Dysbiosis by neutralizing commensal mediated inhibition of pathobionts

Yeast cell wall derivatives as a potential strategy for modulating oral microbiota and dental plaque biofilm

Introduction

Derivatives from Saccharomyces cerevisiae yeast including yeast extracts and yeast cell walls are sustainable sources of valuable nutrients, including dietary fibers and proteins. Previous studies have shown that certain components from these yeast derivatives can inhibit the growth of harmful intestinal bacteria and promote the growth of beneficial bacteria. However, the effects of yeast derivatives on oral health have not yet been investigated.

Methods

An in vitro oral biofilm model was employed to examine the impacts of yeast derivatives on the oral microbiota and their potential benefits for maintaining oral homeostasis. The model incorporated dental plaque donor material from both healthy and periodontitis diagnosed individuals. Biofilm formation, density, and microbial composition were quantified. Additionally, the production of short-chain fatty acids in the biofilm supernatants was measured.

Results

Yeast extracts had only minor effects on oral biofilm formation. In contrast, yeast cell wall derivatives, which are rich in polysaccharides such as beta-glucans and mannans, significantly reduced the density of the oral biofilms in vitro. This reduction in biofilm density was associated with an overall shift in the bacterial community composition, including an increase in beneficial bacteria and a decrease in the abundance of Tannerella forsythia, an important species involved in bacterial coaggregation and the development and maturation of the oral biofilm. Furthermore, the yeast cell wall derivatives decreased the production of short-chain fatty acids, including acetic and butyric acid. These findings were consistent across both healthy and periodontitis microbiomes.

Conclusion

This study has demonstrated the potential of yeast cell wall derivatives to positively impact oral health by significantly reducing biofilm density, modulating the oral microbial composition, and decreasing the production of short-chain fatty acids. The observed effects highlight the promising applications of these yeast-based compounds as an approach to managing oral diseases. Further research is needed to fully elucidate the mechanisms of action and explore the clinical potential of yeast cell wall derivatives in promoting and maintaining oral health.

Quantifying synthetic bacterial community composition with flow cytometry: efficacy in mock communities and challenges in co-cultures

Determination of bacterial community composition in synthetic communities is critical for understanding microbial systems. The community composition is typically determined through bacterial plating or through PCR-based methods, which can be labor-intensive, expensive, or prone to bias. Simultaneously, flow cytometry has been suggested as a cheap and fast alternative. However, since the technique captures the phenotypic state of bacterial cells, accurate determination of community composition could be affected when bacteria are co-cultured. We investigated the performance of flow cytometry for quantifying oral synthetic communities and compared it to the performance of strain specific qPCR and 16S rRNA gene amplicon sequencing. Therefore, axenic cultures, mock communities and co-cultures of oral bacteria were prepared. Random forest classifiers trained on flow cytometry data of axenic cultures were used to determine the composition of the synthetic communities, as well as strain specific qPCR and 16S rRNA gene amplicon sequencing. Flow cytometry was shown to have a lower average root mean squared error and outperformed the PCR-based methods in even mock communities (flow cytometry: 0.11 ± 0.04; qPCR: 0.26 ± 0.09; amplicon sequencing: 0.15 ± 0.01). When bacteria were co-cultured, neither flow cytometry, strain-specific qPCR, nor 16S rRNA gene amplicon sequencing resulted in similar community composition. Performance of flow cytometry was decreased compared with mock communities due to changing phenotypes. Finally, discrepancies between flow cytometry and strain-specific qPCR were found. These findings highlight the challenges ahead for quantifying community composition in co-cultures by flow cytometry.IMPORTANCEQuantification of bacterial composition in synthetic communities is crucial for understanding and steering microbial interactions. Traditional approaches like plating, strain-specific qPCR, and amplicon sequencing are often labor-intensive and expensive and limit high-throughput experiments. Recently, flow cytometry has been suggested as a swift and cheap alternative for quantifying communities and has been successfully demonstrated on simple bacterial mock communities. However, since flow cytometry measures the phenotypic state of cells, measurements can be affected by differing phenotypes. Especially, changing phenotypes resulting from co-culturing bacteria can have a profound effect on the applicability of the technique in this context. This research illustrates the feasibility and challenges of flow cytometry for the determination of community structure in synthetic mock communities and co-cultures.

Gut microbial dysbiosis and inflammation: Impact on periodontal health

Periodontitis is widely acknowledged as the most prevalent type of oral inflammation, arising from the dynamic interplay between oral pathogens and the host's immune responses. It is also recognized as a contributing factor to various systemic diseases. Dysbiosis of the oral microbiota can significantly alter the composition and diversity of the gut microbiota. Researchers have delved into the links between periodontitis and systemic diseases through the "oral-gut" axis. However, whether the associations between periodontitis and the gut microbiota are simply correlative or driven by causative mechanistic interactions remains uncertain. This review investigates how dysbiosis of the gut microbiota impacts periodontitis, drawing on existing preclinical and clinical data. This study highlights potential mechanisms of this interaction, including alterations in subgingival microbiota, oral mucosal barrier function, neutrophil activity, and abnormal T-cell recycling, and offers new perspectives for managing periodontitis, especially in cases linked to systemic diseases.

Biosynthesis of mitis group streptococcal glycolipids and their roles in physiology and antibiotic susceptibility

Bacterial cell surface components such as lipoteichoic acids (LTAs) play critical roles in host-microbe interactions and alter host responses based on their chemical structures. Mitis group streptococci have commensal and pathogenic interactions with the human host and produce Type IV LTAs that are slightly different in chemical structures between species. To reveal the molecular bases for the intricate interactions between MGS and human hosts, a detailed understanding of the structure and biosynthetic process of MGS LTAs is needed. In this study, we used genomic and lipidomic techniques to elucidate the biosynthetic processes of Type IV LTA and its associated glycolipid anchors, monohexosyl-diacylglycerol and dihexosyl-diacyglycerol, in the infectious endocarditis isolate Streptococcus sp. strain 1643. Through establishing a murine sepsis model, we validated the essentiality of these glycolipids in the full virulence of S. mitis. Additionally, we found that these glycolipids play an important role in protecting the bacteria from antimicrobials. Overall, results obtained through this study both confirm and dispute aspects of the existing model of glycolipids biosynthesis, provide insights into the fundamental roles of bacterial glycolipids, as well as suggest the potential of targeting glycolipids for developing antimicrobial therapeutics.

Effects of clear aligners and traditional removable appliances on oral microbiome in mixed dentition: a comparative study

BACKGROUND

This prospective study aims to investigate the comparative effects of clear aligners (CA) and traditional removable appliances (RA) on the cariogenic risk of patients in mixed dentition, focusing on the oral microbiome.

METHODS

25 children were included and assigned into CA and RA groups. Supragingival plaque and saliva samples were collected, and clinical parameters including Decay-missing-filled teeth index (DMFT), Plaque Index (PI) and Gorelick Index (GI) were recorded before treatment (T0) and after 6-month follow-up (T1). DNA was extracted from supragingival plaque and saliva and analyzed via 16S rDNA gene sequencing.

RESULTS

Clinical parameters showed no statistically significant difference between groups at each time point or within group over time (p > 0.05). In both RA and CA groups, saliva exhibited significantly higher alpha diversity compared to supragingival plaque at T1, as indicated by the significantly higher Chao1 and Shannon indexes (p < 0.05). Regarding beta diversity, significant difference was observed in saliva and supragingival plaque samples between T0 and T1 within group RA (p < 0.05, Adonis), whereas no such significance was noted in the CA group (p > 0.05, Adonis). At the genus level, Lactobacillus exhibited a statistically significant increase in saliva and supragingival plaque of group RA from T0 to T1 (p < 0.05), and an increasing trend in the group CA without statistical significance (p > 0.05). At T1, Lactobacillus levels were comparable between groups, whereas species-level analysis revealed distinct cariogenic species.

CONCLUSION

Both clear aligners and traditional removable appliances resulted in elevated cariogenic risk of patients in mixed dentition at the microbial level. Distinct alterations in cariogenic species were observed to be induced by various orthodontic appliances.

Electrolyzed Saline Targets Biofilm Periodontal Pathogens In Vitro

Preventing the development and recurrence of periodontal diseases often includes antimicrobial mouthrinses to control the growth of the periodontal pathogens. Most antimicrobials are nonselective, targeting the symbiotic oral species as well as the dysbiosis-inducing ones. This affects the overall microbial composition and metabolic activity and consequently the host-microbe interactions, which can be detrimental (associated with inflammation) or beneficial (health-associated). Consequently, guiding the antimicrobial effect for modulating the microbial composition to a health-associated one should be considered. For such an approach, this study investigated electrolyzed saline as a novel rinse. Electrolyzed saline was prepared from sterile saline using a portable electrolysis device. Multispecies oral homeostatic and dysbiotic biofilms were grown on hydroxyapatite discs and rinsed daily with electrolyzed saline (EOS). Corresponding positive (NaOCl) and negative (phosphate-buffered saline) controls were included. After 3 rinses, biofilms were analyzed with viability quantitative polymerase chain reaction and scanning electron microscopy. Supernatants of rinsed biofilms were used for metabolic activity analysis (high-performance liquid chromatography) through measuring organic acid content. In addition, human oral keratinocytes (HOKs) were exposed to EOS to test biocompatibility (cytotoxicity and inflammation induction) and also to rinsed biofilms to assess their immunogenicity after rinsing. Rinsing the dysbiotic biofilms with EOS could reduce the counts of the pathobionts (>3 log10 Geq/mm2 reduction) and avert biofilm dysbiosis (≤1% pathobiont abundance), leading to the dominance of commensal species (≥99%), which altered both biofilm metabolism and interleukin 8 (IL-8) induction in HOKs. EOS had no harmful effects on homeostatic biofilms. The scanning electron micrographs confirmed the same. In addition, tested concentrations of EOS did not have any cytotoxic effects and did not induce IL-8 production in HOKs. EOS showed promising results for diverting dysbiosis in in vitro rinsed biofilms and controlling key periopathogens, with no toxic effects on commensal species or human cells. This novel rinsing should be considered for clinical applications.

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.

Molecular commensalism-how to investigate underappreciated health-associated polymicrobial communities

The study of human commensal bacteria began with the first observation of prokaryotes >340 years ago. Since then, the study of human-associated microbes has been justifiably biased toward the study of infectious pathogens. However, the role of commensal microbes has in recent years begun to be understood with some appreciation of them as potential protectors of host health rather than bystanders. As our understanding of these valuable microbes grows, it highlights how much more remains to be learned about them and their roles in maintaining health. We note here that a thorough framework for the study of commensals, both in vivo and in vitro is overall lacking compared to well-developed methodologies for pathogens. The modification and application of methods for the study of pathogens can work well for the study of commensals but is not alone sufficient to properly characterize their relationships. This is because commensals live in homeostasis with the host and within complex communities. One difficulty is determining which commensals have a quantifiable impact on community structure and stability as well as host health, vs benign microbes that may indeed serve only as bystanders. Human microbiomes are composed of bacteria, archaea, fungi, and viruses. This review focuses particularly on oral bacteria, yet many of the principles of commensal impacts on host health observed in the mouth can translate well to other host sites. Here, we discuss the value of commensals, the shortcomings involved in model systems for their study, and some of the more notable impacts they have upon not only each other but host health.

Human Serum Supplementation Promotes Streptococcus mitis Growth and Induces Specific Transcriptomic Responses

Streptococcus mitis is a normal member of the human oral microbiota and a leading opportunistic pathogen causing infective endocarditis (IE). Despite the complex interactions between S. mitis and the human host, understanding of S. mitis physiology and its mechanisms of adaptation to host-associated environments is inadequate, especially compared with other IE bacterial pathogens. This study reports the growth-promoting effects of human serum on S. mitis and other pathogenic streptococci, including S. oralis, S. pneumoniae, and S. agalactiae. Using transcriptomic analyses, we identified that, with the addition of human serum, S. mitis downregulates uptake systems for metal ions and sugars, fatty acid biosynthetic genes, and genes involved in stress response and other processes related with growth and replication. S. mitis upregulates uptake systems for amino acids and short peptides in response to human serum. Zinc availability and environmental signals sensed by the induced short peptide binding proteins were not sufficient to confer the growth-promoting effects. More investigation is required to establish the mechanism for growth promotion. Overall, our study contributes to the fundamental understanding of S. mitis physiology under host-associated conditions. IMPORTANCE S. mitis is exposed to human serum components during commensalism in the human mouth and bloodstream pathogenesis. However, the physiological effects of serum components on this bacterium remain unclear. Using transcriptomic analyses, S. mitis biological processes that respond to the presence of human serum were revealed, improving the fundamental understanding of S. mitis physiology in human host conditions.

Simultaneous Chemical Mapping of Live Biofilm Microenvironmental pH and Hydrogen Peroxide in Real Time with a Triple Scanning Electrochemical Microscopy Tip

Dental plaque biofilm is a complex ecosystem. The distribution of microbial species in the biofilm is heavily influenced by local chemical interactions that result from diverse metabolic activities and the nature of the released molecules. As a relevant example, H2O2-producing bacteria can antagonize disease-associated bacteria, leading to the maintenance of a healthy oral microbiome. Herein, we report the development of a triple-sensor (redox, pH, and H2O2) scanning electrochemical microscopy (SECM) tip capable of simultaneously mapping the pH and H2O2 concentration produced by a dental plaque-derived multispecies biofilm grown on hydroxyapatite. The pH sensor of the triple SECM tip showed a near Nernstian slope of -71.1 ± 2 mV/pH (N = 3), whereas the H2O2 sensor showed a slope of -0.052 ± 0.002 nA/μM H2O2 at pH 7.2 and a detection limit of 1.0 ± 0.2 μM (N = 7). There is no significant difference in the sensitivities of H2O2 sensors at pH 6.2, 7.2, and 8.2 at 95% CI (N = 7). The pH and H2O2 sensors demonstrated excellent reversibility with response times of 3 and 5 s, respectively, along with reliable stability over 4 h at 37 °C. The sensors did not show any cross talk between pH and H2O2 concentration ([H2O2]) measurements, highlighting the accuracy and versatility of the SECM tip. Simultaneous chemical imaging of pH and [H2O2] across the biofilm revealed a clustered distribution of local H2O2 concentrations, ranging from 0 to 17 μM. Conversely, the local pH remained constant at 7.2. The relation of local chemical profiles and the distribution of bacterial species within the oral microbiome was experimentally investigated in the context of bacterial H2O2 antagonism. The benefit of clustered H2O2 production was that the total area of H2O2 produced by smaller clusters was 67% more than that of a single cluster with the same starting number of bacteria. Thus, this triple SECM tip can potentially be used to study local molecular mechanisms that result in dysbiosis of the oral microbiome.

Antimicrobial potential of known and novel probiotics on in vitro periodontitis biofilms

Several oral diseases are characterized by a shift within the oral microbiome towards a pathogenic, dysbiotic composition. Broad-spectrum antimicrobials are often part of patient care. However, because of the rising antibiotic resistance, alternatives are increasingly desirable. Alternatively, supplying beneficial species through probiotics is increasingly showing favorable results. Unfortunately, these probiotics are rarely evaluated comparatively. In this study, the in vitro effects of three known and three novel Lactobacillus strains, together with four novel Streptococcus salivarius strains were comparatively evaluated for antagonistic effects on proximal agar growth, antimicrobial properties of probiotic supernatant and the probiotic's effects on in vitro periodontal biofilms. Strain-specific effects were observed as differences in efficacy between genera and differences within genera. While some of the Lactobacillus candidates were able to reduce the periodontal pathobiont A. actinomycetemcomitans, the S. salivarius strains were not. However, the S. salivarius strains were more effective against periodontal pathobionts P. intermedia, P. gingivalis, and F. nucleatum. Vexingly, most of the Lactobacillus strains also negatively affected the prevalence of commensal species within the biofilms, while this was lower for S. salivarius strains. Both within lactobacilli and streptococci, some strains showed significantly more inhibition of the pathobionts, indicating the importance of proper strain selection. Additionally, some species showed reductions in non-target species, which can result in unexpected and unexplored effects on the whole microbiome.

Mode of killing determines the necrotrophic response of oral bacteria

Background

Bacteria respond to changes in their environment, such as nutrient depletion and antimicrobials exposure. Antimicrobials result not only in bacterial death, but also have a hand in determining species abundances and ecology of the oral biofilms. Proximity of dead bacterial cells to living ones is an important environmental change or stress factor. Dead bacteria represent high concentrations of nutrients, such as proteins, lipids, sugars, and nucleic acids. Living bacteria can use these biomasses as a nutrients source, which is termed necrotrophy.

Aim

This study investigates the effect of exposing living oral bacteria (planktonic and biofilms) to their dead siblings after being killed by heat or hydrogen peroxide.

Results

Tested bacterial species showed different responses towards the dead cells, depending on the mode of killing, the nutritional value of the culture media, and the the dead cells density. The multispecies oral biofilms showed different responses towards the supplementation of dead cells during biofilm development, while matured biofilms were more resilient.

Conclusion

This study indicates that dead bacteria resulting from antiseptics use may imbalance the nutrient availability in the oral cavity, resulting in overgrowth of opportunistic species, and hence ecological changes in oral communities, or introducing new bacterial phenotypes.

Glycerol strengthens probiotic effect of Limosilactobacillus reuteri in oral biofilms: a synergistic synbiotic approach

Both in vitro and in vivo studies have shown that the probiotic Limosilactobacillus reuteri can improve oral health. L. reuteri species are known to produce the antimicrobial 'reuterin' from glycerol. In order to further increase its antimicrobial activity, this study evaluated the effect of the combined use of glycerol and Limosilactobacillus reuteri (ATCC PTA 5289) in view of using a synergistic synbiotic over a probiotic. An antagonistic agar growth and a multispecies biofilm model showed that the antimicrobial potential of the probiotic was significantly enhanced against periodontal pathobionts and anaerobic commensals when supplemented with glycerol. Synbiotic biofilms also showed a significant reduction in inflammatory expression of human oral keratinocytes (HOK-18A), but only when the keratinocytes were preincubated with the probiotic. Probiotic preincubation of keratinocytes or probiotic- and synbiotic treatment of biofilms alone were insufficient to significantly reduce inflammatory expression. Overall, this study shows that combining glycerol with the probiotic L. reuteri into a synergistic synbiotic can greatly improve the effectiveness of the latter. One sentence summary: The use of a synbiotic formulation of Limosilactobacillus reuteri with glycerol over the probiotic improves antimicrobial effects and reduced inflammatory response to oral biofilms. This article is protected by copyright. All rights reserved.

Streptococcus gordonii-Induced miRNAs Regulate CCL20 Responses in Human Oral Epithelial Cells

The mechanisms through which oral commensal bacteria mitigates uncontrolled inflammatory responses of the oral mucosa remain unknown. Here, we show that representative oral bacterial species normally associated with oral health [S. gordonii (Sg), V. parvula (Vp), A. naeslundii (An), C. sputigena (Cs), and N. mucosa (Nm)] enhanced differential chemokine responses in oral epithelial cells (OECs), with some bacteria (An, Vp, and Nm) inducing higher chemokine levels (CXCL1, CXCL8) than others (Sg, Cs). Although all bacterial species (except Cs) increased CCL20 mRNA levels consistent with protein elevations in cell lysates, only An, Vp, and Nm induced higher CCL20 secretion, similar to the effect of the oral pathogen F. nucleatum (Fn). In contrast, most CCL20 remained associated with OECs exposed to Sg and negligible amounts released into the cell supernatants. Consistently, Sg attenuated An-induced CCL20. MiR-4516 and miR-663a were identified as Sg-specifically induced miRNAs modulating validated targets of chemokine-associated pathways. Cell transfection with miR-4516 and miR-663a decreased An- and Fn-induced CCL20. MiRNA upregulation and attenuation of An-induced CCL20 by Sg were reversed by catalase. Up-regulation of both miRNAs was specifically enhanced by oral streptococci H2O2-producers. These findings suggest that CCL20 levels produced by OECs in response to bacterial challenge are regulated by Sg-induced miR-4516 and miR-663a in a mechanism that involves hydrogen peroxide. This type of molecular mechanism could partly explain the central role of specific oral streptococcal species in balancing inflammatory and antimicrobial responses given the critical role of CCL20 in innate (antimicrobial) and adaptive immunity (modulates Th17 responses).

Antimicrobial Mechanisms of Leucocyte- and Platelet Rich Fibrin Exudate Against Planktonic Porphyromonas gingivalis and Within Multi-Species Biofilm: A Pilot Study

Leucocyte- and platelet rich fibrin (L-PRF) is an autologous biomaterial used in regenerative procedures. It has an antimicrobial activity against P. gingivalis although the mechanism is not fully understood. It was hypothesized that L-PRF exudate releases hydrogen peroxide and antimicrobial peptides that inhibit P. gingivalis growth. Agar plate and planktonic culture experiments showed that the antimicrobial effect of L-PRF exudate against P. gingivalis was supressed by peroxidase or pepsin exposure. In developing multi-species biofilms, the antimicrobial effect of L-PRF exudate was blocked only by peroxidase, increasing P. gingivalis growth with 1.3 log genome equivalents. However, no effect was shown on other bacteria. Pre-formed multi-species biofilm trials showed no antimicrobial effect of L-PRF exudate against P. gingivalis or other species. Our findings showed that L-PRF exudate may release peroxide and peptides, which may be responsible for its antimicrobial effect against P. gingivalis. In addition, L-PRF exudate had an antimicrobial effect against P. gingivalis in an in vitro developing multi-species biofilm.

Differences in chlorhexidine mouthrinses formulations influence the quantitative and qualitative changes in in-vitro oral biofilms

OBJECTIVE

Chlorhexidine mouthrinses are marketed in different formulations. This study aimed at investigating qualitative and quantitative changes in in-vitro multispecies oral biofilms, induced by different chlorhexidine-containing mouthrinses.

BACKGROUND DATA

Earlier studies comparing chlorhexidine mouthrinses are either clinical studies or in-vitro studies assessing the antimicrobial efficacy of the mouthrinses. However, no clear investigations are available regarding ecological impact of different chlorhexidine formulations on in-vitro multispecies oral biofilms after rinsing with different chlorhexidine formulations.

METHODS

Nine commercially available chlorhexidine mouthrinses were selected. Multispecies oral communities (14 species) were grown for 48 h in a Biostat-B Twin bioreactor. After that, they were used to develop biofilms on the surface of hydroxyapatite disks in 24-well pates for 48 h. Biofilms were then rinsed once or multiple times with the corresponding mouthrinse. Biofilms were collected before starting the rinsing experiment and every 24 h for 3 days and vitality quantitative PCR was performed. The experiment was repeated 3 independent times on 3 different days and the results were analyzed using a linear mixed model.

RESULTS

The mouthrinses provoked different effects in terms of change in total viable bacterial load (VBL), ecology, and community structure of the multispecies biofilms. There was no relation between chlorhexidine concentrations, presence, or absence of cetylpyridinium chloride and/or alcohol, and the observed effects. Some tested chlorhexidine mouthrinses (MC, HG, HH, and HI) strongly lowered the total VBL (≈10⁰⁷ Geq/ml), but disrupted biofilm symbiosis (≥40% of the biofilms communities are pathobionts). On the other hand, other tested chlorhexidine mouthrinses (MD, ME, and HF) had limited impact on total VBL (≥10¹⁰ Geq/ml), but improved the biofilm ecology and community structure (≤10% of the biofilms communities are pathobionts).

CONCLUSION

Not all chlorhexidine mouthrinses have the same effect on oral biofilms. Their effect seems to be strongly product dependent and vary according to their compositions and formulations.

Comparison of the modulatory effects of three structurally similar potential prebiotic substrates on an in vitro multi-species oral biofilm

Previous research identified potential prebiotic substrates for oral health like the structural analogues N-acetyl-D-mannosamine (NADM) and N-acetyl-D-glucosamine (NADG). The main hypothesis of the current study was twofold. Firstly, it was hypothesized that the modulatory effects of NADM are not limited to changes in multi-species oral biofilm composition, but also include effects on metabolism, virulence, and inflammatory potential. Secondly, the presence and orientation of their N-acetyl group could play a role. Therefore, a comparison was made between the effects of NADM, NADG and D-(+)-mannose on multi-species oral biofilms. Besides a beneficial compositional shift, NADM-treated biofilms also showed an altered metabolism, a reduced virulence and a decreased inflammatory potential. At a substrate concentration of 1 M, these effects were pronounced for all biofilm aspects, whereas at ~ 0.05 M (1%_(w/v)) only the effects on virulence were pronounced. When comparing between substrates, both the presence and orientation of the N-acetyl group played a role. However, this was generally only at 1 M and dependent on the biofilm aspect. Overall, NADM was found to have different effects at two concentrations that beneficially modulate in vitro multi-species oral biofilm composition, metabolism, virulence and inflammatory potential. The presence and orientation of the N-acetyl group influenced these effects.

Potential prebiotic substrates modulate composition, metabolism, virulence and inflammatory potential of an in vitro multi-species oral biofilm

Background: Modulation of the commensal oral microbiota constitutes a promising preventive/therapeutic approach in oral healthcare. The use of prebiotics for maintaining/restoring the health-associated homeostasis of the oral microbiota has become an important research topic.

Aims: This study hypothesised that in vitro 14-species oral biofilms can be modulated by (in)direct stimulation of beneficial/commensal bacteria with new potential prebiotic substrates tested at 1 M and 1%_(w/v), resulting in more host-compatible biofilms with fewer pathogens, decreased virulence and less inflammatory potential.

Methods: Established biofilms were repeatedly rinsed with N-acetyl-D-glucosamine, α-D-lactose, D-(+)-trehalose or D-(+)-raffinose at 1 M or 1%_(w/v). Biofilm composition, metabolic profile, virulence and inflammatory potential were eventually determined.

Results: Repeated rinsing caused a shift towards a more health-associated microbiological composition, an altered metabolic profile, often downregulated virulence gene expression and decreased the inflammatory potential on oral keratinocytes. At 1 M, the substrates had pronounced effects on all biofilm aspects, whereas at 1%_(w/v) they had a pronounced effect on virulence gene expression and a limited effect on inflammatory potential.

Conclusion: Overall, this study identified four new potential prebiotic substrates that exhibit different modulatory effects at two different concentrations that cause in vitro multi-species oral biofilms to become more host-compatible.

Polymicrobial communities in periodontal disease: Their quasi-organismal nature and dialogue with the host

In health, indigenous polymicrobial communities at mucosal surfaces maintain an ecological balance via both inter-microbial and host-microbial interactions that promote their own and the host's fitness, while preventing invasion by exogenous pathogens. However, genetic and acquired destabilizing factors (including immune deficiencies, immunoregulatory defects, smoking, diet, obesity, diabetes and other systemic diseases, and aging) may disrupt this homeostatic balance, leading to selective outgrowth of species with the potential for destructive inflammation. This process, known as dysbiosis, underlies the development of periodontitis in susceptible hosts. The pathogenic process is not linear but involves a positive-feedback loop between dysbiosis and the host inflammatory response. The dysbiotic community is essentially a quasi-organismal entity, where constituent organisms communicate via sophisticated physical and chemical signals and display functional specialization (eg, accessory pathogens, keystone pathogens, pathobionts), which enables polymicrobial synergy and dictates the community's pathogenic potential or nososymbiocity. In this review, we discuss early and recent studies in support of the polymicrobial synergy and dysbiosis model of periodontal disease pathogenesis. According to this concept, disease is not caused by individual "causative pathogens" but rather by reciprocally reinforced interactions between physically and metabolically integrated polymicrobial communities and a dysregulated host inflammatory response.

Streptococcus pneumoniae, S. mitis, and S. oralis Produce a Phosphatidylglycerol-Dependent, ltaS-Independent Glycerophosphate-Linked Glycolipid

Lipoteichoic acid (LTA) is a Gram-positive bacterial cell surface polymer that participates in host-microbe interactions. It was previously reported that the major human pathogen Streptococcus pneumoniae and the closely related oral commensals S. mitis and S. oralis produce type IV LTAs. Herein, using liquid chromatography/mass spectrometry-based lipidomic analysis, we found that in addition to type IV LTA biosynthetic precursors, S. mitis, S. oralis, and S. pneumoniae also produce glycerophosphate (Gro-P)-linked dihexosyl (DH)-diacylglycerol (DAG), which is a biosynthetic precursor of type I LTA. cdsA and pgsA mutants produce DHDAG but lack (Gro-P)-DHDAG, indicating that the Gro-P moiety is derived from phosphatidylglycerol (PG), whose biosynthesis requires these genes. S. mitis, but not S. pneumoniae or S. oralis, encodes an ortholog of the PG-dependent type I LTA synthase, ltaS. By heterologous expression analyses, we confirmed that S. mitisltaS confers poly(Gro-P) synthesis in both Escherichia coli and Staphylococcus aureus and that S. mitisltaS can rescue the growth defect of an S. aureusltaS mutant. However, we do not detect a poly(Gro-P) polymer in S. mitis using an anti-type I LTA antibody. Moreover, Gro-P-linked DHDAG is still synthesized by an S. mitisltaS mutant, demonstrating that S. mitis LtaS does not catalyze Gro-P transfer to DHDAG. Finally, an S. mitisltaS mutant has increased sensitivity to human serum, demonstrating that ltaS confers a beneficial but currently undefined function in S. mitis. Overall, our results demonstrate that S. mitis, S. pneumoniae, and S. oralis produce a Gro-P-linked glycolipid via a PG-dependent, ltaS-independent mechanism.

IMPORTANCE The cell wall is a critical structural component of bacterial cells that confers important physiological functions. For pathogens, it is a site of host-pathogen interactions. In this work, we analyze the glycolipids synthesized by the mitis group streptococcal species, S. pneumoniae, S. oralis, and S. mitis. We find that all produce the glycolipid, glycerophosphate (Gro-P)-linked dihexosyl (DH)-diacylglycerol (DAG), which is a precursor for the cell wall polymer type I lipoteichoic acid in other bacteria. We investigate whether the known enzyme for type I LTA synthesis, LtaS, plays a role in synthesizing this molecule in S. mitis. Our results indicate that a novel mechanism is responsible. Our results are significant because they identify a novel feature of S. pneumoniae, S. oralis, and S. mitis glycolipid biology.

Antibiofilm effects of titanium surfaces modified by laser texturing and hot-pressing sintering with silver

Peri-implant diseases are one of the main causes of dental implant failure. New strategies for dental implants manufacturing have been developed to prevent the accumulation of bacteria and related inflammatory reactions. The main aim of this work was to develop laser-treated titanium surfaces covered with silver that generate a electrical dipole to inhibit the oral bacteria accumulation. Two approaches were developed for that purpose. In one approach a pattern of different titanium dioxide thickness was produced on the titanium surface, using a Q-Switched Nd:YAG laser system operating at 1064 nm. The second approach was to incorporate silver particles on a laser textured titanium surface. The incorporation of the silver was performed by laser sintering and hot-pressing approaches. The anti-biofilm effect of the discs were tested against biofilms involving 14 different bacterial strains growth for 24 and 72 hr. The morphological aspects of the surfaces were evaluated by optical and field emission guns scanning electronical microscopy (FEGSEM) and therefore the wettability and roughness were also assessed. Physicochemical analyses revealed that the test surfaces were hydrophilic and moderately rough. The oxidized titanium surfaces showed no signs of antibacterial effects when compared to polished discs. However, the discs with silver revealed a decrease of accumulation of Porphyromonas gingivalis and Prevotella intermedia strains. Thus, the combination of Nd:YAG laser irradiation and hot-pressing was effective to produce silver-based patterns on titanium surfaces to inhibit the growth of pathogenic bacterial species. The laser parameters can be optimized to achieve different patterns, roughness, and thickness of the modified titanium layer regarding the type and region of the implant.

Implications of the Human Gut-Brain and Gut-Cancer Axes for Future Nanomedicine

Recent clinical and pathological evidence have implicated the gut microbiota as a nexus for modulating the homeostasis of the human body, impacting conditions from cancer and dementia to obesity and social behavior. The connections between microbiota and human diseases offer numerous opportunities in medicine, most of which have limited or no therapeutic solutions available. In light of this paradigm-setting trend in science, this review aims to provide a comprehensive and timely summary of the mechanistic pathways governing the gut microbiota and their implications for nanomedicines targeting cancer and neurodegenerative diseases. Specifically, we discuss in parallel the beneficial and pathogenic relationship of the gut microbiota along the gut-brain and gut-cancer axes, elaborate on the impact of dysbiosis and the gastrointestinal corona on the efficacy of nanomedicines, and highlight a molecular mimicry that manipulates the universal cross-β backbone of bacterial amyloid to accelerate neurological disorders. This review further offers a forward-looking section on the rational design of cancer and dementia nanomedicines exploiting the gut-brain and gut-cancer axes.

Clinical and Microbiological Effects of Weekly Supragingival Irrigation with Aerosolized 0.5% Hydrogen Peroxide and Formation of Cavitation Bubbles in Gingival Tissues after This Irrigation: A Six-Month Randomized Clinical Trial

Introduction

The study investigated the effect of weekly supragingival irrigation with aerosolized 0.5% hydrogen peroxide (H₂O₂) solution as a maintenance periodontal therapy on clinical and microbiological parameters in patients with chronic periodontitis. The other purpose was to investigate whether cavitation bubbles can penetrate not only into periodontitis-damaged tissues but also into ex vivo porcine healthy periodontal tissues.

Materials and Methods

The study included 35 systemically healthy patients with chronic periodontitis (CP). After nonsurgical periodontal debridement (NSPD), all patients were randomized into two groups: the Control group (NSDP alone, n = 18) and the Test group (NSDP plus supragingival irrigation, n = 17). Clinical (Approximal Plaque Index (API), Bleeding Index (BI), and Modified Gingival Index (MGI)) and microbiological (Polymerase Chain Reaction technology (using a micro-IDent® kit)) measurements were performed at the initial time point, 3 months, and 6 months after NSPD. The impact of supragingival irrigation on diseased gingival tissues of CP patients (n = 5) and on ex vivo porcine healthy gingival tissue samples (n = 3) was evaluated to estimate morphological changes in healthy and diseased gingival tissues.

Results

Morphological data revealed that supragingival irrigation caused the formation of cavitation bubbles in diseased gingival tissue of CP patients and in healthy porcine gingival tissues. The decrease in API, BI, and MGI scores after 6 months in the Test group significantly (p ≤ 0.01, p ≤ 0.05, and p ≤ 0.01, respectively) exceeded that in the Control group. Test group patients demonstrated a decrease in periodontal sites showing Pocket Probing Depth > 4 mm and, after 6 months, a statistically significant decrease in the proportion of periopathogenic bacteria.

Conclusion

The effectiveness of mechanical periodontal treatment combined with weekly supragingival irrigation with aerosolized 0.5% H₂O₂ solution on clinical and microbiological parameters of periodontal tissues of periodontitis patients is reliably higher than that of mechanical periodontal debridement alone. It has been found that cavitation bubbles as a result of irrigation with the aerosolized 0.5% hydrogen peroxide solution can form not only in periodontal tissues of periodontitis patients but also in ex vivo porcine healthy gingival tissues.

Metagenomic Assessment of Different Interventions for Treatment of Chronic Periodontitis: A Systematic Review and Meta-Analysis

Background:

Chronic periodontitis is attributed to oral microbial imbalance and host inflammatory reaction.

Objective:

Our review addresses the question of: Are the available interventions able to regain oral microbial balance in patients having chronic periodontitis?

Data Sources:

We performed a comprehensive systematic search of MEDLine via Pubmed, Cochrane CENTRAL, Clinicalkey, Clarivate Analytics, Springer materials, Wiley, SAGE, Elsevier, Taylor & Francis group, and Wolter Kluwer, together with hand searching and searching the grey literature.

Eligibility Criteria:

We included interventional studies testing the microbiome analysis using metagenomic techniques as an outcome to any intervention for chronic periodontitis.

Study Appraisal and Synthesis Methods:

All studies were imported in Mendeley. The risk of bias was assessed using the specific tool for each study design. The results were analysed using RevMan. All the review steps were performed in duplicates.

Results:

The search yielded 2700 records. After exclusion steps, 10 records were found eligible. We included 5 RCTs, 1 non-RCT, 3 before-and-after studies, and 1 ongoing study. The studies tested non-surgical periodontal treatment with and without antibiotic coverage, probiotics, sodium hypochlorite rinse, and different toothpaste ingredients. One RCT tested the use of enamel matrix derivatives in cases with furcation involvement.

Limitations:

The eligible available studies were small in number. Also, the risk of bias and lack of a standardized protocol impaired the ability to pool all the results.

Conclusions:

The body of the available evidence is not sufficient, and future studies are recommended to better evaluate the effect of periodontal treatments on the periodontal microbiome.

Terpinen-4-ol and carvacrol affect multi-species biofilm composition

The aim of this study was to investigate the cytotoxic activity and inhibitory effect of terpinen-4-ol (T4ol) and carvacrol against single- and multi-species biofilms. The toxicity of each compound was tested on oral keratinocytes and evaluated by XTT assay. Inhibition and eradication of single-species biofilms were analyzed by crystal violet assay and the effect on multi-species biofilm composition was evaluated by qPCR. T4ol and carvacrol did not affect the epithelial cell viability, in contrast to chlorhexidine, which showed a high cytotoxic effect. Inhibition and eradication of single-species biofilms treated with T4ol and carvacrol were observed. The same inhibitory effect was observed for multi-species biofilms, especially on periodontal pathogens. In conclusion, specific concentrations of T4ol and carvacrol without toxicity towards the epithelial cells reduced the numbers of periodontal pathogens in single- and multi-species biofilms.

Aggregatibacter actinomycetemcomitans mediates protection of Porphyromonas gingivalis from Streptococcus sanguinis hydrogen peroxide production in multi-species biofilms

Mixed species biofilms are shaped and influenced by interactions between species. In the oral cavity, dysbiosis of the microbiome leads to diseases such as periodontitis. Porphyromonas gingivalis is a keystone pathogen of periodontitis. In this study, we showed that polymicrobial biofilm formation promoted the tolerance of Porphyromonas gingivalis to oxidative stress under micro-aerobic conditions. The presence of Streptococcus sanguinis, an oral commensal bacterium, inhibited the survival of P. gingivalis in dual-species biofilms via the secretion of hydrogen peroxide (H₂O₂). Interestingly, this repression could be attenuated by the presence of Aggregatibacter actinomycetemcomitans in tri-species biofilms. It was also shown that the katA gene, encoding a cytoplasmic catalase in A. actinomycetemcomitans, was responsible for the reduction of H₂O₂ produced by S. sanguinis, which consequently increased the biomass of P. gingivalis in tri-species biofilms. Collectively, these findings reveal that polymicrobial interactions play important roles in shaping bacterial community in biofilm. The existence of catalase producers may support the colonization of pathogens vulnerable to H₂O₂, in the oral cavity. The catalase may be a potential drug target to aid in the prevention of periodontitis.

Rapid Bactericidal Action of Propolis against Porphyromonas gingivalis

Propolis, a resinous substance produced by bees, is used as a folk medicine for treatment of periodontal diseases. However, its mode of the action and the compounds responsible for its activities remain obscure. In the present study, we comprehensively investigated the antibacterial activities of ethanol-extracted propolis (EEP) and EEP-derived compounds toward Porphyromonas gingivalis, a keystone pathogen for periodontal diseases. Broth microdilution and agar dilution assays were used to determine the minimum inhibitory concentrations of EEP against a range of oral bacterial species, of which P. gingivalis showed a higher level of sensitivity than oral commensals such as streptococci. Its antibacterial activity toward P. gingivalis was maintained even after extensive heat treatment, demonstrating a high level of thermostability. EEP also induced death of P. gingivalis cells by increasing membrane permeability within 30 min. Spatiotemporal analysis based on high-speed atomic force microscopy revealed that EEP immediately triggered development of aberrant membrane blebs, followed by bleb fusion events on the bacterial surface. Furthermore, we isolated artepillin C, baccharin, and ursolic acid from EEP as antibacterial compounds against P. gingivalis. Of those, artepillin C and baccharin showed bacteriostatic activities with membrane blebbing, while ursolic acid showed bactericidal activity with membrane rupture. In particular, ursolic acid demonstrated a greater ability to affect bacterial membrane potential with increased membrane permeability, probably because of its highly lipophilic nature as compared with other compounds. Taken together, these findings provide mechanistic insight into the antibacterial activities of EEP and its exquisite membrane-targeting antibacterial compounds and imply the applicability of narrow-spectrum therapeutics with EEP for treatment of periodontitis. In addition, the advanced technology utilized in the present study to visualize the nanometer-scale dynamics of microorganisms will contribute to expanding our understanding of the activities of antimicrobials and the mechanism of drug resistance in bacteria.

Dysbiotic Biofilms Deregulate the Periodontal Inflammatory Response

Periodontal diseases originate from a dysbiosis within the oral microbiota, which is associated with a deregulation of the host immune response. Although little is known about the initiation of dysbiosis, it has been shown that H₂O₂ production is one of the main mechanisms by which some commensal bacteria suppress the outgrowth of pathobionts. Current models emphasize the critical nature of complex microbial biofilms that form unique microbial ecologies and of their change during transition from health (homeostatic) to disease (dysbiotic). However, very little is known on how this alters their virulence and host responses. The objective of this study was to determine differences in virulence gene expression by pathobionts and the inflammatory host response in homeostatic and dysbiotic biofilms originating from the same ecology. Quantitative polymerase chain reaction was performed to quantify the pathobiont outgrowth. Expression analysis of bacterial virulence and cellular inflammatory genes together with cytokine enzyme-linked immunosorbent assays were used to detect differences in bacterial virulence and to analyze potential differences in inflammatory response. An increase in pathobionts in induced dysbiotic biofilms was observed compared to homeostatic biofilms. The main virulence genes of all pathobionts were upregulated in dysbiotic biofilms. Exposure of these dysbiotic biofilms to epithelial and fibroblast cultures increased the expression of interleukin (IL)-6, IL-1β, tumor necrosis factor-α, and matrix metalloprotease 8, but especially the chemokine CXCL8 (IL-8). Conversely, homeostatic and beneficial biofilms had a minor immune response at the messenger RNA and protein level. Overall, induced dysbiotic biofilms enriched in pathobionts and virulence factors significantly increased the inflammatory response compared to homeostatic and commensal biofilms.

Plasticity of the Pyruvate Node Modulates Hydrogen Peroxide Production and Acid Tolerance in Multiple Oral Streptococci

Commensal Streptococcus sanguinis and Streptococcus gordonii are pioneer oral biofilm colonizers. Characteristic for both is the SpxB-dependent production of H₂O₂, which is crucial for inhibiting competing biofilm members, especially the cariogenic species Streptococcus mutans H₂O₂ production is strongly affected by environmental conditions, but few mechanisms are known. Dental plaque pH is one of the key parameters dictating dental plaque ecology and ultimately oral health status. Therefore, the objective of the current study was to characterize the effects of environmental pH on H₂O₂ production by S. sanguinis and S. gordoniiS. sanguinis H₂O₂ production was not found to be affected by moderate changes in environmental pH, whereas S. gordonii H₂O₂ production declined markedly in response to lower pH. Further investigation into the pyruvate node, the central metabolic switch modulating H₂O₂ or lactic acid production, revealed increased lactic acid levels for S. gordonii at pH 6. The bias for lactic acid production at pH 6 resulted in concomitant improvement in the survival of S. gordonii at low pH and seems to constitute part of the acid tolerance response of S. gordonii Differential responses to pH similarly affect other oral streptococcal species, suggesting that the observed results are part of a larger phenomenon linking environmental pH, central metabolism, and the capacity to produce antagonistic amounts of H₂O₂IMPORTANCE Oral biofilms are subject to frequent and dramatic changes in pH. S. sanguinis and S. gordonii can compete with caries- and periodontitis-associated pathogens by generating H₂O₂ Therefore, it is crucial to understand how S. sanguinis and S. gordonii adapt to low pH and maintain their competitiveness under acid stress. The present study provides evidence that certain oral bacteria respond to environmental pH changes by tuning their metabolic output in favor of lactic acid production, to increase their acid survival, while others maintain their H₂O₂ production at a constant level. The differential control of H₂O₂ production provides important insights into the role of environmental conditions for growth competition of the oral flora.

Necrotrophic growth of periodontopathogens is a novel virulence factor in oral biofilms

The oral use of antimicrobial agents embedded in toothpastes and mouth rinses results in an oral microbial massacre with high amounts of dead bacteria in close proximity to few surviving bacteria. It was hypothesized that this provides the surviving pathogenic bacteria a large amount of dead microbial biomass as a nutritional source for growth (necrotrophy). This study demonstrated the necrotrophic growth of periodontal pathogens in the presence of different dead oral species. In addition, the presence of dead bacteria resulted in an outgrowth of several periodontal pathogens in complex multi-species biofilms. Additionally, upon contact with dead oral bacteria, virulence genes of P. intermedia and P. gingivalis were up-regulated (necrovirulence). This resulted in a more pronounced epithelial cytotoxicity (necrotoxicity). These findings indicate that presence of dead bacteria induce necrotrophy, necrovirulence and necrotoxicity in several oral pathogens.