Adherence of Streptococcus sanguis to conformationally specific determinants in fibronectin

The choline-binding protein PspC of Streptococcus pneumoniae interacts with the C-terminal heparin-binding domain of vitronectin

Adherence of Streptococcus pneumoniae is directly mediated by interactions of adhesins with eukaryotic cellular receptors or indirectly by exploiting matrix and serum proteins as molecular bridges. Pneumococci engage vitronectin, the human adhesive glycoprotein and complement inhibitor, to facilitate attachment to epithelial cells of the mucosal cavity, thereby modulating host cell signaling. In this study, we identified PspC as a vitronectin-binding protein interacting with the C-terminal heparin-binding domain of vitronectin. PspC is a multifunctional surface-exposed choline-binding protein displaying various adhesive properties. Vitronectin binding required the R domains in the mature PspC protein, which are also essential for the interaction with the ectodomain of the polymeric immunoglobulin receptor and secretory IgA. Consequently, secretory IgA competitively inhibited binding of vitronectin to purified PspC and to PspC-expressing pneumococci. In contrast, Factor H, which binds to the N-terminal part of mature PspC molecules, did not interfere with the PspC-vitronectin interaction. Using a series of vitronectin peptides, the C-terminal heparin-binding domain was shown to be essential for the interaction of soluble vitronectin with PspC. Binding experiments with immobilized vitronectin suggested a region N-terminal to the identified heparin-binding domain as an additional binding region for PspC, suggesting that soluble, immobilized, as well as cellularly bound vitronectin possesses different conformations. Finally, vitronectin bound to PspC was functionally active and inhibited the deposition of the terminal complement complex. In conclusion, this study identifies and characterizes (on the molecular level) the interaction between the pneumococcal adhesin PspC and the human glycoprotein vitronectin.

Staphylococcus aureus SasA is responsible for binding to the salivary agglutinin gp340, derived from human saliva

Staphylococcus aureus is a major human pathogen that can colonize the nasal cavity, skin, intestine, and oral cavity as a commensal bacterium. gp340, also known as DMBT1 (deleted in malignant brain tumors 1), is associated with epithelial differentiation and innate immunity. In the oral cavity, gp340 induces salivary aggregation with several oral bacteria and promotes bacterial adhesion to tissues such as the teeth and mucosa. S. aureus is often isolated from the oral cavity, but the mechanism underlying its persistence in the oral cavity remains unclear. In this study, we investigated the interaction between S. aureus and gp340 and found that S. aureus interacts with saliva- and gp340-coated resin. We then identified the S. aureus factor(s) responsible for binding to gp340. The cell surface protein SasA, which is rich in basic amino acids (BR domain) at the N terminus, was responsible for binding to gp340. Inactivation of the sasA gene resulted in a significant decrease in S. aureus binding to gp340-coated resin. Also, recombinant SasA protein (rSasA) showed binding affinity to gp340, which was inhibited by the addition of N-acetylneuraminic acid. Surface plasmon resonance analysis showed that rSasA significantly bound to the NeuAcα(2-3)Galβ(1-4)GlcNAc structure. These results indicate that SasA is responsible for binding to gp340 via the N-acetylneuraminic acid moiety.

Fibronectin in the palatine tonsil as a susceptibility marker in Egyptian rheumatic families: histological and immunohistochemical studies

Rheumatic fever (RF) and rheumatic heart disease (RHD) are the multisystem autoimmune sequel of group A streptococci (GAS) infection of the upper respiratory passages, mainly tonsillopharyngitis. The major receptor on the surface of human palatine tonsil for GAS is fibronectin (FN; adhesin receptor). Early detection of RF susceptibility is considered as an important aim of this study. Therefore, the present study aimed to use FN immunoreactivity (FN-ir) as a marker for early detection of rheumatic susceptible children with palatine tonsil crypts surface epithelium. A total of 30 palatine tonsillar specimens were obtained from children aged from 3 to 15 years. Histological studies showed moderate vascular changes and more than four apparent epithelial disruptions in the crypt epithelium. FN-ir showed a significant increase in FN in the basal layers of surface epithelium, subepithelial connective tissue and interfollicular areas. Tonsils of children in rheumatic families showed significant increase in FN in subepithelial connective tissue areas with more than one apparent crypt epithelial disruption compared to normal children. We can conclude that FN plays a central role in the RF and differentially distributed in the functional compartments of the palatine tonsil in children with RHD, so FN-ir can be used as a marker for rheumatic susceptibility.

Calcium binding to leptospira outer membrane antigen LipL32 is not necessary for its interaction with plasma fibronectin, collagen type IV, and plasminogen

LipL32 is the most abundant outer membrane protein from pathogenic Leptospira and has been shown to bind extracellular matrix (ECM) proteins as well as Ca(2+). Recent crystal structures have been obtained for the protein in the apo- and Ca(2+)-bound forms. In this work, we produced three LipL32 mutants (D163-168A, Q67A, and S247A) and evaluated their ability to interact with Ca(2+) and with ECM glycoproteins and human plasminogen. The D163-168A mutant modifies aspartate residues involved in Ca(2+) binding, whereas the other two modify residues in a cavity on the other side of the protein structure. Loss of calcium binding in the D163-D168A mutant was confirmed using intrinsic tryptophan fluorescence, circular dichroism, and thermal denaturation whereas the Q67A and S247A mutants presented the same Ca(2+) affinity as the wild-type protein. We then evaluated if Ca(2+) binding to LipL32 would be crucial for its interaction with collagen type IV and plasma proteins fibronectin and plasminogen. Surprisingly, the wild-type protein and all three mutants, including the D163-168A variant, bound to these ECM proteins with very similar affinities, both in the presence and absence of Ca(2+) ions. In conclusion, calcium binding to LipL32 may be important to stabilize the protein, but is not necessary to mediate interaction with host extracellular matrix proteins.

The ability of haemolysins expressed by atypical enteropathogenic Escherichia coli to bind to extracellular matrix components

Typical and atypical enteropathogenic Escherichia coli (EPEC) are considered important bacterial causes of diarrhoea. Considering the repertoire of virulence genes, atypical EPEC (aEPEC) is a heterogeneous group, harbouring genes that are found in other diarrheagenic E. coli pathotypes, such as those encoding haemolysins. Haemolysins are cytolytic toxins that lyse host cells disrupting the function of the plasma membrane. In addition, these cytolysins mediate a connection to vascular tissue and/or blood components, such as plasma and cellular fibronectin. Therefore, we investigated the haemolytic activity of 72 aEPEC isolates and determined the correlation of this phenotype with the presence of genes encoding enterohaemolysins (Ehly) and cytolysin A (ClyA). In addition, the correlation between the expression of haemolysins and the ability of these secreted proteins to adhere to extracellular matrix (ECM) components was also assessed in this study. Our findings demonstrate that a subset of aEPEC presents haemolytic activity due to the expression of Ehlys and/or ClyA and that this activity is closely related to the ability of these isolates to bind to ECM components.

A Collagen-Binding S-Layer Protein in Lactobacillus crispatus

Two S-layer-expressing strains, Lactobacillus crispatus JCM 5810 and Lactobacillus acidophilus JCM 1132, were assessed for adherence to proteins of the mammalian extracellular matrix. L. crispatus JCM 5810 adhered efficiently to immobilized type IV and I collagens, laminin, and, with a lower affinity, to type V collagen and fibronectin. Strain JCM 1132 did not exhibit detectable adhesiveness. Within the fibronectin molecule, JCM 5810 recognized the 120-kDa cell-binding fragment of the protein, while no bacterial adhesion to the amino-terminal 30-kDa or the gelatin-binding 40-kDa fragment was detected. JCM 5810 but not JCM 1132 also bound (sup125)I-labelled soluble type IV collagen, and this binding was efficiently inhibited by unlabelled type IV and I collagens and less efficiently by type V collagen, but not by laminin or fibronectin. L. crispatus JCM 5810 but not L. acidophilus JCM 1132 also adhered to Matrigel, a reconstituted basement membrane preparation from mouse sarcoma cells, as well as to the extracellular matrix prepared from human Intestine 407 cells. S-layers from both strains were extracted with 2 M guanidine hydrochloride, separated by electrophoresis, and transferred to nitrocellulose sheets. The S-layer protein from JCM 5810 bound (sup125)I-labelled type IV collagen, whereas no binding was seen with the S-layer protein from JCM 1132. Binding of (sup125)I-collagen IV to the JCM 5810 S-layer protein was effectively inhibited by unlabelled type I and IV collagens but not by type V collagen, laminin, or fibronectin. It was concluded that L. crispatus JCM 5810 has the capacity to adhere to human subintestinal extracellular matrix via a collagen-binding S-layer.

Streptococcus mutans autolysin AtlA is a fibronectin-binding protein and contributes to bacterial survival in the bloodstream and virulence for infective endocarditis

Streptococcus mutans, a commensal of the human oral cavity, can survive in the bloodstream and cause infective endocarditis (IE). However, the virulence factors associated with this manifestation of disease are not known. Here, we demonstrate that AtlA, an autolysin of S. mutans is a newly identified fibronectin (Fn) binding protein and contributes to bacterial resistance to phagocytosis and survival in the bloodstream. Interestingly, prior exposure to plasma at low concentrations was sufficient to enhance bacterial survival in the circulation. Calcium ions at physiological plasma concentrations induced maturation of AtlA from the 104-90 kDa isoform resulting in increased Fn binding and resistance to phagocytosis. An isogenic mutant strain defective in AtlA expression exhibited reduced survival and virulence when tested in a rat model of IE compared with the wild-type and complemented strains. The data presented suggest that plasma components utilized by S. mutans enhanced survival in the circulation and AtlA is a virulence factor associated with infective endocarditis.

Multiple adhesin proteins on the cell surface of Streptococcus gordonii are involved in adhesion to human fibronectin

Adhesion of bacterial cells to fibronectin (FN) is thought to be a pivotal step in the pathogenesis of invasive infectious diseases. Viridans group streptococci such as Streptococcus gordonii are considered commensal members of the oral microflora, but are important pathogens in infective endocarditis. S. gordonii expresses a battery of cell-surface adhesins that act alone or in concert to bind host receptors. Here, we employed molecular genetic approaches to determine the relative contributions of five known S. gordonii surface proteins to adherence to human FN. Binding levels to FN by isogenic mutants lacking Hsa glycoprotein were reduced by 70 %, while mutants lacking CshA and CshB fibrillar proteins showed approximately 30 % reduced binding. By contrast, disruption of antigen I/II adhesin genes sspA and sspB in a wild-type background did not result in reduced FN binding. Enzymic removal of sialic acids from FN led to reduced S. gordonii DL1 adhesion (>50 %), but did not affect binding by the hsa mutant, indicating that Hsa interacts with sialic acid moieties on FN. Conversely, desialylation of FN did not affect adherence levels of Lactococcus lactis cells expressing SspA or SspB polypeptides. Complementation of the hsa mutant partially restored adhesion to FN. A model is proposed for FN binding by S. gordonii in which Hsa and CshA/CshB are primary adhesins, and SspA or SspB play secondary roles. Understanding the basis of oral streptococcal interactions with FN will provide a foundation for development of new strategies to control infective endocarditis.

Analysis of gene expression profiles in the liver and spleen of mice infected with Trypanosoma evansi by using a cDNA microarray

Trypanosoma evansi, the cause of the disease Surra in livestock, is the most widely geographically distributed pathogenic trypanosome occurring in Africa, South and Central America, and Asia, where it causes significant economic loss. Although many studies have described the histopathology induced in the organs of mice infected with T. evansi, few studies have been conducted on gene expression in these organs. Here we used complementary DNA microarray to analyze the gene expression profiles in the liver and spleen of mice infected with T. evansi (STIB 806) at the peak parasitemia (7 days after infection). A total of 14,000 sequences including full length and partial complementary DNAs representing novel, known, and control genes of mouse were analyzed. Results from GeneOntology annotation showed that 158 genes in the liver and 73 genes in the spleen were up-regulated in the infected mice and that 178 genes in the liver and 117 genes in the spleen of infected mice were down-regulated compared with control (non-infected) mice. Most of these genes are metabolism, transport, protein biosynthesis, transcription factors, and nucleic acid binding protein-related genes. The changes of some important genes, such as heat shock protein 70 and proliferating cell nuclear antigen, were confirmed by quantitative reverse transcriptase polymerase chain reaction and immunohistochemistry. TdT-mediated dUTP-digoxigenin nick end labeling analysis results revealed that extensive apoptosis occurred in the liver of infected mice at the peak of parasitemia. Our results provide a comprehensive profile of changes in gene expression in the liver and spleen of mice infected with T. evansi and may be helpful in understanding the pathogenesis of Surra at a molecular level.

In LipL32, the major leptospiral lipoprotein, the C terminus is the primary immunogenic domain and mediates interaction with collagen IV and plasma fibronectin

LipL32 is the major leptospiral outer membrane lipoprotein expressed during infection and is the immunodominant antigen recognized during the humoral immune response to leptospirosis in humans. In this study, we investigated novel aspects of LipL32. In order to define the immunodominant domains(s) of the molecule, subfragments corresponding to the N-terminal, intermediate, and C-terminal portions of the LipL32 gene were cloned and the proteins were expressed and purified by metal affinity chromatography. Our immunoblot results indicate that the C-terminal and intermediate domains of LipL32 are recognized by sera of patients with laboratory-confirmed leptospirosis. An immunoglobulin M response was detected exclusively against the LipL32 C-terminal fragment in both the acute and convalescent phases of illness. We also evaluated the capacity of LipL32 to interact with extracellular matrix (ECM) components. Dose-dependent, specific binding of LipL32 to collagen type IV and plasma fibronectin was observed, and the binding capacity could be attributed to the C-terminal portion of this molecule. Both heparin and gelatin could inhibit LipL32 binding to fibronectin in a concentration-dependent manner, indicating that the 30-kDa heparin-binding and 45-kDa gelatin-binding domains of fibronectin are involved in this interaction. Taken together, our results provide evidence that the LipL32 C terminus is recognized early in the course of infection and is the domain responsible for mediating interaction with ECM proteins.

High-affinity interaction between fibronectin and the group B streptococcal C5a peptidase is unaffected by a naturally occurring four-amino-acid deletion that eliminates peptidase activity

The streptococcal C5a peptidase (ScpB) of group B streptococci (GBS) is found in virtually all clinical GBS isolates and is required for mucosal colonization in a neonatal mouse model. ScpB inhibits neutrophil chemotaxis by enzymatically cleaving the complement component C5a. We previously identified a second function of ScpB as a fibronectin (Fn) adhesin using phage display. However, phage display can identify low-affinity interactions. We therefore measured the affinity of both full-length recombinant ScpB (FL-ScpB) and the 110-amino-acid phage display fragment (Scp-PDF) for immobilized Fn using surface plasmon resonance. The affinity for Fn was very high for both FL-ScpB (equilibrium dissociation constant [KD] = 4.0 nM) and Scp-PDF (KD = 4.4 nM) and is consistent with a biologically significant role for the adhesin activity of ScpB. We also studied the Fn adhesin activity of a common natural variant of ScpB (ScpBDelta) that contains a 4-amino-acid deletion that eliminates peptidase activity. The integrity of scpB is otherwise maintained, suggesting that the Fn adhesin activity of ScpB may be responsible for its conservation in these strains. The affinities of both FL-ScpBDelta (KD = 2.4 nM) and ScpBDelta-PDF (KD = 1.4 nM) for Fn are unaffected by the deletion. Complementation in trans by both scpB and scpBDelta corrected the Fn-binding defect of an scpB deletion mutant GBS strain to an identical degree. The high affinity of ScpB for Fn and the maintenance of this affinity in ScpBDelta support our hypothesis that the Fn adhesin activity of scpB plays a role in virulence.

Fluid- or surface-phase human salivary scavenger protein gp340 exposes different bacterial recognition properties

Salivary scavenger receptor cysteine-rich protein gp340 aggregates streptococci and other bacteria as part of the host innate defense system at mucosal surfaces. In this article, we have investigated the properties of fluid-phase gp340 and hydroxylapatite surface-adsorbed gp340 in aggregation and adherence, respectively, of viridans group streptococci (e.g., Streptococcus gordonii and Streptococcus mutans), non-viridans group streptococci (e.g., Streptococcus pyogenes and Streptococcus suis), and oral Actinomyces. Fluid-phase gp340 and surface-phase gp340 bioforms were differentially recognized by streptococci, which formed three phenotypic groupings according to their modes of interaction with gp340. Group I streptococci were aggregated by and adhered to gp340, and group II streptococci preferentially adhered to surface-bound gp340, while group III streptococci were preferentially aggregated by gp340. Each species of Streptococcus tested was found to contain strains representative of at least two of these gp340 interaction groupings. The gp340 interaction modes I to III and sugar specificities of gp340 binding strains coincided for several species. Many gp340 interactions were sialidase sensitive, and each of the interaction modes (I to III) for S. gordonii was correlated with a variant of sialic acid specificity. Adherence of S. gordonii DL1 (Challis) to surface-bound gp340 was dependent upon expression of the sialic acid binding adhesin Hsa. However, aggregation of cells by fluid-phase gp340 was independent of Hsa and involved SspA and SspB (antigen I/II family) polypeptides. Conversely, both gp340-mediated aggregation and adherence of S. mutans NG8 involved antigen I/II polypeptide. Deletion of the mga virulence regulator gene in S. pyogenes resulted in increased cell aggregation by gp340. These results suggest that salivary gp340 recognizes different bacterial receptors according to whether gp340 is present in the fluid phase or surface bound. This phase-associated differential recognition by gp340 of streptococcal species of different levels of virulence and diverse origins may mediate alternative host responses to commensal or pathogenic bacterial phenotypes.

Single species biofilm-forming ability of root canal isolates on gutta-percha points

The participation of bacterial biofilms in the over-filled gutta-percha points associated with refractory periapical periodontitis has recently been reported. This study investigated the initial biofilm-forming ability of root canal isolates (Enterococcus faecalis, Streptococcus sanguis, Strep. intermedius, Strep. pyogenes, Staphylococcus aureus, Fusobacterium nucleatum, Propionibacterium acnes, Porphyromonas gingivalis and Prevotella intermedia) on gutta-percha points in vitro. Each bacterial strain was suspended in 100% cell culture medium or in culture medium containing 4.5, 45 or 90% (vol/vol) serum. The bacterial suspensions were then co-incubated anaerobically with gutta-percha points for 7 d. The gutta-percha points were processed for scanning electron microscopic observation and examined for biofilm presence and thickness. E. faecalis, Strep. sanguis, Strep. intermedius, Strep. pyogenes and Staph. aureus biofilms were generated on the surfaces of the specimens incubated in culture medium supplemented with 45 or 90% (vol/vol) serum. The E. faecalis and Strep. sanguis biofilms were significantly thicker than those of Strep. intermedius, Strep. pyogenes and Staph. aureus. No biofilms were detected on the specimens incubated with F. nucleatum, Prop. acnes, Porph. gingivalis and Prev. intermedia. These findings suggest that Gram-positive facultative anaerobes have the ability to colonize and form extracellular matrices on gutta-percha points, while serum plays a crucial role in biofilm formation.

Immunofluorescence and flow cytometry analysis of fibronectin and laminin binding to Sporothrix schenckii yeast cells and conidia

The adherence of Sporothrix schenckii yeast cells to several extracellular matrix (ECM) components has already been demonstrated, but the mechanisms of these interactions remained to be defined. In indirect immunofluorescence assays with polyclonal antibodies directed towards the ECM proteins, both hyphae and yeast cells of S. schenckii exhibited the ability to bind laminin and fibronectin. Flow cytometry confirmed the binding of these proteins, and revealed a significant greater binding capability for the yeast cells than for the conidia. Fibronectin and laminin binding was dose-dependent and specific. In addition, competition experiments with synthetic peptides mimicking the adhesive sequences of these proteins, or with cell wall fractions and carbohydrates constitutive of their sugar chains, were performed in order to specify the peptide or carbohydrate motifs involved in the recognition process. A 50% reduction was noticed in fibronectin binding in the presence of the synthetic peptide RGD, and a 38% reduction in laminin binding with the peptide YIGSR. Some carbohydrate-containing fractions of the yeast cell wall also inhibited the binding of fibronectin, but had no significant effect on laminin binding. Together, these results suggest the presence at the yeast surface of distinct receptors for laminin and fibronectin.

Treponema pallidum fibronectin-binding proteins

Putative adhesins were predicted by computer analysis of the Treponema pallidum genome. Two treponemal proteins, Tp0155 and Tp0483, demonstrated specific attachment to fibronectin, blocked bacterial adherence to fibronectin-coated slides, and supported attachment of fibronectin-producing mammalian cells. These results suggest Tp0155 and Tp0483 are fibronectin-binding proteins mediating T. pallidum-host interactions.

Fibronectin mediates Opc-dependent internalization of Neisseria meningitidis in human brain microvascular endothelial cells

A central step in the pathogenesis of bacterial meningitis caused by Neisseria meningitidis (the meningococcus) is the interaction of the bacteria with cells of the blood-brain barrier. In the present study, we analysed the invasive potential of two strains representing hypervirulent meningococcal lineages of the ET-5 and ET-37 complex in human brain-derived endothelial cells (HBEMCs). In contrast to previous observations made with epithelial cells and human umbilical vein-derived endothelial cells (HUVECs), significant internalization of encapsulated meningococci by HBMECs was observed. However, this uptake was found only for the ET-5 complex isolate MC 58, and not for an ET-37 complex strain. Furthermore, the uptake of meningococci by HBMECs depended on the presence of human serum, whereas serum of bovine origin did not promote the internalization of meningococci in HBMECs. By mutagenesis experiments, we demonstrate that internalization depended on the expression of the opc gene, which is present in meningococci of the ET-5 complex, but absent in ET-37 complex meningococci. Chromatographic separation of human serum proteins revealed fibronectin as the uptake-promoting serum factor, which binds to HBMECs via alpha 5 beta 1 integrin receptors. These data provide evidence for unique molecular mechanisms of the interaction of meningococci with endothelial cells of the blood-brain barrier and contribute to our understanding of the pathogenesis of meningitis caused by meningococci of different clonal lineages.

Expression of fibronectin-binding protein FbpA modulates adhesion in Streptococcus gordonii

Fibronectin binding is considered to be an important virulence factor in streptococcal infections. Adhesion of the oral bacterium Streptococcus gordonii to immobilized forms of fibronectin is mediated, in part, by a high molecular mass wall-anchored protein designated CshA. In this study, a second fibronectin-binding protein of S. gordonii is described that has been designated as FbpA (62.7 kDa). This protein, which is encoded by a gene located immediately downstream of the cshA gene, shows 85 and 81% identity to the fibronectin-binding proteins PavA, of Streptococcus pneumoniae, and FBP54, of Streptococcus pyogenes, respectively. Purified recombinant FbpA bound to immobilized human fibronectin in a dose-dependant manner, and isogenic mutants in which the fbpA gene was inactivated were impaired in their binding to fibronectin. This effect was apparent only for cells in the exponential phase of growth, and was associated with reduced surface hydrophobicity and the surface expression of CshA. Cells in the stationary phase of growth were unaffected in their ability to bind to fibronectin. By utilizing gene promoter fusions with cat (encoding chloramphenicol O-acetyltransferase), it was demonstrated that cshA expression was down-regulated during the exponential phase of growth in the fbpA mutant. Expression of fbpA, but not cshA, was sensitive to atmospheric O2 levels, and was found to be up-regulated in the presence of elevated O2 levels. The results suggest that FbpA plays a regulatory role in the modulation of CshA expression and, thus, affects the adhesion of S. gordonii to fibronectin.

Biofilms: survival mechanisms of clinically relevant microorganisms

Though biofilms were first described by Antonie van Leeuwenhoek, the theory describing the biofilm process was not developed until 1978. We now understand that biofilms are universal, occurring in aquatic and industrial water systems as well as a large number of environments and medical devices relevant for public health. Using tools such as the scanning electron microscope and, more recently, the confocal laser scanning microscope, biofilm researchers now understand that biofilms are not unstructured, homogeneous deposits of cells and accumulated slime, but complex communities of surface-associated cells enclosed in a polymer matrix containing open water channels. Further studies have shown that the biofilm phenotype can be described in terms of the genes expressed by biofilm-associated cells. Microorganisms growing in a biofilm are highly resistant to antimicrobial agents by one or more mechanisms. Biofilm-associated microorganisms have been shown to be associated with several human diseases, such as native valve endocarditis and cystic fibrosis, and to colonize a wide variety of medical devices. Though epidemiologic evidence points to biofilms as a source of several infectious diseases, the exact mechanisms by which biofilm-associated microorganisms elicit disease are poorly understood. Detachment of cells or cell aggregates, production of endotoxin, increased resistance to the host immune system, and provision of a niche for the generation of resistant organisms are all biofilm processes which could initiate the disease process. Effective strategies to prevent or control biofilms on medical devices must take into consideration the unique and tenacious nature of biofilms. Current intervention strategies are designed to prevent initial device colonization, minimize microbial cell attachment to the device, penetrate the biofilm matrix and kill the associated cells, or remove the device from the patient. In the future, treatments may be based on inhibition of genes involved in cell attachment and biofilm formation.

Streptococcus anginosus adheres to vascular endothelium basement membrane and purified extracellular matrix proteins

The mechanisms of bacterial adherence in the initial stages of native valve endocarditis are unclear, especially in patients without valve disease or the presence of a platelet-fibrin thrombus. Extracellular matrix may act as a ligand in areas of exposed basement membrane on the endothelial monolayer. In this study, adherence of 55 clinical blood and 21 oral viridans streptococcal isolates was examined using purified extracellular matrix compounds. The majority of blood and oral isolates exhibited adherence to purified laminin, fibronectin, and fibrinogen, with lesser adherence to type I and IV collagens. Adherence to laminin and fibronectin was concentration dependent, saturable, and competitively inhibited with soluble ligand. A Streptococcus anginosus isolate and other viridans strains exhibiting a strong laminin adherence phenotype bound extensively to the endothelial aspect of human and porcine valve tissue sections and were inhibited by soluble laminin and anti-laminin antibody fragments. Using a novel native porcine valve explant adherence model, we localized binding to areas of exposed basement membrane by confocal and scanning electron microscopy. These studies support the hypothesis that bacterial adherence to exposed basement membrane plays a role in the initial phase of native valve endocarditis.

Functional variation of the antigen I/II surface protein in Streptococcus mutans and Streptococcus intermedius

Although Streptococcus intermedius and Streptococcus mutans are regarded as members of the commensal microflora of the body, S. intermedius is often associated with deep-seated purulent infections, whereas S. mutans is frequently associated with dental caries. In this study, we investigated the roles of the S. mutans and S. intermedius antigen I/II proteins in adhesion and modulation of cell surface characteristics. By using isogenic mutants, we show that the antigen I/II in S. mutans, but not in S. intermedius, was involved in adhesion to a salivary film under flowing conditions, as well as in binding to rat collagen type I. Binding to human fibronectin was a common function associated with the S. mutans and S. intermedius antigen I/II. Adhesion of S. mutans or S. intermedius to human collagen types I or IV was negligible. Hydrophobicity, as measured by water contact angles, and zeta potentials were unaltered in the S. intermedius mutant. The S. mutans isogenic mutants, on the other hand, exhibited more positive zeta potentials at physiological pH values than did the wild type. The results indicate common and species-specific roles for the antigen I/II in mediating the attachment of S. mutans and S. intermedius to host components and in determining cell surface properties.

Different adhesins for type IV collagen on Candida albicans: identification of a lectin-like adhesin recognizing the 7S(IV) domain

Adherence of the opportunistic pathogen Candida albicans to basement membrane (BM) proteins is considered a crucial step in the development of candidiasis. In this study the interactions of C. albicans yeast cells with the three main domains of type IV collagen, a major BM glycoprotein, were analysed. C. albicans adhered to the three immobilized domains by different mechanisms. Adhesion to the N-terminal cross-linking domain (7S) required the presence of divalent cations, whereas interaction with the central collagenous domain (CC) was cation-independent. Recognition of the C-terminal non-collagenous domain (NC1) was partially cation-dependent. Binding inhibition assays with the corresponding domains in soluble form showed that these interactions were specific. Both Ca(2+) and Mg(2+) promoted adhesion to the 7S domain and the interaction was completely abolished by EDTA. Treatment of the 7S domain, or its subunits, with N-glycosidase F reduced yeast binding by approximately 70%. Moreover, several sugars known to be part of the N-linked oligosaccharide chains of collagen IV inhibited adhesion to immobilized 7S; N-acetylglucosamine, L-fucose and methylmannoside caused a similar inhibition whereas N-acetyllactosamine was a more effective inhibitor. In contrast, glucose, galactose, lactose or heparan sulfate did not affect yeast binding. Combinations of the inhibitory sugars at suboptimal inhibition concentrations did not reduce C. albicans adhesion more than the individual sugars, pointing to a single lectin as responsible for the interaction. These results taken together show that C. albicans utilizes several adhesins for interacting with type IV collagen, and that at least one of them is a lectin which recognizes the 7S(IV) oligosaccharide residues as its receptor.

Binding of oral streptococci to human fibrinogen

The interaction of oral streptococci with human fibrinogen was investigated. Streptococcus gordonii was chosen as a representative species to study the binding to fibrinogen. S. gordonii DL1 adhered to immobilized fibrinogen and bovine serum albumin. Binding to immobilized fibrinogen was saturable, concentration and temperature dependent. The binding of S. gordonii DL1 to fibrinogen was inhibited by anti-fibrinogen antibody. Heating of the bacteria for 1 h at 95 degrees C resulted in 90% inhibition of the binding. Trypsin treatment of the bacteria resulted in decreased binding. Neither lipoteichoic acid nor culturing of the bacteria in a sucrose-supplemented medium had any effect on the binding. S. gordonii, Streptococcus sanguinis, Streptococcus mitis, and Streptococcus oralis bound to the immobilized fibrinogen, but mutans streptococci did not. None of the oral streptococci tested bound to the fibrinogen in fluid phase. These results suggest that the binding of S. gordonii DL1 to immobilized fibrinogen is mediated through a specific protein adhesin-receptor interaction, and fibrinogen acts as a cryptitope.

Delivery systems for penetration enhancement of peptide and protein drugs: design considerations

This paper discusses the challenges to be met in designing delivery systems that maximize the absorption of peptide and protein drugs from the gastrointestinal and respiratory tracts. The ideal delivery system for either route of administration is one that will release its contents only at a favorable region of absorption, where the delivery system attaches by virtue of specific interaction with surface determinants unique to that region and where the delivery system travels at a rate independent of the transitory constraints inherent of the route of administration. Such a delivery system, which is as yet unavailable, will benefit not only peptide and protein drugs, but other poorly absorbed drugs.

Environmental regulation of glycosidase and peptidase production by Streptococcus gordonii FSS2

The synthesis of cell-associated and secreted proteins by Streptococcus gordonii FSS2, an infective endocarditis (IE) isolate, was influenced by both environmental pH and carbon source. Controlling the pH at 7.5 in stirred batch cultures showed that cell-associated and secreted protein concentrations were increased during late exponential and stationary phase by 68% and 125%, respectively, compared with similar cultures without pH control. The expression of five glycosidase and eight peptidase activities were examined using fluorogen-labelled synthetic substrates. Enzyme activities were significantly down-regulated during exponential growth, increasing during stationary phase (P<0.01) whether the culture pH was controlled at pH 7.5 or allowed to fall naturally to pH 4.4. Culture-supernatant activities were significantly increased (P<0.05) when the pH was maintained at 6.0 or 7.5, indicating modulation of enzyme activity by pH. Growth under nitrogen-limitation/glucose-excess conditions resulted in a significant repression of cell-associated glycosidase activities (P<0.01), whilst in the supernatant, activities were generally reduced. The expression of peptidase activities in the culture supernatant did not significantly change. The results suggest a possible role for catabolite repression by glucose in regulating enzyme expression. When S. gordonii FSS2 was cultured with 50% (v/v) added heat-inactivated foetal bovine serum, several cell-associated enzyme activities increased initially but were then reduced as the culture time was extended to 116 h. Culture-supernatant enzyme activities (N-acetyl-beta-D-glucosaminidase, N-acetyl-beta-D-galactosaminidase, thrombin, Hageman factor, collagenase and chymotrypsin), however, were significantly increased (P<0.01) over the same time period. The findings indicated that most of the important glycosidases synthesized by S. gordonii FSS2 were down-regulated by acid growth conditions and may also be subject to catabolite repression by glucose but conversely may be up-regulated by growth in serum. These results may have implications for streptococcal growth in an IE vegetation and in the mouth between meals or during sleep.

Identification of a fibronectin binding protein from Streptococcus mutans

The interaction of viridans streptococci with components of the extracellular matrix (ECM) plays an important role in the pathogenesis of infective endocarditis. We have identified a surface protein of Streptococcus mutans which binds the ECM constituent fibronectin (Fn). Initially, we found that S. mutans could adsorb soluble Fn in plasma, but with lower efficiency than Streptococcus pyogenes. In addition, S. mutans could bind immobilized Fn in a dose-dependent manner when tested using an enzyme-linked immunosorbent assay. Crude extracts of cell wall-associated proteins or extracellular proteins from S. mutans MT8148 specifically bound Fn through a protein with the molecular mass of ca. 130 kDa, as detected by far-Western immunoblotting. The candidate Fn binding protein (FBP-130) was purified to near homogeneity by using Fn coupled Sepharose 4B affinity column chromatography. A rabbit polyclonal antibody against FBP-130 reacted specifically with a protein of molecular mass of ca. 130 kDa in both cell wall and extracellular fractions, and the abundance of FBP was higher in the former than in the latter fractions. The purified FBP bound specifically to immobilized Fn, whereas the binding of soluble Fn to coated FBP could only be detected in the presence of high concentrations of Fn. The purified FBP, as well as anti-FBP immunoglobulin G, inhibited the adherence of S. mutans to immobilized Fn and endothelial cells (ECV304) in a dose-dependent manner. These results demonstrated that FBP-130 mediated the adherence of S. mutans specifically to Fn and endothelial cells in vitro. The characteristics of S. mutans and FBP-130 in binding Fn confirmed that viridans streptococci adopt different strategies in their interaction with ECM.

Binding of the periodontal pathogen Actinobacillus actinomycetemcomitans to extracellular matrix proteins

The interaction of Actinobacillus actinomycetemcomitans, an important pathogen implicated in juvenile and adult periodontitis, with collagenous and noncollagenous proteins of the extracellular matrix was investigated. A. actinomycetemcomitans SUNY 465 bound to immobilized type I, II, III and V but not type IV collagen. Binding to immobilized collagen was saturable and concentration dependent. This interaction could not be inhibited by soluble collagen, suggesting that binding was dependent on a specific collagen conformation. Bacteria grown anaerobically exhibited decreased collagen-binding activity as compared with organisms grown acrobically. Bacterial outer membrane proteins were essential for binding to collagen. A actinomycetemcomitans SUNY 465 also bound to immobilized fibronectin. In contrast, bacteria did not bind to fibrinogen, bone sialoprotein, alpha 2-HS glycoprotein or albumin. The mechanism of the interaction with fibronectin was more complex, possibly involving both protein and nonproteinaceous components. The majority of other A. actinomycetemcomitans strains tested bound to extracellular matrix proteins in a manner similar to SUNY 465 but with minor variation. These results demonstrate that A. actinomycetemcomitans binds to proteins found in connective tissue. The interaction with extracellular matrix proteins may contribute to the virulence of this pathogen at oral and extraoral sites of infection.

Binding of immobilized fibronectin by biliary drain isolates

Occlusion of biliary stents, as the result of bacterial adhesion and colonization onto biliary stents, still remains a major problem. Biliary proteins, such as fibronectin (Fn) and vitronectin (Vn), have been presumed to be involved in the process of bacterial adhesion to biliary biomaterial. In the present study, Fn binding by 5 strains of E. coli isolated from biliary drains or from bile was studied. All strains did not bind detectable amounts of soluble Fn but bound to immobilized plasma Fn. Adhesion of four strains of E. coli to ovalbumin was reduced by periodate treatment of ovalbumin, but adhesion to Fn was unaffected. Adhesion was inhibited by mannose-containing saccharides, trypsin treatment of the protein, and protease treatment of the bacterial cells. Autoradiography showed that components of cell extracts from three E. coli strains bind 125I-Fn but not a 150 kD Fn fragment. The findings indicate that the adhesion of these bacteria to Fn is a protein-protein interaction, inhibited by D-mannose, and possibly mediated by fimbrial components.

A matrix form of fibronectin mediates enhanced binding of Streptococcus pyogenes to host tissue

The pathogenic Gram-positive bacterium Streptococcus pyogenes (group A streptococcus) binds to fibronectin via protein F. In this study, we have investigated the binding properties of protein F to various multimeric tissue forms of fibronectin that appear on cell surfaces and in the extracellular matrix. We show that binding of S. pyogenes through protein F is more efficient to an in vitro-derived polymerized form of fibronectin (superfibronectin) than to soluble fibronectin immobilized in a solid phase. In addition, Chinese hamster ovary cells overexpressing the alpha5beta1 integrin produced an increased amount of a fibronectin matrix and consequently bound a higher number of S. pyogenes cells. Inhibition and direct binding assays using purified proteins demonstrated that binding to a fibronectin matrix involved both domains of protein F (UR and RD2) that have previously been implicated in interactions with fibronectin. Using intact S. pyogenes bacteria in which various domains of protein F were expressed as hybrids with the surface-exposed region of an unrelated protein, we revealed that, in contrast to the predominantly UR-mediated binding to soluble fibronectin, the maximal binding to the fibronectin matrix required RD2 in addition to UR. Since in some infections S. pyogenes may initially encounter a matrix form of fibronectin, these results suggest that UR and RD2 may be important for the initiation of streptococcal infectious processes.

Streptococcal adhesion and colonization

Streptococci express arrays of adhesins on their cell surfaces that facilitate adherence to substrates present in their natural environment within the mammalian host. A consequence of such promiscuous binding ability is that streptococcal cells may adhere simultaneously to a spectrum of substrates, including salivary glycoproteins, extracellular matrix and serum components, host cells, and other microbial cells. The multiplicity of streptococcal adherence interactions accounts, at least in part, for their success in colonizing the oral and epithelial surfaces of humans. Adhesion facilitates colonization and may be a precursor to tissue invasion and immune modulation, events that presage the development of disease. Many of the streptococcal adhesins and virulence-related factors are cell-wall-associated proteins containing repeated sequence blocks of amino acids. Linear sequences, both within the blocks and within non-repetitive regions of the proteins, have been implicated in substrate binding. Sequences and functions of these proteins among the streptococci have become assorted through gene duplication and horizontal transfer between bacterial populations. Several adhesins identified and characterized through in vitro binding assays have been analyzed for in vivo expression and function by means of animal models used for colonization and virulence. Information on the molecular structure of adhesins as related to their in vivo function will allow for the rational design of novel acellular vaccines, recombinant antibodies, and adhesion agonists for the future control or prevention of streptococcal colonization and streptococcal diseases.

Cell surface polypeptide CshA mediates binding of Streptococcus gordonii to other oral bacteria and to immobilized fibronectin

Isogenic mutants of Streptococcus gordonii DL1 (Challis) in which the genes encoding high-molecular-mass cell surface polypeptides CshA and/or CshB were inactivated were deficient in binding to four strains of Actinomyces naeslundii and two strains of Streptococcus oralis. Lactose-sensitive interactions of S. gordonii with A. naeslundii ATCC 12104 and PK606 were associated with expression of cshA but not of cshB. Lactose-insensitive interactions of S. gordonii with A. naeslundii T14V and WVU627, and with S. oralis C104 and 34, were dependent on expression of cshA and cshB. S. gordonii DL1 cells bound to immobilized human fibronectin (Fn), but not to soluble Fn, in a dose-dependent manner, and binding was noninhibitable by heparin. S. gordonii cshA and cshB mutants were also deficient in binding to immobilized human Fn. Antibodies to an NH2-terminal nonrepetitive region (amino acid residues 42 to 886) of recombinant CshA inhibited binding of S. gordonii DL1 cells to A. naeslundii T14V and PK606 and to immobilized Fn. Conversely, antibodies to an amino acid repeat block segment of the COOH-terminal domain (amino acid residues 2026 to 2508) were not inhibitory to adherence. Assays using CshA-specific antibodies revealed that surface expression of CshA was reduced in cshB mutants. The results suggest that CshA acts as a multifunctional adhesin in S. gordonii and that major adhesion-mediating sequences are specified within the nonrepetitive NH2-terminal region of the polypeptide.

Influence of agr on fibrinogen binding in Staphylococcus aureus Newman

The ability of Staphylococcus aureus to bind fibrinogen is believed to be important in promoting bacterial adherence to both intravascular catheters and host tissues during infection. We investigated the influence of the global regulator agr on the fibrinogen binding capacity and its relationship to the expression of coagulase (encoded by coa) and clumping factor (encoded by clfA) in strain Newman. Strains were obtained by transducing site-specific mutations of clfA, coa, and agr into strain Newman to obtain single, double, and triple mutants of the respective genes. As expected, the clfA mutant bound less soluble 125I-labeled fibrinogen than the corresponding coa mutant in agr+ strains; however, with agr mutant strains, the upregulation in fibrinogen binding capacity correlated mostly with the increased expression and transcription of coagulase as shown by Western (immunoblot) and Northern (RNA) blot analysis. In particular, the coa agr double mutant resulted in a significant reduction in fibrinogen binding compared with that of the agr mutant. The contribution of clfA to fibrinogen binding in agr-negative strains was less than that of coa (32,740 +/- 1,189 versus 18,141 +/- 334 and 38,919 +/- 1,021 cpm for clfA agr, coa agr, and the single agr mutant, respectively). Thus, coagulase is a major binding protein for soluble fibrinogen in the agr-negative background. In in vitro microtiter and catheter adherence assays with solid-phase fibrinogen, clumping factor, but not coagulase, plays a major role in binding to immobilized fibrinogen. coa transcription was negatively modulated by agr and occurred mainly during the exponential growth phase. In contrast, clfA transcription was agr independent and was strongest during the postexponential phase. Although an agr coa clfA triple mutant bound less soluble fibrinogen than the agr coa double mutant (8,504 +/- 831 versus 18,141 +/- 334 cpm), significant residual fibrinogen binding capacity remained in the triple mutant, thus suggesting an additional fibrinogen binding component. By using direct ligand affinity blotting with 125I-fibrinogen, we could identify coagulase and an additional unidentified 52-kDa protein as a fibrinogen binding component in cell extracts. This band was absent in the extract of the coa clfA double mutant.

Adherence of Streptococcus pneumoniae to immobilized fibronectin

Adherence to extracellular matrix proteins, such as fibronectin, affords pathogens with a mechanism to invade injured epithelia. Streptococcus pneumoniae was found to adhere to immobilized fibronectin more avidly than other streptococci and staphylococci do. Binding was dose, time, and temperature dependent. Trypsin treatment of the bacteria resulted in decreased binding, suggesting that the bacterial adhesive component was a protein. Fragments of fibronectin generated by proteolysis or by expression of recombinant gene segments were compared for the ability to bind pneumococci and to compete against bacterial binding to immobilized fibronectin. Fragments from the carboxy-terminal heparin binding domain were consistently active, suggesting that this region contains the pneumococcal binding site, a region distinct from that supporting the attachment of most other bacteria.

Platelet receptors for the Streptococcus sanguis adhesin and aggregation-associated antigens are distinguished by anti-idiotypical monoclonal antibodies

Platelets aggregate in response to an adhesin and the platelet aggregation-associated protein (PAAP) expressed on the cell surfaces of certain strains of Streptococcus sanguis. We sought to identify the corresponding PAAP receptor and accessory adhesin binding sites on platelets. Since the adhesion(s) of S. sanguis for platelets has not been characterized, an anti-idiotype (anti-id) murine monoclonal antibody (MAb2) strategy was developed. First, MAb1s that distinguished the adhesin and PAAP antigens on the surface of S. sanguis I 133-79 were selected. Fab fragments of MAb1.2 (immunoglobulin G2b [IgG2b]; 70 pmol) reacted with 5 x 10(7) cells of S. sanguis to completely inhibit the aggregation of human platelets in plasma. Under similar conditions, MAb1.1 (IgG1) inhibited the adhesion of S. sanguis cells to platelets by a maximum of 34%, with a comparatively small effect on platelet aggregation. Together, these two MAb1s inhibited S. sanguis-platelet adhesion by 63%. In Western immunoblots, both MAb1s reacted with S. sanguis 133-79 87- and 150-kDa surface proteins and MAb1.2 also reacted with purified type I collagen. The hybridomas producing MAb1.1 and MAb1.2 were then injected into BALB/c mice. Enlarged spleens were harvested, and a panel of MAb2 hybridomas was prepared. To identify anti-ids against the specific MAb1s, the MAb2 panel was screened by enzyme-linked immunosorbent assay for reaction with rabbit polyclonal IgG antibodies against the 87- and 150-kDa antigens. The reactions between the specific rabbit antibodies and anti-ids were inhibited by the 87- and 150-kDa antigens. When preincubated with platelets, MAb2.1 (counterpart of MAb1.1) inhibited adhesion to platelets maximally by 46% and MAb2.2 (anti-MAb1.2) inhibited adhesion to platelets maximally by 35%. Together, both MAb2s inhibited the adhesion of S. sanguis to platelets by 81%. MAb2.2 also inhibited induction of platelet aggregation. MAb2.2 immunoprecipitated a biotinylated platelet membrane antigen of 170 kDa (unreduced); MAb2.1 precipitated membrane antigens of 175- and 230-kDa (unreduced). Therefore, platelet binding sites and the receptor for the S. sanguis adhesin and PAAP, respectively, are distinguished by the anti-id MAb2s.

Group B streptococci adhere to a variant of fibronectin attached to a solid phase

Group B streptococci (GBS) are the leading cause of neonatal pneumonia and meningitis. Adherence of GBS to host tissues may play an important role in the pathogenesis of infection. The host molecules which mediate GBS adherence to host tissues are unknown. Many bacterial pathogens adhere to fibronectin, an important component of the extracellular matrix (ECM). Some pathogens adhere to both immobilized and soluble fibronectin, while others adhere to immobilized fibronectin, but not to soluble fibronectin. Previous data indicated that GBS do not adhere to soluble fibronectin. We studied the ability of GBS to adhere to immobilized fibronectin. Forty-five per cent of the input inoculum of COH1, a virulent GBS isolate, adhered to fibronectin immobilized on polystyrene. COH1 did not adhere to the other ECM proteins tested (laminin, type I collagen, vitronectin, and tenascin). Nine out of nine GBS strains from human sources tested adhered specifically to fibronectin at levels varying from 4-60%. We considered the possibility that GBS were adherent to a contaminant in the fibronectin preparation. Properties of fibronectin, including the presence of an immunologic epitope of fibronectin and binding to collagen, were verified to be properties of the molecule to which GBS adhere. COH1 adhered to fibronectin captured by a monoclonal antibody to fibronectin (FN-15), confirming that the molecule to which GBS adhere bears immunologic determinants of fibronectin. Adherence of COH1 to fibronectin was inhibited by collagen, confirming that the molecule to which GBS adhere binds to collagen. These data strongly suggest that GBS adhere to fibronectin, and not to a contaminant.(ABSTRACT TRUNCATED AT 250 WORDS)

Cloning, sequencing, and expression of a fibronectin/fibrinogen-binding protein from group A streptococci

Lipoteichoic acid and several streptococcal proteins have been reported to bind fibronectin (Fn) or fibrinogen (Fgn), which may serve as host receptors. We searched for such proteins by screening a library of genes from M type 5 group A streptococci cloned into Escherichia coli. Lysates of clones were probed with biotinylated Fn and biotinylated Fgn. One clone expressed a 54-kDa protein that reacted with Fn and Fgn. The protein, termed FBP54, was purified and used to immunize rabbits. Anti-FBP54 serum reacted with purified, recombinant FBP54 and with a protein of similar electrophoretic mobility in extracts of M type 5, 6, and 24 streptococci. Anti-FBP54 serum also reacted with 5 of 15 strains of intact, live streptococci, suggesting that FBP54 may be a surface antigen. Southern blot analysis confirmed that the gene is found in group A streptococci but not in Staphylococcus aureus or E. coli. The cloned gene was sequenced and contained an open reading frame encoding a protein with a calculated molecular weight of 54,186. Partial amino acid sequencing of purified FBP54 confirmed that this open reading frame encoded the protein. As determined by utilizing fusion proteins containing truncated forms of FBP54, the primary Fn/Fgn-binding domain appears to be contained in residues 1 to 89. These data suggest that FBP54 may be a surface protein of streptococci that reacts with both Fn and Fgn and therefore may participate in the adhesion of group A streptococci to host cells.

Saliva-bacterium interactions in oral microbial ecology

Saliva is thought to have a significant impact on the colonization of microorganisms in the oral cavity. Salivary components may participate in this process by one of four general mechanisms: binding to microorganisms to facilitate their clearance from the oral cavity, serving as receptors in oral pellicles for microbial adhesion to host surfaces, inhibiting microbial growth or mediating microbial killing, and serving as microbial nutritional substrates. This article reviews information pertinent to the molecular interaction of salivary components with bacteria (primarily the oral streptococci and Actinomyces) and explores the implications of these interactions for oral bacterial colonization and dental plaque formation. Knowledge of the molecular mechanisms controlling bacterial colonization of the oral cavity may suggest methods to prevent not only dental plaque formation but also serious medical infections that may follow microbial colonization of the oral cavity.

Bacterial-protein interactions in the oral cavity

Bacteria in the oral cavity must interact with salivary proteins if they are to survive. Such interactions can take several forms, either providing nutrients, a means of adhesion to surfaces, or resulting in aggregation or killing and, therefore, clearance of organisms. Recent work has provided an insight into the mechanisms of some of these bacterial-protein interactions, revealing complexity and diversity. For example, the interaction between a putative Streptococcus mutans adhesin, P1 (B, I/II, etc.), and a parotid glycoprotein results in adhesion when it occurs at a surface or aggregation when in solution, and different domains of P1 appear to be involved in the two processes. An alternative strategy is employed by Actinomyces viscosus, which interacts, via its type-1 fimbriae, with a proline-rich salivary protein; however, this interaction occurs only when the PRP is adsorbed to a surface. A. viscosus takes advantage of a conformational change in the PRP when it becomes surface-bound, which exposes a cryptic part of the molecule. A third, and intriguing, type of interaction is seen between various streptococci and salivary amylase. This does not result in either adherence or aggregation but provides organisms with the ability to utilize starch breakdown products for metabolism. An understanding of the mechanisms involved in bacterial-protein interactions could conceivably lead to novel methods for controlling specific pathogens, but the systems operating in the mouth are numerous, complex, and diverse.

Glucosyltransferase mediates adhesion of Streptococcus gordonii to human endothelial cells in vitro

Human umbilical vein endothelial cells (HUVEC) were used as an experimental host model to investigate the mechanism(s) of streptococcal adhesion in infective endocarditis. Adhesion activity of Streptococcus gordonii was maximal during the logarithmic phase of growth and was greatly reduced or eliminated by pretreatment of bacteria with heat, formaldehyde, or trypsin. At saturating numbers of streptococci, an average of 81 bacteria were bound per HUVEC. Streptococcal adhesion was inhibited by low-molecular-weight dextran and heparin but not by sucrose, fibronectin, or laminin. Adhesion was also prevented by pretreatment of HUVEC with proteins dissociated from the surface of S. gordonii with 10 mM EDTA or isolated from spent culture medium. Western blot (immunoblot) assays detected a single adhesion protein of 153 kDa (AP153) on HUVEC after incubation with unfractionated extracts of streptococci. The adhesin exhibited glucosyltransferase (GTF) activity when incubated with sucrose and Triton X-100 after sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The AP153 was purified by affinity chromatography on dextran beads and show to have binding activity for HUVEC, GTF activity, an amino acid composition similar to that reported for GTF of S. gordonii, and the ability to inhibit S. gordonii adhesion. Incubation of the streptococci with antibodies to the adhesin inhibited bacterial attachment to HUVEC monolayers. These results indicate that surface-localized GTF mediates adhesion of S. gordonii to HUVEC in vitro and may serve as a mechanism for colonization of the endocardium in infective endocarditis.

Colonization of the murine oral cavity by Streptococcus gordonii

Streptococcus gordonii DL1 (Challis) colonized the oral cavities of BALB/c mice that lacked streptococci, enterococci, and lactobacilli (LF mice) as members of an otherwise complex digestive tract microflora. Conventional mice, in comparison, were refractory to colonization by S. gordonii. Mice that harbored lactobacilli but were free of streptococci and enterococci (EF mice) had a lower incidence of colonization by S. gordonii than LF animals. The LF mouse system should be useful in the study of the molecular mechanisms that enable S. gordonii to inhabit the oral cavity.

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.

Functional heterogeneity of type 1 fimbriae of Escherichia coli

Escherichia coli and other members of the family Enterobacteriaceae express surface fibrillar structures, fimbriae, that promote bacterial adhesion to host receptors. Type 1 fimbriae possess a lectinlike component, FimH, that is commonly thought to cause binding to mannose-containing oligosaccharides of host receptors. Since adhesion of type 1 fimbriated organisms are inhibited by mannose, the reactions are described as mannose sensitive (MS). We have studied the adhesion of the type 1 fimbriated CSH-50 strain of E. coli (which expresses only type 1 fimbriae) to fibronectin (FN). E. coli CSH-50 does not bind detectable amounts of soluble FN but adheres well to immobilized plasma or cellular FN. This adhesion was inhibited by mannose-containing saccharides. By using purified domains of FN, it was found that E. coli CSH-50 adheres primarily to the amino-terminal and gelatin-binding domains, only one of which is glycosylated, in an MS fashion. Binding of the mannose-specific lectin concanavalin A to FN and ovalbumin was eliminated or reduced, respectively, by incubation with periodate or endoglycosidase. Adhesion of E. coli CSH-50 to ovalbumin was reduced by these treatments, but adhesion to FN was unaffected. E. coli CSH-50 also adheres to a synthetic peptide copying a portion of the amino-terminal FN domain (FNsp1) in an MS fashion. Purified CSH-50 fimbriae bound to immobilized FN and FNsp1 in an MS fashion and inhibited adhesion of intact organisms. However, fimbriae purified from HB101 (pPKL4), a recombinant strain harboring the entire type 1 fim gene locus and expressing functional type 1 fimbriae, neither bound to FN or FNsp1 nor inhibited E. coli adhesion to immobilized FN or FNsp1. These novel findings suggest that there are two forms of type 1 MS fimbriae. One form exhibits only the well-known MS lectinlike activity that requires a substratum of mannose-containing glycoproteins. The other form exhibits not only the MS lectinlike activity but also binds to nonglycosylated regions of proteins in an MS manner.

Influence of saliva on aggregation and adherence of Streptococcus gordonii HG 222

The influence of saliva on the aggregation and adherence of Streptococcus gordonii HG 222 was studied. The aggregation was measured spectrophotometrically, and the adherence of S. gordonii to microtiter plate wells was measured in an enzyme-linked immunosorbent assay system. The aggregation of HG 222 was induced primarily by mucous saliva, whereas the adherence of HG 222 to microtiter plates was mediated by both mucous and serous saliva. Fractions of submandibular saliva, obtained by gel filtration and containing low-molecular-weight mucins (MG-2), induced both bacterial aggregation and adherence. Purified MG-2 induced aggregation and promoted adherence, whereas high-molecular-weight mucins (MG-1) did not. After incubating clarified human whole saliva with HG 222, only MG-2, and not MG-1, was bound by the bacteria. Proline-rich proteins (PRPs) and proline-rich glycoprotein (PRG) promoted the adherence of HG 222. These proteins in solution bound to HG 222 but did not induce aggregation of the bacterial cells. PRPs and PRG in solution were not able to inhibit adherence to microtiter plate wells coated with the same components. Purified alpha-amylase hardly promoted adherence to microtiter plates but, in the soluble state, readily bound to HG 222. In conclusion, these results indicate that the aggregation of S. gordonii HG 222 is mediated primarily by MG-2. These mucins also promote adherence. Several other salivary components, such as PRPs and PRG, are also involved in the adherence of HG 222.

Rapid identification of fibronectin, vitronectin, laminin, and collagen cell surface binding proteins on coagulase-negative staphylococci by particle agglutination assays

Seventeen strains of ten different species of coagulase-negative staphylococci were shown to interact with collagen, laminin, fibronectin, and vitronectin immobilized on latex beads. Different species of coagulase-negative staphylococci have different capacities to agglutinate proteins. Cells of 18 strains of Staphylococcus haemolyticus reacted more strongly than did cells of 18 Staphylococcus epidermidis strains with proteincoated latex beads, although no significant difference in cell surface hydrophobicity or charge could be shown. The cell surface receptors of S. haemolyticus were more heat and protease resistant than were Staphylococcus aureus receptors. Strains of Staphylococcus saprophyticus isolated from urinary tract infections showed a high capacity to adhere to laminin. The ability to agglutinate fibronectin and collagen was common among coagulase-negative staphylococci isolated from other infections; 55% (31 of 56) and 63% (35 of 56) agglutinated fibronectin and/or collagen. S. haemolyticus and S. epidermidis bound to both N-terminal (29-kDa) and C-terminal (120-kDa) fragments of fibronectin.