Effect of arginine on the growth and biofilm formation of oral bacteria

Antibacterial and mechanical properties of arginine-containing glass ionomer cements

OBJECTIVE

The study investigated the effect of incorporating l-arginine (Arg) in a glass ionomer cement (GIC) on its mechanical properties and antibacterial potential.

METHODS

Pre-determined proportions (1%, 2%, and 4% by wt.) of Arg were incorporated in GIC powder; while GIC without Arg served as control. The flexural strength, nanohardness, surface roughness, elemental analysis using SEM-EDX (n = 6) and F/Arg/Ca/Al/Si release in deionized water for 21 days were assessed. The antibacterial potential was evaluated in a multi-species biofilm model with Streptococcus mutans, Streptococcus sanguinis, Streptococcus gordonii, and Lactobacillus acidophilus for 72 h. Real-time qPCR was used to analyse biofilm bacterial concentrations. Propidium monoazide modification of real-time qPCR was performed to quantify viable/dead bacteria. The pH, lactic acid, ADS activity, and H₂O₂ metabolism were measured. Confocal microscopy was used to investigate the biofilm bacterial live/dead cells, density, and thickness.

RESULTS

There was no difference in flexural strength among the different groups (p > 0.05). No significant difference in nanohardness and surface roughness was observed between 4% Arg + GIC and control (p > 0.05). The 4% Arg + GIC showed significantly higher F/Arg/Al/Si release than the other groups (p < 0.05), reduced total bacterial concentration and growth inhibition of viable S. mutans and S. sanguinis (p < 0.05). Lactic acid formation for 4% Arg + GIC was significantly higher than 1% Arg + GIC (p < 0.05). The spent media pH of 4% Arg + GIC was higher than the other groups (p < 0.05), with proportionately lower ammonia and higher H₂O₂ released (p < 0.05).

SIGNIFICANCE

Addition of 4% l-arginine in GIC enhanced its antibacterial activity via a biofilm modulatory effect for microbial homeostasis, with no detrimental effect on its mechanical properties.

Effects of resveratrol on cariogenic virulence properties of Streptococcus mutans

Background

Streptococcus mutans is the principal etiological agent of human dental caries. The major virulence factors of S. mutans are acid production, acid tolerance, extracellular polysaccharide (EPS) synthesis and biofilm formation. The aim of this study is to evaluate the effect of resveratrol, a natural compound, on virulence properties of S. mutans.

Results

Resveratrol at sub-MIC levels significantly decreased acid production and acid tolerance, inhibited synthesis of water-soluble polysaccharide and water-insoluble polysaccharide, compromised biofilm formation. Related virulence gene expression (ldh, relA, gtfC, comDE) was down-regulated with increasing concentrations of resveratrol.

Conclusions

Resveratrol has an inhibitory effect on S. mutans cariogenic virulence properties and it represents a promising anticariogenic agent.

Surface properties and bacterial adhesion of bulk-fill composite resins

OBJECTIVES

The aim of the present study was to evaluate the Streptococcus mutans and Streptococcus mitis adhesion and related surface properties of bulk-fill resin composite.

METHODS

Four novel bulk-fill composite with different composition were used; Sonic Fill-2 (KSF), Filtek BulkFill (FBF), Admira Fusion X-tra (AFX), Beautifil Bulk Restorative (SBB) and a control group (glass) were included in the study. After standardized surface polishing procedure, surface properties of composite specimens were evaluated using surface roughness (SR) measurements by a profilometer, hydrophobicity and surface free energy (SFE) analyses, elemental and topographic analyses by SEM-EDS. To evaluate the bacterial adhesion, composite specimens were immersed in artificial saliva and mucin for pellicle development. After 1-h immersion, bacterial suspension was added to the pellicle-coated specimens, which were incubated at 37 °C in 5% CO₂ atmosphere for 24 h. Adhered bacteria counts were determined as x10⁸ Cfu/ml. Bacterial adhesion was also investigated using confocal laser scanning microscopy.

RESULTS

No statistically significant differences were found among bulk fill composites in terms of surface roughness while glass showed the lowest Ra values. The lowest contact angle values were found in the control group and Sonic Fill-2 while the highest SFE values were observed in these materials. No statistically significant differences were found between the S. mutans counts. For S. Mitis adhesion, the highest value was found in Sonic Fill-2 and no significant differences were observed between the other groups.

CONCLUSIONS

SR of bulk-fill composite resins had no effect on bacterial adhesion. However, bacterial adhesion increased with higher SFE values.

CLINICAL SIGNIFICANCE

Although the surface roughness of composites used in the study is similar, in clinically, S. mitis adhesion may be more in the KSF group because of high surface free energy.

A universal adhesive incorporating antimicrobial peptide nisin: effects on Streptococcus mutans and saliva-derived multispecies biofilms

For purpose of enhancing the antibacterial activity of a universal adhesive, the antimicrobial peptide nisin was incorporated into Single Bond Universal and its antibacterial effect on Streptococcus mutans monospecific biofilms and saliva-derived multispecies biofilms was studied. Nisin was incorporated into Single Bond Universal and the antibacterial activity was examined by confocal laser scanning microscopy (CLSM), reverse transcription-quantitative polymerase chain reaction (qRT-PCR), phenol-sulfuric acid method and lactate dehydrogenase enzymatic method. The bonding properties were tested by microtensile bond strength (μTBS) and degree of conversion (DC). Data were analyzed by one-way analysis of variance (ANOVA) and least significant difference multiple comparison tests (P < 0.05). The Single Bond Universal incorporated with 3% (w/v) nisin could significantly inhibit the growth of the S. mutans monospecific biofilms (P< 0.01) and decrease the expression of genes related to extracellular polysaccharide (EPS) synthesis (gtfB, gtfC, gtfD and spaP) and acidogenicity (ldh) (P < 0.05). 3% (w/v) nisin-incorporated Single Bond Universal could also inhibit the growth of saliva-derived multispecies biofilms and decrease the excretion of EPS and lactic acid ( P< 0.05). μTBS and DC of 3% (w/v) nisin-incorporated Single Bond Universal did not deteriorate obviously (P > 0.05). In conclusion, 3% (w/v) nisin-incorporated Single Bond Universal substantially inhibited the growth of both S. mutans monospecific and saliva-derived multispecies biofilms without compromising the bonding properties.

Effects of Ag/ZnO nanocomposite at sub-minimum inhibitory concentrations on virulence factors of Streptococcus mutans

OBJECTIVE

Streptococcus mutans (S. mutans), the main pathogen of dental caries, could be well killed by Ag/ZnO nanocomposite. However, effects on virulence factors remain to be elucidated. This study investigated effects of Ag/ZnO at sub-minimum inhibitory concentrations (sub-MICs) on virulence factors of S. mutans and related genes expressions.

DESIGN

Effects of Ag/ZnO on the growth of S. mutans was investigated by growth curves and MTT staining method. The influence of Ag/ZnO at sub-MICs on biofilm formation was measured by the crystal violet staining method and observed by a scanning electron microscopy. Adherence, cell-surface hydrophobicity, acidogenicity and extracellular polysaccharides (EPS) of S. mutans after treatment by Ag/ZnO at sub-MICs were also investigated. Virulence factors related genes expressions after treated by Ag/ZnO at 1/2 MIC was conducted by the quantitative real-time PCR (qRT-PCR) method.

RESULTS

Sub-MICs of Ag/ZnO exhibited a dose-dependent inhibition on the virulence factors of S. mutans. Specially, Ag/ZnO at 1/2 MIC decreased 69.00 % biofilm formation, 31.78 % sucrose-independent and 48.08 % sucrose-dependent adherence, 69.44 % cell-surface hydrophobicity and 72.45 % water-soluble and 90.60 % water-insoluble EPS. Furthermore, the expression of virulence factors related genes was significantly suppressed by Ag/ZnO at 1/2 MIC.

CONCLUSIONS

Ag/ZnO at sub-MICs inhibited multiple virulence factors of S. mutans through downregulating the related genes. Ag/ZnO nanocomposite could be used for prevention of dental caries at low dosage.

Transcriptome, Phenotypic, and Virulence Analysis of Streptococcus sanguinis SK36 Wild Type and Its CcpA-Null Derivative (ΔCcpA)

Catabolic control protein (CcpA) is linked to complex carbohydrate utilization and virulence factor in many bacteria species, influences the transcription of target genes by many mechanisms. To characterize the activity and regulatory mechanisms of CcpA in Streptococcus sanguinis, here, we analyzed the transcriptome of Streptococcus sanguinis SK36 and its CcpA-null derivative (ΔCcpA) using RNA-seq. Compared to the regulon of CcpA in SK36 in the RegPrecise database, we found that only minority of differentially expressed genes (DEGs) contained putative catabolite response element (cre) in their regulatory regions, indicating that many genes could have been affected indirectly by the loss of CcpA and analyzing the sequence of the promoter region using prediction tools is not a desirable method to recognize potential target genes of global regulator CcpA. Gene ontology and pathway analysis of DEGs revealed that CcpA exerts an influence predominantly involved in carbon catabolite metabolism and some amino acid catabolite pathways, which has been linked to expression of virulence genes in many pathogens and coordinately regulate the disease progression in vivo studies. However, in some scenarios, differences observed at the transcript level could not reflect the real differences at the protein level. Therefore, to confirm the differences in phenotype and virulence of SK36 and ΔCcpA, we characterized the role of CcpA in the regulation of biofilm development, EPS production and the virulence of Streptococcus sanguinis. Results showed CcpA inactivation impaired biofilm and EPS formation, and CcpA also involved in virulence in rabbit infective endocarditis model. These findings will undoubtedly contribute to investigate the mechanistic links between the global regulator CcpA and the virulence of Streptococcus sanguinis, further broaden our understanding of the relationship between basic metabolic processes and virulence.

The Oral Bacterium Fusobacterium nucleatum Binds Staphylococcus aureus and Alters Expression of the Staphylococcal Accessory Regulator sarA

Staphylococcus aureus, an opportunistic pathogen member of the nasal and skin microbiota, can also be found in human oral samples and has been linked to infectious diseases of the oral cavity. As the nasal and oral cavities are anatomically connected, it is currently unclear whether S. aureus can colonize the oral cavity and become part of the oral microbiota, or if its presence in the oral cavity is simply transient. To start addressing this question, we assessed S. aureus ability to directly bind selected members of the oral microbiota as well as its ability to integrate into a human-derived complex oral microbial community in vitro. Our data show that S. aureus forms aggregates with Fusobacterium nucleatum and Porphyromonas gingivalis and that it can incorporate into the human-derived in vitro oral community. Further analysis of the F. nucleatum-S. aureus interaction revealed that the outer-membrane adhesin RadD is partially involved in aggregate formation and that the RadD-mediated interaction leads to an increase in expression of the staphylococcal global regulator gene sarA. Our findings lend support to the notion that S. aureus can become part of the complex microbiota of the human mouth, which could serve as a reservoir for S. aureus. Furthermore, direct interaction with key members of the oral microbiota could affect S. aureus pathogenicity contributing to the development of several S. aureus associated oral infections.

Effect of commercial herbal toothpastes and mouth rinses on the prevention of enamel demineralization using a microcosm biofilm model

This work evaluated the effects of commercial toothpastes and mouth rinses containing natural/herbal agents on biofilm viability, extracellular polysaccharide (EPS) production and on enamel demineralization in vitro. Microcosm biofilm was produced on bovine enamel for 5 days and treated daily with: Orgânico natural^® (toothpaste/mouth rinse), Boni Natural Menta & Malaleuca^® (toothpaste/mouth rinse), Propolis & Myrrh^® (toothpaste), Colgate Total 12 Clean Mint^® (toothpaste, positive control), Malvatricin^® Plus (mouth rinse), PerioGard^® (mouth rinse, positive control) or PBS (negative control). Tom's Propolis & Myrrh^® and Colgate Total 12^® toothpastes and Malvatricin^® Plus and PerioGard^® mouth rinses significantly reduced biofilm viability (p < 0.05). Only PerioGard^® had significant effects on biofilm thickness and EPS. Despite the indication that Tom's Propolis & Myrrh^® significantly reduced lesion depth, only Colgate Total 12^® significantly reduced mineral loss. Malvatricin^® Plus significantly reduced mineral loss and lesion depth, as did PerioGard^®. Some herbal products, Malvatricin^® Plus and Tom's Propolis & Myrrh^®, showed anticaries effects.

The combined antimicrobial effect of arginine and fluoride toothpaste

The aim of the study was to investigate the antibacterial effect of arginine (Arg) in NaF toothpaste. 24-h mono-/3-species biofilm cultures of S. mutans, S. sanguis and S. gordonii inoculated sHA discs were subjected to treatment with toothpaste supernatants prepared as - [1]:2% Arg -NaF (0.147% F), [2]:4% Arg-NaF (0.144% F), [3]:8% Arg - NaF (0.138% F), [4]:NaF (0.15%) and [5]:deionized water. After 24-h incubation, the mono-species biofilms were subjected to viability assay using WST-8, SEM and confocal imaging (CLSM). The 3-species biofilm were quantified for bacterial composition by PCR analysis, SEM, CLSM, and RNA isolation with reverse-transcription PCR analysis. Increasing arginine concentrations in NaF toothpaste had no effect on microbial viability. The mono-/3-species biofilm imaging depicted that the 2% Arg-NaF and 4% Arg-NaF had a biofilm disrupting effect. The 3-species biofilm bacterial composition indicated that the 2% Arg-NaF group maintained an ecological homeostasis by inhibiting S. mutans growth and enriching the growth of S. sanguis and S. gordonii. The 2% Arg-NaF group significantly downregulated the expression of virulent gtfB gene and upregulated the expression of sagP with relative dominance of arcA. Incorporation of 2% arginine in NaF toothpaste might enrich the alkali-producing bacteria and provide enhanced counter mechanisms against cariogenic pathogen when compared to NaF toothpaste.

Prevention of dental caries as a non-communicable disease

Today, dental caries is regarded as a preventable non-communicable disease (NCD) that affects a majority of the population across their lifespan. As such, it shares a number of behavioural, socio-economic, and lifestyle factors with other NCDs, such as overweight and diabetes, and should be subjected to a similar model of chronic disease management. Caries prevention has traditionally relied on fluoride exposure, diet control, thorough oral hygiene, and antibacterial measures. Prevention of caries as an NCD does certainly not disqualify these methods, but brings them into a new context. This conference paper provides a brief review on how common preventive measures can interfere with the drivers of dysbiosis and promote the growth of health-associated clusters in the oral microbiome. Besides the established routines of regular toothbrushing with fluoride products, there is an opportunity for additional technologies, based on ecological principles, to address and modify the oral biofilm. Methods to reduce dietary sugar intake, slow down plaque metabolism, and support saliva functions should be further developed and investigated in terms of efficacy, compliance, and cost-effectiveness. Furthermore, biofilm engineering through pre- and probiotics early in life to support microbial diversity seem promising in order to obtain a sustained caries-preventive effect.

The Role of Exopolysaccharides in Oral Biofilms

The oral cavity contains a rich consortium of exopolysaccharide-producing microbes. These extracellular polysaccharides comprise a major component of the oral biofilm. Together with extracellular proteins, DNA, and lipids, they form the biofilm matrix, which contributes to bacterial colonization, biofilm formation and maintenance, and pathogenesis. While a number of oral microbes have been studied in detail with regard to biofilm formation and pathogenesis, the exopolysaccharides have been well characterized for only select organisms, namely Streptococcus mutans and Aggregatibacter actinomycetemcomitans. Studies on the exopolysaccharides of other oral organisms, however, are in their infancy. In this review, we present the current research on exopolysaccharides of oral microbes regarding their biosynthesis, regulation, contributions to biofilm formation and stability of the matrix, and immune evasion. In addition, insight into the role of exopolysaccharides in biofilms is highlighted through the evaluation of emerging techniques such as pH probing of biofilm colonies, solid-state nuclear magnetic resonance for macromolecular interactions within biofilms, and super-resolution microscopy analysis of biofilm development. Finally, exopolysaccharide as a potential nutrient source for species within a biofilm is discussed.

Critical Appraisal of Oral Pre- and Probiotics for Caries Prevention and Care

In recent years, the concept of preventing caries-related microbial dysbiosis by enhancing the growth and survival of health-associated oral microbiota has emerged. In this article, the current evidence for the role of oral pre- and probiotics in caries prevention and caries management is discussed. Prebiotics are defined as "substrates that are selectively utilized by host microorganisms conferring a health benefit." With regard to caries, this would include alkali-generating substances such as urea and arginine, which are metabolized by some oral bacteria, resulting in ammonia production and increase in pH. While there is no evidence that urea added to chewing gums or mouth rinses significantly contributes to caries inhibition, multiple studies have shown that arginine in consumer products can exert an inhibitory effect on the caries process. Probiotics are "live microorganisms which when administrated in adequate amounts confer a health benefit on the host." Clinical trials have suggested that school-based programs with milk supplemented with probiotics and probiotic lozenges can reduce caries development in preschool children and in schoolchildren with high caries risk. Due to issues with research ethics (prebiotics) and risk of bias (prebiotics, probiotics), the confidence in the effect estimate is however limited. Further long-term clinical studies are needed with orally derived probiotic candidates, including the health-economic perspectives. In particular, the development and evaluation of oral synbiotic products, containing both prebiotics and a probiotic, would be of interest in the future management of dental caries.

Effect of polyphenol-rich cranberry extracts on cariogenic biofilm properties and microbial composition of polymicrobial biofilms

OBJECTIVE

To investigate the effect of cranberry extracts on saliva-derived polymicrobial biofilms with regards to biofilm biomass, acidogenicity, exopolysaccharide (EPS)/microbial biovolumes, colony forming unit (CFU) counts, and the relative abundance of specific caries- and health-associated bacteria.

METHODS

Saliva-derived polymicrobial biofilms were grown for 96 h in a cariogenic environment and treated for 2 min every 12 h over the entire biofilm growth period with 500 μg/mL cranberry extract or vehicle control. The effect of the cranberry extract on biofilm behaviour was evaluated using different assays and its influence on key cariogenic and health-associated bacterial populations was assessed with a microarray real-time quantitative PCR method.

RESULTS

Cranberry-treated biofilms showed significant drops in biomass (38% reduction, P <  0.001), acidogenicity (44% reduction, P <  0.001), EPS/microbial biovolume ratios (P =  0.033), and CFU counts (51% reduction, P =  0.001). Furthermore, the cranberry extracts effected a significantly lower relative abundance of caries-associated Streptococcus sobrinus (fold change 0.004, P =  0.002) and Provotella denticola (0.002, P <  0.001), and a significantly higher relative abundance of the health-associated Streptococcus sanguinis (fold change 90.715, P =  0.001).

CONCLUSIONS

The cranberry extract lowered biofilm biomass, acidogenicity, EPS/microbial biovolumes, CFU counts, and modulated a beneficial microbial ecological change in saliva-derived polymicrobial biofilms.

Exploiting the Oral Microbiome to Prevent Tooth Decay: Has Evolution Already Provided the Best Tools?

To compete in the relatively exposed oral cavity, resident microbes must avoid being replaced by newcomers. This selective constraint, coupled with pressure on the host to cultivate a beneficial microbiome, has rendered a commensal oral microbiota that displays colonization resistance, protecting the human host from invasive species, including pathogens. Rapid increases in carbohydrate consumption have disrupted the evolved homeostasis between the oral microbiota and dental health, reflected by the high prevalence of dental caries. Development of novel modalities to prevent caries has been the subject of a breadth of research. This mini review provides highlights of these endeavors and discusses the rationale and pitfalls behind the major avenues of approach. Despite efficacy, fluoride and other broad-spectrum interventions are unlikely to further reduce the incidence of dental caries. The most promising methodologies in development are those that exploit the exclusive nature of the healthy oral microbiome. Probiotics derived from the dental plaque of healthy individuals sharply antagonize cariogenic species, such as Streptococcus mutans. Meanwhile, targeted antimicrobials allow for the killing of specific pathogens, allowing reestablishment of a healthy microbiome, presumably with its protective effects. The oral microbiota manufactures a massive array of small molecules, some of which are correlated with health and are likely to antagonize pathogens. The prohibitive cost associated with sufficiently rigorous clinical trials, and the status of dental caries as a non-life-threatening condition will likely continue to impede the advancement of new therapeutics to market. Nevertheless, there is room for optimism, as it appears evolution may have already provided the best tools.

Genome shuffling enhances stress tolerance of Zymomonas mobilis to two inhibitors

BACKGROUND

Furfural and acetic acid are the two major inhibitors generated during lignocellulose pretreatment and hydrolysis, would severely inhibit the cell growth, metabolism, and ethanol fermentation efficiency of Zymomonas mobilis. Effective genome shuffling mediated by protoplast electrofusion was developed and then applied to Z. mobilis.

RESULTS

After two rounds of genome shuffling, 10 different mutants with improved cell growth and ethanol yield in the presence of 5.0 g/L acetic acid and 3.0 g/L furfural were obtained. The two most prominent genome-shuffled strains, 532 and 533, were further investigated along with parental strains in the presence of 7.0 g/L acetic acid and 3.0 g/L furfural. The results showed that mutants 532 and 533 were superior to the parental strain AQ8-1 in the presence of 7.0 g/L acetic acid, with a shorter fermentation time (30 h) and higher productivity than AQ8-1. Mutant 533 exhibited subtle differences from parental strain F34 in the presence of 3.0 g/L furfural. Mutations present in 10 genome-shuffled strains were identified via whole-genome resequencing, and the source of each mutation was identified as either de novo mutation or recombination of the parent genes.

CONCLUSIONS

These results indicate that genome shuffling is an efficient method for enhancing stress tolerance in Z. mobilis. The engineered strains generated in this study could be potential cellulosic ethanol producers in the future.

Novel Approaches to the Control of Oral Microbial Biofilms

Effective management of biofilm-related oral infectious diseases is a global challenge. Oral biofilm presents increased resistance to antimicrobial agents and elevated virulence compared with planktonic bacteria. Antimicrobial agents, such as chlorhexidine, have proven effective in the disruption/inhibition of oral biofilm. However, the challenge of precisely and continuously eliminating the specific pathogens without disturbing the microbial ecology still exists, which is a major factor in determining the virulence of a multispecies microbial consortium and the consequent development of oral infectious diseases. Therefore, several novel approaches are being developed to inhibit biofilm virulence without necessarily inducing microbial dysbiosis of the oral cavity. Nanoparticles, such as pH-responsive enzyme-mimic nanoparticles, have been developed to specifically target the acidic niches within the oral biofilm where tooth demineralization readily occurs, in effect controlling dental caries. Quaternary ammonium salts (QAS) such as dimethylaminododecyl methacrylate (DMADDM), when incorporated into dental adhesives or resin composite, have also shown excellent and durable antimicrobial activity and thus could effectively inhibit the occurrence of secondary caries. In addition, custom-designed small molecules, natural products and their derivatives, as well as basic amino acids such as arginine, have demonstrated ecological effects by modulating the virulence of the oral biofilm without universally killing the commensal bacteria, indicating a promising approach to the management of oral infectious diseases such as dental caries and periodontal diseases. This article aims to introduce these novel approaches that have shown potential in the control of oral biofilm. These methods may be utilized in the near future to effectively promote the clinical management of oral infectious diseases and thus benefit oral health.

Streptococcus sanguinis biofilm formation & interaction with oral pathogens

Caries and periodontitis are the two most common human dental diseases and are caused by dysbiosis of oral flora. Although commensal microorganisms have been demonstrated to protect against pathogens and promote oral health, most previous studies have addressed pathogenesis rather than commensalism. Streptococcus sanguinis is a commensal bacterium that is abundant in the oral biofilm and whose presence is correlated with health. Here, we focus on the mechanism of biofilm formation in S. sanguinis and the interaction of S. sanguinis with caries- and periodontitis-associated pathogens. In addition, since S. sanguinis is well known as a cause of infective endocarditis, we discuss the relationship between S. sanguinis biofilm formation and its pathogenicity in endocarditis.

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.

Purification and Characterization of a Biofilm-Degradable Dextranase from a Marine Bacterium

This study evaluated the ability of a dextranase from a marine bacterium Catenovulum sp. (Cadex) to impede formation of Streptococcus mutans biofilms, a primary pathogen of dental caries, one of the most common human infectious diseases. Cadex was purified 29.6-fold and had a specific activity of 2309 U/mg protein and molecular weight of 75 kDa. Cadex showed maximum activity at pH 8.0 and 40 °C and was stable at temperatures under 30 °C and at pH ranging from 5.0 to 11.0. A metal ion and chemical dependency study showed that Mn²⁺ and Sr²⁺ exerted positive effects on Cadex, whereas Cu²⁺, Fe³⁺, Zn²⁺, Cd²⁺, Ni²⁺, and Co²⁺ functioned as inhibitors. Several teeth rinsing product reagents, including carboxybenzene, ethanol, sodium fluoride, and xylitol were found to have no effects on Cadex activity. A substrate specificity study showed that Cadex specifically cleaved the α-1,6 glycosidic bond. Thin layer chromatogram and high-performance liquid chromatography indicated that the main hydrolysis products were isomaltoogligosaccharides. Crystal violet staining and scanning electron microscopy showed that Cadex impeded the formation of S. mutans biofilm to some extent. In conclusion, Cadex from a marine bacterium was shown to be an alkaline and cold-adapted endo-type dextranase suitable for development of a novel marine agent for the treatment of dental caries.

ciaR impacts biofilm formation by regulating an arginine biosynthesis pathway in Streptococcus sanguinis SK36

Streptococcus sanguinis is an early colonizer of the tooth surface and competes with oral pathogens such as Streptococcus mutans to maintain oral health. However, little is known about its mechanism of biofilm formation. Here, we show that mutation of the ciaR gene, encoding the response regulator of the CiaRH two-component system in S. sanguinis SK36, produced a fragile biofilm. Cell aggregation, gtfP gene expression and water-insoluble glucan production were all reduced, which suggested polysaccharide production was decreased in ΔciaR. RNA sequencing and qRT-PCR revealed that arginine biosynthesis genes (argR, argB, argC, argG, argH and argJ) and two arginine/histidine permease genes (SSA_1568 and SSA_1569) were upregulated in ΔciaR. In contrast to ΔciaR, most of strains constructed to contain deletions in each of these genes produced more biofilm and water-insoluble glucan than SK36. A ΔciaRΔargB double mutant was completely restored for the gtfP gene expression, glucan production and biofilm formation ability that was lost in ΔciaR, indicating that argB was essential for ciaR to regulate biofilm formation. We conclude that by promoting the expression of arginine biosynthetic genes, especially argB gene, the ciaR mutation reduced polysaccharide production, resulting in the formation of a fragile biofilm in Streptococcus sanguinis.