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

Enhanced anti-biofilm and anti-caries potential of arginine combined with calcium glycerophosphate and fluoride

OBJECTIVE

The aim of this work was to evaluate the antibiofilm and anticaries properties of the association of arginine (Arg) with calcium glycerophosphate (CaGP) and fluoride (F).

METHODS

An active attachment, polymicrobial biofilm model obtained from saliva and bovine teeth discs were used. After the initial biofilm growth period, the enamel discs were transferred to culture medium. The treatment solutions were added to the culture media to achieve the desired final concentration. The following groups were used: negative control (Control); F (110 ppm F); CaGP (0.05 %); Arg (0.8 %) and their associations (F + CaGP; Arg + F; Arg + CaGP; Arg +F + CaGP). The following analyses were carried out: bacterial viability (total bacteria, aciduric bacteria and mutans streptococci), pH assessment of the spent culture medium, dry weight quantification, evaluation of surface hardness loss (%SH) and subsurface mineral content. Normality and homoscedasticity were tested (Shapiro-Wilk and Levene's test) and the following tests were applied: two-way ANOVA (acidogenicity), Kruskall-Wallis (microbial viability) and one way ANOVA (dry weight, %SH, mineral content).

RESULTS

The association Arg + F + CaGP resulted in the lowest surface hardness loss in tooth enamel (-10.9 ± 2.3 %; p < 0.05). Arg +F + CaGP exhibited highest values of subsurface mineral content (10.1 ± 2.9 gHAP/cm3) in comparison to Control and F (p < 0.05). In comparison to Control and F, Arg +F + CaGP promoted the highest reduction in aciduric bacteria and mutans streptococci (5.7 ± 0.4; 4.4 ± 0.5 logCFU/mL, p < 0.05).

CONCLUSIONS

The Arg-F-Ca association demonstrated to be the most effective combination in protecting the loss of surface hardness and subsurface mineral content, in addition to controlling important virulence factors of the cariogenic biofilm.

CLINICAL SIGNIFICANCE

Our findings provide evidence that the Arg-F-Ca association showed an additive effect, particularly concerning protection against enamel demineralization. The combination of these compounds may be a strategy for patients at high risk of caries.

Formulation of arginine-loaded mesoporous silica nanoparticles (Arg@MSNs) modified orthodontic adhesive

OBJECTIVES

The objective of this study was to synthesize arginine loaded mesoporous silica nanoparticles (Arg@MSNs), develop a novel orthodontic adhesive using Arg@MSNs as modifiers, and investigate the adhesive performance, antibacterial activity, and biocompatibility.

METHODS

Arg@MSNs were synthesized by immobilizing arginine into MSNs and characterized using transmission electron microscope (TEM), dynamic light scattering (DLS), and Fourier Transform Infrared Spectrometer (FT-IR). Arg@MSNs were incorporated into Transbond XT adhesive with different mass fraction to form functional adhesives. The degree of conversion (DC), arginine release behavior, adhesive performance, antibacterial activity against Streptococcus mutans biofilm, and cytotoxicity were comprehensively evaluated.

RESULTS

TEM, DLS, and FT-IR characterizations confirmed the successful preparation of Arg@MSNs. The incorporation of Arg@MSNs did not significantly affect DC and exhibited clinically acceptable bonding strength. Compared to the commercial control, the Arg@MSNs modified adhesives greatly suppressed the metabolic activity and polysaccharide production while increased the biofilm pH values. The cell counting kit (CCK)-8 test indicated no cytotoxicity.

CONCLUSIONS

The novel orthodontic adhesive containing Arg@MSNs exhibited significantly enhanced antibacterial activities and inhibitory effects on acid production compared to the commercial adhesive without compromising their bonding strength or biocompatibility.

CLINICAL SIGNIFICANCE

The novel orthodontic adhesive containing Arg@MSNs exhibits potential clinical benefits in preventing demineralization of enamel surfaces around or beneath orthodontic brackets due to its enhanced antibacterial activities and acid-producing inhibitory effects.

Arginine and sodium fluoride affect the microbial composition and reduce biofilm metabolism and enamel mineral loss in an oral microcosm model

OBJECTIVE

To assess the effects of arginine, with or without sodium fluoride (NaF; 1,450 ppm), on saliva-derived microcosm biofilms and enamel demineralization.

METHODS

Saliva-derived biofilms were grown on bovine enamel blocks in 0.2 % sucrose-containing modified McBain medium, according to six experimental groups: control (McBain 0.2 %); 2.5 % arginine; 8 % arginine; NaF; 2.5 % arginine with NaF; and 8 % arginine with NaF. After 5 days of growth, biofilm viability was assessed by colony-forming units counting, laser scanning confocal microscopy was used to determine biofilm vitality and extracellular polysaccharide (EPS) production, while biofilm metabolism was evaluated using the resazurin assay and lactic acid quantification. Demineralization was evaluated by measuring pH in the culture medium and calcium release. Data were analyzed by Kruskal-Wallis' and Dunn's tests (p < 0.05).

RESULTS

8 % arginine with NaF showed the strongest reduction in total streptococci and total microorganism counts, with no significant difference compared to arginine without NaF. Neither 2.5 % arginine alone nor NaF alone significantly reduced microbial counts compared to the control, although in combination, a reduction in all microbial groups was observed. Similar trends were found for biofilm vitality and EPS, and calcium released to the growth medium.

CONCLUSIONS

8 % Arginine, with or without NaF, exhibited the strongest antimicrobial activity and reduced enamel calcium loss. Also, NaF enhanced the effects of 2.5 % arginine, yielding similar results to 8 % arginine for most parameters analyzed.

CLINICAL SIGNIFICANCE

The results provided further evidence on how arginine, with or without NaF, affects oral microcosm biofilms and enamel mineral loss.

Bacterial adhesion to composite resins produced by additive and subtractive manufacturing

The aim of this study was to evaluate the surface roughness and contact angle of composite resins produced by CAD/CAM milling and three-dimensional (3D) printing for permanent restorations as well as the adhesion of S. mutans and S. sanguinis bacteria to these composites. Three CAD/CAM milling composite resins (Vita Enamic-VE, Cerasmart-CE, Lava Ultimate-LU) and three 3D printing resins (Varseo Smile Crown plus-VSC, Saremco print Crowntech-SPC, Formlabs 3B Permanent crown-FLP) were selected. Twenty samples were prepared for each group. Using a contact profilometer, the surface roughness was determined, and an optical goniometer was used to quantify the contact angle. To evaluate the bacterial adhesion, composite specimens were immersed in mucin containing artificial saliva. All samples were incubated for 24 h at 37°C in 5% CO2. CFUs were determined by counting colonies after the incubation period. Surface roughness values of test samples were the highest in the Group VSC [0.46 (0.14) µm], whereas the lowest values were found in the Group LU [0.23 (0.05) µm]. There was no statistically significant difference between the groups in contact angle values (p > 0.05). The S. mutans adhesion extent on the Group SPC was statistically higher compared to all other materials with p < 0.05. For S. sanguinis, the lowest bacterial adhesion value was recorded in Group CE (3.00 × 104 CFU/ml) and statistically significant differences were found with Group VE and VSC (p < 0.05). Different digital manufacturing techniques and material compositions can affect the surface roughnesses of composite resins. All composite resin samples have hydrophobic characteristics. Microbial adhesion of the tested composite resins may be varied depending on the bacterial species. S. mutans showed much more adhesion to these materials than S. sanguinis.

Extracellular Vehicles from Commensal Skin Malassezia restricta Inhibit Staphylococcus aureus Proliferation and Biofilm Formation

The colonizing microbiota on the body surface play a crucial role in barrier function. Staphylococcus aureus (S. aureus) is a significant contributor to skin infection, and the utilization of colonization resistance of skin commensal microorganisms to counteract the invasion of pathogens is a viable approach. However, most studies on colonization resistance have focused on skin bacteria, with limited research on the resistance of skin fungal communities to pathogenic bacteria. Extracellular vehicles (EVs) play an important role in the colonization of microbial niches and the interaction between distinct strains. This paper explores the impact of Malassezia restricta (M. restricta), the fungus that dominates the normal healthy skin microbiota, on the proliferation of S. aureus by examining the distribution disparities between the two microorganisms. Based on the extraction of EVs, the bacterial growth curve, and biofilm formation, it was determined that the EVs of M. restricta effectively suppressed the growth and biofilm formation of S. aureus. The presence of diverse metabolites was identified as the primary factor responsible for the growth inhibition of S. aureus, specifically in relation to glycerol phospholipid metabolism, ABC transport, and arginine synthesis. These findings offer valuable experimental evidence for understanding microbial symbiosis and interactions within healthy skin.

Preparation of arginine-loaded mesoporous silica nanoparticles (Arg@MSNs) to improve the mechanical and antibacterial properties of denture base resin

STATEMENT OF PROBLEM

Whether the incorporation of arginine-loaded mesoporous silica nanoparticles (Arg@MSNs) into denture base resin can improve the mechanical and antibacterial properties is unclear.

PURPOSE

The purpose of this in vitro study was to synthesis Arg@MSNs and explore how Arg@MSNs incorporation affects the mechanical and antibacterial properties of denture base resin.

MATERIAL AND METHODS

Arg@MSNs were synthesized via a sol-gel process and characterized by transmission electron microscopy (TEM), dynamic light scattering (DLS), and X-ray diffraction (XRD). The prepared Arg@MSNs at different weight ratio concentrations were added into denture base resin as the experimental group, and unmodified denture base resin was the control. The fracture surface and arginine release behavior of each specimen were detected using scanning electron microscopy (SEM) and ultra-high-performance liquid chromatography-tandem mass spectrometer (UHPLC-HESI-MS/MS), respectively. Three-point bend tests were applied using a universal testing machine for evaluation of the mechanical properties of each group (n=5). Antibacterial efficiency (n=3) was evaluated by both quantitative and qualitative analysis using Streptococcus mutans. The cytotoxic effect of the Arg@MSN-modified denture base resin was investigated using a cell counting kit (CCK)-8 test. Data were subjected to 1-way analysis of variance followed by the post hoc Tukey honestly significant difference test (ɑ=.05).

RESULTS

The prepared Arg@MSNs had good monodispersity and spherical morphology. Arg@MSN concentration at 0.5 wt%, 1 wt%, and 2.5 wt% resulted in enhanced mechanical properties, while those at 5 wt% were adversely impacted. Biofilm pH values increased with the incorporation of Arg@MSNs, and the antibacterial performance was improved. The CCK-8 test revealed that all formulations were not cytotoxic.

CONCLUSIONS

The addition of Arg@MSNs into denture base resin can enhance its mechanical properties and improve its antibacterial performance without any apparent cytotoxic effect.

Deciphering the mechanism of anti-quorum sensing post-biotic mediators against Streptococcus mutans

OBJECTIVE

Glucosyltransferases (Gtfs) and quorum sensing (QS) mediated transduction genes play critical roles in the pathogenesis of Streptococcus mutan-mediated dental caries. Therefore, targeting gtfs and QS-mediated virulence genes have therefore emerged as an intriguing goal for efficient therapeutic approaches that block cariogenic biofilms.

METHODS

Post-biotic mediators (PMs) obtained from our previously isolated and characterized beneficial bacteria Enterobacter colacae PS-74 was assessed for its antibiofilm potential against S. mutans. According to the transcriptome method, qRT-PCR analysis was performed against virulence genes. For microscopic visualization, SEM and CLSM analyses were used to confirm the inhibitory effects of PMs.

RESULTS

PMs dramatically reduced the expression of QS signal transduction, glucan metabolism, and biofilm-regulated genes such gtfB, gtfC, ComDE, VicR, brpA in S. mutans, which validates the outcomes of in vitro result. Their unique metabolites may help to control biofilm formation by eluding antimicrobial resistance.

CONCLUSION

Considering the above findings, PMs may deem to be an innovative, alluring, and secure method for preventing dental caries due to their biological activity. Our study unravels the inhibitory effect of PMs, which will contribute to instruct drug design strategies for effective inhibition of S. mutans biofilms.

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.

Ecological influence by colonization of fluoride-resistant Streptococcus mutans in oral biofilm

Background

Dental caries is one of the oldest and most common infections in humans. Improved oral hygiene practices and the presence of fluoride in dentifrices and mouth rinses have greatly reduced the prevalence of dental caries. However, increased fluoride resistance in microbial communities is concerning. Here, we studied the effect of fluoride-resistant Streptococcus mutans (S. mutans) on oral microbial ecology and compare it with wild-type S. mutans in vitro.

Methods

Biofilm was evaluated for its polysaccharide content, scanning electron microscopy (SEM) imaging, acid-producing ability, and related lactic dehydrogenase (LDH), arginine deiminase (ADS), and urease enzymatic activity determination. Fluorescence in situ hybridization (FISH) and quantitative real-time polymerase chain reaction (qRT-PCR) were used to evaluate the S. mutans ratio within the biofilm. It was followed by 16S rRNA sequencing to define the oral microbial community.

Results

Fluoride-resistant S. mutans produced increased polysaccharides in presence of NaF (P < 0.05). The enzymatic activities related to both acid and base generation were less affected by the fluoride. In presence of 275 ppm NaF, the pH in the fluoride-resistant strain sample was lower than the wild type. We observed that with the biofilm development and accumulative fluoride concentration, the fluoride-resistant strain had positive relationships with other bacteria within the oral microbial community, which enhanced its colonization and survival. Compared to the wild type, fluoride-resistant strain significantly increased the diversity and difference of oral microbial community at the initial stage of biofilm formation (4 and 24 h) and at a low fluoride environment (0 and 275 ppm NaF) (P < 0.05). Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis revealed that fluoride-resistant strain enhanced the metabolic pathways and glucose transfer.

Conclusions

Fluoride-resistant S. mutans affected the microecological balance of oral biofilm and its cariogenic properties in vitro, indicating its negative impact on fluoride's caries prevention effect.

Combined remineralizing effect of arginine and fluoride on artificially demineralized human primary dentin evaluated using quantitative light induced fluorescence

Introduction

One the most common chronic dental diseases affecting children is dental caries. Dentin caries is a condition in which caries has progressed to the dentin and caused a significant depth of lesion. Clinical studies have revealed that an increased caries risk is associated with a decreased alkali-producing capacity of the microbial populations colonizing the oral cavity of adults, which arginine somewhat compensates for.

Aims

To evaluate the remineralizing efficacy of fluoridated toothpaste, with fluoride-arginine containing toothpaste on demineralized dentin of primary teeth using quantitative light-induced fluorescence™.

Materials and Methods

Forty-five primary molars were decoronated and sectioned to prepare dentin specimens and mounted in an acrylic block in a uniform manner using a customized acrylic jig. Samples were randomized into three groups, were subjected to demineralization to create artificial dentin caries lesion. Following this, all the 45 samples were subjected to multispecies bacterial pH cycling for 21 days. All the specimens were evaluated for postdemineralization, pH cycling day 7, 14, and 21 on QLF™.

Results

On day 21, maximum fluorescence gain was observed by the positive control group followed by the arginine and negative control group. The variation observed between positive control and arginine group was found to be statistically significant.

Conclusions

An in vitro development of artificial caries such as demineralized lesion on primary dentin sample using plaque biofilm was observed successfully under QLF after 72 h. Arginine in combination with fluoride showed almost similar remineralization of demineralized primary dentin compared to fluoride alone after 21 days of multispecies bacterial pH cycling.

Synbiotic-fluoride synergism on enamel remineralization, cytotoxicity and genotoxicity

OBJECTIVE(S)

The objectives of the present study were to examine the - a) enamel remineralization potential of synbiotic-fluoride (SF) therapy using a multi-species bacterial pH-cycling model; and b) cytotoxic and genotoxic effects of SF therapy extracts.

MATERIALS AND METHODS

The SF therapy group comprised of 2% arginine (Arg), 0.2% NaF, and a probiotic Lactobacillus rhamnosus GG (LRG). The intervention groups studied were: 1) No treatment; 2) 2% Arg; 3) 0.2% NaF; 4) LRG; 5) 2% Arg+0.2% NaF; 6) 2% Arg+LRG; 7) 0.2% NaF+LRG; and 8) 2% Arg+0.2% NaF+LRG (SF therapy). The enamel remineralization potential of SF therapy was investigated under cariogenic biofilm challenge; while the cytotoxicity and genotoxicity of SF therapy extracts were examined on HGF-1 and Chinese hamster fibroblast V79, respectively. To determine the remineralization effect, the specimens were subjected to mineral density (MD) assessment using micro-CT, Ca/P molar ratio with SEM-EDX, and enamel fluoride uptake (EFU) estimates. The HGF-1 proliferation assessment was quantified using MTT/CCK-8 assays with qualitative analysis by nuclei staining Hoechst-based fluorescence imaging. The genotoxicity was determined by micronuclei formation test.

RESULTS

Mineral gain and %remineralization derived from MD assessment for the SF therapy were significantly higher than the other groups (p<0.05). The %ΔCa/P for the SF and 2% Arg+0.2% NaF were significantly higher than the other groups (p<0.05). The SF and 2% Arg+0.2% NaF groups had the highest EFU compared to the other groups (p<0.05). No significant difference in the %viable HGF-1 cells were observed between the treatment interventions and no treatment group (p>0.05). Compared to the EMS-positive control, the micronuclei formation for all the intervention groups was significantly lower (p<0.05), with no significant difference among the treatment groups (p>0.05).

CONCLUSION

The SF therapy enhanced enamel remineralization with no biocompatibility concerns.

CLINICAL SIGNIFICANCE

With the enhanced enamel remineralization potential discerned in the present study, the SF therapy can be used as a promising caries-preventive agent targeted for high caries-risk individuals.

Purification and characterization of cold-adapted and salt-tolerant dextranase from Cellulosimicrobium sp. THN1 and its potential application for treatment of dental plaque

The cold-adapted and/or salt-tolerant enzymes from marine microorganisms were confirmed to be meritorious tools to enhance the efficiency of biocatalysis in industrial biotechnology. We purified and characterized a dextranase CeDex from the marine bacterium Cellulosimicrobium sp. THN1. CeDex acted in alkaline pHs (7.5-8.5) and a broad temperature range (10-50°C) with sufficient pH stability and thermostability. Remarkably, CeDex retained approximately 40% of its maximal activities at 4°C and increased its activity to 150% in 4 M NaCl, displaying prominently cold adaptation and salt tolerance. Moreover, CeDex was greatly stimulated by Mg2+, Na+, Ba2+, Ca2+ and Sr2+, and sugarcane juice always contains K+, Ca2+, Mg2+ and Na+, so CeDex will be suitable for removing dextran in the sugar industry. The main hydrolysate of CeDex was isomaltotriose, accompanied by isomaltotetraose, long-chain IOMs, and a small amount of isomaltose. The amino acid sequence of CeDex was identified from the THN1 genomic sequence by Nano LC-MS/MS and classified into the GH49 family. Notably, CeDex could prevent the formation of Streptococcus mutans biofilm and disassemble existing biofilms at 10 U/ml concentration and would have great potential to defeat biofilm-related dental caries.

Taurine promotes Oreochromis niloticus survival against Edwardsiella tarda infection

Edwardsiella tarda represents one of the most important pathogens that infects a variety of hosts including aquatic animals and humans. The outbreak of E. tarda infection is frequently reported in aquaculture that causes huge economic loss. Due to the widespread of antibiotic resistance, available antibiotics to treat bacterial infection are limited. Therefore, enhancing aquatic animals to survive upon E. tarda infection become an urgent issue. In this study, we profiled the metabolomic change of tilapia in-between the dying and survival fish upon E. tarda infection. The dying and survival fish mounts differential metabolic response, from which we identify a key metabolite, taurine, whose abundance is increased in both the survival group and the dying group but is more significant in the survival group. Exogenous taurine increases tilapia survival rate by 37.5% upon E. tarda infection. Further quantitative PCR analysis demonstrate taurine increases the expression of immune genes in liver, spleen and head kidney. Therefore, our study shows a new strategy to enhance fish immune response against bacterial infection.

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.

Noval porous phosphate-solubilizing bacteria beads loaded with BC/nZVI enhanced the transformation of lead fractions and its microecological regulation mechanism in soil

Soil lead pollution becomes a serious environmental problem. Microbial remediation has received widespread attentions due to high efficiency and no secondary pollution. In this research, a noval porous spherical phosphate-solubilizing bacteria bead loaded with biochar/nZVI (Bio-bead) was used to passivate lead in soil, and the effects and microecological regulation mechanisms of this process were also investigated. The results showed that the pH, OM, and AP of soil in the Bio-bead group were increased and the ORP was decreased over time compared with the blank group. The proportion of stable (oxidizable and residue) fractions of lead in Bio-bead group (45%) was much higher than that of the blank group (35%). In addition, the result of microbial community structure showed that Bio-beads did not change the species of dominant bacterial, excepting the abundance of Pseudomonas increased significantly and the abundance of Sphingomonas reduced during remediation. Redundancy analysis showed that pH, OM, AP and the ratio of residual and oxidizable fractions lead in soil were positively correlated with the abundance of Pseudomonas, while ORP was negatively correlated with the abundance of Pseudomonas. These findings have proved that Bio-bead is a potential strategy for remediation of lead-contaminated soil even in complexed soils.

Teg58, a small regulatory RNA, is involved in regulating arginine biosynthesis and biofilm formation in Staphylococcus aureus

Staphylococcus aureus adapts to different environments by sensing and responding to diverse environmental cues. The responses are coordinately regulated by regulatory proteins, and small regulatory RNAs at the transcriptional and translational levels. Here, we characterized teg58, a SarA repressed sRNA, using ChIP-Seq and RNA-Seq analysis of a sarA mutant. Phenotypic and genetic analyses indicated that inactivation of teg58 led to reduced biofilm formation in a process that is independent of SarA, agr, PIA, and PSMs. RNA-Seq analysis of teg58 mutant revealed up-regulation of arginine biosynthesis genes (i.e., argGH) as well as the ability of the mutant to grow in a chemical defined medium (CDM) lacking L-arginine. Exogenous L-arginine or endogenous induction of argGH led to decreased biofilm formation in parental strains. Further analysis in vitro and in vivo demonstrated that the specific interaction between teg58 and the argGH occurred at the post-transcriptional level to repress arginine synthesis. Biochemical and genetic analyses of various arginine catabolic pathway genes demonstrated that the catabolic pathway did not play a significant role in reduced biofilm formation in the teg58 mutant. Overall, results suggest that teg58 is a regulatory sRNA that plays an important role in modulating arginine biosynthesis and biofilm formation in S. aureus.

Synergy effects of copper and L-arginine on osteogenic, angiogenic, and antibacterial activities

Copper (Cu) ions have been found to exert antibacterial and angiogenic effects. However, some studies have indicated that it inhibits osteogenesis at high concentrations. On the other hand, L-arginine (Arg) is a semi-essential amino acid required for various biological processes, including osteogenic and angiogenic activities. As a result, we hypothesized that combining Arg with Cu ions would reduce its inhibitory effects on osteogenesis while increasing its angiogenic and antibacterial capabilities. To assess osteogenic and angiogenic activities, we employed rat bone marrow mesenchymal stem cells (MSCs) and human umbilical vein endothelial cells (HUVECs), respectively. The gram-positive bacteria Staphylococcus epidermidis (S. epidermidis), Staphylococcus aureus (S. aureus), and the gram-negative bacterium Escherichia coli (E. coli) were used to investigate bacterial behaviors. According to ALP activity and calcium deposition outcomes, copper ions inhibited osteogenic development of MSCs at 100 µM; however, Arg supplementation somewhat mitigated the inhibitory effects. Furthermore, Copper and Arg synergistically stimulated migration and tube formation of HUVECs. According to our findings, copper ions and Arg in the range of 1-100 µM had no antibacterial effect on any examined bacteria. However, at a dose of 20 mM, copper demonstrated antibacterial activity, which was boosted by Arg. Overall, these findings suggest that a combination of copper and Arg may be more beneficial for bone regeneration than either copper or Arg alone.

The Arginine Biosynthesis Pathway of Candida albicans Regulates Its Cross-Kingdom Interaction with Actinomyces viscosus to Promote Root Caries

The cross-kingdom interactions between Candida albicans and Actinomyces viscosus play critical roles in root caries. However, the key pathway by which C. albicans regulates its interactions with A. viscosus is unclear. Here, we first employed 39 volunteers with root caries and 37 caries-free volunteers, and found that the abundances of C. albicans and A. viscosus were significantly increased in the individuals with root caries and showed a strong positive correlation. Their dual-species combination synergistically promoted biofilm formation and root caries in rats. The arginine biosynthesis pathway of C. albicans was significantly upregulated in dual-species biofilms and dental plaques from another 10 root caries volunteers compared with the 10 caries-free volunteers. The exogenous addition of arginine increased the cariogenicity of the dual-species biofilm. The C. albicansARG4, a key gene from the arginine biosynthesis pathway, null mutant failed to promote dual-species biofilm formation and root caries in rats; however, the addition of arginine restored its synergistic actions with A. viscosus. Our results identified the critical roles of the C. albicans arginine biosynthesis pathway in its cross-kingdom interactions with A. viscosus for the first time and indicated that targeting this pathway was a practical way to treat root caries caused by multiple species.

IMPORTANCE Root caries is a critical problem that threatens the oral health of the elderly population. Our results identified the essential roles of the C. albicans arginine biosynthesis pathway in its cross-kingdom interactions with A. viscosus in root caries for the first time and indicated that targeting this pathway was a practical way to treat root caries caused by multiple species.

Effect of 8% arginine toothpaste on Streptococcus mutans in patients undergoing fixed orthodontic treatment: randomized controlled trial

Objective:

To assess the effect of toothpaste containing 8% arginine on Streptococcus mutans (S. mutans) in dental plaque around orthodontic brackets, and to draw a comparison with a regular fluoride toothpaste.

Trial design:

A single-center, parallel-arm, triple-blind, randomized controlled trial was conducted.

Methods:

The clinical trial was conducted at the Orthodontic Clinic, School of Dentistry, Shiraz University of Medical Sciences, Shiraz, Iran. Seventy-two patients (age range: 15-30 years) who required fixed orthodontic treatment were recruited and randomly assigned to arginine and fluoride groups. Randomization was performed using RANDOM.ORG online software, and the participants were divided into two parallel groups, with a 1:1 allocation ratio. Patients were requested to brush their teeth twice daily for 30 days with an experimental toothpaste. Plaque sampling was performed at two intervals, namely at the beginning of the study (T₀) and 30 days later (T₁). Real-time PCR was used to assess plaque samples in terms of the number of S. mutans surrounding stainless steel brackets in orthodontic patients. A triple-blind design was employed.

Results:

The baseline characteristics (age, sex, and the relative number of S. mutans) between the groups were similar (p>0.05). Only the arginine group showed a significant decrease in the relative number of bacteria between T₀ and T₁ (p=0.02).

Conclusion:

Arginine is an important prebiotic agent in maintaining healthy oral biofilms, and prevent dental caries during fixed orthodontic treatments.

Trial registration:

The trial was registered at the Iranian Registry of Clinical Trials (IRCT20181121041713N2), https://en.irct.ir/user/trial/42409/view.

Oralbiotica/Oralbiotics: The Impact of Oral Microbiota on Dental Health and Demineralization: A Systematic Review of the Literature

The oral microbiota plays a vital role in the human microbiome and oral health. Imbalances between microbes and their hosts can lead to oral and systemic disorders such as diabetes or cardiovascular disease. The purpose of this review is to investigate the literature evidence of oral microbiota dysbiosis on oral health and discuss current knowledge and emerging mechanisms governing oral polymicrobial synergy and dysbiosis; both have enhanced our understanding of pathogenic mechanisms and aided the design of innovative therapeutic approaches as ORALBIOTICA for oral diseases such as demineralization. PubMed, Web of Science, Google Scholar, Scopus, Cochrane Library, EMBEDDED, Dentistry & Oral Sciences Source via EBSCO, APA PsycINFO, APA PsyArticles, and DRUGS@FDA were searched for publications that matched our topic from January 2017 to 22 April 2022, with an English language constraint using the following Boolean keywords: ("microbio*" and "demineralization*") AND ("oral microbiota" and "demineralization"). Twenty-two studies were included for qualitative analysis. As seen by the studies included in this review, the balance of the microbiota is unstable and influenced by oral hygiene, the presence of orthodontic devices in the oral cavity and poor eating habits that can modify its composition and behavior in both positive and negative ways, increasing the development of demineralization, caries processes, and periodontal disease. Under conditions of dysbiosis, favored by an acidic environment, the reproduction of specific bacterial strains increases, favoring cariogenic ones such as Bifidobacterium dentium, Bifidobacterium longum, and S. mutans, than S. salivarius and A. viscosus, and increasing of Firmicutes strains to the disadvantage of Bacteroidetes. Microbial balance can be restored by using probiotics and prebiotics to manage and treat oral diseases, as evidenced by mouthwashes or dietary modifications that can influence microbiota balance and prevent or slow disease progression.

Strategies to Combat Caries by Maintaining the Integrity of Biofilm and Homeostasis during the Rapid Phase of Supragingival Plaque Formation

Bacteria in the oral cavity, including commensals and opportunistic pathogens, are organized into highly specialized sessile communities, coexisting in homeostasis with the host under healthy conditions. A dysbiotic environment during biofilm evolution, however, allows opportunistic pathogens to become the dominant species at caries-affected sites at the expense of health-associated taxa. Combining tooth brushing with dentifrices or rinses combat the onset of caries by partially removes plaque, but resulting in the biofilm remaining in an immature state with undesirables’ consequences on homeostasis and oral ecosystem. This leads to the need for therapeutic pathways that focus on preserving balance in the oral microbiota and applying strategies to combat caries by maintaining biofilm integrity and homeostasis during the rapid phase of supragingival plaque formation. Adhesion, nutrition, and communication are fundamental in this phase in which the bacteria that have survived these adverse conditions rebuild and reorganize the biofilm, and are considered targets for designing preventive strategies to guide the biofilm towards a composition compatible with health. The present review summarizes the most important advances and future prospects for therapies based on the maintenance of biofilm integrity and homeostasis as a preventive measure of dysbiosis focused on these three key factors during the rapid phase of plaque formation.

The arginine deaminase system plays distinct roles in Borrelia burgdorferi and Borrelia hermsii

Borrelia species are amino acid auxotrophs that utilize di- and tri- peptides obtained through their oligopeptide transport system to supply amino acids for replicative growth during their enzootic cycles. However, Borrelia species from both the Lyme disease (LD) and relapsing fever (RF) groups harbor an amino acid transport and catabolism system, the Arginine Deiminase System (ADI), that could potentially augment intracellular L-arginine required for growth. RF spirochetes contain a “complete”, four gene ADI (arcA, B, D, and C) while LD spirochetes harbor arcA, B, and sometimes D but lack arcC (encoding carbamate kinase). In this study, we evaluated the role of the ADI system in bacterial survival and virulence and discovered important differences in RF and LD ADIs. Both in vitro and in a murine model of infection, B. hermsii cells significantly reduced extracellular L-arginine levels and that reduction was dependent on arginine deiminase expression. Conversely, B. burgdorferi did not reduce the concentration of L-arginine during in vitro growth experiments nor during infection of the mammalian host, suggesting a fundamental difference in the ability to directly utilize L-arginine compared to B. hermsii. Further experiments using a panel of mutants generated in both B. burgdorferi and B. hermsii, identified important differences in growth characteristics and ADI transcription and protein expression. We also found that the ADI system plays a key role in blood and spleen colonization in RF spirochetes. In this study we have identified divergent metabolic strategies in two closely related human pathogens, that ultimately impacts the host-pathogen interface during infection.

Reports of tick-borne diseases have been steadily increasing in the US and the number of Lyme disease cases caused by B. burgdorferi have tripled since the late 1990’s. Although less common, cases of tick-borne relapsing fever, caused by B. hermsii and B. turicatae in the US, have increased as well. While transmitted by different ticks and maintained in unique enzootic cycles, the closely related spirochetes B. burgdorferi and B. hermsii share numerous genetic features including a truncated and streamlined capacity for metabolic activity. In this study we combine genetic and biochemical assays to define the role of the ADI in the infective cycles of B. burgdorferi and B. hermsii. When we compared B. burgdorferi and B. hermsii, we identified important differences in their respective ADI’s including operon arrangement, sensitivity to L-arginine and L-ornithine levels, as well as gene and protein expression. In addition, we show that arginine deiminase is required to reduce host L-arginine levels during murine infection with B. hermsii. This study provides new insights into the metabolic activities of two medically relevant spirochetes and highlights the dynamic nature of host-pathogen interactions.

Analyses of the Effects of Arginine, Nicotine, Serotype and Collagen-Binding Proteins on Biofilm Development by 33 Strains of Streptococcus mutans

Streptococcus mutans serotype k strains comprise <3% of oral isolates of S. mutans but are prominent in diseased cardiovascular (CV) tissue. Collagen binding protein (CBP) genes, cbm and cnm, are prevalent in serotype k strains and are associated with endothelial cell invasion. Nicotine increases biofilm formation by serotype c strains of S. mutans, but its effects on serotype k strains and strains with CBP are unknown. Saliva contains arginine which alters certain properties of the extracellular polysaccharides (EPS) in S. mutans biofilm. We examined whether nicotine and arginine affect sucrose-induced biofilm of S. mutans serotypes k (n = 23) and c (n = 10) strains with and without CBP genes. Biofilm mass, metabolism, bacterial proliferation, and EPS production were assessed. Nicotine increased biomass and metabolic activity (p < 0.0001); arginine alone had no effect. The presence of a CBP gene (either cbm or cnm) had a significant effect on biofilm production, but serotype did not. Nicotine increased bacterial proliferation and the effect was greater in CBP + strains compared to strains lacking CBP genes. Addition of arginine with nicotine decreased both bacterial mass and EPS compared to biofilm grown in nicotine alone. EPS production was greater in cnm + than cbm + strains (p < 0.0001). Given the findings of S. mutans in diseased CV tissue, a nicotine induced increase in biofilm production by CBP + strains may be a key link between tobacco use and CV diseases.

Arginine-induced metabolomic perturbation in Streptococcus mutans

Background

Streptococcus mutans is a major pathogen responsible for dental caries. Arginine is a promising potential caries preventive agent which can inhibit the growth of S. mutans. However, the mechanism whereby arginine inhibits S. mutans growth remains unclear.

Aim

To assess the impact of arginine-induced metabolomic perturbations on S. mutans under biofilm conditions.

Methods

We identified 5,933 and 7,413 ions in positive (ESI+) and negative (ESI-) electrospray ion modes, respectively, with a total of 11.05% and 11.58% differential ions subsequently detected in two respective modes. Further analyses of these metabolites led to identification of 8 and 22 metabolic pathways that were affected by arginine treatment in ESI+ and ESI- modes.,

Results

Once or twice daily treatments of S. mutans biofilms with arginine resulted in reductions in biofilm biomass. Significant reductions in EPS production were observed following twice daily arginine treatments. Identified metabolites that were significantly differentially abundant following arginine treatment were associated with glycolysis metabolism, amino sugar and nucleotide sugar metabolism, and peptidoglycan synthesis.

Conclusions

Arginine can reduce S. mutans biofilm growth and acid production by inhibiting glycolysis, amino sugar and nucleotide sugar metabolism, and peptidoglycan synthesis.

The acid-resistance potential of arginine-fluoride varnish treated enamel

The study objective was to examine the acid-resistance potential of enamel carious lesions treated with arginine (Arg)-sodium fluoride (NaF) varnishes using nano-mechanical testing and chemical mapping. L-arginine (at 1%, 2%, & 4%) was incorporated in 5% NaF varnish. The experimental/control groups were: 1% Arg-NaF, 2% Arg-NaF, 4% Arg-NaF, NaF, and no treatment. Enamel specimen blocks were subjected to incipient carious lesion formation. After treatment, the specimens underwent chemical pH-cycling for 8-days and acid challenge for 2 h. The specimens were characterised for surface nano-hardness (SNH) and calcium/phosphate content of the treated lesions to determine enamel solubility reduction (ESR). Post-acid challenge, X-ray diffraction crystallography (XRD), and energy dispersive X-ray spectrophotometry (EDX) were performed. The SNH for 2%/4% Arg-NaF demonstrated a higher resistance to acid challenge with significantly higher SNH recovery than NaF varnish (p<0.05). The ESR potential of 2%/4% Arg-NaF varnish was significantly higher than NaF varnish (p<0.05). The XRD crystalline phases demonstrated that 2%/4% Arg-NaF had intense hydroxyapatite peaks discerning its increased potential to resist demineralization than NaF varnish. The EDX results showed that 2%/4% Arg-NaF demonstrated Ca/P ratio closer to hydroxyapatite (~1.67) post-acid challenge. Incorporating 2%/4% L-arginine in a 5% NaF varnish enhances the acid-resistance potential of NaF varnish.

Concentration-Dependent Multi-Potentiality of L-Arginine: Antimicrobial Effect, Hydroxyapatite Stability, and MMPs Inhibition

This study's objective was to examine L-arginine (L-arg) supplementation's effect on mono-species biofilm (Streptococcus mutans/Streptococcus sanguinis) growth and underlying enamel substrates. The experimental groups were 1%, 2%, and 4% arg, and 0.9% NaCl was used as the vehicle control. Sterilised enamel blocks were subjected to 7-day treatment with test solutions and S. mutans/S. sanguinis inoculum in BHI. Post-treatment, the treated biofilms stained for live/dead bacterial cells were analysed using confocal microscopy. The enamel specimens were analysed using X-ray diffraction crystallography (XRD), Raman spectroscopy (RS), and transmission electron microscopy (TEM). The molecular interactions between arg and MMP-2/MMP-9 were determined by computational molecular docking and MMP assays. With increasing arg concentrations, bacterial survival significantly decreased (p < 0.05). The XRD peak intensity with 1%/2% arg was significantly higher than with 4% arg and the control (p < 0.05). The bands associated with the mineral phase by RS were significantly accentuated in the 1%/2% arg specimens compared to in other groups (p < 0.05). The TEM analysis revealed that 4% arg exhibited an ill-defined shape of enamel crystals. Docking of arg molecules to MMPs appears feasible, with arg inhibiting MMP-2/MMP-9 (p < 0.05). L-arginine supplementation has an antimicrobial effect on mono-species biofilm. L-arginine treatment at lower (1%/2%) concentrations exhibits enamel hydroxyapatite stability, while the molecule has the potential to inhibit MMP-2/MMP-9.

Relationship between Saliva and Sublingual Immunotherapy

The demand for allergen specific immunotherapy (AIT), especially sublingual immunotherapy (SLIT), is increasing because of its efficacy in inducing clinical remission of allergic diseases and its low risk of side effects. Since not all patients that undergo SLIT demonstrate an improvement in allergic symptoms, the development of biomarkers to predict the outcome and adjuvants for SLIT is desired. Saliva is the first target with which tablets used in SLIT come into contact, and salivary pH, chemical properties or microbiome composition are reported to possibly be associated with the outcome of SLIT. Antibodies such as IgG4 and IgA not only in the serum but also in the saliva are increased after SLIT and may also be associated with the efficacy of SLIT. The development of the metagenomic sequencing technique makes it possible to determine the microbiome composition and ratio of each bacterium, and researchers can investigate the relationships between specific bacteria and the immune response. Some bacteria are reported to improve the SLIT outcome and have the potential to be used as biomarkers for the selection of patients and as adjuvants in SLIT. Here, we introduce biomarkers for SLIT and present recent findings regarding the relationship between saliva and SLIT.

The induction of inflammation by the cGAS-STING pathway in human dental pulp cells: A laboratory investigation

AIM

To explore the presence of the cGAS-STING inflammatory pathway in human pulp tissue and human dental pulp cells (HDPCs).

METHODOLOGY

Pulp tissue was collected from freshly extracted human healthy third molars or third molars with irreversible pulpitis. Quantitative real-time polymerase chain reaction (qRT-PCR) and enzyme-linked immunoassay (ELISA) were performed to assess IFN-β, TNF and IL-6. Human dental pulp cells prepared from healthy human pulp tissues were transfected with interferon stimulatory DNA (ISD), bacterial genomic DNA, bacterial cyclic dinucleotides c-di-AMP, c-di-GMP or host cyclic dinucleotide cGAMP. SiRNA was used to knock down the endogenous cGAS or STING. G140 and H-151 were used to inhibit cGAS and STING respectively. Amlexanox and BAY 11-7082 were used to inhibit TBK1 and NF-κB respectively. qRT-PCR and ELISA were performed to detect the level of IFN-β, TNF and IL-6. Western blot was performed to evaluate the TBK1, IRF3 and p65 phosphorylation. The Student's t-test and one-way anova were used for statistical analysis.

RESULTS

IFN-β, TNF and IL-6 were up-regulated in the inflamed human dental pulp tissue. CGAS and STING mRNA were increased in the inflamed human dental pulp tissue and detected in HDPCs prepared from healthy human pulp tissues. ISD transfection induced TBK1, IRF3 and p65 phosphorylation as well as IFN-β, TNF and IL-6 production. IFN-β, TNF and IL-6 production were also induced by transfection of bacterial and host cyclic dinucleotides or bacteria DNA. ISD or bacteria DNA transfection elevated the intracellular levels of cGAMP. Knock-down of cGAS or STING, as well as using cGAS inhibitor G140 or STING inhibitor H-151 abolished the IFN-β, TNF and IL-6 production induced by ISD transfection. Knock-down of STING or using STING inhibitor H-151 abolished the IFN-β, TNF and IL-6 induction by transfection of bacterial and host cyclic dinucleotides. Both Amlexanox and BAY 11-7082 inhibited IFN-β, TNF and IL-6 production triggered by ISD and cyclic dinucleotides transfection.

CONCLUSIONS

Human dental pulp cells expressed an intact cGAS-STING signalling axis. The cGAS-STING signalling axis may play an important role in pulp inflammation and immune defence.

The Current Strategies in Controlling Oral Diseases by Herbal and Chemical Materials

Dental plaque is a biofilm composed of complex microbial communities. It is the main cause of major dental diseases such as caries and periodontal diseases. In a healthy state, there is a delicate balance between the dental biofilm and host tissues. Nevertheless, due to the oral cavity changes, this biofilm can become pathogenic. The pathogenic biofilm shifts the balance from demineralization-remineralization to demineralization and results in dental caries. Dentists should consider caries as a result of biological processes of dental plaque and seek treatments for the etiologic factors, not merely look for the treatment of the outcome caused by biofilm, i.e., dental caries. Caries prevention strategies can be classified into three groups based on the role and responsibility of the individuals doing them: (1) community-based strategy, (2) dental professionals-based strategy, and (3) individual-based strategy. The community-based methods include fluoridation of water, salt, and milk. The dental professionals-based methods include professional tooth cleaning and use of varnish, fluoride gel and foam, fissure sealant, and antimicrobial agents. The individual-based (self-care) methods include the use of fluoride toothpaste, fluoride supplements, fluoride mouthwashes, fluoride gels, chlorhexidine gels and mouthwashes, slow-release fluoride devices, oral hygiene, diet control, and noncariogenic sweeteners such as xylitol. This study aimed to study the research in the recent five years (2015–2020) to identify the characteristics of dental biofilm and its role in dental caries and explore the employed approaches to prevent the related infections.

Assessing biofilm inhibition and immunomodulatory activity of small amounts of synthetic host defense peptides synthesized using SPOT-array technology

Peptides are promising drug candidates because of their diversity, biocompatibility and spectrum of activities. Here, we describe a protocol for high-throughput screening of SPOT-peptide arrays to assess the antibiofilm, antimicrobial and immunomodulatory activities of synthetic peptides. It is a Protocol Extension of our previous Nature Protocols article, which describes the synthesis of SPOT-peptide arrays and assays for screening antimicrobial activity. This latest protocol allows the simultaneous assessment of hundreds of synthetic host defense peptides to define their overall activity profiles and identify candidate sequences that are suitable for further characterization and development as anti-infectives. When coupled with the SPOT-array technology for peptide synthesis, the described procedures are rapid, inexpensive and straightforward for peptide library screening. The protocols can be implemented in most microbiology or immunology research laboratories without the need for specialists. The time to complete each step ranges between 1 and 4 h with overnight pauses, and datasets related to the antibiofilm and immunomodulatory activities of a large set of peptide sequences can be generated in a few days.

The effect of arginine-fluoride varnish on biochemical composition of multi-species biofilm

OBJECTIVE

To examine the biochemical components of multi-species biofilm on the arginine (Arg)-sodium fluoride (NaF) varnish-treated enamel following bacterial pH-cycling.

METHODS

l-arginine (at 1%, 2%, & 4% w/v.) was incorporated in a 5% NaF varnish. The experimental and control groups were: 1%, 2%, 4% Arg-NaF, NaF, and no treatment. Enamel blocks were prepared, acid-etched, varnish-treated and then subjected to 72 h bacterial pH-cycling in an oral biofilm reactor. The organic (carbohydrates, proteins, amyloids, and eDNA) and inorganic components (calcium, inorganic phosphate, F) were assayed for the obtained biofilm suspensions. The biofilms were stained for exopolysaccharides (EPS)/bacteria and the respective proportions of live/dead bacteria was determined using confocal imaging.

RESULTS

The total carbohydrate content of the biofilm was the lowest for the 2% and 4% Arg-NaF (p < 0.05). Except for 2% Arg-NaF, the biofilm proteins for 4% Arg-NaF were significantly higher than the other groups (p < 0.05). The amyloids for Arg-NaF groups were significantly lower than the controls (p < 0.05). The eDNA for 4% Arg-NaF was significantly higher than the controls (p < 0.05). The 2% and 4% Arg-NaF-treated enamel had increased biofilm Pi and F compared to the NaF-treated enamel (p < 0.05). The proportion of biofilm EPS matrix to bacteria was significantly reduced in Arg-NaF groups compared to the controls (p < 0.05). The dead bacterial proportions of 4% Arg-NaF were significantly higher than the controls (p < 0.05).

CONCLUSION

Higher concentrations (i.e. 2%/4%) of Arg in 5% NaF varnish have the potential to modulate the biochemical composition of the biofilm growing on the treated enamel.

NLRP6-caspase 4 inflammasome activation in response to cariogenic bacterial lipoteichoic acid in human dental pulp inflammation

AIM

To explore the presence and function of NLRP6-caspase 4 inflammasome in human pulp tissue and human dental pulp cells (HDPCs).

METHODOLOGY

Pulp tissue was collected from freshly extracted human caries-free third molars and third molars with irreversible pulpitis. Quantitative real-time polymerase chain reaction (qRT-PCR) and western blot were performed to assess the expression of NLRP6-caspase 4 inflammasome. HDPCs were prepared from normal human pulp tissues and challenged with Porphyromonas gingivalis LPS. Enzyme-linked immunosorbent assay (ELISA) and qRT-PCR were performed to assess if LPS can upregulate NLRP6 and caspase-4. HDPCs were further challenged with LPS followed with cytosolic Streptococcus mutans lipoteichoic acid (LTA). SiRNA targeting NLRP6 and Casp4 and pharmacology inhibitor Ac-FLTD-CMK and MCC950 were used to assess if Streptococcus mutans LTA can activate the NLRP6 but not the NLRP3 inflammasome. Western blot and ELISA were performed to evaluate inflammasome activation. The Student's t-test and one-way anova were used for statistical analysis.

RESULTS

NLRP6-caspase 4 inflammasome was upregulated and activated in inflamed human dental pulp tissue. In HDPCs, Porphyromonas gingivalis LPS upregulated the expression of NLRP6, CASP1 and CASP4 in a type I interferon dependent manner. After LPS priming, cytosolic Streptococcus mutans LTA triggered NLRP6-caspase 4 inflammasome activation. Knockdown of NLRP6 or CASP4 using siRNA or using pharmacology inhibitor Ac-FLTD-CMK but not MCC950 efficiently suppressed inflammasome activation by cytosolic LTA.

CONCLUSIONS

NLRP6-caspase 4 inflammasome may play an important role in pulp inflammation and immune defence. Inflammatory caspases represent a pharmacological target to restrain pulpal inflammation.

Combined effect of arginine and fluoride on the growth of Lactobacillus rhamnosus GG

The objectives of the in vitro study were: (1) to investigate the effect of combining L-arginine (Arg) and NaF on the growth of Lactobacillus rhamnosus GG (LRG); and (2) to identify an optimum synergistic concentration for the synbiotic (Arg + LRG)-fluoride (SF) therapy. 1% Arg + 2000-ppm NaF (A-SF) and 2% Arg + 2000-ppm NaF (B-SF) demonstrated antagonism against LRG (FIC > 4.0). Both XTT (2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide) and WST-8 (2-(2-methoxy-4-nitrophenyl)-3-(4-nitrophenyl)-5-(2,4-disulfophenyl)-2H-tetrazolium, monosodium salt) assays showed that A-SF and B-SF enhanced the growth of LRG when compared to 2000-ppm NaF and LRG control. Colony forming units, bacterial weight, and biofilm thickness of A-SF and B-SF were significantly higher than 2000-ppm NaF and LRG control. Biofilm imaging depicted that 2000-ppm NaF inhibited biofilm formation; while 1%/2% Arg, A-SF, and B-SF increased biofilm growth of LRG. Lactic acid formation was the lowest for 2000-ppm NaF, followed by A-SF and then B-SF. The SF buffer potential after 24 h was the highest for B-SF, and then A-SF. Biofilm pH for B-SF was closest to neutral. Fluoride, Arg and LRG bioavailability remained unaffected in B-SF. The relative gene expression for arcA, argG, and argH was significantly higher for B-SF than the respective controls. In conclusion, combining 2% Arg, 2000-ppm NaF, and LRG provides an optimum synbiotic-fluoride synergism.

Physicochemical Characteristics of Arginine Enriched NaF Varnish: An In Vitro Study

The in vitro study objectives were to investigate the effect of arginine (Arg) incorporation in a 5% sodium fluoride (NaF) varnish on its physical and chemical properties including F/Arg release. Six experimental formulations were prepared with L-arginine (L-Arg) and L-arginine monohydrochloride at 2%, 4%, and 8% w/v in a 5% NaF varnish, which served as a control. The varnishes were subjected to assessments for adhesion, viscosity, and NaF extraction. Molecular dynamics were simulated to identify post-dynamics total energy for NaF=Arg/Arg>NaF/Arg<NaF concentrations. The Arg/F varnish release profiles were determined in polyacrylic lactate buffer (pH-4.5; 7 days) and artificial saliva (pH-7; 1 h, 24 h, and 12 weeks). Incorporation of L-Arg in NaF varnish significantly influences physical properties ameliorating retention (p < 0.001). L-Arg in NaF varnish institutes the Arg-F complex. Molecular dynamics suggests that NaF>Arg concentration denotes the stabilized environment compared to NaF<Arg (p < 0.001). The 2% Arg-NaF exhibits periodic perennial Arg/F release and shows significantly higher integrated mean F release than NaF (p < 0.001). Incorporating 2% L-arginine in 5% NaF varnish improves its physical properties and renders a stable matrix with enduring higher F/Arg release than control.

Sulfated vizantin causes detachment of biofilms composed mainly of the genus Streptococcus without affecting bacterial growth and viability

BACKGROUND

Sulfated vizantin, a recently developed immunostimulant, has also been found to exert antibiofilm properties. It acts not as a bactericide, but as a detachment-promoting agent by reducing the biofilm structural stability. This study aimed to investigate the mechanism underlying this activity and its species specificity using two distinct ex vivo oral biofilm models derived from human saliva.

RESULTS

The biofilm, composed mainly of the genus Streptococcus and containing 50 μM of sulfated vizantin, detached significantly from its basal surface with rotation at 500 rpm for only 15 s, even when 0.2% sucrose was supplied. Expression analyses for genes associated with biofilm formation and bacterial adhesion following identification of the Streptococcus species, revealed that a variety of Streptococcus species in a cariogenic biofilm showed downregulation of genes encoding glucosyltransferases involved in the biosynthesis of water-soluble glucan. The expression of some genes encoding surface proteins was also downregulated. Of the two quorum sensing systems involved in the genus Streptococcus, the expression of luxS in three species, Streptococcus oralis, Streptococcus gordonii, and Streptococcus mutans, was significantly downregulated in the presence of 50 μM sulfated vizantin. Biofilm detachment may be facilitated by the reduced structural stability due to these modulations. As a non-specific reaction, 50 μM sulfated vizantin decreased cell surface hydrophobicity by binding to the cell surface, resulting in reduced bacterial adherence.

CONCLUSION

Sulfated vizantin may be a candidate for a new antibiofilm strategy targeting the biofilm matrix while preserving the resident microflora.

Enamel remineralization potential of arginine-fluoride varnish in a multi-species bacterial pH-cycling model

OBJECTIVES

To examine the enamel fluoride uptake and remineralization potential of arginine-fluoride (Arg-NaF) varnishes in a simulated clinical condition using a multi-species bacterial pH-cycling model.

METHODS

L-Arginine (at 1 %, 2 %, and 4 % by wt.) was incorporated in a 5 % NaF varnish. Experimental and control groups were: 1 % Arg-NaF; 2 % Arg-NaF; 4 % Arg-NaF; NaF and no treatment. Artificial incipient caries-like lesions were formed on 30 enamel specimen blocks (n = 6). The specimens underwent multi-species bacterial pH-cycling in an artificial mouth system using oral biofilm reactor for 72 h after treatment. The specimens were evaluated for mineral density using micro-CT, Ca/P ratio with SEM-EDX, enamel fluoride uptake (EFU) and plaque fluoride uptake (PFU).

RESULTS

Increasing concentrations of Arg in NaF varnish significantly increased the EFU of incipient caries-like lesions (p < 0.001). The PFU for 1 % Arg-NaF was significantly higher than 4 % Arg-NaF and the control NaF (p < 0.05). Post pH-cycling, Ca/P ratio with 1 %/2 % Arg-NaF was closest to hydroxyapatite (1.67). Mineral gain and % remineralization of 1 %/2 % Arg-NaF was significantly higher than the control NaF varnish (p < 0.05).

CONCLUSION

The prebiotic L-arginine (at 1 %/2 % by wt.) in a 5 % NaF varnish enhanced the enamel fluoride uptake and remineralization potential of the conventional 5 % NaF varnish.

CLINICAL SIGNIFICANCE

The Arg-NaF varnish addresses the limitations of fluorides on cariogenic biofilms. The Arg-NaF varnish appears a promising caries-preventive regimen that counters the pathogenic biofilms by Arg and promotes remineralization with fluorides. In high caries-risk patients, professional application of Arg-NaF varnish might aid to alleviate the global burden of dental caries.

Effective passivation of lead by phosphate solubilizing bacteria capsules containing tricalcium phosphate

Phosphate solubilizing bacteria (PSBs) shows high potential to be used for lead passivation in sediments due to the abilities of releasing phosphate and the subsequent formation of insoluble Pb-phosphate compounds. In this research, microbial capsules implemented with sodium alginate and CaCl₂, containing Leclercia adecarboxylata L15 (a lead resistant PSB) and Ca₃(PO₄)₂, were developed and the performance on lead passivation under different conditions was examined. The optimal concentrations of sodium alginate and CaCl₂ for formulating the capsules were determined to be 0.3% and 10%, respectively. The removal efficiency of Pb²⁺ by capsules containing L15 and Ca₃(PO₄)₂ was up to 98% with a capsule dosage of 2%, initial Pb²⁺ concentration of 1mM and pH of 3.0, which was better than that of free L15 (18%) and capsules containing only L15 (34%). Lead was immobilized via the formation of Pb₅(PO₄)₃Cl on the surface and Pb₃(PO₄)₂ in the interior of the capsules. The simulated sediment remediation experiments showed that the acid soluble fraction of lead reduced from 28% to 14% and transformed into more stable fractions after 10 days. The experiment results indicated that PSBs capsules coupled with phosphate materials have a great promise for application in remediation of lead contaminated sediments.

Probiotic Effects of Lactobacillus paracasei 28.4 to Inhibit Streptococcus mutans in a Gellan-Based Formulation

Streptococcus mutans is considered to be a major bacterium involved in dental caries, and the control of virulence mechanisms is fundamental to prevent disease. Probiotics present a promising preventive method; however, the use of probiotics requires its incorporation into delivery materials to facilitate oral colonization. Thus, we performed a comprehensive study examining preventive effects of Lactobacillus paracasei 28.4-enriched gellan hydrogel materials to inhibit S. mutans in planktonic and biofilm states, addressing its influence in the production of extracellular polysaccharides (EPS) and altered gene expression of several cariogenic virulence factors. L. paracasei 28.4, a strain isolated from the oral cavity of a caries-free individual, was incorporated in three gellan hydrogels (0.5%, 0.75%, and 1% w/v). The pretreatment with probiotic-gellan formulations provided a release of L. paracasei cells over 24 h that was sufficient to inhibit the planktonic growth of S. mutans, independent of the gellan concentrations and pH variations. This pretreatment also had inhibitory activity against S. mutans biofilms, exhibiting a reduction of 0.57 to 1.54 log₁₀ in CFU/mL (p < 0.0001) and a decrease of 68.8 to 71.3% in total biomass (p < 0.0001) compared with the control group. These inhibitory effects were associated with the decreased production of EPS by 80% (p < 0.0001) and the downregulation of luxS, brpA, gbpB, and gtfB genes. The gellan formulation containing L. paracasei 28.4 exhibited probiotic effects for preventing S. mutans growth, biofilm formation, and production of cariogenic factors to suggest possible use in tooth decay prevention.

A Scoping Review on Arginine in Caries Prevention

OBJECTIVES

Emerging science on arginine or arginine formulations has driven the need to examine the research in the field. The scoping study objectives were (1) to identify the extent, range, and type of evidence on the role of arginine or arginine formulations in caries prevention and (2) to explore the future scope of research on arginine-containing caries-preventive agents.

METHODS

A systematic search was performed in PubMed, Scopus, and Web of Science. In vitro studies, clinical trials, narrative reviews, systematic reviews and or meta-analysis, and umbrella reviews or meta-evaluation examining arginine or arginine formulations for caries prevention were included. The data-charting process involved extracting variables followed by evidence synthesis. Arginine variants investigated up to date were discussed to explore future scope of research.

RESULTS

Thirty-nine articles were included for review from 105 identified citations comprising of in vitro studies, clinical trials, and reviews. Most articles studied 1.5% arginine-fluoride toothpaste. Most studies were from Asia, followed by North America, with fewest studies from Europe and South America. Arginine or arginine formulations demonstrated a superior caries-preventive effect compared with their matched controls (including fluorides); however, the evidence is with high risk of bias. Until now, three arginine variants have been investigated with l-arginine monohydrochloride as the least explored variant.

CONCLUSIONS

The evidence on the caries-preventive effect of arginine or arginine formulations has a high risk of bias. High-quality clinical trials are needed to assess the caries-preventive potential of arginine in commercial formulations. The role of l-arginine monohydrochloride in caries prevention can further be explored by incorporating in self-applied and professionally applied caries-preventive agents.

Streptococcus mutans Membrane Vesicles Harboring Glucosyltransferases Augment Candida albicans Biofilm Development

Candida albicans, as the most common fungus in the oral cavity, is often detected in early childhood caries. Streptococcus mutans is the major etiological agent of dental caries, but the role of S. mutans on C. albicans growth and biofilm development remains to be elucidated. Membrane vesicles (MVs) are a cell-secreted subcellular fraction that play an important role in intercellular communication and disease progression. In the present study, we investigated whether MVs from S. mutans augment C. albicans growth and biofilm development. The results indicated that S. mutans MVs augmented C. albicans biofilm development but had no significant effect on C. albicans growth under planktonic conditions. Subsequently, we labeled S. mutans MVs with PKH26 and used confocal laser scanning microscopy (CLSM) to track S. mutans MVs, which were observed to be located in the C. albicans biofilm extracellular matrix. Monosaccharide tests showed that S. mutans MVs contribute to sucrose metabolism in C. albicans. Polysaccharides were significantly enriched in the S. mutans MV-treated group. MVs from ΔgtfBC mutant strains were compared with those from the wild-type S. mutans. The results revealed that MVs from the ΔgtfBC mutant had no effect on C. albicans biofilm formation and exopolysaccharide production. In addition, C. albicans biofilm transcriptional regulators (Ndt80, Als1, Mnn9, Van1, Pmr1, Gca1, and Big1) expression were upregulated in S. mutans MV-treated group. In summary, the results of the present study showed that S. mutans MVs harboring glucosyltransferases involved in exopolysaccharide production augment C. albicans biofilm development, revealing a key role for S. mutans MVs in cross-kingdom interactions between S. mutans and C. albicans.

Synbiotics in caries prevention: A scoping review

The scoping review aimed to examine the evidence on the role of synbiotics in caries prevention. PubMed, SCOPUS, and Web of Science databases search were performed. Any in vitro study, clinical trial, systematic review with/without meta-analysis, umbrella review/meta-evaluation, narrative review addressing the role of synbiotics in caries prevention were included in the scoping review. Data were extracted from the included studies using pre-approved registered protocol. Twenty-eight records were identified, of which 5 in vitro studies, 1 quasi-experimental clinical trial and 1 narrative review were included in the present review. No controlled clinical trials or systematic reviews on the role of synbiotics in caries prevention could be identified. Except 1, all in vitro studies examined the combined effect of saccharides and lactobacilli spp. as potential synbiotics on the growth of Streptococcus mutans. However, the proposed synbiotics in 4 in vitro studies either did not qualify or remained ambiguous of its eligibility as a potential synbiotic for caries prevention. One recent in vitro study explored the possibility of L-arginine and Lactobacillus rhamnosus GG synbiotic for caries prevention. The quasi-experimental clinical study without a control arm did not explicitly mention the intervention composition and thus, its synbiotic potential remains unclear. A narrative review highlighted the potential of combining arginine (prebiotic) with arginolytic bacteria (probiotic) as a synbiotic, which appears promising for caries prevention. The eligibility of the proposed synbiotics as a true synbiotic needs to be carefully addressed. Due to a lack of controlled clinical studies on synbiotics for caries prevention, evidence on their caries-preventive potential is weak. Future studies are needed to examine the combination of amino acids (esp. arginine) with probiotics as a potential synbiotic against cariogenic pathogens.

In Vitro Evaluation of the Antibacterial Properties of Tea Tree Oil on Planktonic and Biofilm-Forming Streptococcus mutans

Streptococcus mutans (S. mutans) is the principal etiologic agent in the occurrence of human dental caries and the formation of biofilms on the surface of teeth. Tea tree oil (TTO) has been demonstrated to exhibit a wide range of pharmacological actions that can effectively inhibit the activity of bacteria. In this context, we evaluated the in vitro antimicrobial effects of TTO on S. mutans both during planktonic growth and in biofilms compared with 0.2% CHX. We determined the minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) using the microdilution method, the bacteriostatic rate using an MTT assay, and the antimicrobial time using a time-kill assay. Then, we explored the effects of TTO on acid production and cell integrity. Furthermore, the effects of TTO on the biomass and bacterial activity of S. mutans biofilms were studied. Finally, scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM) were used to investigate the structure and activity of biofilms. The MIC and MBC values were 0.125% and 0.25%, and the bacterial inhibition rate was concentration dependent. TTO can effectively inhibit bacterial acid production and destroy the integrity of the cell membrane. Electron micrographs revealed a reduction in bacterial aggregation, inhibited biofilm formation, and reduced biofilm thickness. The effect of TTO was the same as that of 0.2% CHX at a specific concentration. In summary, we suggest that TTO is a potential anticariogenic agent that can be used against S. mutans.

Influence of different ceramic materials and surface treatments on the adhesion of Prevotella intermedia

Ceramics are used in oral rehabilitation; however, these materials are prone to formation of biofilms that may cause periodontal diseases. This study aimed to evaluate the influence of distinct surface treatments on ceramic surface roughness and biofilm formation of oral bacteria (Prevotella intermedia). Eighty-four specimens of the following four ceramic systems were produced: LC - leucite-based glass ceramic, LD - lithium disilicate-based glass ceramic, LSZ - glass ceramic based on zirconia-reinforced lithium silicate, and ZR - monolithic zirconia. These were submitted to three different surface treatment protocols: C - control, G - glazing, and GDB - grinding with diamond bur (n = 7). The surface characteristics were assessed using a confocal laser microscope (Ra) and a scanning electron microscope (SEM). Thereafter, the groups were contaminated with a bacterial strain of P. intermedia ATCC 25611. The biofilms formed were quantified by counting the colony forming units (CFUs) and analyzed with scanning electron microscope (SEM) and confocal laser scanning microscope (CLSM). Data were analyzed by using a 2-way ANOVA and the Tukey test (ɑ = 0.05). Results showed that greater roughness was associated with GDB (p < 0.05). The same was also true for the ceramic material ZR (p < 0.05). There was a statistical significant difference in the CFU counts between the materials (p < 0.05) that revealed a greater amount of bacterial adhesion in the LC and ZR groups (p > 0.05). Thus, it was suggested that the surface roughness of the ceramic materials favored bacterial adhesion; and thus, finishing of ceramic surfaces with GDB should be avoided.

Utilization of the extract of Cedrus deodara (Roxb. ex D.Don) G. Don against the biofilm formation and the expression of virulence genes of cariogenic bacterium Streptococcus mutans

ETHNOPHARMACOLOGICAL RELEVANCE

Cedrus deodara (Roxb. ex D.Don) G. Don is applied as anti-inflammatory and anti-infection agents in folklore medicine.

AIM OF THE STUDY

The present study aimed to assess the antimicrobial activity of Cedrus deodara (Roxb. ex D.Don) G. Don extract (CDE) against Streptococcus mutans biofilm formation and its biocompatibility, as well as to identify its chemical components.

MATERIALS AND METHODS

Confocal laser scanning microscopy (CLSM), crystal violet staining, and CFU counting assay were applied to investigate the effect of CDE on S. mutans biofilm formation and extracellular polysaccharides (EPS) synthesis. The microstructure of S. mutans biofilms formed on glass coverslips and bovine enamel treated with CDE was observed by scanning electron microscopy (SEM). qRT-PCR was used to measure the expression of virulence genes gtfB, gtfC, and gtfD, and zymogram assay was performed to investigate the enzymatic activity of Gtfs. Moreover, HPLC-MS and NMR were applied to identify its chemical components. CCK-8 assay was also performed on human oral cells to evaluate its biocompatibility.

RESULTS

Under the treatment of CDE, S. mutans formed less biofilm on both coverslips and enamel surfaces and synthesized less EPS. Moreover, CDE downregulated the expression of gtf genes and inhibited the enzymatic activity of Gtfs. According to HPLC-MS and NMR results, molecular structures of six main compounds in CDE were identified. CDE also has a good biocompatibility.

CONCLUSIONS

CDE exhibits inhibitory activity against S. mutans and a good biocompatibility. It has the potential to be developed as anti-caries agents for clinical use.

Small noncoding RNA sRNA0426 is involved in regulating biofilm formation in Streptococcus mutans

Evidence suggests that small noncoding RNAs (sRNAs) are involved in the complex regulatory networks governing biofilm formation. Few studies have investigated the role of sRNAs in Streptococcus mutans (S. mutans). In the present study, the association between sRNA and biofilm formation in S. mutans was explored. sRNAs that are differentially expressed in the biofilm and planktonic states of this bacterium were identified by quantitative real‐time PCR (qRT‐PCR). Confocal laser scanning microscopy was used to investigate the characteristics of biofilm formation in a standard strain of S. mutans (UA159, ATCC 700610) and ten clinical strains. Bioinformatics analyses were employed to predict and examine potential sRNA regulatory pathways. The results showed that sRNA0426 has a strong positive relationship with dynamic biofilm formation. Moreover, sRNA0426 expression was positively correlated with exopolysaccharide (EPS) production. Bioinformatics analyses showed that sRNA0426 is involved in biofilm formation such as metabolic pathways, especially carbon metabolism. Five target mRNAs (GtfB, GtfC, GtfD, ComE, and CcpA) involved in the synthesis of EPS were selected for further evaluation; the expression levels of three of these mRNAs (GtfB, GtfC, and CcpA) were positively correlated with sRNA0426 expression levels, and the expression level of one (ComE) was negatively correlated. In conclusion, the results suggested that sRNA0426 may play an important and positive role in the biofilm formation of S. mutans and provide novel insight into the S. mutans biofilm regulatory network.

Effect of arginine on microorganisms involved in dental caries: a systematic literature review of in vitro studies

This systematic review aimed to discuss the effects of arginine on caries-related microorganisms in different in vitro biofilm models. The eligibility criteria were in vitro studies that evaluated the effect of arginine at different concentrations on caries-related microorganisms using biofilm models. Eighteen studies published between 2012 and 2019 were included. Different bacterial species were studied. Seventeen studies (94.4%) achieved a low risk of bias and only one showed a medium risk of bias. The studies showed that arginine is a promising approach for the ecological management of dental caries. The focus of this review was to evaluate the effects of arginine on microorganisms involved in the mechanism of dental caries.

Development of a multispecies periodontal biofilm model within a stirred bioreactor

The objective of this work was to develop a subgingival biofilm model using a stirred bioreactor. Discs of bovine teeth were adapted to a stirred bioreactor filled with a culture medium containing bacterial species associated with periodontal health or disease. After anaerobic incubation, the biofilms growing on the substratum surfaces were collected and analyzed. The mean number of Colony-forming Units (CFUs) varied, but with no difference between 3 and 7 days of biofilm formation (p > 0.05). Scanning Electron Microscopy (SEM) analysis showed a uniform biofilm layer covering the cement layer of the root surface containing bacteria with diverse morphology. In checkerboard DNA-DNA hybridization, bacterial species were identified in both biofilms. In conclusion, a subgingival biofilm model was developed using a stirred bioreactor, allowing the in vitro reproduction of complex microbial communities. This is an advanced model that may be useful to mimic complex clinical periodontal biofilms.

Xylitol and erythritol inhibit real-time biofilm formation of Streptococcus mutans

Background

Regular consumption of xylitol decreases the number of cariogenic streptococci in dental plaque. In vitro biofilm models to study the mechanism of xylitol action have been set-up, but the obtained results are contradictory. Biofilm growth is a dynamic process with time-specific characteristics that may remain undetected in conventional end-point biofilm tests. In this study we used an impedance spectroscopy instrument, xCELLigence Real Time Cell Analyzer (RTCA), that allows label-free, non-invasive real-time monitoring of biofilm formation, to explore effects of xylitol on biofilm formation by Streptococcus mutans. Based on the obtained information of biofilm dynamics, we assessed the number of viable bacteria, the polysaccharide content, and the expression levels of selected genes involved in glucan-mediated biofilm formation in different biofilm stages. Xylitol inhibition was compared with that of erythritol; another polyol suggested to have a positive impact on oral health.

Results

Our results showed that real-time monitoring provided new information of polyol-induced changes in S. mutans biofilm formation dynamics. The inhibitory effect of polyols was more pronounced in the early stages of biofilm formation but affected also the measured total amount of formed biofilm. Effects seen in the real-time biofilm assay were only partially explained by changes in CFU values and polysaccharide amounts in the biofilms. Both xylitol and erythritol inhibited real-time biofilm formation by all the nine tested S. mutans strains. Sensitivity of the strains to inhibition varied: some were more sensitive to xylitol and some to erythritol. Xylitol also modified the expression levels of gbpB, gtfB, gtfC and gtfD genes that are important in polysaccharide-mediated adherence of S. mutans.

Conclusion

The erythritol- and xylitol- induced inhibition of biofilm formation was only partly explained by decrease in the number of viable S. mutans cells or the amount of polysaccharides in the biofilm matrix, suggesting that in addition to reduced proliferation also the matrix composition and thereby the surface attachment quality of biofilm matrix may be altered by the polyols.

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.