Specific inhibitors of bacterial adhesion: observations from the study of gram-positive bacteria that initiate biofilm formation on the tooth surface

Glycolanguage of the oral microbiota

The oral cavity harbors a diverse and dynamic bacterial biofilm community which is pivotal to oral health maintenance and, if turning dysbiotic, can contribute to various diseases. Glycans as unsurpassed carriers of biological information are participating in underlying processes that shape oral health and disease. Bacterial glycoinfrastructure-encompassing compounds as diverse as glycoproteins, lipopolysaccharides (LPSs), cell wall glycopolymers, and exopolysaccharides-is well known to influence bacterial fitness, with direct effects on bacterial physiology, immunogenicity, lifestyle, and interaction and colonization capabilities. Thus, understanding oral bacterias' glycoinfrastructure and encoded glycolanguage is key to elucidating their pathogenicity mechanisms and developing targeted strategies for therapeutic intervention. Driven by their known immunological role, most research in oral glycobiology has been directed onto LPSs, whereas, recently, glycoproteins have been gaining increased interest. This review draws a multifaceted picture of the glycolanguage, with a focus on glycoproteins, manifested in prominent oral bacteria, such as streptococci, Porphyromonas gingivalis, Tannerella forsythia, and Fusobacterium nucleatum. We first define the characteristics of the different glycoconjugate classes and then summarize the current status of knowledge of the structural diversity of glycoconjugates produced by oral bacteria, describe governing biosynthetic pathways, and list biological roles of these energetically costly compounds. Additionally, we highlight emerging research on the unraveling impact of oral glycoinfrastructure on dental caries, periodontitis, and systemic conditions. By integrating current knowledge and identifying knowledge gaps, this review underscores the importance of studying the glycolanguage oral bacteria speak to advance our understanding of oral microbiology and develop novel antimicrobials.

Caries Management-The Role of Surface Interactions in De- and Remineralization-Processes

BACKGROUND

Bioadhesion and surface interactions on enamel are of essential relevance for initiation, progression and prevention of caries and erosions. Salivary proteins on and within initial carious and erosive lesions can facilitate or aggravate de- and remineralization. This applies for the pellicle layer, the subsurface pellicle and for proteins within initial carious lesions. Little is known about these proteinaceous structures related to initial caries and erosion. Accordingly, there is a considerable demand for an understanding of the underlying processes occurring at the interface between the tooth surface and the oral cavity in order to develop novel agents that limit and modulate caries and erosion. Objectives and findings: The present paper depicts the current knowledge of the processes occurring at the interface of the tooth surface and the oral fluids. Proteinaceous layers on dental hard tissues can prevent or aggravate demineralization processes, whereas proteins within initial erosive or carious lesions might hinder remineralization considerably and restrict the entry of ions into lesions.

CONCLUSIONS

Despite the fact that organic-inorganic surface interactions are of essential relevance for de- and remineralization processes at the tooth surface, there is limited knowledge on these clinically relevant phenomena. Accordingly, intensive research is necessary to develop new approaches in preventive dentistry.

Bioadhesion in the oral cavity and approaches for biofilm management by surface modifications

BACKGROUND

All soft and solid surface structures in the oral cavity are covered by the acquired pellicle followed by bacterial colonization. This applies for natural structures as well as for restorative or prosthetic materials; the adherent bacterial biofilm is associated among others with the development of caries, periodontal diseases, peri-implantitis, or denture-associated stomatitis. Accordingly, there is a considerable demand for novel materials and coatings that limit and modulate bacterial attachment and/or propagation of microorganisms.

OBJECTIVES AND FINDINGS

The present paper depicts the current knowledge on the impact of different physicochemical surface characteristics on bioadsorption in the oral cavity. Furthermore, it was carved out which strategies were developed in dental research and general surface science to inhibit bacterial colonization and to delay biofilm formation by low-fouling or "easy-to-clean" surfaces. These include the modulation of physicochemical properties such as periodic topographies, roughness, surface free energy, or hardness. In recent years, a large emphasis was laid on micro- and nanostructured surfaces and on liquid repellent superhydrophic as well as superhydrophilic interfaces. Materials incorporating mobile or bound nanoparticles promoting bacteriostatic or bacteriotoxic properties were also used. Recently, chemically textured interfaces gained increasing interest and could represent promising solutions for innovative antibioadhesion interfaces. Due to the unique conditions in the oral cavity, mainly in vivo or in situ studies were considered in the review.

CONCLUSION

Despite many promising approaches for modulation of biofilm formation in the oral cavity, the ubiquitous phenomenon of bioadsorption and adhesion pellicle formation in the challenging oral milieu masks surface properties and therewith hampers low-fouling strategies.

CLINICAL RELEVANCE

Improved dental materials and surface coatings with easy-to-clean properties have the potential to improve oral health, but extensive and systematic research is required in this field to develop biocompatible and effective substances.

Interbacterial Adhesion Networks within Early Oral Biofilms of Single Human Hosts

Specific interbacterial adhesion, termed coaggregation, is well established for three early colonizers of the plaque biofilm: streptococci, actinomyces, and veillonellae. However, little is known about interactions of other early colonizers and about the extent of interactions within the bacterial community from a single host. To address these gaps, subject-specific culture collections from two individuals were established using an intraoral biofilm retrieval device. Molecular taxonomy (Human Oral Microbe Identification Microarray [HOMIM]) analysis of biofilm samples confirmed the integrity and completeness of the collections. HOMIM analysis verified the isolation of Streptococcus gordonii and S. anginosus from only one subject, as well as isolation of a previously uncultivated streptococcal phylotype from the other subject. Strains representative of clonal diversity within each collection were further characterized. Greater than 70% of these streptococcal strains from each subject coaggregated with at least one other coisolate. One-third of the strains carry a known coaggregation mediator: receptor polysaccharide (RPS). Almost all nonstreptococcal isolates coaggregated with other coisolates. Importantly, certain Rothia strains demonstrated more coaggregations with their coisolated bacteria than did any Streptococcus or Actinomyces strain, and certain Haemophilus isolates participated in twice as many. Confocal microscopy of undisturbed biofilms showed that Rothia and Haemophilus each occur in small multispecies microcolonies. However, in confluent high-biomass regions, Rothia occurred in islands whereas Haemophilus was distributed throughout. Together, the data demonstrate that coaggregation networks within an individual's oral microflora are extensive and that Rothia and Haemophilus can be important initiators of cell-cell interactions in the early biofilm.IMPORTANCE Extensive involvement of specific interbacterial adhesion in dental plaque biofilm formation has been postulated based on in vitro coaggregation between oral bacteria from culture collections that are not subject specific. In the present study, subject-specific culture collections were obtained from early plaque biofilm of two volunteers, and coaggregations within each culture collection were assayed. Coaggregations, several of which involved a coaggregation-mediating cell surface molecule known from well-studied streptococci, were widespread. Unexpectedly, the little-studied organisms Haemophilus and Rothia participated in the greatest numbers of interactions with community members; these two organisms showed different distributions within the undisturbed biofilm. The data show that coaggregation networks encompass most organisms within the biofilm community of each individual, and they indicate prominent participation of organisms such as Haemophilus and Rothia in early plaque biofilm formation.

Composition and development of oral bacterial communities

The oral bacterial microbiome encompasses approximately 700 commonly occurring phylotypes, approximately half of which can be present at any time in any individual. These bacteria are largely indigenous to the oral cavity; this limited habitat range suggests that interactions between the various phylotypes, and between the phylotypes and their environment, are crucial for their existence. Molecular cataloging has confirmed many basic observations on the composition of the oral microbiome that were formulated well before ribosomal RNA-based systematics, but the power and the scope of molecular taxonomy have resulted in the discovery of new phylotypes and, more importantly, have made possible a level of bacterial community analysis that was unachievable with classical methods. Bacterial community structure varies with location within the mouth, and changes in community structure are related to disease initiation and disease progression. Factors that influence the formation and the evolution of communities include selective adherence to epithelial or tooth surfaces, specific cell-to-cell binding as a driver of early community composition, and interorganismal interaction leading to alteration of the local environment, which represents the first step on the road to oral disease. A comprehensive understanding of how these factors interact to drive changes in the composition of the oral microbial community can lead to new strategies for the inhibition of periodontal diseases and dental caries.

Actinomyces naeslundii GroEL-dependent initial attachment and biofilm formation in a flow cell system

Actinomyces naeslundii is an early colonizer with important roles in the development of the oral biofilm. The effects of butyric acid, one of short chain fatty acids in A. naeslundii biofilm formation was observed using a flow cell system with Tryptic soy broth without dextrose and with 0.25% sucrose (TSB sucrose). Significant biofilms were established involving live and dead cells in TSB sucrose with 60mM butyric acid but not in concentrations of 6, 30, 40, and 50mM. Biofilm formation failed in 60mM sodium butyrate but biofilm level in 60mM sodium butyrate (pH4.7) adjusted with hydrochloric acid as 60mM butyric media (pH4.7) was similar to biofilm levels in 60mM butyric acid. Therefore, butyric acid and low pH are required for significant biofilm formation in the flow cell. To determine the mechanism of biofilm formation, we investigated initial A. naeslundii colonization in various conditions and effects of anti-GroEL antibody. The initial colonization was observed in the 60mM butyric acid condition and anti-GroEL antibody inhibited the initial colonization. In conclusion, we established a new biofilm formation model in which butyric acid induces GroEL-dependent initial colonization of A. naeslundii resulting in significant biofilm formation in a flow system.

The pilin protein FimP from Actinomyces oris: crystal structure and sequence analyses

The Actinomyces oris type-1 pili are important for the initial formation of dental plaque by binding to salivary proteins that adhere to the tooth surface. Here we present the X-ray structure of FimP, the protein that is polymerized into the type-1 pilus stalk, assisted by a pili-specific sortase. FimP consists of three tandem IgG-like domains. The middle and C-terminal domains contain one autocatalyzed intramolecular isopeptide bond each, a feature used by Gram-positive bacteria for stabilization of surface proteins. While the N-terminal domain harbours all the residues necessary for forming an isopeptide bond, no such bond is observed in the crystal structure of this unpolymerized form of FimP. The monomer is further stabilized by one disulfide bond each in the N- and C-terminal domains as well as by a metal-coordinated loop protruding from the C-terminal domain. A lysine, predicted to be crucial for FimP polymerization by covalent attachment to a threonine from another subunit, is located at the rim of a groove lined with conserved residues. The groove may function as a docking site for the sortase-FimP complex. We also present sequence analyses performed on the genes encoding FimP as well as the related FimA, obtained from clinical isolates.

The scientific exploration of saliva in the post-proteomic era: from database back to basic function

The proteome of human saliva can be considered as being essentially completed. Diagnostic markers for a number of diseases have been identified among salivary proteins and peptides, taking advantage of saliva as an easy-to-obtain biological fluid. Yet, the majority of disease markers identified so far are serum components and not intrinsic proteins produced by the salivary glands. Furthermore, despite the fact that saliva is essential for protecting the oral integuments and dentition, little progress has been made in finding risk predictors in the salivary proteome for dental caries or periodontal disease. Since salivary proteins, and in particular the attached glycans, play an important role in interactions with the microbial world, the salivary glycoproteome and other post-translational modifications of salivary proteins need to be studied. Risk markers for microbial diseases, including dental caries, are likely to be discovered among the highly glycosylated major protein species in saliva. This review will attempt to raise new ideas and also point to under-researched areas that may hold promise for future applicability in oral diagnostics and prediction of oral disease.

Structural determinants of Actinomyces sortase SrtC2 required for membrane localization and assembly of type 2 fimbriae for interbacterial coaggregation and oral biofilm formation

As a pioneer colonizer of the oral cavity, Actinomyces oris expresses proteinaceous pili (also called fimbriae) to mediate the following two key events in biofilm formation: adherence to saliva deposits on enamel and interbacterial associations. Assembly of type 2 fimbriae that directly facilitate coaggregation with oral streptococci and Actinomyces biofilm development requires the class C sortase SrtC2. Although the general sortase-associated mechanisms have been elucidated, several structural attributes unique to the class C sortases require functional investigation. Mutational studies reported here suggest that the N-terminal transmembrane (TM) region of SrtC2, predicted to contain a signal peptide sequence, is cleaved off the mature protein and that this processing is critical for the proper integration of the enzyme at the cytoplasmic membrane, which is mediated by the extended hydrophobic C terminus containing a TM domain and a cytoplasmic tail. Deletion of this putative TM or the entire cytoplasmic domain abolished the enzyme localization and functionality. Alanine substitution of the conserved catalytic Cys-His dyad abrogated the SrtC2 enzymatic activity. In contrast, mutations designed to alter a "lid" domain that covers the catalytic pocket of a class C sortase showed no effect on enzyme activity. Finally, each of the deleterious mutations that affected SrtC2 activity or membrane localization also eliminated Actinomyces species biofilm development and bacterial coaggregation with streptococci. We conclude that the N terminus of SrtC2, which contains the signal sequence, is required for proper protein translocation and maturation, while the extended C-terminal hydrophobic region serves as a stable membrane anchor for proper enzyme functionality.

Two autonomous structural modules in the fimbrial shaft adhesin FimA mediate Actinomyces interactions with streptococci and host cells during oral biofilm development

By combining X-ray crystallography and modelling, we describe here the atomic structure of distinct adhesive moieties of FimA, the shaft fimbrillin of Actinomyces type 2 fimbriae, which uniquely mediates the receptor-dependent intercellular interactions between Actinomyces and oral streptococci as well as host cells during the development of oral biofilms. The FimA adhesin is built with three IgG-like domains, each of which harbours an intramolecular isopeptide bond, previously described in several Gram-positive pilins. Genetic and biochemical studies demonstrate that although these isopeptide bonds are dispensable for fimbrial assembly, cell-cell interactions and biofilm formation, they contribute significantly to the proteolytic stability of FimA. Remarkably, FimA harbours two autonomous adhesive modules, which structurally resemble the Staphylococcus aureus Cna B domain. Each isolated module can bind the plasma glycoprotein asialofetuin as well as the polysaccharide receptors present on the surface of oral streptococci and epithelial cells. Thus, FimA should serve as an excellent paradigm for the development of therapeutic strategies and elucidating the precise molecular mechanisms underlying the interactions between cellular receptors and Gram-positive fimbriae.

Structure of type 3Gn coaggregation receptor polysaccharide from Streptococcus cristatus LS4

The presence of a novel coaggregation receptor polysaccharide (RPS) on the dental plaque isolate Streptococcus cristatus LS4 was suggested by this strain's antigenic and coaggregation properties. Examination of RPS isolated from strain LS4 by a combination of 2-dimensional and pseudo 3-dimensional single quantum heteronuclear NMR methods that included detection of (13)C chemical shifts at high resolution revealed the following repeat unit structure: →6)-β-d-Galf-(1→6)-β-d-GalpNAc-(1→3)-α-d-Galp-(1→P→6)-α-d-Galp-(1→3)-β-L-Rhap-(1→4)-β-d-Glcp-(1→. The identification of this polysaccharide as RPS3Gn, a new structural type, was established by the α-d-Galp-containing epitope of RPS serotype 3 and Gn recognition motif (i.e., β-d-GalpNAc (1→3)-α-d-Galp) for coaggregation with other bacteria.

Dual function of a tip fimbrillin of Actinomyces in fimbrial assembly and receptor binding

Interaction of Actinomyces oris with salivary proline-rich proteins (PRPs), which serve as fimbrial receptors, involves type 1 fimbriae. Encoded by the gene locus fimQ-fimP-srtC1, the type 1 fimbria is comprised of the fimbrial shaft FimP and the tip fimbrillin FimQ. Fimbrial polymerization requires the fimbria-specific sortase SrtC1, which catalyzes covalent linkage of fimbrial subunits. Using genetics, biochemical methods, and electron microscopy, we provide evidence that the tip fimbrillin, FimQ, is involved in fimbrial assembly and interaction with PRPs. Specifically, while deletion of fimP completely abolished the type 1 fimbrial structures, surface display of monomeric FimQ was not affected by this mutation. Surprisingly, deletion of fimQ significantly reduced surface assembly of the type 1 fimbriae. This defect was rescued by recombinant FimQ ectopically expressed from a plasmid. In agreement with the role of type 1 fimbriae in binding to PRPs, aggregation of A. oris with PRP-coated beads was abrogated in cells lacking srtC1 or fimP. This aggregation defect of the ΔfimP mutant was mainly due to significant reduction of FimQ on the bacterial surface, as the aggregation was not observed in a strain lacking fimQ. Increasing expression of FimQ in the ΔfimP mutant enhanced aggregation, while overexpression of FimP in the ΔfimQ mutant did not. Furthermore, recombinant FimQ, not FimP, bound surface-associated PRPs in a dose-dependent manner. Thus, not only does FimQ function as the major adhesin of the type 1 fimbriae, it also plays an important role in fimbrial assembly.

The Actinomyces oris type 2 fimbrial shaft FimA mediates co-aggregation with oral streptococci, adherence to red blood cells and biofilm development

Interbacterial interactions between oral streptococci and actinomyces and their adherence to tooth surface and the associated host cells are key early events that promote development of the complex oral biofilm referred to as dental plaque. These interactions depend largely on a lectin-like activity associated with the Actinomyces oris type 2 fimbria, a surface structure assembled by sortase (SrtC2)-dependent polymerization of the shaft and tip fimbrillins, FimA and FimB respectively. To dissect the function of specific fimbrillins in various adherence processes, we have developed a convenient new technology for generating unmarked deletion mutants of A. oris. Here, we show that the fimB mutant, which produced type 2 fimbriae composed only of FimA, like the wild type co-aggregated strongly with receptor-bearing streptococci, agglutinated with sialidase-treated red blood cells, and formed monospecies biofilm. In contrast, the fimA and srtC2 mutants lacked type 2 fimbriae and were non-adherent in each of these assays. Plasmid-based expression of the deleted gene in respective mutants restored adherence to wild-type levels. These findings uncover the importance of the lectin-like activity of the polymeric FimA shaft rather than the tip. The multivalent adhesive function of FimA makes it an ideal molecule for exploring novel intervention strategies to control plaque biofilm formation.

Molecular characterization and therapeutic potential of a marine bacterium Pseudoalteromonas sp. KMM 701 alpha-galactosidase

An alpha-galactosidase capable of converting B red blood cells into the universal blood type cells at the neutral pH was produced by a novel obligate marine bacterium strain KMM 701 (VKM B-2135 D). The organism is heterotrophic, aerobic, and halophilic and requires Na+ ions and temperature up to 34 degrees C for its growth. The strain has a unique combination of polysaccharide-degrading enzymes. Its single intracellular alpha-galactosidase exceeded other glycoside hydrolases in the level of expression up to 20-fold. The alpha-galactosidase was purified to determine the N-terminal amino acid sequences and new activities. It was found to inhibit Corynebacterium diphtheria adhesion to host buccal epithelium cell surfaces with high effectiveness. The nucleotide sequence of the homodimeric alpha-galactosidase indicates that its subunit is composed of 710 amino acid residues with a calculated Mr of 80,055. This alpha-galactosidase shares structural property with 36 family glycoside hydrolases. The properties of the enzyme are likely to be highly beneficial for medicinal purposes.

Shear-enhanced oral microbial adhesion

Shear-enhanced adhesion, although not observed for fimbria-mediated adhesion of oral Actinomyces spp., was noted for Hsa-mediated adhesion of Streptococcus gordonii to sialic acid-containing receptors, an interaction implicated in the pathogenesis of infective endocarditis.

Oral bacterial adhesion forces to biomaterial surfaces constituting the bracket-adhesive-enamel junction in orthodontic treatment

Bacterial adhesion to biomaterial surfaces constituting the bracket-adhesive-enamel junction represents a growing problem in orthodontics, because bacteria can adversely affect treatment by causing demineralization of the enamel surface around the brackets. It is important to know the forces with which bacteria adhere to the surfaces of these junction materials, as the strength of these forces will determine how easy it will be to remove the bacteria. We compared the adhesion forces of five initially colonizing and four cariogenic strains of bacteria to an orthodontic adhesive, stainless steel, and enamel, with and without a salivary conditioning film. Adhesion forces were determined using atomic force microscopy and a bacterial probe. In the absence of a salivary conditioning film, the strongest bacterial adhesion forces occurred to the adhesive surface (-2.9 to -6.9 nN), while adhesion forces to the enamel surfaces were lowest (-0.8 to -2.7 nN). In the presence of a salivary conditioning film, adhesion forces were reduced strongly, to less than 1 nN, and the differences between the various materials were reduced. Generally, however, initial colonizers of dental hard surfaces presented stronger adhesion forces to the different materials (-4.7 and -0.6 nN in the absence and presence of a salivary conditioning film, respectively) than cariogenic strains (-1.8 and -0.5 nN).

Specific antibody activity, glycan heterogeneity and polyreactivity contribute to the protective activity of S-IgA at mucosal surfaces

An explanation of the principles and mechanisms involved in peaceful co-existence between animals and the huge, diverse, and ever-changing microbiota that resides on their mucosal surfaces represents a challenging puzzle that is fundamental in everyday survival. In addition to mechanical barriers and a variety of innate defense factors, mucosal immunoglobulins (Igs) provide protection by two complementary mechanisms: specific antibody activity and innate, Ig glycan-mediated binding, both of which serve to contain the mucosal microbiota in its physiological niche. Thus, the interaction of bacterial ligands with IgA glycans constitutes a discrete mechanism that is independent of antibody specificity and operates primarily in the intestinal tract. This mucosal site is by far the most heavily colonized with an enormously diverse bacterial population, as well as the most abundant production site for antibodies, predominantly of the IgA isotype, in the entire immune system. In embodying both adaptive and innate immune mechanisms within a single molecule, S-IgA maintains comprehensive protection of mucosal surfaces with economy of structure and function.

Amended description of the genes for synthesis of Actinomyces naeslundii T14V type 1 fimbriae and associated adhesin

The type 1 fimbriae of Actinomyces naeslundii T14V mediate adhesion of this gram-positive species to the tooth surface. The present findings show that the locus for type 1 fimbria production in this strain includes three genes, fimQ for a minor fimbrial subunit that appears to be an adhesin, fimP for the major structural subunit, and srtC1 for a type 1 fimbria-specific sortase involved in the assembly of these structures.

Interaction between GIC and S. sanguis biofilms: Antibacterial properties and changes of surface hardness

OBJECTIVE

The aim of this study was to investigate the interaction of Streptococcus sanguis with two glass-ionomer formulations (GIC:A containing fluoride and GIC:B without fluoride) with particular reference to bacterial growth and changes in hardness of the cement with respect to time.

MATERIALS AND METHODS

Discs of two water activated glass-ionomer cements were prepared according to the manufacturer's instruction. Hydroxyapatite discs (HA) were used as controls. 3D laser scanning technique was used to characterize surface roughness and area of the substrate prior to growing biofilms. Surface hardness was evaluated before and after biofilm growth. A constant depth film fermenter system (CDFF) was used to grow S. sanguis biofilms on the specimens in a similar manner to that described previously by Wilson et al. in 1995. For susceptibility measurement, specimens were removed from CDFF aseptically over periods up to 14d after the first colonization with bacteria. Counts of viable bacterial in the accumulating biofilm layer on each surface were measured and converted to colony forming units per unit surface area. To determine the effect of storage media, hardness discs were exposed to distilled water, lactic acid pH 4, lactic acid pH 5, citric acid pH 5, artificial saliva and S. sanguis biofilms. Twenty-four hours after preparing and subsequent autoclaving, specimens were transferred to a vessel containing 40 ml storage medium. The specimens were investigated for periods up to 7d.

RESULTS

The viable counts of S. sanguis per mm2 on GIC:A were significantly less than those on HA and GIC:B during the first 5d (p<0.05). The viable counts of bacteria on the surface of GIC:B were lower during the initial 5d when compared to HA. Exposure of GIC:A and GIC:B to different medium produced softening to the surface of cement. It is apparent that the effects of the biofilms are significantly greater than storage in water but similar to storage in lactic acid pH 5.

CONCLUSIONS

This investigation showed that the growth of S. sanguis biofilms were significantly affected by both glass-ionomer formulations, the greater reduction being noted on the surface of the fluoride containing GIC. S. sanguis biofilms produced reduction on the surface hardness of the cement equivalent to that seen after immersion in lactic acid at pH 5. This indicates that while S. sanguis biofilm is affected by the GIC, there is also a decrease in hardness of the cement indicating some cement degradation.

Adhesion of viridans group streptococci to sialic acid-, galactose- and N-acetylgalactosamine-containing receptors

The binding of 10 viridans group streptococci to sialic acid-, galactose (Gal)- and N-acetylgalactosamine (GalNAc)-containing receptors was defined by analysis of the interactions between these bacteria and structurally defined glycoconjugates, host cells and other streptococci. All interactions with sialic acid-containing receptors were Ca(2+)-independent as they were not affected by ethyleneglycoltetraacetic acid (EGTA), whereas all interactions with Gal- and GalNAc-containing receptors were Ca(2+)-dependent. Recognition of sialic acid-, Gal- and GalNAc-containing receptors varied widely among the strains examined, in a manner consistent with the association of each of the three lectin-like activities with a different bacterial cell surface component.

The Fap1 fimbrial adhesin is a glycoprotein: antibodies specific for the glycan moiety block the adhesion of Streptococcus parasanguis in an in vitro tooth model

Streptococcus parasanguis is a primary colonizer of the tooth surface and plays a pivotal role in the formation of dental plaque. The fimbriae of S. parasanguis are important in mediating adhesion to saliva-coated hydroxylapatite (SHA), an in vitro tooth adhesion model. The Fap1 adhesin has been identified as the major fimbrial subunit, and recent studies suggest that Fap1 is a glycoprotein. Monosaccharide analysis of Fap1 purified from the culture supernatant of S. parasanguis indicated the presence of rhamnose, glucose, galactose, N-acetylglucosamine and N-acetylgalactosamine. A glycopeptide moiety was isolated from a pronase digest of Fap1 and purified by immunoaffinity chromatography. The monosaccharide composition of the purified glycopeptide was similar to that of the intact molecule. The functionality of the glycan moiety was determined using monoclonal antibodies (MAbs) specific for the intact Fap1 glycoprotein. These antibodies were grouped into two categories based on their ability to block adhesion of S. parasanguis to SHA and their corresponding specificity for either protein or glycan epitopes of the Fap1 protein. 'Non-blocking' MAb epitopes were mapped to unique protein sequences in the N-terminus of the Fap1 protein using non-glycosylated recombinant Fap1 proteins (rFap1 and drFap1) expressed in Escherichia coli. In contrast, the 'blocking' antibodies did not bind to the recombinant Fap1 proteins, and were effectively competed by the binding to the purified glycopeptide. These data suggest that the 'blocking' antibodies are specific for the glycan moiety and that the adhesion of S. parasanguis is mediated by sugar residues associated with Fap1.

Molecular and genetic analyses of Actinomyces spp

Members of the genus Actinomyces are predominant primary colonizers of the oral cavity and play an important role in initiating plaque development. These bacteria have evolved unique mechanisms that favor colonization and persistence in this micro-environment. The expression of cell-surface fimbriae is correlated with the ability of these bacteria to adhere to specific receptors on the tooth and mucosal surfaces, and to interact with other plaque bacteria. The elaboration of sialidase is thought to enhance fimbriae-mediated adherence by unmasking the fimbrial receptors on mammalian cells. The presence of certain cell-associated or extracellular enzymes, including those involved in sucrose or urea metabolism, may provide the means for these bacteria to thrive under conditions when other growth nutrients are not available. Moreover, these enzyme activities may influence the distribution of other plaque bacteria and promote selection for Actinomyces spp. in certain ecological niches. The recent development of a genetic transfer system for Actinomyces spp. has allowed for studies the results of which demonstrate the existence of multiple genes involved in fimbriae synthesis and function, and facilitated the construction of allelic replacement mutants at each gene locus. Analyses of these mutants have revealed a direct correlation between the synthesis of assembled fimbriae and the observed adherence properties. Further genetic analysis of the various enzyme activities detected from strains of Actinomyces should allow for an assessment of the role of these components in microbial ecology, and their contribution to the overall success of Actinomyces spp. as a primary colonizer and a key player in oral health and disease.

The importance of fimbriae in the virulence and ecology of some oral bacteria

Cumulative evidence indicates that bacterial adherence to mucosal and tooth surfaces as well as bacterial coaggregation are essential steps for colonization of various oral bacterial species. Bacterial fimbriae have been shown to play an important role in the interaction between bacteria and host cells or among bacterial cells. The properties of fimbriae from selected species of oral bacteria are discussed in terms of virulence traits and ecological significance. Among others, Porphyromonas gingivalis fimbriae have been most extensively studied. The fimbrial structure is composed of 41-kDa fimbrillin proteins. DNA sequencing of the fimbrillin gene (fimA) from nine strains of P. gingivalis suggests intraspecies variation in the structure of fimA, while retaining common immunochemical specificities. P. gingivalis fimbriae exhibit a wide variety of biological activities including immunogenicity, binding to various host proteins, stimulation of cytokine production and promotion of bone resorption, Actinobacillus actinomycetemcomitans also possesses fimbriae; however, little is known concerning their chemical, genetical, and biological properties. Fimbriae of Prevotella intermedia are shown to induce hemagglutination reaction, while those of Prevotella loescheii are found to cause coaggregation with other bacteria, i.e., Actinomyces viscosus and sanguis streptococci. Fimbriae from gram-positive oral bacteria such as oral Actinomyces and sanguis streptococci are described. These fimbriae may participate in coaggregation, binding to saliva-coated hydroxyapatite or glycoprotein of the surface layer of oral epithelial cells. Taken together, fimbriae are key components in cell-to-surface and cell-to-cell adherence of oral bacteria and pathogenesis of some oral and systemic diseases.

Survival of oral bacteria

The global distribution of individual species of oral bacteria demonstrates their ability to survive among their human hosts. Such an ubiquitous existence is the result of efficient transmission of strains and their persistence in the oral environment. Genetic analysis has identified specific clones of pathogenic bacteria causing infection. Presumably, these express virulence-associated characteristics enhancing colonization and survival in their hosts. A similar situation may occur with the oral resident flora, where genetic variants may express specific phenotypic characteristics related to survival. Survival in the mouth is enhanced by dental plaque formation, where persistence is associated with the bacteria's capacity not only to adhere and grow, but also to withstand oxygen, wide fluctuations in pH and carbohydrate concentration, and a diverse array of microbial interactions. Streptococcus mutans has been discussed as a 'model' organism possessing the biochemical flexibility that permits it to persist and dominate the indigenous microflora under conditions of stress.

Structural and antigenic types of cell wall polysaccharides from viridans group streptococci with receptors for oral actinomyces and streptococcal lectins

Lectin-mediated interactions between oral viridans group streptococci and actinomyces may play an important role in microbial colonization of the tooth surface. The presence of two host-like motifs, either GalNAc beta1-->3Gal (Gn) or Gal beta1-->3GalNAc (G), in the cell wall polysaccharides of five streptococcal strains accounts for the lactose-sensitive coaggregations of these bacteria with Actinomyces naeslundii. Three streptococcal strains which have Gn-containing polysaccharides also participate in GalNAc-sensitive coaggregations with strains of Streptococcus gordonii and S. sanguis. Each Gn- or G-containing polysaccharide is composed of a distinct phosphodiester-linked hexa- or heptasaccharide repeating unit. The occurrence of these polysaccharides on 19 additional viridans group streptococcal strains that participate in lactose-sensitive coaggregations with actinomyces was examined. Negatively charged polysaccharides that reacted with Bauhinia purpurea agglutinin, a Gal and GalNAc binding plant lectin, were isolated from 17 strains by anion exchange column chromatography of mutanolysin-cell wall digests. Results from nuclear magnetic resonance and immunodiffusion identified each of 16 polysaccharides as a known Gn- or G-containing structural type and one polysaccharide as a new but closely related Gn-containing type. Unlike the reactions of lectins, the cross-reactions of most rabbit antisera with these polysaccharides were correlated with structural features other than the host-like motifs. Gn-containing polysaccharides occurred primarily on the strains of S. sanguis and S. oralis while G-containing polysaccharides were more common among the strains of S. gordonii and S. mitis examined. The findings strongly support the hypothesis that lectin-mediated recognition of these streptococci by other oral bacteria depends on a family of antigenically diverse Gn- and G-containing cell wall polysaccharides, the occurrence of which may differ between streptococcal species.