Environmental stimuli shape biofilm formation and the virulence of periodontal pathogens

Machine learning enabled design features of antimicrobial peptides selectively targeting peri-implant disease progression

Peri-implantitis is a complex infectious disease that manifests as progressive loss of alveolar bone around the dental implants and hyper-inflammation associated with microbial dysbiosis. Using antibiotics in treating peri-implantitis is controversial because of antibiotic resistance threats, the non-selective suppression of pathogens and commensals within the microbial community, and potentially serious systemic sequelae. Therefore, conventional treatment for peri-implantitis comprises mechanical debridement by nonsurgical or surgical approaches with adjunct local microbicidal agents. Consequently, current treatment options may not prevent relapses, as the pathogens either remain unaffected or quickly re-emerge after treatment. Successful mitigation of disease progression in peri-implantitis requires a specific mode of treatment capable of targeting keystone pathogens and restoring bacterial community balance toward commensal species. Antimicrobial peptides (AMPs) hold promise as alternative therapeutics through their bacterial specificity and targeted inhibitory activity. However, peptide sequence space exhibits complex relationships such as sparse vector encoding of sequences, including combinatorial and discrete functions describing peptide antimicrobial activity. In this paper, we generated a transparent Machine Learning (ML) model that identifies sequence-function relationships based on rough set theory using simple summaries of the hydropathic features of AMPs. Comparing the hydropathic features of peptides according to their differential activity for different classes of bacteria empowered predictability of antimicrobial targeting. Enriching the sequence diversity by a genetic algorithm, we generated numerous candidate AMPs designed for selectively targeting pathogens and predicted their activity using classifying rough sets. Empirical growth inhibition data is iteratively fed back into our ML training to generate new peptides, resulting in increasingly more rigorous rules for which peptides match targeted inhibition levels for specific bacterial strains. The subsequent top scoring candidates were empirically tested for their inhibition against keystone and accessory peri-implantitis pathogens as well as an oral commensal bacterium. A novel peptide, VL-13, was confirmed to be selectively active against a keystone pathogen. Considering the continually increasing number of oral implants placed each year and the complexity of the disease progression, prevalence of peri-implant diseases continues to rise. Our approach offers transparent ML-enabled paths towards developing antimicrobial peptide-based therapies targeting the changes in the microbial communities that can beneficially impact disease progression.

Porphyromonas gingivalis Induces Proinflammatory Cytokine Expression Leading to Apoptotic Death through the Oxidative Stress/NF-κB Pathway in Brain Endothelial Cells

Porphyromonas gingivalis, a periodontal pathogen, has been proposed to cause blood vessel injury leading to cerebrovascular diseases such as stroke. Brain endothelial cells compose the blood-brain barrier that protects homeostasis of the central nervous system. However, whether P. gingivalis causes the death of endothelial cells and the underlying mechanisms remain unclear. This study aimed to investigate the impact and regulatory mechanisms of P. gingivalis infection in brain endothelial cells. We used bEnd.3 cells and primary mouse endothelial cells to assess the effects of P. gingivalis on endothelial cells. Our results showed that infection with live P. gingivalis, unlike heat-killed P. gingivalis, triggers brain endothelial cell death by inducing cell apoptosis. Moreover, P. gingivalis infection increased intracellular reactive oxygen species (ROS) production, activated NF-κB, and up-regulated the expression of IL-1β and TNF-α. Furthermore, N-acetyl-L-cysteine (NAC), a most frequently used antioxidant, treatment significantly reduced P. gingivalis-induced cell apoptosis and brain endothelial cell death. The enhancement of ROS production, NF-κB p65 activation, and proinflammatory cytokine expression was also attenuated by NAC treatment. The impact of P. gingivalis on brain endothelial cells was also confirmed using adult primary mouse brain endothelial cells (MBECs). In summary, our results showed that P. gingivalis up-regulates IL-1β and TNF-α protein expression, which consequently causes cell death of brain endothelial cells through the ROS/NF-κB pathway. Our results, together with the results of previous case-control studies and epidemiologic reports, strongly support the hypothesis that periodontal infection increases the risk of developing cerebrovascular disease.

Adverse effects of electronic cigarettes on the disease-naive oral microbiome

Six percent of Americans, including 3 million high schoolers, use e-cigarettes, which contain potentially toxic substances, volatile organic compounds, and metals. We present the first human study on the effects of e-cigarette exposure in the oral cavity. By interrogating both immunoinflammatory responses and microbial functional dynamics, we discovered pathogen overrepresentation, higher virulence signatures, and a brisk proinflammatory signal in clinically healthy e-cigarette users, equivalent to patients with severe periodontitis. Using RNA sequencing and confocal and electron microscopy to validate these findings, we demonstrate that the carbon-rich glycol/glycerol vehicle is an important catalyst in transforming biofilm architecture within 24 hours of exposure. Last, a machine-learning classifier trained on the metagenomic signatures of e-cigarettes identified as e-cigarette users both those individuals who used e-cigarettes to quit smoking, and those who use both e-cigarettes and cigarettes. The present study questions the safety of e-cigarettes and the harm reduction narrative promoted by advertising campaigns.

Effects of d-valine on periodontal or peri-implant pathogens: Porphyromonas gingivalis biofilm

BACKGROUND

When presented with a surface or an interface, bacteria often grow as biofilms in which cells are held together by an extracellular matrix. Biofilm formation on implants is an initiating factor for their failure. Porphyromonas gingivalis is the primary etiologic bacteria of initiation and progression of periodontal disease. This microorganism is also the risk factor of many systemic diseases, such as cardiovascular disease, diabetes, and pulmonary infection. To date, no medication that can remove such biofilm has been accepted for clinical use. D-valine (D-val) can reportedly inhibit the formation of biofilm and/or trigger the scattering of mature biofilm. Accordingly, this study investigated the effects of d-val on single-species P. gingivalis biofilms in vitro.

METHODS

P. gingivalis grown in brain heart infusion culture with or without d-val was inoculated in 24- or 96-well plates. After incubation for 72 hours, biomass via crystal violet staining, extracellular polysaccharide production by biofilms, and scanning electron microscopy (SEM) were used to determine the d-val concentration that can effectively prevent P. gingivalis biofilm formation.

RESULTS

Experimental results showed that d-val effectively inhibited biofilm formation at concentrations ≥50 mM (mMol/L), and that d-val inhibition increased with increased concentration. Moreover, at high concentrations, the bacterial form changed from the normal baseball form into a rodlike shape. d-val also notably affected extracellular polysaccharide production by P. gingivalis.

CONCLUSIONS

d-val can inhibit P. gingivalis biofilm formation, and high concentrations can affect bacterial morphology.

The fight for invincibility: Environmental stress response mechanisms and Aeromonas hydrophila

Aeromonas hydrophila is a freshwater-dwelling zoonotic bacterium that has economic importance in aquaculture. In the past decade, Aeromonas hydrophila has become increasingly important because of its emergence as a food-borne zoonotic pathogen that is resistant to different treatment regimes. Being an aquatic bacterium, Aeromonas hydrophila is frequently subjected to several stressful environmental conditions, including changes in temperature, acidic pH and starvation that challenge its survival. To cope with these stressful conditions, like every cell, A. hydrophila possesses stress response mechanisms, such as alternative sigma factors, two-component systems, heat shock proteins, cold shock proteins, and acid tolerance response systems that eventually lead the fittest to survive. Moreover, the establishment of genetic variations among the strains related to environmental stress is also of great concern. This review presents the understandings based on inter-strain variations and stress response behavior of A. hydrophila that are important to control the increasing outbreaks of this bacterium in both human populations and aquaculture.

Potassium is a key signal in host-microbiome dysbiosis in periodontitis

Dysbiosis, or the imbalance in the structural and/or functional properties of the microbiome, is at the origin of important infectious inflammatory diseases such as inflammatory bowel disease (IBD) and periodontal disease. Periodontitis is a polymicrobial inflammatory disease that affects a large proportion of the world's population and has been associated with a wide variety of systemic health conditions, such as diabetes, cardiovascular and respiratory diseases. Dysbiosis has been identified as a key element in the development of the disease. However, the precise mechanisms and environmental signals that lead to the initiation of dysbiosis in the human microbiome are largely unknown. In a series of previous in vivo studies using metatranscriptomic analysis of periodontitis and its progression we identified several functional signatures that were highly associated with the disease. Among them, potassium ion transport appeared to be key in the process of pathogenesis. To confirm its importance we performed a series of in vitro experiments, in which we demonstrated that potassium levels a increased the virulence of the oral community as a whole and at the same time altering the immune response of gingival epithelium, increasing the production of TNF-α and reducing the expression of IL-6 and the antimicrobial peptide human β-defensin 3 (hBD-3). These results indicate that levels of potassium in the periodontal pocket could be an important element in of dysbiosis in the oral microbiome. They are a starting point for the identification of key environmental signals that modify the behavior of the oral microbiome from a symbiotic community to a dysbiotic one.

Homeostasis of the human microbiome plays a key role in maintaining the healthy status of the human body. Changes in composition and function of the human microbiome (dysbiosis) are at the origin of important infectious inflammatory diseases such as inflammatory bowel disease (IBD) and periodontal disease. However, the environmental elements that trigger the development of dysbiotic diseases are largely unknown. In previous studies, using community-wide transcriptome analysis, we identified ion potassium transport as one of the most important functions in the pathogenesis of periodontitis and its progression. Here, we confirm with a series of in vitro experiments that potassium can act as an important signal in the dysbiotic process inducing pathogenesis in the oral microbiome and altering the host response in front of the microbial challenge that could lead to microbial immune subversion. Our study provides new insights into the important role that ion potassium plays a signal in oral dysbiosis during periodontitis.

Novel multifunctional dental bonding agent for Class-V restorations to inhibit periodontal biofilms

We recently developed a dental bonding agent to bond restorations to teeth using nanoparticles of amorphous calcium phosphate (NACP) for remineralization with rechargeable calcium and phosphate ion release. The objectives of this study were to: (1) incorporate an antibacterial monomer dimethylaminohexadecyl methacrylate (DMAHDM) and a protein-repellent agent 2-methacryloyloxyethyl phosphorylcholine (MPC); and (2) investigate protein adsorption and periodontitis-related biofilms for the first time. A primer, used to prime tooth structures for bonding, was made with pyromellitic glycerol dimethacrylate (PMGDM) and 2-hydroxyethyl methacrylate (HEMA). An adhesive was made with PMGDM, ethoxylated bisphenol A dimethacrylate and HEMA. NACP, MPC and DMAHDM were incorporated. Streptococcus gordonii, Actinomyces naeslundii, Porphyromonas gingivalis, Fusobacterium nucleatum were cultured to form single and multi-species biofilms. Colony-forming units (CFU), live/dead, metabolic activity, and polysaccharide were measured. Adding DMAHDM, MPC and NACP into the bonding agent did not compromise the dentin bond strength (p > 0.1). Bonding agents with 5% MPC reduced protein adsorption to 1/15 that of the control (p < 0.05). Bonding agents with 5% DMAHDM + 5% MPC had much greater reduction in biofilms than DMAHDM or MPC alone (p < 0.05). Biofilm CFU was reduced by 3 to 4 log via DMAHDM + MPC. Metabolic activities and polysaccharide of biofilms were also substantially reduced (p < 0.05). In conclusion, a novel bonding agent was developed for dental restorations with inhibition of biofilms, reducing CFU by 3 to 4 log. Besides remineralizartion and acid-neutralization via NACP to inhibit caries as shown previously, the multifunctional adhesive is promising for root restorations with subgingival margins to suppress periodontal pathogens and protect the periodontium.

A new mathematical model of bacterial interactions in two-species oral biofilms

Periodontitis are bacterial inflammatory diseases, where the bacterial biofilms present on the tooth-supporting tissues switch from a healthy state towards a pathogenic state. Among bacterial species involved in the disease, Porphyromonas gingivalis has been shown to induce dysbiosis, and to induce virulence of otherwise healthy bacteria like Streptococcus gordonii. During biofilm development, primary colonizers such as S. gordonii first attach to the surface and allow the subsequent adhesion of periodontal pathogens such as P. gingivalis. Interactions between those two bacteria have been extensively studied during the adhesion step of the biofilm. The aim of the study was to understand interactions of both species during the growing phase of the biofilm, for which little knowledge is available, using a mathematical model. This two-species biofilm model was based on a substrate-dependent growth, implemented with damage parameters, and validated thanks to data obtained on experimental biofilms. Three different hypothesis of interactions were proposed and assayed using this model: independence, competition between both bacteria species, or induction of toxicity by one species for the other species. Adequacy between experimental and simulated biofilms were found with the last hypothetic mathematical model. This new mathematical model of two species bacteria biofilms, dependent on different substrates for growing, can be applied to any bacteria species, environmental conditions, or steps of biofilm development. It will be of great interest for exploring bacterial interactions in biofilm conditions.

Effect of bioactive dental adhesive on periodontal and endodontic pathogens

The objectives of this study were to: (1) develop a new bioactive dental bonding agent with nanoparticles of amorphous calcium phosphate and dimethylaminohexadecyl methacrylate for tooth root caries restorations and endodontic applications, and (2) investigate biofilm inhibition by the bioactive bonding agent against eight species of periodontal and endodontic pathogens for the first time. Bonding agent was formulated with 5 % of dimethylaminohexadecyl methacrylate. Nanoparticles of amorphous calcium phosphate at 30 wt% was mixed into adhesive. Eight species of biofilms were grown on resins: Porphyromonas gingivalis, Prevotella intermedia, Prevotella nigrescens, Aggregatibacter actinomycetemcomitans, Fusobacterium nucleatum, Parvimonas micra, Enterococcus faecalis, Enterococcus faecium. Colony-forming units, live/dead assay, biomass, metabolic activity and polysaccharide of biofilms were determined. The results showed that adding dimethylaminohexadecyl methacrylate and nanoparticles of amorphous calcium phosphate into bonding agent did not decrease dentin bond strength (P > 0.1). Adding dimethylaminohexadecyl methacrylate reduced the colony-forming units of all eight species of biofilms by nearly three orders of magnitude. The killing efficacy of dimethylaminohexadecyl methacrylate resin was: P. gingivalis > A. actinomycetemcomitans > P. intermedia > P. nigrescens > F. nucleatum > P. micra > E. faecalis > E. faecium. Dimethylaminohexadecyl methacrylate resin had much less biomass, metabolic activity and polysaccharide of biofilms than those without dimethylaminohexadecyl methacrylate (P < 0.05). In conclusion, a novel dental adhesive was developed for root caries and endodontic applications, showing potent inhibition of biofilms of eight species of periodontal and endodontic pathogens, and reducing colony-forming units by three orders of magnitude. The bioactive adhesive is promising for tooth root restorations to provide subgingival margins with anti-periodontal pathogen capabilities, and for endodontic sealer applications to combat endodontic biofilms.

Novel bioactive nanocomposite for Class-V restorations to inhibit periodontitis-related pathogens

OBJECTIVES

The occurrence of tooth root caries is increasing as the world population ages and tooth retention in seniors increases. Class V restorations with subgingival margins are difficult to clean and often lead to periodontitis. The objectives of this study were to develop a Class V composite containing dimethylaminohexadecyl methacrylate (DMAHDM) and nanoparticles of amorphous calcium phosphate (NACP), and investigate mechanical properties and the inhibition of six species of periodontitis-related biofilms for the first time.

METHODS

Ethoxylated bisphenol A dimethacrylate (EBPADMA) and pyromellitic glycerol dimethacrylate (PMGDM) were mixed at 1:1 mass ratio to form the resin matrix. DMAHDM, NACP, and glass particles were incorporated at 3%, 20% and 50% by mass, respectively. Six species were tested: Porphyromonas gingivalis, Prevotella intermedia, Prevotella nigrescens, Aggregatibacter actinomycetemcomitans, Fusobacterium nucleatum and Enterococcus faecalis. Colony-forming units (CFU), live/dead assay, biomass via crystal violet staining, and polysaccharide production by biofilms were determined on composites.

RESULT

Adding 3% DMAHDM to composite did not affect the flexure strength and elastic modulus (p>0.1). For all six species of periodontal pathogens, the DMAHDM composite had biofilm CFU nearly three orders of magnitude less than that without DMAHDM. The killing efficacy of DMAHDM composite against the six species was: E. faecalis<F. nucleatum<P. nigrescens=P. intermedia<A. actinomycetemcomitans<P. gingivalis. Biofilm biomass and polysaccharide were also greatly reduced via DMAHDM (p<0.05).

SIGNIFICANCE

The novel nanocomposite containing DMAHDM and NACP showed strong inhibiting effect against all six species of periodontitis-related pathogens. This composite is promising for Class V restorations to restore root caries and combat periodontitis.

Java project on periodontal diseases: effect of vitamin C/calcium threonate/citrus flavonoids supplementation on periodontal pathogens, CRP and HbA1c

OBJECTIVE

To assess in a periodontally diseased rural population deprived from regular dental care and having poor dietary conditions, the effect of vitamin C/calcium threonate/citrus flavonoids (VitC/Ca/Fl) supplementation on subgingival microbiota and plasma levels of vitamin C, HbA1c and hsCRP.

MATERIAL & METHODS

The study population consisted of 98 subjects who previously participated in a prospective study on the natural history of periodontitis. Participants were instructed to consume one tablet/day containing 200 mg Ester C(®) calcium ascorbate, 25 mg calcium threonate and 100 mg citrus flavonoids for 90 days. Following parameters were evaluated: prevalence/amount of seven traditional periodontal pathogens, cytomegalovirus, Epstein-Barr virus (EBV); and plasma levels of vitamin C, HbA1c and hsCRP.

RESULTS

After VitC/Ca/Fl supplementation, 100% of subjects showed normal plasma vitamin C values compared to 55% before. At baseline, 48% of subjects harboured Aggregatibacter actinomycetemcomitans, >97% the other periodontal pathogens and 73% EBV. Supplementation with VitC/Ca/F reduced the subgingival load of all studied bacteria (p-values: 0.014-0.0001) and EBV (p < 0.0001) substantially in all initially positive subjects. Plasma levels of HbA1c and hsCRP dropped in all subjects (p < 0.0001).

CONCLUSION

This uncontrolled study suggested that supplemental VitC/Ca/Fl may be helpful in reducing subgingival numbers of periodontal pathogens and EBV, and promoting systemic health.

Functional signatures of oral dysbiosis during periodontitis progression revealed by microbial metatranscriptome analysis

BACKGROUND

Periodontitis is a polymicrobial biofilm-induced inflammatory disease that affects 743 million people worldwide. The current model to explain periodontitis progression proposes that changes in the relative abundance of members of the oral microbiome lead to dysbiosis in the host-microbiome crosstalk and then to inflammation and bone loss. Using combined metagenome/metatranscriptome analysis of the subgingival microbiome in progressing and non-progressing sites, we have characterized the distinct molecular signatures of periodontitis progression.

METHODS

Metatranscriptome analysis was conducted on samples from subgingival biofilms from progressing and stable sites from periodontitis patients. Community-wide expression profiles were obtained using Next Generation Sequencing (Illumina). Sequences were aligned using 'bowtie2' against a constructed oral microbiome database. Differential expression analysis was performed using the non-parametric algorithm implemented on the R package 'NOISeqBio'. We summarized global functional activities of the oral microbial community by set enrichment analysis based on the Gene Ontology (GO) orthology.

RESULTS

Gene ontology enrichment analysis showed an over-representation in the baseline of active sites of terms related to cell motility, lipid A and peptidoglycan biosynthesis, and transport of iron, potassium, and amino acids. Periodontal pathogens (Tannerella forsythia and Porphyromonas gingivalis) upregulated different TonB-dependent receptors, peptidases, proteases, aerotolerance genes, iron transport genes, hemolysins, and CRISPR-associated genes. Surprisingly, organisms that have not been usually associated with the disease (Streptococcus oralis, Streptococcus mutans, Streptococcus intermedius, Streptococcus mitis, Veillonella parvula, and Pseudomonas fluorenscens) were highly active transcribing putative virulence factors. We detected patterns of activities associated with progression of clinical traits. Among those we found that the profiles of expression of cobalamin biosynthesis, proteolysis, and potassium transport were associated with the evolution towards disease.

CONCLUSIONS

We identified metabolic changes in the microbial community associated with the initial stages of dysbiosis. Regardless of the overall composition of the community, certain metabolic signatures are consistent with disease progression. Our results suggest that the whole community, and not just a handful of oral pathogens, is responsible for an increase in virulence that leads to progression.

TRIAL REGISTRATION

NCT01489839, 6 December 2011.

Synthesis of new carolacton derivatives and their activity against biofilms of oral bacteria

Carolacton, a secondary metabolite isolated from the extracts ofSorangium cellulosum, causes membrane damage and cell death in biofilms of different oral bacteria.

Filifactor alocis: The Newly Discovered Kid on the Block with Special Talents

Infection-induced periodontal disease has been primarily focused on a small group of periodontal pathogens. A paradigm shift, based on data emerging from the oral microbiome project, now suggests the involvement of as-yet-unculturable and fastidious organisms. Collectively, these studies have demonstrated that there are changes in the periodontal status associated with shifts in the composition of the bacterial community in the periodontal pocket. In addition, it is likely that the emerging new pathogens may play a more significant role in the disease. One of the organisms previously unrecognized is Filifactor alocis. While this Gram-positive anaerobic rod has been identified in peri-implantitis, in endodontic infections, and in patients with localized aggressive periodontitis, its presence is now observed at significantly higher levels in patients with adult periodontitis or refractory periodontitis. Its colonization properties and its potential virulence attributes support the proposal that F. alocis should be included as a diagnostic indicator of periodontal disease. Moreover, these emerging characteristics would be consistent with the polymicrobial synergy and dysbiosis (PSD) periodontal pathogenesis model. Here, unique characteristics of F. alocis are discussed. F. alocis has specific factors that can modulate multiple changes in the microbial community and host cell proteome. It is likely that such variations at the molecular level are responsible for the functional changes required to mediate the pathogenic process.

Life in a Diverse Oral Community - Strategies for Oxidative Stress Survival

BACKGROUND

While the oral cavity harbors more than 680 bacterial species, the interaction and association of selected bacterial species play a role in periodontal diseases. Bacterial species including Porphyromonas gingivalis, Treponema denticola and Tannerella forsythia, a consortium previously designated as the "red complex" is now being expanded to include other new emerging pathogens that are significantly associated with periodontal disease.

HIGHLIGHT

In addition to novel mechanisms for oxidative resistance of individual species, community dynamics may lead to an overall strategy for survival in the inflammatory environment of the periodontal pocket. Complex systems controlled by response regulators protect against oxidative and nitrosative stress.

CONCLUSION

The combination of these multifaceted strategies would provide a comprehensive defense and support system against the repetitive host immune response to promote microbial persistence and disease.

Salivary markers of oxidative stress in patients with obstructive sleep apnea treated with continuous positive airway pressure

PURPOSE

Obstructive sleep apnea syndrome (OSAS) is characterized by elevated oxidative stress. Measurement of oxidative stress in saliva seems to be promising in long-term treatment monitoring of OSAS patients. In this study, our aim was to investigate whether short-term continuous positive airway pressure (CPAP) treatment would influence oxidative stress in saliva.

METHODS

Patients with diagnosed OSAS (16 women, 28 men) underwent polysomnography during the first night and CPAP treatment during the second night. Saliva samples were taken in the evening and morning on both days. Markers of oxidative stress and antioxidant status were analyzed in saliva.

RESULTS

Evening concentrations of the salivary thiobarbituric acid reacting substances (p < 0.001), advanced glycation end-products (p < 0.001), and advanced oxidation protein products (p < 0.01) were significantly lower than morning values during the diagnostic night. However, salivary concentrations of none of the oxidative stress markers were significantly influenced by the CPAP treatment. No changes in salivary antioxidant status after CPAP therapy were found.

CONCLUSION

Salivary markers of oxidative stress and antioxidant status do not change significantly after one night treatment with CPAP. On the contrary, after 1 month with CPAP therapy, reduced markers of oxidative stress were reported. Therefore, the future studies should be focused on finding the optimal sampling frequency to clarify the potential of saliva for the monitoring of OSAS treatment.