Adherence of Staphylococcus aureus is enhanced by an endogenous secreted protein with broad binding activity

A novel mechanism for enhancement of adherence of Staphylococcus aureus to host components is described. A secreted protein, Eap (extracellular adherence protein), was purified from the supernatant of S. aureus Newman and found to be able to bind to at least seven plasma proteins, e.g., fibronectin, the alpha-chain of fibrinogen, and prothrombin, and to the surface of S. aureus. Eap bound much less to cells of Staphylococcus epidermidis, Streptococcus mutans, or Escherichia coli. The protein can form oligomeric forms and is able to cause agglutination of S. aureus. Binding of S. aureus to fibroblasts and epithelial cells was significantly enhanced by addition of Eap, presumably due to its affinity both for plasma proteins on the cells and for the bacteria.     

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.     

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.     

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.     

Eap1p, a novel eukaryotic translation initiation factor 4E-associated protein in Saccharomyces cerevisiae

Ribosome binding to eukaryotic mRNA is a multistep process which is mediated by the cap structure [m(7)G(5')ppp(5')N, where N is any nucleotide] present at the 5' termini of all cellular (with the exception of organellar) mRNAs. The heterotrimeric complex, eukaryotic initiation factor 4F (eIF4F), interacts directly with the cap structure via the eIF4E subunit and functions to assemble a ribosomal initiation complex on the mRNA. In mammalian cells, eIF4E activity is regulated in part by three related translational repressors (4E-BPs), which bind to eIF4E directly and preclude the assembly of eIF4F. No structural counterpart to 4E-BPs exists in the budding yeast, Saccharomyces cerevisiae. However, a functional homolog (named p20) has been described which blocks cap-dependent translation by a mechanism analogous to that of 4E-BPs. We report here on the characterization of a novel yeast eIF4E-associated protein (Eap1p) which can also regulate translation through binding to eIF4E. Eap1p shares limited homology to p20 in a region which contains the canonical eIF4E-binding motif. Deletion of this domain or point mutation abolishes the interaction of Eap1p with eIF4E. Eap1p competes with eIF4G (the large subunit of the cap-binding complex, eIF4F) and p20 for binding to eIF4E in vivo and inhibits cap-dependent translation in vitro. Targeted disruption of the EAP1 gene results in a temperature-sensitive phenotype and also confers partial resistance to growth inhibition by rapamycin. These data indicate that Eap1p plays a role in cell growth and implicates this protein in the TOR signaling cascade of S. cerevisiae.     

Anchorless adhesins and invasins of Gram-positive bacteria: a new class of virulence factors

Bacterial adherence to and invasion of eukaryotic cells are important mechanisms of pathogenicity. Most Gram-positive bacteria interact with the components of the host extracellular matrix (ECM) to adhere to, colonize and invade cells and tissues. The bacterial proteins that bind to components of the ECM harbour signal sequences for their secretion and mechanisms of anchoring to the host cell surface. However, in recent years, some cell-surface adhesins and invasins of Gram-positive bacteria have been described that do not possess a signal sequence or a membrane anchor. These proteins are secreted by an as-yet-unknown mechanism and are probably localized on the bacterial surface by reassociation. These anchorless but surface-located adhesins and invasins represent a new class of virulence factors.     

Staphylococcus aureus extracellular adherence protein serves as anti-inflammatory factor by inhibiting the recruitment of host leukocytes

Staphylococcus aureus is a human pathogen that secretes proteins that contribute to bacterial colonization. Here we describe the extracellular adherence protein (Eap) as a novel anti-inflammatory factor that inhibits host leukocyte recruitment. Due to its direct interactions with the host adhesive proteins intercellular adhesion molecule 1 (ICAM-1), fibrinogen or vitronectin, Eap disrupted beta(2)-integrin and urokinase receptor mediated leukocyte adhesion in vitro. Whereas Eap-expressing S. aureus induced a 2 3-fold lower neutrophil recruitment in bacterial peritonitis in mice as compared with an Eap-negative strain, isolated Eap prevented beta(2)-integrin-dependent neutrophil recruitment in a mouse model of acute thioglycollate-induced peritonitis. Thus, the specific interactions with ICAM-1 and extracellular matrix proteins render Eap a potent anti-inflammatory factor, which may serve as a new therapeutic substance to block leukocyte extravasation in patients with hyperinflammatory pathologies.     

Alpha-toxin interferes with integrin-mediated adhesion and internalization of Staphylococcus aureus by epithelial cells

Staphylococcus aureus is an important human and animal pathogen. During infection, this bacterium is able to attach to and enter host cells by using its cell surface-associated factors to bind to the host's extracellular matrix (ECM) proteins. In this study, we determined that a protein exported by S. aureus, alpha-toxin, can interfere with the integrin-mediated adhesion and internalization of S. aureus by human lung epithelial cells (A549). The downregulation of alpha-toxin production significantly increased bacterial adhesion and invasion into the epithelial cells. In contrast, bacterial adhesion and invasion was inhibited by both overproduction of alpha-toxin and the addition of alpha-toxin to the culture medium. Moreover, our results showed that the quantitative effects on invasion closely parallel those of adherence. This suggests that the effect on invasion is probably secondary to, and a consequence of, the reduced adherence caused by alpha-toxin exposure. Specifically, we demonstrated that alpha-toxin interacts with the hosts' ECM protein's receptor, beta1-integrin, which indicates that beta1-integrin may be a potential receptor of alpha-toxin on epithelial cells. Taken together, our results indicate that exported alpha-toxin inhibits the adhesion and internalization of S. aureus by interfering with integrin-mediated pathogen-host cell interactions.     

Clumping factor B, a fibrinogen-binding MSCRAMM (microbial surface components recognizing adhesive matrix molecules) adhesin of Staphylococcus aureus, also binds to the tail region of type I cytokeratin 10

The primary habitat of Staphylococcus aureus in humans is the moist squamous epithelium of the anterior nares. We showed previously that S. aureus adheres to desquamated epithelial cells and that clumping factor B (ClfB), a surface-located MSCRAMM (microbial surface components recognizing adhesive matrix molecules) known for its ability to bind to the alpha-chain of fibrinogen, is partly responsible (O'Brien, L. M., Walsh, E. J., Massey, R. C., Peacock, S. J., and Foster, T. J. (2002) Cell. Microbiol. 4, 759-770). We identified cytokeratin 10 (K10) as the ligand recognized by ClfB. Here we have shown that purified recombinant human and murine K10 immobilized on a plastic surface supports adherence of S. aureus in a ClfB-dependent manner. Furthermore, the recombinant A domain of ClfB (rClfB 45-542) bound to immobilized K10 dose-dependently and saturably. Subdomains of human and murine K10 were expressed and purified. The N-terminal head domain (residues 1-145) did not support the binding of rClfB or adherence of S. aureus ClfB+. In contrast, the C-terminal tail domains (human rHK10 452-593, mouse rMK10 454-570) promoted avid binding and adherence. Isothermal titration microcalorimetry and intrinsic tryptophan fluorescence experiments gave dissociation constants for rClfB 45-542 binding to rMK10 454-570 of 1.4 and 1.7 microM, respectively. The tail region of K10 is composed largely of quasi-repeats of Tyr-(Gly/Ser)n. A synthetic peptide corresponding to a typical glycine loop (YGGGSSGGGSSGGY; Y-Y loop peptide) inhibited the adherence of S. aureus ClfB+ to immobilized MK10 to a level of 80%, whereas control peptides had no effect. The KD of rClfB 45-542 for the Y-Y loop peptide was 5.3 microm by intrinsic tryptophan fluorescence. Thus ClfB binds to the glycine loop region of the tail domain of keratin 10 where there are probably multiple binding sites. Binding is discussed in the context of the dock-lock-latch model for MSCRAMM-ligand interactions. We provide an explanation for the molecular basis for S. aureus adherence to the squamous epithelium and suggest that nasal colonization might be prevented by reagents that inhibit this interaction.     

Identification and Characterization of a Novel 38.5-Kilodalton Cell Surface Protein of Staphylococcus aureus with Extended-Spectrum Binding Activity for Extracellular Matrix and Plasma Proteins

The ability to attach to host ligands is a well-established pathogenic factor in invasive Staphylococcus aureus disease. In addition to the family of adhesive proteins bound to the cell wall via the sortase A (srtA) mechanism, secreted proteins such as the fibrinogen-binding protein Efb, the extracellular adhesion protein Eap, or coagulase have been found to interact with various extracellular host molecules. Here we describe a novel protein, the extracellular matrix protein-binding protein (Emp) initially identified in Western ligand blots as a 40-kDa protein due to its broad-spectrum recognition of fibronectin, fibrinogen, collagen, and vitronectin. Emp is expressed in the stationary growth phase and is closely associated with the cell surface and yet is extractable by sodium dodecyl sulfate. The conferring gene emp (1,023 nucleotides) encodes a signal peptide of 26 amino acids and a mature protein of a calculated molecular mass of 35.5 kDa. Using PCR, emp was demonstrated in all 240 S. aureus isolates of a defined clinical strain collection as well as in 6 S. aureus laboratory strains, whereas it is lacking in all 10 S. epidermidis strains tested. Construction of an allelic replacement mutant (mEmp50) revealed the absence of Emp in mEmp50, a significantly decreased adhesion of mEmp50 to immobilized fibronectin and fibrinogen, and restoration of these characteristics upon complementation of mEmp50. Emp expression was also demonstrable upon heterologous complementation of S. carnosus. rEmp expressed in Escherichia coli interacted with fibronectin, fibrinogen, and vitronectin in surface plasmon resonance experiments at a K(d) of 21 nM, 91 nM, and 122 pM, respectively. In conclusion, the biologic characterization of Emp suggests that it is a member of the group of secreted S. aureus molecules that interact with an extended spectrum of host ligands and thereby contribute to S. aureus pathogenicity.     

Staphylococcus aureus clumping factor B (ClfB) promotes adherence to human type I cytokeratin 10: implications for nasal colonization

Staphylococcus aureus is an important cause of sepsis in both community and hospital settings, a major risk factor for which is nasal carriage of the bacterium. Eradication of carriage by topical antibiotics reduces sepsis rates in high-risk individuals, an important strategy for the reduction of nosocomial infection in targeted patient populations. Understanding the mechanisms by which S. aureus adheres to nasal epithelial cells in vivo may lead to alternative methods of decolonization that do not rely on sustained antimicrobial susceptibility. Here, we demonstrate for the first time that the S. aureus surface-expressed protein, clumping factor B (ClfB), promotes adherence to immobilized epidermal cytokeratins in vitro . By expressing a range of S. aureus adhesins on the surface of the heterologous host Lactococcus lactis , we demonstrated that adherence to epidermal cytokeratins was conferred by ClfB. Adherence of wild-type S. aureus was inhibited by recombinant ClfB protein or anti-ClfB antibodies, and S. aureus mutants defective in ClfB adhered poorly to epidermal cytokeratins. Expression of ClfB promoted adherence of L. lactis to human desquamated nasal epithelial cells, and a mutant of S. aureus defective in ClfB had reduced adherence compared with wild type. ClfB also promoted adherence of L. lactis cells to a human keratinocyte cell line. Cytokeratin 10 molecules were shown by flow cytometry to be exposed on the surface of both desquamated nasal epithelial cells and keratinocytes. Cytokeratin 10 was also detected on the surface of desquamated human nasal cells using immunofluorescence, and recombinant ClfB protein was shown to bind to cytokeratin K10 extracted from these cells. We also showed that ClfB is transcribed by S. aureus in the human nares. We propose that ClfB is a major determinant in S. aureus nasal colonization.     

Attachment of Staphylococcus aureus to eukaryotic cells and experimental pitfalls in staphylococcal adherence assays: a critical appraisal.

Staphylococcus aureus is a bacterial species with pathogenic potential to both humans and animals. The primary natural niche is said to be the human vestibulum nasi from where bacterial cells may spread to the environment or additional anatomical sites such as the perineum or the hands, where residence is usually transient. Apparently, S. aureus is capable of a precise and balanced interaction with specific types of eukaryotic nasal cells. Although a wide variety of important bacterial ligands and possible eukaryote receptors have been described, the precise mechanisms leading to persistent bacterial colonization and, even more importantly, associated infection have not yet been elucidated in detail. This may be a consequence of the fact that most of the adherence factors have been studied individually in simplified in vitro systems, not taking the complexity of multi-factorial in vivo cell-cell interactions into account. An overall scheme of the initial and sequential interactions leading to S. aureus colonization of eukaryotic cell surfaces has not yet emerged. This review concisely describes the current state of affairs in the multi-disciplinary field of staphylococcal adherence research. Specific emphasis is placed upon the pros and cons of the various artificial, mostly in vitro models employed to study the interaction between bacterial and human or animal cells.     

Co-operative binding of human fibronectin to Sfbl protein triggers streptococcal invasion into respiratory epithelial cells

Streptococcal fibronectin binding protein I (SfbI) mediates adherence to and invasion of Streptococcus pyogenes into human epithelial cells. In this study, we analysed the binding activity of distinct domains of SfbI protein towards its ligand, the extracellular matrix component fibronectin, as well as the biological implication of the binding events during the infection process. By using purified recombinant SfbI derivatives as well as in vivo expressed SfbI domains on the surface of heterologous organism Streptococcus gordonii , we were able to dissociate the two major streptococcal target domains on the human fibronectin molecule. The SfbI repeat region exclusively bound to the 30 kDa N-terminal fragment of fibronectin, whereas the SfbI spacer region exclusively bound to the 45 kDa collagen-binding fragment of fibronectin. In the case of native surface-expressed SfbI protein, an induced fit mode of bacteria–fibronectin interaction was identified. We demonstrate that binding of the 30 kDa fibronectin fragment to the repeat region of SfbI protein co-operatively activates the adjacent SfbI spacer domain to bind the 45 kDa fibronectin fragment. The biological consequence arising from this novel mode of fibronectin targeting was analysed in eukaryotic cell invasion assays. The repeat region of SfbI protein is mediating adherence and constitutes a prerequisite for subsequent invasion, whereas the SfbI spacer domain efficiently triggers the invasion process of streptococci into the eukaryotic cell. Thus, we were able to dissect bacterial adhesion from invasion by manipulating one protein. SfbI protein therefore represents a highly evolved prokaryotic molecule that exploits the host factor fibronectin not only for extracellular targeting but also for its subsequent activation that leads to efficient cellular invasion.     

Inhibition of breast cancer cell adhesion and bone metastasis by the extracellular adherence protein of Staphylococcus aureus

Bone metastasis is a common sequelae of breast cancer and the interaction of alpha v beta3-integrin with osteopontin (OPN) found in the extracellular matrix of mineralized tissues is implicated in this process. The integrin-dependent proadhesive and promigratory functions of OPN are particularly attributed to the 40 kD N-terminal fragment that derives upon matrix metalloproteinase (MMP) cleavage. Based on the broad repertoire of interactions between Staphylococcus aureus extracellular adherence protein (Eap) and host components, we here characterized Eap to specifically interact with recombinant full-length OPN and the 40 kD N-terminal MMP cleavage fragment, but not with the 32 kD or the 25 kD C-terminal fragments of OPN. Eap thereby prevented the OPN/alpha v beta3-integrin interaction, as well as the alpha v beta3-integrin-dependent adhesion of MDA-MB-231 breast cancer cells to full-length OPN or to the 40 kD fragment and the migration of these cells towards OPN. Furthermore, Eap treatment markedly impaired the development of osseous metastasis of human MDA-MB-231 cells in vivo. Taken together, Eap may represent an attractive novel treatment for the prevention of breast cancer bone metastasis.     

Incubation of Streptococcus uberis with extracellular matrix proteins enhances adherence to and internalization into bovine mammary epithelial cells

Two strains of Streptococcus uberis (UT 888 and UT 366) isolated from cows with clinical mastitis were co-cultured with bovine mammary epithelial cells (MAC-T) with and without laminin, fibrinogen, fibronectin or collagen. Incubation of S. uberis with extracellular matrix proteins (ECMPs) increased adherence to and internalization into MAC-T cells. Both strains of S. uberis exhibited greater adherence when co-cultured in the presence of collagen than with any other ECMP. However, adherence was always higher when strains were co-cultured with ECMP than in medium alone. S. uberis UT 888 adhered better to MAC-T cells than S. uberis UT 366. The influence of ECMPs on bacterial internalization into MAC-T cells was similar to adherence, however, differences among ECMPs were less noticeable. S. uberis UT 888 had a higher internalization index than S. uberis UT 366. It is possible that ECMPs induce or up-regulate proteins that selectively adhere to ECMPs which could serve as a bridge between the eukaryotic cell and the bacterial pathogen that leads to internalization of the ECMP-bound pathogen into the mammary epithelial cell.     

Staphylococcus aureus extracellular adherence protein (Eap) reduces immune cell phenotype in developing but not in established atherosclerotic lesions

Atherosclerosis is a chronic, inflammatory disease of the vessel wall where triggered immune cells bind to inflamed endothelium, extravasate and sustain local inflammation. Leukocyte adhesion and extravasation are mediated by adhesion molecules expressed by activated endothelial cells, like intercellular adhesion molecule 1 (ICAM-1). Extracellular adherence protein (Eap) from Staphylococcus aureus binds to a plethora of extracellular matrix proteins, including ICAM-1 and its ligands macrophage-1 antigen (Mac-1, α_Mβ₂) and lymphocyte function-associated antigen 1 (LFA-1, α_Lβ₂), thereby disrupting the interaction between leukocytes and endothelial cells. We aimed to use Eap to inhibit the interaction of leukocytes with activated endothelial cells in settings of developing and established atherosclerosis in apolipoprotein E (ApoE) deficient mice on high-fat diet. In developing atherosclerosis, Eap treatment reduced circulating platelet-neutrophil aggregates as well as infiltration of T cells and neutrophils into the growing plaque, accompanied by reduced formation of neutrophil extracellular traps (NETs). However, plaque size did not change. Intervention treatment with Eap of already established plaques did not result in cellular or morphological plaque changes, whereas T cell infiltration was increased and thereby again modulated by Eap. We conclude that although Eap leads to cellular changes in developing plaques, clinical implications might be limited as patients are usually treated at a more advanced stage of disease progression. Hence, usage of Eap might be an interesting mechanistic tool for cellular infiltration during plaque development in basic research but not a clinical target.     

The fibronectin binding proteins of Staphylococcus aureus are required for adhesion to and invasion of bovine mammary gland cells

We recently described adhesion to and invasion of bovine mammary gland cells by Staphylococcus aureus in vitro. Here, we show that the levels of adhesion and invasion are dependent on the bacterial growth phase and are controlled by the agr locus. Incubation of exponential growth phase cells of S. aureus with mammary gland cells resulted in bacterial cell clumping. Strains of S. aureus deficient in expression of the fibronectin binding proteins (FnBPA and FnBPB) failed to clump and their ability to adhere to and to invade the bovine mammary gland cells is strongly reduced. This indicates that the fibronectin binding proteins are essential for S. aureus adhesion to and invasion of bovine mammary gland cells.     

Incorporation of carbon from decomposing litter of two pioneer plant species into microbial communities of the detritusphere

For several Staphylococci, such as Staphylococcus aureus, Staphylococcus saprophyticus, and Staphylococcus epidermidis, invasion of eukaryotic cells has been described and this mechanism has been considered an important part of the infection process. The fibrinogen-binding protein (Fbl) of Staphylococcus lugdunensis, a homolog of the clumping factor A of S. aureus, has been described as fibrinogen-binding adhesin and might promote invasion of cells. We therefore characterized several clinical strains of S. lugdunensis in terms of whole cell fibrinogen and fibronectin binding and correlated these results with the invasion of epithelial and endothelial cells by S. lugdunensis. We described for the first time invasion of cells by S. lugdunensis. As invasion of cells by S. lugdunensis was only partly inhibited by cytochalasin D in contrast to a complete inhibition of invasion of cells by S. aureus, further invasion mechanisms are likely to be present in S. lugdunensis. In addition, the Fbl of S. lugdunensis is not involved in the invasion of cells as ruled out by an isogenic fbl mutant.