Analysis of the Streptococcus mutans Proteome during Acid and Oxidative Stress Reveals Modules of Protein Coexpression and an Expanded Role for the TreR Transcriptional Regulator

Multifunctional Temporary Dental Nanofillers Enhanced with Synergistically Active Chlorine-Containing Molecules against Streptococcus mutans and Its Effects on Oral Epithelial Cells

Temporary dental fillers are critical for safeguarding teeth during the period between caries removal and permanent restoration. However, conventional fillers often lack sufficient antimicrobial properties to prevent bacterial colonization. To address this issue, the study researches on the development of antimicrobial Temporary Dental Nano-Fillers (TDNF) capable of targeting multiple cariogenic pathogens, including Streptococcus mutans, Lactobacillus casei, Candida albicans, and mixed-species planktonic cells/biofilms, which play a significant role in the progression of dental caries. The TDNF was formulated using a combination of Chloramine-T (CRT) and Cetylpyridinium Chloride (CPC), both known for their antimicrobial efficacy, and embedded in a nanoparticle matrix of hydroxyapatite (HAP) and silicon dioxide (SiO2). The synergistic antimicrobial effect of CRT and CPC, with MIC90 values of 12.5 and 6.25 ppm, respectively, displayed potent activity against S. mutans. Proteomic analysis, including gene ontology and protein-protein interaction network evaluations, further confirmed significant disruptions in S. mutans metabolic and stress response pathways, highlighting the bactericidal effectiveness of the formulation against S. mutans. Additionally, the formulation demonstrated sustained antimicrobial efficacy against other cariogenic pathogens such as L. casei, C. albicans and mixed-species planktonic cells and biofilms over a 16-day period. The TDNF (HAP+SiO2+CRT+CPC matrix) exhibited superior mechanical properties with a compressive strength of 237.7 MPa, flexural strength of 124.3 MPa, and shear bond strength of 52 MPa. Biocompatibility tests conducted on human oral squamous carcinoma cells (OECM-1) indicated over 95% cell viability, affirming its safety for preclinical or clinical applications. The multifunctional TDNF developed in this study successfully combines mechanical reinforcement with broad-spectrum antimicrobial efficacy, offering a promising interim solution in dental restorations. Its ability to protect against microbial colonization, while maintaining structural stability, positions it as an effective temporary material that enhances patient outcomes during the period before permanent restoration.

Genetic characterization of glyoxalase pathway in oral streptococci and its contribution to interbacterial competition

Objectives

To analyze contributions to microbial ecology of Reactive Electrophile Species (RES), including methylglyoxal, generated during glycolysis.

Methods

Genetic analyses were performed on the glyoxalase pathway in Streptococcus mutans (SM) and Streptococcus sanguinis (SS), followed by phenotypic assays and transcription analysis.

Results

Deleting glyoxalase I (lguL) reduced RES tolerance to a far greater extent in SM than in SS, decreasing the competitiveness of SM against SS. Although SM displays a greater RES tolerance than SS, lguL-null mutants of either species showed similar tolerance; a finding consistent with the ability of methylglyoxal to induce the expression of lguL in SM, but not in SS. A novel paralogue of lguL (named gloA2) was identified in most streptococci. SM mutant ∆gloA2SM showed little change in methylglyoxal tolerance yet a significant growth defect and increased autolysis on fructose, a phenotype reversed by the addition of glutathione, or by the deletion of a fructose: phosphotransferase system (PTS) that generates fructose-1-phosphate (F-1-P).

Conclusions

Fructose contributes to RES generation in a PTS-specific manner, and GloA2 may be required to degrade certain RES derived from F-1-P. This study reveals the critical roles of RES in fitness and interbacterial competition and the effects of PTS in modulating RES metabolism.

SMU_1361c regulates the oxidative stress response of Streptococcus mutans

Dental caries is the most common chronic infectious disease around the world and disproportionately affects the marginalized socioeconomic group. Streptococcus mutans, considered a primary etiological agent of caries, depends on the coordinated physiological response to tolerate the oxidative stress generated by commensal species within dental plaque, which is a critical aspect of its pathogenicity. Here, we identified and characterized a novel tetracycline repressor family regulator, SMU_1361c, which appears to be acquired by the bacteria via horizontal gene transfer. Surprisingly, smu_1361c functions as a negative transcriptional regulator to regulate gene expression outside its operon and is involved in the oxidative stress response of S. mutans. The smu_1361c overexpression strain UA159/pDL278-1361c was more susceptible to oxidative stress and less competitive against hydrogen peroxide generated by commensal species Streptococcus gordonii and Streptococcus sanguinis. Transcriptomics analysis revealed that smu_1361c overexpression resulted in the significant downregulation of 22 genes, mainly belonging to three gene clusters responsible for the oxidative stress response. The conversed DNA binding motif of SMU_1361c was determined by electrophoretic mobility shift and DNase I footprinting assay with purified SMU_1361c protein; therefore, smu_1361c is directly involved in gene transcription related to the oxidative stress response. Crucially, our finding provides a new understanding of how S. mutans deals with the oxidative stress that is required for pathogenesis and will facilitate the development of new and improved therapeutic approaches for dental caries.IMPORTANCEStreptococcus mutans is the major organism associated with the development of dental caries, which globally is the most common chronic disease. To persist and survive in biofilms, S. mutans must compete with commensal species that occupy the same ecological niche. Here, we uncover a novel molecular mechanism of how tetracycline repressor family regulator smu_1361c is involved in the oxidative stress response through transcriptomics analysis, electrophoretic mobility shift assay, and DNase I footprinting assay. Furthermore, we demonstrated that smu_1361c mediates S. mutans sensitivity to oxidative stress and competitiveness with commensal streptococci. Therefore, this study has revealed a previously unknown regulation between smu_1361c and genes outside its operon and demonstrated the importance of smu_1361c in the oxidative stress response and the fitness of S. mutans within the plaque biofilms, which can be exploited as a new therapy to modulate ecological homeostasis and prevent dental caries.

Determination of dysbiosis by the method of multiplex real-time polymerase chain reaction in chronic catarrhal gingivitis in children

OBJECTIVE

Aim: The aim of the study was to determine the quantitative and qualitative characteristics of the microbiota of dento-gingival plaque in children to improve the quality of treatment of chronic catarrhal gingivitis.

PATIENTS AND METHODS

Materials and Methods: It was examined 16 children aged 9-16 years with a diagnosis of K05.1: chronic gingivitis and 10 persons with intact gums were taken as a comparison group. A clinical dental examination was performed on the study participants and a sample was taken to determine the bacteria in the periodontal plaque.

RESULTS

Results: The results of statistical processing of the research data allowed us to establish that in patients with chronic gingivitis, quantitative indicators of the total bacterial mass, Lactobacillus spp., Enterobacteriaceae, Gardnerella vaginalis/Prevotella bivia/Porphyromonas spp. in the sample of periodontal plaque significantly exceeded the indicators of healthy patients. It was determined that the examined children with chronic gingivitis, the total number of Lactobacillus spp. significantly exceeds its amount in people with intact gums.

CONCLUSION

Conclusions: The changes in the quantitative and qualitative characteristics of the main representatives of the microf i lm of dento-gingival plaque, which characterize dysbiosis, are of signif i cant clinical signif i cance. Study of the quantitative characteristics of Lactobacterium spp., Enterobacterium spp., Streptococcacea spp., Gardnerella spp., Prevotella spp., Porphyromonas spp., Eubacteridacea spp., Mycoplasma (hominis + genitalium), Candida spp. is a diagnostic factor in determining the condition of the mucous membrane of the oral cavity.

Bacterial acid stress response: from cellular changes to antibiotic tolerance and phenotypic heterogeneity

Most bacteria are neutralophiles but can survive fluctuations in pH in their environment. Herein, we provide an overview of the adaptation of several human, soil, and food bacteria to acid stress, mainly based on next-generation sequencing studies, highlighting common and specific strategies. We also discuss the interplay between acid stress response and antibiotic tolerance, as well as the response of individual cells.

Illuminating the oral microbiome and its host interactions: recent advancements in omics and bioinformatics technologies in the context of oral microbiome research

The oral microbiota has an enormous impact on human health, with oral dysbiosis now linked to many oral and systemic diseases. Recent advancements in sequencing, mass spectrometry, bioinformatics, computational biology, and machine learning are revolutionizing oral microbiome research, enabling analysis at an unprecedented scale and level of resolution using omics approaches. This review contains a comprehensive perspective of the current state-of-the-art tools available to perform genomics, metagenomics, phylogenomics, pangenomics, transcriptomics, proteomics, metabolomics, lipidomics, and multi-omics analysis on (all) microbiomes, and then provides examples of how the techniques have been applied to research of the oral microbiome, specifically. Key findings of these studies and remaining challenges for the field are highlighted. Although the methods discussed here are placed in the context of their contributions to oral microbiome research specifically, they are pertinent to the study of any microbiome, and the intended audience of this includes researchers would simply like to get an introduction to microbial omics and/or an update on the latest omics methods. Continued research of the oral microbiota using omics approaches is crucial and will lead to dramatic improvements in human health, longevity, and quality of life.

Interactive Effect of Salivary Protein Carbonyl, Total Glutathione, pH, and Flow Rate on Root Caries Severity: A Case-Control Study

Aims and Objectives

Oxidant and antioxidant components in saliva play an essential role in caries development. The purpose of the current study was to disclose the interactive effect of salivary protein carbonyl (PC), total glutathione (GSH), pH, and flow rate on root caries severity.

Materials and Methods

The control and study groups consisted of 90 older adults of both genders classified into six groups: normal salivary flow rate with no root caries (control), normal salivary flow rate with incipient root caries, normal salivary flow rate with shallow root caries, hyposalivation with no root caries, hyposalivation with incipient root caries, and hyposalivation with shallow root caries. Each group consisted of 15 older adults. The study participants were selected from those patients who attended the teaching hospital at the College of the Dentistry/University of Baghdad and fit the study's criteria. Unstimulated saliva was collected. Both salivary pH and flow rate were determined immediately. After that, saliva was subjected to biochemical analysis to determine PC and total GSH levels colorimetrically. Root surface caries was diagnosed clinically using the Root Caries Index. Data were statistically analyzed using descriptive statistics, two-way univariate analysis of variance, two-way multivariate analysis of variance, and Pearson's correlation coefficient (α = 5%).

Results

Salivary total glutathione revealed a significant interactive effect with salivary flow rate and root decay severity. Levels of salivary total GSH were significantly higher in subjects with shallow root caries than those with incipient root caries; no root caries levels of salivary PC were significantly high in the hyposalivation group, but no correlation with caries severity was found. High root caries severity was found to be associated with reduced salivary pH and flow rate.

Conclusion

A significant interactive effect was recorded for salivary flow rate, pH, and total GSH on root caries severity except for salivary PC.

The Baker Lab at the OHSU School of Dentistry: leveraging bioinformatics and molecular biology to discover how the bacteria that live in our mouth impact human health and disease

The microorganisms living in the human oral cavity, collectively known as the oral microbiota, play a critical role in not only oral health, but systemic and overall health. The Baker Lab leverages emerging technologies in bioinformatics and molecular biology to answer fundamental questions regarding the ecology, physiology, and pathogenesis of the oral microbiota. We use a microbial 'omics approach, which has included pioneering the use of nanopore sequencing on saliva and oral bacterial RNA. The resulting work discovered novel bacterial species and biosynthetic pathways which impact the ecology of the oral microbiota and its relationship to human disease. This article will briefly define the oral microbiota. It will also summarize how bioinformatics and 'omics-based research have revolutionized oral health research. The article will then provide a broad summary of our past, present and future research and educational programs.

mucG, mucH, and mucI Modulate Production of Mutanocyclin and Reutericyclins in Streptococcus mutans B04Sm5

Streptococcus mutans is considered a primary etiologic agent of dental caries, which is the most common chronic infectious disease worldwide. S. mutans B04Sm5 was recently shown to produce reutericyclins and mutanocyclin through the muc biosynthetic gene cluster and to utilize reutericyclins to inhibit the growth of neighboring commensal streptococci. In this study, examination of S. mutans and muc phylogeny suggested evolution of an ancestral S. mutans muc into three lineages within one S. mutans clade and then horizontal transfer of muc to other S. mutans clades. The roles of the mucG and mucH transcriptional regulators and the mucI transporter were also examined. mucH was demonstrated to encode a transcriptional activator of muc. mucH deletion reduced production of mutanocyclin and reutericyclins and eliminated the impaired growth and inhibition of neighboring streptococci phenotypes, which are associated with reutericyclin production. ΔmucG had increased mutanocyclin and reutericyclin production, which impaired growth and increased the ability to inhibit neighboring streptococci. However, deletion of mucG also caused reduced expression of mucD, mucE, and mucI. Deletion of mucI reduced mutanocyclin and reutericylin production but enhanced growth, suggesting that mucI may not transport reutericyclin as its homolog does in Limosilactobacillus reuteri. Further research is needed to determine the roles of mucG and mucI and to identify any cofactors affecting the activity of the mucG and mucH regulators. Overall, this study provided pangenome and phylogenetic analyses that serve as a resource for S. mutans research and began elucidation of the regulation of reutericyclins and mutanocyclin production in S. mutans. IMPORTANCE S. mutans must be able to outcompete neighboring organisms in its ecological niche in order to cause dental caries. S. mutans B04Sm5 inhibited the growth of neighboring commensal streptococci through production of reutericyclins via the muc biosynthetic gene cluster. In this study, an S. mutans pangenome database and updated phylogenetic tree were generated that will serve as valuable resources for the S. mutans research community and that provide insights into the carriage and evolution of S. mutans muc. The MucG and MucH regulators, and the MucI transporter, were shown to modulate production of reutericyclins and mutanocyclin. These genes also affected the ability of S. mutans to inhibit neighboring commensals, suggesting that they may play a role in S. mutans virulence.