Hydroxychalcone inhibitors of Streptococcus mutans glucosyl transferases and biofilms as potential anticaries agents

Tetracyclic homoisoflavanoid (+)-brazilin: a natural product inhibits c-di-AMP-producing enzyme and Streptococcus mutans biofilms

The tenacious biofilms formed by Streptococcus mutans are resistant to conventional antibiotics and current treatments. There is a growing need for novel therapeutics that selectively inhibit S. mutans biofilms while preserving the normal oral microenvironment. Previous studies have shown that increased levels of cyclic di-AMP, an important secondary messenger synthesized by diadenylate cyclase (DAC), favored biofilm formation in S. mutans. Thus, targeting S. mutans DAC is a novel strategy to inhibit S. mutans biofilms. We screened a small NCI library of natural products using a fluorescence detection assay. (+)-Brazilin, a tetracyclic homoisoflavanoid found in the heartwood of Caesalpinia sappan, was identified as one of the 11 "hits," with the greatest reduction (>99%) in fluorescence at 100 µM. The smDAC inhibitory profiles of the 11 "hits" established by a quantitative high-performance liquid chromatography assay revealed that (+)-brazilin had the most enzymatic inhibitory activity (87% at 100 µM) and was further studied to determine its half maximal inhibitory concentration (IC50 = 25.1 ± 0.98 µM). (+)-Brazilin non-competitively inhibits smDAC's enzymatic activity (Ki = 140.0 ± 27.13 µM), as determined by a steady-state Michaelis-Menten kinetics assay. In addition, (+)-brazilin's binding profile with smDAC (Kd = 11.87 µM) was illustrated by a tyrosine intrinsic fluorescence quenching assay. Furthermore, at low micromolar concentrations, (+)-brazilin selectively inhibited the biofilm of S. mutans (IC50 = 21.0 ± 0.60 µM) and other oral bacteria. S. mutans biofilms were inhibited by a factor of 105 in colony-forming units when treated with 50 µM (+)-brazilin. In addition, a significant dose-dependent reduction in extracellular DNA and glucan levels was evident by fluorescence microscopy imaging of S. mutans biofilms exposed to different concentrations of (+)-brazilin. Furthermore, colonization of S. mutans on a representative model of enamel using suspended hydroxyapatite discs showed a >90% reduction with 50 µM (+)-brazilin. In summary, we have identified a drug-like natural product inhibitor of S. mutans biofilm that not only binds to smDAC but can also inhibit the function of smDAC. (+)-Brazilin could be a good candidate for further development as a potent therapeutic for the prevention and treatment of dental caries.IMPORTANCEThis study represents a significant advancement in our understanding of potential therapeutic options for combating cariogenic biofilms produced by Streptococcus mutans. The research delves into the use of (+)-brazilin, a natural product, as a potent inhibitor of Streptococcus mutans' diadenylate cyclase (smDAC), an enzyme crucial in the formation of biofilms. The study establishes (+)-brazilin as a non-competitive inhibitor of smDAC while providing initial insights into its binding mechanism. What makes this finding even more promising is that (+)-brazilin does not limit its inhibitory effects to S. mutans alone. Instead, it demonstrates efficacy in hindering biofilms in other oral bacteria as well. The broader spectrum of anti-biofilm activity suggests that (+)-brazilin could potentially serve as a versatile tool in a natural product-based treatment for combating a range of conditions caused by resilient biofilms.

Flavonoids effects against bacteria associated to periodontal disease and dental caries: a scoping review

This scoping review focused on exploring the efficacy of flavonoids against bacteria associated with dental caries and periodontal diseases. Inclusion criteria comprise studies investigating the antibacterial effects of flavonoids against bacteria linked to caries or periodontal diseases, both pure or diluted in vehicle forms. The search, conducted in August 2023, in databases including PubMed/MEDLINE, Scopus, Web of Science, Embase, LILACS, and Gray Literature. Out of the initial 1125 studies, 79 met the inclusion criteria, majority in vitro studies. Prominent flavonoids tested included epigallocatechin-gallate, apigenin, quercetin, and myricetin. Predominant findings consistently pointed to bacteriostatic, bactericidal, and antibiofilm activities. The study primarily investigated bacteria associated with dental caries, followed by periodontopathogens. A higher number of publications presented positive antibacterial results against Streptococcus mutans in comparison to Porphyromonas gingivalis. These encouraging findings underline the potential applicability of commercially available flavonoids in materials or therapies, underscoring the need for further exploration in this field.

Hydrogel-Encapsulated Biofilm Inhibitors Abrogate the Cariogenic Activity of Streptococcus mutans

We designed and synthesized analogues of a previously identified biofilm inhibitor IIIC5 to improve solubility, retain inhibitory activities, and to facilitate encapsulation into pH-responsive hydrogel microparticles. The optimized lead compound HA5 showed improved solubility of 120.09 μg/mL, inhibited Streptococcus mutans biofilm with an IC50 value of 6.42 μM, and did not affect the growth of oral commensal species up to a 15-fold higher concentration. The cocrystal structure of HA5 with GtfB catalytic domain determined at 2.35 Å resolution revealed its active site interactions. The ability of HA5 to inhibit S. mutans Gtfs and to reduce glucan production has been demonstrated. The hydrogel-encapsulated biofilm inhibitor (HEBI), generated by encapsulating HA5 in hydrogel, selectively inhibited S. mutans biofilms like HA5. Treatment of S. mutans-infected rats with HA5 or HEBI resulted in a significant reduction in buccal, sulcal, and proximal dental caries compared to untreated, infected rats.

Application of fluoride disturbs plaque microecology and promotes remineralization of enamel initial caries

Background

The caries-preventive effect of topical fluoride application has been corroborated by a number of clinical studies. However, the effect of fluoride on oral microecology remains unclear.

Objective

To monitor the effect of fluoride on dental plaque microecology and demineralization/remineralization balance of enamel initial caries.

Methods

Three-year-old children were enrolled and treated with fluoride at baseline and 6 months. International Caries Detection and Assessment System II indices of 52 subjects were measured at baseline, 3, 6, and 12 months. Supragingival plaque samples of 12 subjects were collected at baseline, 3 and 14 days for 16S rRNA sequencing.

Results

Changes in microbial community structure were observed at 3 days after fluoridation. Significant changes in the relative abundance of microorganisms were observed after fluoride application, especially Capnocytophaga, unidentified Prevotellaceae and Rothia. Functional prediction revealed that cell movement, carbohydrate and energy metabolism were affected significantly after fluoride application. Fluoride significantly inhibited enamel demineralization and promoted remineralization of early demineralized caries enamel at 3 months.

Conclusion

Fluoride application significantly inhibited the progression of enamel initial caries and reversed the demineralization process, possibly by disturbing dental plaque microecology and modulating the physicochemical action of demineralization/remineralization. This deepened our understanding of caries-preventive effects and mechanisms of fluoride.

[Materials for Selective Inhibition of Streptococcus mutans and Progress in Relevant Research]

Dental caries is a disease in which chronic progressive destruction of the hard dental tissues occurs under the influence of multiple factors, among which, bacterial infection being the most important one. Dental plaque biofilm is a key factor in the pathogenesis of dental caries. Under normal circumstances, microorganisms within the biofilm maintain a dynamic balance through coordination, competition, and antagonism. However, when the environment changes, the balance in the biofilm will be disrupted, and the number of cariogenic bacteria, especially Streptococcus mutans ( S. mutans), will increase significantly, thereby causing the production of large amounts of organic acids on the tooth surface, tooth demineralization, and the formation of dental caries. Therefore, finding ways to restore the dynamic balance of oral microorganisms through selective inhibition of S. mutans is key to the prevention and treatment of dental caries. Herein, we reviewed the research progress of recent years in the development of materials with selective antibacterial effect, intending to provide references for the further development of drugs for the prevention and treatment of dental caries. Future studies should focus on the following aspects, mechanism, clinical efficacy, chemical modification, and safety, to supplement and make improvements on the existing relevant research, and to promote progress in research and development of drugs for the prevention and treatment of dental caries.

Distinct Agents Induce Streptococcus mutans Cells with Altered Biofilm Formation Capacity

Dental caries is a multifactorial biofilm- and sugar-dependent disease. This study investigated the influence of different agents on the induction of surviving Streptococcus mutans cells after successive treatment cycles and characterized the biofilms formed by these cells recovered posttreatment. The agents (with their main targets listed in parentheses) were compound 1771 (lipoteichoic acids), 4′ hydroxychalcone (exopolysaccharides), myricetin (exopolysaccharides), tt-farnesol (cytoplasmatic membrane), sodium fluoride (enolase—glycolysis), chlorhexidine (antimicrobial), and vehicle. Recovered cells from biofilms were generated from exposure to each agent during 10 cycles of consecutive treatments (modeled on a polystyrene plate bottom). The recovered cell counting was different for each agent. The recovered cells from each group were grown as biofilms on saliva-coated hydroxyapatite discs (culture medium with sucrose/starch). In S. mutans biofilms formed by cells recovered from biofilms previously exposed to compound 1771, 4′ hydroxychalcone, or myricetin, cells presented higher expression of the 16S rRNA, gyrA (DNA replication and transcription), gtfB (insoluble exopolysaccharides), and eno (enolase—glycolysis) genes and lower quantities of insoluble dry weight and insoluble exopolysaccharides than those derived from other agents. These findings were confirmed by the smaller biovolume of bacteria and/or exopolysaccharides and the biofilm distribution (coverage area). Moreover, preexposure to chlorhexidine increased exopolysaccharide production. Therefore, agents with different targets induce cells with distinct biofilm formation capacities, which is critical for developing formulations for biofilm control.

IMPORTANCE This article addresses the effect of distinct agents with distinct targets in the bacterial cell (cytoplasmatic membrane and glycolysis), the cell’s extracellular synthesis of exopolysaccharides that are important for cariogenic extracellular matrix construction and biofilm buildup in the generation of cells that persisted after treatment, and how these cells form biofilms in vitro. For example, if preexposure to an agent augments the production of virulence determinants, such as exopolysaccharides, its clinical value may be inadequate. Modification of biofilm formation capacity after exposure to agents is critical for the development of formulations for biofilm control to prevent caries, a ubiquitous disease associated with biofilm and diet.

Topical Application of 4'-Hydroxychalcone in Combination with tt-Farnesol Is Effective against Candida albicans and Streptococcus mutans Biofilms

Candida albicans and Streptococcus mutans interaction in the presence of dietary sucrose yields a complex biofilm with an organized and structured extracellular matrix that increases the tolerance to environmental stress, including antimicrobials. Both species are found in severe early childhood caries lesions. Thus, compounds 4'-hydroxychalcone (C135) (flavonoid intermediate metabolites), tt-farnesol (Far) (terpenoid), and sodium fluoride (F) were tested either isolated or combined as topical treatments (5 min twice daily) against C. albicans and S. mutans dual-species biofilms grown on saliva-coated hydroxyapatite discs. The biofilms were evaluated for gene expression, microbial population, biochemical components, and three-dimensional (3D) structural organization via confocal microscopy and scanning electron microscopy (SEM). The cytotoxicity of formulations was tested on the keratinocyte monolayer. C135 + Far + F promoted lower gene expression of fungal genes associated with β-glucan synthesis (BGL2, FKS1) and remodeling (XOG1, PHR1, PHR2), oxidative stress (SOD1), and drug tolerance (CDR1, ERG11) and higher expression of bacterial nox1 (oxidative and acidic stress tolerance). C135 + Far yielded less insoluble exopolysaccharides, biomass, and proteins (insoluble portion) and lower expression of BGL2, ERG11, SOD1, and PHR2. C135 + F, C135 + Far + F, and C135 rendered lower biomass, thickness, and coverage percentage (confocal microscopy). C135 + Far and C135 + Far + F maintained C. albicans as yeast morphology (SEM). Therefore, the formulations with C135 affected fungal and bacterial targets but exerted a more pronounced effect against fungal cells.

Diaryl Urea Derivative Molecule Inhibits Cariogenic Streptococcus mutans by Affecting Exopolysaccharide Synthesis, Stress Response, and Nitrogen Metabolism

Different small molecules have been developed to target cariogenic bacteria Streptococcus mutans. Based on target-based designing and in silico screening, a novel diaryl urea derivative, 1,3-bis[3,5-bis(trifluoromethyl)phenyl]urea (BPU), has previously been found effective in inhibiting the growth of S. mutans. However, the exact mechanism remains unclear. This current study aimed to explore the antimicrobial and antibiofilm effects of BPU on S. mutans and locate key enzymes and biological processes affected by the molecule via in silico molecular docking analysis and transcriptomic profile. Our in vitro results confirmed that BPU was capable of inhibiting planktonic growth as well as biofilm formation of S. mutans. The virtual binding analysis predicted that the molecule had strong binding potentials with vital enzymes (3AIC and 2ZID) involved in extracellular exopolysaccharide (EPS) synthesis. The predicted inhibitive binding was further confirmed by in vitro quantification of EPS, which found a decreased amount of EPS in the biofilms. The transcriptomic profile also found differential expression of genes involved in EPS synthesis. Moreover, the transcriptomic profile implied alterations in stress response and nitrogen metabolism in S. mutans treated with BPU. Examination of differentially expressed genes involved in these biological processes revealed that altered gene expression could contribute to impaired growth, biofilm formation, and competitiveness of S. mutans. In conclusion, the novel diaryl urea derivative BPU can inhibit the virulence of S. mutans by affecting different biological processes and serves as a potent anti-caries agent.

Virtual Screening, Synthesis and Biological Evaluation of Streptococcus mutans Mediated Biofilm Inhibitors

Dental caries, a global oral health concern, is a biofilm-mediated disease. Streptococcus mutans, the most prevalent oral microbiota, produces extracellular enzymes, including glycosyltransferases responsible for sucrose polymerization. In bacterial communities, the biofilm matrix confers resistance to host immune responses and antibiotics. Thus, in cases of chronic dental caries, inhibiting bacterial biofilm assembly should prevent demineralization of tooth enamel, thereby preventing tooth decay. A high throughput screening was performed in the present study to identify small molecule inhibitors of S. mutans glycosyltransferases. Multiple pharmacophore models were developed, validated with multiple datasets, and used for virtual screening against large chemical databases. Over 3000 drug-like hits were obtained that were analyzed to explore their binding mode. Finally, six compounds that showed good binding affinities were further analyzed for ADME (absorption, distribution, metabolism, and excretion) properties. The obtained in silico hits were evaluated for in vitro biofilm formation. The compounds displayed excellent antibiofilm activities with minimum inhibitory concentration (MIC) values of 15.26–250 µg/mL.

Small Molecule Compounds, A Novel Strategy against Streptococcus mutans

Dental caries, as a common oral infectious disease, is a worldwide public health issue. Oral biofilms are the main cause of dental caries. Streptococcus mutans (S. mutans) is well recognized as the major causative factor of dental caries within oral biofilms. In addition to mechanical removal such as tooth brushing and flossing, the topical application of antimicrobial agents is necessarily adjuvant to the control of caries particularly for high-risk populations. The mainstay antimicrobial agents for caries such as chlorhexidine have limitations including taste confusions, mucosal soreness, tooth discoloration, and disruption of an oral microbial equilibrium. Antimicrobial small molecules are promising in the control of S. mutans due to good antimicrobial activity, good selectivity, and low toxicity. In this paper, we discussed the application of antimicrobial small molecules to the control of S. mutans, with a particular focus on the identification and development of active compounds and their modes of action against the growth and virulence of S. mutans.

Compounds with Distinct Targets Present Diverse Antimicrobial and Antibiofilm Efficacy against Candida albicans and Streptococcus mutans, and Combinations of Compounds Potentiate Their Effect

Candida albicans and Streptococcus mutans interact synergistically in biofilms associated with a severe form of dental caries. Their synergism is driven by dietary sucrose. Thus, it is necessary to devise strategies to hinder the development of those biofilms and prevent cavities. Six compounds [tt-farnesol (sesquiterpene alcohol that decreases the bacterium acidogenicity and aciduricity and a quorum sensing fungal molecule), myricetin (flavonoid that interferes with S. mutans exopolysaccharides production), two 2'-hydroxychalcones and 4'-hydroxychalcone (intermediate metabolites for flavonoids), compound 1771 (inhibitor of lipoteichoic synthase in Gram-positive bacteria)] with targets in both fungus and bacterium and their products were investigated for their antimicrobial and antibiofilm activities against single-species cultures. The compounds and concentrations effective on single-species biofilms were tested alone and combined with or without fluoride to control initial and pre-formed dual-species biofilms. All the selected treatments eliminated both species on initial biofilms. In contrast, some combinations eliminated the bacterium and others the fungus in pre-formed biofilms. The combinations 4'-hydroxychalcone+tt-farnesol+myricetin, 4'-hydroxychalcone+tt-farnesol+fluoride, and all compounds together with fluoride were effective against both species in pre-formed biofilms. Therefore, combinations of compounds with distinct targets can prevent C. albicans and S. mutans dual-species biofilm build-up in vitro.

Prioritization and characterization of validated biofilm blockers targeting glucosyltransferase C of Streptococcus mutans

To date, several Glucosyltransferase C (GtfC) inhibitors have been identified and experimentally validated. All these inhibitors have been validated at different experimental conditions like degree of purity, animal models, kinetic conditions, experimental environment etc.; and most of these inhibitors (ligands) proved to be quite effective in their respective validation environment. However, due to varied experimental validation conditions, and absence of molecular interaction data, there is no way to prioritize these validated ligands for their inhibition potential against GtfC. The present study is a novel attempt of comparative evaluation of the interaction of the validated ligands on a single platform and under similar conditions with a dual objective, i.e. ligand prioritization for their respective inhibitory potential and elucidation of the involved unknown molecular interactions. Carbohydrate derivatives (6-Deoxy sucrose and Trichloro-galactosucrose) were identified as the most promising GtfC inhibitors. In addition, Asp588, Trp517, and Asn481 amino acid residues of the domain A1 proved vital for the inhibitory effect. The study highlights the importance of the comparative analysis of the validated ligands in order to identify the most promising leads for drug discovery against dental caries.

Chalcone T4, a novel chalconic compound, inhibits inflammatory bone resorption in vivo and suppresses osteoclastogenesis in vitro

OBJECTIVE

This study aimed to assess the effect of a novel synthetic chalcone, Chalcone T4, on a murine model of periodontitis and on RANKL-induced osteoclastogenesis in vitro.

BACKGROUND

Chalcones are natural compounds with anti-inflammatory properties, and its synthetic analogs with enhanced biological effects have potential as therapeutic agents. Periodontitis is characterized by chronic inflammation of the periodontium and alveolar bone resorption. Safe and effective anti-inflammatory agents can have an important additive effect in the treatment in this disease.

METHODS

Periodontitis was induced via the installation of a ligature around the first molar. Rats (n = 32) received Chalcone T4 (5 and 50 mg/kg) or distilled water by gavage daily for 15 days. Outcomes assessed were bone resorption (μCT), TNF-α production (ELISA), cellular infiltrate, and collagen content (stereometric analysis, CD45+ cells by immunohistochemistry), and activation of NFATc1 and NF-kB (immunohistochemistry). In vitro, RAW 264.7 were treated with Chalcone T4 and stimulated with RANKL for assessment of osteoclast differentiation (actin ring staining) and activity (pit assay).

RESULTS

Chalcone T4 significantly reduced periodontitis-associated bone resorption, as well as the cellular infiltrate, while increasing the collagen content. Production of TNF-α, infiltration of CD45-positive cells, and NF-kB activation were markedly reduced. In vitro, chalcone T4 inhibited both osteoclast differentiation and activity.

CONCLUSION

Chalcone T4 significantly inhibited alveolar bone resorption and inflammation in vivo and RANKL-induced osteoclastogenesis in vitro, suggesting a therapeutic role for this compound in the treatment of periodontitis.

Discovery of Potent Inhibitors of Streptococcus mutans Biofilm with Antivirulence Activity

Dental caries is a bacterial infectious disease characterized by demineralization of the tooth enamel. Treatment of this disease with conventional antibiotics is largely ineffective as the cariogenic bacteria form tenacious biofilms that are resistant to such treatments. The main etiological agent for dental caries is the bacterium Streptococcus mutans. S. mutans readily forms biofilms on the tooth surface and rapidly produces lactic acid from dietary sucrose. Glucosyl transferases (Gtfs) secreted by S. mutans are mainly responsible for the production of exopolysaccharides that are crucial for the biofilm architecture. Thus, inhibiting S. mutans' Gtfs is an effective approach to develop selective biofilm inhibitors that do not affect the growth of oral commensals. Herein, we report a library of 90 analogs of the previously identified lead compound, G43, and exploration of its structure activity relationships (SAR). All compounds were evaluated for the inhibition of S. mutans biofilms and bacterial growth. Selected compounds from this library were further evaluated for enzyme inhibition against Gtfs using a zymogram assay and for growth inhibition against oral commensal bacterial species such as Streptococcus gordonii and Streptococcus sanguinis. This study has led to the discovery of several new biofilm inhibitors with enhanced potency and selectivity. One of the leads, III _F1 , showed marked reduction in buccal, sulcal, and proximal caries scores in a rat model of dental caries.

Selective Inhibition of Streptococci Biofilm Growth via a Hydroxylated Azobenzene Coating

Strategies to engineer surfaces that can enable the selective inhibition of bacterial pathogens while preserving beneficial microbes can serve as tools to precisely edit the microbiome. In the oral microbiome, this selectivity is crucial in preventing the proliferation of cariogenic species such as Streptococcus mutans (S. mutans). In this communication, coatings consisting of a covalently tethered hydroxylated azobenzene (OH-AAZO) on glassy acrylic resins are studied and characterized for their ability to selectively prevent the attachment and growth of oral Streptococci biofilms. The coating applied on the surface of glassy resins inhibits the growth and proliferation of cariogenic S. mutans and S. oralis biofilms while A. actinomycetemcomitans, S. aureus, and E. coli biofilms are unaffected by the coating . The antibacterial effect is characterized as a function of both the OH-AAZO concentration in the coatings (≥50 mg mL-1) and the structure of the monomer in the coating. Preliminary mechanistic results suggest that the targeted bactericidal effect against Streptococci species is caused by a disruption of membrane ion potential, inducing cell death.

Oral microbiota and Alzheimer's disease: Do all roads lead to Rome?

Alzheimer's disease (AD) is a progressive neurodegenerative pathology affecting milions of people worldwide associated with deposition of senile plaques. While the genetic and environmental risk factors associated with the onset and consolidation of late onset AD are heterogeneous and sporadic, growing evidence also suggests a potential link between some infectious diseases caused by oral microbiota and AD. Oral microbiota dysbiosis is purported to contribute either directly to amyloid protein production, or indirectly to neuroinflammation, occurring as a consequence of bacterial invasion. Over the last decade, the development of Human Oral Microbiome database (HOMD) has deepened our understanding of oral microbes and their different roles during the human lifetime. Oral pathogens mostly cause caries, periodontal disease, and edentulism in aged population, and, in particular, alterations of the oral microbiota causing chronic periodontal disease have been associated with the risk of AD. Here we describe how different alterations of the oral microbiota may be linked to AD, highlighting the importance of a good oral hygiene for the prevention of oral microbiota dysbiosis.

Targeting S. mutans biofilms: a perspective on preventing dental caries

The prevalence of biofilm diseases, and dental caries in particular, have encouraged extensive research on S. mutans biofilms, including methods of preventing its formation. Numerous small molecules with specific anti-biofilm activity against this pathogen have been isolated and synthesized. Generally, these molecules can be characterized into three categories: sucrose-dependent anti-adhesion, sucrose-independent anti-adhesion and cellular signaling interference. This review aims to provide an overview of the current small molecule strategies used for targeting S. mutans biofilms, and a perspective of the future for the field.

Lactobacillus rhamnosus biosurfactant inhibits biofilm formation and gene expression of caries-inducing Streptococcus mutans

BACKGROUND

It is cleared that some probiotic strains inhibit biofilm formation of oral bacteria, but its mechanisms are not clearly understood yet. It is proposed that one of the mechanisms can be biosurfactant production, a structurally diverse group of surface-active compounds synthesized by microorganisms. Hence, this study focused on the evaluation of the anti-biofilm and antiadhesive activities of the L. rhamnosus derived-biosurfactant against Streptococcus mutans and its effect on gtfB/C and ftf genes expression level.

MATERIALS AND METHODS

In this in vitro study Lactobacillus rhamnosus ATCC7469 overnight culture was used for biosurfactant production. The biosurfactant effect on the surface tension reduction was confirmed by drop collapse method. Chemical bonds in the biosurfactant were identified by Fourier transform infrared (FTIR). Anti-biofilm and antiadhesive activities of the biosurfactant were determined on glass slides and in 96-well culture plates, respectively. The effect of the biosurfactant on gtfB/C and ftf genes expression level was also investigated after biofilm formation, total RNA extraction, and reverse transcription by quantitative real-time reverse transcriptase polymerase chain reaction (PCR) assay (quantitative PCR). The data were assessed by one-way analysis of variance in the Tukey-Kramer postdeviation test for all pairs. P < 0.05 was considered statistically significant.

RESULTS

The FTIR results of biosurfactant showed that it was protein rich. It also showed anti-biofilm formation activity on the glass slide and antiadhesive activity till 40% on microtiter plate wells. It also showed a significant reduction (P < 0.05) in gtfB/C and ftf genes expression level.

CONCLUSION

L. rhamnosus-derived biosurfactant exhibits a significant inhibitory effect on biofilm formation ability of S. mutans due to downregulation of biofilm formation associated genes, gtfB/C and ftf. L. rhamnosus-derived biosurfactant with substantial antiadhesive activity is suitable candidates for use in new generations of microbial antiadhesive agents.

Inhibition of Streptococcus mutans Biofilms by the Natural Stilbene Piceatannol Through the Inhibition of Glucosyltransferases

Removal of oral biofilms involves the use of broad-spectrum antimicrobials, which eradicate both pathogenic and protective oral commensal species. Ideal therapeutics for dental caries should be able to selectively inhibit pathogenic biofilms caused by Streptococcus mutans. S. mutans extracellular glucosyltransferases (Gtfs), particularly GtfB and GtfC, synthesize predominantly water-insoluble glucans, which contribute to the structural scaffold of biofilms. The lead stilbene identified through our docking study against the catalytic domain of GtfC is a natural product known as piceatannol, which inhibited S. mutans biofilm formation in a dose-dependent manner, with considerable selectivity over growth inhibition of S. mutans and commensal streptococci. Binding kinetic analysis of piceatannol was performed using Octet RED against both GtfB and GtfC, which produced low micromolar K_D values. Piceatannol inhibited S. mutans colonization in an in vivo drosophila model and a rat model of dental caries.

Proteomic and bioinformatics analysis of human saliva for the dental-risk assessment

Background: Dental caries disease is a dynamic process with a multi-factorial etiology. It is manifested by demineralization of enamel followed by damage spreading into the tooth inner structure. Successful early diagnosis could identify caries-risk and improve dental screening, providing a baseline for evaluating personalized dental treatment and prevention strategies. Methodology: Salivary proteome of the whole unstimulated saliva (WUS) samples was assessed in caries-free and caries-susceptible individuals of older adolescent age with permanent dentition using a nano-HPLC and MALDI-TOF/TOF mass spectrometry. Results: 554 proteins in the caries-free and 695 proteins in the caries-susceptible group were identified. Assessment using bioinformatics tools and Gene Ontology (GO) term enrichment analysis revealed qualitative differences between these two proteomes. Members of the caries-susceptible group exhibited a branch of cytokine binding gene products responsible for the regulation of immune and inflammatory responses to infections. Inspection of molecular functions and biological processes of caries-susceptible saliva samples revealed significant categories predominantly related to the activity of proteolytic peptidases, and the regulation of metabolic and catabolic processes of carbohydrates. Conclusions: Proteomic analysis of the whole saliva revealed information about potential risk factors associated with the development of caries-susceptibility and provides a better understanding of tooth protection mechanisms.

Structure-Based Discovery of Small Molecule Inhibitors of Cariogenic Virulence

Streptococcus mutans employs a key virulence factor, three glucosyltransferase (GtfBCD) enzymes to establish cariogenic biofilms. Therefore, the inhibition of GtfBCD would provide anti-virulence therapeutics. Here a small molecule library of 500,000 small molecule compounds was screened in silico against the available crystal structure of the GtfC catalytic domain. Based on the predicted binding affinities and drug-like properties, small molecules were selected and evaluated for their ability to reduce S. mutans biofilms, as well as inhibit the activity of Gtfs. The most potent inhibitor was further characterized for Gtf binding using OctetRed instrument, which yielded low micromolar K_D against GtfB and nanomolar K_D against GtfC, demonstrating selectivity towards GtfC. Additionally, the lead compound did not affect the overall growth of S. mutans and commensal oral bacteria, and selectively inhibit the biofilm formation by S. mutans, indicative of its selectivity and non-bactericidal nature. The lead compound also effectively reduced cariogenicity in vivo in a rat model of dental caries. An analog that docked poorly in the GtfC catalytic domain failed to inhibit the activity of Gtfs and S. mutans biofilms, signifying the specificity of the lead compound. This report illustrates the validity and potential of structure-based design of anti-S. mutans virulence inhibitors.