Therapeutic Strategies Targeting Cariogenic Biofilm Microenvironment

Epigallocatechin gallate reduces the virulence of cariogenic Streptococcus mutans biofilm by affecting the synthesis of biofilm matrix components

INTRODUCTION

There have been reports on the effects of epigallocatechin gallate (EGCG) against Streptococcus mutans viability and acidogenesis. However, the effects of EGCG on the virulence of S. mutans biofilm development have yet to be fully investigated using validated cariogenic biofilm models.

OBJECTIVE

Thus, this study aimed to evaluate the effects of EGCG on S. mutans biofilm virulence using a validated cariogenic model and clinically relevant treatment regimens, twice a day for 1.5 min.

METHODS

Effects of EGCG on bacterial viability, polyssacharide synthesis and biofilm acidogenesis were evaluated. The morphology and 3D structure of the biofilms were evaluated by scanning electron (SEM) and confocal laser scanning microscopy, respectively.

RESULTS

No significant change in S. mutans viability or culture medium pH were observed when comparing EGCG-treated and NaCl-treated biofilms. EGCG significantly reduced the accumulation of soluble and insoluble polysaccharides, resulting in the formation of a biofilm with interspaced exopolysaccharide-microcolony complexes unevenly distributed on enamel. The SEM images of the biofilm treated with EGCG depict multilayers of cells arranged in short chains of microorganisms adhered to an unstructured matrix, which is not continuous and does not enmesh or protect the microorganisms entirely. Importantly, confocal images demonstrated that treatment with EGCG affected the 3D structure and organization of S. mutans biofilm, which presented a biofilm matrix more confined to the location of the microcolonies.

CONCLUSION

In conclusion, EGCG lowered the virulence of S. mutans matrix-rich biofilm by reducing the synthesis of biofilm matrix components, altering the biofilm matrix structure, organization, and distribution.

Effect of flavonoids from grape seed and cranberry extracts on the microbiological activity of Streptococcus mutans: a systematic review of in vitro studies

OBJECTIVE

To provide an overview of the available scientific evidence from in vitro studies regarding the effect induced by the flavonoids contained in grape seed extracts (GSE) and cranberry on the microbiological activity of Streptococcus mutans (S. mutans).

METHODS

This systematic review was performed following the parameters of the PRISMA statement (Preferred Reporting Items for Systematic Reviews and Meta-Analysis). Electronic and manual searches were conducted using PubMed, ScienceDirect, Web of Science, EBSCO, and Cochrane databases. Reference lists of selected articles were reviewed to identify relevant studies. The search was not limited by year and was conducted solely in English. Eligible studies comprised publications describing in vitro studies that evaluated the effect of flavonoids derived from GSE and cranberry extracts on the microbiological activity of S. mutans. Common variables were identified to consolidate the data. Authors of this review independently screened search results, extracted data, and assessed the risk of bias.

RESULTS

Of the 420 studies identified from the different databases, 22 publications were finally selected for review. The risk of bias was low in 13 articles and moderate in 9. The studies analyzed in this review revealed that cranberry extract has an inhibitory effect on the bacterial growth of S. mutans in ranges from 0.5 mg/mL to 25 mg/mL, and GSE exerts a similar effect from 0.5 mg/mL to 250 mg/mL. Additionally, the extracts or their fractions showed reduced biofilm formation capacity, decreased polymicrobial biofilm biomass, deregulation of glycosyltransferases (Gtf) B and C expression, and buffering of pH drop. In addition to adequate antioxidant activity related to polyphenol content.

CONCLUSIONS

The overall results showed that the extracts of cranberry and grape seed were effective in reducing the virulence factors of the oral pathogen. According to the data, proanthocyanidins are the active components in cranberry and grape seed that effectively resist S. mutans. They can inhibit the formation of insoluble polysaccharides in the extracellular matrix and prevent glycan-mediated adhesion, cohesion, and aggregation of the proteins in S. mutans. This suggests that these natural extracts could play an important role in the prevention of cariogenic bacterial colonization, as well as induce a decrease in their microbiological activity.

Biochemical properties of a Flavobacterium johnsoniae dextranase and its biotechnological potential for Streptococcus mutans biofilm degradation

Cariogenic biofilms have a matrix rich in exopolysaccharides (EPS), mutans and dextrans, that contribute to caries development. Although several physical and chemical treatments can be employed to remove oral biofilms, those are only partly efficient and use of biofilm-degrading enzymes represents an exciting opportunity to improve the performance of oral hygiene products. In the present study, a member of a glycosyl hydrolase family 66 from Flavobacterium johnsoniae (FjGH66) was heterologously expressed and biochemically characterized. The recombinant FjGH66 showed a hydrolytic activity against an early EPS-containing S. mutans biofilm, and, when associated with a α-(1,3)-glucosyl hydrolase (mutanase) from GH87 family, displayed outstanding performance, removing more than 80% of the plate-adhered biofilm. The mixture containing FjGH66 and Prevotella melaninogenica GH87 α-1,3-mutanase was added to a commercial mouthwash liquid to synergistically remove the biofilm. Dental floss and polyethylene disks coated with biofilm-degrading enzymes also degraded plate-adhered biofilm with a high efficiency. The results presented in this study might be valuable for future development of novel oral hygiene products.

Anti-caries Streptococcus spp.: A potential preventive tool for special needs patients

INTRODUCTION

Probiotics are living microorganisms that act on the host-microbiome interface to restore the microbiota's physiological homeostasis. Numerous probiotics have been marketed with inhibitory activity against Streptococcus mutans and consequently with a potential anti-caries effect, mainly of the genera Lactobacillus and Bifidobacterium, whose main disadvantage is their limited ability to settle in the oral cavity.

METHODS

This narrative review describes the main Streptococcus spp. with probiotic anti-Streptococcus mutans activity, whose substantivity is greater than that of Lactobacillus spp. and consequently with anti-caries potentiality. We performed a literature review in the PubMed, Science Direct and Google Scholar databases of articles published in English (without time restriction) related to caries and probiotics.

RESULTS

The potential identified anti-caries probiotics included Streptococcus spp. A12, Streptococcus oralis (AJ3), Streptococcus oligofermentans, Streptococcus salivarius (K12, M18, JH, LAB813, 24SMB), Streptococcus spp. with arginolytic activity (S. sanguinis, S. gordonii, S. ratti, S. parasanguinis, S. intermedius, S. australis, and S. cristatus), Streptococcus rattus (JH145), Streptococcus dentisani and Streptococcus downii.

CONCLUSIONS

The possibility of using these Streptococcus spp. as probiotics that inhibit the growth of dental plaque and the development of carious lesions represents a potential tool of particular interest for individuals with physical or intellectual disabilities that impede the routine and effective application of mechanical dental plaque removal techniques.

Platelet Membrane-Enclosed Bioorthogonal Catalysis for Combating Dental Caries

Platelets have shown promise as a means to combat bacterial infections, fostering the development of innovative therapeutic approaches. However, several challenges persist, including cargo loading issues, limited efficacy against biofilms, and concerns regarding the impact of payloads on the platelet carriers. Here, human platelet membrane vesicles (h-PMVs) encapsulating supramolecular metal catalysts (SMCs) as "nanofactories" to convert prodrugs into antimicrobial compounds within close proximity to bacteria are introduced. Having established the feasibility and effectiveness of the SMCs within h-PMVs, referred to as the PLT-reactor, to activate pro-antibiotic drugs (pro-ciprofloxacin and pro-moxifloxacin) using model organisms (Escherichia coli ATCC 25922 and Staphylococcus aureus ATCC 25923), the investigation is subsequently extended to oral biofilms, with a particular emphasis on Streptococcus mutans 3065. This "bind and kill" strategy demonstrates the potent antimicrobial specificity of the PLT-reactor through localized antibiotic production. h-PMVs play a pivotal role by enabling precise targeting of pathogenic biofilms on natural teeth while minimizing potential hemolytic effects. The finding indicates that platelet membrane-cloaked surfaces exhibit robust, multifaceted, and pathogen-specific binding affinity with excellent biocompatibility, making them a promising alternative to antibody-based therapies for infectious diseases.

Mechanism of Action of Streptococcus downii, a New Bacterial Species with Probiotic Potential

Streptococcus downii is a recently reported bacterial species of oral origin, with inhibitory capacity against Streptococcus mutans, Actinomyces naeslundii, Veillonella parvula and Aggregatibacter actinomycetemcomitans, which confers upon it the potential of being an oral probiotic. The aim of the present study was to identify the potential mechanisms by which S. downii exerts its inhibitory effect on S. mutans. To this end, the study assessed the consumption of glucose and proteins available in the culture medium, the modification of the pH, the production of short-chain fatty acids, the changes in the protein panel of the inhibition halo, the production of hydrogen peroxide and the effect of proteinase K. There were no differences in the glucose values or in the protein content of the medium, but there was a reduction in pH (with no effect on the growth of S. mutans). Significant increases were detected in the levels of lactic and formic acid (with no effect on the growth of S. mutans), as well as changes in the peptide panel (with no effect on the growth of S. mutans). The inhibitory effect was maintained in the presence of peroxidase but disappeared after adding proteinase K. Based on these results, it is suggested that the main mechanism of inhibition of S. downii against S. mutans is the production of bacteriocins.

Anticariogenic Activity of Celastrol and Its Enhancement of Streptococcal Antagonism in Multispecies Biofilm

Dental caries is a chronic disease resulting from dysbiosis in the oral microbiome. Antagonism of commensal Streptococcus sanguinis and Streptococcus gordonii against cariogenic Streptococcus mutans is pivotal to keep the microecological balance. However, concerns are growing on antimicrobial agents in anticaries therapy, for broad spectrum antimicrobials may have a profound impact on the oral microbial community, especially on commensals. Here, we report celastrol, extracted from Traditional Chinese Medicine's Tripterygium wilfordii (TW) plant, as a promising anticaries candidate. Our results revealed that celastrol showed antibacterial and antibiofilm activity against cariogenic bacteria S. mutans while exhibiting low cytotoxicity. By using a multispecies biofilm formed by S. mutans UA159, S. sanguinis SK36, and S. gordonii DL1, we observed that even at relatively low concentrations, celastrol reduced S. mutans proportion and thereby inhibited lactic acid production as well as water-insoluble glucan formation. We found that celastrol thwarted S. mutans outgrowth through the activation of pyruvate oxidase (SpxB) and H2O2-dependent antagonism between commensal oral streptococci and S. mutans. Our data reveal new anticaries properties of celastrol that enhance oral streptococcal antagonism, which thwarts S. mutans outgrowth, indicating its potential to maintain oral microbial balance for prospective anticaries therapy.

pH-activated antibiofilm strategies for controlling dental caries

Dental biofilms are highly assembled microbial communities surrounded by an extracellular matrix, which protects the resident microbes. The microbes, including commensal bacteria and opportunistic pathogens, coexist with each other to maintain relative balance under healthy conditions. However, under hostile conditions such as sugar intake and poor oral care, biofilms can generate excessive acids. Prolonged low pH in biofilm increases proportions of acidogenic and aciduric microbes, which breaks the ecological equilibrium and finally causes dental caries. Given the complexity of oral microenvironment, controlling the acidic biofilms using antimicrobials that are activated at low pH could be a desirable approach to control dental caries. Therefore, recent researches have focused on designing novel kinds of pH-activated strategies, including pH-responsive antimicrobial agents and pH-sensitive drug delivery systems. These agents exert antibacterial properties only under low pH conditions, so they are able to disrupt acidic biofilms without breaking the neutral microenvironment and biodiversity in the mouth. The mechanisms of low pH activation are mainly based on protonation and deprotonation reactions, acids labile linkages, and H⁺-triggered reactive oxygen species production. This review summarized pH-activated antibiofilm strategies to control dental caries, concentrating on their effect, mechanisms of action, and biocompatibility, as well as the limitation of current research and the prospects for future study.

Biofilm ecology associated with dental caries: Understanding of microbial interactions in oral communities leads to development of therapeutic strategies targeting cariogenic biofilms

A biofilm is a sessile community characterized by cells attached to the surface and organized into a complex structural arrangement. Dental caries is a biofilm-dependent oral disease caused by infection with cariogenic pathogens, such as Streptococcus mutans, and associated with frequent exposure to a sugar-rich diet and poor oral hygiene. The virulence of cariogenic biofilms is often associated with the spatial organization of S. mutans enmeshed with exopolysaccharides on tooth surfaces. However, in the oral cavity, S. mutans does not act alone, and several other microbes contribute to cariogenic biofilm formation. Microbial communities in cariogenic biofilms are spatially organized into complex structural arrangements of various microbes and extracellular matrices. The balance of microbiota diversity with reduced diversity and a high proportion of acidogenic-aciduric microbiota within the biofilm is closely related to the disease state. Understanding the characteristics of polymicrobial biofilms and the association of microbial interactions within the biofilm (e.g., symbiosis, cooperation, and competition) in terms of their potential role in the pathogenesis of oral disease would help develop new strategies for interventions in virulent biofilm formation.

Relation between caries experience and the consumption of sweetened drinks and processed food in children: A population-based study

OBJECTIVES

Diet can play a role in caries disease and the consumption of ultra-processed foods has increased over the years. The purpose was to propose predictive models on the relation between caries experience, diet, sex, and oral health aspects.

METHODS

This cross-sectional study included 5213 schoolchildren aged 2-11 years and a questionnaire based on WHO Oral Health Survey was applied to assess the intake of sugary foods, oral hygiene practices, access to health services and parents' perception; dmft/DMFT index, biofilm accumulation and orthodontic treatment need were assessed by 6 calibrated dentists.

RESULTS

The logistic model showed that female sex and presence of biofilm increased the chance of having early childhood caries; besides, this chance increased by 17% for each additional day of sweetened drink intake. In children aged 6-11 years, a negative binomial regression model showed that the absence of biofilm and frequency of toothbrushing were related to lower caries index, while male sex and the consumption of salty snacks and cake/cookies were related to higher dmft+DMFT index. Disagreement or weak agreement between caregivers' perception of the presence of dental caries and children's need for dental treatment was found.

CONCLUSION

Early childhood caries was dependent on the consumption of sweetened drinks and the presence of biofilm, while in older children the caries experience was predicted by the consumption of snacks, cakes and biscuits, biofilm accumulation and toothbrushing frequency, emphasizing the need of health education to encourage healthy eating habits and oral care with an approach to parents/caregivers to prevent dental caries development.

Targeting cariogenic pathogens and promoting competitiveness of commensal bacteria with a novel pH-responsive antimicrobial peptide

Novel ecological antimicrobial approaches to dental caries focus on inhibiting cariogenic pathogens while enhancing the growth of health-associated commensal communities or suppressing cariogenic virulence without affecting the diversity of oral microbiota, which emphasize the crucial role of establishing a healthy microbiome in caries prevention. Considering that the acidified cariogenic microenvironment leads to the dysbiosis of microecology and demineralization of enamel, exploiting the acidic pH as a bioresponsive trigger to help materials and medications target cariogenic pathogens is a promising strategy to develop novel anticaries approaches. In this study, a pH-responsive antimicrobial peptide, LH12, was designed utilizing the pH-sensitivity of histidine, which showed higher cationicity and stronger interactions with bacterial cytomembranes at acidic pH. Streptococcus mutans was used as the in vitro caries model to evaluate the inhibitory effects of LH12 on the cariogenic properties, such as biofilm formation, biofilm morphology, acidurance, acidogenicity, and exopolysaccharides synthesis. The dual-species model of Streptococcus mutans and Streptococcus gordonii was established in vitro to evaluate the regulation effects of LH12 on the mixed species microbial community containing both cariogenic bacteria and commensal bacteria. LH12 suppressed the cariogenic properties and regulated the bacterial composition to a healthier condition through a dual-functional mechanism. Firstly, LH12-targeted cariogenic pathogens in response to the acidified microenvironment and suppressed the cariogenic virulence by inhibiting the expression of multiple virulence genes and two-component signal transduction systems. Additionally, LH12 elevated H₂O₂ production of the commensal bacteria and subsequently improved the ecological competitiveness of the commensals. The dual-functional mechanism made LH12 a potential bioresponsive approach to caries management.

Farnesol delivery via polymeric nanoparticle carriers inhibits cariogenic cross-kingdom biofilms and prevents enamel demineralization

Streptococcus mutans and Candida albicans are frequently detected together in the plaque from patients with early childhood caries (ECC) and synergistically interact to form a cariogenic cross-kingdom biofilm. However, this biofilm is difficult to control. Thus, to achieve maximal efficacy within the complex biofilm microenvironment, nanoparticle carriers have shown increased interest in treating oral biofilms in recent years. Here, we assessed the anti-biofilm efficacy of farnesol (Far), a hydrophobic antibacterial drug and repressor of Candida filamentous forms, against cross-kingdom biofilms employing drug delivery via polymeric nanoparticle carriers (NPCs). We also evaluated the effect of the strategy on teeth enamel demineralization. The farnesol-loaded NPCs (NPC+Far) resulted in a 2-log CFU/mL reduction of S. mutans and C. albicans (hydroxyapatite disc biofilm model). High-resolution confocal images further confirmed a significant reduction in exopolysaccharides, smaller microcolonies of S. mutans, and no hyphal form of C. albicans after treatment with NPC+Far on human tooth enamel (HT) slabs, altering the biofilm 3D structure. Furthermore, NPC+Far treatment was highly effective in preventing enamel demineralization on HT, reducing lesion depth (79% reduction) and mineral loss (85% reduction) versus vehicle PBS-treated HT, while NPC or Far alone had no differences with the PBS. The drug delivery via polymeric NPCs has the potential for targeting bacterial-fungal biofilms associated with a prevalent and costly pediatric oral disease, such as ECC.

Cymbopogon citratus Essential Oil Increases the Effect of Digluconate Chlorhexidine on Microcosm Biofilms

The aim of this study was to evaluate the effect of the Cymbopogon citratus essential oil and its association with chlorhexidine on cariogenic microcosm biofilm composition and acidogenicity. Minimum inhibitory and bactericide concentrations from the essential oil and chlorhexidine were determined by broth microdilution assay. Microcosms (polymicrobial) biofilms were produced on glass coverslips, using inoculum from human saliva in McBain culture medium (0.5% sucrose exposure for 6 h/day) for 3 days in 24-well plates. The biofilms were treated twice a day and their composition was evaluated by microorganism quantification. The acidogenicity was evaluated by measuring the pH of the spent culture medium in contact with the biofilm. Overall, the association of C. citratus and chlorhexidine reduced total bacterial counts and aciduric bacteria (maximum reduction of 3.55 log UFC/mL) in microcosm biofilms. This group also presented the lowest acidogenicity even when exposed to sucrose-containing medium. C. citratus essential oil increases the effect of digluconate chlorhexidine on microcosm biofilms. Based on these findings, this study can contribute to the development of new formulations that might allow for the use of mouthwashes for a shorter period, which may reduce undesirable effects and increase patient compliance to the treatment.

Lactobacillus cell envelope-coated nanoparticles for antibiotic delivery against cariogenic biofilm and dental caries

Background

Due to their prevalence, dental caries ranks first among all diseases endangering human health. Therefore, the prevention of caries is of great significance, as caries have become a serious public health problem worldwide. Currently, using nanoscale drug delivery systems to prevent caries has received increased attention. However, the preventive efficacy of these systems is substantially limited due to the unique physiological structure of cariogenic biofilms. Thus, novel strategies aimed at combating cariogenic biofilms to improve preventive efficiency against caries are meaningful and very necessary. Herein, inspired by cell membrane coating technology and Lactobacillus strains, we coated triclosan (TCS)-loaded poly(lactic-co-glycolic acid) (PLGA) nanoparticles (TCS@PLGA-NPs) with an envelope of Lactobacillus (LA/TCS@PLGA-NPs) and investigated their potential as a nanoparticle delivery system against cariogenic biofilms and dental caries.

Results

LA/TCS@PLGA-NPs were successfully prepared with favorable properties, including a coated envelope, controllable size, negative charge, sustained drug-release kinetics and so on. The LA/TCS@PLGA-NPs inherited native properties from the source cell surface, thus the LA/TCS@PLGA-NPs adhered to S. mutans, integrated into the S. mutans biofilm, and interfered with the biofilm formation of S. mutans. The nanoparticles significantly inhibited the activity, biomass and virulence gene expression of S. mutans biofilms in vitro. Additionally, LA/TCS@PLGA-NPs exhibited a long-lasting inhibitory effect on the progression of caries in vivo. The safety performance of the nanoparticles is also favorable.

Conclusions

Our findings reveal that the antibiofilm effect of LA/TCS@PLGA-NPs relies not only on the inheritance of native properties from the Lactobacillus cell surface but also on the inhibitory effect on the activity, biomass and virulence of S. mutans biofilms. Thus, these nanoparticles could be considered feasible candidates for a new class of effective drug delivery systems for the prevention of caries. Furthermore, this work provides new insights into cell membrane coating technology and presents a novel strategy to combat bacterial biofilms and associated infections.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-022-01563-x.

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

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

Dental Materials for Oral Microbiota Dysbiosis: An Update

The balance or dysbiosis of the microbial community is a major factor in maintaining human health or causing disease. The unique microenvironment of the oral cavity provides optimal conditions for colonization and proliferation of microbiota, regulated through complex biological signaling systems and interactions with the host. Once the oral microbiota is out of balance, microorganisms produce virulence factors and metabolites, which will cause dental caries, periodontal disease, etc. Microbial metabolism and host immune response change the local microenvironment in turn and further promote the excessive proliferation of dominant microbes in dysbiosis. As the product of interdisciplinary development of materials science, stomatology, and biomedical engineering, oral biomaterials are playing an increasingly important role in regulating the balance of the oral microbiome and treating oral diseases. In this perspective, we discuss the mechanisms underlying the pathogenesis of oral microbiota dysbiosis and introduce emerging materials focusing on oral microbiota dysbiosis in recent years, including inorganic materials, organic materials, and some biomolecules. In addition, the limitations of the current study and possible research trends are also summarized. It is hoped that this review can provide reference and enlightenment for subsequent research on effective treatment strategies for diseases related to oral microbiota dysbiosis.

Real-time monitoring of the pH microenvironment at the interface of multispecies biofilm and dental composites

Bacterial-mediated local pH change plays an important role in altering the integrity of resin dental composite materials in a dynamic environment such as the oral cavity. To address this, we developed a 300-μm-diameter, flexible, solid-state potentiometric pH microsensor capable of detecting and quantifying the local pH microenvironment at the interface of multispecies biofilm and dental resin in real time over 10 days. We used fluorinated poly(3,4-ethylenedioxythiophene) as the back contact in our newly developed pH sensor, along with a PVC-based ion-selective membrane and PTFE-AF coating. The high temporal resolution pH data demonstrated pH changes from 7 to 6 and 7 to 5.8 for the first 2 days and then fluctuated between 6.5 to 6 and 6 to 5.5 for the remaining 8 days with the resin composite or glass slide substrate respectively. We could observe the fluctuations in pH mediated by lactic acid production within the biofilm and the re-establishment of pH back to 7. However, acid production started to overwhelm buffering capacity with the continuous feed of sucrose cycles and reduced the local pH nearer to 5.5. No such changes or fluctuations were observed above the biofilm, as the pH remained at 7.0 ± 0.2 for 10 days. The localized real-time monitoring of the pH within the biofilm showed that the pH shift underneath the biofilm could lead to damage to the underlying material and their interface but cannot be sensed external to the biofilm.

Nicotinamide could reduce growth and cariogenic virulence of Streptococcus mutans

Dental caries is among the most prevalent chronic oral infectious diseases. Streptococcus mutans, a major cariogenic bacterial species, possesses several cariogenicity-associated characteristics, including exopolysaccharides (EPS) synthesis, biofilm formation, acidogenicity, and aciduricity. Nicotinamide (NAM), a form of vitamin B3, is a non-toxic, orally available, and inexpensive compound. The present study investigated the inhibitory effects of NAM on the cariogenic virulence factors of S. mutans in vitro and in vivo. NAM inhibited the growth of S. mutans UA159 and the clinical isolates. In addition, there was a decrease in the acid production and acid tolerance ability, as well as biofilm formation and EPS production of S. mutans after NAM treatment. Global gene expression profiling showed that 128 and 58 genes were significantly downregulated and upregulated, respectively, in NAM-treated S. mutans strains. The differentially expressed genes were mainly associated with carbohydrate transport and metabolism, glycolysis, acid tolerance. Moreover, in a rat caries model, NAM significantly reduced the incidence and severity of smooth and sulcal-surface caries in vivo. NAM exhibited good antimicrobial properties against S. mutans, indicating its potential value for antibiofilm and anti-caries applications.

The Influence of Preventive Regimens Containing Different Toothpastes on Caries Risk of High-Risk Patients: A Randomized Clinical Trial

BACKGROUND: The main objective of conservative dentistry is maintaining the health of the dentition and restored teeth free from dental caries. The prevention of dental caries can be achieved by personal prevention programs at home, dental health care professional, and public health application programs. Based on knowledge related to the etiology and pathogenesis of dental caries, this provides a chance for application of effective prevention program for the prevention of dental caries. AIM: This study aimed to evaluate the effect of different preventive regimens using different toothpastes on caries risk using cariogram and decayed, missing, and filled (DMF) scores of high caries risk patients. MATERIALS AND METHODS: The study was conducted on 66 participants with high caries risk. Participants were divided into three groups, 22 participant each. According to the test regimen, where (A1) participants were exposed to a regimen including dual zinc plus arginine-based toothpaste (Colgate total), (A2) participants were exposed to a regimen including zinc-based toothpaste (Crest complete), and (A3) control group was participants that were exposed to a regimen including fluoride-based toothpaste (Signal). The study was carried for 1 year, assessment of cariogram and DMF scores was done in four intervals: T0: baseline, T3: after 3 months, T6: after 6 months, and T12: after 12 months. RESULTS: According to cariogram, there was a statistically significant difference between Groups A1, A2, and A3, where p < 0.001. However, DMF scores of all groups showed no statistically significant difference between the three groups. CONCLUSIONS: Dual zinc plus arginine-based toothpaste is a superior caries preventive regimen in high caries risk patients. CLINICAL SIGNIFICANCE: The benefits of preventive regimen to the practitioner will be providing a non-invasive, and cost-efficient method to prevent dental caries. Benefits to the patient will be an improvement of oral hygiene, prevention of dental caries, and maintain healthy dental supporting structures.

[Inhibitory Effects of Nicotinamide on Streptococcus mutans Growth and Biofilm Formation]

Objective

To explore the effects of nicotinamide (NAM) on the growth, biofilm formation and exopolysaccharides (EPS) production of Streptococcus mutans.

Methods

The minimum inhibitory concentration (MIC) of NAM on S. mutanswas determined by the planktonic bacterial susceptibility assay. The NAM mass concentrations were set as 1/2 MIC, 1/4 MIC and 1/8 MIC for hree separate treatment groups. Culture medium without NAM was used in the negative control group and culture medium containing 0.1 mg/mL NaF was used for the positive control group (except for the scanning electron microscopy). The growth curves of S. mutans under different NAM concentrations were drawn. Crystal violet assay and anthrone-sulfuric acid method were used to explore the effects of NAM on S. mutans biofilm formation and water-insoluble EPS production, respectively. The morphology and structure of S. mutansplanktons and biofilms after NAM treatment were observed by scanning electron microscopy.

Results

The MIC of NAM on S. mutans was 32 μg/μL. After 16 μg/μL (1/2 MIC), 8 μg/μL (1/4 MIC) and 4 μg/μL (1/8 MIC) NAM treatments, S. mutans growth and biofilm formation were inhibited, with the 16 μg/μL NAM group displaying the most significant inhibitory effects. The synthesis of EPS decreased significantly in the 16 μg/μL and 8 μg/μL NAM groups in comparison with that of the negative control group (P<0.05). Under scanning electron microscope, the cell length of S. mutans was shortened, the cell width was extended, and the length/width ratio was decreased, showing significant difference when comparing the 16 μg/μL and 8 μg/μL NAM groups with the negative control group (P<0.05).

Conclusion

Under the influence of NAM at certain concenrations, the growth, biofilm formation, and EPS synthesis of S. mutanswere inhibited.

Manganese oxide nanomaterials for bacterial infection detection and therapy

Bacterial infection has received substantial attention and poses a serious threat to human health. Although antibiotics can effectively fight against bacterial infection, the occurrence of antibiotic resistance has become increasingly serious in recent years, which tremendously hinders its clinical application. Consequently, it is urgent to explore novel strategies to achieve efficacious treatment of bacterial diagnosis and detection. Manganese dioxide (MnO₂) nanomaterial has been extensively reported in tumor therapy. Nevertheless, there are few antibacterial reviews of MnO₂. Herein, we will discuss the applications of MnO₂ in the detection and treatment of bacterial infection, including photodynamic therapy, immunotherapy, improvement of hypoxia, dual-modal combination therapy, reactive oxygen species scavenging, magnetic resonance imaging, optical application of acoustic imaging, and so forth. This review is expected to provide meaningful guidance on further research of MnO₂ nanomaterial for antibacterial applications.

The vicK gene of Streptococcus mutans mediates its cariogenicity via exopolysaccharides metabolism

Streptococcus mutans (S. mutans) is generally regarded as a major contributor to dental caries because of its ability to synthesize extracellular polysaccharides (EPS) that aid in the formation of plaque biofilm. The VicRKX system of S. mutans plays an important role in biofilm formation. The aim of this study was to investigate the effects of vicK gene on specific characteristics of EPS in S. mutans biofilm. We constructed single-species biofilms formed by different mutants of vicK gene. Production and distribution of EPS were detected through atomic force microscopy, scanning electron microscopy and confocal laser scanning microscopy. Microcosmic structures of EPS were analyzed by gel permeation chromatography and gas chromatography-mass spectrometry. Cariogenicity of the vicK mutant was assessed in a specific pathogen-free rat model. Transcriptional levels of cariogenicity-associated genes were confirmed by quantitative real-time polymerase chain reaction. The results showed that deletion of vicK gene suppressed biofilm formation as well as EPS production, and EPS were synthesized mostly around the cells. Molecular weight and monosaccharide components underwent evident alterations. Biofilms formed in vivo were sparse and contributed a decreased degree of caries. Moreover, expressional levels of genes related to EPS synthesis were down-regulated, except for gtfB. Our report demonstrates that vicK gene enhances biofilm formation and subsequent caries development. And this may due to its regulations on EPS metabolism, like synthesis or microcosmic features of EPS. This study suggests that vicK gene and EPS can be considered as promising targets to modulate dental caries.

Bioresponsive nanotherapy for preventing dental caries by inhibiting multispecies cariogenic biofilms

Early childhood caries (ECC) is a public healthcare concern that greatly reduces the quality of life of young children. As a leading factor of ECC, cariogenic biofilms are composed of acidogenic/aciduric pathogens and extracellular polysaccharides (EPSs), creating an acidic and protected microenvironment. Antimicrobial photodynamic therapy (aPDT) is a noninvasive, painless, and efficient therapeutic approach that is suitable for treating ECC. However, due to the hyperfine structure of cariogenic biofilms, most photosensitizers (PSs) could not access and penetrate deeply in biofilms, which dramatically hamper their efficiency in the clinic. Herein, bioresponsive nanoparticle loaded with chlorin e6 (MPP-Ce6) is developed, which largely increases the penetration depth (by over 75%) and retention (by over 100%) of PS in the biofilm compared with free Ce6. Furthermore, MPP-Ce6-mediated aPDT not only kills the bacteria in preformed biofilms but also inhibits multispecies biofilm formation. A rampant caries model is established to mimic ECC in vivo, where the population of cariogenic bacteria is decreased to 10% after MPP-Ce6-mediated aPDT. Importantly, the number and severity of carious lesions are efficiently reduced via Keyes’ scoring and micro-CT analysis. This simple but effective strategy can serve as a promising approach for daily oral hygiene in preventing ECC.

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A pH-responsive nano-system is developed for biofilm-targeted drug delivery.

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The nano-system could overcome biological barriers and penetrate deeply in biofilms.

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This nano-system facilitates aPDT to kill bacteria in deep cariogenic biofilm.

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This strategy prevents the progression of early childhood caries in a rat model.

Potassium iodide enhances inactivation of Streptococcus mutans biofilm in antimicrobial photodynamic therapy with red laser

OBJECTIVE

To evaluate the effect of potassium iodide (KI) addition on antimicrobial photodynamic therapy (aPDT) mediated by red laser (λ = 660 nm) and methylene blue in Streptococcus mutans biofilm model.

METHODS

S. mutans biofilms were cultured in 96-well plates containing BHI broth with 1% sucrose for 18 h, 10% CO₂ and 37°C and divided in groups (n = 3, in triplicate): C (NaCl 0.9%); CX (0.2% chlorhexidine); P (photosensitizer); KI (10, 25 and 50 mM); PKI (10, 25 and 50 mM); L (L 1: : 100 J/cm², 9 J; L2: 200 J/cm², 18 J); PL (photosensitizer + L1 or L2); KIL (KI at 10, 25 and 50 mM + L1 or L2); and PKIL (photosensitizer + 10, 25 and 50 mM KI + L1 or L2). Biofilms were submitted to three pre-irradiation (PI) times (5, 10, and 15 min). After the treatments, microbial counting's reduction was analyzed by Kruskal-Wallis and post-hoc Dunn's tests, respectively, and the interaction between light parameters and the PI times by two-way ANOVA (p < 0.05).

RESULTS

The S. mutans viability significantly reduced in all aPDT groups, in the presence or absence of KI (p < 0.05). For all PI times, PKIL groups (10, 25, and 50 mM) significantly differed from PL groups (p < 0.05) with a reduction of 9.0 logs reached at 50 mM of KI with 15 min of PI, irradiated at 18 J. We found no significant interaction between PI time and irradiation (p > 0.05).

CONCLUSION

Addition KI to TFDA mediated by methylene blue and red laser promoted an additional effect in reducing the microbial viability of S. mutans biofilm.

Stimuli-Responsive Nanoplatform-Assisted Photodynamic Therapy Against Bacterial Infections

Bacterial infections are common diseases causing tremendous deaths in clinical settings. It has been a big challenge to human beings because of the antibiotics abuse and the newly emerging microbes. Photodynamic therapy (PDT) is a reactive oxygen species-based therapeutic technique through light-activated photosensitizer (PS). Recent studies have highlighted the potential of PDT as an alternative method of antibacterial treatment for its broad applicability and high efficiency. However, there are some shortcomings due to the low selectivity and specificity of PS. Growing evidence has shown that drug delivery nanoplatforms have unique advantages in enhancing therapeutic efficacy of drugs. Particularly, stimuli-responsive nanoplatforms, as a promising delivery system, provide great opportunities for the effective delivery of PS. In the present mini-review, we briefly introduced the unique microenvironment in bacterial infection tissues and the application of PDT on bacterial infections. Then we review the stimuli-responsive nanoplatforms (including pH-, enzymes-, redox-, magnetic-, and electric-) used in PDT against bacterial infections. Lastly, some perspectives have also been proposed to further promote the future developments of antibacterial PDT.

Bacterial adhesion to collagens: implications for biofilm formation and disease progression in the oral cavity

Collagen is the most abundant structural protein in the body and the main component of the extracellular matrix of most tissues, including dentine and periodontal tissues. Despite the well-characterized role of collagen and specifically type-I collagen, as a ligand for host cells, its role as a substrate for bacterial adhesion and biofilm formation is less explored. Therefore, the purpose of this review is to discuss recent findings regarding the adhesion of oral bacteria to collagen surfaces and its role in the progression and severity of oral and systemic diseases. Initial oral colonizers such as streptococci have evolved collagen-binding proteins (cbp) that are important for the colonization of dentine and periodontal tissues. Also, periodontal pathogens such as Porphyromonas gingivalis and Tannerella forsythia utilise cbps for tissue sensing and subsequent invasion. The implications of bacteria-collagen coupling in the context of collagen biomaterials and regenerative dentistry approaches are also addressed. Furthermore, the importance of interdisciplinary techniques such as atomic force microscopy for the nanocharacterization of bacteria-collagen interactions is also considered. Overall, understanding the process of oral bacterial adhesion onto collagen is important for developing future therapeutic approaches against oral and systemic diseases, by modulating the early stages of biofilm formation.

A novel anticaries agent, honokiol-loaded poly(amido amine) dendrimer, for simultaneous long-term antibacterial treatment and remineralization of demineralized enamel

OBJECTIVE

Existing agents to induce enamel self-repair and inhibit the progression of dental caries in the early stage have been proven to be inadequate and far from satisfactory. In this study, a honokiol-loaded poly(amido amine) (PAMAM) dendrimer (PAMH) was constructed to combat early caries lesions in enamel.

METHODS

PAMH was prepared via a codissolution method. Computational simulation analysis was used to explore the mechanism of honokiol release. The cytotoxicity of PAMH was tested. The antibacterial effects of PAMH were tested by planktonic growth assays and biofilm formation inhibition assays. The remineralization effect of PAMH was examined via transverse microradiography and scanning electron microscopy after a pH cycling model. The in vivo anti-caries effect of PAMH was carried out in a rat model.

RESULTS

Honokiol released from PAMH was slower but more durable in a cariogenic pH environment than in a neutral pH environment, which could be explained through the computational simulation analysis results. Under electrostatic action, P3 beads with the same charge repelled each other and extended outwards, resulting in the rapid expansion of the PAMAM dendrimer and accelerating the release of the drug. At a low pH of 5.5, the protonated P3 beads were not charged and the protonated P1 beads were positively charged. However, the electrostatic repulsive interaction between protonated P1 beads was restricted by the P3 beads in the outermost layer of the PAMAM dendrimer, so the swelling rate was relatively slow, resulting in the slow release of drug molecules in the acidic environment. The cytotoxicity demonstration and the biocompatibility experiment in animal study showed that PAMH is biologically safe. PAMH showed excellent enamel remineralizing ability after pH cycling and showed a long-term antibacterial effect in vitro. Meanwhile, PAMH showed long-term anticaries efficacy in vivo.

SIGNIFICANCE

Our findings indicated that PAMH had great potential to combat early caries lesions in enamel for future clinical application.

Cariogenic Biofilm: Pathology-Related Phenotypes and Targeted Therapy

The initiation and development of cariogenic (that is, caries-related) biofilms are the result of the disruption of homeostasis in the oral microenvironment. There is a daily accumulation of dental biofilm on the surface of teeth and its matrix of extracellular polymers supports the host in its defense against invading microbes, thus helping to achieve oral microbial homeostasis. However, the homeostasis can be broken down under certain circumstances such as during long-term exposure to a low pH environment which results in the dominance of acidogenic and acid-tolerating species in the dental biofilm and, thus, triggers the shift of harmless biofilm to an acidic one. This work aims to explore microbial diversity and the quorum sensing of dental biofilm and their important contributions to oral health and disease. The complex and multispecies ecosystems of the cariogenic biofilm pose significant challenges for the modulation of the oral microenvironment. Promising treatment strategies are those that target cariogenic niches with high specificity without disrupting the balance of the surrounding oral microbiota. Here, we summarized the recent advances in modulating cariogenic biofilm and/or controlling its pathogenic traits.

Isolation and Characterization of Streptococcus mutans Phage as a Possible Treatment Agent for Caries

Streptococcus mutans is a key bacterium in dental caries, one of the most prevalent chronic infectious diseases. Conventional treatment fails to specifically target the pathogenic bacteria, while tending to eradicate commensal bacteria. Thus, caries remains one of the most common and challenging diseases. Phage therapy, which involves the use of bacterial viruses as anti-bacterial agents, has been gaining interest worldwide. Nevertheless, to date, only a few phages have been isolated against S. mutans. In this study, we describe the isolation and characterization of a new S. mutans phage, termed SMHBZ8, from hundreds of human saliva samples that were collected, filtered, and screened. The SMHBZ8 genome was sequenced and analyzed, visualized by TEM, and its antibacterial properties were evaluated in various states. In addition, we tested the lytic efficacy of SMHBZ8 against S. mutans in a human cariogenic dentin model. The isolation and characterization of SMHBZ8 may be the first step towards developing a potential phage therapy for dental caries.

Single DNase or Proteinase Treatment Induces Change in Composition and Structural Integrity of Multispecies Oral Biofilms

Biofilm virulence is mainly based on its bacterial cell surrounding biofilm matrix, which contains a scaffold of exopolysaccharides, carbohydrates, proteins, lipids, and nucleic acids. Targeting these nucleid acids or proteins could enable an efficient biofilm control. Therefore, the study aimed to test the effect of deoxyribonuclease I (DNase I) and proteinase K on oral biofilms. Six-species biofilms (Streptococcus mutans, Streptococcus oralis, Actinomyces oris, Fusobacterium nucleatum, Veillonella dispar, and Candida albicans) were exposed to DNase I (0.001 mg/mL, 0.002 mg/mL) or proteinase K (0.05 mg/mL, 0.1 mg/mL) for 1 h during biofilm formation. After 64 h, biofilms were harvested, quantified by culture analysis and visualized by image analysis using CLSM (confocal laser scanning microscopy). Statistical analysis was performed by ANOVA, followed by the Tukey test at a 5% significance level. The biofilm treatment with proteinase K induced a significant increase of Logs₁₀ counts in S. mutans and a decrease in C. albicans, while biofilm thickness was reduced from 28.5 μm (control) to 9.07 μm (0.05 mg/mL) and 7.4 μm (0.1 mg/mL). Treatment with DNase I had no effect on the total bacterial growth within the biofilm. Targeting proteins of biofilms by proteinase K are promising adjunctive tool for biofilm control.

Diagnosis of Biofilm-Associated Peri-Implant Disease Using a Fluorescence-Based Approach

Dental implants have become a routine component of daily dental practice and the demand for dental implants is expected to increase significantly in the future. Despite the high success rates of dental implants, failures do occur, resulting in discomfort, rampant destruction of the oral health, or painful and costly surgical replacement of a failed implant. Peri-implant diseases are inflammatory conditions affecting the soft/hard tissues surrounding a functional dental implant. Plenty of experimental evidence indicates that the accumulation of dental plaque at the soft tissue-implant interface and the subsequent local inflammatory response seems to be key in the pathogenesis of the peri-implant mucositis. Such peri-implant-soft tissue interface is less effective than natural teeth in resisting bacterial invasion, enhancing vulnerability to subsequent peri-implant disease. Furthermore, in certain individuals, it will progress to peri-implantitis, resulting in alveolar bone loss and implant failure. Although early diagnosis and accurate identification of risk factors are extremely important to effectively prevent peri-implant diseases, current systematic reviews revealed that a uniform classification and diagnostic methodology for peri-implantitis are lacking. Recent progress on fluorescence-based technology enabled rapid diagnosis of the disease and effective removal of plaques. Here, we briefly review biofilm-associated peri-implant diseases and propose a fluorescence-based approach for more accurate and objective diagnoses. A fluorescence-based diagnosis tool through headlights combined with special-filtered dental loupes may serve as a hands-free solution for both precise diagnosis and effective removal of plaque-biofilms.

Antibiofilm effects of Thymus vulgaris and Hyptis spicigera essential oils on cariogenic bacteria

Aim: The inhibitory and antibiofilm effects of Thymus vulgaris (EOTv) and Hyptis spicigera essential oils (EOHs) on cariogenic microorganisms were evaluated. Materials & methods: The chemical characterization of EOTv was performed by gas chromatography/mass spectrometry. Streptococcus mutans, Streptococcus gordonii, Streptococcus sanguinis, Streptococcus mitis, Streptococcus sobrinus, Lactobacillus acidophilus and Actinomyces naeslundii were used for agar diffusion assays and determination of minimal inhibitory and minimal bactericide concentrations. In addition, 20 streptococci and lactobacilli clinical isolates were also tested. The effects of essential oil on microbial initial biofilm formation and on preformed microcosm biofilm formed from human saliva were studied. Results & conclusion: Both essential oils had inhibitory effects on the cariogenic species and reduced the bacterial adherence to dental enamel. Essential oils were able to disrupt preformed microcosm biofilms. Thymus vulgaris and Hyptis spicigera essential oils have potential to be used in the development of formulations to the control of cariogenic biofilms.

The pH-Responsive Property of Antimicrobial Peptide GH12 Enhances Its Anticaries Effects at Acidic pH

Dental caries is closely related to the acidification of the biofilms on the tooth surface, in which cariogenic bacteria bring about a dramatic pH decrease and disrupt remineralisation equilibrium upon the fermentation of dietary sugars. Thus, approaches targeting the acidified niches with enhanced anticaries activities at acidic pH are highly desirable. In our previous study, a cationic amphipathic α-helical antimicrobial peptide GH12 (Gly-Leu-Leu-Trp-His-Leu-Leu-His-His-Leu-Leu-His-NH2) was designed with good stability, low cytotoxicity, and excellent antibacterial effects. Considering its potent antibacterial activity against the acidogenic bacteria and its histidine-rich sequence, it was speculated that GH12 might show enhanced antimicrobial effects at an acidic pH. In this study, the pH-responsive property of GH12 was determined to evaluate its potential as a smart acid-activated anticaries agent. GH12 possessed much lower minimal inhibitory concentrations and minimal bactericidal concentrations against various kinds of bacteria at pH 5.5 than at pH 7.2. Employing Streptococcus mutans, the principal caries pathogen, as the model system, it was found that GH12 showed much stronger bactericidal effects on both planktonic S. mutans and S. mutans embedded in the biofilm at pH 5.5. In addition, short-term treatment with GH12 showed much more effective inhibitory effects on water-insoluble exopolysaccharides synthesis and lactic acid production of the preformed S. mutans biofilm at pH 5.5. As for the mechanism exploration, it was found that the net positive charge of GH12 increased and the tryptophan fluorescence intensity heightened with the peak shifting towards the short wavelength at pH 5.5, which demonstrated that GH12 could be more easily attracted to the anionic microbial cell membranes and that GH12 showed stronger interactions with the lipid membranes. In conclusion, acidic pH enhanced the antibacterial and antibiofilm activities of GH12, and GH12 is a potential smart anticaries agent targeting the cariogenic acidic microenvironment.

Antimicrobial Peptide GH12 Prevents Dental Caries by Regulating Dental Plaque Microbiota

Due to the complex microecology and microenvironment of dental plaque, novel caries prevention strategies require modulating the microbial communities ecologically and reducing the cariogenic properties effectively. Antimicrobial peptide GH12 reduced the lactic acid production and exopolysaccharide (EPS) synthesis of a Streptococcus mutans biofilm and a three-species biofilm in vitro in previous studies. However, the anticaries effects and microecological effects of GH12 remained to be investigated in a complex biofilm model in vitro and an animal caries model in vivo In the present study, GH12 at 64 mg/liter showed the most effective inhibition of lactic acid production, EPS synthesis, pH decline, and biofilm integrity of human dental plaque-derived multispecies biofilms in vitro, and GH12 at 64 mg/liter was therefore chosen for use in subsequent in vitro and in vivo assays. When treated with 64-mg/liter GH12, the dental plaque-derived multispecies biofilms sampled from healthy volunteers maintained its microbial diversity and showed a microbial community structure similar to that of the control group. In the rat caries model with a caries-promoting diet, 64-mg/liter GH12 regulated the microbiota of dental plaque, in which the abundance of caries-associated bacteria was decreased and the abundance of commensal bacteria was increased. In addition, 64-mg/liter GH12 significantly reduced the caries scores of sulcal and smooth surface caries in all locations. In conclusion, GH12 inhibited the cariogenic properties of dental plaque without perturbing the dental plaque microbiota of healthy individuals and GH12 regulated the dysbiotic microbial ecology and arrested caries development under cariogenic conditions.IMPORTANCE The anticaries effects and microecological regulation effects of the antimicrobial peptide GH12 were evaluated systematically in vitro and in vivo GH12 inhibited the cariogenic virulence of dental plaque without overintervening in the microbial ecology of healthy individuals in vitro GH12 regulated the microbial ecology of dental plaque to a certain extent in vivo under cariogenic conditions, increased the proportion of commensal bacteria, and decreased the abundance of caries-associated bacteria. GH12 significantly suppressed the incidence and severity of dental caries in vivo This study thus describes an alternative antimicrobial therapy for dental caries.

Carbon source utilization patterns in dental plaque and microbial responses to sucrose, lactose, and phenylalanine consumption in severe early childhood caries

Background

Severe early childhood caries (S-ECC) is mainly caused by the interaction of microbiota and environmental factors. However, the metabolic profiles of S-ECC microbial communities and the community-level microbial responses to carbohydrates and amino acids are poorly understood.

Methods

We collected supragingival plaques from 15 caries-free (CF) and 14 S-ECC children. Cultivation on Biolog AN microplates together with next-generation sequencing was used to analyze sole carbon source utilization patterns and microbial responses to sucrose, lactose and phenylalanine.

Results

S-ECC plaques had greater overall metabolic activity than those of CF ones. Comparing with CF, S-ECC plaques utilized more sucrose and lactose but less phenylalanine and then had greater response to carbohydrates. A remarkable increase of non-mutans Streptococci was observed in sucrose and lactose consumption. Lactose led to less differently distributed taxa than sucrose in both CF and S-ECC groups. Sucrose made the originally different S-ECC and CF communities eventually became similar to each other, but they remained dissimilar in lactose.

Conclusion

S-ECC plaques had more active interaction with cariogenic carbohydrates like sucrose and lactose than healthy plaques. We supported lactose has less cariogenicity compared with sucrose from microbial community structural aspect. Phenylalanine may have a potentially inhibitory effect on caries development.

Dynamics of Dissolution, Killing, and Inhibition of Dental Plaque Biofilm

The present study aims to establish a standardized model that makes it possible to evaluate the dynamic dissolution of biofilm, killing of biofilm microbes and inhibition of growth of biofilm by disinfecting solutions. Biofilm was grown from dental plaque bacteria on collagen-coated hydroxyapatite (HA) disks for 3 days or 3 weeks under anaerobic conditions. Biofilms were stained with the LIVE/DEAD viability stain and subjected to sterile water, 2% sodium hypochlorite (NaOCl), 6% NaOCl, or 2% chlorhexidine (CHX) for 32 min. Dynamic change in fluorescence on bacterial cells and extracellular polymeric substance (EPS) during the exposure was analyzed using Alexa Fluor 647-labeled dextran conjugate and a live-cell imaging confocal laser scanning microscopy (LC-CLSM). The biofilm structures after treatments were visualized by scanning electron microscopy (SEM). The treated biofilms on HA disks were collected and subjected to colony forming unit (CFU) counting. Another set of sterile HA disks were coated with CHX prior to the monitoring of plaque biofilm growth for 12 h. The LC-CLSM results showed that NaOCl dissolved biofilm effectively, more so at a higher concentration and longer exposure time. Six percent NaOCl was the most effective at dissolving and killing bacteria (e.g., 99% bacterial reduction in 3-day-old biofilm and 95% bacterial reduction in 3-week-old biofilm in 32 min) followed by 2% NaOCl and CHX. Sodium hypochlorite dissolved over 99.9% of the EPS whereas CHX only slightly reduced the EPS biovolume in 32 min. CFU results indicated that the dispersed biofilm bacteria are more resistant than planktonic bacteria to disinfectants. SEM showed the disruption of biofilm after exposures to CHX and NaOCl. The use of 2% CHX and sterile water did not result in biofilm dissolution. However, prior exposure of the HA disks to 2 and 0.2% CHX for 3 min prevented biofilm from growing on the HA disk surfaces for at least 12 h. This new platform has the potential to aid in a better understanding of the antibiofilm properties of oral disinfectants.

Biofilm Matrixome: Extracellular Components in Structured Microbial Communities

Biofilms consist of microbial communities embedded in a 3D extracellular matrix. The matrix is composed of a complex array of extracellular polymeric substances (EPS) that contribute to the unique attributes of biofilm lifestyle and virulence. This ensemble of chemically and functionally diverse biomolecules is termed the 'matrixome'. The composition and mechanisms of EPS matrix formation, and its role in biofilm biology, function, and microenvironment are being revealed. This perspective article highlights recent advances about the multifaceted role of the 'matrixome' in the development, physical-chemical properties, and virulence of biofilms. We emphasize that targeting biofilm-specific conditions such as the matrixome could lead to precise and effective antibiofilm approaches. We also discuss the limited knowledge in the context of polymicrobial biofilms, and the need for more in-depth analyses of the EPS matrix in mixed communities that are associated with many human infectious diseases.

Biofilm Microenvironment-Responsive Nanotheranostics for Dual-Mode Imaging and Hypoxia-Relief-Enhanced Photodynamic Therapy of Bacterial Infections

The formation of bacterial biofilms closely associates with infectious diseases. Until now, precise diagnosis and effective treatment of bacterial biofilm infections are still in great need. Herein, a novel multifunctional theranostic nanoplatform based on MnO₂ nanosheets (MnO₂ NSs) has been designed to achieve pH-responsive dual-mode imaging and hypoxia-relief-enhanced antimicrobial photodynamic therapy (aPDT) of bacterial biofilm infections. In this study, MnO₂ NSs were modified with bovine serum albumin (BSA) and polyethylene glycol (PEG) and then loaded with chlorin e6 (Ce6) as photosensitizer to form MnO₂-BSA/PEG-Ce6 nanosheets (MBP-Ce6 NSs). After being delivered into the bacterial biofilm-infected tissues, the MBP-Ce6 NSs could be decomposed in acidic biofilm microenvironment and release Ce6 with Mn²⁺, which subsequently activate both fluorescence (FL) and magnetic resonance (MR) signals for effective dual-mode FL/MR imaging of bacterial biofilm infections. Meanwhile, MnO₂ could catalyze the decomposing of H₂O₂ in biofilm-infected tissues into O₂ and relieve the hypoxic condition of biofilm, which significantly enhances the efficacy of aPDT. An in vitro study showed that MBP-Ce6 NSs could significantly reduce the number of methicillin-resistant Staphylococcus aureus (MRSA) in biofilms after 635 nm laser irradiation. Guided by FL/MR imaging, MRSA biofilm-infected mice can be efficiently treated by MBP-Ce6 NSs-based aPDT. Overall, MBP-Ce6 NSs not only possess biofilm microenvironment-responsive dual-mode FL/MR imaging ability but also have significantly enhanced aPDT efficacy by relieving the hypoxia habitat of biofilm, which provides a promising theranostic nanoplatform for bacterial biofilm infections.

Combined DNase and Proteinase Treatment Interferes with Composition and Structural Integrity of Multispecies Oral Biofilms

Modification of oral biofilms adhering to dental hard tissues could lead to new treatment approaches in cariology and periodontology. In this study the impact of DNase I and/or proteinase K on the formation of a simulated supragingival biofilm was investigated in vitro. Six-species biofilms were grown anaerobically in the presence of DNase I and proteinase K. After 64 h biofilms were either harvested and quantified by culture analysis or proceeded to staining followed by confocal laser scanning microscopy. Microbial cells were stained using DNA-dyes or fluorescent in situ hybridization. Exopolysaccharides, eDNA and exoproteins were stained with Calcofluor, anti-DNA-antibody, and Sypro^TM Ruby, respectively. Overall, results showed that neither DNase I nor proteinase K had an impact on total colony-forming units (CFUs) compared to the control without enzymes. However, DNase I significantly suppressed the growth of Actinomyces oris, Fusobacterium nucleatum, Streptococcus mutans, Streptococcus oralis and Candida albicans. Proteinase K treatment induced significant increase in S. mutans and S. oralis CFUs (p < 0.001), whereas C. albicans and V. dispar showed lower CFUs compared to the control. Interestingly, confocal images visualized the biofilm degradation caused by DNase I and proteinase K. Thus, enzymatic treatment should be combined with conventional antimicrobial agents aiming at both bactericidal effectiveness and biofilm dispersal.

Solidago virgaurea L. Plant Extract Targeted Against Candida albicans to Reduce Oral Microbial Biomass: a Double Blind Randomized Trial on Healthy Adults

Oral microbiome plays an important part on oral health and endogenous bacteria and fungi should not be eradicated. However, their proliferation must be controlled by oral hygiene care. In vitro, Solidago virgaurea ssp. virgaurea L. (SV) plant extract inhibits the adherence and hyphal formation of a fungus, Candida albicans. It reduces the biomass of Candida-bacterial biofilms but not fungal or bacterial growth. Unlike chemical antiseptics, like triclosan and chlorhexidine for instance, SV is a plant extract easily biodegradable. The purpose of this study was to assess the in vivo effectiveness of SV extract in reducing oral biomass. A randomized, double-blind clinical study, with dental plaque evaluation designed to assess the effectiveness of a fluorinated toothpaste containing SV (Bucovia™, Givaudan, Vernier, Switzerland) was conducted. Sixty-six subjects (SV group n = 33 vs. control n = 33) brushed their teeth twice a day for a 4-week period. Supragingival dental plaque was sampled. Total bacterial load (broad spectral bacterial quantitative Polymerase Chain Reaction (qPCR)), C. albicans and seven bacterial species were quantified by qPCR. In the Intervention group, there was a decrease of Total bacterial load (ΔD0D28 p = 0.005 and ΔD14D28 p = 0.026), Streptococcus mutans (ΔD0D14 p = 0.024) and C. albicans (ΔD0D28 p = 0.022). In the Control group Total bacterial load tended to decrease from baseline to day 28 (ΔD0D28 p = 0.062 and ΔD14D28 p = 0.009). Plaque Index and Gingival Index improved in both groups.

Sucrose promotes caries progression by disrupting the microecological balance in oral biofilms: an in vitro study

Sucrose has long been regarded as the most cariogenic carbohydrate. However, why sucrose causes severer dental caries than other sugars is largely unknown. Considering that caries is a polymicrobial infection resulting from dysbiosis of oral biofilms, we hypothesized that sucrose can introduce a microbiota imbalance favoring caries to a greater degree than other sugars. To test this hypothesis, an in vitro saliva-derived multispecies biofilm model was established, and by comparing caries lesions on enamel blocks cocultured with biofilms treated with sucrose, glucose and lactose, we confirmed that this model can reproduce the in vivo finding that sucrose has the strongest cariogenic potential. In parallel, compared to a control treatment, sucrose treatment led to significant changes within the microbial structure and assembly of oral microflora, while no significant difference was detected between the lactose/glucose treatment group and the control. Specifically, sucrose supplementation disrupted the homeostasis between acid-producing and alkali-producing bacteria. Consistent with microbial dysbiosis, we observed the most significant disequilibrium between acid and alkali metabolism in sucrose-treated biofilms. Taken together, our data indicate that the cariogenicity of sugars is closely related to their ability to regulate the oral microecology. These findings advance our understanding of caries etiology from an ecological perspective.

Approaches to Modulate Biofilm Ecology

Dental caries is closely related to a dysbiosis of the microbial consortia of supragingival oral biofilms driven by a sugar-frequent and acidic-pH environment. The pH is a key factor affecting the homeostasis of supragingival biofilms seen in health. There is increasing interest on the ecological dynamics of the oral microbiome and how a dysbiotic microbiota can be successfully replaced by health-beneficial flora. The concept of preventing the microbial dysbiosis related to caries through modulation of sugar intake and pH has fully emerged.

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.