Comparison of the initial streptococcal microflora on dental enamel in caries-active and in caries-inactive individuals

Bidirectional effects of neutrophils on Streptococcus oralis biofilms in vitro

Background

Streptococcus oralis is a commensal bacterium and an early biofilm coloniser found in the human oral cavity. One of the biofilm matrix constituents is bacterial extracellular DNA (eDNA). Neutrophils are innate immune cells that respond to biofilms, employing antimicrobial mechanisms such as neutrophil extracellular trap (NET) and reactive oxygen species (ROS) release. Here, bidirectional effects of neutrophils on S. oralis biofilms were investigated.

Materials and methods

Isolated neutrophils were introduced to S. oralis biofilms at different stages of biofilm development. Biofilm quantity was assessed by crystal violet technique, confocal microscopy and CFU enumeration. Surface adhesion during shear stress was quantified by spectrophotometry. Bacterial and neutrophil extracellular DNA within biofilms and ROS production were analysed using fluorescence and luminescence assays, and neutrophil-eDNA interactions were investigated by flow cytometry and fluorescence microscopy.

Results

Neutrophils decreased S. oralis biofilm quantity transiently and reduced eDNA but did not affect biofilm surface adhesion. Unexpectedly, CFUs were increased by neutrophils. Bacterial DNA was found to co-localise with neutrophil membranes. Neutrophils produced elevated total and intracellular ROS, however, no NETs in response to biofilms.

Conclusion

Neutrophils in vitro are not excessively activated by S. oralis biofilms but are able to reduce biofilm quantity in the short-term, possibly through interfering with eDNA.

The formation of cariogenic plaque to contemporary adhesive restorative materials: an in vitro study

The research exploiting the ability of dental materials to induce or prevent secondary caries (SC) development still seems inconclusive. Controlling bacterial adhesion by releasing bacteriostatic ions and improving the surface structure has been suggested to reduce the occurrence of SC. This paper analyses the impact of five distinctively composed dental materials on cariogenic biofilm formation. Forty-five specimens of three composites (CeramX Spectra ST, Admira Fusion, Beautifil II) and two glass-ionomers (Fuji II LC, Caredyne Restore), respectively, were incubated in bacterial suspension composed of Streptococcus mutans, Lactobacillus acidophilus, Streptococcus mitis, Streptococcus sanguinis, and Streptococcus salivarius at pH 7.0 and 5.5. Coverslips were used as a control. Adhered bacteria were collected after 2, 4, 6, 12, 24, and 48 h and analyzed using quantitative polymerase chain reaction (qPCR). Fluoride leakage was measured at each collection. The specimens' surface topography was assessed using interferometry. In the present study, surface roughness seemed to have a partial role in bacterial adhesion and biofilm formation, together with chemical composition of the materials tested. Despite differences in fluoride leakage, biofilm accumulation was similar across materials, but the number of adhered bacteria differed significantly. A release of other ions may also affect adhesion. These variations suggest that certain materials may be more prone to initiating secondary caries.

Surface roughness associated with bacterial adhesion on dental resin-based materials

This study investigates the surface quality and bacterial adhesion properties of various dental materials, including indirect composites, veneering composites, direct composites, polyether ether ketone (PEEK), and two millable polymethyl methacrylate (PMMA). Material specimens were processed following manufacturer instructions, initially evaluated for surface roughness and Streptococcus sanguinis (S. sanguinis) adhesion. Subsequently, toothbrushing simulation was employed to simulate aging, and changes in material surfaces were assessed via roughness measurements and bacterial adhesion testing. Prior to simulated aging, direct and indirect composites exhibited the lowest roughness values. However, after the simulated toothbrushing, veneering composites displayed the highest roughness levels. Both PMMA materials demonstrated the highest S. sanguinis adhesion levels, both before and after artificial aging. Interestingly, the indirect composite material showed a reduction in bacterial adhesion following toothbrushing simulation. Surprisingly, this study did not reveal a clear correlation between roughness and bacterial adhesion.

Bacterial adhesion and surface properties of computer-aided design-computer-aided manufacturing restorative materials

PURPOSE

This study aimed to evaluate the surface properties and bacterial adhesion of computer-aided design-computer-aided manufacturing (CAD-CAM) restorative materials.

METHODS

Four CAD-CAM resin-based blocks (Vita Enamic, Shofu block HC, Cerasmart [CS] and Lava Ultimate [LU]) and a leucite-reinforced glass ceramic block (IPS Empress CAD) were used in the present study. Specimens prepared with dimensions of 10 × 10 × 1 mm were polished. Surface characteristics were assessed with hydrophobicity and surface free energy (SFE) analysis. Surface roughness was measured using a profilometer, and elemental and topographic evaluations were performed with SEM-EDX analysis. After being kept in artificial saliva for 1 h, Streptococcus mutans (S. mutans) and Streptococcus mitis (S. mitis) were incubated separately in 5% CO2 atmosphere at 37°C for 24 h. The adhered bacteria were counted as ×108 CFU/mL.

RESULTS

Surface roughness, contact angle and SFE measurement values were found to be in the range of 0.144-0.264 Ra, 28.362°-70.074° and 39.65-63.62 mN/m, respectively. The highest adhered amount of S. mutans was found in CS and the lowest in LU, while there was no significant difference between the amounts of adhered S. mitis.

CONCLUSION

Despite differences in the surface properties of the materials used for the study, the materials exhibited identical properties with respect to bacterial adhesion.

Insights into the enigma of oral streptococci in carcinogenesis

SUMMARYThe genus Streptococcus consists of a taxonomically diverse group of Gram-positive bacteria that have earned significant scientific interest due to their physiological and pathogenic characteristics. Within the genus Streptococcus, viridans group streptococci (VGS) play a significant role in the oral ecosystem, constituting approximately 80% of the oral biofilm. Their primary role as pioneering colonizers in the oral cavity with multifaceted interactions like adherence, metabolic signaling, and quorum sensing contributes significantly to the complex dynamics of the oral biofilm, thus shaping oral health and disease outcomes. Perturbations in oral streptococci composition drive oral dysbiosis and therefore impact host-pathogen interactions, resulting in oral inflammation and representing VGS as an opportunistic pathogen. The association of oral streptococci in tumors across distant organs, spanning the esophagus, stomach, pancreas, and colon, illuminates a potential association between oral streptococci, inflammation, and tumorigenesis. This finding emphasizes the need for further investigations into the role of oral streptococci in mucosal homeostasis and their involvement in carcinogenesis. Hence, here, we review the significance of oral streptococci in biofilm dynamics and how the perturbation may impact mucosal immunopathogenesis in the context of cancer, with a vision of exploiting oral streptococci for cancer intervention and for the development of non-invasive cancer diagnosis.

SepM mutation in Streptococcus mutans clinical isolates and related function analysis

BACKGROUND

Streptococcus mutans (S. mutans) is an important pathogenic bacterium that causes dental caries, while Streptococcus gordonii (S. gordonii) is a non-cariogenic bacterium that inhibits the growth of S. mutans. The SepM protein can promote the inhibitory ability of S. mutans against S. gordonii by cleaving CSP-21 and activating the ComDE two-component system. This study was designed to explore sepM mutation in S. mutans clinical isolates and related function in the regulation of interactions with S. gordonii.

METHODS

The S. mutans clinical strains that can inhibit the growth of S. gordonii constitute the inhibitory group. 286 C-serotype S. mutans strains were categorized into S. gordonii inhibitory (n = 114) and non-inhibitory bacteria (n = 172). We detected sanger sequencing of sepM gene, the expression levels of related genes and proteins in clinical isolates, obtained prokaryotic expression and purification of mutated proteins, and analyzed the effect of the target mutations on the binding between SepM and CSP-21.

RESULTS

We found that C482T, G533A, and G661A missense mutations were presented at significantly higher frequency in the inhibitory group relative to the non-inhibitory group. There was no significant difference in the expression of the sepM gene between selected clinical isolates harboring the G533A mutation and the control group. The expression levels of SepM, phosphorylated ComD, and ComE in the mutation group were significantly higher than those in the control group. SepM_control and SepM_D221N (G661A at the gene level) were found to contain two residues close to the active center while SepM_G178D (G533A at the gene level) contained three residues close to the active center. At 25 °C and a pH of 5.5, SepM_D221N (G661A) exhibited higher affinity for CSP-21 (KD = 8.25 µM) than did the SepM control (KD = 33.1 µM), and at 25 °C and a pH of 7.5, SepM_G178D (G533A) exhibited higher affinity (KD = 3.02 µM) than the SepM control (KD = 15.9 µM). It means that it is pH dependent.

CONCLUSIONS

Our data suggest that increased cleavage of CSP-21 by the the mutant SepM may be a reason for the higher inhibitory effect of S. mutans on S. gordonii .

Characterization of MdpS: an in-depth analysis of a MUC5B-degrading protease from Streptococcus oralis

Oral biofilms, comprising hundreds of bacteria and other microorganisms on oral mucosal and dental surfaces, play a central role in oral health and disease dynamics. Streptococcus oralis, a key constituent of these biofilms, contributes significantly to the formation of which, serving as an early colonizer and microcolony scaffold. The interaction between S. oralis and the orally predominant mucin, MUC5B, is pivotal in biofilm development, yet the mechanism underlying MUC5B degradation remains poorly understood. This study introduces MdpS (Mucin Degrading Protease from Streptococcus oralis), a protease that extensively hydrolyses MUC5B and offers an insight into its evolutionary conservation, physicochemical properties, and substrate- and amino acid specificity. MdpS exhibits high sequence conservation within the species and also explicitly among early biofilm colonizing streptococci. It is a calcium or magnesium dependent serine protease with strict physicochemical preferences, including narrow pH and temperature tolerance, and high sensitivity to increasing concentrations of sodium chloride and reducing agents. Furthermore, MdpS primarily hydrolyzes proteins with O-glycans, but also shows activity toward immunoglobulins IgA1/2 and IgM, suggesting potential immunomodulatory effects. Significantly, MdpS extensively degrades MUC5B in the N- and C-terminal domains, emphasizing its role in mucin degradation, with implications for carbon and nitrogen sequestration for S. oralis or oral biofilm cross-feeding. Moreover, depending on substrate glycosylation, the amino acids serine, threonine or cysteine triggers the enzymatic action. Understanding the interplay between S. oralis and MUC5B, facilitated by MdpS, has significant implications for the management of a healthy eubiotic oral microenvironment, offering potential targets for interventions aimed at modulating oral biofilm composition and succession. Additionally, since MdpS does not rely on O-glycan removal prior to extensive peptide backbone hydrolysis, the MdpS data challenges the current model of MUC5B degradation. These findings emphasize the necessity for further research in this field.

Detection, Diagnosis, and Monitoring of Early Caries: The Future of Individualized Dental Care

Dental caries remains a significant global health issue. It was highlighted by the World Health Organization's 2022 reports that despite the efforts and scientific advancements in caries detection and management, the situation has only marginally improved over the past three decades. The persistence of this problem may be linked to outdated concepts developed almost a century ago but are still guiding dentists' approach to caries management today. There is a need to reconsider professional strategies for preventing and managing the disease. Contemporary dentistry could benefit from embracing new concepts and technologies for caries detection and management. Dentists should explore, among others, alternative methods for caries detection such as optical-based caries detection. These tools have been established for over a decade and they align with current disease understanding and international recommendations, emphasizing early detection and minimally invasive management. This narrative review presents the current state of knowledge and recent trends in caries detection, diagnosis, monitoring, and management, offering insights into future perspectives for clinical applications and research topics.

Structural vaccinology-based design of multi-epitopes vaccine against Streptococcus gordonii and validation using molecular modeling and immune simulation approaches

Streptococcus gordonii is an oral bacterium colonizing the dental cavity and leading to plaque formation. This pervasive colonizer is also the etiologic agent of bacterial endocarditis and has a major role in infective endocarditis. The bacteria reach the heart through oral bleeding, leading to inflammation of cardiovascular valves. Over the past 50 years, it has shown a significant pathogenic role in immunocompromised and neutropenic patients. Since antibiotic resistance has created prophylaxis failure towards infective endocarditis, a potent therapeutic candidate is needed. Therefore, multi-epitopes vaccine offers advantages over the other approaches. Thus, herein, numerous molecular-omics tools were exploited to mine immunogenic peptides, i.e., T-cell and B-cell epitopes, and construct a vaccine sequence. Our findings revealed a total of 24 epitopes, including CTL, HTL, and B-cell are responsible for imparting immune responses, which were combined with the help of different linkers, and MEVC was constructed. Multifactorial validation of the candidate vaccine was performed to minimize the risk factors. The final sequence was docked with TLR2 to validate its conformation compatibility with receptor and long-term interactions stability. Our analysis revealed that the vaccine construct is immunogenic and non-allergenic. The construct also established various contacts with the immune receptor. Finally, the vaccine sequence was reverse-translated, optimized for codon usage, and analyzed for expression in the Escherichia coli K12 strain. Maximum expression was noted with a CAI score of 0.95. In silico immune simulation revealed that the antigen was neutralized on the 3rd day after injection. In conclusion, the current study warrants validation of the vaccine construct both in in vitro and in vivo models for accurate therapeutic intervention.

Heat Shock Protein Inhibitors Show Synergistic Antibacterial Effects with Photodynamic Therapy on Caries-Related Streptococci In Vitro and In Vivo

Caries are chronic infections in which the cariogenic biofilm plays a critical role in disease occurrence and progression. Photodynamic therapy (PDT) is a new effective treatment that is receiving wide attention in the antibacterial field, but it can lead to the upregulation of heat shock proteins (HSPs), which enhances bacterial resistance. Herein, we incorporated HSP inhibitors with PDT to evaluate the effect on Streptococcus mutans, Streptococcus sobrinus, and Streptococcus sanguinis under planktonic conditions and on cariogenic biofilms. Additionally, a model of caries was established in 2-week-old rats, and anticaries properties were evaluated by Keyes' scoring. Importantly, the combination of HSP inhibitors and PDT had outstanding efficiency in inhibiting the growth of tested Streptococcus strains and the formation of either monomicrobial or multispecies biofilms in vitro. In addition, the quantity of colonized streptococci and the severity of carious lesions were also distinctly suppressed in vivo. Overall, the synergistic application of HSP inhibitors and PDT has promising potential in the prevention and treatment of dental caries. IMPORTANCE Effective therapies for the prevention and control of caries are urgently needed. Cariogenic streptococci play a key role in the occurrence and progression of caries. Recently, photodynamic therapy has been demonstrated to have good antibacterial efficiency, but it can cause a heat shock response in bacteria, which may weaken its practical effects. We indicate here an effective therapeutic strategy of combining heat shock protein inhibitors and photodynamic therapy, which shows excellent inhibition toward three dominant streptococci related to caries and suppression of carious progression in a rat model. Further development for clinical application is promising.

Molecular and regulatory mechanisms of oxidative stress adaptation in Streptococcus mutans

Dental caries is a chronic progressive disease, which destructs dental hard tissues under the influence of multiple factors, mainly bacteria. Streptococcus mutans is the main cariogenic bacteria. However, its cariogenic virulence is affected by environmental stress such as oxidative stress, nutrient deficiency, and low pH to some extent. Oxidative stress is one of the main stresses that S. mutans faces in oral cavity. But there are a variety of protective molecules to resist oxidative stress in S. mutans, including superoxide dismutase, nicotinamide adenine dinucleotide oxidase, Dps-like peroxide resistance protein, alkyl-hydrogen peroxide reductase, thioredoxin, glutamate-reducing protein system, and some metabolic substances. Additionally, some transcriptional regulatory factors (SloR, PerR, Rex, Spx, etc.) and two-component systems are also closely related to oxidative stress adaptation by modulating the expression of protective molecules. This review summarizes the research progress of protective molecules and regulatory mechanisms (mainly transcription factors) of oxidative stress adaptation of S. mutans.

Genomic Diversity among Actinomyces naeslundii Strains and Closely Related Species

The aim of this study was to investigate and clarify the ambiguous taxonomy of Actinomyces naeslundii and its closely related species using state-of-the-art high-throughput sequencing techniques, and, furthermore, to determine whether sub-clusters identified within Actinomyces oris and Actinomyces naeslundii in a previous study by multi locus sequence typing (MLST) using concatenation of seven housekeeping genes should either be classified as subspecies or distinct species. The strains in this study were broadly classified under Actinomyces naeslundii group as A. naeslundii genospecies I and genospecies II. Based on MLST data analysis, these were further classified as A. oris and A. naeslundii. The whole genome sequencing of selected strains of A. oris (n = 17) and A. naeslundii (n = 19) was carried out using Illumina Genome Analyzer IIxe and Roche 454 allowing paired-end and single-reads sequencing, respectively. The sequences obtained were aligned using CLC Genomic workbench version 5.1 and annotated using RAST (Rapid Annotation using Subsystem Technology) release version 59 accessible online. Additionally, genomes of seven publicly available strains of Actinomyces (k20, MG1, c505, OT175, OT171, OT170, and A. johnsonii) were also included. Comparative genomic analysis (CGA) using Mauve, Progressive Mauve, gene-by-gene, Core, and Pan Genome, and finally Digital DNA-DNA homology (DDH) analysis was carried out. DDH values were obtained using in silico genome-genome comparison. Evolutionary analysis using ClonalFrame was also undertaken. The mutation and recombination events were compared using chi-square test among A. oris and A. naeslundii isolates (analysis methods are not included in the study). CGA results were consistent with previous traditional classification using MLST. It was found that strains of Actinomyces k20, MG1, c505, and OT175 clustered in A. oris group of isolates, while OT171, OT170, and A. johnsonii appeared as separate branches. Similar clustering to MLST was observed for other isolates. The mutation and recombination events were significantly higher in A. oris than A. naeslundii, highlighting the diversity of A. oris strains in the oral cavity. These findings suggest that A. oris forms six distinct groups, whereas A. naeslundii forms three. The correct designation of isolates will help in the identification of clinical Actinomyces isolates found in dental plaque. Easily accessible online genomic sequence data will also accelerate the investigation of the biochemical characterisation and pathogenesis of this important group of micro-organisms.

Site-tropism of streptococci in the oral microbiome

A detailed understanding of where bacteria localize is necessary to advance microbial ecology and microbiome-based therapeutics. The site-specialist hypothesis predicts that most microbes in the human oral cavity have a primary habitat type within the mouth where they are most abundant. We asked whether this hypothesis accurately describes the distribution of the members of the genus Streptococcus, a clinically relevant taxon that dominates most oral sites. Prior analysis of 16S rRNA gene sequencing data indicated that some oral Streptococcus clades are site-specialists while others may be generalists. However, within complex microbial populations composed of numerous closely related species and strains, such as the oral streptococci, genome-scale analysis is necessary to provide the resolution to discriminate closely related taxa with distinct functional roles. Here, we assess whether individual species within this genus are specialists using publicly available genomic sequence data that provide species-level resolution. We chose a set of high-quality representative genomes for human oral Streptococcus species. Onto these genomes, we mapped shotgun metagenomic sequencing reads from supragingival plaque, tongue dorsum, and other sites in the oral cavity. We found that every abundant Streptococcus species in the healthy human oral cavity showed strong site-tropism and that even closely related species such as S. mitis, S. oralis, and S. infantis specialized in different sites. These findings indicate that closely related bacteria can have distinct habitat distributions in the absence of dispersal limitation and under similar environmental conditions and immune regimes. Substantial overlap between the core genes of these three species suggests that site-specialization is determined by subtle differences in genomic content.

Oral Commensal Streptococci: Gatekeepers of the Oral Cavity

Oral commensal streptococci are primary colonizers of the oral cavity. These streptococci produce many adhesins, metabolites, and antimicrobials that modulate microbial succession and diversity within the oral cavity. Often, oral commensal streptococci antagonize cariogenic and periodontal pathogens such as Streptococcus mutans and Porphyromonas gingivalis, respectively. Mechanisms of antagonism are varied and range from the generation of hydrogen peroxide, competitive metabolite scavenging, the generation of reactive nitrogen intermediates, and bacteriocin production. Furthermore, several oral commensal streptococci have been shown to alter the host immune response at steady state and in response to oral pathogens. Collectively, these features highlight the remarkable ability of oral commensal streptococci to regulate the structure and function of the oral microbiome. In this review, we discuss mechanisms used by oral commensal streptococci to interact with diverse oral pathogens, both physically and through the production of antimicrobials. Finally, we conclude by exploring the critical roles of oral commensal streptococci in modulating the host immune response and maintaining health and homeostasis.

Surface roughness and Streptococcus mutans adhesion on surface sealant agent coupled interim crown materials after dynamic loading

Background

With the application of surface sealant agents, smooth surfaces can be achieved in a shorter time when compared with conventional polishing. However, studies on the performance of these agents against chewing forces are not many. The purpose of this study was to evaluate the surface roughness and Streptococcus mutans adhesion on surface sealent coupled interim prosthetic materials after chewing simulation.

Methods

One hundred and twelve specimens were fabricated from two poly(methyl methacrylate) (Tab 2000, Dentalon Plus) and two bis-acryl (Tempofit, Protemp 4) interim crown materials and divided into 4 groups (n = 7) according to applied surface treatment: conventional polishing (control) and 3 surface sealant (Palaseal, Optiglaze, Biscover) coupling methods. The surface roughness values (R_a) were measured with a profilometer before (Ra0) and after aging through dynamic loading in a multifunctional chewing simulator for 10,000 cycles at 50 N load combined with integral thermocycling (between 5 and 55 °C) (Ra1). Specimens were incubated with Streptococcus mutans suspension and the total number of adherent bacteria was calculated by multiplying the counted bacterial colonies with the dilution coefficient.

Results

Surface sealant agent application significantly decreased the surface roughness compared with conventionally polished specimens, except for Optiglaze or BisCover LV applied Protemp 4 and Palaseal or Biscover LV applied Tempofit. Surface roughness after dynamic loading showed a statistically significant increase in all groups, except for the control groups of Tab 2000 and Protemp 4. A positive correlation was found between surface roughness values of interim prosthodontic materials and the quantitiy of Streptococcus Mutans.

Conclusions

Even though surface sealant agent application significantly decreased the surface roughness compared with conventionally polished specimens, dynamic loading significantly increased the surface roughness of all surface sealant coupled materials. The R_a values of all test groups were higher than the plaque accumulation threshold (0.20 µm). Streptococcus mutans adhered more on rougher surfaces.

Streptococcus oralis Employs Multiple Mechanisms of Salivary Mucin Binding That Differ Between Strains

Streptococcus oralis is an oral commensal and opportunistic pathogen that can enter the bloodstream and cause bacteremia and infective endocarditis. Here, we investigated the mechanisms of S. oralis binding to oral mucins using clinical isolates, isogenic mutants and glycoconjugates. S. oralis bound to both MUC5B and MUC7, with a higher level of binding to MUC7. Mass spectrometry identified 128 glycans on MUC5B, MUC7 and the salivary agglutinin (SAG). MUC7/SAG contained a higher relative abundance of Lewis type structures, including Lewis b/y, sialyl-Lewis a/x and α2,3-linked sialic acid, compared to MUC5B. S. oralis subsp. oralis binding to MUC5B and MUC7/SAG was inhibited by Lewis b and Lacto-N-tetraose glycoconjugates. In addition, S. oralis binding to MUC7/SAG was inhibited by sialyl Lewis x. Binding was not inhibited by Lacto-N-fucopentaose, H type 2 and Lewis x conjugates. These data suggest that three distinct carbohydrate binding specificities are involved in S. oralis subsp. oralis binding to oral mucins and that the mechanisms of binding MUC5B and MUC7 differ. Efficient binding of S. oralis subsp. oralis to MUC5B and MUC7 required the gene encoding sortase A, suggesting that the adhesin(s) are LPXTG-containing surface protein(s). Further investigation demonstrated that one of these adhesins is the sialic acid binding protein AsaA.

Antiplanktonic and Antibiofilm Activity of Rheum palmatum against Streptococcus oralis and Porphyromonas gingivalis

Periodontitis and peri-implantitis are inflammatory conditions with a high global prevalence. Oral pathogens such as Porphyromonas gingivalis play a crucial role in the development of dysbiotic biofilms associated with both diseases. The aim of our study was to identify plant-derived substances which mainly inhibit the growth of "disease promoting bacteria", by comparing the effect of Rheum palmatum root extract against P. gingivalis and the commensal species Streptococcus oralis. Antiplanktonic activity was determined by measuring optical density and metabolic activity. Antibiofilm activity was quantified using metabolic activity assays and live/dead fluorescence staining combined with confocal laser scanning microscopy. At concentrations of 3.9 mg/L, R. palmatum root extract selectively inhibited planktonic growth of the oral pathogen P. gingivalis, while not inhibiting growth of S. oralis. Selective effects also occurred in mature biofilms, as P. gingivalis was significantly more stressed and inhibited than S. oralis. Our studies show that low concentrations of R. palmatum root extract specifically inhibit P. gingivalis growth, and offer a promising approach for the development of a potential topical agent to prevent alterations in the microbiome due to overgrowth of pathogenic P. gingivalis.

The antimicrobial effect of Rosmarinus officinalis extracts on oral initial adhesion ex vivo

Objective

In the last few decades, there has been a growing worldwide interest in the use of plant extracts for the prevention of oral diseases. The main focus of this interest lies in the identification and isolation of substances that limit the formation of microbial biofilm which plays a major role in the development of caries, periodontitis, and peri-implantitis. In this clinical ex vivo study, we investigated the antimicrobial effects of Rosmarinus officinalis extract against oral microorganisms within in situ initial oral biofilms.

Materials and methods

Initial in situ biofilm samples (2 h) from six healthy volunteers were treated ex vivo with R. officinalis extract at concentrations of 20 mg/ml and 30 mg/ml. The number of viable bacterial cells was determined by counting the colony-forming units. All surviving bacteria were isolated in pure cultures and identified using MALDI-TOF and biochemical testing procedures. Additionally, live/dead staining in combination with epifluorescence microscopy was used for visualizing the antimicrobial effects in the initial biofilms.

Results

The number of colony-forming units in the R. officinalis–treated biofilms was significantly lower than in the untreated controls (p < 0.001). The reduction range of log10 was 1.64–2.78 and 2.41–3.23 for aerobic and anaerobic bacteria, respectively. Regarding the bacterial composition, large intra- and interindividual variability were observed. Except for Campylobacter spp., the average amount of all bacterial taxa was lower after treatment with R. officinalis than in the untreated biofilms. A total of 49 different species were detected in the untreated biofilms, while only 11 bacterial species were detected in the R. officinalis–treated biofilms. Live/dead staining confirmed that the R. officinalis–treated biofilms had significantly lower numbers of surviving bacteria than the untreated biofilms.

Conclusions

The treatment with R. officinalis extract has a significant potential to eliminate microbial oral initial biofilms.

Clinical relevance

The results of this study encourage the use of R. officinalis extracts in biofilm control and thus in the treatment of caries and periodontitis as a herbal adjuvant to synthetic substances.

Oral streptococci subvert the host innate immune response through hydrogen peroxide

In periodontal health, oral streptococci constitute up to 80% of the plaque biofilm. Yet, destructive inflammatory events of the periodontium are rare. This observation suggests that oral streptococci may possess mechanisms to co-exist with the host. However, the mechanisms employed by oral streptococci to modulate the innate immune response have not been well studied. One of the key virulence factors produced by oral streptococci is hydrogen peroxide (H₂O₂). In mammalian cells, H₂O₂ triggers the activation of nuclear factor erythroid 2-related factor 2 (Nrf2), a key pathway mediating antioxidant defence. This study aimed to determine (1) if H₂O₂ producing oral streptococci activated the Nrf2 pathway in macrophages, and (2) if the activation of Nrf2 influenced the innate immune response. We found that oral streptococci downregulated the innate immune response in a H₂O₂ dependent manner through the activation of the Nrf2. The activation of the Nrf2 signalling pathway led to the inhibition of nuclear factor kappa-light-chain-enhancer of activated B cells (NFĸB), the key transcription factor regulating pro-inflammatory response. This study showed for the first time that oral streptococci are unlikely passive bystanders but could play an active role in the maintenance of periodontal health by preventing overt inflammation.

Effects of pH on the Properties of Membrane Vesicles Including Glucosyltransferase in Streptococcus mutans

Streptococcus mutans releases membrane vesicles (MVs) and induces MV-dependent biofilm formation. Glucosyltransferases (Gtfs) are bound to MVs and contribute to the adhesion and glucans-dependent biofilm formation of early adherent bacteria on the tooth surface. The biofilm formation of S. mutans may be controlled depending on whether the initial pH tends to be acidic or alkaline. In this study, the characteristics and effects of MVs extracted from various conditions {(initial pH 6.0 and 8.0 media prepared with lactic acid (LA) and acetic acid (AA), and with NaOH (NO), respectively)} on the biofilm formation of S. mutans and early adherent bacteria were investigated. The quantitative changes in glucans between primary pH 6.0 and 8.0 conditions were observed, associated with different activities affecting MV-dependent biofilm formation. The decreased amount of Gtfs on MVs under the initial pH 6.0 conditions strongly guided low levels of MV-dependent biofilm formation. However, in the initial pH 6.0 and 8.0 solutions prepared with AA and NO, the MVs in the biofilm appeared to be formed by the expression of glucans and/or extracellular DNA. These results suggest that the environmental pH conditions established by acid and alkaline factors determine the differences in the local pathogenic activities of biofilm development in the oral cavity.

Freitas-Fernandes L, Fidalgo TKS, Tadeu Lopes R, Valente AP, R. Arnold R, de Aguiar Ribeiro A. The bacterial microbiome and metabolome in caries progression and arrest

Aim: This in vivo experimental study investigated bacterial microbiome and metabolome longitudinal changes associated with enamel caries lesion progression and arrest. Methods: We induced natural caries activity in three caries-free volunteers prior to four premolar extractions for orthodontic reasons. The experimental model included placement of a modified orthodontic band on smooth surfaces and a mesh on occlusal surfaces. We applied the caries-inducing protocol for 4- and 6-weeks, and subsequently promoted caries lesion arrest via a 2-week toothbrushing period. Lesions were verified clinically and quantitated via micro-CT enamel density measurements. The biofilm microbial composition was determined via 16S rRNA gene Illumina sequencing and NMR spectrometry was used for metabolomics. Results: Biofilm maturation and caries lesion progression were characterized by an increase in Gram-negative anaerobes, including Veillonella and Prevotella. Streptococcus was associated caries lesion progression, while a more equal distribution of Streptococcus, Bifidobacterium, Atopobium, Prevotella, Veillonella, and Saccharibacteria (TM7) characterized arrest. Lactate, acetate, pyruvate, alanine, valine, and sugars were more abundant in mature biofilms compared to newly formed biofilms. Conclusions: These longitudinal bacterial microbiome and metabolome results provide novel mechanistic insights into the role of the biofilm in caries progression and arrest and offer promising candidate biomarkers for validation in future studies.

Surface Roughness and Streptococcus mutans Adhesion on Metallic and Ceramic Fixed Prosthodontic Materials after Scaling

The aim of this study was to evaluate the surface roughness of fixed prosthodontic materials after polishing or roughening with a stainless steel curette or ultrasonic scaler and to examine the effect of these on Streptococcus mutans adhesion and biofilm accumulation. Thirty specimens (10 × 10 × 3 mm³) of zirconia (Zr), pressed lithium disilicate (LDS-Press), milled lithium disilicate glazed (LDS-Glaze), titanium grade V (Ti) and cobalt-chromium (CoCr) were divided into three groups (n = 10) according to surface treatment: polished (C), roughened with stainless steel curette (SC), roughened with ultrasonic scaler (US). Surface roughness values (Sa, Sq) were measured with a spinning disc confocal microscope, and contact angles and surface free energy (SFE) were measured with a contact angle meter. The specimens were covered with sterilized human saliva and immersed into Streptococcus mutans suspensions for bacterial adhesion. The biofilm was allowed to form for 24 h. Sa values were in the range of 0.008–0.139 µm depending on the material and surface treatment. Curette and ultrasonic scaling increased the surface roughness in LDS-Glaze (p < 0.05), Ti (p < 0.01) and CoCr (p < 0.001), however, surface roughness did not affect bacterial adhesion. Zr C and US had a higher bacterial adhesion percentage compared to LDS-Glaze C and US (p = 0.03). There were no differences between study materials in terms of biofilm accumulation.

No man's land: Species-specific formation of exclusion zones bordering Actinomyces graevenitzii microcolonies in nanoliter cultures

To survive within complex environmental niches, including the human host, bacteria have evolved intricate interspecies communities driven by competition for limited nutrients, cooperation via complementary metabolic proficiencies, and establishment of homeostatic relationships with the host immune system. The study of such complex, interdependent relationships is often hampered by the challenges of culturing many bacterial strains in research settings and the limited set of tools available for studying the dynamic behavior of multiple bacterial species at the microscale. Here, we utilize a microfluidic‐based co‐culture system and time‐lapse imaging to characterize dynamic interactions between Streptococcus species, Staphylococcus aureus, and Actinomyces species. Co‐culture of Streptococcus cristatus or S. salivarius in nanoliter compartments with Actinomyces graevenitzii revealed localized exclusion of Streptococcus and Staphylococcus from media immediately surrounding A. graevenitzii microcolonies. This community structure did not occur with S. mitis or S. oralis strains or in co‐cultures containing other Actinomycetaceae species such as S. odontolyticus or A. naeslundii. Moreover, fewer neutrophils were attracted to compartments containing both A. graevenitzii and Staphylococcus aureus than to an equal number of either species alone, suggesting a possible survival benefit together during immune responses.

Uncovering Roles of Streptococcus gordonii SrtA-Processed Proteins in the Biofilm Lifestyle

Streptococcus gordonii is a commensal oral organism. Harmless in the oral cavity, S. gordonii is an opportunistic pathogen. S. gordonii adheres to body surfaces using surface adhesive proteins (adhesins), which are critical to subsequent formation of biofilm communities. As in most Gram-positive bacteria, S. gordonii surface proteins containing the C-terminal LPXTG motif cleavage sequence are processed by sortase A (SrtA) to become covalently attached to the cell wall. To characterize the functional diversity and redundancy in the family of SrtA-processed proteins, an S. gordonii DL1 markerless deletion mutant library was constructed of each of the 26 putative SrtA-processed proteins. Each library member was evaluated for growth in rich medium, biofilm formation on plastic, saliva and salivary fractions, cell surface hydrophobicity (CSH), hemagglutination, and integration into an ex vivo plaque biofilm community. Library members were compared to the non-SrtA-processed adhesins AbpA and AbpB. While no major growth differences in rich medium were observed, many S. gordonii LPXTG/A proteins impacted biofilm formation on one or more of the substrates. Several mutants showed significant differences in hemagglutination, hydrophobicity, or fitness in the ex vivo plaque model. From the identification of redundant and unique functions in these in vitro and ex vivo systems, functional stratification among the LPXTG/A proteins is apparent.IMPORTANCE S. gordonii interactions with its environment depend on the complement of cell wall proteins. A subset of these cell wall proteins requires processing by the enzyme sortase A (SrtA). The identification of SrtA-processed proteins and their functional characterization will help the community to better understand how S. gordonii engages with its surroundings, including other microbes, integrates into the plaque community, adheres to the tooth surface, and hematogenously disseminates to cause blood-borne infections. This study identified 26 putative SrtA-processed proteins through creation of a markerless deletion mutant library. The library was subject to functional screens that were chosen to better understand key aspects of S. gordonii physiology and pathogenesis.

Red fluorescence threshold for assessing the lesion activity of early caries

PURPOSE

The aim of this study was to determine a red fluorescence threshold for differentiating active from inactive non-cavitated carious lesions.

METHODS

Using the Nyvad criteria, 30 human teeth with non-cavitated carious lesions were divided into active lesions (15 teeth) and inactive lesions (15 teeth). Using the blue light of a quantitative light-induced fluorescence-digital camera, the red fluorescence of the lesions was measured as the ΔR value. By live/dead bacterial staining, bacterial viability was calculated as the Ratio_G/G+R. The ΔR and Ratio_G/G+R of active and inactive lesions were compared. The relationship between ΔR and Ratio_G/G+R was also analyzed. The ΔR threshold was determined for the classification of lesion activity, and its validity was tested.

RESULTS

The mean ΔR of active lesions was 1.85 fold higher than that of inactive lesions (p < 0.001), and the Ratio_G/G+R of active lesions was 1.97 fold higher than that of inactive lesions (p < 0.001). There was a significant positive correlation between the ΔR and the Ratio_G/G+R in non-cavitated carious lesions (p < 0.05). The ΔR threshold for the differentiating non-cavitated carious lesions by activity status was 37.55, and the sensitivity and specificity were both 83.33 %.

CONCLUSIONS

A red fluorescence threshold for categorizing non-cavitated carious lesion activity based on microbial metabolic activity was determined. Accurate evaluation of the activity status of non-cavitated carious lesions will assist in diagnosis and treatment planning for patients with dental caries.

The distribution of cultivable oral anaerobic microbiota identified by MALDI-TOF MS in healthy subjects and in patients with periodontal disease

In this study, we aimed to identify the cultivatable oral anaerobic bacterial distribution in oral cavity by MALDI-TOF Biotyper. The bacterial distribution of three groups, including subjects with/without periodontal disease, two clusters of age (60 years as the cutoff), and before/after treatment, were investigated in this study. There were 38 participants recruited in this study, involving 18 subjects with moderate to severe periodontal-infected patients and 20 healthy controls. Total number of 126 bacterial species were identified by MALDI-TOF MS. The relative abundance of Streptococcus gordonii and Streptococcus intermedius in periodontal patients is higher than healthy controls indicating potential biomarkers for periodontal disease. Participants with periodontal disease were subdivided in to two clusters of age (60 years as the cutoff), 11 and 7 participants were age <60 years and>60 years, respectively. Meanwhile, the incidence of Streptococcus pneumoniae and Streptococcus oralis infection were higher in the subjects above 60 years old than below. Moreover, the bacterial distribution between pre-treatment and post-treatment was similar indicating that basic treatment without the ability to redistribute the microbiota. In summary, the cultivable oral anaerobic bacteria were identified by MALDI-TOF MS and the bacterial distribution shifting was shown to be associated with the progress of periodontal disease to aging and basic treatment. This study provided information for diagnosis and treatment guidelines for oral healthcare.

Roles of membrane vesicles from Streptococcus mutans for the induction of antibodies to glucosyltransferase in mucosal immunity

Glucosyltransferase (Gtf) B and GtfC from Streptococcus mutans are key enzymes for the development of biofilm-associated diseases such as dental caries. Gtfs are involved in membrane vesicles (MVs) and function in the formation of biofilms by initial colonizers such as Streptococcus mitis and Streptococcus oralis on the tooth surface. Therefore, MVs may be important virulence factors and targets for the prevention of biofilm-associated disease. To clarify how GtfB encoded by gtfB and GtfC encoded by gtfC associate with MVs and whether MVs are effective as a mucosal immunogen to induce the production of antibodies against Gtfs, MVs from S. mutans UA159 wild-type (WT), gtfB^-, gtfC^- and gtfB^-C^- were extracted from culture supernatants by ultracentrifugation and observed by scanning electron microscopy. Compared with GtfB, GtfC was mainly contained in MVs and regulated the size and aggregation of MVs, and the biofilm formation of S. mutans. The intranasal immunization of BALB/c mice with MVs plus a TLR3 agonist, poly(I-C), was performed 2 or 3 times for 5 weeks, with an interval of 2 or 3 weeks. MVs from all strains caused anti-MV IgA and IgG antibody production. In quality analysis of these antibodies, the IgA and IgG antibodies produced by immunization with MVs from WT and gtfB^- strains reacted with Gtfs in the saliva, nasal wash and serum but those produced by immunization with MVs from gtfC^- and gtfB^-C^- strains did not. S. mutans MVs mainly formed by GtfC are an intriguing immunogen for the production of anti-Gtf antibodies in mucosal immunogenicity.

Integrated hypothesis of dental caries and periodontal diseases

This review considers an integrated hypothesis of dental caries and periodontal diseases that builds on theoretical ecological principles. The backbone of the hypothesis is based on the dynamic stability stage of the oral microbiota, at which intrinsic (mainly saliva and gingival crevicular fluid) and bacterial (mainly metabolic) resilience factors maintain ecological dynamic stability, compatible with clinical health. However, loss of intrinsic resilience factors and/or prolonged changes in the availability of microbial metabolic substrates may shift the ecological balance of the microbiota into either saccharolytic (acidogenic) or amino acid-degrading/proteolytic (alkalinogenic) stages, depending on the nature of the predominant substrates, leading to clinical diseases. Therefore, to maintain and restore the dynamic stability of the oral microbiota, it is necessary to control the drivers of disease, such as salivary flow and influx of bacterial nutrients into the oral cavity. Contrary to conventional wisdom, excessive intake of fermentable carbohydrates may contribute to inflammation in periodontal tissues resulting from hyperglycaemia. An integrated hypothesis emphasizes that both dental caries and periodontal diseases originate in the dynamic stability stage and emerge in response to nutritional imbalances in the microbiota. Periodontal diseases may belong to the sugar driven inflammatory diseases, similar to diabetes, obesity, and cardiovascular diseases.

The inhibitory effects of polypyrrole on the biofilm formation of Streptococcus mutans

Streptococcus mutans primary thrives on the biofilm formation on the tooth surface in sticky biofilms and under certain conditions can lead to carious lesions on the tooth surface. To search for a new preventive material for oral biofilm-associated diseases, including dental caries, we investigated the effects of polypyrrole, which contains an electrochemical polymer and causes protonation and incorporation of anion under low pH condition, on the biofilm formation of S. mutans and other streptococci. In this study, polypyrrole was applied in biofilm formation assays with the S. mutans strains UA159 and its gtfB and gtfC double mutant (gtfBC mutant), S. sanguinis, S. mitis and S. gordonii on human saliva and bovine serum albumin-coated 96-well microtiter plates in tryptic soy broth supplemented with 0.25% sucrose. The effects of polypyrrole on biofilm formation were quantitatively and qualitatively observed. High concentrations of polypyrrole significantly inhibited the biofilm formation of S. mutans UA159 and S. sanguinis. As an inhibition mechanism, polypyrrole attached to the surface of bacterial cells, increased chains and aggregates, and incorporated proteins involving GTF-I and GTF-SI produced by S. mutans. In contrast, the biofilm formation of gtfBC mutant, S. sanguinis, S. mitis and S. gordonii was temporarily induced by the addition of low polypyrrole concentrations on human saliva-coated plate but not on the uncoated and bovine serum albumin-coated plates. Moreover, biofilm formation depended on live cells and, likewise, specific interaction between cells and binding components in saliva. However, these biofilms were easily removed by increased frequency of water washing. In this regard, the physical and electrochemical properties in polypyrrole worked effectively in the removal of streptococci biofilms. Polypyrrole may have the potential to alter the development of biofilms associated with dental diseases.

PcsB Expression Diversity Influences on Streptococcus mitis Phenotypes Associated With Host Persistence and Virulence

S. mitis is an abundant member of the commensal microbiota of the oral cavity and pharynx, which has the potential to promote systemic infections. By analyzing a collection of S. mitis strains isolated from the oral cavity at commensal states or from systemic infections (blood strains), we established that S. mitis ubiquitously express the surface immunodominant protein, PcsB (also called GbpB), required for binding to sucrose-derived exopolysaccharides (EPS). Immuno dot blot assays with anti-PcsB antibodies and RT-qPCR transcription analyses revealed strain-specific profiles of PcsB production associated with diversity in pcsB transcriptional activities. Additionally, blood strains showed significantly higher levels of PcsB expression compared to commensal isolates. Because Streptococcus mutans co-colonizes S. mitis dental biofilms, and secretes glucosyltransferases (GtfB/C/D) for the synthesis of highly insoluble EPS from sucrose, profiles of S. mitis binding to EPS, biofilm formation and evasion of the complement system were assessed in sucrose-containing BHI medium supplemented or not with filter-sterilized S. mutans culture supernatants. These analyses showed significant S. mitis binding to EPS and biofilm formation in the presence of S. mutans supernatants supplemented with sucrose, compared to BHI or BHI-sucrose medium. In addition, these phenotypes were abolished if strains were grown in culture supernatants of a gtfBCD-defective S. mutans mutant. Importantly, GtfB/C/D-associated phenotypes were enhanced in high PcsB-expressing strains, compared to low PcsB producers. Increased PcsB expression was further correlated with increased resistance to deposition of C3b/iC3b of the complement system after exposure to human serum, when strains were previously grown in the presence of S. mutans supernatants. Finally, analyses of PcsB polymorphisms and bioinformatic prediction of epitopes with significant binding to MHC class II alleles revealed that blood isolates harbor PcsB polymorphisms in its functionally conserved CHAP-domain, suggesting antigenic variation. These findings reveal important roles of PcsB in S. mitis-host interactions under commensal and pathogenic states, highlighting the need for studies to elucidate mechanisms regulating PcsB expression in this species.

DNA finger printing of S. Mutans present in the saliva of caries active children and those associated with intellectual disability - An RAPD analysis

Aim

The aim of this study is, to evaluate and compare the diversity of S. Mutans genotypes with respect to caries activity among normal children and intellectually disabled children, which would enable the clinician to plan better strategies for early caries detection, management and prevention.

Materials and methods

Genotyping of S. Mutans was done by collecting the saliva samples from 40 caries active children (20 normal and 20 children associated with intellectual disability by Rapid amplified polymorphic DNA analysis using three arbitrarily primers (P1, P2, P3). Rapid amplified polymorphic DNA (RAPD) is preferred because of its reliability, reproducibility in generating genetic fingerprints of Streptococcus isolates.

Results

Number of bacterial counts in Group I showed a mean of 111.6500 followed by the Group II with a mean of 102.6500. Therefore, the difference in the number of bacterial counts was not significant between the two groups (p < 0.001). Genotype encoding Primer 1 was present in almost 82.5% of the total population of both groups. Genotype encoding Primer 2 was present in 95% of the total population. Whereas, Genotype encoding Primer 3 was present in 20% of children associated with intellectual disability and 95% of normal children.

Interpretation and conclusion

There was no significant difference in S. Mutans count of normal caries active children to that of caries active children with intellectual disability, but, there was a significance difference in the distribution of S. Mutans genotypes in both the groups.

Potential effects of Psidium sp., Mangifera sp., Mentha sp. and its mixture (PEM) in reducing bacterial populations in biofilms, adherence and acid production of S. sanguinis and S. mutans

OBJECTIVE

Psidium sp., Mangifera sp. and Mentha sp. and its mixture (PEM) are known to have antimicrobial and anti-adherence effects.

DESIGN

Here, we have investigated these individual plant extracts and its synergistic mixture (PEM) for its anti-cariogenic effect to reduce populations of single and mixed-species of Streptococcus sanguinis and Streptococcus mutans in a planktonic or/and biofilm and their others reduced virulence. Bacterial populations in the biofilm after 24 h, hydrophobic cell surface activity to n-hexadecane and pH changes at 5 min' intervals until 90 min of incubation were recorded. Total phenolic content and bioactive compounds in the crude aqueous plant extracts were analysed. Regulatory gene expressions of S. mutans adhesins genes (gtfB, gtfC, gbpB and spaP) upon treatment with PEM were investigated in planktonic and biofilm conditions.

RESULTS

All plant extracts strongly reduced S. mutans in the biofilm compared to S. sanguinis in single and mixed-species. PEM reduced S. mutans by 84% with S. sanguinis 87% in the mixed population. Psidium sp. and PEM highly reduced cell-surface hydrophobicity of the two bacteria thus reducing adherence and biofilm formation. PEM and Mangifera sp. lowered initial pH change in the mixed populations of S. sanguinis and S. mutans. PEM downregulated the S. mutans gtfB gene expression in the single species planktonic and mixed-species biofilms.

CONCLUSIONS

The effectiveness of PEM in reducing S. mutans within the biofilm, cell-surface hydrophobicity, acid production and adhesin gene (gtfB) expression in mixed-species with S. sanguinis indicates its potential as an antibacterial agent against dental caries. This is attributed to the phenolic content in the PEM.

Effects of Complex DNA and MVs with GTF Extracted from Streptococcus mutans on the Oral Biofilm

Streptococcus mutans is one of the principal pathogens for the development of dental caries. Oral biofilms formed by S. mutans are constructed of insoluble glucan formation induced by the principal enzymes, GTF-I and GTF-SI, in sucrose-containing conditions. However, as another means of biofilm formation, extracellular DNA (eDNA) and membrane vesicles (MVs) are also contributors. To explore the roles of eDNA and MVs for biofilm formation, short and whole size pure DNAs, two types of sub-purified DNAs and MVs were extracted from S. mutans by beads destruction, treatment of proteinase K, and ultracentrifugation of culture supernatant, and applied into the biofilm formation assay using the S. mutans UA159 gtfBC mutant, which lost GTF-I and GTF-SI, on a human saliva-coated 96 well microtiter plate in sucrose-containing conditions. Sub-purified DNAs after cell lysis by beads destruction for total 90 and 180 s showed a complex form of short-size DNA with various proteins and MVs associated with GTF-I and GTF-SI, and induced significantly higher biofilm formation of the S. mutans UA159.gtfBC mutant than no sample (p < 0.05). Short-size pure DNA without proteins induced biofilm formation but whole-size pure DNA did not. Moreover, the complex form of MV associated with GTFs and short-size DNA showed significantly higher biofilm formation of initial colonizers on the human tooth surface such as Streptococcus mitis than no sample (p < 0.05). The short-size DNAs associated with MVs and GTFs are important contributors to the biofilm formation and may be one of additional targets for the prevention of oral biofilm-associated diseases.

Management of deep caries and the exposed pulp

Caries prevalence remains high throughout the world, with the burden of disease increasingly affecting older and socially disadvantaged groups in Western cultures. If left untreated, caries will advance through dentine stimulating pulpitis and eventually pulp infection and necrosis; however, if conservatively managed, pulpal recovery occurs even in deep carious lesions. Traditionally, deep caries management was destructive with nonselective (complete) removal of all carious dentine; however, the promotion of minimally invasive biologically based treatment strategies has been advocated for selective (partial) caries removal and a reduced risk of pulp exposure. Selective caries removal strategies can be one-visit as indirect pulp treatment or two-visit using a stepwise approach. Management strategies for the treatment of the cariously exposed pulp are also shifting with avoidance of pulpectomy and the re-emergence of vital pulp treatment (VPT) techniques such as partial and complete pulpotomy. These changes stem from an improved understanding of the pulp-dentine complex's defensive and reparative response to irritation, with harnessing the release of bioactive dentine matrix components and careful handling of the damaged tissue considered critical. Notably, the development of new pulp capping materials such as mineral trioxide aggregate, which although not an ideal material, has resulted in more predictable treatments from both a histological and a clinical perspective. Unfortunately, the changes in management are only supported by relatively weak evidence with case series, cohort studies and preliminary studies containing low patient numbers forming the bulk of the evidence. As a result, critical questions related to the superiority of one caries removal technique over another, the best pulp capping biomaterial or whether pulp exposure is a negative prognostic factor remain unanswered. There is an urgent need to promote minimally invasive treatment strategies in Operative Dentistry and Endodontology; however, the development of accurate diagnostic tools, evidence-based management strategies and education in management of the exposed pulp are critical in the future.

Antimicrobial, Cytotoxic, and Anti-Inflammatory Activities of Pimenta dioica and Rosmarinus officinalis Essential Oils

Essential oils (EOs) are natural products composed of a mixture of volatile and aromatic compounds extracted from different parts of plants that have shown antimicrobial activities against pathogens. In this study, EOs extracted from Pimenta dioica (Myrtaceae) and Rosmarinus officinalis (Lamiaceae) were assessed for their antimicrobial activities using a panel of pathogenic Gram-positive, Gram-negative, and fungal strains. The antimicrobial activity was measured by the minimal inhibitory concentration required for the growth inhibition of the microorganisms. The cytotoxicity of the EOs was tested ex vivo using the model of human-derived macrophage THP-1 cells. In addition, an inflammatory response was evaluated using the anti-inflammatory cytokine IL-10 and the proinflammatory cytokines IL-6 and TNF-α. Results showed that both EOs had antimicrobial activity and different pathogens were exposed to concentrations ranging between 600 and 2000 μg/mL. In addition, the EOs showed no inflammatory activity when exposed to human macrophages, but a potent anti-inflammatory activity was measured when the oil from Rosmarinus officinalis was exposed to macrophages. This study demonstrates that the use of EOs is an effective alternative for pathogenic bacterial and fungal control, alone or in combination with antibiotic therapy. Moreover, the oil extracted from Rosmarinus officinalis could be used as potent anti-inflammatory agent.

Analysis of oral bacterial communities: comparison of HOMINGS with a tree-based approach implemented in QIIME

Background: Molecular taxonomic assignments in oral microbial communities have been made using probe-matching approaches, but never compared to those obtained by more readily accepted tree-based approaches. Objective:  To compare community composition profiles obtained from a probe-matching approach (HOMINGS) to those from a closed-ended tree-based approach (QIIME using the eHOMD database). Design:  HOMINGS and QIIME were used for parallel analysis of ten mock community samples, and of 119 supragingival plaque samples from ecologically unique sites (sound tooth surfaces in healthy subjects, sound tooth surfaces in patients with primary Sjögren’s Syndrome, and carious lesions in Sjögren’s Syndrome patients). Linear discriminant analysis Effective Size (LEfSe) was used to identify discriminating taxa among the natural plaque samples. Results: Community composition profiles of all samples were congruent between the two analysis aproaches. Alpha and beta diversity of the natural plaque communities were likewise similar. Communities from pSS patients and those from individuals with normal salivary flow differed in alpha and beta diversity. Both classification approaches yielded differences in composition predicted for samples from these subject cohorts, and discriminating taxa were similar between approaches. Conclusions: A direct comparison demonstrates that HOMINGS is largely equivalent to the tree-based approach as implemented here.

Potential role for Streptococcus gordonii-derived hydrogen peroxide in heme acquisition by Porphyromonas gingivalis

Streptococcus gordonii, an accessory pathogen and early colonizer of plaque, co-aggregates with many oral species including Porphyromonas gingivalis. It causes α-hemolysis on blood agar, a process mediated by H₂ O₂ and thought to involve concomitant oxidation of hemoglobin (Hb). Porphyromonas gingivalis has a growth requirement for heme, which is acquired mainly from Hb. The paradigm for Hb heme acquisition involves the initial oxidation of oxyhemoglobin (oxyHb) to methemoglobin (metHb), followed by heme release and extraction through the actions of K-gingipain protease and/or the HmuY hemophore-like protein. The ability of S. gordonii to mediate Hb oxidation may potentially aid heme capture during co-aggregation with P. gingivalis. Hemoglobin derived from zones of S. gordonii α-hemolysis was found to be metHb. Generation of metHb from oxyHb by S. gordonii cells was inhibited by catalase, and correlated with levels of cellular H₂ O₂ production. Generation of metHb by S. gordonii occurred through the higher Hb oxidation state of ferrylhemoglobin. Heme complexation by the P. gingivalis HmuY was employed as a measure of the ease of heme capture from metHb. HmuY was able to extract iron(III)protoporphyrin IX from metHb derived from zones of S. gordonii α-hemolysis and from metHb generated by the action of S. gordonii cells on isolated oxyHb. The rate of HmuY-Fe(III)heme complex formation from S. gordonii-mediated metHb was greater than from an equivalent concentration of auto-oxidized metHb. It is concluded that S. gordonii may potentially aid heme acquisition by P. gingivalis by facilitating metHb formation in the presence of oxyHb.

Quorum Sensing Modulates the Epibiotic-Parasitic Relationship Between Actinomyces odontolyticus and Its Saccharibacteria epibiont, a Nanosynbacter lyticus Strain, TM7x

The ultra-small, obligate parasitic epibiont, TM7x, the first and only current member of the long-elusive Saccharibacteria (formerly the TM7 phylum) phylum to be cultivated, was isolated in co-culture with its bacterial host, Actinomyces odontolyticus subspecies actinosynbacter, XH001. Initial phenotypic characterization of the TM7x-associated XH001 co-culture revealed enhanced biofilm formation in the presence of TM7x compared to XH001 as monoculture. Genomic analysis and previously published transcriptomic profiling of XH001 also revealed the presence of a putative AI-2 quorum sensing (QS) operon, which was highly upregulated upon association of TM7x with XH001. This analysis revealed that the most highly induced gene in XH001 was an lsrB ortholog, which encodes a putative periplasmic binding protein for the auto inducer (AI)-2 QS signaling molecule. Further genomic analyses suggested the lsrB operon in XH001 is a putative hybrid AI-2/ribose transport operon as well as the existence of a luxS ortholog, which encodes the AI-2 synthase. In this study, the potential role of AI-2 QS in the epibiotic-parasitic relationship between XH001 and TM7x in the context of biofilm formation was investigated. A genetic system for XH001 was developed to generate lsrB and luxS gene deletion mutants in XH001. Phenotypic characterization demonstrated that deletion mutations in either lsrB or luxS did not affect XH001's growth dynamic, mono-species biofilm formation capability, nor its ability to associate with TM7x. TM7x association with XH001 induced lsrB gene expression in a luxS-dependent manner. Intriguingly, unlike wild type XH001, which displayed significantly increased biofilm formation upon establishing the epibiotic-parasitic relationship with TM7x, XH001ΔlsrB, and XH001ΔluxS mutants failed to achieve enhanced biofilm formation when associated with TM7x. In conclusion, we demonstrated a significant role for AI-2 QS in modulating dual-species biofilm formation when XH001 and TM7x establish their epibiotic-parasitic relationship.

Anti-bacterium influenced corrosion effect of antibacterial Ti-3Cu alloy in Staphylococcus aureus suspension for biomedical application

Titanium and titanium alloys have been widely used as dental and orthopedic materials. The infection and the bacterium influenced corrosion both are concerned problems. Ti-3Cu alloy exhibits strong antibacterial properties against E. coli and S. aureus. The strong antibacterial properties of Ti-3Cu provides with a potential new method to reduce the bacterium influenced corrosion. S. aureus suspension was selected to simulate a serious bacterial condition. The corrosion behavior of Ti-3Cu alloy in S. aureus suspension was investigated by an electrochemical testing and an immersion test in comparison with pure titanium. Electrochemical results showed that Ti-3Cu exhibited a much better anti-corrosion property than cp-Ti in S. aureus suspension. Surface observation demonstrated that no corrosion pit was observed on Ti-3Cu alloy after 30 days immersion in the suspension while lots of corrosion pits were found on cp-Ti. The biofilm formation on the surface was observed by scanning electronic microscopy (SEM) in different periods. It has been revealed that S. aureus could grow and gather on the surface of cp-Ti to form biofilm after 18 h immersion, but only several bacteria were found on Ti-3Cu alloy even after 24 h immersion, displaying that Ti-3Cu alloy exhibits very strong anti-adhesion properties against S. aureus. It was concluded that Ti-3Cu performs a super anti-corrosion property due to the strong anti-adhesion property, in which Ti₂Cu precipitate plays a critical role.

Comparison of initial oral microbiomes of young adults with and without cavitated dentin caries lesions using an in situ biofilm model

Dental caries is caused by acids released from bacterial biofilms. However, the in vivo formation of initial biofilms in relation to caries remains largely unexplored. The aim of this study was to compare the oral microbiome during the initial phase of bacterial colonization for individuals with (CC) and without (NC) cavitated dentin caries lesions. Bovine enamel slabs on acrylic splints were worn by the volunteers (CC: 14, NC: 13) for in situ biofilm formation (2 h, 4 h, 8 h, 1 ml saliva as reference). Sequencing of the V1/V2 regions of the 16S rRNA gene was performed (MiSeq). The relative abundances of individual operational taxonomic units (OTUs) were compared between samples from the CC group and the NC group. Random forests models were furthermore trained to separate the groups. While the overall heterogeneity did not differ substantially between CC and NC individuals, several individual OTUs were found to have significantly different relative abundances. For the 8 h samples, most of the significant OTUs showed higher relative abundances in the CC group, while the majority of significant OTUs in the saliva samples were more abundant in the NC group. Furthermore, using OTU signatures enabled a separation between both groups, with area-under-the-curve (AUC) values of ~0.8. In summary, the results suggest that initial oral biofilms provide the potential to differentiate between CC and NC individuals.

Surface properties of dental zirconia ceramics affected by ultrasonic scaling and low-temperature degradation

Zirconia (3Y-TZP) dental prostheses are widely used in clinical dentistry. However, the effect of ultrasonic scaling performed as a part of professional tooth cleaning on 3Y-TZP dental prostheses, especially in conjunction with low-temperature degradation (LTD), has not been fully investigated. The present study aimed to evaluate the influence of ultrasonic scaling and LTD on the surface properties of 3Y-TZP in relation to bacterial adhesion on the treated surface. 3Y-TZP specimens (4 × 4 × 2 mm) were polished and then subjected to autoclaving at 134°C for 100 h to induce LTD, followed by 10 rounds of ultrasonic scaling using a steel scaler tip for 1 min each. Surface roughness, crystalline structure, wettability, and hardness were analyzed by optical interferometry, X-ray diffraction analysis, contact angle measurement, and nano-indentation technique, respectively. Subsequently, bacterial adhesion onto the treated 3Y-TZP surface was evaluated using Streptococcus mitis and S. oralis. The results demonstrated that the combination of ultrasonic scaling and LTD significantly increased the Sa value (surface roughness parameter) of the polished 3Y-TZP surface from 1.6 nm to 117 nm. LTD affected the crystalline structure, causing phase transformation from the tetragonal to the monoclinic phase, and decreased both the contact angle and surface hardness. However, bacterial adhesion was not influenced by these changes in surface properties. The present study suggests that ultrasonic scaling may be acceptable for debridement of 3Y-TZP dental prostheses because it did not facilitate bacterial adhesion even in the combination with LTD, although it did cause slight roughening of the surface.

Glycan recognition at the saliva - oral microbiome interface

The mouth is a first critical interface where most potentially harmful substances or pathogens contact the host environment. Adaptive and innate immune defense mechanisms are established there to inactivate or eliminate pathogenic microbes that traverse the oral environment on the way to their target organs and tissues. Protein and glycoprotein components of saliva play a particularly important role in modulating the oral microbiota and helping with the clearance of pathogens. It has long been acknowledged that glycobiological and glycoimmunological aspects play a pivotal role in oral host-microbe, microbe-host, and microbe-microbe interactions in the mouth. In this review, we aim to delineate how glycan-mediated host defense mechanisms in the oral cavity support human health. We will describe the role of glycans attached to large molecular size salivary glycoproteins which act as a first line of primordial host defense in the human mouth. We will further discuss how glycan recognition contributes to both colonization and clearance of oral microbes.

Role of Neuraminidase-Producing Bacteria in Exposing Cryptic Carbohydrate Receptors for Streptococcus gordonii Adherence

Streptococcus gordonii is an early colonizer of the oral cavity. Although a variety of S. gordonii adherence mechanisms have been described, current dogma is that the major receptor for S. gordonii is sialic acid. However, as many bacterial species in the oral cavity produce neuraminidase that can cleave terminal sialic acid, it is unclear whether S. gordonii relies on sialic acid for adherence to oral surfaces or if this species has developed alternative binding strategies. Previous studies have examined adherence to immobilized glycoconjugates and identified binding to additional glycans, but no prior studies have defined the contribution of these different glycan structures in adherence to oral epithelial cells. We determined that the majority of S. gordonii strains tested did not rely on sialic acid for efficient adherence. In fact, adherence of some strains was significantly increased following neuraminidase treatment. Further investigation of representative strains that do not rely on sialic acid for adherence revealed binding not only to sialic acid via the serine-rich repeat protein GspB but also to β-1,4-linked galactose. Adherence to this carbohydrate occurs via an unknown adhesin distinct from those utilized by Streptococcus oralis and Streptococcus pneumoniae Demonstrating the potential biological relevance of binding to this cryptic receptor, we established that S. oralis increases S. gordonii adherence in a neuraminidase-dependent manner. These data suggest that S. gordonii has evolved to simultaneously utilize both terminal and cryptic receptors in response to the production of neuraminidase by other species in the oral environment.

Development and characterization of an oral multispecies biofilm implant flow chamber model

Peri-implant infections are the most common cause of implant failure in modern dental implantology. These are caused by the formation of biofilms on the implant surface and consist of oral commensal and pathogenic bacteria, which harm adjacent soft and hard tissues and may ultimately lead to implant loss. In order to improve the clinical situation, there has to be a better understanding of biofilm formation on abiotic surfaces. Therefore, we successfully developed a system to cultivate an oral multispecies biofilm model in a flow chamber system, optimized for the evaluation of biofilm formation on solid materials by direct microscopic investigation. The model contains four relevant oral bacterial species: Streptococcus oralis, Actinomyces naeslundii, Veillonella dispar and Porphyromonas gingivalis in ratios similar to the native situation. The reliability of the developed “Hanoverian Oral Multispecies Biofilm Implant Flow Chamber” (HOBIC) model was verified. Biofilm volume and live/dead distribution within biofilms were determined by fluorescence staining and confocal laser scanning microcopy (CLSM). The individual species distribution was analyzed using quantitative real time PCR with propidium monoazide pretreatment (PMA-qRT-PCR) and by urea-NaCl fluorescence in situ hybridization (urea-NaCl-FISH). This in vitro model may be used to analyze biofilm formation on dental implants in more detail and to develop future implant systems with improved material properties.

Differential oxidative stress tolerance of Streptococcus mutans isolates affects competition in an ecological mixed-species biofilm model

Streptococcus mutans strongly influences the development of pathogenic biofilms associated with dental caries. Our understanding of S. mutans behaviour in biofilms is based on a few well-characterized laboratory strains; however, individual isolates vary widely in genome content and virulence-associated phenotypes, such as biofilm formation and environmental stress sensitivity. Using an ecological biofilm model, we assessed the impact of co-cultivation of several S. mutans isolates with Streptococcus oralis and Actinomyces naeslundii on biofilm composition following exposure to sucrose. The laboratory reference strain S. mutans UA159 and clinical isolates Smu44 (most aciduric), Smu56 (altered biofilm formation) and Smu81 (more sensitive to oxidative stress) were used. Our data revealed S. mutans isolates varied in their ability to compete and become dominant in the biofilm after the addition of sucrose, and this difference correlated with sensitivity to H₂ O₂ produced by S. oralis. Smu81 was particularly sensitive to H₂ O₂ and could not compete with S. oralis in mixed-species biofilm, despite forming robust biofilms on its own. Thus, diminished oxidative stress tolerance in S. mutans isolates can impair their ability to compete in complex biofilms, even in the presence of sucrose, which could influence the progression of a healthy biofilm community to one capable of causing disease.

Two-component signal transduction systems in oral bacteria

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

Effect of water containing organic acids on aspiration pneumonia-causative bacteria in the biofilm on the tooth surface

Background/purpose

The tooth surface is a source of oral microbes in dentulous individuals, it is difficult for elderly people requiring nursing care to perform mechanical tooth cleaning by themselves. The objective of this study was to investigate the antimicrobial effect of water containing organic acids (WOA) made by some organic acids as food additives on chemical cleaning for elderly people on aspiration pneumonia-causative bacteria in the biofilm on the tooth surface.

Materials and methods

Ninety-six specimens made from bovine incisors were divided into four groups and incubated with one of four aspiration pneumonia-causative bacteria. Each group was further divided into six subgroups according to treatment as follows: control group (DW), chlorhexidine gluconate solution group (CHX), WOA group (WOA), ultrasonic treatment in distilled water group (DW-U), ultrasonic treatment in chlorhexidine gluconate solution group (CHX-U) or ultrasonic treatment in WOA group (WOA-U). After treatment, the levels of viable microbes in the biofilm were evaluated by quantitative adenosine triphosphate analysis and compared among the six groups.

Results

For every evaluated microbe, there were significant differences between DW and WOA, and DW and WOA-U. However, there was no significant difference among the WOA, DW-U, CHX-U and WOA-U groups. These results suggested that the antimicrobial effect of WOA on microbes attached to the tooth surface was similar to that of ultrasonic cleaning.

Conclusion

WOA has an antimicrobial effect on microbes in the biofilm on the tooth surface.

[The origin of hydrogen peroxide in oral cavity and its role in oral microecology balance]

Hydrogen peroxide, an important antimicrobial agent in oral cavity, plays a significant role in the balance of oral microecology. At the early stage of biofilm formation, about 80% of the detected initial colonizers belong to the genus Streptococcus. These oral streptococci use different oxidase to produce hydrogen peroxide. Recent studies showed that the produced hydrogen peroxide plays a critical role in modulating oral microecology. Hydrogen peroxide modulates biofilm development attributed to its growth inhibitory nature. Hydrogen peroxide production is closely associated with extracellular DNA(eDNA) release from microbe and the development of its competent cell which are critical for biofilm development and also serves as source for horizontal gene transfer. Microbe also can reduce the damage to themselves through several detoxification mechanisms. Moreover, hydrogen peroxide is also involved in the regulation of interactions between oral microorganisms and host. Taken together, hydrogen peroxide is an imperative ecological factor that contributes to the microbial equilibrium in the oral cavity. Here we will give a brief review of both the origin and the function in the oral microecology balance of hydrogen peroxide.