Adsorption of glucosyltransferase to saliva coated hydroxyapatite. Possible mechanism for sucrose dependent bacterial colonization of teeth

Enzymology and Ultrastructure of the in situ Pellicle in Caries-Active and Caries-Inactive Patients

Aim: The present study aimed to evaluate the impact of caries activity on the key enzymes and the ultrastructure of the in situ pellicle. Methods: Pellicle formation was performed on bovine enamel slabs. Intraoral exposure (3, 30, and 120 min) was accomplished by 14 caries-active (DMFS: 22.7 ± 12.1) and 13 caries-inactive (DMFS: 1.5 ± 1.8) individuals. The enzyme activities (lysozyme, peroxidase, α-amylase, glycosyltransferase [GTF]) in the in situ pellicle and resting saliva of all participants were analyzed directly after oral exposure. In addition, a simultaneous visualization of these enzymes, extracellular glucans, and adherent bacteria was carried out. Fluorescent patterns were analyzed with fluorescence labeling and 4′,6-diamidino-2-phenylindole/concanavalin A staining. In addition, the distribution of GTF B, C, and D and the ultrastructure of the pellicle were examined by gold immunolabeling and transmission electron microscopy with selected samples. Results: Enzyme activities of amylase, peroxidase, lysozyme, and GTF were detected on all enamel slabs in an active conformation. Neither exposure time nor caries activity had an impact on the enzyme activities. Gold immunolabeling indicated that the pellicle of caries-active subjects tends to more GTF D molecules. The pellicles of caries-inactive and -active individuals revealed a similar ultrastructural pattern. Conclusion: The enzyme activities as well as the pellicle's ultrastructure are of high similarity in caries-active and -inactive subjects. Thereby, oral exposure time has no significant influence. This reflects a high uniformity during the initial phase of bioadhesion (3-120 min) concerning enzymatic functions. However, there is a tendency towards more GTF D in caries-active individuals.

Norspermidine changes the basic structure of S. mutans biofilm

The factors regulating the assembly of the three-dimensional structure of Streptococcus mutans biofilms remain obscure. Polyamines are essential in biofilm formation of certain bacteria. Norspermidine, an unusual polyamine, has been a controversial polyamine that can lead to biofilm disassembly. However, the role of norspermidine in S. mutans biofilms remains unknown. Therefore, the present study investigated the impact of norspermidine on S. mutans biofilms. The different architectures of the biofilms in norspermidine and control groups indicated that the basic units, bacteria-exopolysaccharide units (BEUs), represent the exopolysaccharide (EPS) and bacterial assembly pattern in S. mutans biofilms. In addition, norspermidine inhibited S. mutans biofilm formation and changed the basic composition of the biofilm, which led to an unusual EPS architecture. Therefore, 5 mM norspermidine inhibited biofilm formation both by decreasing the rate of cell viability and changing the biofilm structure. Gene-expression microarray analysis indicated that the formation of an irregular architecture in the norspermidine group was potentially attributable to the downregulation of elements of the quorum-sensing system (by 2.7–15-fold). The present study suggested that the BEUs are a basic structure of S. mutans biofilm and its assembly is regulated majorly by the quorum-sensing system. Norspermidine can lead to structure change in BEUs by influencing S. mutans quorum-sensing system.

Inhibition of Streptococcus mutans polysaccharide synthesis by molecules targeting glycosyltransferase activity

Glycosyltransferase (Gtf) is one of the crucial virulence factors of Streptococcus mutans, a major etiological pathogen of dental caries. All the available evidence indicates that extracellular polysaccharide, particularly glucans produced by S. mutans Gtfs, contribute to the cariogenicity of dental biofilms. Therefore, inhibition of Gtf activity and the consequential polysaccharide synthesis may impair the virulence of cariogenic biofilms, which could be an alternative strategy to prevent the biofilm-related disease. Up to now, many Gtf inhibitors have been recognized in natural products, which remain the major and largely unexplored source of Gtf inhibitors. These include catechin-based polyphenols, flavonoids, proanthocyanidin oligomers, polymeric polyphenols, and some other plant-derived compounds. Metal ions, oxidizing agents, and some other synthetic compounds represent another source of Gtf inhibitors, with some novel molecules either discovered by structure-based virtual screening or synthesized based on key structures of known inhibitors as templates. Antibodies that inhibit one or more Gtfs have also been developed as topical agents. Although many agents have been shown to possess potent inhibitory activity against glucan synthesis by Gtfs, bacterial cell adherence, and caries development in animal models, much research remains to be performed to find out their mechanism of action, biological safety, cariostatic efficacies, and overall influence on the entire oral community. As a strategy to inhibit the virulence of cariogenic microbes rather than eradicate them from the microbial community, Gtf inhibition represents an approach of great potential to prevent dental caries.

Modulation of Biofilm Exopolysaccharides by the Streptococcus mutans vicX Gene

The cariogenic pathogen Streptococcus mutans effectively utilizes dietary sucrose for the synthesis of exopolysaccharide, which act as a scaffold for its biofilm, thus contributing to its pathogenicity, environmental stress tolerance, and antimicrobial resistance. The two-component system VicRK of S. mutans regulates a group of virulence genes that are associated with biofilm matrix synthesis. Knockout of vicX affects biofilm formation, oxidative stress tolerance, and transformation of S. mutans. However, little is known regarding the vicX-modulated structural characteristics of the exopolysaccharides underlying the biofilm formation and the phenotypes of the vicX mutants. Here, we identified the role of vicX in the structural characteristics of the exopolysaccharide matrix and biofilm physiology. The vicX mutant (SmuvicX) biofilms seemingly exhibited "desertification" with architecturally impaired exopolysaccharide-enmeshed cell clusters, compared with the UA159 strain (S. mutans wild type strain). Concomitantly, SmuvicX showed a decrease in water-insoluble glucan (WIG) synthesis and in WIG/water-soluble glucan (WSG) ratio. Gel permeation chromatography (GPC) showed that the WIG isolated from the SmuvicX biofilms had a much lower molecular weight compared with the UA159 strain indicating differences in polysaccharide chain lengths. A monosaccharide composition analysis demonstrated the importance of the vicX gene in the glucose metabolism. We performed metabolite profiling via (1)H nuclear magnetic resonance spectroscopy, which showed that several chemical shifts were absent in both WSG and WIG of SmuvicX biofilms compared with the UA159 strain. Thus, the modulation of structural characteristics of exopolysaccharide by vicX provides new insights into the interaction between the exopolysaccharide structure, gene functions, and cariogenicity. Our results suggest that vicX gene modulates the structural characteristics of exopolysaccharide associated with cariogenicity, which may be explored as a potential target that contributes to dental caries management. Furthermore, the methods used to purify the EPS of S. mutans biofilms and to analyze multiple aspects of its structure (GPC, gas chromatography-mass spectrometry, and (1)H nuclear magnetic resonance spectroscopy) may be useful approaches to determine the roles of other virulence genes for dental caries prevention.

Comparing the cariogenic species Streptococcus sobrinus and S. mutans on whole genome level

Background

Two closely related species of mutans streptococci, namely Streptococcus mutans and Streptococcus sobrinus, are associated with dental caries in humans. Their acidogenic and aciduric capacity is directly associated with the cariogenic potential of these bacteria. To survive acidic and temporarily harsh conditions in the human oral cavity with hundreds of other microbial co-colonizers as competitors, both species have developed numerous mechanisms for adaptation.

Objectives

The recently published novel genome information for both species is used to elucidate genetic similarities but especially differences and to discuss the impact on cariogenicity of the corresponding phenotypic properties including adhesion, carbohydrate uptake and fermentation, acid tolerance, signaling by two component systems, competence, and oxidative stress resistance.

Conclusions

S. sobrinus can down-regulate the SpaA-mediated adherence to the pellicle. It has a smaller number of two-component signaling systems and bacteriocin-related genes than S. mutans, but all or even more immunity proteins. It lacks the central competence genes comC, comS, and comR. There are more genes coding for glucosyltransferases and a novel energy production pathway formed by lactate oxidase, which is not found in S. mutans. Both species show considerable differences in the regulation of fructan catabolism. However, both S. mutans and S. sobrinus share most of these traits and should therefore be considered as equally virulent with regard to dental caries.

Global analysis of saliva as a source of bacterial genes for insights into human population structure and migration studies

BACKGROUND

The genetic diversity of the human microbiome holds great potential for shedding light on the history of our ancestors. Helicobacter pylori is the most prominent example as its analysis allowed a fine-scale resolution of past migration patterns including some that could not be distinguished using human genetic markers. However studies of H. pylori require stomach biopsies, which severely limits the number of samples that can be analysed. By focussing on the house-keeping gene gdh (coding for the glucose-6-phosphate dehydrogenase), on the virulence gene gtf (coding for the glucosyltransferase) of mitis-streptococci and on the 16S-23S rRNA internal transcribed spacer (ITS) region of the Fusobacterium nucleatum/periodonticum-group we here tested the hypothesis that bacterial genes from human saliva have the potential for distinguishing human populations.

RESULTS

Analysis of 10 individuals from each of seven geographic regions, encompassing Africa, Asia and Europe, revealed that the genes gdh and ITS exhibited the highest number of polymorphic sites (59% and 79%, respectively) and most OTUs (defined at 99% identity) were unique to a given country. In contrast, the gene gtf had the lowest number of polymorphic sites (21%), and most OTUs were shared among countries. Most of the variation in the gdh and ITS genes was explained by the high clonal diversity within individuals (around 80%) followed by inter-individual variation of around 20%, leaving the geographic region as providing virtually no source of sequence variation. Conversely, for gtf the variation within individuals accounted for 32%, between individuals for 57% and among geographic regions for 11%. This geographic signature persisted upon extension of the analysis to four additional locations from the American continent. Pearson correlation analysis, pairwise Fst-cluster analysis as well as UniFrac analyses consistently supported a tree structure in which the European countries clustered tightly together and branched with American countries and South Africa, to the exclusion of Asian countries and the Congo.

CONCLUSION

This study shows that saliva harbours protein-coding bacterial genes that are geographically structured, and which could potentially be used for addressing previously unresolved human migration events.

The exopolysaccharide matrix modulates the interaction between 3D architecture and virulence of a mixed-species oral biofilm

Virulent biofilms are responsible for a range of infections, including oral diseases. All biofilms harbor a microbial-derived extracellular-matrix. The exopolysaccharides (EPS) formed on tooth-pellicle and bacterial surfaces provide binding sites for microorganisms; eventually the accumulated EPS enmeshes microbial cells. The metabolic activity of the bacteria within this matrix leads to acidification of the milieu. We explored the mechanisms through which the Streptococcus mutans-produced EPS-matrix modulates the three-dimensional (3D) architecture and the population shifts during morphogenesis of biofilms on a saliva-coated-apatitic surface using a mixed-bacterial species system. Concomitantly, we examined whether the matrix influences the development of pH-microenvironments within intact-biofilms using a novel 3D in situ pH-mapping technique. Data reveal that the production of the EPS-matrix helps to create spatial heterogeneities by forming an intricate network of exopolysaccharide-enmeshed bacterial-islets (microcolonies) through localized cell-to-matrix interactions. This complex 3D architecture creates compartmentalized acidic and EPS-rich microenvironments throughout the biofilm, which triggers the dominance of pathogenic S. mutans within a mixed-species system. The establishment of a 3D-matrix and EPS-enmeshed microcolonies were largely mediated by the S. mutans gtfB/gtfC genes, expression of which was enhanced in the presence of Actinomyces naeslundii and Streptococcus oralis. Acidic pockets were found only in the interiors of bacterial-islets that are protected by EPS, which impedes rapid neutralization by buffer (pH 7.0). As a result, regions of low pH (<5.5) were detected at specific locations along the surface of attachment. Resistance to chlorhexidine was enhanced in cells within EPS-microcolony complexes compared to those outside such structures within the biofilm. Our results illustrate the critical interaction between matrix architecture and pH heterogeneity in the 3D environment. The formation of structured acidic-microenvironments in close proximity to the apatite-surface is an essential factor associated with virulence in cariogenic-biofilms. These observations may have relevance beyond the mouth, as matrix is inherent to all biofilms.

Salivary proteins as predictors and controls for oral health

We will provide a translational view of using the recent technological advances in dental research for predicting, monitoring, and preventing the development of oral diseases by investigating the diagnostic and therapeutic role of salivary proteins. New analytical state-of-the-art technologies such as mass spectrometry and atomic force microscopy have revolutionized the field of oral biology. These novel technologies open avenues for a comprehensive characterization of the salivary proteins followed by the evaluation of the physiological functions which could make possible in a near future the development of a new series of synthetic protein for therapeutic propose able to prevent global oral diseases such as periodontal disease and dental caries, the two most prevalent oral diseases in the World.

Natural products in caries research: current (limited) knowledge, challenges and future perspective

Dental caries is the most prevalent and costly oral infectious disease worldwide. Virulent biofilms firmly attached to tooth surfaces are prime biological factors associated with this disease. The formation of an exopolysaccharide-rich biofilm matrix, acidification of the milieu and persistent low pH at the tooth-biofilm interface are major controlling virulence factors that modulate dental caries pathogenesis. Each one offers a selective therapeutic target for prevention. Although fluoride, delivered in various modalities, remains the mainstay for the prevention of caries, additional approaches are required to enhance its effectiveness. Available antiplaque approaches are based on the use of broad-spectrum microbicidal agents, e.g. chlorhexidine. Natural products offer a rich source of structurally diverse substances with a wide range of biological activities, which could be useful for the development of alternative or adjunctive anticaries therapies. However, it is a challenging approach owing to complex chemistry and isolation procedures to derive active compounds from natural products. Furthermore, most of the studies have been focused on the general inhibitory effects on glucan synthesis as well as on bacterial metabolism and growth, often employing methods that do not address the pathophysiological aspects of the disease (e.g. bacteria in biofilms) and the length of exposure/retention in the mouth. Thus, the true value of natural products in caries prevention and/or their exact mechanisms of action remain largely unknown. Nevertheless, natural substances potentially active against virulent properties of cariogenic organisms have been identified. This review focuses on gaps in the current knowledge and presents a model for investigating the use of natural products in anticaries chemotherapy.

Biology of Streptococcus mutans-derived glucosyltransferases: role in extracellular matrix formation of cariogenic biofilms

The importance of Streptococcus mutans in the etiology and pathogenesis of dental caries is certainly controversial, in part because excessive attention is paid to the numbers of S. mutans and acid production while the matrix within dental plaque has been neglected. S. mutans does not always dominate within plaque; many organisms are equally acidogenic and aciduric. It is also recognized that glucosyltransferases from S. mutans (Gtfs) play critical roles in the development of virulent dental plaque. Gtfs adsorb to enamel synthesizing glucans in situ, providing sites for avid colonization by microorganisms and an insoluble matrix for plaque. Gtfs also adsorb to surfaces of other oral microorganisms converting them to glucan producers. S. mutans expresses 3 genetically distinct Gtfs; each appears to play a different but overlapping role in the formation of virulent plaque. GtfC is adsorbed to enamel within pellicle whereas GtfB binds avidly to bacteria promoting tight cell clustering, and enhancing cohesion of plaque. GtfD forms a soluble, readily metabolizable polysaccharide and acts as a primer for GtfB. The behavior of soluble Gtfs does not mirror that observed with surface-adsorbed enzymes. Furthermore, the structure of polysaccharide matrix changes over time as a result of the action of mutanases and dextranases within plaque. Gtfs at distinct loci offer chemotherapeutic targets to prevent caries. Nevertheless, agents that inhibit Gtfs in solution frequently have a reduced or no effect on adsorbed enzymes. Clearly, conformational changes and reactions of Gtfs on surfaces are complex and modulate the pathogenesis of dental caries in situ, deserving further investigation.

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.

Role of a cell surface-associated protein in adherence and dental caries

Insertional inactivation of the Streptococcus mutans spaP gene was used to construct an isogenic mutant (834) of strain NG8 (serotype c) which lacked the major cell surface-associated protein referred to as P1 (15). Results of several studies suggest that P1 is involved in the adherence of S. mutans to saliva-coated apatite surfaces. With an in vitro model system of hydroxyapatite (HA) beads coated with parotid saliva (PS) and additional HA surfaces coated with PS and in situ-formed glucan, it was observed that mutant 834 adhered poorly to the PS/HA surfaces. In contrast, both parent and mutant strains bound to the PS-glucan/HA surface. Groups of intact and desalivated rats were infected with each strain to determine relative capacities to induce dental caries. Rats were fed a highly cariogenic diet containing 56% sucrose for 3 to 5 weeks. Each strain colonized the rodent model and caused similar levels of smooth-surface caries under these dietary conditions. It was concluded that P1 influences the ability of organisms to adhere to saliva-coated surfaces and possibly affects primary colonization of the oral cavity in the absence of a glucan surface but has no effect on glucan-mediated adherence in vitro or in vivo.