The virulence of Streptococcus mutans and the ability to form biofilms

Effects of Hydrogen-rich Water on Cariogenic Bacteria

Context

Some kinds of electrolysed water have been reported to exhibit antioxidant and bactericidal activity. However, studies on the effect of electrolysed hydrogen-rich water (EHW) with a neutral pH on cariogenic bacteria are limited.

Aim

This study aimed to evaluate the feasibility of using EHW as a mouthwash by examining its various effects on cariogenic bacteria.

Materials and Methods

To test the bactericidal and anti-biofilm formation effects of EHW on Streptococcus mutans and Streptococcus sobrinus, bacterial growth curves, colony-forming unit (CFU) counts, and crystal violet staining of biofilms were examined after exposing the bacterial pellets to EHW or tap water as a control for one minute. In addition, the expressions of glucosyltransferase and glucan-binding proteins encoding genes were examined using real-time PCR.

Results

Bacterial growth and biofilm formation were inhibited, and the number of CFUs was significantly reduced in the EHW group compared to the control group. The expression of genes encoding glucosyltransferases (gtfB, gtfC, and gtfI) and glucan-binding proteins (gbpC and dblB) were also decreased in the EHW group compared to the control.

Conclusions

Exposing cariogenic bacteria to EHW at neutral pH for one minute can effectively inhibit bacterial growth and biofilm formation in vitro, suggesting that EHW is a promising mouthwash.

Regulatory mechanisms of exopolysaccharide synthesis and biofilm formation in Streptococcus mutans

Background

Dental caries is a chronic, multifactorial and biofilm-mediated oral bacterial infection affecting almost every age group and every geographical region. Streptococcus mutans is considered an important pathogen responsible for the initiation and development of dental caries. It produces exopolysaccharides in situ to promote the colonization of cariogenic bacteria and coordinate dental biofilm development.

Objective

The understanding of the regulatory mechanism of S. mutans biofilm formation can provide a theoretical basis for the prevention and treatment of caries.

Design

At present, an increasing number of studies have identified many regulatory systems in S. mutans that regulate biofilm formation, including second messengers (e.g. c-di-AMP, Ap4A), transcription factors (e.g. EpsR, RcrR, StsR, AhrC, FruR), two-component systems (e.g. CovR, VicR), small RNA (including sRNA0426, srn92532, and srn133489), acetylation modifications (e.g. ActG), CRISPR-associated proteins (e.g. Cas3), PTS systems (e.g. EIIAB), quorum-sensing signaling system (e.g. LuxS), enzymes (including Dex, YidC, CopZ, EzrA, lmrB, SprV, RecA, PdxR, MurI) and small-molecule metabolites.

Results

This review summarizes the recent progress in the molecular regulatory mechanisms of exopolysaccharides synthesis and biofilm formation in S. mutans.

Roles of Streptococcus mutans-Candida albicans interaction in early childhood caries: a literature review

As one of the most common oral diseases in kids, early childhood caries affects the health of children throughout the world. Clinical investigations show the copresence of Candida albicans and Streptococcus mutans in ECC lesions, and mechanistic studies reveal co-existence of C. albicans and S. mutans affects both of their cariogenicity. Clearly a comprehensive understanding of the interkingdom interaction between these two microorganisms has important implications for ECC treatment and prevention. To this end, this review summarizes advances in our understanding of the virulence of both C. albicans and S. mutans. More importantly, the synergistic and antagonistic interactions between these two microbes are discussed.

The cell wall lipoprotein CD1687 acts as a DNA binding protein during deoxycholate-induced biofilm formation in Clostridioides difficile

The ability of bacterial pathogens to establish recurrent and persistent infections is frequently associated with their ability to form biofilms. Clostridioides difficile infections have a high rate of recurrence and relapses and it is hypothesized that biofilms are involved in its pathogenicity and persistence. Biofilm formation by C. difficile is still poorly understood. It has been shown that specific molecules such as deoxycholate (DCA) or metronidazole induce biofilm formation, but the mechanisms involved remain elusive. In this study, we describe the role of the C. difficile lipoprotein CD1687 during DCA-induced biofilm formation. We showed that the expression of CD1687, which is part of an operon within the CD1685-CD1689 gene cluster, is controlled by multiple transcription starting sites and some are induced in response to DCA. Only CD1687 is required for biofilm formation and the overexpression of CD1687 is sufficient to induce biofilm formation. Using RNAseq analysis, we showed that CD1687 affects the expression of transporters and metabolic pathways and we identified several potential binding partners by pull-down assay, including transport-associated extracellular proteins. We then demonstrated that CD1687 is surface exposed in C. difficile, and that this localization is required for DCA-induced biofilm formation. Given this localization and the fact that C. difficile forms eDNA-rich biofilms, we confirmed that CD1687 binds DNA in a non-specific manner. We thus hypothesize that CD1687 is a component of the downstream response to DCA leading to biofilm formation by promoting interaction between the cells and the biofilm matrix by binding eDNA.

Identification of the antibacterial action mechanism of curcumin on Streptococcus mutans through transcriptome profiling

OBJECTIVE

The purpose of this study was to explore the effect and mechanism responsible for how curcumin affects the biofilm formation by Streptococcus mutans (S. mutans).

DESIGN

The antibacterial activity of curcumin was evaluated by measuring the minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC). The mass of the biofilm was measured by crystal violet staining. Transcriptome sequencing was used to obtain all the transcript information associated with the biological activity of curcumin-treated S. mutans. Real-time quantitative PCR (qRT-PCR) was performed to examine the expression levels of related biofilm formation genes.

RESULTS

The MIC value for curcumin was 64 μM. Curcumin inhibited the formation of a biofilm by S. mutans and degraded mature biofilms. A gene ontology enrichment analysis showed that the DEGs were significantly relevant to biofilm formation. In addition, 17 significantly enriched Kyoto Encyclopedia of Genes and Genomes pathways (p ≤ 0.01) were identified and were potentially associated with the biochemical metabolic processes of S. mutans. DEGs associated with the biofilm formation of S. mutants, including gtfB, gtfC, rgpG, spaP, spxA1, spxA2, bacA, lrgB, and gshAB. The qRT-PCR results were consistent with transcriptome sequencing that the expression levels of gtfB, gtfC, rgpG, and spaP significantly decreased in the curcumin-treated group, whereas the expression levels of spx1, spx2, bacA, lrgB, and gshAB were up-regulated.

CONCLUSIONS

Curcumin showed marked inhibitory effects against the formation of biofilms by S. mutans and degradation of formed biofilms.

Symbiotic relationship between Prevotella denticola and Streptococcus mutans enhances virulence of plaque biofilms

OBJECTIVES

This study aimed to explore that whether interactions between Prevotella denticola and Streptococcus mutans could promote the establishment of hypervirulent biofilms on teeth surface and eventually influence the occurrence and development of caries.

DESIGN

Based on single-species biofilms of either P. denticola or S. mutans, and dual-species biofilms of both bacteria, we compared the virulence properties associated with cariogenicity in vitro, including carbohydrate metabolism and acid productivity, synthesis of extracellular polysaccharides, biomass and architecture of biofilms, level of enamel demineralization and expression of virulence genes associated with carbohydrate metabolism and adhesion in S. mutans.

RESULTS

The data demonstrated that, compared to single-species of above two taxa, dual-species produced lactate by metabolizing carbohydrates at a higher level during the observation period. Moreover, dual-species biofilms accrued more biomass and exhibited more dense microcolonies and abundant extracellular matrix. And it's noticeable that the level of enamel demineralization in dual-species biofilms was more augmented than that of single-species. In addition, the presence of P. denticola induced the expression of virulence genes gtfs and gbpB in S. mutans.

CONCLUSIONS

Symbiotic relationship between P. denticola and S. mutans enhances caries-associated virulence of plaque biofilms, which might provide new strategies for effective prevention and treatment of caries.

The effect of synbiotic-fluoride therapy on multi-species biofilm

OBJECTIVES

The study objective was to examine the effect of synbiotic-fluoride (SF) therapy within a multi-species cariogenic biofilm model system comprising of S. mutans, S. sanguinis, and S. gordonii.

METHODS

The SF therapy was prepared using 2% L-arginine (Arg), 0.2% NaF and probiotic L. rhamnosus GG (LRG). The 8 treatment groups were: Group 1: No treatment, Group 2: 2% Arg, Group 3: 0.2% NaF, Group 4: LRG, Group 5: 2% Arg+0.2% NaF, Group 6: 2% Arg+LRG, Group 7: 0.2% NaF+LRG, and Group 8: SF therapy (2% Arg+0.2% NaF +LRG). Multi-species biofilm model over 96 h comprising Streptococcus mutans, Streptococcus sanguinis, and Streptococcus gordonii was utilized. The biofilms received cariogenic challenge and SF therapy 2 × /day. The extracellular matrix components were analyzed for carbohydrates, proteins, and extra-cellular DNA (eDNA). The live/dead cells were imaged and quantified using confocal microscopy. The viable/dead bacterial concentrations were estimated using propidium monoazide-quantitative polymerase chain reaction (PMA-qPCR). The gene expressions for gtfB, sagP, arcA, argG, and argH were measured using real-time reverse transcriptase qPCR.

RESULTS

Carbohydrates and protein content with SF therapy were higher than non-LRG containing groups, while eDNA content was lower than other groups (p<0.05). Live bacterial proportions determined using confocal imaging with SF therapy were the lowest (p<0.05). The 2% Arg+LRG and SF therapy showed higher viable L. rhamnosus GG than 0.2% NaF+LRG (p<0.05). The dead S. mutans with SF therapy were higher than the other groups (p<0.05) with no difference from 2% Arg+0.2% NaF and 2% Arg+LRG (p>0.05). The SF therapy significantly downregulates gtfB and upregulates sagP, arcA, argG, argH gene expression (p<0.05).

CONCLUSION

Synbiotic-fluoride therapy effectuates multi-fold changes in the multi-species biofilm matrix and cellular components leading to superior ecological homeostasis than its individual contents, prebiotics (arginine), probiotic (L. rhamnosus GG), and fluorides (NaF).

CLINICAL SIGNIFICANCE

The ecological-based synbiotic-fluoride caries-preventive therapy aids in maintaining biofilm homeostasis to preempt/restore dysbiosis thereby sustaining dynamic-diverse health-associated microbial stability significant as a preventive regimen for high caries-risk patients.

A novel glass ionomer cement with silver zeolite for restorative dentistry

OBJECTIVE

To develop an antimicrobial silver zeolite glass ionomer cement (SZ-GIC) and determine its biocompatibility, physical, adhesive and antibacterial properties.

METHODS

Silver nitrate and sodium zeolite were used to synthesize silver zeolite (SZ). SZ-GICs were prepared by incorporating SZ into GIC at 5% (SZ-GIC5), 2% (SZ-GIC2), or 1% (SZ-GIC1) by weight, respectively. The SZ-GICs were characterized by evaluating surface morphology, topography and elemental composition. SZ-GICs' biocompatibility was assessed by evaluating cell cytotoxicity. Their physical properties were determined by testing setting time, compressive strength, flexural strength, water sorption and solubility. Their adhesive property was assessed by evaluating micro-tensile bond strength. Their antibacterial properties were assessed by evaluating biofilm growth kinetic, metabolic activity, viability and morphology. GIC was used as a control.

RESULTS

SZ was a three-dimensional crystalline mineral. SZ-GICs (including SZ-GIC 5, 2 and 1) showed similar surface morphology and topography to GIC. SZ-GIC1 and GIC had no difference in cell cytotoxicity (p>0.05). SZ-GICs and GIC showed no difference in setting time (p>0.05). SZ-GICs had higher compressive and flexural strength than GIC (p<0.05). SZ-GIC2 and SZ-GIC1 showed lower water sorption and solubility than GIC (p<0.05). SZ-GICs had higher micro-tensile bond strength than GIC (p<0.05). Biofilms on SZ-GICs' surfaces showed lower colony-forming units, decreased metabolic activities, higher percentages of dead cells and more ruptured bacterial cells compared with those on GIC.

CONCLUSION

SZ-GIC with silver zeolite at 1% by weight are as biocompatible as conventional GIC. The SZ-GICs have enhanced physical, adhesive and antibacterial properties than GIC.

CLINICAL SIGNIFICANCE

A silver zeolite glass ionomer cement was developed. The SZ-GICs have great potential for caries prevention and management.

Synchrotron X-ray Studies of the Structural and Functional Hierarchies in Mineralised Human Dental Enamel: A State-of-the-Art Review

Hard dental tissues possess a complex hierarchical structure that is particularly evident in enamel, the most mineralised substance in the human body. Its complex and interlinked organisation at the Ångstrom (crystal lattice), nano-, micro-, and macro-scales is the result of evolutionary optimisation for mechanical and functional performance: hardness and stiffness, fracture toughness, thermal, and chemical resistance. Understanding the physical-chemical-structural relationships at each scale requires the application of appropriately sensitive and resolving probes. Synchrotron X-ray techniques offer the possibility to progress significantly beyond the capabilities of conventional laboratory instruments, i.e., X-ray diffractometers, and electron and atomic force microscopes. The last few decades have witnessed the accumulation of results obtained from X-ray scattering (diffraction), spectroscopy (including polarisation analysis), and imaging (including ptychography and tomography). The current article presents a multi-disciplinary review of nearly 40 years of discoveries and advancements, primarily pertaining to the study of enamel and its demineralisation (caries), but also linked to the investigations of other mineralised tissues such as dentine, bone, etc. The modelling approaches informed by these observations are also overviewed. The strategic aim of the present review was to identify and evaluate prospective avenues for analysing dental tissues and developing treatments and prophylaxis for improved dental health.

Six Spain Thymus essential oils composition analysis and their in vitro and in silico study against Streptococcus mutans

BACKGROUND

Streptococcus mutans is a well-known oral pathogen that plays a critical role in the development of dental caries. Many studies have been directed to discover the chemical compounds present in natural products to inhibit the growth and biofilm formation activity of S. mutans. Thymus essential oils exhibit good inhibition on the growth and pathogenesis of S. mutans. However, details about the active compounds in Thymus essential oil and the inhibition mechanism still remain unclear. The aim of this study was to investigate the antimicrobial activity of 6 Thymus species (Three samples of Thymus vulgaris, two samples of Thymus zygis, and one sample of Thymus satureioides essential oils) on S. mutans, to identify the potential active components, and to reveal the underlying mechanism.

METHODS

The composition of Thymus essential oils was analyzed by gas chromatography-mass spectrometry. And its antibacterial effect was evaluated based on the bacterial growth, acid production, biofilm formation and genetic expression of virulence factors by S. mutans. Potential active components of the Thymus essential oil were identified using molecular docking and correlation analysis.

RESULTS

GC-MS analysis showed that the major components in the 6 Spain Thymus essential oils were linalool, α-terpineol, p-cymene, thymol and carvacrol. MIC and MBC analysis showed that 3 Thymus essential oils showed very sensitive antimicrobial activity, and were chosen for further analysis. The 3 Thymus essential oil exhibited a significant inhibitory effect on acid production, adherence and biofilm formation of S. mutans and the expression of virulence genes, such as brpA, gbpB, gtfB, gtfC, gtfD, vicR, spaP and relA. Correlation analysis showed that phenolic components, such as carvacrol and thymol, were positively related to DIZ value, which suggests that they are the potential antimicrobial components. Molecular docking between the Thymus essential oil components and virulence proteins also found that carvacrol and thymol exhibited strong binding affinity with functional domains of virulence genes.

CONCLUSIONS

Thymus essential oil showed significant inhibition against the growth and pathogenesis of S. mutans depending on their composition and concentration. And phenolic compounds, such as carvacrol and thymol, are the major active components. Thymus essential oil could be used in oral healthcare products as a potential anti-caries ingredient.

Anti-Bacterial and Anti-Biofilm Activities of Anandamide against the Cariogenic Streptococcus mutans

Streptococcus mutans is a cariogenic bacterium in the oral cavity involved in plaque formation and dental caries. The endocannabinoid anandamide (AEA), a naturally occurring bioactive lipid, has been shown to have anti-bacterial and anti-biofilm activities against Staphylococcus aureus. We aimed here to study its effects on S. mutans viability, biofilm formation and extracellular polysaccharide substance (EPS) production. S. mutans were cultivated in the absence or presence of various concentrations of AEA, and the planktonic growth was followed by changes in optical density (OD) and colony-forming units (CFU). The resulting biofilms were examined by MTT metabolic assay, Crystal Violet (CV) staining, spinning disk confocal microscopy (SDCM) and high-resolution scanning electron microscopy (HR-SEM). The EPS production was determined by Congo Red and fluorescent dextran staining. Membrane potential and membrane permeability were determined by diethyloxacarbocyanine iodide (DiOC2(3)) and SYTO 9/propidium iodide (PI) staining, respectively, using flow cytometry. We observed that AEA was bactericidal to S. mutans at 12.5 µg/mL and prevented biofilm formation at the same concentration. AEA reduced the biofilm thickness and biomass with concomitant reduction in total EPS production, although there was a net increase in EPS per bacterium. Preformed biofilms were significantly affected at 50 µg/mL AEA. We further show that AEA increased the membrane permeability and induced membrane hyperpolarization of these bacteria. AEA caused S. mutans to become elongated at the minimum inhibitory concentration (MIC). Gene expression studies showed a significant increase in the cell division gene ftsZ. The concentrations of AEA needed for the anti-bacterial effects were below the cytotoxic concentration for normal Vero epithelial cells. Altogether, our data show that AEA has anti-bacterial and anti-biofilm activities against S. mutans and may have a potential role in preventing biofilms as a therapeutic measure.

Novel Lactotransferrin-Derived Antimicrobial Peptide LF-1 Inhibits the Cariogenic Virulence Factors of Streptococcus mutans

We previously developed a novel lactotransferrin-derived antimicrobial peptide, LF-1, with selective antibacterial activity against the characteristic cariogenic bacterium Streptococcus mutans. This study further investigated the effects of LF-1 on the cariogenic virulence factors of S. mutans and evaluated the changes in virulence-associated enzymes and genes; the viability, acidogenicity, and aciduricity of planktonic S. mutans; and initial colonisation and biofilm formation after treatment with LF-1. The method of qRT-PCR was used to evaluate S. mutans virulence-associated gene expression. LF-1 interfered with the cell viability of S. mutans within 6 h. LF-1 inhibited the acidogenicity and aciduricity of S. mutans, with reduced lactic acid production and survival in a lethal acidic environment, and inactivated lactate dehydrogenase and F1F0-ATPase activity. LF-1 decreased surface-adherent S. mutans within 60 min and inhibited S. mutans biofilm formation, where scanning electron microscopy and confocal laser scanning microscopy showed reduced extracellular matrix and bacteria. LF-1 downregulates S. mutans virulence-associated gene expression. LF-1 inhibited the growth and cariogenic virulence factors of S. mutans in vitro with a reduction in key enzymatic activity and downregulation of virulence-associated gene expression. LF-1 has promising application prospects in the fight against S. mutans and dental caries.

mltG gene deletion mitigated virulence potential of Streptococcus mutans: An in-vitro, ex-situ and in-vivo study

Bacterial cells are surrounded by a peptidoglycan (PG) cell wall, which is essential for cell integrity and intrinsic biogenesis pathways; hence, the cell wall is a potential target for several antibiotics. Among several lytic transglycosylases (LTs), the mltG gene plays a crucial role in the synthesis of peripheral PG. It localises the re-modelled PGs for septum formation and cleavage across the bacterial cell wall during daughter cells separation. However, the role of mltG gene in bacterial virulence, particularly in Gram-positive bacteria during dentine biofilm and caries development, has remained unexplored. Hence, we exploited Gram-positive Streptococcus mutans cells for the very first time to construct a mltG knock-out bacterial strain, e.g., ΔmltG S. mutans. Systematic comparative investigations revealed that doubling time (Td), survival, enzymatic efficiencies, pH tolerance, bio-synthesise of lipid, proteins and DNA, biofilm formation and dentine lesions were significantly (p < 0.001) compromised in case of ΔmltG S. mutans than wild type strain. The qRT-PCR based gene expression profiling revealed that transcriptional expression of critically important genes involved in biofilm, metabolism, and stress response were dysregulated in the mutant. Besides, an incredible reduction in dentine caries development was found in the molar teeth of Wistar rats and also in human extracted teeth. Concisely, these trends obtained evidently advocated the fact that the deletion of mltG gene can be a potential target to impair the S. mutans virulence through severe growth retardation, thereby reducing the virulence potential of S. mutans.

Polysaccharides' Structures and Functions in Biofilm Architecture of Antimicrobial-Resistant (AMR) Pathogens

Bacteria and fungi have developed resistance to the existing therapies such as antibiotics and antifungal drugs, and multiple mechanisms are mediating this resistance. Among these, the formation of an extracellular matrix embedding different bacterial cells, called biofilm, is an effective strategy through which bacterial and fungal cells are establishing a relationship in a unique environment. The biofilm provides them the possibility to transfer genes conferring resistance, to prevent them from desiccation and to impede the penetration of antibiotics or antifungal drugs. Biofilms are formed of several constituents including extracellular DNA, proteins and polysaccharides. Depending on the bacteria, different polysaccharides form the biofilm matrix in different microorganisms, some of them involved in the first stage of cells' attachment to surfaces and to each other, and some responsible for giving the biofilm structure resistance and stability. In this review, we describe the structure and the role of different polysaccharides in bacterial and fungal biofilms, we revise the analytical methods to characterize them quantitatively and qualitatively and finally we provide an overview of potential new antimicrobial therapies able to inhibit biofilm formation by targeting exopolysaccharides.

Potential Effect of Giant Freshwater Prawn Shell Nano Chitosan in Inhibiting the Development of Streptococcus mutans and Streptococcus sanguinis Biofilm In Vitro

An oral biofilm comprises a variety of bacteria including Streptococcus mutans and Streptococcus sanguinis that cause human infections, such as caries and periodontitis. Thus, biofilm management plays an important part in the prevention and treatment of oral diseases. Nano chitosan is a bioactive material that has antimicrobial activities. This in vitro study aimed to evaluate the effect of nano chitosan synthesized from giant freshwater prawn shells (PSNC) on S. mutans and S. sanguinis biofilm development. PSNC was prepared from the extracted chitosan of giant freshwater prawn (Macrobrachium rosenbergii) shells using the ionic gelation method. The effect of PSNC on S. mutans ATCC 25175 and S. sanguinis ATCC10556 biofilm formation was evaluated using the crystal violet assay. Both bacteria were inoculated in the presence of various concentrations (5, 2.5, and 1.25 mg/ml) of PSNC for 24 h and 48 h. Confocal laser scanning microscopy (CLSM) and scanning electron microscopy were performed to visualize and study the biofilm architectural features. The biofilms were stained with the BacLight Bacterial Viability Kit prior to CLSM observation to monitor the viability of the biofilm. The results showed that PSNC exposure for 24 h and 48 h inhibited the formation of S. mutans and S. sanguinis biofilms. The biofilm formation inhibition percentage increased with an increase in the PSNC concentration (p < 0.05). The highest inhibitory activity was shown at 5 mg/ml PSNC (p < 0.05). Those findings were confirmed by the subsequent findings using the CLSM and SEM analyses. The biofilm architecture was strongly disrupted upon treatment with PSNC. After exposure to 5 mg/ml PSNC, the number of bacteria significantly decreased. The remaining bacteria were seen as individual cells, showing damaged cells. In conclusion, PSNC inhibits the development of S. mutans and S. sanguinis biofilm in vitro, indicating the potential of PSNC in clinical application for oral bacterial infection, prevention, and treatment.

Copper ions inhibit Streptococcus mutans-Veillonella parvula dual biofilm by activating Streptococcus mutans reactive nitrogen species

BACKGROUND

To investigate the inhibition mechanism of copper ions on Streptococcus mutans-Veillonella parvula dual biofilm.

METHODS

S. mutans-V. parvula dual biofilm was constructed and copper ions were added at different concentrations. After the biofilm was collected, RNA-seq and qRT-PCR were then performed to get gene information.

RESULTS

The coculture of S. mutans and V. parvula formed a significantly better dual biofilm of larger biomass than S. mutans mono biofilm. And copper ions showed a more significant inhibitory effect on S. mutans-V. parvula dual biofilm than on S. mutans mono biofilm when copper ions concentration reached 100 µM, and copper ions showed a decreased inhibitory effect on S. gordonii-V. parvula dual biofilm and S. sanguis-V.parvula dual biofilm than on the two mono biofilms as the concentration of copper ions increased. And common trace elements such as iron, magnesium, and zinc showed no inhibitory effect difference on S. mutans-V. parvula dual biofilm. The RNA-seq results showed a significant difference in the expression of a new ABC transporter SMU_651c, SMU_652c, SMU_653c, and S. mutans copper chaperone copYAZ. SMU_651c, SMU_652c, and SMU_653c were predicted to function as nitrite/nitrate transporter-related proteins, which suggested the specific inhibition of copper ions on S. mutans-V. parvula dual biofilm may be caused by the activation of S. mutans reactive nitrogen species.

CONCLUSIONS

Streptococcus mutans and Veillonella parvula are symbiotic, forming a dual biofilm of larger biomass to better resist the external antibacterial substances, which may increase the virulence of S. mutans. While common trace elements such as iron, magnesium, and zinc showed no specific inhibitory effect on S. mutans-V. parvula dual biofilm, copper ion had a unique inhibitory effect on S. mutans-V. parvula dual biofilm which may be caused by activating S. mutans RNS when copper ions concentration reached 250 µM.

Synergistic inhibitory activity of Glycyrrhizae Radix and Rubi Fructus extracts on biofilm formation of Streptococcus mutans

BACKGROUND

Streptococcus mutans is a bacterium that causes oral diseases. Plaque, a biofilm produced by S. mutans and other bacteria, makes it difficult to remove cariogenic oral microorganisms, including biofilm producers. Glucan synthesis by glucosyltransferase is one of the mechanisms underlying plaque formation. This study demonstrates the effectiveness of inhibiting biofilm formation by interfering with the glucosyltransferase activity of S. mutans using edible herbal medicines.

METHODS

This study investigated the inhibitory activity of Glycyrrhizae Radix extract, Rubi Fructus extract, glycyrrhizin from Glycyrrhizae Radix, and ellagic acid from Rubi Fructus against glucosyltransferase activity of S. mutans. Enzyme kinetic analysis identified the mechanism by which glycyrrhizin and ellagic acid inhibit enzyme activity.

RESULTS

The conditions for synergistically inhibiting biofilm formation by combining Glycyrrhizae Radix and Rubi Fructus extracts were identified. Biofilm formation was also synergistically inhibited by mixing their respective active constituents, glycyrrhizin and ellagic acid. Glycyrrhizin and ellagic acid inhibited glucosyltransferase via noncompetitive and uncompetitive mechanisms, respectively, indicating that they inhibit it via distinct mechanisms.

CONCLUSIONS

This study presents an effective oral hygiene method using the synergistic activity of two natural plant extracts to inhibit biofilm formation through different inhibitory mechanisms against glucosyltransferase of S. mutans.

Characterization, antibacterial, antioxidant, antidiabetic, and anti-inflammatory activities of green synthesized silver nanoparticles using Phragmanthera austroarabica A. G. Mill and J. A. Nyberg extract

Introduction

Diabetes mellitus is a chronic metabolic disorder that exhibited great expansion all over the world. It is becoming an epidemic disease adding a major burden to the health care system, particularly in developing countries.

Methods

The plant under investigation in the current study Phragmanthera austroarabica A. G. Mill and J. A. Nyberg is traditionally used in Saudi Arabia for the treatment of diabetes mellitus. The methanolic extract (200 mg/kg) of the plant and pure gallic acid (40 mg/kg), a major metabolite of the plant, as well as their silver nanoparticle formulae (AgNPs) were evaluated for their antidiabetic activity.

Results and Discussion

The results showed a decrease in body fat, obesity, an improvement in lipid profiles, normalization of hyperglycemia, insulin resistance, and hyperinsulinemia, and an improvement in liver tissue structure and function. However, the results obtained from AgNPs for both extract and the pure gallic acid were better in most measured parameters. Additionally, the activity of both the crude extract of the plant and its AgNPs were evaluated against a number of gram-positive, gram-negative bacteria and fungi. Although the activity of the crude extract ranged from moderate to weak or even non-active, the AgNPs of the plant extract clearly enhanced the antimicrobial activity. AgNPs of the extract demonstrated remarkable activity, especially against the Gram-negative pathogens Proteus vulgaris (MIC 2.5 μg/ml) and Pseudomonas aeruginosa (MIC 5 μg/ml). Furthermore, a promising antimicrobial activity was shown against the Gram-positive pathogen Streptococcus mutants (MIC 1.25 μg/ml).

Orofacial clefts alter early life oral microbiome maturation towards higher levels of potentially pathogenic species: A prospective observational study

Orofacial clefts (OFC) present different phenotypes with a postnatal challenge for oral microbiota development. In order to investigate the impact of OFC on oral microbiota, smear samples from 15 neonates with OFC and 17 neonates without OFC were collected from two oral niches (tongue, cheek) at two time points, i.e. after birth (T0: Ø3d OFC group; Ø2d control group) and 4-5 weeks later (T1: Ø32d OFC group; Ø31d control group). Subsequently, the samples were analyzed using next-generation sequencing. We detected a significant increase of alpha diversity and anaerobic and Gram-negative species from T0 to T1 in both groups. Further, we found that at T1 OFC neonates presented a significantly lower alpha diversity (lowest values for high cleft severity) and significantly higher levels of Enterobacteriaceae (Citrobacter, Enterobacter, Escherichia-Shigella, Klebsiella), Enterococcus, Bifidobacterium, Corynebacterium, Lactocaseibacillus, Staphylococcus, Acinetobacter and Lawsonella compared to controls. Notably, neonates with unilateral and bilateral cleft lip and palate (UCLP/BCLP) presented similarities in beta diversity and a mixture with skin microbiota. However, significant differences were seen in neonates with cleft palate only compared to UCLP/BCLP with higher levels of anaerobic species. Our findings revealed an influence of OFC as well as cleft phenotype and severity on postnatal oral microbiota maturation.

Construction of an antibacterial low-defect hybrid layer by facile PEI electrostatic assembly promotes dentin bonding

Dentin bonding is the most common form of human tissue repair among tissue-biomaterial adhesions, concerning billions of people's oral health worldwide. However, insufficient adhesive infiltration in the demineralized dentin matrix (DDM) always produces numerous defects in the bonding interface termed the hybrid layer, which causes high levels of bacteria-related secondary dental diseases, and less than 50% of the bonding lasts more than 5 years. Therefore, it is urgent and vital to construct an antibacterial low-defect hybrid layer to solve the durability-related problems. A DDM with a hydrogel-like surface formed by the hydration of highly-anionic non-collagenous proteins (NCPs) is firstly used as a template to electrostatically assemble polyethyleneimine (PEI). The formation of a stable antibacterial polyelectrolyte complex of PEI/NCPs rapidly eliminates NCP hydration capacity and significantly improves the infiltration of various adhesives. Simultaneously, both the PEI during the assembly and the PEI-assembled DDM can directly destroy a biofilm of S. Mutans on the DDM. Consequently, a long-term antibacterial and low-defect hybrid layer is successfully created, which greatly improves the bonding effectiveness. This helps to improve the clinical treatment of bacteria-based dental diseases and the tooth-restoration repair effect and prevent secondary dental diseases, having significance in clinical dentistry and providing insights for other tissue-biomaterial adhesions.

Gas Chromatography-Mass Spectrometry (GC-MS) Metabolite Profiling of Citrus limon (L.) Osbeck Juice Extract Evaluated for its Antimicrobial Activity Against Streptococcus mutans

Purpose The present study aimed to determine the antimicrobial nature of Citrus limon juice extract against Streptococcus mutans and to identify its metabolic profile by gas chromatography-mass spectrometry (GC-MS) technique. Materials and methods The cariogenic bacteria S. mutans were procured from Microbial Type Culture Collection and Gene Bank (MTCC), Chandigarh, India, and revived on brain heart infusion (BHI) agar. The C. limon (L.) Osbeck fruits were authenticated from the University of Trans-Disciplinary Health Sciences and Technology (TDU), Bengaluru, India. The antibacterial property of lyophilized lemon juice extract (LJE) dissolved in methanol was evaluated against S. mutans (MTCC 497) by the agar well diffusion assay. GC-MS technique was employed to identify the volatile metabolite profile of the methanolic LJE sample. The metabolite masses of the respective compounds were identified using the National Institute of Standards and Technology (NIST) library. Results The methanolic LJE sample concentration from 5 to 25 mg/ml did not demonstrate antimicrobial activity, while 30 to 100 mg/ml displayed antibacterial activity against S. mutans. Chlorohexidine (100 µg/ml) was used as the positive control, while methanol was used as the negative control. Significant antimicrobial metabolites were detected in the methanolic LJE sample by GC-MS analysis. Maleic anhydride, succinic anhydride, 6-Oxa-bicyclo[3.1.0] hexan-3-one, and 3-methyl-2,5-Furandione were the key metabolites identified in the methanolic LJE sample.  Conclusion The present study reports that C. limon is a potential candidate for the pharmaceutical industry as it possesses bioactive compounds demonstrating therapeutic properties. Further investigations are warranted to determine the individual and synergetic effects of identified metabolites in the methanolic LJE sample for its antimicrobial property. Special attention needs to be focussed on translational research for the development of anti-caries products from C. limon.

Periapical lesion following Cnm-positive Streptococcus mutans pulp infection worsens cerebral hemorrhage onset in an SHRSP rat model

Cerebral hemorrhage severely affects the daily life of affected individuals. Streptococcus mutans and its adhesion factor Cnm increase the adverse effects of cerebral hemorrhages. However, the mechanism by which Cnm-positive bacteria migrate from apical lesions to cerebral hemorrhage sites is unclear. Therefore, we established an S. mutans-infected apical lesion in a rat model of hypertension and investigated the neurological symptoms associated with cerebral hemorrhage. Eighteen 12-week-old stroke-prone spontaneously hypertensive rats were randomly divided into three groups, i.e. the no infection (control), dental infection with S. mutans KSM153 wild type (Cnm positive), and KSM153 Δcnm groups. Immunofluorescent staining was performed to visualize S. mutans protein. Serum interleukin-1β levels were measured. The adhesion of S. mutans to the extracellular matrix and human fibroblast cells was also analyzed. Serum antibody titers against S. mutans were comparable between Cnm positive and knockout mutants. However, 3-10 days post-infection, neurological symptom scores and cerebral hemorrhage scores were higher in Cnm-positive rats than in knockout mutants. The localization of S. mutans-derived protein was observed in the vicinity of disrupted blood vessels. Serum interleukin-1β levels significantly increased post-KSM153 WT infection. Cnm-positive S. mutans clinical isolates showed increased adhesion to the extracellular matrix, human dental pulp cells, and human umbilical vein endothelial cells compared with the Cnm-negative S. mutans isolates. In conclusion, Cnm-positive bacteria colonize the apical lesion site using the extracellular matrix as a foothold and affect cerebral hemorrhage via the bloodstream.

Transposon mutagenesis in oral streptococcus

Oral streptococci are gram-positive facultative anaerobic bacteria that are normal inhabitants of the human oral cavity and play an important role in maintaining oral microecological balance and pathogenesis. Transposon mutagenesis is an effective genetic manipulation strategy for studying the function of genomic features. In order to study cariogenic related genes and crucial biological element genes of oral Streptococcus, transposon mutagenesis was widely used to identify functional genes. With the advent of next-generation sequencing (NGS) technology and the development of transposon random mutation library construction methods, transposon insertion sequencing (TIS) came into being. Benefiting from high-throughput advances in NGS, TIS was able to evaluate the fitness contribution and essentiality of genetic features in the bacterial genome. The application of transposon mutagenesis, including TIS, to oral streptococci provided a massive amount of valuable detailed linkage data between genetic fitness and genetic backgrounds, further clarify the processes of colonization, virulence, and persistence and provides a more reliable basis for investigating relationships with host ecology and disease status. This review focuses on transposon mutagenesis, including TIS, and its applicability in oral streptococci.

Anti-Bacterial Effect of Cannabidiol against the Cariogenic Streptococcus mutans Bacterium: An In Vitro Study

Dental caries is caused by biofilm-forming acidogenic bacteria, especially Streptococcus mutans, and is still one of the most prevalent human bacterial diseases. The potential use of cannabidiol (CBD) in anti-bacterial therapies has recently emerged. Here we have studied the anti-bacterial and anti-biofilm activity of CBD against S. mutans. We measured minimum inhibitory concentration (MIC) and minimum biofilm inhibitory concentration (MBIC). The bacterial growth and changes in pH values were measured in a kinetic study. The biofilm biomass was assessed by Crystal Violet staining and 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) metabolic assay. Spinning Disk Confocal Microscopy (SDCM) was used to assess biofilm structure, bacterial viability and extracellular polysaccharide (EPS) production. CBD inhibited S. mutans planktonic growth and biofilm formation in a dose-dependent manner, with similar MIC and MBIC values (5 µg/mL). CBD prevented the bacteria-mediated reduction in pH values that correlated with bacterial growth inhibition. SDCM showed a decrease of 50-fold in live bacteria and EPS production. CBD significantly reduced the viability of preformed biofilms at 7.5 µg/mL with an 80 ± 3.1% reduction of metabolic activity. At concentrations above 20 µg/mL, there was almost no bacterial recovery in the CBD-treated preformed biofilms even 48 h after drug withdrawal. Notably, precoating of the culture plate surfaces with CBD prior to incubation with bacteria inhibited biofilm development. Additionally, CBD was found to induce membrane hyperpolarization in S. mutans. Thus, CBD affects multiple processes in S. mutans including its cariogenic properties. In conclusion, we show that CBD has a strong inhibitory effect against cariogenic bacteria, suggesting that it is a potential drug adjuvant for reducing oral pathogenic bacterial load as well as protecting against dental caries.

Antibacterial and Antibiofilm Activity of Carvacrol against Oral Pathogenic Bacteria

Faced with the current situation of high rates of microbial resistance, together with the scarcity of new antibiotics, it is necessary to search for and identify new antimicrobials, preferably natural, to alleviate this situation. The aim of this work was to evaluate the antibacterial activity of carvacrol (CAR), a phenolic compound of essential oils, against pathogenic microorganisms causing oral infections, such as Streptococcus mutans and S. sanguinis, never evaluated before. The minimum inhibitory and the minimum bactericidal concentration were 93.4 μg/mL and 373.6 μg/mL, respectively, for the two strains. The growth kinetics under different concentrations of CAR, as well as the bactericidal power were determined. The subinhibitory concentrations delayed and decreased bacterial growth. Its efficacy on mature biofilms was also tested. Finally, the possible hemolytic effect of CAR, not observable at the bactericidal concentrations under study, was evaluated. Findings obtained point to CAR as an excellent alternative agent to safely prevent periodontal diseases. In addition, it is important to highlight the use of an experimental methodology that includes dual-species biofilm and subinhibitory concentration models to determine optimal CAR treatment concentrations. Thus, CAR could be used preventively in mouthwashes or biomaterials, or in treatments to avoid existing antibiotic resistance.

The Antimicrobial and Anti-Biofilm Effects of Hypericum perforatum Oil on Common Pathogens of Periodontitis: An In Vitro Study

The antibacterial and anti-biofilm effects of Hypericum perforatum oil against the common pathogens of periodontitis (Escherichia coli, Streptococcus mutans, Staphylococcus aureus, Enterococcus faecalis, Porphyromonas gingivalis) was investigated. Disk diffusion (DD), minimum inhibitory concentration (MIC), and minimum bactericidal concentration (MBC) approaches were applied to test the antimicrobial effects. In order to determine the anti-biofilm effects, the amount of bacterial biofilm formation was assessed using the microtiter plate technique. The anti-biofilm effects were then confirmed by determining the minimum biofilm inhibitor concentration (MBIC). The MIC, MBC, MBIC, and DD values were 64, 256, 512 μg/mL, and 14 mm for Staphylococcus aureus; 128, 256, 512 μg/mL, and 16 mm for Streptococcus mutans; 256, 512, 256 μg/mL, and 20 mm for Escherichia coli; 32, 128, 512 µg/mL, and 16 mm for Enterococcus faecalis; and 64, 128, 256 µg/mL, and 15 mm for Porphyromonas gingivalis, respectively. According to our results, Hypericum perforatum oil has antibacterial and anti-biofilm properties against the common bacteria associated with periodontitis.

Reverse effects of Streptococcus mutans physiological states on neutrophil extracellular traps formation as a strategy to escape neutrophil killing

Bacteria in nature are present in different lifestyles with distinct characteristics. Streptococcus mutans is the etiologic pathogen of dental caries and could easily gain access into the bloodstream after oral surgery and adopt a biofilm lifestyle, resulting in infective endocarditis. A growing amount of evidence have revealed that the large web-like structure composed of extracellular DNA and antimicrobial proteins released by neutrophils, named Neutrophil Extracellular Traps (NETs), play an active role in the defense against bacterial invasion. The present study demonstrated that NETs formation was discriminatively affected by S. mutans biofilm and its planktonic counterpart. The free-floating planktonic S. mutans exhibited an active NETs response, whereas the biofilm community exhibited a reverse negative NETs response. Besides, impaired biofilm killing correlated with the decrease in NETs production. Unlike planktonic cells, biofilm avoided the burst of reactive oxygen species (ROS) when co-culture with neutrophils, and the NADPH-oxidase pathway was partially involved. A mice infection model also supported the distinguishing response of neutrophils challenged by different lifestyles of S. mutans. In conclusion, different bacterial physiological states can affect the distinct response of the host-microbe interaction, thus contributing to the anti-pathogen immune response activation and immune surveillance survival.

Lactobacilli, a Weapon to Counteract Pathogens through the Inhibition of Their Virulence Factors

To date, several studies have reported an alarming increase in pathogen resistance to current antibiotic therapies and treatments. Therefore, the search for effective alternatives to counter their spread and the onset of infections is becoming increasingly important.

Caffeic Acid Phenethyl Ester (CAPE) Inhibits Cross-Kingdom Biofilm Formation of Streptococcus mutans and Candida albicans

Streptococcus mutans and Candida albicans exhibit strong cariogenicity through cross-kingdom biofilm formation during the pathogenesis of dental caries. Caffeic acid phenethyl ester (CAPE), a natural compound, has potential antimicrobial effects on each species individually, but there are no reports of its effect on this dual-species biofilm. This study aimed to explore the effects of CAPE on cariogenic biofilm formation by S. mutans and C. albicans and the related mechanisms. The effect of CAPE on planktonic cell growth was investigated, and crystal violet staining, the anthrone-sulfuric acid assay and confocal laser scanning microscopy were used to evaluate biofilm formation. The structures of the formed biofilms were observed using scanning electron microscopy. To explain the antimicrobial effect of CAPE, quantitative real-time PCR (qRT-PCR) was applied to monitor the relative expression levels of cariogenic genes. Finally, the biocompatibility of CAPE in human oral keratinocytes (HOKs) was evaluated using the CCK-8 assay. The results showed that CAPE suppressed the growth, biofilm formation and extracellular polysaccharides (EPS) synthesis of C. albicans and S. mutans in the coculture system of the two species. The expression of the gtf gene was also suppressed by CAPE. The efficacy of CAPE was concentration dependent, and the compound exhibited acceptable biocompatibility. Our research lays the foundation for further study of the application of the natural compound CAPE as a potential antimicrobial agent to control dental caries-associated cross-kingdom biofilms. IMPORTANCE Severe dental caries is a multimicrobial infectious disease that is strongly induced by the cross-kingdom biofilm formed by S. mutans and C. albicans. This study aimed to investigate the potential of caffeic acid phenethyl ester (CAPE) as a natural product in the prevention of severe caries. This study clarified the inhibitory effect of CAPE on cariogenic biofilm formation and the control of cariogenic genes. It deepens our understanding of the synergistic cariogenic effect of S. mutans and C. albicans and provides a new perspective for the prevention and control of dental caries with CAPE. These findings may contribute to the development of CAPE as a promising antimicrobial agent targeting this caries-related cross-kingdom biofilm.

Traditional Chinese Medicine Compounds Containing Lonicera japonica, Chrysanthemum morifolium, and Siraitia grosvenorii Inhibits the Growth of Streptococcus mutans

Postoperative sore throat (POST) is one of the common complications after endotracheal intubation under general anesthesia. This work attempted to design and screen out the traditional Chinese medicine (TCM) compounds containing Lonicera japonica Thunb., Chrysanthemum morifolium Ramat., and Siraitia grosvenorii (Swingle) C. Jeffrey ex A. M. Lu et Z. Y. Zhang, and further explored its antibacterial effect on POST. The antibacterial activities of Lonicera japonica, Chrysanthemum morifolium, and Siraitia grosvenorii on Streptococcus mutans (S. mutans) UA159 was measured. Lonicera japonica (40 mg/mL), Chrysanthemum morifolium (10 mg/mL), and Siraitia grosvenorii (10 mg/mL) effectively inhibited the growth of S. mutans. Then, 5 different TCM compounds were designed using the U5 (5³) uniform design experimentation method. TCM compound C3 (50 mg/mL Lonicera japonica, 10 mg/mL Chrysanthemum morifolium, and 15 mg/mL Siraitia grosvenorii) significantly promoted the inhibition zone and inhibited the biofilm formation of S. mutans. In addition, TCM compound C3 exerted great antibacterial effects on S. mutans and had the least effect on cell viability of primary human pharyngeal epithelial cells. In conclusion, this work demonstrated that TCM compound containing Lonicera japonica, Chrysanthemum morifolium, and Siraitia grosvenorii inhibited the growth of S. mutans. Thus, this study provides a theoretical basis for screening out the optimal compatibility of effective components in TCM mouthwash for relieving POST.

Biofilms: Formation, Research Models, Potential Targets, and Methods for Prevention and Treatment

Due to the continuous rise in biofilm-related infections, biofilms seriously threaten human health. The formation of biofilms makes conventional antibiotics ineffective and dampens immune clearance. Therefore, it is important to understand the mechanisms of biofilm formation and develop novel strategies to treat biofilms more effectively. This review article begins with an introduction to biofilm formation in various clinical scenarios and their corresponding therapy. Established biofilm models used in research are then summarized. The potential targets which may assist in the development of new strategies for combating biofilms are further discussed. The novel technologies developed recently for the prevention and treatment of biofilms including antimicrobial surface coatings, physical removal of biofilms, development of new antimicrobial molecules, and delivery of antimicrobial agents are subsequently presented. Finally, directions for future studies are pointed out.

Oral Microbiome and Dental Caries Development

Dental caries remains the most prevalent oral disease worldwide. The development of dental caries is highly associated with the microbiota in the oral cavity. Microbiological research of dental caries has been conducted for over a century, with conventional culture-based methods and targeted molecular methods being used in order to identify the microorganisms related to dental caries. These methods’ major limitation is that they can identify only part of the culturable microorganisms in the oral cavity. Introducing sequencing-based technology and bioinformatics analysis has boosted oral microbiome research and greatly expanded the understanding of complex oral microbiology. With the continuing revolution of molecular technologies and the accumulated sequence data of the oral microbiome, researchers have realized that microbial composition alone may be insufficient to uncover the relationship between caries and the microbiome. Most updated evidence has coupled metagenomics with transcriptomics and metabolomics techniques in order to comprehensively understand the microbial contribution to dental caries. Therefore, the objective of this article is to give an overview of the research of the oral microbiome and the development of dental caries. This article reviews the classical concepts of the microbiological aspect of dental caries and updates the knowledge of caries microbiology with the results of current studies on the oral microbiome. This paper also provides an update on the caries etiological theory, the microorganisms related to caries development, and the shifts in the microbiome in dental caries development.

Chemical Profile and Biological Activities of Essential Oil from Piper arboreum for Development and Improvement of Mouthwash

Studies show that more consumers are using natural health products in the modern world. We have noticed a growing demand in markets and the professional community for mouthwashes that contain natural compounds. The objective of this study was to assess the chemical characterization and microbiological potential of the essential oil Piper arboreum (EOPa) to provide data to enable the development of a low-cost mouthwash. The evaluation of the antibacterial and bacterial resistance modulating activity was performed by the microdilution method to determine the minimum inhibitory concentration. The chemical components were characterized by gas chromatography coupled with mass spectrometry, which identified 20 chemical constituents, with caryophyllene oxide being one of the major compounds. The EOPa showed an MIC ≥ 1024 µg/mL for all bacterial strains used in the tests. When evaluating the modulating activity of EOPa combined with chlorhexidine, mouthwash and antibiotics against the bacterial resistance, the oil limited synergistic activity between the MIC of the products tested in combination (37% to 87.5%). Therefore, we recommend expanding the tests with greater variation in the EOPa concentration and the products used, as well as toxicity assessments and in vivo testing, with the purpose of the development of a possible low-cost mouthwash base that is accessible to the most vulnerable populations.

Antibacterial dental resin composites (DRCs) with synthesized bis-quaternary ammonium monomethacrylates as antibacterial agents

Three bi-quaternary ammonium methacrylates (biQAMA-12, biQAMA-14, and biQAMA-16) with different alkyl chain length were synthesized with the purpose of endowing dental resin composites (DRCs) with antibacterial activity without sacrificing physicochemical properties of DRCs. All of biQAMAs were confirmed by ¹H-NMR spectra and incorporated into Bis-GMA/TEGDMA (60 wt/40 wt) resin matrix with a mass fraction of 5 wt% as antibacterial agent. The obtained resin matrixes were mixed with commercial silaned glass fillers at a mass ratio of 30 wt/70 wt to prepare antibacterial DRCs. The double bond conversion (DC), antibacterial activity against S. mutans., surface charge density, water contact angle, water sorption (WS) and solubility (SL), mechanical properties, and cytotoxicity of biQAMAs containing DRCs were investigated. The DRC without biQAMAs was used as control. The results showed that all biQAMAs containing DRCs had antibacterial rate higher than 90%, and DRC with biQAMA-12 had the highest antibacterial rate due to its highest surface charge density. Adding 5 wt% of biQAMAs would not bring out negative effect on physicochemical properties of DRCs, except for increasing WS, but the resultant WS still met the ISO requirement on WS of restorative materials. Both biQAMA-14 and biQAMA-16 containing DRCs showed higher cytotoxicity than control, thus biQAMA-12 was considered as the optimal antibacterial agent in this research.

Evaluation of Cytotoxic and Antibacterial Effect of Methanolic Extract of Paeonia lactiflora

Background and objectives: Bacterial antibiotics have had several side effects. Therefore, interest in natural substances with less side effects is increasing these days. Paeonia lactiflora, the root of Paeonia lactiflora, is used as a raw material for medicines. In this study, we investigated the antibacterial effect and the cytotoxicity of Paeonia lactiflora extract. Materials and Methods: For cytotoxicity, MTT analysis according to ISO 10993-5 was performed. The antibacterial test of the Paeonia lactiflora was determined from bacterial viability, Inhibition zone test, CFU (colony forming unit) and SEM (scanning electron microscope). To confirm the antibacterial component of Paeonia lactiflora, the content of flavonoids and polyphenols was analyzed. Results: Our results showed that Paeonia lactiflora extract contained flavonoids and polyphenols, which exhibited antimicrobial activity against Streptococcus mutans (S. mutans) and Candida albicans (C. ablicans). Further, the cytotoxicity of Paeonia lactiflora extract was low. Conclusions: We believe that our study makes a significant contribution to the literature because it demonstrates that Paeonia lactiflora extract can be used as an antibiotic.

Flavonoid Baicalein Suppresses Oral Biofilms and Protects Enamel Hardness to Combat Dental Caries

The objectives of this study were to investigate the effects of a novel method using flavonoids to inhibit Streptococcus mutans (S. mutans), Candida albicans (C. albicans) and dual-species biofilms and to protect enamel hardness in a biofilm-based caries model for the first time. Several flavonoids, including baicalein, naringenin and catechin, were tested. Gold-standard chlorhexidine (CHX) and untreated (UC) groups served as controls. Optimal concentrations were determined by cytotoxicity assay. Biofilm MTT, colony-forming-units (CFUs), biofilm biomass, lactic acid and polysaccharide production were evaluated. Real-time-polymerase-chain reaction (qRT-PCR) was used to determine gene expressions in biofilms. Demineralization of human enamel was induced via S. mutans-C. albicans biofilms, and enamel hardness was measured. Compared to CHX and UC groups, the baicalein group achieved the greatest reduction in S. mutans, C. albicans and S. mutans-C. albicans biofilms, yielding the least metabolic activity, polysaccharide synthesis and lactic acid production (p < 0.05). The biofilm CFU was decreased in baicalein group by 5 logs, 4 logs, 5 logs, for S. mutans, C. albicans and S. mutans-C. albicans biofilms, respectively, compared to UC group. When tested in a S. mutans-C. albicans in vitro caries model, the baicalein group substantially reduced enamel demineralization under biofilms, yielding an enamel hardness that was 2.75 times greater than that of UC group. Hence, the novel baicalein method is promising to inhibit dental caries by reducing biofilm formation and protecting enamel hardness.

Triclosan antimicrobial activity against dental-caries-related bacteria

Triclosan (TCS) is a chlorinated diphenyl ether and a possible active agent against microorganisms. Due to its probability of reducing dental plaque accumulation, TCS can be added as a substance for oral hygiene. Aim: To evaluate the efficacy and antimicrobial capacity of TCS against Pseudomonas aeruginosa and Streptococcus mutans. Methods: This work evaluates the percentage of bacteria inhibition of P. aeruginosa (ATCC 27853) and S. mutans (ATCC 25175). TCS concentrations between 2 and 128 μg.mL-1 were tested. Results: An inhibitory potential of TCS was found against S. mutans. No percentage of inhibition was detected against P. aeruginosa (technical and biological triplicate). Conclusion: TCS, an antimicrobial agent used in dentifrices, can reduce S. mutans levels therefore these dentifrices should be indicated for patients with a high risk of caries. However, further study is needed, including antimicrobial analyses against other microbial conditions.

Inhibition of Biofilm Formation and Virulence Factors of Cariogenic Oral Pathogen Streptococcus mutans by Shikimic Acid

Streptococcus mutans is known as an important oral pathogen causing dental caries, a widespread oral infectious disease. S. mutans synthesize exopolysaccharide (EPS) using glucosyltransferases (Gtfs), resulting in biofilm formation on the tooth surface. Bacterial cells in the biofilms become strongly resistant to a harsh environment, such as antibiotics and host defense mechanisms, making biofilm-based infections difficult to eliminate. Discovering novel antibiofilm agents, especially from natural products, helps to develop effective strategies against this kind of diseases. The present study investigated the inhibitory effect of shikimic acid (SA), one abundant compound derived from Illicium verum extract, on the biofilm formation of S. mutans. We found SA can reduce the EPS synthesized by this oral pathogen and modulate the transcription of biofilm formation related genes, leading to fewer bacterial cells in its biofilm. SA also interacted with cell membrane and membrane proteins, causing damage to bacterial cells. Ex vivo testing of biofilm formation on bovine teeth showed SA strongly decreased the number of S. mutans cells and the number of EPS accumulated on dental enamel surfaces. Moreover, SA exhibits almost no toxicity to human oral cells evaluated by in vitro biocompatibility assay. In conclusion, shikimic acid exhibits remarkable antibiofilm activity against S. mutans and has the potential to be further developed as a novel anticaries agent. IMPORTANCE Natural products are an important and cost-effective source for screening antimicrobial agents. Here, we identified one compound, shikimic acid, from Illicium verum extract, exhibiting antimicrobial activity against S. mutans proliferation. It also inhibits biofilm formation of this bacteria through decreasing Gtf expression and EPS synthesis. Furthermore, this compound exhibits no significant cytotoxicity at its MIC against S. mutans, providing evidence for its clinical application.

Effect of solid-state fermentation and ultrasonication processes on antimicrobial and antioxidant properties of algae extracts

Algal biomass (AB) is prospective source of valuable compounds, however, Baltic Sea macroalgae have some challenges, because of their high microbial and chemical contamination. These problems can be solved, by using appropriate technologies for AG pre-treatment. The aim of this study was to evaluate the influence of two pre-treatments, solid-state fermentation with the Lactiplantibacillus plantarum LUHS135 and ultrasonication, on the antioxidant and antimicrobial characteristics of macro- (Cladophora rupestris, Cladophora glomerata, Furcellaria lumbricalis, Ulva intestinalis) and Spirulina (Arthrospira platensis) extracts. Also, combinations of extracts and LUHS135 were developed and their characteristics were evaluated. The total phenolic compound content was determined from the calibration curve and expressed in mg of gallic acid equivalents; antioxidant activity was measured by a Trolox equivalent antioxidant capacity assay using the DPPH^• (1,1-diphenyl-2-picrylhydrazyl), ABTS^•+ 2,2′-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid), FRAP (Ferric Reducing Ability of Plasma) discoloration methods. Antimicrobial activity was measured by using agar well diffusion assay and in a liquid medium. The highest DPPH^• and ABTS^•+ was shown by C.rupestris and F.lumbricalis extract × LUHS135 combinations, the highest FRAP - by non-pretreated C.rupestris and F.lumbricalis extract × LUHS135 combinations. Ultrasonicated samples inhibited four out of seven tested pathogens. Finally, the tested pre-treatments showed good perspectives and can be recommended for AB valorization.

Surface degradation and biofilm formation on hybrid and nanohybrid composites after immersion in different liquids

PURPOSE

This study evaluated the association of surface degradation and formation of Streptococcus mutans (S. mutans) biofilm in resin-based composites (RBCs) after storage in different acidic liquids.

METHODS

To evaluate microhardness and surface micromorphology, hybrid and nanohybrid RBC discs were stored in artificial gastric acid, cola drink, orange juice, artificial saliva, and distilled water for three intervals of 15 min per day for 7, 15, and 30 days. After 30 days of storage, surface roughness was analyzed, and the RBC discs were placed in a biofilm reactor inoculated with S. mutans to evaluate surface biofilm formation.

RESULTS

As compared with nanohybrid RBCs, roughness and surface microhardness values were significantly lower (P < 0.05) for hybrid RBCs stored in artificial gastric acid, followed by specimens stored in cola drink and orange juice. Artificial gastric acid caused greater surface degradation, which increased the biomass of S. mutans on the surface of both RBC types.

CONCLUSION

Surface degradation of hybrid and nanohybrid RBCs correlated with the pH of the liquid, while S. mutans biofilm formation was associated with increased surface roughness in hybrid RBCs.

Exploration of Streptococcus core genome to reveal druggable targets and novel therapeutics against S. pneumoniae

Streptococcus pneumoniae (S. pneumoniae), the major etiological agent of community-acquired pneumonia (CAP) contributes significantly to the global burden of infectious diseases which is getting resistant day by day. Nearly 30% of the S. pneumoniae genomes encode hypothetical proteins (HPs), and better understandings of these HPs in virulence and pathogenicity plausibly decipher new treatments. Some of the HPs are present across many Streptococcus species, systematic assessment of these unexplored HPs will disclose prospective drug targets. In this study, through a stringent bioinformatics analysis of the core genome and proteome of S. pneumoniae PCS8235, we identified and analyzed 28 HPs that are common in many Streptococcus species and might have a potential role in the virulence or pathogenesis of the bacteria. Functional annotations of the proteins were conducted based on the physicochemical properties, subcellular localization, virulence prediction, protein-protein interactions, and identification of essential genes, to find potentially druggable proteins among 28 HPs. The majority of the HPs are involved in bacterial transcription and translation. Besides, some of them were homologs of enzymes, binding proteins, transporters, and regulators. Protein-protein interactions revealed HP PCS8235_RS05845 made the highest interactions with other HPs and also has TRP structural motif along with virulent and pathogenic properties indicating it has critical cellular functions and might go under unconventional protein secretions. The second highest interacting protein HP PCS8235_RS02595 interacts with the Regulator of chromosomal segregation (RocS) which participates in chromosome segregation and nucleoid protection in S. pneumoniae. In this interacting network, 54% of protein members have virulent properties and 40% contain pathogenic properties. Among them, most of these proteins circulate in the cytoplasmic area and have hydrophilic properties. Finally, molecular docking and dynamics simulation demonstrated that the antimalarial drug Artenimol can act as a drug repurposing candidate against HP PCS8235_RS 04650 of S. pneumoniae. Hence, the present study could aid in drugs against S. pneumoniae.

Prevalence of Methicillin and β−Lactamase Resistant Pathogens Associated with Oral and Periodontal Disease of Children in Mymensingh, Bangladesh

Oral and periodontal diseases (OPD) is considered one of the main problems of dentistry worldwide. This study aimed to estimate the prevalence of oral and periodontal pathogenic bacteria along with their antimicrobial resistance pattern in 131 children patients aged between 4–10 years who attended in Mymensingh Medical College Hospital during October 2019 to March 2020. OPD pathogens were identified through isolation, cultural and biochemical properties, and nucleic acid detection. The isolates were subjected to antimicrobial susceptibility to 12 antibiotics commonly used in dentistry. In addition, the isolates were analyzed molecularly for the presence of six virulence and three antibacterial resistance genes. Five pathogens were identified, of which Staphylococcus aureus (S. aureus) (49%) and S. salivarius (46%) were noticed frequently; other bacteria included S. mutans (16.8%), S. sobrinus (0.8%) and L. fermentum (13.7%). The virulence genes—clumping factor A (clfA) was detected in 62.5% isolates of S. aureus, and gelatinase enzyme E (gelE) gene was detected in 5% isolates of S. salivarius, while other virulence genes were not detected. All the tested isolates were multidrug-resistant. The overall prevalence of MDR S. aureus, Streptococcus spp. and L. fermentum was 92.2%, 95.1% and 100%, respectively. It was observed that a high proportion of isolates were found resistant to 5–8 antibiotics. A majority of S. aureus, Streptococcus spp., and L. fermentum isolates tested positive for the β−lactamase resistance genes blaTEM and cfxA, as well as the methicillin resistance gene mecA. Phylogenetically, the resistance genes showed variable genetic character among Bangladeshi bacterial pathogens. In conclusion, S. aureus and S. salivarius were major OPD pathogens in patients attended in Mymensingh Medical College Hospital of Bangladesh, and most were Beta-lactam and methicillin resistant.

Copper-containing nanoparticles: Mechanism of antimicrobial effect and application in dentistry-a narrative review

Copper has been used as an antimicrobial agent long time ago. Nowadays, copper-containing nanoparticles (NPs) with antimicrobial properties have been widely used in all aspects of our daily life. Copper-containing NPs may also be incorporated or coated on the surface of dental materials to inhibit oral pathogenic microorganisms. This review aims to detail copper-containing NPs' antimicrobial mechanism, cytotoxic effect and their application in dentistry.

Profiles of sugar fermenting bacteria of the oral cavity among children with dental caries attending stomatology services at Ruhengeri referral hospital in Musanze District, Northern Rwanda

BACKGROUND

Dental caries remains a public health threat of concern among children. About 2.3 billion people are affected by dental caries, of which 530 million are children globally.

OBJECTIVE

This study was carried out to identify sugar fermenting bacteria in the oral cavity and their antibiotic susceptibility pattern, assess the association with sugar fermenter bacteria and dental caries and evaluate dental caries outcomes among children.

MATERIALS AND METHODS

This was a cross-sectional study conducted between October 2021 and February 2022 at Ruhengeri Referral Hospital. About 136 oral swab samples were collected from children with and without dental caries at 1:1 ratio. The samples were put in Stuart sterile container and transported to INES-clinical microbiology laboratory for microbial identification. Logistic regression analysis of demographic characteristics was performed to study the relationship between demographic variables and dental caries. Chi-square test was performed for the association between variables.

RESULTS

About 67.6% were male, while children of age 7-9 years (64.7%) dominated the age groups. Lactobacilli spp (15.29%) and Streptococcus mutans (12.94%) were the most predominant microorganisms observed in the oral cavity among children with dental caries. The S. mutans (x² = 27.03, P < 0.00001, 95% confidence interval [CI]=0.2901-0.5785), S. aureus (x² = 34.59, P < 0.00001, 95% CI = 0.3541-0.6292), Enterobacter aerogenes (x² = 13.5, P = 0.000239, 95% CI = 0.151-0.4622), Serratia marcescens (x² = 11.64, P = 0.00645, 95% CI = 0.1275-0.4418) and Klebsiella pneumonia (x² = 13.51, P = 0.000237, 95% CI = 0.1511-0.4623) were significantly associated with dental caries. Teeth loss (x² = 51.04, P < 0.00001, 95% CI = 0.4757-0.7205), teeth pain (x² = 5.05, P = 0.0246, 95% CI = 0.0249-0.33499), and infection (x² = 4.73, P = 0.02964, 95% CI = 0.0186-0.3441) were dental outcomes associated with tooth decay. Ciprofloxacin, clindamycin, and amoxicillin were the most sensitive antibiotics, while vancomycin and chloramphenicol were the most resistant.

CONCLUSION

Sugar consumption favours the growth of sugar fermenter bacteria that cause dental caries among children. Dental caries is associated with adverse oral health outcomes among children. Oral health education is recommended for children. Parents are advised to reduce the consumption of sugary food for their children for oral health safety.

Hydroxyethyl Cellulose Promotes the Mucin Retention of Herbal Extracts Active against Streptococcus mutans

Streptococcus mutans is considered a major cariogenic bacterium. Most anti-cariogenic dentifrices are limited by a short exposure time. The aim of the present study was to test the hypothesis that adding a mucoadhesive agent to the formulation may increase its bioavailability and efficacy. We tested the effect of adding hydroxyethyl cellulose (HEC) to an herbal extract solution containing lavender, echinacea, sage, and mastic gum, which have been previously shown to be effective against Streptococcus mutans. Mucin-coated wells were treated with four test solutions: saline, herbal extracts, herbal extracts with HEC, and chlorhexidine. The wells were incubated with Streptococcus mutans and studied for biofilm formation (Crystal violet assay), acid production (lactate assay), acid tolerance (ATPase assay), and exopolysaccharide (EPS) production using fluorescent microscopy. The results showed that the addition of HEC to the herbal extract solution caused a significant reduction in Streptococcus mutans biofilm formation, lactic acid production, and EPS quantity (p < 0.001). These results suggest that HEC may be a beneficial added excipient to herbal extracts in an anti-cariogenic formulation.

Novel Options to Counteract Oral Biofilm Formation: In Vitro Evidence

Biofilm production on biotic and abiotic surfaces is crucial in the pathogenesis of most infections, particularly those occurring in the oral cavity. Its prevention and/or control may greatly facilitate the management of patients with oral diseases. Here, the antibiofilm activity of a biomimetic hydroxyapatite and a natural compound, MicroRepair (MicroR) and pomegranate (PomeGr), respectively, was assessed. By luminescence/fluorescence-based assays, Pseudomonas aeruginosa (P. aeruginosa), Staphylococcus aureus (S. aureus) and Candida albicans (C. albicans) were tested for biofilm production in the presence of MicroR and/or PomeGr. We found that both MicroR and PomeGr could affected biofilm production; however, the efficacy of the two, given alone or in combination, varied according to the microbial agent considered. These data open to clinical studies aimed at defining the most efficacious protocols to counteract oral biofilm-associated infections.

Raffinose Inhibits Streptococcus mutans Biofilm Formation by Targeting Glucosyltransferase

Streptococcus mutans is a representative biofilm-forming bacterium that causes dental caries through glucosyltransferase (GTF) activity. Glucans are synthesized from sucrose by GTFs and provide binding sites for S. mutans to adhere tightly to the tooth enamel. Therefore, if a novel compound that interferes with GTF function is developed, biofilm formation control in S. mutans would be possible. We discovered that raffinose, an oligosaccharide from natural products, strongly inhibited biofilm formation, GTF-related gene expression, and glucan production. Furthermore, biofilm inhibition on saliva-coated hydroxyapatite discs through the reduction of bacterial adhesion indicated the applicability of raffinose in oral health. These effects of raffinose appear to be due to its ability to modulate GTF activity in S. mutans. Hence, raffinose may be considered an antibiofilm agent for use as a substance for oral supplies and dental materials to prevent dental caries. IMPORTANCE Dental caries is the most prevalent infectious disease and is expensive to manage. Dental biofilms can be eliminated via mechanical treatment or inhibited using antibiotics. However, bacteria that are not entirely removed or are resistant to antibiotics can still form biofilms. In this study, we found that raffinose inhibited biofilm formation by S. mutans, a causative agent of dental caries, possibly through binding to GtfC. Our findings support the notion that biofilm inhibition by raffinose can be exerted by interference with GTF function, compensating for the shortcomings of existing commercialized antibiofilm methods. Furthermore, raffinose is an ingredient derived from natural products and can be safely utilized in humans; it has no smell and tastes sweet. Therefore, raffinose, which can control S. mutans biofilm formation, has been suggested as a substance for oral supplies and dental materials to prevent dental caries.

Inhibition of Streptococcus mutans adhesion and biofilm formation with small-molecule inhibitors of sortase A from Juniperus chinensis

Background

Streptococcus mutans, an important Gram-positive pathogen in dental caries, uses sortase A (SrtA) to anchor surface proteins to the bacterial cell wall, thereby promoting biofilm formation and attachment to the tooth surface.

Design

Based on activity-guided separation, inhibitors of S. mutans SrtA were isolated from Juniperus chinensis and identified through combined spectroscopic analysis. Further effects of isolated SrtA inhibitor on S. mutans were evaluated on bacterial aggregation, adherence and biofilm formation.

Results

Six compounds (1–6) were isolated from the dried heartwood of J. chinensis. A novel compound designated 3’,3”-dihydroxy-(−)-matairesinol (1) was identified, which exhibited potent inhibitory activity toward S. mutans SrtA (IC₅₀ = 16.1 μM) without affecting microbial viability (minimum inhibitory concentration > 300 μM). The results of subsequent bioassays using compound 1 indicated that this compound inhibits S. mutans aggregation, adhesion and biofilm formation on solid surfaces by inhibiting SrtA activity. The onset and magnitude of inhibition of adherence and biofilm formation in S. mutans treated with compound 1 at 4× the SrtA IC₅₀ are comparable to the behaviors of the untreated srtA-deletion mutant.

Conclusion

Our findings suggest that small-molecule inhibitors of S. mutans SrtA may be useful for the prevention of dental plaque and treatment of dental microbial diseases.