non-redundant proteins were identified and analyzed via an easy and rapid protein sample preparation procedure. The results allowed the differentiation of several proteome datasets from the different strains (common, accessory, and unique datasets), which were used to determine relevant functional pathways and differentiate the strains into different Euclidean hierarchical clusters. Moreover, a predicted protein-protein interaction network of the foodborne S. aureus strains was created. The whole confidence network contains 77 nodes and 769 interactions. Most of the identified proteins were surface-associated proteins that were related to pathways and networks of energy, lipid metabolism and virulence. Twenty-seven virulence factors were identified, and most of them corresponded to autolysins, N-acetylmuramoyl-L-alanine amidases, phenol-soluble modulins, extracellular fibrinogen-binding proteins and virulence factor EsxA. Potential species-specific peptide biomarkers were screened. Twenty-one species-specific peptide biomarkers, belonging to eight different proteins (nickel-ABC transporter, N-acetylmuramoyl-L-alanine amidase, autolysin, clumping factor A, gram-positive signal peptide YSIRK, cysteine protease/staphopain, transcriptional regulator MarR, and transcriptional regulator Sar-A), were proposed to identify S. aureus. These results constitute the first major dataset of peptides and proteins of foodborne S. aureus strains. This repository may be useful for further studies, for the development of new therapeutic treatments for S. aureus food intoxications and for microbial source-tracking in foodstuffs.

Role of SCCmec type in resistance to the synergistic activity of oxacillin and cefoxitin in MRSA

β-lactam antibiotics target penicillin-binding proteins (PBPs) preventing peptidoglycan synthesis and this inhibition is circumvented in methicillin resistant Staphylococcus aureus (MRSA) strains through the expression of an additional PBP, named PBP2A. This enzyme is encoded by the mecA gene located within the Staphylococcal Chromosome Cassette mec (SCCmec) mobile genetic element, of which there are 12 types described to date. Previous investigations aimed at analysing the synergistic activity of two β-lactams, oxacillin and cefoxitin, found that SCCmec type IV community-acquired MRSA strains exhibited increased susceptibility to oxacillin in the presence of cefoxitin, while hospital-acquired MRSA strains were unaffected. However, it is not clear if these differences in β-lactam resistance are indeed a consequence of the presence of the different SCCmec types. To address this question, we have exchanged the SCCmec type I in COL (HA-MRSA) for the SCCmec type IV from MW2 (CA-MRSA). This exchange did not decrease the resistance of COL against oxacillin and cefoxitin, as observed in MW2, indicating that genetic features residing outside of the SCCmec element are likely to be responsible for the discrepancy in oxacillin and cefoxitin synergy against these MRSA strains.

Dysregulation of the endothelium following Staphylococcus aureus infection

The cardiovascular system is typically a sterile environment; however entry of a microorganism into the circulation can cause potentially life threatening cardiac and/or vascular disease. Staphylococcus aureus endothelial cell interactions are arguably the most important interactions in the pathogenesis of cardiovascular infection. These interactions can trigger cardiac valve destruction in the case of endocarditis, multi-organ dysfunction in the case of sepsis and coagulopathy. Here, we review the interactions between S. aureus and endothelial cells and discuss the implications of these interactions in the progression of cardiovascular infection.

Secreted proteases control autolysin-mediated biofilm growth of Staphylococcus aureus

Staphylococcus epidermidis, a commensal of humans, secretes Esp protease to prevent Staphylococcus aureus biofilm formation and colonization. Blocking S. aureus colonization may reduce the incidence of invasive infectious diseases; however, the mechanism whereby Esp disrupts biofilms is unknown. We show here that Esp cleaves autolysin (Atl)-derived murein hydrolases and prevents staphylococcal release of DNA, which serves as extracellular matrix in biofilms. The three-dimensional structure of Esp was revealed by x-ray crystallography and shown to be highly similar to that of S. aureus V8 (SspA). Both atl and sspA are necessary for biofilm formation, and purified SspA cleaves Atl-derived murein hydrolases. Thus, S. aureus biofilms are formed via the controlled secretion and proteolysis of autolysin, and this developmental program appears to be perturbed by the Esp protease of S. epidermidis.

Staphylococcus aureus virulence factors in evasion from innate immune defenses in human and animal diseases

In the last decades, Staphylococcus aureus acquired a dramatic relevance in human and veterinary medicine for different reasons, one of them represented by the increasing prevalence of antibiotic resistant strains. However, antibiotic resistance is not the only weapon in the arsenal of S. aureus. Indeed, these bacteria have plenty of virulence factors, including a vast ability to evade host immune defenses. The innate immune system represents the first line of defense against invading pathogens. This system consists of three major effector mechanisms: antimicrobial peptides and enzymes, the complement system and phagocytes. In this review, we focused on S. aureus virulence factors involved in the immune evasion in the first phases of infection: TLR recognition avoidance, adhesins affecting immune response and resistance to host defenses peptides and polypeptides. Studies of innate immune defenses and their role against S. aureus are important in human and veterinary medicine given the problems related to S. aureus antimicrobial resistance. Moreover, due to the pathogen ability to manipulate the immune response, these data are needed to develop efficacious vaccines or molecules against S. aureus.

Staphylococcus aureus extracellular adherence protein triggers TNFα release, promoting attachment to endothelial cells via protein A

Staphylococcus aureus is a leading cause of bacteraemia, which frequently results in complications such as infective endocarditis, osteomyelitis and exit from the bloodstream to cause metastatic abscesses. Interaction with endothelial cells is critical to these complications and several bacterial proteins have been shown to be involved. The S. aureus extracellular adhesion protein (Eap) has many functions, it binds several host glyco-proteins and has both pro- and anti-inflammatory activity. Unfortunately its role in vivo has not been robustly tested to date, due to difficulties in complementing its activity in mutant strains. We previously found Eap to have pro-inflammatory activity, and here show that purified native Eap triggered TNFα release in whole human blood in a dose-dependent manner. This level of TNFα increased adhesion of S. aureus to endothelial cells 4-fold via a mechanism involving protein A on the bacterial surface and gC1qR/p33 on the endothelial cell surface. The contribution this and other Eap activities play in disease severity during bacteraemia was tested by constructing an isogenic set of strains in which the eap gene was inactivated and complemented by inserting an intact copy elsewhere on the bacterial chromosome. Using a murine bacteraemia model we found that Eap expressing strains cause a more severe infection, demonstrating its role in invasive disease.

Staphylococcal extracellular adherence protein induces platelet activation by stimulation of thiol isomerases

OBJECTIVE

Staphylococcus aureus can induce platelet aggregation. The rapidity and degree of this correlates with the severity of disseminated intravascular coagulation, and depends on platelet peptidoglycans. Surface-located thiol isomerases play an important role in platelet activation. The staphylococcal extracellular adherence protein (Eap) functions as an adhesin for host plasma proteins. Therefore we tested the effect of Eap on platelets.

METHODS AND RESULTS

We found a strong stimulation of the platelet-surface thiol isomerases protein disulfide isomerase and endoplasmic reticulum stress proteins 57 and 72 by Eap. Eap induced thiol isomerase-dependent glycoprotein IIb/IIIa activation, granule secretion, and platelet aggregation. Treatment of platelets with thiol blockers, bacitracin, and anti-protein disulfide isomerase antibody inhibited Eap-induced platelet activation. The effect of Eap on platelets and protein disulfide isomerase activity was completely blocked by glycosaminoglycans. Inhibition by the hydrophobic probe bis(1-anilinonaphthalene 8-sulfonate) suggested the involvement of hydrophobic sites in protein disulfide isomerase and platelet activation by Eap.

CONCLUSIONS

In the present study, we found an additional and yet unknown mechanism of platelet activation by a bacterial adhesin, involving stimulation of thiol isomerases. The thiol isomerase stimulatory and prothrombotic features of a microbial secreted protein are probably not restricted to S aureus and Eap. Because many microorganisms are coated with amyloidogenic proteins, it is likely that the observed mechanism is a more general one.

A play in four acts: Staphylococcus aureus abscess formation

Staphylococcus aureus is an important human pathogen that causes skin and soft tissue abscesses. Abscess formation is not unique to staphylococcal infection and purulent discharge has been widely considered a physiological feature of healing and tissue repair. Here we present a different view, whereby S. aureus deploys specific virulence factors to promote abscess lesions that are distinctive for this pathogen. In support of this model, only live S. aureus is able to form abscesses, requiring genes that act at one or more of four discrete stages during the development of these infectious lesions. Protein A and coagulases are distinctive virulence attributes for S. aureus, and humoral immune responses specific for these polypeptides provide protection against abscess formation in animal models of staphylococcal disease.

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.

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.

Genetic variation in Staphylococcus aureus surface and immune evasion genes is lineage associated: implications for vaccine design and host-pathogen interactions

Background

S. aureus is a coloniser and pathogen of humans and mammals. Whole genome sequences of 58 strains of S. aureus in the public domain and data from multi-strain microarrays were compared to assess variation in the sequence of proteins known or putatively interacting with host.

Results

These included 24 surface proteins implicated in adhesion (ClfA, ClfB, Cna, Eap, Ebh, EbpS, FnBPA, FnBPB, IsaB, IsdA, IsdB, IsdH, SasB, SasC, SasD, SasF, SasG, SasH, SasK, SdrC, SdrD, SdrE, Spa and SraP) and 13 secreted proteins implicated in immune response evasion (Coa, Ecb, Efb, Emp, EsaC, EsxA, EssC, FLIPr, FLIPr like, Sbi, SCIN-B, SCIN-C, VWbp) located on the stable core genome. Many surface protein genes were missing or truncated, unlike immune evasion genes, and several distinct variants were identified. Domain variants were lineage specific. Unrelated lineages often possess the same sequence variant domains proving that horizontal transfer and recombination has contributed to their evolution. Surprisingly, sequenced strains from four animal S. aureus strains had surface and immune evasion proteins remarkably similar to those found in human strains, yet putative targets of these proteins vary substantially between different hosts. This suggests these proteins are not essential for virulence. However, the most variant protein domains were the putative functional regions and there is biological evidence that variants can be functional, arguing they do play a role.

Conclusion

Surface and immune evasion genes are candidates for S. aureus vaccines, and their distribution and functionality is key. Vaccines should contain cocktails of antigens representing all variants or they will not protect against naturally occurring S. aureus populations.

Extracellular adherence protein (Eap) from Staphylococcus aureus does not function as a superantigen

Extracellular adherence protein (Eap) from Staphylococcus aureus has been reported to have strong anti-inflammatory properties, which make Eap a potential anti-inflammatory agent. However, Eap has also been demonstrated to trigger T-cell activation and to share structural homology with superantigens. In this study, we focused on whether Eap fulfilled the definition criteria for a superantigen. We demonstrate that T-cell activation by Eap is dependent on both major histocompatibility complex class II and intercellular adhesion molecule type 1, that cellular processing is required for Eap to elicit T-cell proliferation, and that the kinetics of proliferation resemble the profile of a conventional antigen and not that of a superantigen.

Pathogenic Bacterial Proteins and their Anti-Inflammatory Effects in the Eukaryotic Host

Bacteria use multiple strategies to bypass the inflammatory responses in order to survive in the host cells. In this review, we discuss the mechanism of the bacerial proteins in inhibiting inflammation. We highlight the anti-inflammatory roles of the type three secretion proteins including Salmonella AvrA, Enteropathogenic Escherichia coli Cif, and Yersinia YopJ, Staphylococcus aureus extracellular adherence protein, and Chlamydia proteins. We also discuss the research progress on the structures of these anti-inflammatory bacterial proteins. The current therapeutic methods for diseases, such as inflammatory bowel diseases, sclerosis, lack influence on the course of chronic inflammation and infection. Therefore, based on the molecular mechanism of the anti-inflammatory bacterial proteins and their 3-Dimension structure, we can design new peptides or non-peptidic molecules that serve as anti-inflammatory drugs without the possible side effect of promoting bacterial infection.