A Potential New Risk Factor for Stroke: Streptococcus Mutans With Collagen-Binding Protein

Is oral Streptococcus mutans with collagen-binding protein a risk factor for intracranial aneurysm rupture or formation?

OBJECTIVE

Streptococcus mutans (SM) with the collagen-binding protein Cnm is a unique member of the oral resident flora because it causes hemorrhagic vascular disorders. In the multicenter study, we examined the relationship between Cnm-positive SM (CP-SM) and intracranial aneurysm (IA) rupture, which remains unknown.

METHODS

Between May 2013 and June 2018, we collected whole saliva samples from 431 patients with ruptured IAs (RIAs) and 470 patients with unruptured IAs (UIAs). Data were collected on age, sex, smoking and drinking habits, family history of subarachnoid hemorrhage, aneurysm size, number of teeth, and comorbidities of lifestyle disease.

RESULTS

There was no difference in the positivity rate of patients with CP-SM between the patients with RIAs (17.2%) and those with UIAs (19.4%). The rate of positivity for CP-SM was significantly higher in all IAs <5 mm than in those ≥10 mm in diameter (P=0.0304). In the entire cohort, the rate of positivity for CP-SM was lower in larger aneurysms than in smaller aneurysms (P=0.0393).

CONCLUSIONS

The rate of positivity for CP-SM was lower among patients with large UIAs. These findings are consistent with the hypothesis that CP-SM plays a role in the formation of vulnerable IAs that tend to rupture before becoming larger.

The Role of Gut and Oral Microbiota in the Formation and Rupture of Intracranial Aneurysms: A Literature Review

In recent years, there has been a growing interest in the role of the microbiome in cardiovascular and cerebrovascular diseases. Emerging research highlights the potential role of the microbiome in intracranial aneurysm (IA) formation and rupture, particularly in relation to inflammation. In this review, we aim to explore the existing literature regarding the influence of the gut and oral microbiome on IA formation and rupture. In the first section, we provide background information, elucidating the connection between inflammation and aneurysm formation and presenting potential mechanisms of gut-brain interaction. Additionally, we explain the methods for microbiome analysis. The second section reviews existing studies that investigate the relationship between the gut and oral microbiome and IAs. We conclude with a prospective overview, highlighting the extent to which the microbiome is already therapeutically utilized in other fields. Furthermore, we address the challenges associated with the context of IAs that still need to be overcome.

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.

Oral microbiome and ischemic stroke risk among elderly Chinese women

Background

Stroke, a leading cause of disability worldwide, has been associated with periodontitis. However, whether stroke risk is related to oral microbiota remains unknown. This study aims to evaluate the associations between the oral microbiome and ischemic stroke risk.

Methods

In a case-control study of 134 case-control pairs nested within a prospective cohort study, we examined pre-diagnostic oral microbiome in association with stroke risk via shotgun metagenomic sequencing. The microbial sub-community and functional profiling were performed using Latent Dirichlet Allocation and HUMAnN2. Associations of microbial diversity, sub-community structure, and individual microbial features with ischemic stroke risk were evaluated via conditional logistic regression.

Results

Alpha and beta diversities differ significantly between cases and controls. One genus- and two species-level sub-communities were significantly associated with decreased ischemic stroke risk, with odds ratios (95% confidence intervals) of 0.52 (0.31-0.90), 0.51 (0.31-0.84), and 0.60 (0.36-0.99), respectively. These associations were potentially driven by the representative taxa in these sub-communities, i.e., genus Corynebacterium and Lautropia, and species Lautropia mirabilis and Neisseria elongate (p < 0.05). Additionally, 55 taxa, 1,237 gene families, and 90 metabolic pathways were associated with ischemic stroke risk at p < 0.05.

Conclusion

Our study highlights the role of oral microbiota in the etiology of ischemic stroke and calls for further research.

Microbiota present in combined endodontic-periodontal diseases and its risks for endocarditis

INTRODUCTION

Infective endocarditis (IE) is an inflammatory disease usually caused by bacteria that enter the bloodstream and establish infections in the inner linings or valves of the heart, including blood vessels. Despite the availability of modern antimicrobial and surgical treatments, IE continues to cause substantial morbidity and mortality. Oral microbiota is considered one of the most significant risk factors for IE. The objective of this study was to evaluate the microbiota present in root canal (RC) and periodontal pocket (PP) clinical samples in cases with combined endo-periodontal lesions (EPL) to detect species related to IE using NGS.

METHODS

Microbial samples were collected from 15 RCs and their associated PPs, also from 05 RCs with vital pulp tissues (negative control, NC). Genomic studies associated with bioinformatics, combined with structuring of a database (genetic sequences of bacteria reported for infective endocarditis), allowed for the assessment of the microbial community at both sites. Functional prediction was conducted using PICRUSt2.

RESULTS

Parvimonas, Streptococcus, and Enterococcus were the major genera detected in the RCs and PPs. A total of 79, 96, and 11 species were identified in the RCs, PPs, and NCs, respectively. From them, a total of 34 species from RCs, 53 from PPs, and 2 from NCs were related to IE. Functional inference demonstrated that CR and PP microbiological profiles may not be the only risk factors for IE but may also be associated with systemic diseases, including myocarditis, human cytomegalovirus infection, bacterial invasion of epithelial cells, Huntington's disease, amyotrophic lateral sclerosis, and hypertrophic cardiomyopathy. Additionally, it was possible to predict antimicrobial resistance variants for broad-spectrum drugs, including ampicillin, tetracycline, and macrolides.

CONCLUSION

Microorganisms present in the combined EPL may not be the only risk factor for IE but also for systemic diseases. Antimicrobial resistance variants for broad-spectrum drugs were inferred based on PICRUSt-2. State-of-the-art sequencing combined with bioinformatics has proven to be a powerful tool for conducting studies on microbial communities and could considerably assist in the diagnosis of serious infections.

CLINICAL RELEVANCE

Few studies have investigated the microbiota in teeth compromised by combined endo-periodontal lesions (EPL), but none have correlated the microbiological findings to any systemic condition, particularly IE, using NGS techniques. In such cases, the presence of apical periodontitis and periodontal disease can increase IE risk in susceptible patients.

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.

Unlike severe periodontitis, caries does not associate with intracranial aneurysms or aneurysmal subarachnoid hemorrhage

PURPOSE

Periodontal diseases and caries are common oral diseases that predispose to tooth loss if untreated. In this study, we investigated whether loss of teeth or caries associate with intracranial aneurysm (IA) pathology similar to periodontal diseases.

METHODS

A total of 166 patients with either IA or aneurysmal subarachnoid hemorrhage (aSAH) underwent oral examination in Kuopio University Hospital and Tampere University Hospital. Findings were compared to geographically matched controls acquired from cross-sectional Health2000 survey. This study consisted of three sequential steps. First, we compared the number of missing teeth and prevalence of caries in IA and aSAH patients and geographically matched control population, second step was a multivariate analysis including other risk factors, and third step was a 13-year follow-up of the Health2000 survey participants with missing teeth or caries at baseline.

RESULTS

Loss of teeth did not significantly differ between IA patients and controls. In logistic regression model adjusted for known risk factors and demographic data, 1-4 caries lesions (OR: 0.40 95%Cl 0.2-0.9, p = 0.031) was associated with lack of IAs, while age (OR: 1.03 95%Cl 1.01.1 p = 0.024), current smoking (OR: 2.7 95%Cl 1.4-5.1, p = 0.003), and severe periodontitis (OR: 5.99 95%Cl 2.6-13.8, p < 0.001) associated to IA formation. In the cox-regression, severe periodontitis at baseline increased the risk of aSAH (HR: 14.3, 95%Cl 1.5-135.9, p = 0.020) during a 13-year follow-up, while caries or missing teeth did not.

CONCLUSION

Unlike severe periodontitis, caries does not increase the risk of IAs and aSAHs. However, cariogenic bacteria may participate to IA pathology by disseminating to circulation via inflamed gingival tissue.

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.

Infectious Agents and Stroke: A Systematic Review

Introduction:

A major cause of injury and the second cause of death worldwide is stroke. Among several infectious agents considered as the risk factor of stroke, some pathogens demonstrated stronger robust associations with stroke. Proposing an accurate correlation between infectious microorganisms and stroke provides valuable information for early intervention and control of the infections.

Methods:

In this study, we searched the literature using the Web of Science, PMC/Medline via PubMed, and Scopus databases up to July 2018 without time and language restrictions. After quality assessment, 16 articles were included in the study. The whole data extraction process was independently conducted by two reviewers.

Results:

Based on the results of the studies, viruses, such as Hepatitis C virus (HCV), Hepatitis B virus (HBV), Human Immunodeficiency Virus (HIV), Herpes Simplex Virus Type-1, 2 (HSV-1, 2), Varicella-Zoster Virus (VZV or Chickenpox), and West Nile virus (WNV) seem to be common causes of ischemic stroke. Moreover, the association of other microbial categories, such as Streptococcus mutans (in bacteria), Toxocara spp. and Toxoplasma gondii (in parasites), and Rhizopus sp. (in fungi) with stroke was reported.

Conclusion:

Considering the adverse role of the above-mentioned microorganisms, it is necessary to implement some preventive measures for stroke treatment.

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.

Oral microbiota and atherothrombotic carotid plaque vulnerability in periodontitis patients. A cross-sectional study

BACKGROUND

An increased risk of atherothrombotic vascular events has been reported in periodontitis patients. Periodontitis is associated with dysbiotic subgingival biofilms and bacteremia.

OBJECTIVE

We hypothesized (a) that the oral microbiome is associated with the carotid microbiome and (b) that periodontitis could contribute to plaque vulnerability. The aim of this study was to determine the associations between periodontitis, the carotid microbiome, and the local innate immune response in carotid atherothrombotic plaques vulnerable to rupture.

METHODS

In this cross-sectional study, 45 patients admitted for carotid endarterectomy underwent a preoperative periodontal examination. The volume of intraplaque hemorrhage reflected by the hemoglobin level released in carotid-conditioned media was considered as a criterion of carotid plaque vulnerability. Levels of antibodies against periodontal bacteria were determined in sera. The signature of the oral microbiota was assessed by microbial whole-genome sequencing, nested PCR, and immunostaining in carotid plaque samples. Markers of neutrophil recruitment (leukotriene B4), neutrophil activation (myeloperoxidase, defensins), and cytokines were measured in carotid-conditioned media and/or plasma.

RESULTS

All patients exhibited periodontitis. One hundred and forty-four bacterial genera were detected in the carotid microbiome. While Streptococcus was found in 84% of the carotid samples, periodontitis-associated genera were detected in 21%. P. gingivalis DNA and gingipains were also identified in carotid samples. There were significant inverse correlations between periodontal attachment loss/serum anti-P. gingivalis Immunoglobulin A and cytokine inhibiting neutrophils (all P < .01). There were also significant positive correlations between lipopolysaccharides, myeloperoxidase/human neutrophil peptides1-3, and hemoglobin levels (all P < .01).

CONCLUSIONS

In patients at risk of stroke, the carotid plaque microbiome was highly diverse and compatible with an oral origin. Periodontitis was significantly associated with neutrophil activation markers and plaque vulnerability to rupture.

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.

Oral Carriage of Streptococcus mutans Harboring the cnm Gene Relates to an Increased Incidence of Cerebral Microbleeds

Supplemental Digital Content is available in the text.

Cerebral microbleeds (CMB) are associated with stroke and cognitive impairment. We previously reported a high prevalence of CMB in people with Streptococcus mutans expressing Cnm, a collagen-binding protein in the oral cavity. S.mutans is a major pathogen responsible for dental caries. Repeated challenge with S.mutans harboring the cnm gene encoding Cnm induced cerebral bleeding in stroke-prone spontaneously hypertensive rats. The purpose of this longitudinal study is to examine the relationship of cnm-positive S.mutans to the development of CMB.

Usefulness of matrix-assisted laser desorption ionization/time of flight mass spectrometry for the identification of Streptococcus mutans

This study evaluated the reliability of MALDI-TOF MS coupled with statistical tools for the identification of Streptococcus mutans in comparison with PCR-based techniques. Bacterial isolates were identified and serotyped by conventional PCR, using S. mutans species and serotype-specific primers. For bacterial identification, mass spectra data from S. mutans and other streptococci were compared with Biotyper V 3.1 database and the mass peak lists were examined by cluster and principal component (PCA) analysis. Identification of potential biomarkers was performed using UniProtKB/Swiss-Prot and UniProtKB/TrEMBL databases and BLAST tool of the NCBI database. PCR identified 100% of the isolates as S. mutans. S. mutans strains were typed as serotypes c (85.6%), e (8.6%), k (4.8%), and f (0.9%). Although only the 70% of the strains tested were identified at species level by the Biotyper database, PCA and cluster analysis of mass peaks allowed the identification of 100% S. mutans isolates and its differentiation from the other oral and non-oral streptococci. One mass peak at m/z value of 9572.73 was identified as species-specific biomarker for S. mutans. No biomarkers were identified for S. mutans serotypes. KEY POINTS: • MALDI-TOF MS coupled with statistical tools for the identification of S. mutans. • Detection of species identifying biomarkers by MALDI-TOF MS. • PCR identification and serotyping of S. mutans from saliva samples.

Biochemical and microbiological analysis of the saliva of institutionalized elderly: With edentulism, use of dentures and presence of biofilm

BACKGROUND

To analyze biochemical and microbiological parameters of the saliva of institutionalized elders and to investigate the relation of these parameters with edentulism, use of dentures and presence of biofilm.

MATERIAL AND METHODS

A cross-sectional study carried was out in seven long-term institutions. Samples (n=161) of unstimulated saliva were collected for analysis of salivary flow, quantification of total proteins and identification of microorganisms. Oral examination was carried out to verify the number of missing teeth, the use of dentures and the presence of visible biofilm on the surface of teeth and dentures. Associations were performed using chi-square or Fisher's exact test (α<0.05). Mann-Whitney Test was used to identify differences in the salivary flow and total proteins (α<0.05).

RESULTS

There was no association between the type of edentulism and use of dentures with biochemical and microbiological parameters of saliva (p>0.05). Associations were observed between the presence of dentures biofilm and the colonization of Streptococcus sp. (p=0.038) and Candida sp. (p=0.03).

CONCLUSIONS

The absence of teeth and use of dentures do not influence the amount of total proteins and the microorganisms count in saliva. Denture biofilms are associated with the presence of Streptococcus sp. and Candida sp. in saliva of institutionalized elders. Key words:Candida, long-stay institutions for elders, saliva, Streptococcus, Staphylococcus.

Role of oral pathogens in the pathogenesis of intracranial aneurysm: review of existing evidence and potential mechanisms

Degeneration of intracranial aneurysm wall is under active research and recent studies indicate an increased risk of rupture of intracranial aneurysm among patients with periodontal diseases. In addition, oral bacterial DNA has been identified from wall samples of ruptured and unruptured aneurysms. These novel findings led us to evaluate if oral diseases could predispose to pathological changes seen on intracranial aneurysm walls eventually leading to subarachnoid hemorrhage. The aim of this review is to consider mechanisms on the relationship between periodontitis and aneurysm rupture, focusing on recent evidence.

Potential Influences of Gut Microbiota on the Formation of Intracranial Aneurysm

Gut microbiota modulates metabolic and immunoregulatory axes and contributes to the pathophysiology of diseases with inflammatory components, such as atherosclerosis, diabetes mellitus, and ischemic stroke. Inflammation is emerging as a critical player in the pathophysiology of an intracranial aneurysm. Therefore, we hypothesized that the gut microbiota affects aneurysm formation by modulating inflammation. We induced intracranial aneurysms in mice by combining systemic hypertension and a single injection of elastase into the cerebrospinal fluid. Depletion of the gut microbiota was achieved via an oral antibiotic cocktail of vancomycin, metronidazole, ampicillin, and neomycin. Antibiotics were given 3 weeks before aneurysm induction and either continued until the end of the experiment or stopped 1 day before aneurysm induction. We also assessed the effects of the gut microbiota depletion on macrophage infiltration and mRNA levels of inflammatory cytokines. Gut microbiota depletion by antibiotics reduced the incidence when antibiotics were started 3 weeks before aneurysm induction and continued until the end of the experiment (83% versus 6%, P<0.001). Even when antibiotics were stopped 1 day before aneurysm induction, the gut microbiota depletion significantly reduced the incidence of aneurysms (86% versus 28%, P<0.05). Both macrophage infiltration and mRNA levels of inflammatory cytokines were reduced with gut microbiota depletion. These findings suggest that the gut microbiota contributes to the pathophysiology of aneurysms by modulating inflammation. Human studies are needed to determine the exact contribution of the gut microbiota to the pathophysiology of aneurysm formation and disease course in humans.

Annual review of selected scientific literature: A report of the Committee on Scientific Investigation of the American Academy of Restorative Dentistry

This comprehensive review of the 2018 dental literature is provided to inform busy dentists about progress in the profession. Developed by the Committee on Scientific Investigation of the American Academy of Restorative Dentistry, each author brings discipline-specific expertise to one of the 8 sections of the report including (1) prosthodontics; (2) periodontics, alveolar bone, and peri-implant tissues; (3) implant dentistry; (4) dental materials and therapeutics; (5) occlusion and temporomandibular disorders; (6) sleep-related breathing disorders; (7) oral medicine and oral and maxillofacial surgery; and (8) dental caries and cariology. The report targets important information that will likely influence day-to-day treatment decisions. Each review is not intended to stand alone but to update interested readers so that they may visit source materials if greater detail is desired. As the profession continues its march toward evidence-based clinical decision-making, an already voluminous library of potentially valuable dental literature continues to grow. It is the intention of this review and its authors to provide assistance in navigating the extensive dental literature published in 2018. It is our hope that readers find this work useful in the clinical management of patients moving forward.

Inactivation of Streptococcus mutans genes lytST and dltAD impairs its pathogenicity in vivo

Background: Streptococcus mutans orchestrates the development of a biofilm that causes dental caries in the presence of dietary sucrose, and, in the bloodstream, S. mutans can cause systemic infections. The development of a cariogenic biofilm is dependent on the formation of an extracellular matrix rich in exopolysaccharides, which contains extracellular DNA (eDNA) and lipoteichoic acids (LTAs). While the exopolysaccharides are virulence markers, the involvement of genes linked to eDNA and LTAs metabolism in the pathogenicity of S. mutans remains unclear. Objective and Design: In this study, a parental strain S. mutans UA159 and derivative strains carrying single gene deletions were used to investigate the role of eDNA (ΔlytS and ΔlytT), LTA (ΔdltA and ΔdltD), and insoluble exopolysaccharides (ΔgtfB) in virulence in a rodent model of dental caries (rats) and a systemic infection model (Galleria mellonella larvae). Results: Fewer carious lesions were observed on smooth and sulcal surfaces of enamel and dentin of the rats infected with ∆lytS, ∆dltD, and ΔgtfB (vs. the parental strain). Moreover, strains carrying gene deletions prevented the killing of larvae (vs. the parental strain). Conclusions: Altogether, these findings indicate that inactivation of lytST and dltAD impaired S. mutans cariogenicity and virulence in vivo.

Periodontitis and gingival bleeding associate with intracranial aneurysms and risk of aneurysmal subarachnoid hemorrhage

Oral bacteria DNA has been found in intracranial aneurysms (IA) and a high prevalence of periodontitis was reported in IA patients. We investigated whether periodontitis associates with IA formation and aneurysmal subarachnoid hemorrhage (aSAH). First, we compared in a case-control setting the prevalence of periodontal disease in IA patients (42 unruptured IA, 34 ruptured IA) and in age- and gender-matched controls (n = 70) from the same geographical area (Health 2000 Survey, BRIF8901). Next, we investigated whether periodontitis at baseline associated with aSAH in a 13-year follow-up study of 5170 Health 2000 Survey participants. Follow-up data was obtained from national hospital discharge and cause of death registries. Univariate analysis, logistic regression, and Cox-regression were used. Periodontitis (≥ 4mm gingival pocket) and severe periodontitis (≥ 6mm gingival pocket) were found in 92% and 49% of IA patients respectively and associated with IAs (OR 5.3, 95%CI 1.1–25.9, p < 0.000 and OR 6.3, 95%CI 1.3–31.4, p < 0.001, respectively). Gingival bleeding had an even stronger association, especially if detected in 4–6 teeth sextants (OR 34.4, 95%CI 4.2–281.3). Severe periodontitis in ≥ 3 teeth or gingival bleeding in 4–6 teeth sextants at baseline increased the risk of aSAH during follow-up (HR 22.5, 95%CI 3.6–139.5, p = 0.001 and HR 8.3, 95%CI 1.5–46.1, p = 0.015, respectively). Association of periodontitis and gingival bleeding with risk of IA development and aSAH was independent of gender, smoking status, hypertension, or alcohol abuse. Periodontitis and gingival bleeding associate with increased risk for IA formation and eventual aSAH. Further epidemiological and mechanistic studies are indicated.

Collagen-binding Streptococcus mutans tied to cerebral microbleeds and intracerebral hemorrhage

Genome-wide association and candidate gene studies have identified COL4A1 and COL4A2 as risk genes for intracerebral hemorrhage (ICH), suggesting that the disrupted collagen architecture could be a contributory factor in disease onset. Environmental factors that disrupt the vascular collagen architecture may therefore bring about gene–environmental interactions. Certain oral strains of Streptococcus mutans expressing Cnm, a collagen-binding protein, have been found to be responsible for ICH in a preclinical study. In support of this finding, a population-based study showed a close association between Cnm-positive Streptococcus mutans with cerebral microbleeds, a precursor of ICH, and a hospital-based study between such bacteria with cerebral microbleeds and ICH. Taken together, these findings suggest that Cnm-positive Streptococcus mutans serve as an important environmental factor in ICH.