Binding of collagens to an enterotoxigenic strain of Escherichia coli

Changes in Cellular Elasticities and Conformational Properties of Bacterial Surface Biopolymers of Multidrug-Resistant Escherichia coli (MDR-E. coli) Strains in Response to Ampicillin

The roles of the thicknesses and grafting densities of the surface biopolymers of four multi-drug resistant (MDR) Escherichia coli bacterial strains that varied in their biofilm formation in controlling cellular elasticities after exposure to ampicillin were investigated using atomic force microscopy. Exposure to ampicillin was carried out at minimum inhibitory concentrations for different duration times. Our results indicated that the four strains resisted ampicillin through variable mechanisms. Strain A5 did not change its cellular properties upon exposure to ampicillin and as such resisted ampicillin through dormancy. Strain H5 increased its biopolymer brush thickness, adhesion and biofilm formation and kept its roughness, surface area and cell elasticity unchanged upon exposure to ampicillin. As such, this strain likely limits the diffusion of ampicillin by forming strong biofilms. At three hours’ exposure to ampicillin, strains D4 and A9 increased their roughness, surface areas, biofilm formation, and brush thicknesses and decreased their elasticities. Therefore, at short exposure times to ampicillin, these strains resisted ampicillin through forming strong biofilms that impede ampicillin diffusion. At eight hours’ exposure to ampicillin, strains D4 and A9 collapsed their biopolymers, increased their apparent grafting densities and increased their cellular elasticities. Therefore, at long exposure times to ampicillin, cells utilized their higher rigidity to reduce the diffusion of ampicillin into the cells. The findings of this study clearly point to the potential of using the nanoscale characterization of MDR bacterial properties as a means to monitor cell modifications that enhance “phenotypic antibiotic resistance”.

Porphyromonas gingivalis Fimbria-Induced Expression of Inflammatory Cytokines and Cyclooxygenase-2 in Mouse Macrophages and Its Inhibition by the Bioactive Compounds Fibronectin and Melatonin

Porphyromonas gingivalis (Pg) fimbriae, in addition to lipopolysaccharide, are involved in the pathogenesis of periodontal disease. At the same time, bioactive compounds such as fibronectin (FN) and melatonin in saliva and gingival crevicular fluid have been reported to exert a preventive effect against periodontitis. Here, we review current knowledge regarding the potent inhibitory effects of FN and melatonin against Pg fimbria-induced induction of proinflammatory cytokines, cyclooxygenase-2 (COX-2) expression, and NF-kappa B activation in mouse macrophages and discuss their possible clinical application for prevention of periodontal diseases induced by oral bacteria.

Gram-negative bacterial sensors for eukaryotic signal molecules

Ample evidence exists showing that eukaryotic signal molecules synthesized and released by the host can activate the virulence of opportunistic pathogens. The sensitivity of prokaryotes to host signal molecules requires the presence of bacterial sensors. These prokaryotic sensors, or receptors, have a double function: stereospecific recognition in a complex environment and transduction of the message in order to initiate bacterial physiological modifications. As messengers are generally unable to freely cross the bacterial membrane, they require either the presence of sensors anchored in the membrane or transporters allowing direct recognition inside the bacterial cytoplasm. Since the discovery of quorum sensing, it was established that the production of virulence factors by bacteria is tightly growth-phase regulated. It is now obvious that expression of bacterial virulence is also controlled by detection of the eukaryotic messengers released in the micro-environment as endocrine or neuro-endocrine modulators. In the presence of host physiological stress many eukaryotic factors are released and detected by Gram-negative bacteria which in return rapidly adapt their physiology. For instance, Pseudomonas aeruginosa can bind elements of the host immune system such as interferon-γ and dynorphin and then through quorum sensing circuitry enhance its virulence. Escherichia coli sensitivity to the neurohormones of the catecholamines family appears relayed by a recently identified bacterial adrenergic receptor. In the present review, we will describe the mechanisms by which various eukaryotic signal molecules produced by host may activate Gram-negative bacteria virulence. Particular attention will be paid to Pseudomonas, a genus whose representative species, P. aeruginosa, is a common opportunistic pathogen. The discussion will be particularly focused on the pivotal role played by these new types of pathogen sensors from the sensing to the transduction mechanism involved in virulence factors regulation. Finally, we will discuss the consequence of the impact of host signal molecules on commensally or opportunistic pathogens associated with different human tissue.

Adherence, anti-adherence, and oligosaccharides preventing pathogens from sticking to the host

For many pathogenic bacteria, infections are initiated only after the organism has first adhered to the host cell surface. If adherence can be inhibited, then the subsequent infection can also be inhibited. This approach forms the basis of anti-adherence strategies, which have been devised to prevent a variety of bacterial infections. In this chapter, the molecular basis by which respiratory, urinary, and gastrointestinal tract pathogens adhere to host cells will be described. The five general types of anti-adherence agents will also be reviewed. The most well-studied are the receptor analogs, which include oligosaccharides produced synthetically or derived from natural sources, including milk, berries, and other plants. Their ability to inhibit pathogen adherence may lead to development of novel, food-grade anti-infective agents that are inexpensive and safe.

The Role of First Line of Defence Mechanisms in the Pathogenesis of Cellulitis in Broiler Chickens: Skin Structural, Physiological and Cellular Response Factors

The present study examined several basic attributes of first-line defence mechanisms in the skin as potential factors that may explain the susceptibility of broiler chickens to cellulitis. The variables including structural characteristics of the skin, physicochemical properties and cellular responses to the challenge with pathogens were compared between two categories of chickens, a strain of fast-growing commercial broiler chickens (susceptible to cellulitis) and leghorn chickens (resistant to cellulitis). There were substantial differences between leghorns and broilers with regard to physiological characteristics of the skin. Broiler skin was more amenable to injury and the wound-healing process was slow. Compared with leghorns, the lesions resulting from sub-dermal challenge in broilers were more severe and disseminated over a larger area. Mobilization of phagocytic cells (heterophils and macrophages) in leghorns was brisk even in the areas distant from the site of infection, whereas only few heterophils were recruited in the skin of broilers. The functional competence of heterophils in broilers was inferior when compared with leghorns. Based on the present finding, the predisposition of broilers to cellulitis appears to be primarily associated with the inferior first line of defence of their skin. Broilers in commercial situations may be at higher risk to succumb to even minor infection and eventually develop cellulitis because: (1) structural weaknesses of the skin may predispose broilers to skin injury and thus the risk of skin infection by pathogens is increased; (2) broiler skin surface is more likely to provide a conducive environment for colonization of Escherichia coli; (3) in the event of infection, poor recruitment of phagocytic cells to the site of infection may readily lead to widespread colonization of the tissue by pathogens causing cellulitis and (4) poor functional quality of the phagocytic cells that are mobilized compromise the ability of the host to contain the spread of infection.

Mounting of Escherichia coli spheroplasts for AFM imaging

The cytoplasmic membrane of Escherichia coli (E. coli) is the location of numerous, chemically specific transporters and recognition elements. Investigation of this membrane in vivo by atomic force microscopy (AFM) requires removal of the cell wall and stable immobilization of the spheroplast. AFM images demonstrate that spheroplasts can be secured with warm gelatin applied to the mica substrate just before the addition of a spheroplast suspension. The resulting preparation can be repeatedly imaged by AFM over the course of several hours. Confocal fluorescence imaging confirms the association of the spheroplasts with the gelatin layer. Gelatin molecules are known to reorder into a network after heating. Entrapment within this gelatin network is believed to be responsible for the immobilization of spheroplasts on mica.

Evaluation of the adhesive capacity of Escherichia coli isolates associated with avian cellulitis

It has been shown that Escherichia coli isolates from lesions of cellulitis belong to a limited number of clonal groups distinct from those of isolates found in the environment of these birds. In this study, different in vitro methods were used to evaluate adherence properties of E. coli isolates from cellulitis lesions and environments of high- and low-cellulitis prevalence broiler flocks. One hundred isolates were tested by hemagglutination. Adherence to frozen sections of chicken skin and binding to soluble fibronectin were examined for 40 of these 100 isolates by immunofluorescence and by immunocytofluorometry, respectively. Localization of bacterial adherence to skin tissues was confirmed by immunohistochemistry. It was demonstrated that O78:K80 isolates from cellulitis lesions adhered to skin sections to a much greater extent in deeper than in superficial tissue layers. A greater bacterial adherence following growth in TSB at 37 C was demonstrated for isolates from flocks with high prevalence of cellulitis than for isolates from flocks with low prevalence of cellulitis. MANOVA analysis results showed a significant difference between superficial and deep tissue layers only for one set of isolates from flocks with high prevalence of cellulitis. Hemagglutinating activity was variable among the O78:K80 isolates obtained from flocks with high prevalence of cellulitis. The results obtained for some O78:K80 isolates following growth in TSB suggest a role for type 1 fimbriae or F1 in adherence to skin sections. This was reinforced by the finding that adherence was inhibited by D-mannose. Poultry E. coli isolates that express F1 had no affinity for soluble fibronectin, although localization of the adherence in skin sections suggested a role for extracellular matrix components such as collagen and insoluble fibronectin.

Binding of collagen I to Escherichia coli O157:H7 and inhibition by carrageenans

Research at USDA attempts to eliminate or reduce Escherichia coli contamination in meat and poultry foods by understanding the attachment mechanisms. This study utilizes a surface plasmon resonance (SPR) biosensor to determine the interactions of the immobilized E. coli O157:H7 surface with collagen I and selected polysaccharides. The binding and dissociation kinetics of collagen I with E. coli surface molecules had a mean affinity constant (K) of 3 x l0(8) (M(-1)) while the dissociation rate was 4.4 x l0(-5) (S(-1)). Using the SPR biosensor, carrageenan, sodium alginate and pectin were evaluated for their interactions with collagen I and the E. coli surface. Results showed 89% to 100% inhibition by carrageenans and about 50% by sodium alginate and less than 10% by pectin. The biosensor binding studies were augmented by the scanning electron microscopy studies, which also showed the attachment of E. coli to the collagen fibrils of the bovine tissues. These studies serve as the basis for developing new strategies to block bacterial attachment or detach pathogens from animal carcasses.

Isolation of a laminin-binding protein from the protozoan parasite Leishmania donovani that may mediate cell adhesion

Extracellular matrix (ECM)-binding proteins on the surface of Leishmania are thought to play a crucial role in the onset of leishmaniasis, as these parasites invade mononuclear phagocytes in various organs after migrating through the ECM. In a previous report, we presented several lines of evidence suggesting that Leishmania has a specific receptor for laminin, a major ECM protein, with a Kd in the nanomolar range. Here we describe the identification, purification and biochemical characterization of the Leishmania laminin receptor. When the outer membrane proteins of L. donovani were blotted on to nitrocellulose paper and probed with laminin, a prominent laminin-binding protein of 67 kDa was identified. The purified protein was isolated by a three-step process involving DEAE-cellulose, Con A (concanavalin A)-Sepharose and laminin-Sepharose affinity chromatography and was used to raise a monospecific antibody. The same protein was obtained when parasite membrane extracts were adsorbed to antibody affinity matrix and eluted with glycine. The affinity-purified protein bound to laminin in a detergent-solubilized form as well as after integration into artificial bilayers, and was subsequently characterized as an integral membrane protein. Metaperiodate oxidation and metabolic inhibition of glycosylation studies indicate the binding protein to be glycoprotein in nature and that N-linked oligosaccharides play a part in the interaction of laminin with the binding protein. Surface-labelled parasites attached to microtitre wells coated with laminin and the 67 kDa protein blocked the adhesion to laminin substrate. We propose that the 67 kDa protein is an adhesin involved in the attachment of Leishmania to host tissues.

Porphyromonas gingivalis fimbria-stimulated bone resorption is inhibited through binding of the fimbriae to fibronectin

Our most recent study demonstrated that fibronectin is one of the Porphyromonas gingivalis fimbria-binding proteins. In this present study, we demonstrate with mouse embryonic calvarial cells that P. gingivalis fimbria-stimulated bone resorption is inhibited by human fibronectin. The fibronectin inhibition was dose and culture time dependent and was completely neutralized by antifibronectin antibody. The inhibitory action of fibronectin depended on fimbrial interaction with the heparin-binding and cell-attachment domains in the fibronectin structure.

Porphyromonas gingivalis fimbrillin is one of the fibronectin-binding proteins

In this study, we demonstrate that Porphyromonas gingivalis fimbrillin, a major component of bacterial fimbriae, is one of the fibronectin-binding proteins and that fibronectin is a potent inhibitor of the adherence of the bacteria to host cells and of the pathogenesis of the bacterium that acts by binding to the fimbriae. A Western blotting (immunoblotting) assay showed that fibronectin binds strongly to P. gingivalis fimbrillin. The fimbrial binding to fibronectin was also evidenced by a binding assay involving 125I-labeled fimbriae. Furthermore, fibronectin markedly inhibited the fimbria-induced expression of interleukin-1beta and neutrophil-specific chemoattractant KC genes in macrophages. The inhibitory action depended on the fimbrial interaction with heparin-binding and cell attachment domains in the fibronectin structure. The binding of P.gingivalis to mouse peritoneal macrophages via its fimbriae was inhibited by fibronectin. Fibronectin also inhibited the bacterial cell-induced expression of interleukin-1beta and KC genes in the macrophages. These results demonstrate the importance of fibronectin as a modulator of the pathogenic mechanism of P. gingivalis, a pathogen that causes adult periodontal disease.

Binding of outer membrane preparations of Campylobacter jejuni to INT 457 cell membranes and extracellular matrix proteins

Binding of outer membrane (OM) preparations of the thermophilic Campylobacter species C. jejuni to epithelial cell membranes and extracellular matrix proteins were studied in an in vitro model system using enzyme-linked immunosorbent assay. The OM preparations exhibited significant binding to INT 407 intestinal cell membranes. The process of adhesion was modulated by enzymatic, chemical or immunological pretreatment of the bacteria. Following oxidation of the lipopolysaccharide (LPS) with sodium meta-periodate, the OM preparations essentially retained their binding properties. After pretreatment with proteinase K, the OM preparations lost their binding capacity and the apparent molecular mass of the major OM protein shifted from 42 to 24 kDa. Preincubation of C. jejuni bacteria with C. jejuni-specific antiserum reduced adhesion significantly; preincubation with LPS-specific monoclonal antibodies only to a minimal extent. The OM preparations also bound significantly to the extracellular matrix proteins collagen and fibronectin; however, they bound virtually no bovine serum albumin or horse serum.

Identification of the surface component of Streptococcus defectivus that mediates extracellular matrix adherence

Bacterial attachment to host tissue is considered to be a crucial primary step in pathogen infection. Previous studies have shown that Streptococcus defectivus adheres specifically to cell-secreted extracellular matrix (ECM). Though generally not exposed in vivo, this host tissue is exposed at endothelial cell junctions and sites of tissue injury. In this report, we identify a ca. 200-kDa surface protein of S. defectivus involved in ECM adherence. Nitrous acid-derived mutant strains that were unable to bind ECM and which failed to adsorb adhesin-specific antibody from polyclonal inhibitory sera were isolated. A surface protein (ca. 200 kDa) was absent from ECM-nonadherent mutants, indicating its involvement in ECM attachment. Additionally, affinity-purified antibody to the ca. 200-kDa protein inhibited whole-cell S. defectivus ECM attachment, whereas antibody to the same region of the nonadherent mutant cell wall-associated protein profile did not. Furthermore, solubilized cell wall-associated protein extracts of parent but not mutant strains bound ECM, confirming the significance of this protein in ECM adherence. Therefore, we propose that the ca. 200-kDa protein is the major S. defectivus surface component that mediates the ECM attachment of these organisms.

Tumor necrosis factor alpha binding to bacteria: evidence for a high-affinity receptor and alteration of bacterial virulence properties

Human and murine receptors for tumor necrosis factor alpha (TNF-alpha) are present on most somatic cells and have been characterized and cloned. In contrast, very little is currently known about whether TNF-alpha can bind to pathogens and whether such binding results in important biological consequences for the infected host. We now report that a number of gram-negative bacteria have receptors for TNF-alpha. Using 125I-labeled TNF-alpha, we show that Shigella flexneri has 276 receptors for TNF-alpha, with a Kd of 2.5 nM. The binding of labeled TNF-alpha to these bacterial receptors can be inhibited by cold TNF-alpha but not by cold TNF-beta. Binding of 125I-TNF-alpha to S. flexneri was inhibited by trypsin treatment of bacterial cells or incubation at 52 degrees C for 3 min. Monoclonal antibody to either the 55-kDa or the 75-kDa TNF-alpha receptor, which are present on different eukaryotic cells, had no effect on 125I-TNF-alpha binding to bacteria. A number of gram-negative bacteria were capable of binding 125I-TNF-alpha. Gram-positive bacteria bound significantly less 125I-TNF-alpha than gram-negative bacteria. Pretreatment of S. flexneri with TNF-alpha resulted in enhanced bacterial invasion of HeLa cells and enhanced uptake by human and murine macrophages. Pretreatment of HeLa cells with antibody to the 55-kDa TNF-alpha receptor abrogated enhanced invasion of HeLa cells by TNF-alpha-bacterium complexes. These results suggest that TNF-alpha-bacterium complexes can interact with TNF-alpha receptors present on eukaryotic cells. This report shows that gram-negative bacteria have receptors for TNF-alpha and that a virulence property of a bacterium is altered as a consequence of cytokine binding.

Identification of a beta 1 integrin on Mycobacterium avium-Mycobacterium intracellulare

Mycobacterium avium-Mycobacterium intracellulare (MAI) is an opportunistic intracellular pathogen responsible for the highest incidence of disseminated bacterial infection in patients with AIDS. Treatment of the infection is extremely difficult and has shown limited efficacy. A critical event in the initiation of a variety of bacterial infections involves the adherence of bacteria to host cell surfaces. In the present study, we have shown that MAI organisms bind avidly to extracellular matrix proteins such as laminin, collagen I, and fibronectin in an in vitro attachment assay. Immunoblot analysis of a sonicate of MAI with polyclonal antibodies against different integrin receptors indicated that the sonicate cross-reacts with polyclonal antibodies against a human laminin-binding integrin, alpha 3 beta 1, and a human fibronectin-binding integrin, alpha 5 beta 1, although it is reactive with only the beta 1 subunit in the case of both antisera. Antibodies against the alpha 3 beta 1 and alpha 5 beta 1 integrins specifically inhibited the binding of MAI to laminin, collagen I, and fibronectin by 70 to 97%, depending on the ligand, suggesting that the attachment of MAI to these extracellular matrix proteins may be mediated by a beta 1 integrin. Furthermore, the attachment of MAI to laminin, collagen I, and fibronectin was found to be cation dependent. MAI may use this and other beta 1-containing integrins to adhere and penetrate through basement membrane structures that underlie host cell linings. An understanding of the mechanism of attachment and a definition of the adhesive molecules on the surface of MAI may open up new approaches to the prevention of serious infection caused by this organism.

Binding sites in fibronectin for an enterotoxigenic strain of E. coli B342289c

The binding of fibronectin and fibronectin fragments to the enterotoxigenic strain E. coli B34289c was studied. E. coli cells bound to two distinct sites of fibronectin, one being the N-terminal domain, which also contains the binding sites for staphylococci and streptococci, and the other located within the central heparin binding region. In addition, the N-terminal and the heparin binding domain mediated the attachment of bacteria in a solid phase binding assay. E. coli cells expressed two classes of receptors, the first, a 17 kDa protein, recognized by the N-terminal fragment and the second, having a mol. mass of 55 kDa, which interacts with the internal heparin binding domain. Bacterial receptors, which bind the N-terminal end of fibronectin, may be structurally related.