Collagen-binding proteins of Streptococcus mutans and related streptococci

Multilocus sequence typing and phenotypic properties of Streptococcus mutans from Thai children with different caries statuses

BACKGROUND

Streptococcus mutans is studied for its acidogenic and aciduric characteristics, notably its biofilm formation in the presence of sucrose, toward its role in the caries process. Variations in both genotype and phenotype have been reported among clinical isolates of S. mutans. This study aimed to examine genotypic and phenotypic characteristics of S. mutans obtained from Thai children with varying caries statuses.

METHODS

We determined the presence of S. mutans and caries status in 395 children aged 3-4 years. From 325 children carrying S. mutans, we selected 90 with different caries statuses-caries-free (CF; n = 30), low severity of caries (LC; n = 30), or high severity of caries (HC; n = 30). Three isolates of S. mutans were taken from each child, thus, a total of 270 isolates were obtained. Multilocus sequence typing (MLST) was used to genotype the isolates and assess their clonal relationships. The properties, including biofilm formation, collagen binding, and acid production and tolerance were also evaluated.

RESULTS

Children with carious lesions showed a higher detection rate and number of S. mutans in saliva than those without caries. S. mutans from individuals with HC status showed the lowest biofilm formation ability, while this group had the highest detection rate of collagen-binding isolates. There was no difference in acid production or tolerance by caries status. Genotyping by MLST did not reveal any clone of S. mutans specific to CF status. This result remained even when we included MLST data from the open-access PubMLST database. MLST did identify clones containing only strains from caries-affected hosts, but tests of their phenotypic properties did not reveal any differences between S. mutans from these clones and clones that were from both caries-free and caries-affected children.

CONCLUSIONS

The clonal relationships of S. mutans indicated by MLST were not associated with the status of dental caries in the host.

Post-translational modification by the Pgf glycosylation machinery modulates Streptococcus mutans OMZ175 physiology and virulence

Streptococcus mutans is commonly associated with dental caries and the ability to form biofilms is essential for its pathogenicity. We recently identified the Pgf glycosylation machinery of S. mutans, responsible for the post-translational modification of the surface-associated adhesins Cnm and WapA. Since the four-gene pgf operon (pgfS-pgfM1-pgfE-pgfM2) is part of the S. mutans core genome, we hypothesized that the scope of the Pgf system goes beyond Cnm and WapA glycosylation. In silico analyses and tunicamycin sensitivity assays suggested a functional overlap between the Pgf machinery and the rhamnose-glucose polysaccharide synthesis pathway. Phenotypic characterization of pgf mutants (ΔpgfS, ΔpgfE, ΔpgfM1, ΔpgfM2, and Δpgf) revealed that the Pgf system is important for biofilm formation, surface charge, membrane stability, and survival in human saliva. Moreover, deletion of the entire pgf operon (Δpgf strain) resulted in significantly impaired colonization in a rat oral colonization model. Using Cnm as a model, we showed that Cnm is heavily modified with N-acetyl hexosamines but it becomes heavily phosphorylated with the inactivation of the PgfS glycosyltransferase, suggesting a crosstalk between these two post-translational modification mechanisms. Our results revealed that the Pgf machinery contributes to multiple aspects of S. mutans pathobiology that may go beyond Cnm and WapA glycosylation.

The Versatility of Collagen in Pharmacology: Targeting Collagen, Targeting with Collagen

Collagen, a versatile family of proteins with 28 members and 44 genes, is pivotal in maintaining tissue integrity and function. It plays a crucial role in physiological processes like wound healing, hemostasis, and pathological conditions such as fibrosis and cancer. Collagen is a target in these processes. Direct methods for collagen modulation include enzymatic breakdown and molecular binding approaches. For instance, Clostridium histolyticum collagenase is effective in treating localized fibrosis. Polypeptides like collagen-binding domains offer promising avenues for tumor-specific immunotherapy and drug delivery. Indirect targeting of collagen involves regulating cellular processes essential for its synthesis and maturation, such as translation regulation and microRNA activity. Enzymes involved in collagen modification, such as prolyl-hydroxylases or lysyl-oxidases, are also indirect therapeutic targets. From another perspective, collagen is also a natural source of drugs. Enzymatic degradation of collagen generates bioactive fragments known as matrikines and matricryptins, which exhibit diverse pharmacological activities. Overall, collagen-derived peptides present significant therapeutic potential beyond tissue repair, offering various strategies for treating fibrosis, cancer, and genetic disorders. Continued research into specific collagen targeting and the application of collagen and its derivatives may lead to the development of novel treatments for a range of pathological conditions.

The complement system as a key modulator of the oral microbiome in health and disease

In this review, we address the interplay between the complement system and host microbiomes in health and disease, focussing on oral bacteria known to contribute to homeostasis or to promote dysbiosis associated with dental caries and periodontal diseases. Host proteins modulating complement activities in the oral environment and expression profiles of complement proteins in oral tissues were described. In addition, we highlight a sub-set of bacterial proteins involved in complement evasion and/or dysregulation previously characterized in pathogenic species (or strains), but further conserved among prototypical commensal species of the oral microbiome. Potential roles of these proteins in host-microbiome homeostasis and in the emergence of commensal strain lineages with increased virulence were also addressed. Finally, we provide examples of how commensal bacteria might exploit the complement system in competitive or cooperative interactions within the complex microbial communities of oral biofilms. These issues highlight the need for studies investigating the effects of the complement system on bacterial behaviour and competitiveness during their complex interactions within oral and extra-oral host sites.

Human PRH1, PRH2 susceptibility and resistance and Streptococcus mutans virulence phenotypes specify different microbial profiles in caries

BACKGROUND

Lifestyle- and sucrose-dependent polymicrobial ecological shifts are a primary cause of caries in populations with high caries prevalence. In populations with low prevalence, PRH1, PRH2 susceptibility and resistance phenotypes may interact with the Streptococcus mutans adhesin cariogenicity phenotype to affect caries progression, but studies are lacking on how these factors affect the microbial profile of caries.

METHODS

We analysed how the residency and infection profiles of S. mutans adhesin (SpaP A/B/C and Cnm/Cbm) phenotypes and commensal streptococci and lactobacilli influenced caries progression in a prospective case-referent sample of 452 Swedish adolescents with high (P4a), moderate (P6), and low (P1) caries PRH1, PRH2 phenotypes. Isolates of S. mutans from participants were analysed for adhesin expression and glycosylation and in vitro and in situ mechanisms related to caries activity.

FINDINGS

Among adolescents with the resistant (P1) phenotype, infection with S. mutans high-virulence phenotypes was required for caries progression. In contrast, with highly (P4a) or moderately (P6) susceptible phenotypes, caries developed from a broader polymicrobial flora that included moderately cariogenic oral commensal streptococci and lactobacilli and S. mutans phenotypes. High virulence involved unstable residency and fluctuating SpaP ABC, B-1, or Cnm expression/glycosylation phenotypes, whereas low/moderate virulence involved SpaP A phenotypes with stable residency. Adhesin phenotypes did not display changes in individual host residency but were paired within individuals and geographic regions.

INTERPRETATION

These results suggest that receptor PRH1, PRH2 susceptibility and resistance and S. mutans adhesin virulence phenotypes specify different microbial profiles in caries.

FUNDING

Swedish Research Council and funding bodies listed in the acknowledgement section.

Harboring Cnm-expressing Streptococcus mutans in the oral cavity relates to both deep and lobar cerebral microbleeds

BACKGROUND

Cerebral microbleeds (CMBs) influence long-term prognoses of stroke patients. Streptococcus mutans expressing the collagen-binding protein Cnm induces cerebrovascular inflammation, impairing blood brain barrier integrity and causing cerebral bleeding. Here, we examine the association of Cnm-positive S. mutans with CMBs.

METHODS

Acute stroke patients were selected from a single-center registry database. Oral carriage of Cnm-positive or Cnm-negative S. mutans was determined using polymerase chain reaction assays. The associations of Cnm-positive S. mutans with CMB number and specifically the presence of >10 CMBs were examined using quasi-Poisson and logistic regression models, respectively.

RESULTS

This study included 3154 stroke patients, of which 428 patients (median [interquartile range] age, 73.0 [63.0-81.0] years; 269 men [62.9%]) underwent oral bacterial examinations. In total, 326 patients harbored S. mutans. After excluding four patients without imaging data, we compared patients with Cnm-positive (n = 72) and Cnm-negative (n = 250) S. mutans. Harboring Cnm-positive S. mutans was independently associated with the presence of >10 CMBs (adjusted odds ratio 2.20 [1.18-4.10]) and higher numbers of deep and lobar CMBs (adjusted risk ratio 1.61 [1.14-2.27] for deep; 5.14 [2.78-9.51] for lobar), but not infratentorial CMBs, after adjusting for age, sex, hypertension, stroke type, National Institutes of Health Stroke Scale score, and cerebral amyloid angiopathy.

CONCLUSIONS

Harboring Cnm-positive S. mutans was independently associated with a higher number of CMBs in deep and lobar locations. Reducing Cnm-positive S. mutans in the oral cavity may serve as a novel therapeutic approach for stroke.

Antibacterial Effects of Ramulus mori Oligosaccharides against Streptococcus mutans

Ramulus mori has been widely used in traditional Chinese medicine because of its physiological activities, including antibacterial, anti-inflammatory, and antioxidant activities. Antimicrobial properties of Ramulus mori extract have been well described. However, no information is available regarding on Ramulus mori oligosaccharides (RMOS). The aim of this study was to investigate the effects of RMOS on the growth and virulence properties of the cariogenic bacterium Streptococcus mutans. The effects of RMOS on the biofilm structure and virulence gene expression of S. mutans were also evaluated, and the results were compared with the effects of commercial prebiotic galactooligosaccharides. RMOS were found to have an antibacterial effect against S. mutans, resulting in significant reductions in acid production, lactate dehydrogenase activity, adhesion, insoluble extracellular polysaccharide production, glucosyltransferase activity, and biofilm formation in a dose-dependent manner. Moreover, the biofilm structure was visibly damaged. A quantitative real-time PCR assay revealed downregulation of virulence gene-regulated acid production, polysaccharide production, adhesion, biofilm formation, and quorum sensing. These findings suggest that RMOS may be a promising natural product for the prevention of dental caries.

Targeting collagen in tumor extracellular matrix as a novel targeted strategy in cancer immunotherapy

Collagen, the most abundant protein in mammal, is widely expressed in tissues and organs, as well as tumor extracellular matrix. Tumor collagen mainly accumulates in tumor stroma or beneath tumor blood vessel endothelium, and is exposed due to the fragmentary structure of tumor blood vessels. Through the blood vessels with enhanced permeability and retention (EPR) effect, collagen-binding macromolecules could easily bind to tumor collagen and accumulate within tumor, supporting tumor collagen to be a potential tumor-specific target. Recently, numerous studies have verified that targeting collagen within tumor extracellular matrix (TEM) would enhance the accumulation and retention of immunotherapy drugs at tumor, significantly improving their anti-tumor efficacy, as well as avoiding severe adverse effects. In this review, we would summarize the known collagen-binding domains (CBD) or proteins (CBP), their mechanism and application in tumor-targeting immunotherapy, and look forward to future development.

Dental Caries a Risk Factor for Intracerebral Hemorrhage

INTRODUCTION

Streptococcus mutans is a known cause of dental caries that contains a collagen-binding protein, Cnm, and exhibits inhibition of platelet aggregation and matrix metalloproteinase-9 activation. This strain has been linked to aggravation of experimental intracerebral hemorrhage (ICH) and may be a risk factor for ICH. The purpose of this study was to test the association between dental caries and incident ICH.

METHODS

The presence of dental caries and periodontal disease was assessed in subjects from the Dental Atherosclerosis Risk in Communities (DARIC) study without prior stroke or ICH. This cohort was followed for incident ICH over a period of 10 years. Cox regression was used to compute crude and adjusted hazards ratio from the dental assessment.

RESULTS

Among 6,315 subjects, dental surface caries and/or root caries were recorded in 1,338 (27%) subjects. Of those, 7 (0.5%) had incident ICH over a period of 10 years following the visit 4 assessment. Of the remaining 4,977 subjects, 10 (0.2%) had incident ICH. Those with dental caries versus those without dental caries were slightly younger (mean age 62.0 ± 5.7 vs. 62.4 ± 5.6, p = 0.012), had a greater proportion of males (51 vs. 44%, p < 0.001), African Americans (44 vs. 10%, p < 0.001), and were hypertensive (42 vs. 31%, p < 0.001). The association between caries and ICH was significant (crude HR 2.69, 95% CI 1.02-7.06) and strengthened after adjustment for age, gender, race, education level, hypertension, and periodontal disease (adjusted HR 3.88, 95% CI 1.34-11.24).

CONCLUSION

Dental caries is a potential risk for incident ICH after caries detection. Future studies are needed to determine if treatment of dental caries can reduce the risk of ICH.

Dlt operon regulates physiological function and cariogenic virulence in Streptococcus mutans

Streptococcus mutans is one of the major cariogenic pathogens in the oral cavity. The dlt operon is responsible for the process of D-alanylation of lipoteichoic acid and is related to the virulence of S. mutans. The dlt operon contributes to the adhesion, biofilm formation, stress response, interspecies competitiveness and autolysis of S. mutans. In addition, we have summarized the possible regulatory networks of the dlt operon. This review highlights the significant role of the dlt operon in S. mutans and provides new ideas for ecological caries prevention.

Involvement of the Streptococcus mutans PgfE and GalE 4-epimerases in protein glycosylation, carbon metabolism, and cell division

Streptococcus mutans is a key pathogen associated with dental caries and is often implicated in infective endocarditis. This organism forms robust biofilms on tooth surfaces and can use collagen-binding proteins (CBPs) to efficiently colonize collagenous substrates, including dentin and heart valves. One of the best characterized CBPs of S. mutans is Cnm, which contributes to adhesion and invasion of oral epithelial and heart endothelial cells. These virulence properties were subsequently linked to post-translational modification (PTM) of the Cnm threonine-rich repeat region by the Pgf glycosylation machinery, which consists of 4 enzymes: PgfS, PgfM1, PgfE, and PgfM2. Inactivation of the S. mutans pgf genes leads to decreased collagen binding, reduced invasion of human coronary artery endothelial cells, and attenuated virulence in the Galleria mellonella invertebrate model. The present study aimed to better understand Cnm glycosylation and characterize the predicted 4-epimerase, PgfE. Using a truncated Cnm variant containing only 2 threonine-rich repeats, mass spectrometric analysis revealed extensive glycosylation with HexNAc2. Compositional analysis, complemented with lectin blotting, identified the HexNAc2 moieties as GlcNAc and GalNAc. Comparison of PgfE with the other S. mutans 4-epimerase GalE through structural modeling, nuclear magnetic resonance, and capillary electrophoresis demonstrated that GalE is a UDP-Glc-4-epimerase, while PgfE is a GlcNAc-4-epimerase. While PgfE exclusively participates in protein O-glycosylation, we found that GalE affects galactose metabolism and cell division. This study further emphasizes the importance of O-linked protein glycosylation and carbohydrate metabolism in S. mutans and identifies the PTM modifications of the key CBP, Cnm.

Moonlighting proteins [ML proteins]: The pandora's box of insidious oro-dental diseases

Oral pathogens survive in the harsh niche of the oral microbiome on account of a plethora of moonlighting [ML] proteins that can multitask in the oro-mucosal layers. ML proteins are considered as the complex protein hyperspace expressed in many oral bacterial pathogens and encompass many hypothetical and experimentally evidenced proteins that can efficiently assist in the initiation and progression of various oro-dental infections. With the propensity of multi-drug resistance and biofilm formation, unravelling the mysterious functions associated with the oral ML proteins could be essential in targeting the vital oral bacteria and their associated infections. This commentary thus throws insights onto the key clues on various ML proteins that can be considered for the development of therapeutic versatility to curtail the complications caused by various oral bacterial species.

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

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

Clinical characteristics of children and guardians possessing CBP-positive Streptococcus mutans strains: a cross-sectional study

Streptococcus mutans is a major etiological agent for dental caries. We previously demonstrated that S. mutans strains expressing collagen-binding proteins (CBPs) were related to the pathogenesis of systemic diseases. However, their acquisition and colonization remain unknown. Here, we investigated the detection rates of CBP-positive S. mutans strains in children and their guardians to clarify the background for the acquisition and colonization in children. Saliva samples were collected from children and their mothers, and detection of S. mutans and collagen-binding genes (cnm, cbm) was performed by PCR after DNA extraction. The oral status of each child was examined, and their mothers were asked to complete a questionnaire. The isolation rate of Cnm-positive S. mutans was significantly higher in mothers than in children. Notably, the possession rates of CBP-positive strains in children were significantly higher in children whose mothers had CBP-positive strains than in children whose mothers did not have these strains. Furthermore, children with CBP-positive strains had a significantly shorter breastfeeding period than children without these strains. The present results suggest that nutritional feeding habits in infancy are one of the factors involved in the acquisition and colonization of CBP-positive S. mutans strains.

Diversity in Phenotypes Associated With Host Persistence and Systemic Virulence in Streptococcus sanguinis Strains

Streptococcus sanguinis is a pioneer commensal species of dental biofilms, abundant in different oral sites and commonly associated with opportunist cardiovascular infections. In this study, we addressed intra-species functional diversity to better understand the S. sanguinis commensal and pathogenic lifestyles. Multiple phenotypes were screened in nine strains isolated from dental biofilms or from the bloodstream to identify conserved and strain-specific functions involved in biofilm formation and/or persistence in oral and cardiovascular tissues. Strain phenotypes of biofilm maturation were independent of biofilm initiation phenotypes, and significantly influenced by human saliva and by aggregation mediated by sucrose-derived exopolysaccharides (EPS). The production of H2O2 was conserved in most strains, and consistent with variations in extracellular DNA (eDNA) production observed in few strains. The diversity in complement C3b deposition correlated with the rates of opsonophagocytosis by human PMN and was influenced by culture medium and sucrose-derived EPS in a strain-specific fashion. Differences in C3b deposition correlated with strain binding to recognition proteins of the classical pathway, C1q and serum amyloid protein (SAP). Importantly, differences in strain invasiveness into primary human coronary artery endothelial cells (HCAEC) were significantly associated with C3b binding, and in a lesser extent, with binding to host glycoproteins (such as fibrinogen, plasminogen, fibronectin, and collagen). Thus, by identifying conserved and strain-specific phenotypes involved in host persistence and systemic virulence, this study indicates potential new functions involved in systemic virulence and highlights the need of including a wider panel of strains in molecular studies to understand S. sanguinis biology.

Evaluation of the collagen-binding properties and virulence of killed Streptococcus mutans in a silkworm model

Streptococcus mutans, a major pathogen of dental caries, is also known as a causative agent of cardiovascular disease. A 120 kDa collagen-binding protein (Cnm) of S. mutans is an important contributor to the pathogenicity of cardiovascular disease. Although dead bacteria have been detected in cardiovascular specimens by molecular biological methods, the pathogenicity of the bacteria remains unknown. Here, we analyzed the pathogenicity of killed S. mutans by focusing on collagen-binding ability and the effects on silkworms. In live S. mutans, Cnm-positive S. mutans had high collagen-binding activity, while Cnm-negative S. mutans had no such activity. After treatment with killed Cnm-positive S. mutans, amoxicillin-treated bacteria still had collagen-binding ability, while lysozyme-treated bacteria lost this ability. When live and amoxicillin-treated S. mutans strains were administered to silkworms, the survival rates of the silkworms were reduced; this reduction was more pronounced in Cnm-positive S. mutans infection than in Cnm-negative S. mutans infection. However, the administration of any of the lysozyme-treated bacteria did not reduce the survival rate of the silkworms. These results suggest that amoxicillin-killed Cnm-positive S. mutans strains maintain collagen-binding properties and pathogenicity in the silkworm model, and are possibly associated with pathogenicity in cardiovascular diseases.

VicRK and CovR polymorphisms in Streptococcus mutans strains associated with cardiovascular infections

Introduction. Streptococcus mutans, a common species of the oral microbiome, expresses virulence genes promoting cariogenic dental biofilms, persistence in the bloodstream and cardiovascular infections.Gap statement. Virulence gene expression is variable among S. mutans strains and controlled by the transcription regulatory systems VicRK and CovR.Aim. This study investigates polymorphisms in the vicRK and covR loci in S. mutans strains isolated from the oral cavity or from the bloodstream, which were shown to differ in expression of covR, vicRK and downstream genes.Methodology. The transcriptional activities of covR, vicR and vicK were compared by RT-qPCR between blood and oral strains after exposure to human serum. PCR-amplified promoter and/or coding regions of covR and vicRK of 18 strains (11 oral and 7 blood) were sequenced and compared to the reference strain UA159.Results. Serum exposure significantly reduced covR and vicR/K transcript levels in most strains (P<0.05), but reductions were higher in oral than in blood strains. Single-nucleotide polymorphisms (SNPs) were detected in covR regulatory and coding regions, but SNPs affecting the CovR effector domain were only present in two blood strains. Although vicR was highly conserved, vicK showed several SNPs, and SNPs affecting VicK regions important for autokinase activity were found in three blood strains.Conclusions. This study reveals transcriptional and structural diversity in covR and vicR/K, and identifies polymorphisms of functional relevance in blood strains, indicating that covR and vicRK might be important loci for S. mutans adaptation to host selective pressures associated with virulence diversity.

KATSUMATA et al.Comprehensive characterization of sortase A-dependent surface proteins in Streptococcus mutansComprehensive characterization of sortase A-dependent surface proteins in Streptococcus mutans

Streptococcus mutans, a cariogenic pathogen, adheres to the tooth surface and forms a biofilm. Bacterial cell surface proteins are associated with adherence to substrates. Sortase A (SrtA) mediates the localization of proteins with an LPXTG motif-containing proteins to the cell surface by covalent binding to peptidoglycan. In S. mutans UA159, 6 SrtA-dependent proteins, SpaP, WapA, WapE, DexA, FruA, and GbpC, were identified. Although some of these proteins were characterized, a comprehensive analysis of the 6 proteins has not been reported. In this study, we constructed mutants deficient in each of these proteins and the SrtA-deficient mutant. The SrtA-deficient mutant showed drastically decreased binding to salivary components, biofilm formation, bacterial coaggregation activity, hydrophobicity, and cellular matrix binding (collagen type I, fibronectin, and laminin). The SpaP-deficient mutant showed significantly reduced binding to salivary components and partially increased coaggregation with Porphyromonas gingivalis, and decreased hydrophobicity, and collagen binding. The WapA-deficient mutant showed slightly decreased coaggregation with Fusobacterium nucleatum. Although the SrtA-deficient mutant showed drastically altered phenotypes, all SrtA-dependent protein-deficient mutants, except the SpaP-deficient mutant, did not show considerable alterations in binding to salivary components. These results indicate that the 6 proteins may coordinately contribute to these activities. In addition, using genomic data of 125 S. mutans strains, we compared the amino acid sequences of each surface protein and found many variations among strains, which may affect the phenotype of cell surface proteins in S. mutans. This article is protected by copyright. All rights reserved.

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

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

Amyloid Aggregation of Streptococcus mutans Cnm Influences Its Collagen-Binding Activity

The cnm gene, coding for the glycosylated collagen- and laminin-binding surface adhesin Cnm, is found in the genomes of approximately 20% of Streptococcus mutans clinical isolates and is associated with systemic infections and increased caries risk. Other surface-associated collagen-binding proteins of S. mutans, such as P1 and WapA, have been demonstrated to form an amyloid quaternary structure with functional implications within biofilms. In silico analysis predicted that the β-sheet-rich N-terminal collagen-binding domain (CBD) of Cnm has a propensity for amyloid aggregation, whereas the threonine-rich C-terminal domain was predicted to be disorganized. In this study, thioflavin-T fluorescence and electron microscopy were used to show that Cnm forms amyloids in either its native glycosylated or recombinant nonglycosylated form and that the CBD of Cnm is the main amyloidogenic unit of Cnm. We then performed a series of in vitro, ex vivo, and in vivo assays to characterize the amylogenic properties of Cnm. In addition, Congo red birefringence indicated that Cnm is a major amyloidogenic protein of S. mutans biofilms. Competitive binding assays using collagen-coated microtiter plates and dental roots, a substrate rich in collagen, revealed that Cnm monomers inhibit S. mutans binding to collagenous substrates, whereas Cnm amyloid aggregates lose this property. Thus, while Cnm contributes to recognition and initial binding of S. mutans to collagen-rich surfaces, amyloid formation by Cnm might act as a negative regulatory mechanism to modulate collagen-binding activity within S. mutans biofilms and warrants further investigation. IMPORTANCE Streptococcus mutans is a keystone pathogen that promotes caries by acidifying the dental biofilm milieu. The collagen- and laminin-binding glycoprotein Cnm is a virulence factor of S. mutans. Expression of Cnm by S. mutans is hypothesized to contribute to niche expansion, allowing colonization of multiple sites in the body, including collagen-rich surfaces such as dentin and heart valves. Here, we suggest that Cnm function might be modulated by its aggregation status. As a monomer, its primary function is to promote attachment to collagenous substrates via its collagen-binding domain (CBD). However, in later stages of biofilm maturation, the same CBD of Cnm could self-assemble into amyloid fibrils, losing the ability to bind to collagen and likely becoming a component of the biofilm matrix. Our findings shed light on the role of functional amyloids in S. mutans pathobiology and ecology.

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.

Detection of Streptococcus mutans in symptomatic and asymptomatic infected root canals

OBJECTIVES

To investigate the presence of Streptococcus mutans in root canals of symptomatic necrotic teeth (SNT) and their associated acute apical abscesses (AAA) and in the root canals of asymptomatic necrotic teeth (ANT). It also aimed to investigate the presence of the cnm and cbm genes in specimens that harbored S. mutans.

MATERIALS AND METHODS

DNA was extracted from samples collected from 10 patients presenting pulpal necrosis associated with radiographic evidence of apical periodontitis (ANT) and from 10 patients in need of endodontic therapy due to the presence of pulpal necrosis (SNT) and AAA. The control group consisted of 10 patients with teeth with normal vital pulp and requiring endodontic treatment for prosthetic reasons. The presence of S. mutans was detected by quantitative real-time-PCR (qPCR) using species-specific primers. Samples harboring S. mutans were further evaluated for the presence of CBP genes by qPCR as well.

RESULTS

All studied sites showed a high prevalence of S. mutans, except the control group. Specifically, 60% of ANT and 70% of AAA/SNT paired samples were positive for S. mutans. The cnm gene was detected positive for S. mutans only in ANT samples (66.6%). The cbm gene was not detected in any of the investigated sites.

CONCLUSIONS

S. mutans was found in high prevalence in both asymptomatic and symptomatic endodontic infections, including in abscesses, but it was not detected in the root canals of teeth with normal vital pulp. Interestingly, cnm+ S. mutans was only detected in asymptomatic/chronic primary endodontic infections associated with apical lesion. Therefore, it appears that cnm, and possibly other CBPs, may play an underestimated role in chronic endodontic infections.

CLINICAL RELEVANCE

A high prevalence of Streptococcus mutans cnm+ gene was detected only in asymptomatic primary endodontic infections associated with apical lesion. Therefore, it appears that this collagen-binding protein gene plays an underestimated role in asymptomatic/chronic endodontic infections.

In vitro Study of the Role of Human Neutrophil Enzymes on Root Caries Progression

The role of the host immune system in caries progression is mainly speculative, and it is believed that it entails the enzymatic degradation of the dentin organic matrix. The aim of this study was to evaluate the proteolytic effect of human neutrophil enzymes on root caries progression. For this, specimens of bovine root dentin were divided into 4 groups (n = 30): caries (C), caries + neutrophils (C + N), no caries (Control), and no caries + neutrophils (Control + N). Streptococcus mutans biofilm (105 CFU/mL) was grown on the root surface to artificially induce root carious lesions (C and C + N groups). Specimens were then exposed to neutrophils (5 × 106 cells/mL) for 48 h (C + N and Control + N groups). Caries development and neutrophil exposures were repeated a 2nd and 3rd time. Caries depth (CD) and dentin demineralization (DD) were assessed by infiltration of rhodamine B using fluorescence microscopy. Collagen fibril ultrastructure was characterized under a polarized microscope with Picrosirius red staining. There were no significant differences (p > 0.05) in CD and DD between the C and C + N groups for 1, 2, and 3 caries-neutrophil exposures. Immature collagen was significantly less present in the carious groups (C, p = 0.003; C + N, p = 0.01) than in the noncarious groups in the most superficial 200 µm. We thus concluded that human neutrophil enzymes did not influence short-term root caries progression, and immature collagen fibrils were more susceptible to degradation during S. mutans-induced root caries progression.

Collagen Binding Proteins of Gram-Positive Pathogens

Collagens are the primary structural components of mammalian extracellular matrices. In addition, collagens regulate tissue development, regeneration and host defense through interaction with specific cellular receptors. Their unique triple helix structure, which requires a glycine residue every third amino acid, is the defining structural feature of collagens. There are 28 genetically distinct collagens in humans. In addition, several other unrelated human proteins contain a collagen domain. Gram-positive bacteria of the genera Staphylococcus, Streptococcus, Enterococcus, and Bacillus express cell surface proteins that bind to collagen. These proteins of Gram-positive pathogens are modular proteins that can be classified into different structural families. This review will focus on the different structural families of collagen binding proteins of Gram-positive pathogen. We will describe how these proteins interact with the triple helix in collagens and other host proteins containing a collagenous domain and discuss how these interactions can contribute to the pathogenic processes.

Staphylococcus aureus Interferes with Streptococci Spatial Distribution and with Protein Expression of Species within a Polymicrobial Oral Biofilm

We asked whether transient Staphylococcus aureus in the oral environment synergistically interacts with orally associated bacterial species such as Actinomyces oris, Candida albicans, Fusobacterium nucleatum, Streptococcus oralis, Streptococcus mutans, and Veillonella dispar (six-species control biofilm 6S). For this purpose, four modified biofilms with seven species that contain either the wild type strain of the S. aureus genotype (USA300-MRSA WT), its isogenic mutant with MSCRAMM deficiency (USA300-MRSA ΔMSCRAMM), a methicillin-sensitive S. aureus (ST72-MSSA-) or a methicillin-resistant S. aureus (USA800-MRSA) grown on hydroxyapatite disks were examined. Culture analyses, confocal-laser-scanning microscopy and proteome analyses were performed. S. aureus strains affected the amount of supragingival biofilm-associated species differently. The deletion of MSCRAMM genes disrupted the growth of S. aureus and the distribution of S. mutans and S. oralis within the biofilms. In addition, S. aureus caused shifts in the number of detectable proteins of other species in the 6S biofilm. S. aureus (USA300-MRSA WT), aggregated together with early colonizers such as Actinomyces and streptococci, influenced the number of secondary colonizers such as Fusobacterium nucleatum and was involved in structuring the biofilm architecture that triggered the change from a homeostatic biofilm to a dysbiotic biofilm to the development of oral diseases.

Phenotypic and Genotypic Characterization of Streptococcus mutans Strains Isolated from Endodontic Infections

Streptococcus mutans plays an important role in caries etiology and eventually in systemic infections. However, it is often found in infected root canals, but the pathophysiological characteristics of strains residing in this site are largely unknown. Here, we characterized strains of S. mutans isolated from root canals of primary (PI) and secondary/persistent (SI) endodontic infections in relation to serotype and genotype; presence of genes coding for collagen binding proteins (CBPs); collagen binding activity and biofilm formation capacity; ability to withstand environmental stresses; systemic virulence in Galleria mellonella; and invasion of human coronary artery endothelial cells and human dental pupal fibroblasts. Samples from 10 patients with PI and 10 patients with SI were collected, and a total of 14 S. mutans isolates, belonging to 3 genotypes, were obtained. Of these, 13 were serotype c, and 1 was serotype k. When compared with the reference strains, the clinical isolates were hypersensitive to hydrogen peroxide. Remarkably, all 14 strains harbored and expressed the CBP-encoding gene cbm, showing increased binding to collagen, enhanced systemic virulence in G. mellonella, and ability to invade human coronary artery endothelial cells and human dental pupal fibroblasts when compared with CBP-negative strains. Whole genome sequence analysis of PI and SI isolates revealed that these strains are phylogenetically related but genetically distinct from each other. Our findings highlight the importance of CBPs in facilitating colonization and persistence of S. mutans in collagenous substrates such as root canals and their potential role in the pathogenesis of endodontic infections.

PepO is a target of the two-component systems VicRK and CovR required for systemic virulence of Streptococcus mutans

Streptococcus mutans, a cariogenic species, is often associated with cardiovascular infections. Systemic virulence of specific S. mutans serotypes has been associated with the expression of the collagen- and laminin-binding protein Cnm, which is transcriptionally regulated by VicRK and CovR. In this study, we characterized a VicRK- and CovR-regulated gene, pepO, coding for a conserved endopeptidase. Transcriptional and protein analyses revealed that pepO is highly expressed in S. mutans strains resistant to complement immunity (blood isolates) compared to oral isolates. Gel mobility assay, transcriptional, and Western blot analyses revealed that pepO is repressed by VicR and induced by CovR. Deletion of pepO in the Cnm+ strain OMZ175 (OMZpepO) or in the Cnm- UA159 (UApepO) led to an increased susceptibility to C3b deposition, and to low binding to complement proteins C1q and C4BP. Additionally, pepO mutants showed diminished ex vivo survival in human blood and impaired capacity to kill G. mellonella larvae. Inactivation of cnm in OMZ175 (OMZcnm) resulted in increased resistance to C3b deposition and unaltered blood survival, although both pepO and cnm mutants displayed attenuated virulence in G. mellonella. Unlike OMZcnm, OMZpepO could invade HCAEC endothelial cells. Supporting these phenotypes, recombinant proteins rPepO and rCnmA showed specific profiles of binding to C1q, C4BP, and to other plasma (plasminogen, fibronectin) and extracellular matrix proteins (type I collagen, laminin). Therefore this study identifies a novel VicRK/CovR-target required for immune evasion and host persistence, pepO, expanding the roles of VicRK and CovR in regulating S. mutans virulence.

Bioadhesion in the oral cavity and approaches for biofilm management by surface modifications

BACKGROUND

All soft and solid surface structures in the oral cavity are covered by the acquired pellicle followed by bacterial colonization. This applies for natural structures as well as for restorative or prosthetic materials; the adherent bacterial biofilm is associated among others with the development of caries, periodontal diseases, peri-implantitis, or denture-associated stomatitis. Accordingly, there is a considerable demand for novel materials and coatings that limit and modulate bacterial attachment and/or propagation of microorganisms.

OBJECTIVES AND FINDINGS

The present paper depicts the current knowledge on the impact of different physicochemical surface characteristics on bioadsorption in the oral cavity. Furthermore, it was carved out which strategies were developed in dental research and general surface science to inhibit bacterial colonization and to delay biofilm formation by low-fouling or "easy-to-clean" surfaces. These include the modulation of physicochemical properties such as periodic topographies, roughness, surface free energy, or hardness. In recent years, a large emphasis was laid on micro- and nanostructured surfaces and on liquid repellent superhydrophic as well as superhydrophilic interfaces. Materials incorporating mobile or bound nanoparticles promoting bacteriostatic or bacteriotoxic properties were also used. Recently, chemically textured interfaces gained increasing interest and could represent promising solutions for innovative antibioadhesion interfaces. Due to the unique conditions in the oral cavity, mainly in vivo or in situ studies were considered in the review.

CONCLUSION

Despite many promising approaches for modulation of biofilm formation in the oral cavity, the ubiquitous phenomenon of bioadsorption and adhesion pellicle formation in the challenging oral milieu masks surface properties and therewith hampers low-fouling strategies.

CLINICAL RELEVANCE

Improved dental materials and surface coatings with easy-to-clean properties have the potential to improve oral health, but extensive and systematic research is required in this field to develop biocompatible and effective substances.

Lactobacillus Cell Surface Proteins Involved in Interaction with Mucus and Extracellular Matrix Components

The gut microbiota is a complex microbial ecosystem where bacteria, through mutual interactions, cooperate in maintaining of wellbeing and health. Lactobacilli are among the most important constituents of human and animal intestinal microbiota and include many probiotic strains. Their presence ensures protection from invasion of pathogens, as well as stimulation of the immune system and protection of the intestinal flora, often exerted through the ability to interact with mucus and extracellular matrix components. The main factors responsible for mediating adhesion of pathogens and commensals to the gut are cell surface proteins that recognize host targets, as mucus layer and extracellular matrix proteins. In the last years, several adhesins have been reported to be involved in lactobacilli–host interaction often miming the same mechanism used by pathogens.

Functional Analysis of the Collagen Binding Proteins of Streptococcus parasanguinis FW213

Streptococcus parasanguinis is a dominant isolate of dental plaque and an opportunistic pathogen associated with subacute endocarditis. As the expression of collagen binding proteins (CBPs) could promote the establishment of S. parasanguinis in the host, the functions of three putative CBP-encoding loci, Spaf_0420, Spaf_1570, and Spaf_1573, were analyzed using isogenic mutant strains. It was revealed that S. parasanguinis FW213 bound effectively to fibronectin and type I collagen, but the strain's affinity for laminin and type IV collagen was quite low. By using various deletion derivatives, it was found that these three loci mediated the binding of S. parasanguinis to multiple extracellular matrix molecules, with type I collagen as the common substrate. Derivative strains with a deletion in any of the three loci expressed reduced binding to trypsin-treated swine heart valves. The deletion of these loci also reduced the viable count of S. parasanguinis bacteria within macrophages, especially the loss of Spaf_0420, but only strains with deletions in Spaf_0420 and Spaf_1570 expressed reduced virulence in the Galleria mellonella larva model. The deletion of Spaf_1570 and Spaf_1573 affected mainly the structure, but not the overall mass, of biofilm cultures in a flow cell system. Thus, CBPs are likely to be more critical for the initial colonization of S. parasanguinis on host tissues during the development of endocarditis.IMPORTANCE Bacteria generally can utilize multiple adhesins to establish themselves in the host. We found that Streptococcus parasanguinis, a dominant oral commensal and an opportunistic pathogen for subacute endocarditis, possesses at least three collagen-binding proteins that enable S. parasanguinis to successfully colonize damaged heart tissues and escape innate immune clearance. The binding specificities of these three proteins for extracellular matrix molecules differ, although all three proteins participate in biofilm formation by S. parasanguinis The "multiligand for multisubstrate" feature of these adhesins may explain the high adaptability of this microbe to different tissue sites.

Modulatory Effect of Glycated Collagen on Oral Streptococcal Nanoadhesion

Biofilm-mediated oral diseases such as dental caries and periodontal disease remain highly prevalent in populations worldwide. Biofilm formation initiates with the attachment of primary colonizers onto surfaces, and in the context of caries, the adhesion of oral streptococci to dentinal collagen is crucial for biofilm progression. It is known that dentinal collagen suffers from glucose-associated crosslinking as a function of aging or disease; however, the effect of collagen crosslinking on the early adhesion and subsequent biofilm formation of relevant oral streptococci remains unknown. Therefore, the aim of this work was to determine the impact of collagen glycation on the initial adhesion of primary colonizers such as Streptococcus mutans UA159 and Streptococcus sanguinis SK 36, as well as its effect on the early stages of streptococcal biofilm formation in vitro. Type I collagen matrices were crosslinked with either glucose or methylglyoxal. Atomic force microscopy nanocharacterization revealed morphologic and mechanical changes within the collagen matrix as a function of crosslinking, such as a significantly increased elastic modulus in crosslinked fibrils. Increased nanoadhesion forces were observed for S. mutans on crosslinked collagen surfaces as compared with the control, and retraction curves obtained for both streptococcal strains demonstrated nanoscale unbinding behavior consistent with bacterial adhesin-substrate coupling. Overall, glucose-crosslinked substrates specifically promoted the initial adhesion, biofilm formation, and insoluble extracellular polysaccharide production of S. mutans, while methylglyoxal treatment reduced biofilm formation for both strains. Changes in the adhesion behavior and biofilm formation of oral streptococci as a function of collagen glycation could help explain the biofilm dysbiosis seen in older people and patients with diabetes. Further studies are necessary to determine the influence of collagen crosslinking on the balance between acidogenic and nonacidogenic streptococci to aid in the development of novel preventive and therapeutic treatment against dental caries in these patients.

Effect of Rubusoside, a Natural Sucrose Substitute, on Streptococcus mutans Biofilm Cariogenic Potential and Virulence Gene Expression In Vitro

Dental caries is a biofilm-mediated disease in which Streptococcus mutans is the main pathogenic microorganism, and its incidence is closely related to sucrose. Rubusoside is a natural nonnutritive sweetener isolated from Rubus suavissimus S. Lee. This study was designed to determine the effect of this sucrose substitute on the cariogenic properties and virulence gene expression of S. mutans biofilms. S. mutans was exposed to brain heart infusion (BHI) medium (as a control), 1% sucrose-supplemented medium, 1% rubusoside-supplemented medium, and 1% xylitol-supplemented medium. The growth curve of the biofilm was monitored by crystal violet staining, and the pH was measured every 24 h. After 5 days, the biofilms formed on the glass coverslips were recovered to determine the biomass (dry weight and total amount of soluble proteins), numbers of CFU, and amounts of intra- and extracellular polysaccharides. Biofilm structural imaging was performed using a scanning electron microscope (SEM). Virulence gene expression (gtfB, gtfC, gtfD, ftf, spaP, gbpB, ldh, atpF, vicR, and comD) was determined by reverse transcription-quantitative PCR. Growth in rubusoside resulted in lower levels of acid production than observed during growth in sucrose, xylitol, and the control, while it also reduced the level of biofilm accumulation and bacterial viability and even reduced the level of production of extracellular polysaccharides. By SEM, the levels of biofilm formation and extracellular matrix during growth in rubusoside were lower than these levels during growth in sucrose and xylitol. From the perspective of virulence genes, growth in rubusoside and xylitol significantly inhibited the expression of virulence genes compared with their levels of expression after growth in sucrose. Among these genes, gtfB, gtfC, gbpB, ldh, and comD downregulation was found with growth in rubusoside compared with their expression with growth in xylitol. Therefore, rubusoside appears to be less potentially cariogenic than sucrose and xylitol and may become an effective sucrose substitute for caries prevention. Further studies are needed to deepen these findings.IMPORTANCE Dental caries is a major public health challenge and places heavy biological, social, and financial burdens on individuals and health care systems. To palliate the deleterious effect of sucrose on the virulence factors of S. mutans, massive commercial efforts have been oriented toward developing products that may act as sucrose substitutes. Rubusoside, a natural sucrose substitute, is a plant extract with a high level of sweetness. Although some studies have shown that rubusoside does not produce acids or inhibit the growth of S. mutans, little attention has been paid to its effect on dental biofilm and the underlying mechanisms. Our study focuses on the effect of rubusoside on the formation and structure of biofilms and the expression of virulence genes. The results confirm that rubusoside can inhibit accumulation, bacterial viability, polysaccharide production by the biofilm, and related gene expression. These results provide further insight into the cariogenicity of S. mutans biofilms and demonstrate a new perspective for studying the impact of sucrose substitutes on caries.

Clinical Trials with Herbal Products for the Prevention of Dental Caries and Their Quality: A Scoping Study

It is currently recognized that an injudicious strategy about caries in the last decades has been not only focusing of research mostly in children, but also the narrow focusing on fluoride, because despite sufficient availability of fluoride in water and oral healthcare products, caries levels escalate steadily as people get older and caries remain a main public health issue to be settled. In the last two decades the scientific community intensified efforts of exploring other products for caries prevention, herbal products being one of these approaches. Preliminary evidence indicated that clinical trials for caries prevention with herbal products are heterogeneous in design, quality and products evaluated, we therefore performed a scoping review intended to explore the main characteristics of such clinical trials. From an initial collection of 1986 unique papers from different literature databases, 56 articles satisfied the inclusion and exclusion criteria. The species investigated, dosage forms, study designs, duration of intervention, controls, endpoints, quality of reporting, and risk of bias are discussed. Of the trials reviewed here, 85.71% reported positive results but given the methodological flaws and biases affecting them, it is difficult to conclude on the efficacy of those products based on the studies published thus far.

Label-Free Pathogen Detection Based on Yttrium-Doped Carbon Nanoparticles up to Single-Cell Resolution

The capability to detect bacteria at a low cell density is critical to prevent the delay in therapeutic intervention and to avoid the emergence of antibiotic-resistant species. Till date, significant advancement has been made to develop a sensing platform for rapid and reliable bacterial detection. However, critical requirements, that is, limit of detection, fast time of response, ultrasensitivity with high reproducibility, and the ability to distinguish between bacterial strains are yet to be met within a single sensing platform. In this contribution, we present a novel label-free sensor based on pH-sensitive fluorescent yttrium-doped carbon nanoparticles (YCNPs) embedded in agarose that can rapidly and accurately detect and discriminate pathogens in real time. The developed sensor matrix presented pH-triggered aggregation-induced emission quenching of YCNPs in a wide pH range. When the pH decreased from 10.0 to 4.0, the fluorescence of the matrix decreased linearly (R² = 0.9229). The sensor 's high sensitivity in a physiologically relevant pH range enables the monitoring of the presence of live pathogens to single-cell resolution. In addition, the 3D matrix sensor showed low cytotoxicity and long stability (>30 days). Besides, the YCNP platform is stable for several hours (5 h) in a complex medium and does not alter the bacterial activities, allowing real-time monitoring of bacterial growth with a small sample volume (100 μL) and rapid response time (25 min). Furthermore, using machine learning-assisted tools, different bacterial strains with various cell densities were discriminated with an accuracy of almost 100%. Moreover, blends of pathogens and a real-world sample can also be identified accurately, thus enabling the sensor to provide fast and reliable pathogen information for clinical decisions and allowing continuous monitoring of infectious disease trends.

The Pathogenic Factors from Oral Streptococci for Systemic Diseases

The oral cavity is suggested as the reservoir of bacterial infection, and the oral and pharyngeal biofilms formed by oral bacterial flora, which is comprised of over 700 microbial species, have been found to be associated with systemic conditions. Almost all oral microorganisms are non-pathogenic opportunistic commensals to maintain oral health condition and defend against pathogenic microorganisms. However, oral Streptococci, the first microorganisms to colonize oral surfaces and the dominant microorganisms in the human mouth, has recently gained attention as the pathogens of various systemic diseases, such as infective endocarditis, purulent infections, brain hemorrhage, intestinal inflammation, and autoimmune diseases, as well as bacteremia. As pathogenic factors from oral Streptococci, extracellular polymeric substances, toxins, proteins and nucleic acids as well as vesicles, which secrete these components outside of bacterial cells in biofilm, have been reported. Therefore, it is necessary to consider that the relevance of these pathogenic factors to systemic diseases and also vaccine candidates to protect infectious diseases caused by Streptococci. This review article focuses on the mechanistic links among pathogenic factors from oral Streptococci, inflammation, and systemic diseases to provide the current understanding of oral biofilm infections based on biofilm and widespread systemic diseases.

The MSCRAMM Family of Cell-Wall-Anchored Surface Proteins of Gram-Positive Cocci

The microbial surface components recognizing adhesive matrix molecules (MSCRAMMs) are a family of proteins that are defined by the presence of two adjacent IgG-like folded subdomains. These promote binding to ligands by mechanisms that involve major conformational changes exemplified by the binding to fibrinogen by the 'dock-lock-latch' mechanism or to collagen by the 'collagen hug'. Clumping factors A and B are two such MSCRAMMs that have several important roles in the pathogenesis of Staphylococcus aureus infections. MSCRAMM architecture, ligand binding, and roles in infection and colonization are examined with a focus on recent developments with clumping factors.

Pathogenic mechanisms of cariogenic Propionibacterium acidifaciens

OBJECTIVE

Dental caries is one of the most common infectious diseases in humans. Older adults retain more teeth than did earlier generations and thus are at high risk of root caries. The root surface is covered by cementum, which facilitates the spread of caries lesions into dentinal tissues. Propionibacterium acidifaciens has been detected in dentinal caries lesions; however, the pathogenetic mechanisms are not known. The purpose of this study was to investigate the pathogenic mechanisms of cariogenic P. acidifaciens.

METHODS

Saliva-induced aggregation of P. acidifaciens cells and adherence of the organism to saliva-coated hydroxyapatite were examined. Coaggregation of P. acidifaciens with other bacterial cells and binding of the organism to collagen were examined. Effect of Streptococcus mutans on the biofilm formation by P. acidifaciens was also examined. In addition, the effects of acids on the growth of P. acidifaciens were evaluated.

RESULTS

P. acidifaciens exhibited strong binding to collagen but weak or moderate interaction with salivary proteins. P. acidifaciens showed weak coaggregation with streptococcal strains and Fusobacerium nucleatum. Biofilm formation by P. acidifaciens was inhibited by S. mutans. Moreover, P. acidifaciens tolerated to self-produced acids up to threshold concentrations.

CONCLUSIONS

The results suggest that P. acidifaciens can bind to and survive inside dentinal tissue, and its acid production at low pH condition is involved in the development of dentinal caries.

Streptococcus mutans serotypes and collagen-binding proteins Cnm/Cbm in children with caries analysed by PCR

Streptococcus mutans, a primary bacterium associated with dental caries, has four known clinical serotypes (c, e, fand k). Certain serotypes, the presence of multiple serotypes and strains with collagen-binding proteins (CBP, Cnm and Cbm) have been linked with systemic disease. Evaluation of S mutans serotype distribution and caries association is needed in the United States. The purpose of this study was to evaluate the prevalence of S mutans serotypes from two cohorts of African-American children in rural Alabama using three sample types (saliva, plaque and individual S mutans isolates) by PCR detection for association with caries. Detection of CBP was also performed by PCR. In total, 129 children were evaluated and overall prevalence of serotypes were: serotype c(98%), e(26%), f(7%) and k(52%). Serotype c was statistically associated with higher caries scores in older children (P < 0.001) and serotype k was statistically more likely in females (P = 0.004). Fourteen per cent of children had CBP. Thirteen S mutans isolates from five children tested positive for both CBP. This study is the first to report on the prevalence of S mutans serotypes in a US population using the PCR-based approach. The frequency of serotype k in this study is the highest reported in any population, illustrating the need for further study to determine the prevalence of this clinically relevant serotype in the US. This is the first study to report S mutans isolates with both Cnm and Cbm in the same strain, and further analysis is needed to determine the clinical significance of these strains.

Astilbin Inhibits the Activity of Sortase A from Streptococcus mutans

Streptococcus mutans (S. mutans) is the primary etiological agent of dental caries. The S. mutans enzyme sortase A (SrtA) is responsible for anchoring bacterial cell wall surface proteins involved in host cell attachment and biofilm formation. Thus, SrtA is an attractive target for inhibiting dental caries caused by S. mutans-associated acid fermentation. In this study, we observed that astilbin, a flavanone compound extracted from Rhizoma Smilacis Glabrae, has potent inhibitory activity against the S. mutans SrtA, with an IC₅₀ of 7.5 μg/mL. In addition, astilbin was proven to reduce the formation of biofilm while without affecting the growth of S. mutans. The results of a molecular dynamics simulation and a mutation analysis revealed that the Arg213, Leu111, and Leu116 of SrtA are important for the interaction between SrtA and astilbin. The results of this study demonstrate the potential of using astilbin as a nonbactericidal agent to modulate pathogenicity of S. mutans by inhibiting the activity of SrtA.

Whole genome sequence and phenotypic characterization of a Cbm+ serotype e strain of Streptococcus mutans

We report the whole genome sequence of the serotype e Cbm+ strain LAR01 of Streptococcus mutans, a dental pathogen frequently associated with extra-oral infections. The LAR01 genome is a single circular chromosome of 2.1 Mb with a GC content of 36.96%. The genome contains 15 phosphotransferase system gene clusters, seven cell wall-anchored (LPxTG) proteins, all genes required for the development of natural competence and genes coding for mutacins VI and K8. Interestingly, the cbm gene is genetically linked to a putative type VII secretion system that has been found in Mycobacteria and few other Gram-positive bacteria. When compared with the UA159 type strain, phenotypic characterization of LAR01 revealed increased biofilm formation in the presence of either glucose or sucrose but similar abilities to withstand acid and oxidative stresses. LAR01 was unable to inhibit the growth of Strpetococcus gordonii, which is consistent with the genomic data that indicate absence of mutacins that can kill mitis streptococci. On the other hand, LAR01 effectively inhibited growth of other S. mutans strains, suggesting that it may be specialized to outcompete strains from its own species. In vitro and in vivo studies using mutational and heterologous expression approaches revealed that Cbm is a virulence factor of S. mutans by mediating binding to extracellular matrix proteins and intracellular invasion. Collectively, the whole genome sequence analysis and phenotypic characterization of LAR01 provides new insights on the virulence properties of S. mutans and grants further opportunities to understand the genomic fluidity of this important human pathogen.

Streptococcus Mutans Adhesin Biotypes that Match and Predict Individual Caries Development

Dental caries, which affects billions of people, is a chronic infectious disease that involves Streptococcus mutans, which is nevertheless a poor predictor of individual caries development. We therefore investigated if adhesin types of S.mutans with sucrose-independent adhesion to host DMBT1 (i.e. SpaP A, B or C) and collagen (i.e. Cnm, Cbm) match and predict individual differences in caries development. The adhesin types were measured in whole saliva by qPCR in 452 12-year-old Swedish children and related to caries at baseline and prospectively at a 5-year follow-up. Strains isolated from the children were explored for genetic and phenotypic properties. The presence of SpaP B and Cnm subtypes coincided with increased 5-year caries increment, and their binding to DMBT1 and saliva correlated with individual caries scores. The SpaP B subtypes are enriched in amino acid substitutions that coincided with caries and binding and specify biotypes of S. mutans with increased acid tolerance. The findings reveal adhesin subtypes of S. mutans that match and predict individual differences in caries development and provide a rationale for individualized oral care.

•

Adhesin subtypes of Streptococcus mutans match and predict individual caries development.

•

Adhesin binding to salivary DMBT1 correlates with individual caries scores.

•

The adhesin types coincide with distinct biotypes of S. mutans.

Dental caries, which affects billions of people, involves the bacterium Streptococcus mutans, which is nevertheless a poor predictor of caries development. The present findings provide the first evidence that S. mutans adhesin subtypes match and predict individual 5-year caries development in Swedish children. The binding strength of the adhesin subtypes correlates with individual caries scores, and the adhesin subtypes specify biotypes of S. mutans that also differ in acid tolerance. The present findings provide a rationale for individualized oral care and improved systemic health because chronic caries infection and carrying high-virulence strains pose a systemic disease risk.

How to become a killer, or is it all accidental? Virulence strategies in oral streptococci

Streptococci are a diverse group of Gram-positive microorganisms sharing common virulence traits and similar strategies to escape the oral niche and establish an infection in other parts of the host organism. Invasive infection with oral streptococci is "a perfect storm" that requires the concerted action of multiple biotic and abiotic factors. Our understanding of streptococcal pathogenicity and infectivity should probably be less mechanistic and driven not only by the identification of novel virulence factors. The observed diversity of the genus, including the range of virulence and pathogenicity mechanisms, is most likely the result of interspecies interactions, a massive horizontal gene transfer between streptococci within a shared oral niche, recombination events, selection of specialized clones, and modification of regulatory circuits. Selective pressure by the host and bacterial communities is a driving force for the selection of virulence traits and shaping the streptococcal genome. Global regulatory events driving niche adaptation and interactions with bacterial communities and the host steer research interests towards attempts to define the oral interactome on the transcriptional level and define signal cross-feeding and co-expression and co-regulation of virulence genes.

Cyclic Dinucleotides in Oral Bacteria and in Oral Biofilms

Oral cavity acts as a reservoir of bacterial pathogens for systemic infections and several oral microorganisms have been linked to systemic diseases. Quorum sensing and cyclic dinucleotides, two "decision-making" signaling systems, communicate to regulate physiological process in bacteria. Discovery of cyclic dinucleotides has a long history, but the progress in our understanding of how cyclic dinucleotides regulate bacterial lifestyle is relatively new. Oral microorganisms form some of the most intricate biofilms, yet c-di-GMP, and c-di-AMP signaling have been rarely studied in oral biofilms. Recent studies demonstrated that, with the aid of bacterial messenger molecules and their analogs, it is possible to activate host innate and adaptive immune responses and epithelial integrity with a dose that is relevant to inhibit bacterial virulence mechanisms, such as fimbriae and exopolysaccharide production, biofilm formation, and host cell invasion. The aim of this perspective article is to present available information on cyclic dinucleotides in oral bacteria and in oral biofilms. Moreover, technologies that can be used to detect cyclic dinucleotides in oral biofilms are described. Finally, directions for future research are highlighted.