Adhesive properties of strains of Fusobacterium nucleatum of the subspecies nucleatum, vincentii and polymorphum

Reexamining the role of Fusobacterium nucleatum subspecies in clinical and experimental studies

The Gram-negative anaerobic species Fusobacterium nucleatum was originally described as a commensal organism from the human oral microbiome. However, it is now widely recognized as a key inflammophilic pathobiont associated with a wide variety of oral and extraoral diseases. Historically, F. nucleatum has been classified into four subspecies that have been generally considered as functionally interchangeable in their pathogenic potential. Recent studies have challenged this notion, as clinical data reveal a highly biased distribution of F. nucleatum subspecies within disease sites of both inflammatory oral diseases and various malignancies. This review details the historical basis for the F. nucleatum subspecies designations and summarizes our current understanding of the similarities and distinctions between these organisms to provide important context for future clinical and laboratory studies of F. nucleatum.

Functional biomedical materials derived from proteins in the acquired salivary pellicle

In the oral environment, the acquired salivary pellicle (ASP) on the tooth surface comprises proteins, glycoproteins, carbohydrates, and lipids. The ASP can specifically and rapidly adsorb on the enamel surface to provide effective lubrication, protection, hydration, and remineralisation, as well as be recognised by various bacteria to form a microbial biofilm (plaque). The involved proteins, particularly various phosphoproteins such as statherins, histatins, and proline-rich proteins, are vital to their specific functions. This review first describes the relationship between the biological functions of these proteins and their structures. Subsequently, recent advances in functional biomedical materials derived from these proteins are reviewed in terms of dental/bone therapeutic materials, antibacterial materials, tissue engineering materials, and coatings for medical devices. Finally, perspectives and challenges regarding the rational design and biomedical applications of ASP-derived materials are discussed.

Fusobacterium watanabei sp. nov. As additional species within the genus Fusobacerium, isolated from human clinical specimens

Eight spindle-shaped bacteria were isolated from clinical samples in Japan and investigated for their taxonomic position. Phylogenetic trees (based on 16S rRNA, rpoB, zinc protease, and gyrB gene sequence comparisons) showed distinct clustering of eight strains with the type strain of Fusobacterium nucleatum and its closely related species. In silico whole genome comparison analysis based on average nucleotide index based on BLAST (ANIb) and digital DNA-DNA hybridization (dDDH) data between our clinical isolates (PAGU 1795, PAGU 1796^T, and PAGU 1797) and the type strain of the closely related species showed values of less than 92.4% and 49.5%, respectively. On the basis of its phylogenetic and genomic distinctiveness together with differential phenotypic properties and matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF-MS) characteristic signal patterns, we propose Fusobacterium watanabei sp. nov., with the type strain PAGU 1796^T (= GTC 21791^T = CCUG 74246^T).

Role of FAD-I in Fusobacterial Interspecies Interaction and Biofilm Formation

: RadD, a major adhesin of oral fusobacteria, is part of a four-gene operon encoding the small lipoprotein FAD-I and two currently uncharacterized small proteins encoded by the rapA and rapB genes. Previously, we described a role for FAD-I in the induction of human B-defensin 2 (hBD2) upon contact with oral epithelial cells. Here, we investigated potential roles for fad-I, rapA, and rapB in interspecies interaction and biofilm formation. Gene inactivation mutants were generated for each of these genes in the nucleatum and polymorphum subspecies of Fusobacterium nucleatum and characterized for their adherence to partner species, biofilm formation, and operon transcription. Binding to Streptococcus gordonii was increased in all mutant strains with Δfad-I having the most significant effect. This increased adherence was directly proportional to elevated radD transcript levels and resulted in significantly different architecture and height of the biofilms formed by Δfad-I and S. gordonii compared to the wild-type parent. In conclusion, FAD-I is important for fusobacterial interspecies interaction as its lack leads to increased production of the RadD adhesin suggesting a role of FAD-I in its regulation. This regulatory effect does not require the presence of functional RadD.

Protein Profile of the Acquired Enamel Pellicle after Rinsing with Whole Milk, Fat-Free Milk, and Water: An in vivo Study

This study detected changes in the protein profile of the acquired enamel pellicle (AEP) formed in vivo after rinsing with whole milk, fat-free milk, or water. Nine subjects in good oral condition took part in the study. The acquired pellicle was formed in the morning, for 120 min, after prophylaxis with pumice. Following this, the volunteers rinsed with 10 mL of whole milk, fat-free milk, or deionized water for 30 s, following a blinded crossover protocol. After 60 min, the pellicle was collected with filter paper soaked in 3% citric acid and processed for analysis by liquid chromatography-electrospray ionization tandem mass spectrometry. The obtained tandem mass spectrometry spectra were searched against a human protein database (Swiss-Prot). The proteomic data related to protein quantification were analysed using the PLGS software. A total of 260 proteins were successfully identified in the AEP samples collected from all groups. Forty-nine were common to all 3 groups, while 72, 62, and 49 were specific to the groups rinsing with whole milk, fat-free milk, and water, respectively. Some were typical components of the AEP, such as cystatin-B, cystatin-SN, isoforms of α-amylase, IgA and IgG, lysozyme C, protein S100 A78, histatin-1, proline-rich protein 27, statherin, and lactotransferrin. Other proteins are not commonly described as part of the AEP but could act in defence of the organism against pathogens. Distinct proteomic profiles were found in the AEP after rinsing with whole or fat-free milk, which could have an impact on bacterial adhesion and tooth dissolution. The use of fat-free milk could favourably modulate the adhesion of bacteria to the AEP as well as biofilm formation when compared with whole milk.

Influence of lung CT changes in chronic obstructive pulmonary disease (COPD) on the human lung microbiome

BACKGROUND

Changes in microbial community composition in the lung of patients suffering from moderate to severe COPD have been well documented. However, knowledge about specific microbiome structures in the human lung associated with CT defined abnormalities is limited.

METHODS

Bacterial community composition derived from brush samples from lungs of 16 patients suffering from different CT defined subtypes of COPD and 9 healthy subjects was analyzed using a cultivation independent barcoding approach applying 454-pyrosequencing of 16S rRNA gene fragment amplicons.

RESULTS

We could show that bacterial community composition in patients with changes in CT (either airway or emphysema type changes, designated as severe subtypes) was different from community composition in lungs of patients without visible changes in CT as well as from healthy subjects (designated as mild COPD subtype and control group) (PC1, Padj = 0.002). Higher abundance of Prevotella in samples from patients with mild COPD subtype and from controls and of Streptococcus in the severe subtype cases mainly contributed to the separation of bacterial communities of subjects. No significant effects of treatment with inhaled glucocorticoids on bacterial community composition were detected within COPD cases with and without abnormalities in CT in PCoA. Co-occurrence analysis suggests the presence of networks of co-occurring bacteria. Four communities of positively correlated bacteria were revealed. The microbial communities can clearly be distinguished by their associations with the CT defined disease phenotype.

CONCLUSION

Our findings indicate that CT detectable structural changes in the lung of COPD patients, which we termed severe subtypes, are associated with alterations in bacterial communities, which may induce further changes in the interaction between microbes and host cells. This might result in a changed interplay with the host immune system.

Streptococcus mutans SpaP binds to RadD of Fusobacterium nucleatum ssp. polymorphum

Adhesin-mediated bacterial interspecies interactions are important elements in oral biofilm formation. They often occur on a species-specific level, which could determine health or disease association of a biofilm community. Among the key players involved in these processes are the ubiquitous fusobacteria that have been recognized for their ability to interact with numerous different binding partners. Fusobacterial interactions with Streptococcus mutans, an important oral cariogenic pathogen, have previously been described but most studies focused on binding to non-mutans streptococci and specific cognate adhesin pairs remain to be identified. Here, we demonstrated differential binding of oral fusobacteria to S. mutans. Screening of existing mutant derivatives indicated SpaP as the major S. mutans adhesin specific for binding to Fusobacterium nucleatum ssp. polymorphum but none of the other oral fusobacteria tested. We inactivated RadD, a known adhesin of F. nucleatum ssp. nucleatum for interaction with a number of gram-positive species, in F. nucleatum ssp. polymorphum and used a Lactococcus lactis heterologous SpaP expression system to demonstrate SpaP interaction with RadD of F. nucleatum ssp. polymorphum. This is a novel function for SpaP, which has mainly been characterized as an adhesin for binding to host proteins including salivary glycoproteins. In conclusion, we describe an additional role for SpaP as adhesin in interspecies adherence with RadD-SpaP as the interacting adhesin pair for binding between S. mutans and F. nucleatum ssp. polymorphum. Furthermore, S. mutans attachment to oral fusobacteria appears to involve species- and subspecies-dependent adhesin interactions.

Strain-Specific Impact of Fusobacterium nucleatum on Neutrophil Function

BACKGROUND

Neutrophil function is critical for initiation and progression of infecto-inflammatory diseases. Key quorum-sensing plaque bacteria, such as Fusobacterium nucleatum, act as bridging species between early and late colonizer pathogens, such as Porphyromonas gingivalis, as the biofilm ages and periodontal inflammation increases. This study is designed to determine impact of different F. nucleatum strains on neutrophil function.

METHODS

Cells of human promyelocytic leukemia cell line-60 were differentiated into neutrophil-like cells and cultured with F. nucleatum strains of subspecies (ssp.) nucleatum ATCC 25586, ssp. polymorphum ATCC 10953, and ssp. vincentii ATCC 49256. Neutrophil phagocytosis of F. nucleatum strains and neutrophil apoptosis were analyzed by flow cytometry. Superoxide generation was measured by cytochrome C reduction in the presence and absence of N-formyl-L-methionyl-L-leucyl-L-phenylalanine (fMLP) (1 μM) stimulation. Proinflammatory cytokine release was determined after 2, 6, and 24 hours of culture in the presence/absence of different F. nucleatum strains. Expression of Toll-like receptor (TLR)2, TLR4, and nuclear factor (NF)-kappa B mRNA levels were analyzed using real-time quantitative polymerase chain reaction. Each experiment was repeated at least three times in triplicate. Data were analyzed using analysis of variance followed by post hoc Bonferroni correction.

RESULTS

All strains of F. nucleatum significantly increased phagocytic capacity of neutrophils. Neutrophil phagocytosis of F. nucleatum ssp. polymorphum was significantly greater than that of F. nucleatum ssp. vincentii and ssp. nucleatum (P <0.001). F. nucleatum ssp. nucleatum and ssp. polymorphum significantly blocked fMLP-induced superoxide generation (P <0.001). Although F. nucleatum vincentii also reduced superoxide generation (25%), the impact was not as strong as that of ssp. nucleatum (83%) and ssp. polymorphum (100%). All F. nucleatum strains stimulated significant increase in neutrophil apoptosis compared with control (P <0.001) and significantly increased expression of NF-κB mRNA in neutrophils (P <0.05). Levels of interleukin-8 and tumor necrosis factor-α produced by neutrophils were significantly increased in all F. nucleatum groups compared with control (P <0.001).

CONCLUSIONS

These findings suggest that different strains of F. nucleatum impact neutrophil function in different ways. Two of three subspecies blocked neutrophil superoxide generation in response to a secondary stimulus, preventing oxidative killing by neutrophils. The direct role of bridging species in pathogenesis of periodontitis may be greater than previously suspected in which they create a favorable environment for pathogenic transition of the dental ecosystem.

New Insights into the Composition and Functions of the Acquired Enamel Pellicle

The acquired enamel pellicle (AEP) is a thin acellular film that forms on tooth surfaces upon exposure to the oral environment. It consists predominantly of salivary proteins, but also includes non-salivary-derived proteins, carbohydrates, and lipids. Since it is the interface between teeth and the oral environment, the AEP plays a key role in the maintenance of oral health by regulating processes including lubrication, demineralization, and remineralization and shaping the composition of early microbial flora adhering to tooth surfaces. Knowledge of the 3D structure of the AEP and how that correlates with its protective functions may provide insight into several oral pathological states, including caries, erosion, and periodontal disease. This review intends to update readers about the latest discoveries related to the formation, ultrastructure, composition, and functions of the AEP, as well as the future of pellicle research, with particular emphasis on the emerging role of proteomic and microscopy techniques in oral diagnosis and therapeutics.

Maternal oral origin of Fusobacterium nucleatum in adverse pregnancy outcomes as determined using the 16S-23S rRNA gene intergenic transcribed spacer region

Fusobacterium nucleatum, a common Gram-negative anaerobe prevalent in the oral cavity, possesses the ability to colonize the amniotic cavity and the fetus. However, F. nucleatum may also be part of the vaginal microbiota from where it could reach the amniotic tissues. Due to the heterogeneity of F. nucleatum, consisting of five subspecies, analysis at the subspecies/strain level is desirable to determine its precise origin. The aims of this study were: (i) to evaluate the use of the 16S-23S rRNA gene intergenic transcribed spacer (ITS) region as a tool to differentiate subspecies of F. nucleatum, and (ii) to design a simplified technique based on the ITS to determine the origin of F. nucleatum strains associated with adverse pregnancy outcomes. Amplified fragments of the 16S-23S rRNA gene ITS region corresponding to the five subspecies of F. nucleatum were subjected to cloning and sequencing to characterize the different ribosomal operons of the subspecies. Distinctive length and sequence patterns with potential to be used for identification of the subspecies/strain were identified. These were used to evaluate the origin of F. nucleatum identified in neonatal gastric aspirates (swallowed amniotic fluid) by sequence comparisons with the respective oral and vaginal maternal samples. A simplified technique using a strain-specific primer in a more sensitive nested PCR was subsequently developed to analyse ten paired neonatal-maternal samples. Analysing the variable fragment of the ITS region allowed the identification of F. nucleatum subsp. polymorphum from an oral origin as potentially being involved in neonatal infections. Using a strain-specific primer, the F. nucleatum subsp. polymorphum strain was detected in both neonatal gastric aspirates and maternal oral samples in cases of preterm birth from mothers presenting with localized periodontal pockets. Interestingly, the same strain was not present in the vaginal sample of any case investigated. The 16S-23S rRNA gene ITS can be a useful tool to determine the origin of F. nucleatum. The results of this study strongly indicate that F. nucleatum subsp. polymorphum of oral origin could be involved with pregnancy complications.

Quantitative proteomic analysis of the effect of fluoride on the acquired enamel pellicle

The acquired enamel pellicle (AEP) is a thin film formed by the selective adsorption of salivary proteins onto the enamel surface of teeth. The AEP forms a critical interface between the mineral phase of teeth (hydroxyapatite) and the oral microbial biofilm. This biofilm is the key feature responsible for the development of dental caries. Fluoride on enamel surface is well known to reduce caries by reducing the solubility of enamel to acid. Information on the effects of fluoride on AEP formation is limited. This study aimed to investigate the effects of fluoride treatment on hydroxyapatite on the subsequent formation of AEP. In addition, this study pioneered the use of label-free quantitative proteomics to better understand the composition of AEP proteins. Hydroxyapatite discs were randomly divided in 4 groups (n = 10 per group). Each disc was exposed to distilled water (control) or sodium fluoride solution (1, 2 or 5%) for 2 hours. Discs were then washed and immersed in human saliva for an additional 2 hours. AEP from each disc was collected and subjected to liquid chromatography electrospray ionization mass spectrometry for protein identification, characterization and quantification. A total of 45 proteins were present in all four groups, 12 proteins were exclusively present in the control group and another 19 proteins were only present in the discs treated with 5% sodium fluoride. Relative proteomic quantification was carried out for the 45 proteins observed in all four groups. Notably, the concentration of important salivary proteins, such as statherin and histatin 1, decrease with increasing levels of fluoride. It suggests that these proteins are repulsed when hydroxyapatite surface is coated with fluoride. Our data demonstrated that treatment of hydroxyapatite with fluoride (at high concentration) qualitatively and quantitatively modulates AEP formation, effects which in turn will likely impact the formation of oral biofilms.

Structural characterization of a new statherin from pig parotid granules

This study describes the identification and structural characterization of Sus scrofa statherin. HPLC-electrospray ionization mass spectrometry analysis on pig parotid secretory granule extracts evidenced a peptide with a molecular mass value of 5381.1 +/- 0.6 Da and its truncated form, devoid of the C-terminal Ala residue, with a molecular mass value of 5310.1 +/- 0.6 Da. The complete sequence of pig statherin gene was determined by sequencing the full-length cDNA obtained by rapid amplification of cDNA ends. The gene is 549 base pairs long and contains an open reading frame of 185 nucleotides, encoding a 42-amino acid secretory polypeptide with a signal peptide of 19 residues. This sequence presents some typical features of the four statherins characterized till now, showing the highest degree of amino acid identity with bovine (57%) and human statherin (39%). Pig statherin is mono-phoshorylated on Ser-3, while primate statherins already characterized are di-phosphorylated on Ser-2 and Ser-3. This difference, probably connected to the Asp-4 --> Glu substitution, suggests the involvement of the Golgi-casein kinase, which strictly recognizes the SX(E/pS) consensus sequence.

Fusobacterium nucleatum envelope protein FomA is immunogenic and binds to the salivary statherin-derived peptide

We have previously shown that one of the minimal active regions of statherin, a human salivary protein, for binding to Fusobacterium nucleatum is a YQPVPE amino acid sequence. In this study, we identified the FomA protein of F. nucleatum, which is responsible for binding to the statherin-derived YQPVPE peptide. Overlay analysis showed that a 40-kDa protein of the F. nucleatum cell envelope (40-kDa CE) specifically bound to the YQPVPE peptide. The equilibrium association constant between the affinity-purified 40-kDa CE and the YQPVPE peptide was 4.30 x 10(6). Further, the purity and amino acid sequence analyses of the purified 40-kDa CE revealed approximately 98.7% (wt/wt) purity and a high degree of homology with FomA, a major porin protein of F. nucleatum. Thus, a FomA-deficient mutant failed to bind to the YQPVPE peptide. In addition, increased levels of a FomA-specific mucosal IgA antibody (Ab) and plasma IgG and IgA Abs were seen only in mice immunized nasally with cholera toxin (CT) and the purified 40-kDa FomA protein. Interestingly, saliva from mice that received FomA plus CT as a mucosal adjuvant nasally prevented in vitro binding of F. nucleatum to statherin-coated polyvinyl chloride plates. Taken together, these results suggest that induction of specific immunity to the 40-kDa FomA protein of F. nucleatum, which specifically binds to the statherin-derived peptide, may be an effective tool for preventing the formation of F. nucleatum biofilms in the oral cavity.

Autoaggregation response of Fusobacterium nucleatum

Fusobacterium nucleatum is a gram-negative oral bacterial species associated with periodontal disease progression. This species is perhaps best known for its ability to adhere to a vast array of other bacteria and eukaryotic cells. Numerous studies of F. nucleatum have examined various coaggregation partners and inhibitors, but it is largely unknown whether these interactions induce a particular genetic response. We tested coaggregation between F. nucleatum ATCC strain 25586 and various species of Streptococcus in the presence of a semidefined growth medium containing saliva. We found that this condition could support efficient coaggregation but, surprisingly, also stimulated a similar degree of autoaggregation. We further characterized the autoaggregation response, since few reports have examined this in F. nucleatum. After screening several common coaggregation inhibitors, we identified l-lysine as a competitive inhibitor of autoaggregation. We performed a microarray analysis of the planktonic versus autoaggregated cells and found nearly 100 genes that were affected after only about 60 min of aggregation. We tested a subset of these genes via real-time reverse transcription-PCR and confirmed the validity of the microarray results. Some of these genes were also found to be inducible in cell pellets created by centrifugation. Based upon these data, it appears that autoaggregation activates a genetic program that may be utilized for growth in a high cell density environment, such as the oral biofilm.

The Fusobacterium nucleatum outer membrane protein RadD is an arginine-inhibitable adhesin required for inter-species adherence and the structured architecture of multispecies biofilm

A defining characteristic of the suspected periodontal pathogen Fusobacterium nucleatum is its ability to adhere to a plethora of oral bacteria. This distinguishing feature is suggested to play an important role in oral biofilm formation and pathogenesis, with fusobacteria proposed to serve as central 'bridging organisms' in the architecture of the oral biofilm bringing together species which would not interact otherwise. Previous studies indicate that these bacterial interactions are mediated by galactose- or arginine-inhibitable adhesins although genetic evidence for the role and nature of these proposed adhesins remains elusive. To characterize these adhesins at the molecular level, the genetically transformable F. nucleatum strain ATCC 23726 was screened for adherence properties, and arginine-inhibitable adhesion was evident, while galactose-inhibitable adhesion was not detected. Six potential arginine-binding proteins were isolated from the membrane fraction of F. nucleatum ATCC 23726 and identified via mass spectroscopy as members of the outer membrane family of proteins in F. nucleatum. Inactivation of the genes encoding these six candidates for arginine-inhibitable adhesion and two additional homologues revealed that only a mutant derivative carrying an insertion in Fn1526 (now designated as radD) demonstrated significantly decreased co-aggregation with representatives of the gram-positive 'early oral colonizers'. Lack of the 350 kDa outer membrane protein encoded by radD resulted in the failure to form the extensive structured biofilm observed with the parent strain when grown in the presence of Streptococcus sanguinis ATCC 10556. These findings indicate that radD is responsible for arginine-inhibitable adherence of F. nucleatum and provides definitive molecular evidence that F. nucleatum adhesins play a vital role in inter-species adherence and multispecies biofilm formation.

Laboratory maintenance of fusobacteria

This unit describes routine laboratory handling of fusobacteria. Different media that can be used to grow or enrich Fusobacterium nucleatum and other species of this genus are described. The growth and stock conditions as well as the susceptibility of F. nucleatum to oxygen in a pure culture are also discussed.

The structure, dynamics, and energetics of protein adsorption-lessons learned from adsorption of statherin to hydroxyapatite

Proteins are found to be involved in interaction with solid surfaces in numerous natural events. Acidic proteins that adsorb to crystal faces of a biomineral to control the growth and morphology of hard tissue are only one example. Deducing the mechanisms of surface recognition exercised by proteins has implications to osteogenesis, pathological calcification and other proteins functions at their adsorbed state. Statherin is an enamel pellicle protein that inhibits hydroxyapatite nucleation and growth, lubricates the enamel surface, and is recognized by oral bacteria in periodontal diseases. Here, we highlight some of the insights we obtained recently using both thermodynamic and solid state NMR measurements to the adsorption process of statherin to hydroxyapatite. We combine macroscopic energy characterization with microscopic structural findings to present our views of protein adsorption mechanisms and the structural changes accompanying it and discuss the implications of these studies to understanding the functions of the protein adsorbed to the enamel surfaces.

Association of a high-molecular weight arginine-binding protein of Fusobacterium nucleatum ATCC 10953 with adhesion to secretory immunoglobulin A and coaggregation with Streptococcus cristatus

INTRODUCTION

Fusobacterium nucleatum coaggregates with a diverse range of bacterial species, and binds to host tissues and proteins such as immunoglobulin. These interactions may support the attachment of a variety of organisms to oral surfaces and can facilitate the invasion of soft tissues. We hypothesized that coaggregation with streptococci and immunoglobulin binding may occur by a common adhesin sensitive to l-arginine.

METHODS

Repeated mixing of F. nucleatum with non-immune secretory immunoglobulin A (S-IgA) and recovery of non-agglutinating cells isolated a spontaneous mutant (isolate 21) of F. nucleatum that was defective in S-IgA binding. Wild-type and mutant F. nucleatum were compared by coaggregation and adhesion assays.

RESULTS

Isolate 21 exhibited significantly reduced S-IgA binding and coaggregation with oral streptococci but not with Porphyromonas gingivalis. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed that the mutant was deficient compared to wild-type for a single protein of approximately 360 kilodaltons. The corresponding protein was isolated from wild-type F. nucleatum protein preparations by coprecipitation with arginine-agarose beads. This protein was able to bind both Streptococcus cristatus and S-IgA. Mass spectrometry analysis indicated that this protein was closely related to putative autotransporter proteins in other F. nucleatum strains and was a 100% match to the deduced amino acid sequence of a 10,638-base-pair open reading frame in the incomplete genome sequence of F. nucleatum ATCC 10,953. Peptides identified by MS-MS analysis spanned most of the predicted amino acid sequence, suggesting that the mature protein is not subject to postsecretory cleavage.

CONCLUSION

Coaggregation represents a novel function within the autotransporter class of proteins, which are often associated with virulence.

Co-adhesion and biofilm formation by Fusobacterium nucleatum in response to growth pH

Fusobacterium nucleatum is a Gram-negative anaerobic organism considered to play an important role in the progression of periodontal disease and is commonly found in clinical infections of other body sites. Apart from its metabolic versatility, its cell-surface properties enable it to attach to epithelial cells, collagen, gingival epithelial cells and other bacterial genera, but not with other Fusobacteria. The development of periodontitis is associated with a rise in pH in the gingival sulcus to around 8.5, and this is thought to occur by the catabolism of proteins supplied by gingival crevicular fluid. F. nucleatum is commonly isolated from diseased sites and has also been shown to survive in root canal systems at pH 9.0 after Ca(OH)(2) treatment. In order to survive hostile environmental conditions, such as nutrient deprivation and fluctuating temperature and pH, bacteria form biofilms, which are usually made up of multi-species co-aggregates. We have grown F. nucleatum in a chemostat at a growth rate consistent with that of oral bacteria in vivo and report that, at a growth pH of 8.2, F. nucleatum co-adheres and forms a homogeneous biofilm. Cell-surface hydrophobicity was determined in planktonic and co-adhering cells to characterise the interfacial interactions associated with the response to pH. Cell-surface hydrophobicity was found to increase at pH 8.2 and this was also associated with a decrease in the levels of intracellular polyglucose (IP) and an observed change in the bacterial cell morphology. To our knowledge, these results represent the first study in which F. nucleatum has been shown to co-adhere and form a biofilm, which may be important in the organism's persistence during the transition from health to disease in vivo.

Folding of the C-terminal bacterial binding domain in statherin upon adsorption onto hydroxyapatite crystals

Statherin is an enamel pellicle protein that inhibits hydroxyapatite (HAP) nucleation and growth, lubricates the enamel surface, and is recognized by oral bacteria in periodontal diseases. We report here from solid-state NMR measurements that the protein's C-terminal region folds into an alpha-helix upon adsorption to HAP crystals. This region contains the binding sites for bacterial fimbriae that mediate bacterial cell adhesion to the surface of the tooth. The helical segment is shown through long-range distance measurements to fold back onto the intermediate region (residues Y16-P28) defining the global fold of the protein. Statherin, previously shown to be unstructured in solution, undergoes conformation selection on its substrate mineral surface. This surface-induced folding of statherin can be related to its functionality in inhibiting HAP crystal growth and can explain how oral pathogens selectively recognize HAP-bound statherin.

Fusobacterium nucleatum transports noninvasive Streptococcus cristatus into human epithelial cells

Analysis of human buccal epithelial cells frequently reveals an intracellular polymicrobial consortium of bacteria. Although several oral bacteria have been demonstrated to invade cultured epithelial cells, several others appear unable to internalize. We hypothesized that normally noninvasive bacteria may gain entry into epithelial cells via adhesion to invasive bacteria. Fusobacterium nucleatum is capable of binding to and invading oral epithelial cells. By contrast, Streptococcus cristatus binds weakly to host cells and is not internalized. F. nucleatum and S. cristatus coaggregate strongly via an arginine-sensitive interaction. Coincubation of KB or TERT-2 epithelial cells with equal numbers of F. nucleatum and S. cristatus bacteria led to significantly increased numbers of adherent and internalized streptococci. F. nucleatum also promoted invasion of KB cells by other oral streptococci and Actinomyces naeslundii. Dissection of fusobacterial or streptococcal adhesive interactions by using sugars, amino acids, or antibodies demonstrated that this phenomenon is due to direct attachment of S. cristatus to adherent and invading F. nucleatum. Inhibition of F. nucleatum host cell attachment and invasion with galactose, or fusobacterial-streptococcal coaggregation by the arginine homologue l-canavanine, abrogated the increased S. cristatus adhesion to, and invasion of, host cells. In addition, polyclonal antibodies to F. nucleatum, which inhibited fusobacterial attachment to both KB cells and S. cristatus, significantly decreased invasion by both species. Similar decreases were obtained when epithelial cells were pretreated with cytochalasin D, staurosporine, or cycloheximide. These studies indicate that F. nucleatum may facilitate the colonization of epithelial cells by bacteria unable to adhere or invade directly.

Identification and characterization of a novel adhesin unique to oral fusobacteria

Fusobacterium nucleatum is a gram-negative anaerobe that is prevalent in periodontal disease and infections of different parts of the body. The organism has remarkable adherence properties, binding to partners ranging from eukaryotic and prokaryotic cells to extracellular macromolecules. Understanding its adherence is important for understanding the pathogenesis of F. nucleatum. In this study, a novel adhesin, FadA (Fusobacterium adhesin A), was demonstrated to bind to the surface proteins of the oral mucosal KB cells. FadA is composed of 129 amino acid (aa) residues, including an 18-aa signal peptide, with calculated molecular masses of 13.6 kDa for the intact form and 12.6 kDa for the secreted form. It is highly conserved among F. nucleatum, Fusobacterium periodonticum, and Fusobacterium simiae, the three most closely related oral species, but is absent in the nonoral species, including Fusobacterium gonidiaformans, Fusobacterium mortiferum, Fusobacterium naviforme, Fusobacterium russii, and Fusobacterium ulcerans. In addition to FadA, F. nucleatum ATCC 25586 and ATCC 49256 also encode two paralogues, FN1529 and FNV2159, each sharing 31% identity with FadA. A double-crossover fadA deletion mutant, F. nucleatum 12230-US1, was constructed by utilizing a novel sonoporation procedure. The mutant had a slightly slower growth rate, yet its binding to KB and Chinese hamster ovarian cells was reduced by 70 to 80% compared to that of the wild type, indicating that FadA plays an important role in fusobacterial colonization in the host. Furthermore, due to its uniqueness to oral Fusobacterium species, fadA may be used as a marker to detect orally related fusobacteria. F. nucleatum isolated from other parts of the body may originate from the oral cavity.

Protein secretion systems in Fusobacterium nucleatum: Genomic identification of Type 4 piliation and complete Type V pathways brings new insight into mechanisms of pathogenesis

Recent genomic analyses of the two sequenced strains F. nucleatum subsp. nucleatum ATCC 25586 and F. nucleatum subsp. vincentii ATCC 49256 suggested that the major protein secretion systems were absent. However, such a paucity of protein secretion systems is incongruous with F. nucleatum pathogenesis. Moreover, the presence of one or more such systems has been described for every other Gram-negative organism sequenced to date. In this investigation, the question of protein secretion in F. nucleatum was revisited. In the current study, the absence in F. nucleatum of a twin-arginine translocation system (TC #2.A.64.), a Type III secretion system (TC #3.A.6.), a Type IV secretion system (TC #3.A.7.) and a chaperone/usher pathway (TC #1.B.11.) was confirmed. However, contrary to previous findings, our investigations indicated that a Type I protein secretion system was also absent from F. nucleatum. In contrast, members of the holin family (TC #1.E) and the machinery required for a Type 4 piliation/fimbriation system (TC #3.A.15.2.) were identified using a variety of bioinformatic tools. Furthermore, a complete range of proteins resembling members of the Type V secretion pathway, i.e., the Type Va (autotransporter; TC #1.B.12.), Type Vb (two-partner secretion system; TC #1.B.20.) and Type Vc (YadA-like trimeric autotransporter; TC #1.B.42.), was found. This work provides new insight into the protein secretion and virulence mechanisms of F. nucleatum.

Active domains of salivary statherin on apatitic surfaces for binding to Fusobacterium nucleatum cells

Fusobacterium nucleatum can bind to saliva-coated tooth surfaces. However, the nature of the domains of salivary protein that interact with F. nucleatum remains unclear. The ability of individual proteins in human submandibular-sublingual saliva (HSMSL) to bind F. nucleatum cells was examined by dot blot assay; statherin displayed the strongest binding activity. Statherin binding sites were determined based on binding of (125)I-labelled F. nucleatum to statherin-coated hydroxyapatite (sHAP) beads via inhibition assays using synthetic analogous peptide fragments of whole statherin. Analogous peptides corresponding to residues 19-26 and 32-39 of statherin inhibited binding by 77 % and 68 %, respectively. Synthetic peptides were also prepared by serial deletions of individual residues from N- and C-termini of the peptides GPYQPVPE (aa 19-26) and QPYQPQYQ (aa 32-39). The inhibitory effects of peptides YQPVPE (aa 21-26) and PYQPQYQ (aa 33-39) were very similar to those of GPYQPVPE and QPYQPQYQ, respectively. However, additional deletion of residues resulted in significant reduction of the inhibitory effect. Alanine-scan analysis of YQPVPE revealed that all tested peptides retained inhibitory activity; only YAPVPE exhibited significantly decreased inhibitory activity. These findings suggest that YQPVPE and PYQPQYQ may represent the minimal active segments of statherin for binding to F. nucleatum; moreover, Gln may be a key amino acid in the active segment.

Statherin is an in vivo pellicle constituent: identification and immuno-quantification

Recently, we demonstrated that anti-statherin monoclonal antibodies could be generated upon immunisation of mice with in vivo formed human acquired enamel pellicle, indicating that statherin is a constituent of pellicle. To gain insight in the in vivo adsorption behaviour of statherin we tested the abundance of statherin in pellicle and investigated the relationship between statherin and protein levels in salivary secretions and pellicle using a capture ELISA. Statherin levels were approximately 20-fold higher in parotid and submandibular-sublingual secretions than in cleared whole saliva supernatant or pellicle, suggesting the rapid degradation of statherin in the oral cavity. A strong positive correlation was observed between statherin and protein levels in pellicle but not in saliva indicating that statherin and protein adsorption to pellicle are related processes. This indicates that statherin represents the integral part of proteins that constitute the pellicle structure and may play a key role in its formation.

Salivary statherin peptide-binding epitopes of commensal and potentially infectious Actinomyces spp. delineated by a hybrid peptide construct

Adhesion of microorganisms to host receptor molecules such as salivary statherin molecules is a common event in oral microbial colonization. Here we used a hybrid peptide construct (with both a hydroxyapatite-binding portion and a test peptide portion) to map the interaction of Actinomyces species (and Candida albicans) with statherin. Adhesion to hybrid peptides and truncated statherin variants revealed three binding types, types I to III. (i) Type I strains of rat, hamster, and human infection origins bound C-terminal-derived QQYTF and PYQPQY peptides. The QQYTF peptide inhibited statherin binding for some strains but not for others. (ii) Type II strains of human and monkey tooth origins bound middle-region-derived YQPVPE and QPLYPQ peptides. Neither strain was inhibited by soluble peptides. (iii) Type III strains of human infection origins (and C. albicans) did not bind to either statherin-derived peptides or truncated statherin. Moreover, the type I strains inhibited by QQYTF were also inhibited by TF and QAATF peptides and were detached from statherin by the same peptides. In conclusion, it is suggested that commensal and potentially infectious microorganisms bind middle or C-terminal statherin differently and that other microbes might require discontinuous epitopes.

Bacteria-binding plasma proteins in pellicles formed on hydroxyapatite in vitro and on teeth in vivo

Previous studies on dental pellicle formation and bacterial adherence have focussed on saliva and its components. The tooth surface is, however, also exposed to the plasma-derived crevicular fluid. In the present study, (i). plasma proteins in in vitro and in vivo pellicles were examined using sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE), immunoblotting and image analysis and (ii). the adherence of periodontopathogenic bacteria to experimental plasma and saliva pellicles was examined using radio-labelled bacteria and liquid scintillation counting. The plasma components fibrinogen, fibronectin, albumin and IgG were incorporated from plasma in the experimental pellicle and mediated the adherence of Porphyromonas gingivalis, Fusobacterium nucleatum and Actinomyces naeslundii. These proteins were also readily detected in in vivo pellicles and were found to a higher extent in pellicles formed at the gingival part of the tooth surface than at the incisal part.

Ultrastructural analysis of structural framework in dental plaque developing on synthetic carbonate apatite applied to human tooth surfaces

This study focused on determining the structural framework by oral microbiota in supragingival plaque on a carbonate apatite film applied to human tooth surfaces. The sequential phases of plaque formation over a 3-wk period were found to be equivalent to those previously reported for natural tooth surfaces. Scanning electron microscopy of specimens prepared by vertical sectioning demonstrated the organization of two types of framework between certain genera of initial and secondary colonizers in the pre- and post-organization phases, respectively. The initial colonizers in the pre-organization phase were of a coccoid type, while colonizers in the post-organization phase were of a bacillary type. Secondary colonizers, filamentous cells, were common to both frameworks. Transmission electron microscopy using freeze-substitution and immunohistochemistry demonstrated two types of coaggregation, fibril- and saliva-mediated modes, among the plaque microbiota. Coaggregation between microbiota, which organized the framework, showed a tendency to occur in the fibril-mediated mode, and the filamentous secondary colonizers were characterized by inducing multigeneric coaggregation. The present findings indicate that a structural framework and specific cells to form this framework are essential for plaque formation.

Spatial arrangements and associative behavior of species in an in vitro oral biofilm model

The spatial arrangements and associative behavior of Actinomyces naeslundii, Veillonella dispar, Fusobacterium nucleatum, Streptococcus sobrinus, and Streptococcus oralis strains in an in vitro model of supragingival plaque were determined. Using species-specific fluorescence-labeled antibodies in conjunction with confocal laser scanning microscopy, the volumes and distribution of the five strains were assessed during biofilm formation. The volume-derived cell numbers of each strain correlated well with respective culture data. Between 15 min and 64 h, populations of each strain increased in a manner reminiscent of batch growth. The microcolony morphologies of all members of the consortium and their distributions within the biofilm were characterized, as were interspecies associations. Biofilms formed 15 min after inoculation consisted principally of single nonaggregated cells. All five strains adhered strongly to the saliva-conditioned substratum, and therefore, coadhesion played no role during the initial phase of biofilm formation. This observation does not reflect the results of in vitro coaggregation of the five strains, which depended upon the nature of the suspension medium. While the possibility cannot be excluded that some interspecies associations observed at later stages of biofilm formation were initiated by coadhesion, increase in bacterial numbers appeared to be largely a growth phenomenon regulated by the prevailing cultivation conditions.

Attachment of Fusobacterium nucleatum PK1594 to mammalian cells and its coaggregation with periodontopathogenic bacteria are mediated by the same galactose-binding adhesin

It has been shown that Fusobacterium nucleatum PK1594 coaggregates with Prophyromonas gingivalis PK1924 through a galactose-binding adhesin. In the present study, attachment of F. nucleatum PK1594 to a variety of mammalian cells was characterized. F. nucleatum PK1594 attached to all eukaryotic cells tested, including human buccal epithelial cells, gingival and periodontal ligament fibroblasts, HeLa cells and murine lymphocytes, macrophages, and polymorphonuclear leukocytes. These attachments were (i) inhibited by galactose, lactose and N-acetylgalactosamine and (ii) inhibited by monoclonal antibody specific for the galactose-binding adhesin of F. nucleatum PK1594. In addition, a coaggregation-defective mutant of F. nucleatum PK1594 (PK2172), which does not exhibit galactose binding activity, did not attach to the mammalian cells. Coaggregation of F. nucleatum PK1594 with P. gingivalis PK 1924 and Actinobacillus actinomycetemcomitans JP2, but not with other bacteria, showed a similar pattern with sugars, monoclonal antibody, and the adhesin-deficient mutant. The results suggest that the attachment of F. nucleatum PK1594 to mammalian cells and its coaggregation with periodontal pathogens are mediated by the same galactose-binding adhesin.

Fusobacterium nucleatum involvement in adult periodontitis and possible modification of strain classification

BACKGROUND

This investigation was designed to evaluate the involvement of Fusobacterium nucleatum clinical strains in adult periodontitis by subspecies and expression of hemagglutination activity.

METHODS

Forty-nine Fusobacterium strains were isolated from 40 sites in 40 subjects presenting with adult periodontitis. F. nucleatum subspecies identification was based on the electrophoretic migration of glutamate dehydrogenase and 2-oxoglutarate reductase. Hemagglutination activity and inhibition by galactose were tested on sheep erythrocytes.

RESULTS

The 49 isolates belonged to the F. nucleatum species with a predominance of the nucleatum (34.7%) followed by the vincentii (26.5%) subspecies. In parallel, 71% of the strains belonging to the nucleatum subspecies were preferentially associated with Porphyromonas gingivalis. Prevotella intermedia/nigrescens detection was essentially correlated with identification of Fusobacterium nucleatum subspecies vincentii. No correlation was established between any particular subspecies and the pathogenicity factors tested (hemagglutination and production of short-chain fatty acids). On the other hand, significant predominance (65%, P= 0.017) of strongly hemagglutinating strains (titre > or =8 U) was observed in the sites where Porphyromonas gingivalis, Prevotella intermedia/nigrescens and/or Campylobacter rectus were not detected. These strains also showed higher butyric acid production.

CONCLUSION

The importance of the adherence factors for Fusobacterium nucleatum strains and their multimodal aspect may indicate a higher pathogenicity or a higher involvement of certain strains and could lead to a classification of these strains, which is more closely related to their implication in the development of periodontal disease.

beta-lactamase production and antimicrobial susceptibility of oral heterogeneous Fusobacterium nucleatum populations in young children

Oral Fusobacterium nucleatum populations from 20 young, healthy children were examined for beta-lactamase production. Ten children (50%) harbored, altogether, 25 beta-lactamase-positive F. nucleatum isolates that were identified as F. nucleatum subsp. polymorphum, F. nucleatum subsp. nucleatum, and F. nucleatum subsp. vincentii (J. L. Dzink, M. T. Sheenan, and S. S. Socransky, Int. J. Syst. Bacteriol. 40:74-78, 1990). In vitro susceptibility of these beta-lactamase-producing and 26 non-beta-lactamase-producing F. nucleatum isolates was tested with penicillin G, amoxicillin-clavulanic acid, tetracycline hydrochloride, metronidazole, trovafloxacin, and azithromycin. Except for penicillin G, the antimicrobials exhibited good activity against all F. nucleatum isolates.

Delineation of conformational preferences in human salivary statherin by 1H, 31P NMR and CD studies: sequential assignment and structure-function correlations

Membrane-induced solution structure of human salivary statherin, a 43 amino acid residue acidic phosphoprotein, has been investigated by two-dimensional proton nuclear magnetic resonance (2D 1H NMR) spectroscopy. NMR assignments and structural analysis of this phosphoprotein was accomplished by analyzing the pattern of sequential and medium range NOEs, alphaCH chemical shift perturbations and deuterium exchange measurements of the amide proton resonances. The NMR data revealed three distinct structural motifs in the molecule: (1) an alpha-helical structure at the N-terminal domain comprising Asp1-Tyr16, (2) a polyproline type II (PPII) conformation predominantly occurring at the middle proline-rich domain spanning Gly19-Gln35, and (3) a 3(10)-helical structure at the C-terminal Pro36-Phe43 sequence. Presence of a few weak dalphaN(i,i+2) NOEs suggests that N-terminus also possesses minor population of 3(10)-helical conformation. Of the three secondary structural elements, helical structure formed by the N-terminal residues, Asp1-Ile11 appears to be more rigid as observed by the relatively very slow exchange of amide hydrogens of Glu5-Ile11. 31P NMR experiments clearly indicated that N-terminal domain of statherin exists mainly in disordered state in water whereas, upon addition of structure stabilizing co-solvent, 2,2,2-trifluorethanol (TFE), it showed a strong propensity for helical conformation. Calcium ion interaction studies suggested that the disordered N-terminal region encompassing the two vicinal phosphoserines is essential for the binding of calcium ions in vivo. Results from the circular dichroism (CD) experiments were found to be consistent with and complimentary to the NMR data and provided an evidence that non-aqueous environment such as TFE, could induce the protein to fold into helical conformation. The findings that the statherin possesses blended solvent sensitive secondary structural elements and the requirement of non-structured N-terminal region under aqueous environment in calcium ion interaction may be invaluable to understand various physiological functions of statherin in the oral fluid.

Oral microbial ecology and the role of salivary immunoglobulin A

In the oral cavity, indigenous bacteria are often associated with two major oral diseases, caries and periodontal diseases. These diseases seem to appear following an imbalance in the oral resident microbiota, leading to the emergence of potentially pathogenic bacteria. To define the process involved in caries and periodontal diseases, it is necessary to understand the ecology of the oral cavity and to identify the factors responsible for the transition of the oral microbiota from a commensal to a pathogenic relationship with the host. The regulatory forces influencing the oral ecosystem can be divided into three major categories: host related, microbe related, and external factors. Among host factors, secretory immunoglobulin A (SIgA) constitutes the main specific immune defense mechanism in saliva and may play an important role in the homeostasis of the oral microbiota. Naturally occurring SIgA antibodies that are reactive against a variety of indigenous bacteria are detectable in saliva. These antibodies may control the oral microbiota by reducing the adherence of bacteria to the oral mucosa and teeth. It is thought that protection against bacterial etiologic agents of caries and periodontal diseases could be conferred by the induction of SIgA antibodies via the stimulation of the mucosal immune system. However, elucidation of the role of the SIgA immune system in controlling the oral indigenous microbiota is a prerequisite for the development of effective vaccines against these diseases. The role of SIgA antibodies in the acquisition and the regulation of the indigenous microbiota is still controversial. Our review discusses the importance of SIgA among the multiple factors that control the oral microbiota. It describes the oral ecosystems, the principal factors that may control the oral microbiota, a basic knowledge of the secretory immune system, the biological functions of SIgA, and, finally, experiments related to the role of SIgA in oral microbial ecology.

Identification of a Fusobacterium nucleatum PK1594 galactose-binding adhesin which mediates coaggregation with periopathogenic bacteria and hemagglutination

Attachment of Fusobacterium nucleatum to various oral surfaces is mediated by several adhesins anchored on its outer surface. Monoclonal antibodies (MAbs) were prepared and used to identify the putative galactose-binding adhesin of F. nucleatum PK1594. Four unique MAbs, 8G7, 26B9, 28G11, and 29D4, were isolated on the basis of their ability to inhibit coaggregation of F. nucleatum PK1594 with Porphyromonas gingivalis PK1924. All four MAbs were also capable of inhibiting galactose-inhibitable interactions of F. nucleatum PK1594 with other oral gram-negative bacteria and with erythrocytes. Preincubation of F. nucleatum PK1594 with MAb 26B9 or its Fab fragments at concentrations lower than 1 microg/ml resulted in complete inhibition of coaggregation with P. gingivalis PK1924 or hemagglutination. F. nucleatum PK1594 surface components prepared by mild sonication or by extracting whole cells with detergents were subjected to Western blot analysis. None of the MAbs were able to recognize any polypeptide in these experiments. Therefore, detergent extracts of F. nucleatum PK1594 surface components were subjected to three experimental procedures: (i) separation by ion-exchange chromatography and testing of fractions for reaction with MAb 26B9 in an enzyme-linked immunosorbent assay (ELISA), (ii) lactose-Sepharose affinity chromatography and testing of the lactose eluate in ELISA with MAb 26B9, and (iii) immunoseparation with either MAb 26B9 or 8G7. Collectively, the results suggest that the putative adhesin is a 30-kDa outer membrane polypeptide which mediates the coaggregation with P. gingivalis PK1924 as well as other galactose-sensitive interactions of F. nucleatum PK1594.

Mechanism of adsorption of human albumin to titanium in vitro

Our previous studies have shown that human albumin is one of the main salivary proteins that adsorb to titanium (Ti). The goal of the present study was to investigate the role of electrostatic interactions in the adsorption of human albumin to Ti-oxide (TiO2) in vitro. The binding profile of human albumin to Ti was analyzed according to an adsorption isotherm. Purified human serum albumin (HSA) was suspended with native, calcium-, magnesium-, or potassium-treated commercially pure Ti powders, at pH 3.0 and 7.0. The amount of unadsorbed protein in the supernatant fluid was measured. The maximum amount of adsorbed albumin was 0.13 mg/1.0 g Ti. The albumin-Ti association constant was 2.77 mL/mg. Pretreatment of Ti with calcium, or magnesium alone, or combined with increasing pH values (3.0-7.0) resulted in augmented adsorption of HSA to Ti. No increase in adsorption was observed following pretreatment of Ti with potassium. These results point to the involvement of electrostatic interactions in the adsorption of HSA to TiO2.

Binding sites of salivary statherin for Porphyromonas gingivalis recombinant fimbrillin

We investigated the binding sites of salivary statherin involved in the interaction with Porphyromonas gingivalis recombinant fimbrillin (r-Fim). Synthetic peptides representing statherin analogs were used to localize the binding domains of statherin. Peptide F4 (residues 29 to 43) significantly bound to r-Fim and inhibited r-Fim binding to statherin-coated hydroxyapatite beads. Successive peptides in which pairs of amino acid residues were deleted starting at the N terminus of peptide F4 were synthesized. Peptide N1 without Leu-29-Tyr-30 had significantly reduced direct binding and inhibition ability. The deletions of residues 31 to 40 had little effect on interaction with r-Fim. The tripeptide N6 representing Tyr-41-Thr-42-Phe-43 retained significant binding to r-Fim. Another set of peptides was synthesized by deleting individual amino acid residues from the C and N termini of peptide F4 to identify functional residues among the five putative functional residues 29, 30, and 41 to 43. Peptide C1 missing Phe-43 lost over 50% of its binding ability. Binding ability was gradually reduced with deletions from the peptides. Peptide C5 (amino acids 31 to 40) weakly affected direct binding and inhibition. Collectively, the results of this study suggests that Leu-29-Tyr-30 and Tyr-41-Thr-42-Phe-43 are important binding regions that mediate the binding of statherin to P. gingivalis fimbrillin.

Taxonomy, biology, and periodontal aspects of Fusobacterium nucleatum

The pathogenic potential of Fusobacterium nucleatum and its significance in the development of periodontal diseases, as well as in infections in other organs, have gained new interest for several reasons. First, this bacterium has the potential to be pathogenic because of its number and frequency in periodontal lesions, its production of tissue irritants, its synergism with other bacteria in mixed infections, and its ability to form aggregates with other suspected pathogens in periodontal disease and thus act as a bridge between early and late colonizers on the tooth surface. Second, of the microbial species that are statistically associated with periodontal disease, F. nucleatum is the most common in clinical infections of other body sites. Third, during the past few years, new techniques have made it possible to obtain more information about F. nucleatum on the genetic level, thereby also gaining better knowledge of the structure and functions of the outer membrane proteins (OMPs). OMPs are of great interest with respect to coaggregation, cell nutrition, and antibiotic susceptibility. This review covers what is known to date about F. nucleatum in general, such as taxonomy and biology, with special emphasis on its pathogenic potential. Its possible relationship to other periodontal bacteria in the development of periodontal diseases and the possible roles played by OMPs are considered.

Taxonomy, biology, and periodontal aspects of Fusobacterium nucleatum

The pathogenic potential of Fusobacterium nucleatum and its significance in the development of periodontal diseases, as well as in infections in other organs, have gained new interest for several reasons. First, this bacterium has the potential to be pathogenic because of its number and frequency in periodontal lesions, its production of tissue irritants, its synergism with other bacteria in mixed infections, and its ability to form aggregates with other suspected pathogens in periodontal disease and thus act as a bridge between early and late colonizers on the tooth surface. Second, of the microbial species that are statistically associated with periodontal disease, F. nucleatum is the most common in clinical infections of other body sites. Third, during the past few years, new techniques have made it possible to obtain more information about F. nucleatum on the genetic level, thereby also gaining better knowledge of the structure and functions of the outer membrane proteins (OMPs). OMPs are of great interest with respect to coaggregation, cell nutrition, and antibiotic susceptibility. This review covers what is known to date about F. nucleatum in general, such as taxonomy and biology, with special emphasis on its pathogenic potential. Its possible relationship to other periodontal bacteria in the development of periodontal diseases and the possible roles played by OMPs are considered.

Adsorption of human salivary proteins to titanium powder. I. Adsorption of human salivary albumin

Titanium (Ti) is among the most widely used implant materials in dentistry today. The success of Ti implants is associated with their interactions with the surrounding tissues and biological fluids. In the present study, the adsorption of salivary proteins to Ti and the effect of calcium (Ca) on this process were investigated. Untreated and Ca-treated Ti powders were suspended in human clarified whole saliva. After incubation, the supernatant fluid was collected for protein analysis. The powders were then washed and resuspended in EDTA to desorb proteins from Ti surfaces. Sodium dodecylsulphate polyacrylamide gel electrophoresis and Bradford protein assay were conducted to determine the concentration and type of proteins that adsorbed onto Ti surfaces. The presence of Ca ions enhanced the adsorption of salivary proteins to Ti. A 66 kDa protein, identified by immunoblotting as albumin, was found as the main adsorbed salivary protein. Adsorption of albumin to Ti pretreated with Ca was significantly greater than to native Ti. The Ca-dependent adsorption process was reversed by EDTA. The data suggest that salivary albumin is one of the main constituents of a salivary biofilm formed on Ti dental implants and its adsorption to Ti surfaces is Ca-dependent. The presence of albumin on Ti dental implants may affect plaque accumulation on the implants and the biocompatibility of Ti implants.

Characteristics of multimodal co-aggregation between Fusobacterium nucleatum and streptococci

The co-aggregation characteristics between Fusobacterium nucleatum and streptococci were examined to clarify the adherence factors participating in the co-aggregation. Nineteen strains of F. nucleatum were classified into 8 groups according to co-aggregation titer and inhibition by L-arginine, L-lysine and N-acetyl-D-galactosamine (or lactose). The inhibition activity was, however, very different from strain to strain. With two fusobacterial strains, two inhibitors, which were both inhibition negative on their own, completely inhibited the co-aggregation when used together in a mixture. In some co-aggregation pairs, the protease treatment of F. nucleatum inactivated one of the adherence factors, and resulted in the change of inhibition characteristics. These results indicate the multimodal co-aggregation of F. nucleatum with streptococci mediated by L-arginine-sensitive, L-lysine-sensitive, N-acetyl-D-galactosamine-sensitive and in some resistant factors, and that the adherence factor or factors participating the co-aggregation change according to the co-aggregation partners.

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.

Binding of host-associated treponeme proteins to collagens and laminin: a possible mechanism of spirochetal adherence to host tissues

The polypeptides of seven strains of human treponemes were investigated by immunoblot analysis for their binding to the human placental collagens and laminin. Of the treponemal polypeptides, eleven polypeptides, 45-kDa, 49-kDa, and 62-kDa polypeptides from T. pallidum ATCC 27087, a 48-kDa polypeptide from T. phagedenis biotype Reiter, 51-kDa and 53-kDa polypeptides from T. vincentii ATCC 35580, 30-kDa, 53-kDa and 63-kDa polypeptides from T. socranskii subsp. buccale ATCC 35534, a 52-kDa polypeptide from T. denticola ATCC 35405, and a 53-kDa polypeptide from T. denticola ATCC 33520 possessed an ability to bind to the laminin, type I, III, IV, or V collagen. An intermediate-sized human oral isolate strain G7201 did not possess any laminin- or collagen-binding polypeptides. Immunoelectron microscopy using intact treponemal cells with a single collagen-binding polypeptide and the corresponding antisera demonstrated that the 51-kDa and 53-kDa polypeptides from T. vincentii, the 53-kDa polypeptide from T. socranskii subsp. buccale ATCC 35534 and the 52-kDa polypeptide from T. denticola ATCC 35405, were outer envelope proteins.