The virulence of Streptococcus mutans and the ability to form biofilms

Glycosyltransferase-Mediated Biofilm Matrix Dynamics and Virulence of Streptococcus mutans

Streptococcus mutans is a key cariogenic bacterium responsible for the initiation of tooth decay. Biofilm formation is a crucial virulence property. We discovered a putative glycosyltransferase, SMU_833, in S. mutans capable of modulating dynamic interactions between two key biofilm matrix components, glucan and extracellular DNA (eDNA). The deletion of smu_833 decreases glucan and increases eDNA but maintains the overall biofilm biomass. The decrease in glucan is caused by a reduction in GtfB and GtfC, two key enzymes responsible for the synthesis of glucan. The increase in eDNA was accompanied by an elevated production of membrane vesicles, suggesting that SMU_833 modulates the release of eDNA via the membrane vesicles, thereby altering biofilm matrix constituents. Furthermore, glucan and eDNA were colocalized. The complete deletion of gtfBC from the smu_833 mutant significantly reduced the biofilm biomass despite the elevated eDNA, suggesting the requirement of minimal glucans as a binding substrate for eDNA within the biofilm. Despite no changes in overall biofilm biomass, the mutant biofilm was altered in biofilm architecture and was less acidic in vitro Concurrently, the mutant was less virulent in an in vivo rat model of dental caries, demonstrating that SMU_833 is a new virulence factor. Taken together, we conclude that SMU_833 is required for optimal biofilm development and virulence of S. mutans by modulating extracellular matrix components. Our study of SMU_833-modulated biofilm matrix dynamics uncovered a new target that can be used to develop potential therapeutics that prevent and treat dental caries.IMPORTANCE Tooth decay, a costly and painful disease affecting the vast majority of people worldwide, is caused by the bacterium Streptococcus mutans The bacteria utilize dietary sugars to build and strengthen biofilms, trapping acids onto the tooth's surface and causing demineralization and decay of teeth. As knowledge of our body's microbiomes increases, the need for developing therapeutics targeted to disease-causing bacteria has arisen. The significance of our research is in studying and identifying a novel therapeutic target, a dynamic biofilm matrix that is mediated by a new virulence factor and membrane vesicles. The study increases our understanding of S. mutans virulence and also offers a new opportunity to develop effective therapeutics targeting S. mutans In addition, the mechanisms of membrane vesicle-mediated biofilm matrix dynamics are also applicable to other biofilm-driven infectious diseases.

Biofilm development and computational screening for new putative inhibitors of a homolog of the regulatory protein BrpA in Streptococcus dysgalactiae subsp. dysgalactiae

Streptococcus dysgalactiae subsp. dysgalactiae (SDSD), a Lancefield group C streptococci (GCS), is a frequent cause of bovine mastitis. This highly prevalent disease is the costliest in dairy industry. Adherence and biofilm production are important factors in streptoccocal pathogenesis. We have previously described the adhesion and internalization of SDSD isolates in human cells and now we describe the biofilm production capability of this bacterium. In this work we integrated microbiology, imaging and computational methods to evaluate the biofilm production capability of SDSD isolates; to assess the presence of biofilm regulatory protein BrpA homolog in the biofilm producers; and to predict a structural model of BrpA-like protein and its binding to putative inhibitors. Our results show that SDSD isolates form biofilms on abiotic surface such as glass (hydrophilic) and polystyrene (hydrophobic), with the strongest biofilm formation observed in glass. This ability was mainly associated with a proteinaceous extracellular matrix, confirmed by the dispersion of the biofilms after proteinase K and trypsin treatment. The biofilm formation in SDSD isolates was also confirmed by confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM). Under SEM observation, VSD16 isolate formed cell aggregates during biofilm growth while VSD9 and VSD10 formed smooth and filmy layers. We show that brpA-like gene is present and expressed in SDSD biofilm-producing isolates and its expression levels correlated with the biofilm production capability, being more expressed in the late exponential phase of planktonic growth compared to biofilm growth. Fisetin, a known biofilm inhibitor and a putative BrpA binding molecule, dramatically inhibited biofilm formation by the SDSD isolates but did not affect planktonic growth, at the tested concentrations. Homology modeling was used to predict the 3D structure of BrpA-like protein. Using high throughput virtual screening and molecular docking, we selected five ligand molecules with strong binding affinity to the hydrophobic cleft of the protein, making them potential inhibitor candidates of the SDSD BrpA-like protein. These results warrant further investigations for developing novel strategies for SDSD anti-biofilm therapy.

Enamel remineralization and repair results of Biomimetic Hydroxyapatite toothpaste on deciduous teeth: an effective option to fluoride toothpaste

Background

Dental caries is a recognized worldwide public health problem. Despite being one of the most effective strategies against dental caries, the excessive use of fluorine may result in a potential risk of developing dental fluorosis especially in children under age of six. The purpose of this work is to analyze a fluorine-free toothpaste containing Biomimetic Hydroxyapatite to assess enamel re-mineralizing and repairing properties.

Results

The study was performed in vitro and in vivo, comparing the hydroxyapatite toothpaste with two others toothpaste containing different fluorine concentrations. The coating effect of the micro-structured Hydroxyapatite nanoparticles reintegrates the enamel with a biomimetic film reproducing the structure and the morphology of the biologic Hydroxyapatite of the enamel. As demonstrated, the coating is due to the deposit of a new layer of apatite, which presents fewer particles than the natural enamel, not based on the chemical—physical changes occurring in fluorinated toothpastes. Moreover, it shows resistance to brushing as a consequence of chemical bonds between the synthetic and natural crystals of the enamel.

Conclusions

The use of Biomimetic Hydroxyapatite toothpastes has proven to be a valuable prevention measure against dental caries in primary dentition since it prevents the risk of fluorosis.

Novel Assay To Characterize Neutrophil Responses to Oral Biofilms

Neutrophils, the most numerous leukocytes, play an important role in maintaining oral health through interactions with oral microbial biofilms. Both neutrophil hyperactivity and the bacterial subversion of neutrophil responses can cause inflammation-mediated tissue damage like that seen in periodontal disease. We describe here an assay that assesses neutrophil activation responses to monospecies biofilm bacteria in vitro based on the surface expression of cluster of differentiation (CD) markers associated with various neutrophil functions. Most of what we know about neutrophil responses to bacteria is based on in vitro assays that use planktonic bacteria and isolated/preactivated neutrophils, which makes interpretation of the neutrophil responses to bacteria a challenge. An understanding of how neutrophils differentially interact with and respond to commensal and pathogenic oral bacteria is necessary in order to further understand the neutrophil's role in maintaining oral health and the pathogenesis of periodontal disease. In this study, a flow cytometry-based in vitro assay was developed to characterize neutrophil activation states based on CD marker expressions in response to oral monospecies bacterial biofilms. Using this approach, changes in CD marker expressions in response to specific prominent oral commensal and pathogenic bacteria were assayed. Several functional assays, including assays for phagocytosis, production of reactive oxygen species, activation of the transcription factor Nrf2, neutrophil extracellular trap formation, and myeloperoxidase release, were also performed to correlate neutrophil function with CD marker expression. Our results demonstrate that neutrophils display bacterial species-specific responses. This assay can be used to characterize how specific biofilms alter specific neutrophil pathways associated with their activation.

Effects of S. mutans gene-modification and antibacterial calcium phosphate nanocomposite on secondary caries and marginal enamel hardness

Secondary caries at the restoration-tooth margins is a main reason for dental restoration failures. Gene-modification for Streptococcus mutans (S. mutans) and composites containing dimethylaminohexadecyl methacrylate (DMAHDMA) and nanoparticles of amorphous calcium phosphate (NACP) all have the potential to suppress bacterial acids and promote remineralization. However, there has been no report of their effects on marginal caries-inhibition and enamel hardness. The objective of this study was to investigate the effects of gene-modification and DMAHDM–NACP composite restoration on enamel demineralization and hardness at the margins under biofilm acids for the first time. Parent S. mutans and rnc gene-deleted S. mutans were tested side by side. The bioactive composite contained 3% DMAHDM and 30% NACP. Mechanical properties and calcium (Ca) and phosphate (P) ion releases were measured. Colony-forming units (CFU), MTT, lactic acid and polysaccharide of biofilms were evaluated. Demineralization of bovine enamel with composite restorations was induced via biofilms, then enamel hardness was measured. The dual strategy of combining rnc-deletion with DMAHDM+30NACP: (1) achieved the strongest biofilm-inhibition, with the greatest reduction in biofilm CFU by 6 logs; (2) decreased biofilm lactic acid and polysaccharide production by more than 80%; (3) achieved enamel hardness that was 140% higher than that of a commercial fluoride-releasing composite under 30 days of biofilm acids. Therefore, the novel dual approach of rnc gene-deletion and DMAHDM+NACP nanocomposite is promising to inhibit secondary caries at the margins and increase the longevity of tooth restorations.

Secondary caries at the restoration-tooth margins is a main reason for dental restoration failures.

Optical pH measurement system using a single fluorescent dye for assessing susceptibility to dental caries

Sugar-rich diets and poor dental hygiene promote the formation of a biofilm (plaque) that strongly adheres to the dental enamel surface and fosters the evolution of aciduric bacteria. The acid contributes to demineralization of the exterior tooth enamel, which accelerates after the pH drops below a critical value (∼5.5) for extended time periods resulting in the need for restorative procedures. Preventative techniques to alert the dentist and caries-susceptible patients regarding vulnerability to dental decay require a clinical measure of plaque activity. Therefore, there is a need to evaluate the acid production capability of plaque deposits in the pits and fissures of occlusal and interproximal regions. A ratiometric fluorescence pH-sensing device has been developed using an FDA-approved dye and LED excitation. Fluorescein spectral profiles were collected using a spectrometer and analyzed with a spectral unmixing algorithm for calibration over the pH range of 4.5 to 7. An in vivo pilot study on human subjects was performed using a sucrose rinse to accelerate bacterial metabolism and to measure the time-dependent drop in pH. The optical system is relatively immune to confounding factors such as photobleaching, dye concentration, and variation in excitation intensity associated with earlier dye-based pH measurement techniques.

Effect of silver diamine fluoride-potassium iodide and 2% chlorhexidine gluconate cavity cleansers on the bond strength and microleakage of resin-modified glass ionomer cement

Background:

Disinfection of the prepared cavity can be a crucial step in the longevity of restorations. The objective of this study was to compare the antimicrobial action (AMA) of silver diamine fluoride-potassium iodide combination (SDF-KI) with 2% chlorhexidine gluconate (CHX) and to compare the alteration in bond strength and microleakage while using SDF-KI and CHX as cavity cleansers in resin-modified glass ionomer cement (RMGIC) restorations.

Materials and Methods:

Samples were grouped as follows: Group 1: Polyacrylic acid (PAA), Group 2: CHX, Group 3: SDF-KI, and Group 4: Distilled water (CTRL). AMA was assessed by measuring the zone of inhibition of the above-mentioned materials by dispensing them into the punch hole prepared on agar plates with an inoculum of Streptococcus mutans. For assessing the effect of the cavity cleansers on the bond strength of RMGIC, they were applied to the dentinal samples prepared from freshly extracted noncarious molars. After the surface was treated, cylindrical restoration of RMGIC was placed and allowed to set. The shear bond strength was then evaluated using a universal testing machine. Rhodamine-B dye penetration was viewed under a fluorescent microscope to evaluate the microleakage of RMGIC following surface treatment of the standardized cavities prepared on the cervical third of freshly extracted noncarious premolars.

Results:

SDF-KI (34 ± 0.8 mm) showed potent AMA followed by CHX (23.9 ± 0.7 mm) and PAA (12.7 ± 0.8 mm). SDF-KI showed a drastic increase in the bond strength when compared to the PAA, CHX, and CTRL groups. Although the application of SDF-KI showed the least microleakage among all the groups, it was not statistically significant.

Conclusion:

The application of SDF-KI and CHX is useful against S. mutans in an in vitro study. Although SDF-KI group showed the least microleakage among the groups, it was not statistically significant. SDF-KI application has shown a drastic increase in the bond strength of RMGIC although further research is required for the suitable reasoning of the phenomenon.

Enhanced design and formulation of nanoparticles for anti-biofilm drug delivery

Biofilms are surface-bound, structured microbial communities underpinning persistent bacterial infections. Biofilms often create acidic pH microenvironments, providing opportunities to leverage responsive drug delivery systems to improve antibacterial efficacy. Here, the antibacterial efficacy of novel formulations containing pH-responsive polymer nanoparticle carriers (NPCs) and farnesol, a hydrophobic antibacterial drug, were investigated. Multiple farnesol-loaded NPCs, which varied in overall molecular weight and corona-to-core molecular weight ratios (CCRs), were tested using standard and saturated drug loading conditions. NPCs loaded at saturated conditions exhibited ∼300% greater drug loading capacity over standard conditions. Furthermore, saturated loading conditions sustained zero-ordered drug release over 48 hours, which was 3-fold longer than using standard farnesol loading. Anti-biofilm activity of saturated NPC loading was markedly amplified using Streptococcus mutans as a biofilm-forming model organism. Specifically, reductions of ∼2-4 log colony forming unit (CFU) were obtained using microplate and saliva-coated hydroxyapatite biofilm assays. Mechanistically, the new formulation reduced total biomass by disrupting insoluble glucan formation and increased NPC-cell membrane localization. Finally, thonzonium bromide, a highly potent, FDA-approved antibacterial drug with similar alkyl chain structure to farnesol, was also loaded into NPCs and used to treat S. mutans biofilms. Similar to farnesol-loaded NPCs, thonzonium bromide-loaded NPCs increased drug loading capacity ≥2.5-fold, demonstrated nearly zero-order release kinetics over 96 hours, and reduced biofilm cell viability by ∼6 log CFU. This work provides foundational insights that may lead to clinical translation of novel topical biofilm-targeting therapies, such as those for oral diseases.

An Update on the Evolution of Glucosyltransferase (Gtf) Genes in Streptococcus

In many caries-promoting Streptococcus species, glucosyltransferases (Gtfs) are recognized as key enzymes contributing to the modification of biofilm structures, disruption of homeostasis of healthy microbiota community and induction of caries development. It is therefore of great interest to investigate how Gtf genes have evolved in Streptococcus. In this study, we conducted a comprehensive survey of Gtf genes among 872 streptococci genomes of 37 species and identified Gtf genes from 364 genomes of 18 species. To clarify the relationships of these Gtf genes, 45 representative sequences were used for phylogenic analysis, which revealed two clear clades. Clade I included 12 Gtf genes from nine caries-promoting species of the Mutans and Downei groups, which produce enzymes known to synthesize sticky, water-insoluble glucans (WIG) that are critical for modifying biofilm structures. Clade II primarily contained Gtf genes responsible for synthesizing water-soluble glucans (WSG) from all 18 species, and this clade further diverged into three subclades (IIA, IIB, and IIC). An analysis of 16 pairs of duplicated Gtf genes revealed high divergence levels at the C-terminal repeat regions, with ratios of the non-synonymous substitution rate (dN) to synonymous substitution rate (dS) ranging from 0.60 to 1.03, indicating an overall relaxed constraint in this region. However, among the clade I Gtf genes, some individual repeat units possessed strong functional constraints by the same criterion. Structural variations in the repeat regions were also observed, with detection of deletions or recent duplications of individual repeat units. Overall, by establishing an updated phylogeny and further elucidating their evolutionary patterns, this work enabled us to gain a greater understanding of the origination and divergence of Gtf genes in Streptococcus.

Chemical composition of essential oils from different parts of Protium heptaphyllum (Aubl.) Marchand and their in vitro antibacterial activity

In Brazilian folk medicine, Protium heptaphyllum is used to treat inflammatory conditions and to hasten wound repair. This paper aims to investigate the chemical composition and the in vitro antibacterial effects of the essential oils (EOs) obtained from P. heptaphyllum leaves and ripe and unripe fruits against a representative panel of oral pathogens. The GC-FID and GC-MS analysis revealed that the major components determined in P. heptaphyllum essential oils were myrcene (59.0%), β-elemene (17.2%), limonene (12.9%), spathulenol (12.6%), α-cubebene (11.6%), germacrene D (10.6%), trans-nerolidol (9.8%), and α-cadinol (8.8%). The essential oils of the ripe and unripe fruits showed the strongest antibacterial activity against the anaerobic bacteria Prevotella nigrescens (MIC = 50 µg/mL). The leaf essential oil displayed very promising activity against Streptococcus mutans (MIC = 50 µg/mL) and Streptococcus mitis (MIC = 62.5 µg/mL). The antibacterial activity of EOs against oral pathogens is also described for the first time. [Formula: see text].

Effects of Antimicrobial Peptide GH12 on the Cariogenic Properties and Composition of a Cariogenic Multispecies Biofilm

Dental caries is a biofilm-mediated disease that occurs when acidogenic/aciduric bacteria obtain an ecological advantage over commensal species. In previous studies, the effects of the antimicrobial peptide GH12 on planktonic bacteria and monospecies biofilms were confirmed. The objectives of this study were to investigate the effects of GH12 on a cariogenic multispecies biofilm and to preliminarily explain the mechanism. In this biofilm model, Streptococcus mutans ATCC 70061 was the representative of cariogenic bacteria, while Streptococcus gordonii ATCC 35105 and Streptococcus sanguinis JCM 5708 were selected as healthy microbiota. The results showed that GH12 was more effective in suppressing S. mutans than the other two species, with lower MIC and minimal bactericidal concentration (MBC) values among diverse type strains and clinical isolated strains. Therefore, GH12, at no more than 8 mg/liter, was used to selectively suppress S. mutans in the multispecies biofilm. GH12 at 4 mg/liter and 8 mg/liter reduced the cariogenic properties of the multispecies biofilm in biofilm formation, glucan synthesis, and lactic acid production. In addition, GH12 suppressed S. mutans within the multispecies biofilm and changed the bacterial composition. Furthermore, 8 mg/liter GH12 showed a selective bactericidal impact on S. mutans, and GH12 promoted hydrogen peroxide production in S. sanguinis and S. gordonii, which improved their ecological advantages. In conclusion, GH12 inhibited the cariogenic properties and changed the composition of the multispecies biofilm through a two-part mechanism by which GH12 directly suppressed the growth of S. mutans as well as enhanced the ecological competitiveness of S. sanguinis and S. gordonii IMPORTANCE Dental caries is one of the most prevalent chronic infectious diseases worldwide, with substantial economic and quality-of-life impacts. Streptococcus mutans has been considered the principal pathogen of dental caries. To combat dental caries, an antimicrobial peptide, GH12, was designed, and its antibacterial effects on planktonic S. mutans and the monospecies biofilm were confirmed. As etiological concepts of dental caries evolved to include microecosystems, the homeostasis between pathogenic and commensal bacteria and a selective action on cariogenic virulence have increasingly become the focus. The novelty of this research was to study the effects of the antimicrobial peptides on a controlled cariogenic multispecies biofilm model. Notably, the role of an antimicrobial agent in regulating interspecific competition and composition shifts within this multispecies biofilm was investigated. With promising antibacterial and antibiofilm properties, the use of GH12 might be of importance in preventing and controlling caries and other dental infections.

A Chemical Approach to Optimizing Bioactive Glass Dental Composites

The chemical microenvironment surrounding dental composites plays a crucial role in controlling the bacteria grown on these specialized surfaces. In this study, we report a scanning electrochemical microscopy (SECM)-based analytic technique to design and optimize metal ion-releasing bioactive glass (BAG) composites, which showed a significant reduction in biofilm growth. SECM allows positioning of the probe without touching the substrate while mapping the chemical parameters in 3-dimensional space above the substrate. Using SECM and a solid-state H⁺ and Ca²⁺ ion-selective microprobe, we determined that the local Ca²⁺ concentration released by different composites was 10 to 224 µM for a BAG particle size of <5 to 150 µm in the presence of artificial saliva at pH 4.5. The local pH was constant above the composites in the same saliva solution. The released amount of Ca²⁺ was determined to be maximal for particles <38 µm and a BAG volume fraction of 0.32. This optimized BAG-resin composite also showed significant inhibition of biofilm growth (24 ± 5 µm) in comparison with resin-only composites (53 ± 6 µm) after Streptococcus mutans bacteria were grown for 3 d in a basal medium mucin solution. Biofilm morphology and its subsequent volume, as determined by the SECM imaging technique, was (0.59 ± 0.38) × 10⁷ µm³ for BAG-resin composites and (1.29 ± 0.53) × 10⁷ µm³ for resin-only composites. This study thus lays the foundation for a new analytic technique for designing dental composites that are based on the chemical microenvironment created by biomaterials to which bacteria have been exposed.

Antibiofilm effect of chlorhexidine-carrier nanosystem based on iron oxide magnetic nanoparticles and chitosan

This study synthesized and characterized a chlorhexidine (CHX)-carrier nanosystem based on iron oxide magnetic nanoparticles (IONPs) and chitosan (CS), and evaluated its antimicrobial effect on mono- and dual-species biofilms of Candida albicans and Streptococcus mutans. CHX was directly solubilized in CS-coated IONPs and maintained under magnetic stirring for obtaining the IONPs-CS-CHX nanosystem. Antimicrobial susceptibility testing for planktonic cells was performed by determining the minimum inhibitory concentration (MIC) of the nanosystem and controls. The effects of the IONPs-CS-CHX nanosystem on the formation of mono- and dual-species biofilms, as well as on pre-formed biofilms were assessed by quantification of total biomass, metabolic activity and colony-forming units. Data were analyzed by the Kruskal-Wallis' test or one-way analysis of variance, followed by the Student-Newman-Keuls' or Holm-Sidak's tests (α = 0.05), respectively. Physico-chemical results confirmed the formation of a nanosystem with a size smaller than 40 nm. The IONPs-CS-CHX nanosystem and free CHX showed similar MIC values for both species analyzed. In general, biofilm quantification assays revealed that the CHX nanosystem at 78 μg/mL promoted similar or superior antibiofilm effects compared to its counterpart at 39 μg/mL and free CHX at 78 μg/mL. These findings highlight the potential of CS-coated IONPs as preventive or therapeutic agents carrying CHX to fight biofilm-associated oral diseases.

Chemical fabrication of graphene oxide nanosheets attenuates biofilm formation of human clinical pathogens

Graphene oxide (GO) has been recently attracted considerable interest for its potential applications in physical, chemical and biological properties. In the present study, the GO nanosheets were prepared by a chemical exfoliation technique using a modified Hummers method. Initially, the prepared GO nanosheets were confirmed by UV-vis spectroscopy and further characterized by FE-SEM, Edax, HR-TEM and SAED that demonstrated the formation of GO nanosheets with few layers flat sheet structure with hexagonal lattice crystalline nature. The FTIR spectra revealed the presence of various oxygen containing functional groups has been produced from graphite plane by exfoliation technique. The prepared GO nanosheets showed excellent antibiotic resistant activity against planktonic bacteria and more effective to damage the established biofilms and inhibits the biofilm formation of human clinical pathogens like E. coli and P. aeruginosa. Further, the GO nanosheets were found to be non-toxic to normal mammalian cells and there are no apparent morphological changes were observed in control and treated cells. In conclusion, GO nanosheets were effectively preventing the formation of biofilms and kills the represent bacteria that suggested the GO nanosheets could be used for the prevention and treatment of biofilm-related infections.

Relationship between Candida albicans and Streptococcus mutans in early childhood caries, evaluated by quantitative PCR

Background: The aim of this study was to analyze the synergistic relationship between Candida albicans and Streptococcus mutans in children with early childhood caries (ECC) experience.

Methods: Dental plaque and unstimulated saliva samples were taken from 30 subjects aged 3-5 years old, half with (n=15, dmft > 4) and half without (n=15) ECC. The abundance of C. albicans and S. mutans and relative to total bacteria load were quantify by real-time PCR (qPCR). This method was also employed to investigate the mRNA expression of glycosyltransferase ( gtfB) gene in dental plaque. Student’s t-test and Pearson’s correlation were used to perform statistical analysis.

Results: Within the ECC group, the quantity of both microorganisms were higher in the saliva than in dental plaque. The ratio of C. albicans to total bacteria was higher in saliva than in plaque samples (p < 0.05). We observed the opposite for S. mutans (p < 0.05). The different value of C. albicans and S. mutans in saliva was positively correlated, and negatively correlated in dental plaque. Transcription level of S. mutans gtfB showed a positive correlation with C. albicans concentration in dental plaque. 

Conclusion:C. albicans has a positive correlation with cariogenic traits of S. mutans in ECC-related biofilm of young children.

Effect of sodium chloride on gene expression of Streptococcus mutans and zeta potential of demineralized dentin

Purpose

In this work, the effects of sodium chloride (NaCl) on gene expression of planktonic Streptococcus mutans cells are investigated. Also assessed are the effects of NaCl on zeta potential of sound and demineralized dentin.

Methods

The relative level of glucosyltransferase B (gtfB), gtfC and gtfD transcription of S. mutans in the presence of NaCl was evaluated by quantitative polymerase chain reaction (qPCR). The osmolality of varying salt (NaCl) concentrations and their influence on the zeta potential of sound and demineralized dentin was investigated as well.

Results

NaCl significantly reduced the expression of gtfB and C genes in planktonic S. mutans; whereas, gtf D gene expression significantly increased in the presence of NaCl (P < 0.05). NaCl at concentrations of 37.5 mg/ml reduced zeta potential of demineralized dentin, while no significant decrease of zeta potential was found when sound dentin was exposed to this concentration.

Conclusion

NaCl reduces the expression of some gtfs in S. mutans and increases negative potential charge of demineralized dentin.

Photodynamic therapy mediated by chlorin-type photosensitizers against Streptococcus mutans biofilms

Photodynamic therapy (PDT) can be used for the control of oral pathogens and different photosensitizers (PS) have been investigated. This study evaluated the efficacy of PDT against Streptococcus mutans biofilms using two second-generation PS derived from chlorin: Photoditazine® (PDZ) and Fotoenticine® (FTC). These PS were compared to methylene blue (MB), a dye with proven antimicrobial activity against S. mutans. Suspensions of S. mutans were cultured in contact with bovine tooth disks for biofilm formation. After 48 h, the biofilms were treated with PDZ (0.6 mg/mL), FTC (0.6 mg/mL) or MB (1 mg/mL) and submitted to laser irradiation (660 nm, 50 mW/cm²). The biofilms were quantified by the determination of CFU/mL count and analyzed by scanning electron microscopy (SEM). All PS used for PDT reduced the number of S. mutans, with a statistically significant difference compared to the untreated groups. PDT achieved microbial reductions of 4 log with MB and 6 log with PDZ, while the use of FTC resulted in the complete elimination of S. mutans biofilms. SEM analysis confirmed the CFU/mL results, showing that all PS, particularly FTC, were able to detach the biofilms and to eliminate the bacteria. In conclusion, PDT mediated by chlorin-type PS exhibited greater antimicrobial activity against S. mutans than MB-mediated PDT, indicating that these PS can be useful for the control of dental caries.

To Determine the Effect of Chewing Gum Containing Xylitol and Sorbitol on Mutans Streptococci and Lactobacilli Count in Saliva, Plaque, and Gingival Health and to Compare the Efficacy of Chewing Gums

Aims and Objective:

The aim of the study is to determine the effect of chewing gum containing xylitol and sorbitol on mutans streptococci and Lactobacilli count in saliva, plaque, and gingival health and to compare the efficacy of chewing gums.

Materials and Methods:

The study was designed as a double-blinded randomized uncontrolled clinical trial with two parallel arms. A total of 80 students consented and completed the study. The test group (X) received corresponding pellets with xylitol and the control group (S) was given pellets containing sorbitol and maltitol three times daily for 30 days. Clinical scoring and saliva samples were collected at three different intervals, at baseline, 15^th, and 30^th day of the study. The outcome measure was plaque index score, gingival index score, salivary mutans streptococci, and Lactobacilli counts. Data collected were analyzed using Statistical Package for the Social Sciences (SPSS version 19.0).

Results:

There was no statistically significant difference between the mean of mutans streptococci count of test and control group at baseline and 15^th day, but there was statistically highly significant difference (P = 0.00) between the mean of mutans streptococci count in test and control group on the 30^th day. The mean of Lactobacilli count, plaque index, and gingival index score between test and control group showed no statistically significant difference at baseline, 15^th day, and 30^th day.

Conclusion:

The results suggest that only xylitol gum may interfere with the mutans streptococci composition and reduce it after continuous use of 30 days effectively as compared to sorbitol gum, but both the gums are equally effective on salivary Lactobacilli, plaque, and gingiva at different intervals.

Evaluation of physical-mechanical properties, antibacterial effect, and cytotoxicity of temporary restorative materials

The objective of this study was to compare selective physical-mechanical properties, antibacterial effects and cytotoxicity of seven temporary restorative materials (TRM): five resin-based materials [Bioplic (B), Fill Magic Tempo (FM), Fermit inlay (F), Luxatemp LC (L) and Revotek LC (R)], and zinc oxide-eugenol cement (IRM) and glass ionomer cement (GIC) as the controls. Material and methods The physical-mechanical properties were evaluated by determining microleakage (ML), ultimate tensile strength (UTS) and Shore D hardness (SDH). In addition, the polymerization rate (Pr-1), depth of cure (DC), water sorption and solubility (WS/SL) were evaluated. The antimicrobial effects of the materials were assessed by biofilm accumulation of Streptococcus mutans (BT) and the direct contact test (DCT) by exposure to Enterococcus faecalis for 1 and 24 h, and cytotoxicity by MTT assay. The data were analyzed by ANOVA or Kruskall-Wallis tests, and a complementary post-hoc method (p<0.05). Results Group B, followed by FM and GIC had significantly lower percentages of microleakage in comparison with the other groups; Groups FM and L showed the highest WS, while Groups R and FM showed the significantly lowest SL values (p<0.05). Group R showed the statistically highest UTS mean and the lowest DC mean among all groups. Group F showed the lowest S. mutans biofilm accumulation (p=0.023). Only the Group L showed continued effect against E. faecalis after 1 h and 24 h in DCT. The L showed statistically lower viability cell when compared to the other groups. Conclusions These findings suggest the antibacterial effect of the temporary materials Fill Magic and Bioplic against S. mutans, while Luxatemp showed in vitro inhibition of S. mutans biofilm accumulation and E. faecalis growth. Regarding the cell viability test, Luxatemp was the most cytotoxic and Fill Magic was shown to be the least cytotoxic.

Autoregulation of the Streptococcus mutans SloR Metalloregulator Is Constitutive and Driven by an Independent Promoter

Streptococcus mutans, one of ∼600 bacterial species in the human oral cavity, is among the most acidogenic constituents of the plaque biofilm. Considered to be the primary causative agent of dental caries, S. mutans harbors a 25-kDa SloR metalloregulatory protein which controls metal ion transport across the bacterial cell membrane to maintain essential metal ion homeostasis. The expression of SloR derives in part from transcriptional readthrough of the sloABC operon, which encodes a Mn²⁺/Fe²⁺ ABC transport system. Here we describe the details of the sloABC promoter that drives this transcription as well as those for a novel independent promoter in an intergenic region (IGR) that contributes to downstream sloR expression. Reverse transcriptase PCR (RT-PCR) studies support the occurrence of sloR transcription that is independent of sloABC expression, and the results of 5' rapid amplification of cDNA ends (5' RACE) revealed a sloR transcription start site in the IGR, from which the -10 and -35 promoter regions were predicted. The results of gel mobility shift assays support direct SloR binding to the IGR, albeit with a lower affinity than that for SloR binding to the sloABCR promoter. The function of the sloR promoter was validated by semiquantitative real-time PCR (qRT-PCR) experiments. Interestingly, sloR expression was not significantly affected when bacteria were grown in the presence of a high manganese concentration, whereas expression of the sloABC operon was repressed under these conditions. The results of in vitro transcription studies support the occurrence of SloR-mediated transcriptional activation of sloR and repression of sloABC Taken together, these findings implicate SloR as a bifunctional regulator that represses sloABC promoter activity and encourages sloR transcription from an independent promoter.IMPORTANCE Tooth decay is a ubiquitous infectious disease that is especially pervasive in underserved communities worldwide. S. mutans-induced carious lesions cause functional, physical, and/or esthetic impairment in the vast majority of adults and in 60 to 90% of schoolchildren in industrialized countries. Billions of dollars are spent annually on caries treatment, and productivity losses due to absenteeism from the workplace are significant. Research aimed at alleviating S. mutans-induced tooth decay is important because it can address the socioeconomic disparity that is associated with dental cavities and improve overall general health, which is inextricably linked to oral health. Research focused on the S. mutans SloR metalloregulatory protein can guide the development of novel therapeutics and thus alleviate the burden of dental cavities.

High-throughput sequencing identification and characterization of potentially adhesion-related small RNAs in Streptococcus mutans

Purpose

Adherence capacity is one of the principal virulence factors of Streptococcus mutans, and adhesion virulence factors are controlled by small RNAs (sRNAs) at the post-transcriptional level in various bacteria. Here, we aimed to identify and decipher putative adhesion-related sRNAs in clinical strains of S. mutans.

Methodology

RNA deep-sequencing was performed to identify potential sRNAs under different adhesion conditions. The expression of sRNAs was analysed by quantitative real-time PCR (qRT-PCR), and bioinformatic methods were used to predict the functional characteristics of sRNAs.

Results

A total of 736 differentially expressed candidate sRNAs were predicted, and these included 352 sRNAs located on the antisense to mRNA (AM) and 384 sRNAs in intergenic regions (IGRs). The top 7 differentially expressed sRNAs were successfully validated by qRT-PCR in UA159, and 2 of these were further confirmed in 100 clinical isolates. Moreover, the sequences of two sRNAs were conserved in other Streptococcus species, indicating a conserved role in such closely related species. A good correlation between the expression of sRNAs and the adhesion of 100 clinical strains was observed, which, combined with GO and KEGG, provides a perspective for the comprehension of sRNA function annotation.

Conclusion

This study revealed a multitude of novel putative adhesion-related sRNAs in S. mutans and contributed to a better understanding of information concerning the transcriptional regulation of adhesion in S. mutans.

Comparison of the Response of Bacterial IscU and SufU to Zn2+ and Select Transition-Metal Ions

IscU, the central scaffold protein in the bacterial ISC iron-sulfur (Fe-S) cluster biosynthesis system, has long been recognized to bind a Zn²⁺ ion at its active site. While initially regarded as an artifact, Zn²⁺ binding has been shown to induce stabilization of the IscU structure that may mimic a state biologically relevant to IscU's role in Fe-S cluster biosynthesis. More recent studies have revealed that SufU, a homologous protein involved in Fe-S cluster biosynthesis in Gram-positive bacteria, also binds a Zn²⁺ ion with structural implications. Given the widespread occurrence of the "IscU-like" protein fold, particularly among Fe-S cluster biosynthesis systems, an interesting question arises as to whether Zn²⁺ ion binding and the resulting structural alterations are common properties in IscU-like proteins. Interactions between IscU and specific metal ions are investigated and compared side-by-side with those of SufU from a representative Gram-positive bacterium in the phylum Firmicutes. These studies were extended with additional transition metal ions chosen to investigate the influence of coordination geometry on selectivity for binding at the active sites of IscU and SufU. Monitoring and comparing the conformational behavior and stabilization afforded by different transition metal ions upon IscU and SufU revealed similarities between the two proteins and suggest that metal-dependent conformational transitions may be characteristic of U-type proteins involved in Fe-S cluster biosynthesis.

Relationship between the genetic polymorphisms of vicR and vicK Streptococcus mutans genes and early childhood caries in two-year-old children

Background

The VicRK two-component signalling system regulates virulence and cariogenicity in Streptococcus mutans (S. mutans). The purpose of this study was to explore the genetic polymorphisms of the vicR and vicK genes, which are associated with dental caries in children with S. mutans.

Methods

In this study, 121 (from each group) clinical S. mutans strains were isolated from caries-free children and children with high-severity caries to sequence the vicR and vicK genes. Genomic DNA was extracted from S. mutans strains and amplified using PCR. The PCR products were purified and sequenced. A chi-squared test and ABI Variant Reporter software were used to analyse the sequencing results.

Results

The 242 clinically isolated S. mutans strains contained the full-length vicR and vicK genes. No nucleotide sequence insertions or deletions were observed in the two genes. Four silent point mutations were identified in the vicR genes, and no missense mutations could be detected. Forty-one mutations were identified in the vicK genes. In addition to 32 silent mutations, 9 missense mutations at the 173, 337, 470, 1051, 1132, 1258, 1260, 1277, and 1348 bp positions were found. The distribution frequencies of the missense mutations were not significantly different between the groups, except for the C470T mutation. The frequency of the C470T missense mutation was higher in the high-severity caries group than in the caries-free group.

Conclusions

vicR sequences are highly conserved in S. mutans clinical isolates. The locus 470 missense mutation of the vicK gene may be related to caries in children with S. mutans.

Probiotic Lactobacillus sp. inhibit growth, biofilm formation and gene expression of caries-inducing Streptococcus mutans

Streptococcus mutans contributes significantly to dental caries, which arises from homoeostasic imbalance between host and microbiota. We hypothesized that Lactobacillus sp. inhibits growth, biofilm formation and gene expression of Streptococcus mutans. Antibacterial (agar diffusion method) and antibiofilm (crystal violet assay) characteristics of probiotic Lactobacillus sp. against Streptococcus mutans (ATCC 25175) were evaluated. We investigated whether Lactobacillus casei (ATCC 393), Lactobacillus reuteri (ATCC 23272), Lactobacillus plantarum (ATCC 14917) or Lactobacillus salivarius (ATCC 11741) inhibit expression of Streptococcus mutans genes involved in biofilm formation, quorum sensing or stress survival using quantitative real-time polymerase chain reaction (qPCR). Growth changes (OD600) in the presence of pH-neutralized, catalase-treated or trypsin-treated Lactobacillus sp. supernatants were assessed to identify roles of organic acids, peroxides and bacteriocin. Susceptibility testing indicated antibacterial (pH-dependent) and antibiofilm activities of Lactobacillus sp. against Streptococcus mutans. Scanning electron microscopy revealed reduction in microcolony formation and exopolysaccharide structural changes. Of the oral normal flora, L. salivarius exhibited the highest antibiofilm and peroxide-dependent antimicrobial activities. All biofilm-forming cells treated with Lactobacillus sp. supernatants showed reduced expression of genes involved in exopolysaccharide production, acid tolerance and quorum sensing. Thus, Lactobacillus sp. can inhibit tooth decay by limiting growth and virulence properties of Streptococcus mutans.

Curcumin as a Promising Antibacterial Agent: Effects on Metabolism and Biofilm Formation in S. mutans

Streptococcus mutans (S. mutans) has been proved to be the main aetiological factor in dental caries. Curcumin, a natural product, has been shown to exhibit therapeutic antibacterial activity, suggesting that curcumin may be of clinical interest. The objective of this study is to evaluate the inhibitory effects of curcumin on metabolism and biofilm formation in S. mutans using a vitro biofilm model in an artificial oral environment. S. mutans biofilms were treated with varying concentrations of curcumin. The biofilm metabolism and biofilm biomass were assessed by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay and the crystal violet assay. Confocal laser scanning microscopy was used to analyse the composition and extracellular polysaccharide content of S. mutans biofilm after curcumin treatment. The biofilm structure was evaluated using a scanning electron microscope. The gene expression of virulence-related factors was assessed by real-time PCR. The antibiofilm effect of curcumin was compared with that of chlorhexidine. The sessile minimum inhibitory concentration (SMIC50%) of curcumin against S. mutans biofilm was 500 μM. Curcumin reduced the biofilm metabolism from 5 min to 24 h. Curcumin inhibited the quantity of live bacteria and total bacteria in both the short term (5 min) and the long term. Moreover, curcumin decreased the production of extracellular polysaccharide in the short term. The expression of genes related to extracellular polysaccharide synthesis, carbohydrate metabolism, adherence, and the two-component transduction system decreased after curcumin treatment. The chlorhexidine-treated group showed similar results. We speculate that curcumin has the capacity to be developed as an alternative agent with the potential to reduce the pathogenic traits of S. mutans biofilm.

Comparison of biofilm formation and migration of Streptococcus mutans on tooth roots and titanium miniscrews

Periodontitis and peri‐implantitis are inflammatory diseases caused by periodontal pathogenic bacteria leading to destruction of supporting periodontal/peri‐implant tissue. However, the progression of inflammatory process of these two diseases is different. The bacterial biofilm is the source of bacteria during the inflammatory process. As the bacteria migrate down the surface of tooth or titanium implant, the inflammation spreads along with it. Streptococcus mutans has an important role in oral bacterial biofilm formation in early stage biofilm before the microbiota shift to late stage and become more virulent. The other major difference is the existence of periodontal ligament (PDL) cells in normal teeth but not in peri‐implant tissue. This study aims to compare the S. mutans bacterial biofilm formation and migration on 2 different surfaces, tooth root and titanium miniscrew. The biofilm was grown with a flow cells system to imitate the oral dynamic system with PDL cells. The migration distances were measured, and the biofilm morphology was observed. Data showed that the biofilm formation on miniscrew was slower than those on tooth root at 24 hr. However, there were no difference in the morphology of the biofilm formed on the tooth root with those formed on the miniscrew at both 24 and 48 hr. The biofilm migration rate was significantly faster on miniscrew surface compare with those on tooth root when observe at 48 hr (p < .001). There are no significant differences in biofilm migration within miniscrew group and tooth root group despite the exiting of PDL cell (p > .05). The biofilm's migration rate differences on various surfaces could be one of the factors accounting for the different inflammatory progression between periodontitis and peri‐implantitis disease.

Green synthesis of silver nanoparticles combined to calcium glycerophosphate: antimicrobial and antibiofilm activities

AIM

To synthesize, characterize and evaluate the antimicrobial and antibiofilm activities of novel nanocomposites containing silver nanoparticles (AgNPs) associated or not to β-calcium glycerophosphate.

MATERIALS & METHODS

These nanocomposites were produced through a 'green' route using extracts of different parts of pomegranate. Antimicrobial and antibiofilm properties against Candida albicans and Streptococcus mutans were determined by the minimum bactericidal/fungicidal concentration and biofilm density after treatments.

RESULTS

All extracts used were successful in producing AgNPs. Composites made with peel extracts showed the highest antimicrobial and antibiofilm activity against both microorganisms tested and performed similarly or even better than chlorhexidine.

CONCLUSION

AgNPs associated or not to calcium glycerophosphate produced by a 'green' process may be a promising novel antimicrobial agent against oral microorganisms.

Carnosine-graphene oxide conjugates decorated with hydroxyapatite as promising nanocarrier for ICG loading with enhanced antibacterial effects in photodynamic therapy against Streptococcus mutans

Antimicrobial photodynamic therapy (aPDT) has been emerged as a noninvasive strategy to remove bacterial contaminants such as S. mutans from the tooth surface. Photosensitizer (PS), like indocyanine green (ICG), plays a key role in this technique which mainly suffers from the poor stability and concentration-dependent aggregation. An appropriate nanocarrier (NC) with enhanced antibacterial effects could overcome these limitations and improve the efficiency of ICG as a PS. In this study, various ICG-loaded NCs including graphene oxide (GO), GO-carnosine (Car) and GO-Car/Hydroxyapatite (HAp) were synthesized and characterized by Fourier Transform Infrared Spectroscopy (FT-IR), X-ray Diffraction (XRD), Filed Emission Scanning Electron Microscopy (FE-SEM), Energy Dispersive Spectroscopy (EDS), Zeta Potential and Ultraviolet-Visible spectrometry (UV-Vis). The colony forming unit and crystal violet assays were performed to evaluate the antimicrobial and anti-biofilm properties of PSs against S. mutans. The quantitative real-time PCR approach was also applied to determine the expression ratio of the gtfB gene in S. mutans. The zeta potential analysis and UV-Vis spectrometry indicated successful loading of ICG onto/into NCs. GO-Car/HAp showed highest amount of ICG loading (57.52%) and also highest aqueous stability after one week (94%). UV-Vis spectrometry analyses disclosed a red shift from 780 to 800 nm for the characteristic peak of ICG-loaded NCs. In the lack of aPDT, GO-Car@ICG showed the highest decrease in bacterial survival (86.4%) which indicated that Car could significantly promote the antibacterial effect of GO. GO@ICG, GO-Car@ICG and GO-Car/HAp@ICG mediated aPDT, dramatically declined the count of S. mutans strains to 91.2%, 95.5% and 93.2%, respectively (P < 0.05). The GO@ICG, GO-Car@ICG, GO-Car/HAp@ICG significantly suppressed the S. mutans biofilm formation by 51.4%, 63.8%, and 56.8%, respectively (P < 0.05). The expression of gtfB gene was considerably reduced to 6.0, 9.0 and 7.9-fold after aPDT in the presence of GO@ICG, GO-Car@ICG, GO-Car/HAp@ICG, respectively (P < 0.05). It could be concluded that the multi-functionalized GO as a novel nanocarrier could significantly enhance the ICG loading, stability, and improve its inhibitory effects as a photosensitizer in aPDT against S. mutans. These findings might provide opportunity for efficient treatment of local dental infections.

Enterococcus faecalis Hydrolyzes Dental Resin Composites and Adhesives

INTRODUCTION

After root canal treatment, the dentin-sealer interface undergoes degradation, allowing for interfacial microbial biofilm proliferation and treatment failure. Saliva and cariogenic bacteria showed esterase-like activities (ie, cholesterol esterase [CE]-like and/or pseudocholinesterase [PCE]-like) that degrade methacrylate-based resin materials and/or the restoration-tooth interface, increasing microbial interfacial proliferation. Enterococcus faecalis is a gram-positive bacterium that is commonly detected in persistent endodontic infections. The aim of this study was to measure E. faecalis esterase-like, CE-like, and PCE-like activities and to assess the ability of the bacterium to degrade methacrylate-based resin composite (RC) and total-etch (TE) and self-etch (SE) adhesives.

METHODS

CE-like and PCE-like activities from E. faecalis were measured using nitrophenyl and butyrylthiocholine substrates, respectively. The ability of E. faecalis to degrade resin composite, total-etch and self-etch adhesives was examined by quantifying the release of a universal resin degradation by-product (ie, Bis[hydroxypropoxy]-phenyl propane [BisHPPP]) using high-performance liquid chromatography.

RESULTS

E. faecalis showed CE-like (1.23 ± 0.13 U/μg dry bacteria) but no PCE-like activity. After 30 days and/or 14 days of incubation, the amount of BisHPPP released was significantly higher in the presence of bacteria versus media for TE and RC but not SE (P < .05). The amount of BisHPPP released after 30 days of incubation with bacteria was highest for TE (23.69 ± 1.72 μg/cm²) followed by RC (3.43 ± 1.20 μg/cm²) and lowest for SE (0.86 ± 0.44 μg/cm²) (P < .05).

CONCLUSIONS

E. faecalis possesses esterase-like degradative activity toward dental methacrylate resin restoration materials, which could accelerate the degradation of the dentin-methacrylate resin interface, increasing bacterial biofilm proliferation and penetration into the root canal system.

In silico analysis of the competition between Streptococcus sanguinis and Streptococcus mutans in the dental biofilm

During dental caries, the dental biofilm modifies the composition of the hundreds of involved bacterial species. Changing environmental conditions influence competition. A pertinent model to exemplify the complex interplay of the microorganisms in the human dental biofilm is the competition between Streptococcus sanguinis and Streptococcus mutans. It has been reported that children and adults harbor greater numbers of S. sanguinis in the oral cavity, associated with caries-free teeth. Conversely, S. mutans is predominant in individuals with a high number of carious lesions. Competition between both microorganisms stems from the production of H₂ O₂ by S. sanguinis and mutacins, a type of bacteriocins, by S. mutans. There is limited evidence on how S. sanguinis survives its own H₂ O₂ levels, or if it has other mechanisms that might aid in the competition against S. mutans, nonetheless. We performed a genomic and metabolic pathway comparison, coupled with a comprehensive literature review, to better understand the competition between these two species. Results indicated that S. sanguinis can outcompete S. mutans by the production of an enzyme capable of metabolizing H₂ O₂ . S. mutans, however, lacks the enzyme and is susceptible to the peroxide from S. sanguinis. In addition, S. sanguinis can generate energy through gluconeogenesis and seems to have evolved different communication mechanisms, indicating that novel proteins may be responsible for intra-species communication.

Ultrastructural damage in Streptococcus mutans incubated with saliva and histatin 5

OBJECTIVE

To study the ultrastructural alterations induced in Streptococcus mutans (ATCC 25175) incubated with saliva, saliva plus histatin 5 and histatin 5.

METHODS

S. mutans incubated with saliva histatin 5 or a combination of both were morphologically analyzed and counted. The results were expressed as (CFU)ml^-1. Ultrastructural damage was evaluated by transmission electron microscopy. Ultrastructural localization of histatin 5 was examined using immunogold labeling. Apoptotic cell death was determined by flow cytometry (TUNEL).

RESULTS

A decrease in the bacteria numbers was observed after incubation with saliva, saliva with histatin 5 or histatin 5 compared to the control group (p<0.0001). Ultrastructural damage in S. mutans incubated with saliva was found in the cell wall. Saliva plus histatin 5 induced a cytoplasmic granular pattern and decreased the distance between the plasma membrane bilayers, also found after incubation with histatin 5, together with pyknotic nucleoids. Histatin 5 was localized on the bacterial cell walls, plasma membranes, cytoplasm and nucleoids. Apoptosis was found in the bacteria incubated with saliva (63.9%), saliva plus histatin 5 (71.4%) and histatin 5 (29.3%). Apoptosis in the control bacteria was 0.2%.

CONCLUSIONS

Antibacterial activity against S. mutans and the morphological description of damage induced by saliva and histatin 5 was demonstrated. Pyknotic nucleoids observed in S. mutans exposed to saliva, saliva plus histatin 5 and histatin 5 could be an apoptosis-like death mechanism. The knowledge of the damage generated by histatin 5 and its intracellular localization could favor the design of an ideal peptide as a therapeutic agent.

The fructan syndrome: Evolutionary aspects and common themes among plants and microbes

Fructans are multifunctional fructose-based water soluble carbohydrates found in all biological kingdoms but not in animals. Most research has focused on plant and microbial fructans and has received a growing interest because of their practical applications. Nevertheless, the origin of fructan production, the so-called "fructan syndrome," is still unknown. Why fructans only occur in a limited number of plant and microbial species remains unclear. In this review, we provide an overview of plant and microbial fructan research with a focus on fructans as an adaptation to the environment and their role in (a)biotic stress tolerance. The taxonomical and biogeographical distribution of fructans in both kingdoms is discussed and linked (where possible) to environmental factors. Overall, the fructan syndrome may be related to water scarcity and differences in physicochemical properties, for instance, water retaining characteristics, at least partially explain why different fructan types with different branching levels are found in different species. Although a close correlation between environmental stresses and fructan production is quite clear in plants, this link seems to be missing in microbes. We hypothesize that this can be at least partially explained by differential evolutionary timeframes for plants and microbes, combined with potential redundancy effects.

Anticariogenic Activities of <I>Derris reticulata </I>Ethanolic Stem Extract Against <I>Streptococcus mutans</I>

BACKGROUND AND OBJECTIVE

Streptococcus mutans is a dominant causative pathogen of dental caries, which is a major oral health problem affecting million people worldwide. Derris reticulata is a medicinal plant possessing antimicrobial activity against several Gram-positive pathogenic bacteria. None the less, its effects on growth and cariogenic properties of S. mutans has not been clearly established. This study aimed to investigate the antibacterial and anti cariogenic activities of the D. reticulata ethanolic stem extract.

MATERIALS AND METHODS

The TLC analysis was performed to authenticate the D. reticulata sample. Minimum inhibition concentration and minimum bactericidal concentration were determined by using broth dilution and drop plate methods, respectively. Sucrose dependent and sucrose independent-adherences, biofilm formation and glycolytic pH drop assays were performed to evaluate the anticariogenic activity.

RESULTS

The ethanolic stem extract of D. reticulata possessed the antibacterial activity against S. mutans with the MIC and MBC of 0.875±0.250 and 1.750±0.500 mg mL-1, respectively. The extract at the lower concentrations of sub-MIC also had significant inhibitory actions against the cariogenic properties of S. mutans, including surface adherence, biofilm formation and glycolytic acid production.

CONCLUSION

The D. reticulata stem extract had a substantial anticariogenic activities and thus potentially be developed as an oral health care product for dental caries prevention in the near future.

Thymol and carvacrol induce autolysis, stress, growth inhibition and reduce the biofilm formation by Streptococcus mutans

Organic compounds from plants are an attractive alternative to conventional antimicrobial agents. Therefore, two compounds namely M-1 and M-2 were purified from Origanum vulgare L. and were identified as carvacrol and thymol, respectively. Antimicrobial and antibiofilm activities of these compounds along with chlorhexidine digluconate using various assays was determined against dental caries causing bacteria Streptococcus mutans. The IC₅₀ values of carvacrol (M-1) and thymol (M-2) against S. mutans were 65 and 54 µg/ml, respectively. Live and dead staining and the MTT assays reveal that a concentration of 100 µg/ml of these compounds reduced the viability and the metabolic activity of S. mutans by more than 50%. Biofilm formation on the surface of polystyrene plates was significantly reduced by M-1 and M-2 at 100 µg/ml as observed under scanning electron microscope and by colorimetric assay. These results were in agreement with RT-PCR studies. Wherein exposure to 25 µg/ml of M-1 and M-2 showed a 2.2 and 2.4-fold increase in Autolysin gene (AtlE) expression level, respectively. While an increase of 1.3 and 1.4 fold was observed in the super oxide dismutase gene (sodA) activity with the same concentrations of M-1 and M-2, respectively. An increase in the ymcA gene and a decrease in the gtfB gene expression levels was observed following the treatment with M-1 and M-2. These results strongly suggest that carvacrol and thymol isolated from O. vulgare L. exhibit good bactericidal and antibiofilm activity against S. mutans and can be used as a green alternative to control dental caries.

Two-component signal transduction systems in oral bacteria

We present an overview of how members of the oral microbiota respond to their environment by regulating gene expression through two-component signal transduction systems (TCSs) to support conditions compatible with homeostasis in oral biofilms or drive the equilibrium toward dysbiosis in response to environmental changes. Using studies on the sub-gingival Gram-negative anaerobe Porphyromonas gingivalis and Gram-positive streptococci as examples, we focus on the molecular mechanisms involved in activation of TCS and species specificities of TCS regulons.

In vitro and in vivo evaluations of glass-ionomer cement containing chlorhexidine for Atraumatic Restorative Treatment

Objectives:

Addition of chlorhexidine has enhanced the antimicrobial effect of glass ionomer cement (GIC) indicated to Atraumatic Restorative Treatment (ART); however, the impact of this mixture on the properties of these materials and on the longevity of restorations must be investigated. The aim of this study was to evaluate the effects of incorporating chlorhexidine (CHX) in the in vitro biological and chemical-mechanical properties of GIC and in vivo clinical/ microbiological follow-up of the ART with GIC containing or not CHX.

Material and Methods:

For in vitro studies, groups were divided into GIC, GIC with 1.25% CHX, and GIC with 2.5% CHX. Antimicrobial activity of GIC was analyzed using agar diffusion and anti-biofilm assays. Cytotoxic effects, compressive tensile strength, microhardness and fluoride (F) release were also evaluated. A randomized controlled trial was conducted on 36 children that received ART either with GIC or GIC with CHX. Saliva and biofilm were collected for mutans streptococci (MS) counts and the survival rate of restorations was checked after 7 days, 3 months and one year after ART. ANOVA/Tukey or Kruskal-Wallis/ Mann-Whitney tests were performed for in vitro tests and in vivo microbiological analysis. The Kaplan-Meier method and Log rank tests were applied to estimate survival percentages of restorations (p<0.05).

Results:

Incorporation of 1.25% and 2.5% CHX improved the antimicrobial/anti-biofilm activity of GIC, without affecting F release and mechanical characteristics, but 2.5% CHX was cytotoxic. Survival rate of restorations using GIC with 1.25% CHX was similar to GIC. A significant reduction of MS levels was observed for KM+CHX group in children saliva and biofilm 7 days after treatment.

Conclusions:

The incorporation of 1.25% CHX increased the in vitro antimicrobial activity, without changing chemical-mechanical properties of GIC and odontoblast-like cell viability. This combination improved the in vivo short-term microbiological effect without affecting clinical performance of ART restorations.

LT adjuvant modulates epitope specificity and improves the efficacy of murine antibodies elicited by sublingual vaccination with the N-terminal domain of Streptococcus mutans P1

In this study, we evaluated the immunogenicity, protective efficacy and peptide-based immune signatures of antibodies raised in mice after sublingual immunization with a recombinant form of the P1 (aka AgI/II, PAc) adhesin (P1_39-512) of Streptococcus mutans, a major etiological agent of dental caries. Sublingual administration of P1_39-512 in combination with the mucosal adjuvant LTK4R (a derivative of heat-labile LT toxin) induced strong and long-lasting systemic and mucosal immune responses. Incorporation of the adjuvant resulted in an enhancement of the anti-adhesive and anti-colonization activity against S. mutans as evaluated both under in vitro and in vivo conditions. Incorporation of the adjuvant to the vaccine formulation also changed the epitope specificity of the induced antibodies as determined by immunological signatures of sera collected from vaccinated mice. Use of a peptide microarray library led to the identification of peptide targets recognized by antibodies in serum samples with enhanced anti-adhesive effects. Altogether, the results presented herein showed that the sublingual administration of a P1-based subunit vaccine represents a promising approach for the prevention of dental caries caused by S. mutans. In addition, the present study disclosed the role of adjuvants on the epitope specificity and functionality of antibodies raised by subunit vaccines.

Quantification of carious pathogens in the interdental microbiota of young caries-free adults

Background

The majority of caries lesions in adults occur on the proximal tooth surfaces of the posterior teeth. A comprehensive study of the composition of the oral microbiota is fundamental for a better understanding of the etiology of interdental caries.

Methods

Twenty-five caries-free subjects (20–35 years old) were enrolled in the study. The interdental biofilm of four interdental sites were collected. The real-time polymerase chain reaction (PCR) methodology were used to quantify (i) the following bacteria: Streptococcus spp., Streptococcus mutans, Lactobacillus spp., Enterococcus spp., and Enterococcus faecalis; (ii) the fungus Candida albicans; and (iii) total bacteria.

Results

Streptococcus spp. was the most abundant species, followed by Lactobacillus spp. and Enterococcus spp. Streptococcus spp. and Lactobacillus spp. were detected at all tested sites and Enterococcus spp. at 99% of sites. S. mutans was detected at only 28% of the tested sites and C. albicans was detected at 11% of sites. E. faecalis was never detected. In 54.5% of the biofilm inhabited by C. albicans, S. mutans was present. Moreover, 28% of the ID sites co-expressed S. mutans and Lactobacillus spp. The studied pathogens were organized into two correlated groups of species. Strikingly, the fungus C. albicans and the bacteria Enterococcus spp. cluster together, whereas Streptococcus spp., S. mutans and Lactobacillus spp. form one distinct cluster.

Conclusion

The interdental biofilm of young caries-free adults is comprised of pathogens that are able to induce interproximal caries. That several of these pathogens are implicated in heart disease or other systemic diseases is an argument for the disruption of interdental biofilms using daily oral hygiene.

Effects of Cola-Flavored Beverages and Caffeine on Streptococcus mutans Biofilm Formation and Metabolic Activity

OBJECTIVE

To examine the effects of cola-flavored beverages and caffeine on growth and metabolism of Streptococcus mutans biofilm. This study was designed to determine if carbonated beverages or caffeine can increase S. mutans growth and biofilm formation and metabolic activity in vitro, potentially leading to increased S. mutans-associated cariogenicity in children that consume them.

STUDY DESIGN

Six different cola-flavored products, plus pure caffeine, and pure high fructose corn syrup (HFCS), at different concentrations similar to those in the beverages were tested. A 16-hour culture of S. mutans was treated with different dilutions in bacteriological media. To test for the effect on biofilm formation, the biofilm was stained with crystal violet. The absorbance was determined to evaluate biofilm growth. Biofilm metabolic activity was measured based on biofilm having the ability to reduce XTT to a water-soluble orange compound.

RESULTS

The inclusion of HFCS in the beverages, as well as pure HFCS, significantly enhanced bacterial biofilm formation and metabolic activity. Pure caffeine and the presence of caffeine in beverages did not significantly increase biofilm formation, but pure caffeine significantly increased metabolism, and Diet Coke had significantly greater metabolic activity than Caffeine-Free Diet Coke.

CONCLUSIONS

HFCS increases both the biofilm formation and metabolism of S. mutans, and caffeine in some cases increases metabolism of S. mutans.

Raffinose Induces Biofilm Formation by Streptococcus mutans in Low Concentrations of Sucrose by Increasing Production of Extracellular DNA and Fructan

Streptococcus mutans is the primary etiological agent of dental caries and causes tooth decay by forming a firmly attached biofilm on tooth surfaces. Biofilm formation is induced by the presence of sucrose, which is a substrate for the synthesis of extracellular polysaccharides but not in the presence of oligosaccharides. Nonetheless, in this study, we found that raffinose, which is an oligosaccharide with an intestinal regulatory function and antiallergic effect, induced biofilm formation by S. mutans in a mixed culture with sucrose, which was at concentrations less than those required to induce biofilm formation directly. We analyzed the possible mechanism behind the small requirement for sucrose for biofilm formation in the presence of raffinose. Our results suggested that sucrose contributed to an increase in bacterial cell surface hydrophobicity and biofilm formation. Next, we examined how the effects of raffinose interacted with the effects of sucrose for biofilm formation. We showed that the presence of raffinose induced fructan synthesis by fructosyltransferase and aggregated extracellular DNA (eDNA, which is probably genomic DNA released from dead cells) into the biofilm. eDNA seemed to be important for biofilm formation, because the degradation of DNA by DNase I resulted in a significant reduction in biofilm formation. When assessing the role of fructan in biofilm formation, we found that fructan enhanced eDNA-dependent cell aggregation. Therefore, our results show that raffinose and sucrose have cooperative effects and that this induction of biofilm formation depends on supportive elements that mainly consist of eDNA and fructan.IMPORTANCE The sucrose-dependent mechanism of biofilm formation in Streptococcus mutans has been studied extensively. Nonetheless, the effects of carbohydrates other than sucrose are inadequately understood. Our findings concerning raffinose advance the understanding of the mechanism underlying the joint effects of sucrose and other carbohydrates on biofilm formation. Since raffinose has been reported to have positive effects on enterobacterial flora, research on the effects of raffinose on the oral flora are required prior to its use as a beneficial sugar for human health. Here, we showed that raffinose induced biofilm formation by S. mutans in low concentrations of sucrose. The induction of biofilm formation generally generates negative effects on the oral flora. Therefore, we believe that this finding will aid in the development of more effective oral care techniques to maintain oral flora health.

Effects of Arginine on Streptococcus mutans Growth, Virulence Gene Expression, and Stress Tolerance

Streptococcus mutans is a common constituent of oral biofilms and a primary etiologic agent of human dental caries. The bacteria associated with dental caries have potent abilities to produce organic acids from dietary carbohydrates and to grow and metabolize in acidic conditions. By contrast, many commensal bacteria produce ammonia through the arginine deiminase system (ADS), which moderates the pH of oral biofilms. Arginine metabolism by the ADS is a significant deterrent to the initiation and progression of dental caries. In this study, we observed how exogenously provided l-arginine affects the growth, the virulence properties, and the tolerance of environmental stresses of S. mutans Supplementation with 1.5% arginine (final concentration) had an inhibitory effect on the growth of S. mutans in complex and chemically defined media, particularly when cells were exposed to acid or oxidative stress. The genes encoding virulence factors required for attachment/accumulation (gtfB and spaP), bacteriocins (nlmA, nlmB, nlmD, and cipB), and the sigma factor required for competence development (comX) were downregulated during growth with 1.5% arginine. Deep sequencing of RNA (RNA-Seq) comparing the transcriptomes of S. mutans growing in chemically defined media with and without 1.5% arginine revealed differential expression of genes encoding ATP-binding cassette transporters, metal transporters, and constituents required for survival, metabolism, and biofilm formation. Therefore, the mechanisms of action by which arginine inhibits dental caries include direct adverse effects on multiple virulence-related properties of the most common human dental caries pathogen.IMPORTANCE Metabolism of the amino acid arginine by the arginine deiminase system (ADS) of certain oral bacteria raises the pH of dental plaque and provides a selective advantage to health-associated bacteria, thereby protecting the host from dental caries (cavities). Here, we examine the effects of arginine on the cavity-causing bacterium Streptococcus mutans We find that arginine negatively impacts the growth, the pathogenic potential, and the tolerance of environmental stresses in a way that is likely to compromise the ability of S. mutans to cause disease. Using genetic and genomic techniques, multiple mechanisms by which arginine exerts its influence on virulence-related properties of S. mutans are discovered. This report demonstrates that a primary mechanism of action by which arginine inhibits the initiation and progression of dental caries may be by reducing the pathogenic potential of S. mutans.

Novel multifunctional dental cement to prevent enamel demineralization near orthodontic brackets

OBJECTIVES

White spot lesions due to biofilm acid-induced enamel demineralization are prevalent in orthodontic treatments. The aim of this study was to develop a novel bioactive multifunctional cement with protein-repellent, antibacterial and remineralizing capabilities, and investigate the effects on enamel hardness and lesion depth in vitro for the first time.

MATERIALS AND METHODS

2-Methacryloyloxyethyl phosphorylcholine (MPC), dimethylaminohexadecyl methacrylate (DMAHDM), and nanoparticles of amorphous calcium phosphate (NACP) were incorporated into a resin-modified glass ionomer (RMGI). Extracted human premolars had brackets bonded via four groups: (1) Transbond XT (TB), (2) RMGI (GC Ortho LC), (3) RMGI+MPC+DMAHDM, (4) RMGI+MPC+DMAHDM+NACP. Demineralization was induced via a dental plaque microcosm biofilm model. Samples were tested using polarized light microscopy (PLM) for lesion depth. Enamel hardness was tested for different groups.

RESULTS

Incorporating MPC, DMAHDM and NACP did not affect enamel bond strength. "RMGI+MPC+DMAHDM+NACP" group had the least lesion depth in enamel (p<0.05). Groups with NACP had the highest enamel hardness (p<0.05). Mineral loss (ΔS) in enamel for NACP group was about one third that for RMGI control. "RMGI+MPC+DMAHDM" had greater effect on demineralization-inhibition, compared to RMGI and TB controls. "RMGI+MPC+DMAHDM+NACP" was more effective in protecting enamel prisms from dissolution by biofilm acids, compared to RMGI and TB control groups.

CONCLUSION

The Novel "RMGI+MPC+DMAHDM+NACP" cement substantially reduced enamel demineralization adjacent to orthodontic brackets, yielding much less lesion depth and greater enamel hardness under biofilm acid attacks than commercial controls. The clinical significance is that the novel multi-agent (RMGI+MPC+DMAHDM+NACP) method is promising for a wide range of preventive and restorative applications to combat caries.

Thyme Oil Reduces Biofilm Formation and Impairs Virulence of Xanthomonas oryzae

Xanthomonas oryzae pv. oryzae (Xoo), a common bacterial plant pathogen regulates its virulence and biofilm formation attribute via a chemical method of communication. Disabling this mechanism offers a promising alternative to reduce the virulence and pathogencity of the microorganism. In this study, the effect of thyme (THY) oil on Quorum Sensing mediated synthesis of various virulence factors and biofilm formation was analyzed. Treatment of Xoo with 500 ppm THY oil displayed a significant diminution in swimming, swarming, exopolysaccharide and xanthomonadin secretion. However, no effect was observed on bacterial growth kinetics and metabolic activity of the cells. Results were further authenticated by RT-qPCR as significant reduction in motA, motB, and flgE genes was observed upon THY oil treatment. Similarly, the expression of some extracellular enzyme genes such as endoglucanase, xylanase, cellobiosidase, and polygalacturonase was also found to be significantly reduced. However, biochemical plate assays revealed insignificant effect of 500 ppm THY oil on secretion of protease, cellulase, and lipase enzymes. The rpfF gene known to play a crucial role in the virulence of the phytopathogenic bacteria was also significantly reduced in the THY oil treated Xoo cells. HPTLC analysis further revealed significant reduction in DSF and BDSF signaling molecules when Xoo cells were treated with 500 ppm THY oil. Disease reduction was observed in in vitro agar plate assay as lesion length was reduced in THY oil treated Xoo cells when compared with the alone treatment. GC-MS result revealed thymol as the active and major component of THY oil which showed potential binding with rpfF gene. Application of 75 μM thymol resulted in downregulation of gumC, motA, estA, virulence acvB and pglA along with rpfF. The other genes such as cheD, flgA, cheY, and pilA, were not found to be significantly affected. Overall, the results clearly indicated THY oil and its active component Thymol to be a potential candidate for the development of anti-virulence agent which in future when applied in combination with conventional bactericides might not only help in lowering the dose of bactericides but also be successful in curbing the disease progression in rice.