Fibronectin-binding protein A of Staphylococcus aureus has multiple, substituting, binding regions that mediate adherence to fibronectin and invasion of endothelial cells

Internalization of Staphylococcus aureus by human keratinocytes

Staphylococcus aureus is among the most important human pathogens and causes various superficial and systemic infections. The ability of S. aureus to be internalized by, and survive within, host cells, such as keratinocytes, may contribute to the development of persistent or chronic infections and may finally lead to deeper tissue infections or dissemination. To examine the mechanisms of internalization of S. aureus by keratinocytes, isogenic mutants lacking fibronectin-binding proteins (FnBPs), a recombinant protein consisting of the fibronectin-binding domain of S. aureus FnBPs, and an anti-alpha5beta1 antibody were used in cocultures with immortalized keratinocytes and primary keratinocytes. We found that internalization of S. aureus by immortalized keratinocytes requires bacterial FnBPs and is mediated by the major fibronectin-binding integrin alpha5beta1. In contrast to internalization by immortalized keratinocytes, internalization of S. aureus by primary keratinocytes could occur through FnBP-dependent and -independent pathways. S. aureus clumping factor B (ClfB), which was recently determined to bind to epithelial cells, was not involved in the uptake of this bacterium by keratinocytes. The identification of an alternate uptake pathway, which is independent of S. aureus FnBPs and host cell alpha5beta1, has important implications for the design of therapies targeted to bacterial uptake by host cells.

IsdA of Staphylococcus aureus is a broad spectrum, iron-regulated adhesin

As an important facet of host-pathogen interaction, Staphylococcus aureus has the ability to adhere to human extracellular matrix (ECM) components via a range of surface proteins. Here we have shown that IsdA has broad-spectrum ligand-binding activity, including fibrinogen and fibronectin. Mapping studies revealed a distinct domain responsible for ligand binding. This domain is present in a number of iron-regulated proteins of S. aureus and in other Gram-positive organisms. The isdA gene is only expressed in iron-limited conditions under the control of Fur and not in standard laboratory media. Such conditions occur in serum in vitro and during infection. Whole cell binding and clumping assays revealed that when the bacteria are grown under iron-limited conditions, IsdA constitutes a physiologically relevant adhesin to both fibrinogen and fibronectin. Thus for S. aureus, iron is an important marker for the host environment, to which the bacterium responds by differential regulation of at least one element of its adhesive strategy.

Fibronectin binding to the Salmonella enterica serotype Typhimurium ShdA autotransporter protein is inhibited by a monoclonal antibody recognizing the A3 repeat

ShdA is a large outer membrane protein of the autotransporter family whose passenger domain binds the extracellular matrix proteins fibronectin and collagen I, possibly by mimicking the host ligand heparin. The ShdA passenger domain consists of approximately 1,500 amino acid residues that can be divided into two regions based on features of the primary amino acid sequence: an N-terminal nonrepeat region followed by a repeat region composed of two types of imperfect direct amino acid repeats, called type A and type B. The repeat region bound bovine fibronectin with an affinity similar to that for the complete ShdA passenger domain, while the nonrepeat region exhibited comparatively low fibronectin-binding activity. A number of fusion proteins containing truncated fragments of the repeat region did not bind bovine fibronectin. However, binding of the passenger domain to fibronectin was inhibited in the presence of immune serum raised to one truncated fragment of the repeat region that contained repeats A2, B8, A3, and B9. Furthermore, a monoclonal antibody that specifically recognized an epitope in a recombinant protein containing the A3 repeat inhibited binding of ShdA to fibronectin.

BBK32, a fibronectin binding MSCRAMM from Borrelia burgdorferi, contains a disordered region that undergoes a conformational change on ligand binding

BBK32 is a fibronectin-binding lipoprotein on Borrelia burgdorferi, the causative agent of Lyme disease. Analysis using secondary structure prediction programs suggested that BBK32 is composed of two domains, an N-terminal segment lacking well defined secondary structure and a C-terminal segment composed largely of alpha-helices. Analysis of purified recombinant forms of the two domains by circular dichroism spectroscopy, gel permeation chromatography, and intrinsic viscosity determination were consistent with an N-terminal-extended, unstructured segment and a C-terminal globular domain in BBK32. Solid phase binding experiments suggest that the unstructured N-terminal domain binds fibronectin. Analysis of changes in circular dichroism spectra of the N-terminal segment of BBK32 upon binding of the N-terminal domain of fibronectin revealed an increase in beta-sheet content in the complex. Hence, BBK32, which belongs to a different family of proteins and shows no overall sequence similarity with the fibronectin binding MSCRAMMs (microbial surface components recognizing adhesive matrix molecules) of Gram-positive bacteria, binds fibronectin by a mechanism that is reminiscent of the "tandem beta-zipper" previously demonstrated for the fibronectin binding of streptococcal adhesins.

The N-terminal A domain of fibronectin-binding proteins A and B promotes adhesion of Staphylococcus aureus to elastin

The ability of Staphylococcus aureus to adhere to components of the extracellular matrix is an important mechanism for colonization of host tissues during infection. We have previously shown that S. aureus binds elastin, a major component of the extracellular matrix. The integral membrane protein, elastin-binding protein (EbpS), binds soluble elastin peptides and tropoelastin via its surface-exposed N-terminal domain. In this study, we demonstrate that some strains of S. aureus adhere strongly to immobilized human elastin and that this interaction is independent of EbpS but instead is mediated by the fibronectin-binding proteins, FnBPA and FnBPB. Our results show that EbpS mutant cells adhere to elastin-coated plates, whereas the cells negative for FnBPA and FnBPB do not adhere to the plates. Furthermore, only wild-type cells from the exponential phase of growth adhered when FnBPs were expressed maximally. We show that adherence to elastin promoted by FnBPA was not affected by soluble fibronectin, suggesting that the elastin binding domain is distinct from the fibronectin binding regions. Recombinant FnBPA(37-544) (rFnBPA(37-544)) protein corresponding to the A region of FnBPA and anti-FnBPA(37-544) antibodies inhibited FnBPA-mediated bacterial adherence to immobilized elastin. Finally, recombinant A domain proteins, rFnBPA(37-544) and rFnBPB(37-540), bound immobilized elastin dose-dependently and saturably. This interaction was inhibited by soluble elastin peptides, suggesting a specific receptor-ligand interaction.

The novel fibrinogen-binding protein FbsB promotes Streptococcus agalactiae invasion into epithelial cells

Streptococcus agalactiae is a major cause of bacterial sepsis and meningitis in human newborns. The interaction of S. agalactiae with host proteins and the entry into host cells thereby represent important virulence traits of these bacteria. The present report describes the identification of the fbsB gene, encoding a novel fibrinogen-binding protein that plays a crucial role in the invasion of S. agalactiae into human cells. In Western blots and enzyme-linked immunosorbent assay (ELISA) experiments, the FbsB protein was demonstrated to interact with soluble and immobilized fibrinogen. Binding studies showed the N-terminal 388 residues of FbsB and the Aalpha-subunit of human fibrinogen to recognize each other. By reverse transcription (RT)-PCR, the fbsB gene was shown to be cotranscribed with the gbs0851 gene in S. agalactiae. Deletion of the fbsB gene in the genome of S. agalactiae did not influence the binding of the bacteria to fibrinogen, suggesting that FbsB does not participate in the attachment of S. agalactiae to fibrinogen. In tissue culture experiments, however, the fbsB deletion mutant was severely impaired in its invasion into lung epithelial cells. Bacterial invasion could be reestablished by introducing the fbsB gene on a shuttle plasmid into the fbsB deletion mutant. Furthermore, treatment of lung epithelial cells with FbsB fusion protein blocked S. agalactiae invasion of epithelial cells in a dose-dependent fashion. These results suggest an important role of the FbsB protein in the overall process of host cell entry by S. agalactiae.

Report of the National Heart, Lung and Blood Institute-National Institute of Allergy and Infectious Diseases working group on antimicrobial strategies and cardiothoracic surgery

Infections related to cardiac surgery increase morbidity and mortality, and increase cost and use of health resources. With the widespread use of synthetic materials, whether in prosthetic valves or vascular conduits, bacterial infection and, more rarely, fungal complications can be devastating, requiring prolonged antimicrobial therapy and, at times, re-operations with high morbidity and mortality rates. With the US population aging and living longer, cardiac surgery is applied to an older population with significant comorbidities, making the threat from infectious complications significant. The dwindling armamentarium of existing antimicrobial agents, a limited pharmaceutical pipeline of future therapies, and the emergence of antimicrobial-resistant bacteria have increased the challenge of treating cardiothoracic infections. Thus, there is critical need for addressing the existing and emerging issues in this area to develop new safe and effective strategies to address the clinical challenges facing cardiothoracic surgeons. As a result of this need, the National Heart, Lung, and Blood Institute and the National Institute of Allergy and Infectious Diseases convened a Working Group on April 4 and 5, 2002, in Bethesda, Md, which explored both basic science and clinical research opportunities in the prevention and treatment of major infections after cardiac surgery. Because of its importance as the most common pathogen in this setting, the focus of discussions was on the prevention and treatment of Staphylococcus aureus infections. This report summarizes the 5 main areas that the Working Group targeted (epidemiology of infections, molecular mechanisms of infections and complications, current pharmacotherapy, new frontiers, and clinical trial design) and highlights the recommendations that were set forth by the Working Group.

The molecular basis of fibronectin-mediated bacterial adherence to host cells

Many pathogenic Gram-positive bacteria produce cell wall-anchored proteins that bind to components of the extracellular matrix (ECM) of the host. These bacterial MSCRAMMs (microbial surface components recognizing adhesive matrix molecules) are thought to play a critical role in infection. One group of MSCRAMMs, produced by staphylococci and streptococci, targets fibronectin (Fn, a glycoprotein found in the ECM and body fluids of vertebrates) using repeats in the C-terminal region of the bacterial protein. These bacterial Fn-binding proteins (FnBPs) mediate adhesion to host tissue and bacterial uptake into non-phagocytic host cells. Recent studies on interactions between the host and bacterial proteins at the residue-specific level and on the mechanism of host cell invasion are providing a much clearer picture of these processes.

Integrin-mediated invasion of Staphylococcus aureus into human cells requires Src family protein-tyrosine kinases

Staphylococcus aureus, a common cause of nosocomial infections, is able to invade eukaryotic cells by indirectly engaging beta1 integrin-containing host receptors, whereas non-pathogenic Staphylococcus carnosus is not invasive. Here, we identify intracellular signals involved in integrin-initiated internalization of S. aureus. In particular, the host cell actin cytoskeleton and Src family protein-tyrosine kinases (PTKs) are essential to mediate S. aureus invasion. Src PTKs are activated in response to pathogenic S. aureus, but not S. carnosus. In addition, pharmacological and genetic interference with Src PTK function reduces bacterial internalization. Importantly, Src PTK-deficient cells are resistant to S. aureus invasion, demonstrating the essentiality of host Src PTKs in integrin-mediated uptake of this pathogen.

In vivo and in vitro demonstration that Staphylococcus aureus is an intracellular pathogen in the presence or absence of fibronectin-binding proteins

Staphylococcus aureus is the most significant bacterial pathogen associated with bovine mastitis. However, the relevance of intracellular infection to mastitis pathogenesis is poorly understood. We used in vitro assays and a mouse model of mastitis to demonstrate the intracellular component of the infection and to identify the importance of fibronectin-binding proteins in the processes of colonization and internalization. In vitro, a mutant strain, lacking fibronectin-binding protein (FnBPs(-)), had a reduced ability to bind fibronectin and to infect epithelial cells when compared to its parental wild type strain. After 2 h of infection, the internalization of the mutant bacteria into epithelial cell cultures was reduced by 60% compared with the wild type. After in vivo infection, microscopic examination using the FnBPs(-) strain revealed that production of a high density of live bacteria within the mammary gland epithelial cells was delayed. Both parental and mutant strains were identified within neutrophils, macrophages and epithelial cells suggesting a close similarity between the mouse mastitis model and bovine mastitis. These results demonstrate that S. aureus was able to cause an intracellular infection in the mouse model of mastitis and that the elimination of one adhesion protein delayed, but did not prevent, infection.

Genome-based bioinformatic selection of chromosomal Bacillus anthracis putative vaccine candidates coupled with proteomic identification of surface-associated antigens

Bacillus anthracis (Ames strain) chromosome-derived open reading frames (ORFs), predicted to code for surface exposed or virulence related proteins, were selected as B. anthracis-specific vaccine candidates by a multistep computational screen of the entire draft chromosome sequence (February 2001 version, 460 contigs, The Institute for Genomic Research, Rockville, Md.). The selection procedure combined preliminary annotation (sequence similarity searches and domain assignments), prediction of cellular localization, taxonomical and functional screen and additional filtering criteria (size, number of paralogs). The reductive strategy, combined with manual curation, resulted in selection of 240 candidate ORFs encoding proteins with putative known function, as well as 280 proteins of unknown function. Proteomic analysis of two-dimensional gels of a B. anthracis membrane fraction, verified the expression of some gene products. Matrix-assisted laser desorption ionization-time-of-flight mass spectrometry analyses allowed identification of 38 spots cross-reacting with sera from B. anthracis immunized animals. These spots were found to represent eight in vivo immunogens, comprising of EA1, Sap, and 6 proteins whose expression and immunogenicity was not reported before. Five of these 8 immunogens were preselected by the bioinformatic analysis (EA1, Sap, 2 novel SLH proteins and peroxiredoxin/AhpC), as vaccine candidates. This study demonstrates that a combination of the bioinformatic and proteomic strategies may be useful in promoting the development of next generation anthrax vaccine.

The role of fibronectin binding proteins in the pathogenesis of Staphylococcus aureus infections

PURPOSE OF REVIEW

Staphylococcus aureus produces two closely-related fibronectin-binding proteins (FnBPs) that facilitate attachment by this versatile pathogen. Recent studies of staphylococcal FnBP have increased our understanding of the molecular mechanisms that are critical in bacterial-host cell interactions and in infection.

RECENT FINDINGS

This review will summarize current knowledge of the role of the FnBPs of Staphylococcus aureus in the pathogenesis of infection. The FnBPs, which facilitate attachment of this pathogen to host cells and to fibronectin-coated biomaterials, are important mediators of infection in experimental endocarditis. In addition, recent vaccine studies utilizing FnBP derivatives have shown partial protection in animals. FnBPs also act as invasins permitting uptake of the staphylococcus by cultured non-professional phagocytes using host fibronectin to bridge with integrins on the cell surface. However, the precise role of FnBP in tissue invasion and the relevance of intracellular invasion in disease remain to be elucidated.

SUMMARY

FnBP is one of many adhesins expressed by S. aureus that influence host tissue adherence by binding to host fibronectin. FnBP-based vaccine strategies and novel anti-adherence tools based upon FnBP derivatives are in the early stages of investigation but may show promise in preventing staphylococcal infections.

Src kinase has a central role in in vitro cellular internalization of Staphylococcus aureus

Traditionally recognized as an extracellular pathogen, the Gram-positive bacterium Staphylococcus aureus can also be internalized by a variety of cell types in vitro. Internalization is known to involve binding of the host extracellular protein fibronectin to the bacterium, recognition of the fibronectin-coated bacterium by the fibronectin-binding integrin alpha5beta1 on the host cell surface, and integrin-mediated internalization. Here we examine elements of mammalian cell signalling pathways involved in S. aureus internalization. The mouse fibroblast cell line GD25, in which the gene encoding the beta1 integrin subunit is inactivated, has been complemented with a beta1 integrin cDNA encoding a tyrosine (Y) to phenylalanine (F) mutation in each of the two beta1 integrin intracellular NPXY motifs. This cell line, GD25beta1 A Y783/795F, is defective in migration on fibronectin coated surfaces and intracellular signalling activities involving the tyrosine kinase Src. GD25beta1 A Y783/795F cells have a decreased ability to internalize S. aureus compared to GD25beta1 A cells expressing wild-type beta1 integrins. Furthermore, using mouse embryo fibroblasts in which different members of the Src family kinases are genetically inactivated, we demonstrate that optimal internalization is dependent on expression of Src kinase. Interferon, which has been implicated in repression of the effects of the viral homologue of Src inhibits internalization of S. aureus indicating that internalization may be blocked by inhibitors of Src kinase function. We then demonstrate that Src family kinase specific inhibitors effectively block S. aureus internalization into HeLa cells leading to the conclusion that a function unique to Src is required for optimal internalization of S. aureus in vitro.

Pathogenic bacteria attach to human fibronectin through a tandem beta-zipper

Staphylococcus aureus and Streptococcus pyogenes, two important human pathogens, target host fibronectin (Fn) in their adhesion to and invasion of host cells. Fibronectin-binding proteins (FnBPs), anchored in the bacterial cell wall, have multiple Fn-binding repeats in an unfolded region of the protein. The bacterium-binding site in the amino-terminal domain (1-5F1) of Fn contains five sequential Fn type 1 (F1) modules. Here we show the structure of a streptococcal (S. dysgalactiae) FnBP peptide (B3) in complex with the module pair 1F12F1. This identifies 1F1- and 2F1-binding motifs in B3 that form additional antiparallel beta-strands on sequential F1 modules-the first example of a tandem beta-zipper. Sequence analyses of larger regions of FnBPs from S. pyogenes and S. aureus reveal a repeating pattern of F1-binding motifs that match the pattern of F1 modules in 1-5F1 of Fn. In the process of Fn-mediated invasion of host cells, therefore, the bacterial proteins seem to exploit the modular structure of Fn by forming extended tandem beta-zippers. This work is a vital step forward in explaining the full mechanism of the integrin-dependent FnBP-mediated invasion of host cells.

Human transcobalamin II receptor binds to Staphylococcus aureus protein A: implications as to its structure and function

Purified human placental transcobalamin II receptor (TC II-R) dimer of molecular mass 124 kDa bound to Sepharose-linked bacterial immunoglobulin (IgG) binding proteins protein A, protein G, and protein A/G. TC II-R dimer was detected directly, by blotting human placental and rabbit and rat kidney membrane proteins with 125I-protein A, or indirectly, using antiserum to TC II-R or IgG-Fc region and 125I-protein. TC II-R antiserum, but not protein A, protein G, protein A/G, or antiserum to the IgG-Fc region, when added to culture medium of human intestinal epithelial Caco-2 cells or umbilical vein endothelial cells, inhibited ligand binding. However, protein A, protein G, protein A/G, or antiserum to the Fc region inhibited the internalization of the ligand TC II-[57Co]cyanocobalamin. Taken together, these studies strongly suggest TC II-R is an IgG-like molecule that contains an Fc-like region which is important in ligand internalization but not binding.

Fibronectin bound to the surface of Staphylococcus aureus induces association of very late antigen 5 and intracellular signaling factors with macrophage cytoskeleton

Staphylococcus aureus Cowan I and a clinically isolated coagulase-negative Staphylococcus strain, S. saprophyticus 10312, were found to have two fibronectin binding proteins, FnBPA and FnBPB. While both staphylococci bound to serum fibronectin to a similar extent, fibronectin binding significantly increased the phagocytic activity of macrophages against S. aureus (by ca. 150%) but not against S. saprophyticus. This enhancing effect of fibronectin was inhibited by an RGD sequence-containing peptide and also by anti-very late antigen 5 antibody. This suggests that the effect is mediated by very late antigen 5 expressed on macrophages. In macrophages ingesting fibronectin-bound Cowan I, alpha(5) and beta(1) chains were associated with the cytoskeleton. Cytosolic signaling factors such as paxillin, c-Src, and c-Csk were also associated with the cytoskeleton. On the contrary, beta(3) integrin transiently disappeared from the cytoskeleton when macrophages ingested the fibronectin-treated S. aureus Cowan I. Furthermore, the Src kinase family tyrosine kinase Lyn dissociated from the cytoskeleton. These cellular components did not respond in a fibronectin-dependent manner when macrophages phagocytosed S. saprophyticus. This means that only fibronectin-treated S. aureus Cowan I induces the accumulation of very late antigen 5, which in turn induces the association of paxillin and tyrosine kinases. It is thought that the phagocytic activity of macrophages against fibronectin-treated S. aureus was increased by signaling via the activation of very late antigen 5.

Molecular characterization of a novel fibronectin-binding protein of Streptococcus pyogenes strains isolated from toxic shock-like syndrome patients

Group A Streptococcus pyogenes has surface-located fibronectin (Fn)-binding proteins known to be a major virulence factor, which adheres to and invades host cells. We present a novel Fn-binding protein of group A streptococcus serotype M3 and M18 strains isolated from patients with toxic shock-like syndrome (TSLS). By searching the whole genome sequence of an M3 strain from a TSLS patient, an open reading frame was found among the putative surface proteins. It possessed an LPXTG motif and Fn-binding repeat domains in the C-terminal region and was designated as FbaB (Fn-binding protein of group A streptococci type B). The fbaB gene was found in all M3 and M18 strains examined, although not in other M serotypes. Furthermore, FbaB protein was expressed on the cell surface of TSLS strains but not on non-TSLS ones. Enzyme-linked immunosorbent assay and ligand blotting revealed that recombinant FbaB exhibits a strong Fn-binding ability. An FbaB-deficient mutant strain showed 6-fold lower adhesion and invasion efficiencies to HEp-2 cells than the wild type. Moreover, mortality was decreased in mice infected with the mutant strain in comparison to the wild type. These data suggest that FbaB is etiologically involved in the development of invasive streptococcal diseases.

Analysis of Ebh, a 1.1-megadalton cell wall-associated fibronectin-binding protein of Staphylococcus aureus

In order for Staphylococcus aureus to adhere to host extracellular matrix (ECM) substrates, it elicits a wide range of surface proteins. We have characterized a novel approximately 1.1-MDa protein in S. aureus, termed Ebh (for ECM-binding protein homologue), which has homology to other ECM-binding proteins. Ebh consists of several domains, including a large central region with 44 imperfect repeats of 126 amino acids. Expression analysis revealed ebh to be growth phase regulated and repressed by agr. A fragment of the central repeat region of Ebh was cloned, overexpressed, and used in ligand-binding studies to determine Ebh function. The recombinant protein was found to specifically bind human fibronectin. Ebh is produced during human infection since serum samples taken from patients with confirmed S. aureus infections were found to contain anti-Ebh antibodies. Localization studies revealed Ebh to be cell envelope associated and is proposed to form a specialized surface structure involved in cellular adhesion.

Functional blocking of Staphylococcus aureus adhesins following growth in ex vivo media

Defining the role of Staphylococcus aureus adhesins in disease pathogenesis may depend on the use of bacteria grown in culture media that more closely reflect the human milieu than conventional broth. This study examined the functional effect on S. aureus adhesins following growth in an ex vivo medium containing a complex mixture of human proteins (used peritoneal dialysate) relative to growth in Todd-Hewitt broth. The adherence of S. aureus, cultured in dialysate, to fibronectin and fibrinogen was markedly reduced despite the expresion of full-length ClfA, ClfB, and fibronectin-binding proteins. Growth in dialysate resulted in the acquisition of a surface coat, as visualized by transmission electron microscopy, which was shown to contain fibronectin, fibrinogen, and immunoglobulins. Adherence of S. aureus to fibrinogen following growth in dialysate was significantly reduced by expression of protein A but was restored following growth in immunoglobulin-depleted dialysate. We conclude that bacterial adherence to solid-phase protein is critically dependent on the culture medium, that S. aureus adhesins may become saturated with target protein prior to contact with solid surfaces, and that there is an interaction between fibrinogen-binding proteins and immunoglobulin bound to protein A following contact with host proteins. These findings have important implications for future studies of S. aureus adhesins.

Internalization of Staphylococcus aureus by human corneal epithelial cells: role of bacterial fibronectin-binding protein and host cell factors

Wild-type Staphylococcus aureus was observed to be capable of invading human corneal epithelial cells (HCEC) in vitro. Internalization of S. aureus required expression of fibronectin-binding proteins (FnBPs); the capacity of an FnBP-deficient isogenic strain to invade HCEC was reduced by more than 99%. The binding of S. aureus to HCEC did not require viable bacteria, since UV-killed cells were observed to adhere efficiently. Invasion of HCEC by S. aureus involved active host cell mechanisms; uptake was nearly completely eliminated by cytochalasin D and genistein. These data suggest that FnBPs play a key role in host-parasite interactions and may serve as an important adhesin or invasin in ulcerative keratitis caused by S. aureus.

Nonvalvular Intravascular Device-related Infections

Nonvalvular intravascular devices are in widespread use in developed countries and are now more commonly employed than are prosthetic cardiac valves. Although the variety of devices that are included in the category of "nonvalvular" represent a heterogenous collection, there is commonality among several of the devices. This includes their requirement to sustain life and the need for removal for cure if they become infected, which is often due to multidrug-resistant microorganisms. Thus, infection of these devices often presents difficult treatment scenarios. This update will address the pathogenesis and immunobiology of nonvalvular intravascular device-related infections and the epidemiology and treatment of infections of several of these devices that include pacemakers, implantable cardioverter defibrillators, intravascular catheters, vascular grafts and stents, and left ventricular assist devices.

MntR modulates expression of the PerR regulon and superoxide resistance in Staphylococcus aureus through control of manganese uptake

The Staphylococcus aureus DtxR-like protein, MntR, controls expression of the mntABC and mntH genes, which encode putative manganese transporters. Mutation of mntABC produced a growth defect in metal-depleted medium and increased sensitivity to intracellularly generated superoxide radicals. These phenotypes resulted from diminished uptake of manganese and were rescued by the addition of excess Mn(II). Resistance to superoxide was incompletely rescued by Mn(II) for STE035 (mntA mntH), and the strain had reduced virulence in a murine abscess model of infection. Expression of mntABC was repressed by Mn(II) in an MntR-dependent manner, which contrasts with the expression of mntH that was not repressed in elevated Mn(II) and was decreased in an mntR mutant. This demonstrates that MntR acts as a negative and positive regulator of these loci respectively. PerR, the peroxide resistance regulon repressor, acts with MntR to control the expression of mntABC and manganese uptake. The expression of the PerR-regulated genes, katA (catalase), ftn (ferritin) and fur (ferric uptake regulator), was diminished in STE031 (mntR) when grown in excess Mn(II). Therefore, the control of Mn(II)-regulated members of the PerR regulon and the Fur protein is modulated by MntR through its control of Mn(II) uptake. The co-ordinated regulation of metal ion homeostasis and oxidative stress resistance via the regulators MntR, PerR and Fur of S. aureus is discussed.

Host-parasite interactions in Staphylococcus aureus keratitis

Ulcerative keratitis is among the leading ocular bacterial infections, and Streptococcus aureus accounts for approximately 25% of cases in some surveys. Although S. aureus expresses numerous virulence factors, many of which are under the control of staphylococcal global regulatory genes, their pathophysiologic roles in keratitis are largely unknown. Similarly, the nature of the host response during S. aureus keratitis is unclear. Following a review of previously published research on the pathophysiology of S. aureus ocular infection, we present the results of a study designed to assess the host-parasite relationship between S. aureus and human corneal epithelial cells (HCECs) in vitro. In this model system, a wild-type S. aureus strain and its isogenic mutants harboring mutations in agr and sar global regulatory genes or fibronectin-binding proteins A and B (fnbAB) were tested for their ability to bind and invade confluent HCEC monolayers. The contribution of host cell factors was assessed by preincubating HCECs with various inhibitory agents. These studies demonstrated that S. aureus not only adhered to the surface of HCECs but was also internalized, as has been previously observed in other nonocular cell lines. Adherence and invasion of HCECs was saturable at 1 h of incubation in the presence of approximately 10(7) CFU per HCEC monolayer (multiplicity of infection approximately 10). A mutant defective in both agr and sar global regulators was not significantly different in invasive capacity compared to its isogenic wild-type parent strain. In contrast, mutations in fibronectin-binding proteins A and B (fnbAB) reduced the invasiveness of S. aureus by 99% compared to the wild-type strain. Pretreatment of HCECs with colchicine had little effect on S. aureus invasion. In sharp contrast, cytochalasin D and genistein were each capable of inhibiting invasion by >99%. In summary, the results of this study point to fibronectin-binding protein as a key S. aureus surface adhesin facilitating invasion of HCECs in vitro. Furthermore, these results suggest an active mechanism for S. aureus internalization by HCECs, likely involving actin polymerization and tyrosine kinase activity. Additional studies are warranted to determine the applicability of these findings in vivo, and to facilitate the rational design of therapeutic agents aimed at blocking the establishment and progression of S. aureus keratitis.