Beyond Streptococcus mutans: dental caries onset linked to multiple species by 16S rRNA community analysis

Progress in Oral Microbiome Related to Oral and Systemic Diseases: An Update

The human oral microbiome refers to an ecological community of symbiotic and pathogenic microorganisms found in the oral cavity. The oral cavity is an environment that provides various biological niches, such as the teeth, tongue, and oral mucosa. The oral cavity is the gateway between the external environment and the human body, maintaining oral homeostasis, protecting the mouth, and preventing disease. On the flip side, the oral microbiome also plays an important role in the triggering, development, and progression of oral and systemic diseases. In recent years, disease diagnosis through the analysis of the human oral microbiome has been realized with the recent development of innovative detection technology and is overwhelmingly promising compared to the previous era. It has been found that patients with oral and systemic diseases have variations in their oral microbiome compared to normal subjects. This narrative review provides insight into the pathophysiological role that the oral microbiome plays in influencing oral and systemic diseases and furthers the knowledge related to the oral microbiome produced over the past 30 years. A wide range of updates were provided with the latest knowledge of the oral microbiome to help researchers and clinicians in both academic and clinical aspects. The microbial community information can be utilized in non-invasive diagnosis and can help to develop a new paradigm in precision medicine, which will benefit human health in the era of post-metagenomics.

Function-adaptive clustered nanoparticles reverse Streptococcus mutans dental biofilm and maintain microbiota balance

Dental plaques are biofilms that cause dental caries by demineralization with acidogenic bacteria. These bacteria reside inside a protective sheath which makes any curative treatment challenging. We propose an antibiotic-free strategy to disrupt the biofilm by engineered clustered carbon dot nanoparticles that function in the acidic environment of the biofilms. In vitro and ex vivo studies on the mature biofilms of Streptococcus mutans revealed >90% biofilm inhibition associated with the contact-mediated interaction of nanoparticles with the bacterial membrane, excessive reactive oxygen species generation, and DNA fragmentation. An in vivo examination showed that these nanoparticles could effectively suppress the growth of S. mutans. Importantly, 16S rRNA analysis of the dental microbiota showed that the diversity and richness of bacterial species did not substantially change with nanoparticle treatment. Overall, this study presents a safe and effective approach to decrease the dental biofilm formation without disrupting the ecological balance of the oral cavity.

Deacidification of Cranberry Juice Reduces Its Antibacterial Properties against Oral Streptococci but Preserves Barrier Function and Attenuates the Inflammatory Response of Oral Epithelial Cells

Cranberry (Vaccinium macrocarpon) may be a potent natural adjuvant for the prevention of oral diseases due to its anti-adherence, anti-cariogenic, and anti-inflammatory properties. However, the high titrable acidity of cranberry juice (CJ) has been reported to cause gastrointestinal discomfort, leading consumers to restrict their intake of this beverage. Electrodialysis with a bipolar membrane (EDBM) can reduce the organic acid content of CJ while retaining the flavonoids associated with potential health benefits. This study aimed to assess how the deacidification of CJ by EDBM impacts the antibacterial properties of the beverage against cariogenic (Streptococcus mutans, Streptococcus sobrinus) and commensal (Streptococcus gordonii, Streptococcus oralis, Streptococcus salivarius) streptococci, and how it affects oral epithelial barrier function and inflammatory response in an in vitro model. The removal of organic acids from CJ (deacidification rate ≥42%) reduced the bactericidal activity of the beverage against planktonic S. mutans and S. gordonii after a 15-min exposure, whereas only the viability of S. gordonii was significantly impacted by CJ deacidification rate when the bacteria were embedded in a biofilm. Moreover, conditioning saliva-coated hydroxyapatite with undiluted CJ samples significantly lowered the adherence of S. mutans, S. sobrinus, and S. oralis. With respect to epithelial barrier function, exposure to CJ deacidified at a rate of ≥19% maintained the integrity of a keratinocyte monolayer over the course of 24 h compared to raw CJ, as assessed by the determination of transepithelial electrical resistance (TER) and fluorescein isothiocyanate-conjugated dextran paracellular transport. These results can be in part attributed to the inability of the deacidified CJ to disrupt two tight junction proteins, zonula occludens-1 and occludin, following exposure, unlike raw CJ. Deacidification of CJ impacted the secretion of IL-6, but not of IL-8, by oral epithelial cells. In conclusion, deacidification of CJ appears to provide benefits with respect to the maintenance of oral health.

Streptococcus, Centrocestus formosanus and Myxobolus tilapiae concurrent infections in farmed Nile tilapia (Oreochromis niloticus)

Stress triggered concurrent microbial/parasitic infections are prevalent in earthen pond based farmed Nile tilapia Oreochromis niloticus. In the current study, a total of thirty five O. niloticus were collected from a commercial fish farm with a history of severe mortalities at Port Said, Egypt. Nile tilapia samples were subjected to bacteriological, parasitological and pathological examinations. Twenty one Enterococcus fecalis and 15 Streptococcus agalactiae isolates were presumptively identified utilizing the semi-automated API 20 Strept test kit. The identities of the retrieved bacteria were confirmed by the sequencing of 16 S rRNA gene. Moribund O. niloticus were found to be heavily infected by one or both of Centrocestus formosanus encysted metacercariae (EMC) and/or Myxobolus tilapiae spores presenting a unique form of synergistic and/or symbiotic relationship. The identities of both parasites were confirmed through morphological and molecular characterization. Variable circulatory, degenerative, necrotic and proliferative changes were also noticed in hematopoietic organs. Interestingly, multiple myxobolus spores and EMC were noticed in some histological sections. It was obvious that the current concurrent bacterial and parasitic infections are triggered by the deleterious effects of some stressing environmental conditions. The unfavorable climatic conditions (high temperature and high relative humidity) recorded at the surge of mortalities are probable predisposing stress factors.

Cariogenic Biofilm: Pathology-Related Phenotypes and Targeted Therapy

The initiation and development of cariogenic (that is, caries-related) biofilms are the result of the disruption of homeostasis in the oral microenvironment. There is a daily accumulation of dental biofilm on the surface of teeth and its matrix of extracellular polymers supports the host in its defense against invading microbes, thus helping to achieve oral microbial homeostasis. However, the homeostasis can be broken down under certain circumstances such as during long-term exposure to a low pH environment which results in the dominance of acidogenic and acid-tolerating species in the dental biofilm and, thus, triggers the shift of harmless biofilm to an acidic one. This work aims to explore microbial diversity and the quorum sensing of dental biofilm and their important contributions to oral health and disease. The complex and multispecies ecosystems of the cariogenic biofilm pose significant challenges for the modulation of the oral microenvironment. Promising treatment strategies are those that target cariogenic niches with high specificity without disrupting the balance of the surrounding oral microbiota. Here, we summarized the recent advances in modulating cariogenic biofilm and/or controlling its pathogenic traits.

A Review of the Role of Probiotic Supplementation in Dental Caries

Dental diseases are among the common health issues experienced around the world. Dental caries is one of the most predominant oral diseases worldwide. Major factors associated with caries development include poor oral hygiene, the content of specific carbohydrates in the diet, dental biofilm formation, the cariogenic microbial load, reduction in salivary flow, insufficient fluoride exposure, gingival recession, genetic factors, and lack of personal attention to one's dental health. Several preventive measures have been implemented to reduce the risk of the development of caries. Probiotics are live microbes that when administered in suitable amounts confer health benefits on the host; they are recognized as potential adjunct therapeutic agents for several diseases. The present manuscript summarizes recent findings on the role of probiotics in dental caries prevention and the possible mechanisms of probiotic effects. Review of the literature indicates the regular consumption of probiotic products significantly reduced the risk of caries by inhibiting cariogenic bacteria and enriching commensal microbes in the oral cavity. Buffering the salivary pH, production of bacteriocin and enzymes (dextranase, mutanase, and urease), the capacity of competing for the adhesion and colonization on tooth surfaces are the possible mechanisms behind the beneficial effect of probiotics. Further studies are necessary to address the efficacy of long-term probiotic supplementation on the control of dental diseases and the influence of childhood probiotic supplementation on the risk of caries development.

Compositional Differences in the Oral Microbiome of E-cigarette Users

Electronic (e)-cigarettes have been advocated as a safer alternative to conventional tobacco cigarettes. However, there is a paucity of data regarding the impact of e-cigarette aerosol deposition on the human oral microbiome, a key component in human health and disease. We aimed to fill this knowledge gap through a comparative analysis of the microbial community profiles from e-cigarette users and healthy controls [non-smokers/non-vapers (NSNV)]. Moreover, we sought to determine whether e-cigarette aerosol exposure from vaping induces persistent changes in the oral microbiome. To accomplish this, salivary and buccal mucosa samples were collected from e-cigarette users and NSNV controls, with additional oral samples collected from e-cigarette users after 2 weeks of decreased use. Total DNA was extracted from all samples and subjected to PCR amplification and sequencing of the V3-V4 hypervariable regions of the 16S rRNA gene. Our analysis revealed several prominent differences associated with vaping, specific to the sample type (i.e., saliva and buccal). In the saliva, e-cigarette users had a significantly higher alpha diversity, observed operational taxonomic units (OTUs) and Faith's phylogenetic diversity (PD) compared to NSNV controls, which declined with decreased vaping. The buccal mucosa swab samples were marked by a significant shift in beta diversity between e-cigarette users and NSNV controls. There were also significant differences in the relative abundance of several bacterial taxa, with a significant increase in Veillonella and Haemophilus in e-cigarette users. In addition, nasal swabs demonstrated a trend toward higher colonization rates with Staphylococcus aureus in e-cigarette users relative to controls (19 vs. 7.1%; p = n.s.). Overall, these data reveal several notable differences in the oral bacterial community composition and diversity in e-cigarette users as compared to NSNV controls.

Association of Candida albicans and Cbp+ Streptococcus mutans with early childhood caries recurrence

Early childhood caries (ECC) recurrence occurs in approximately 40% of treated cases within one year. The association of Streptococcus mutans and Candida albicans with the onset of ECC is well known. Also, S. mutans strains harboring collagen-binding proteins (Cbps) avidly bind to collagen-rich dentin and are linked to increased caries risk. Here, we investigated the presence of Cbp⁺ S. mutans and C. albicans in saliva and dental plaque of children with varying caries statuses, and their salivary microbiome. In this cross-sectional study, 143 children who were caries-free (n = 73), treated for ECC with no signs of recurrence after 6 months (n = 45), or treated for ECC and experiencing recurrence within 6 months following treatment (n = 25) were enrolled. Co-infection with C. albicans and S. mutans, especially Cbp⁺ S. mutans, was strongly associated with caries recurrence. Subjects of the recurrence group infected with Cbp⁺ S. mutans showed a greater burden of Candida spp. and of Mutans streptococci in dentin than those infected with Cbp^- strains. Salivary microbiome analysis revealed that Streptococcus parasanguinis was overrepresented in the caries recurrence group. Our findings indicate that Cbp⁺ S. mutans and C. albicans are intimately associated with caries recurrence, contributing to the establishment of recalcitrant biofilms.

The predictive power of saliva electrolytes exceeds that of saliva microbiomes in diagnosing early childhood caries

Early childhood caries (ECC) is one of the most prevalent chronic diseases affecting children worldwide, and thus its etiology, diagnosis, and prognosis are of particular clinical significance. This study aims to test the ability of salivary microbiome and electrolytes in diagnosing ECC, and their interplays within the same population. We here simultaneously profiled salivary microbiome and biochemical components of 331 children (166 caries-free (H group) and 165 caries-active children (C group)) aged 4-6 years. We identified both salivary microbial and biochemical dysbiosis associated with ECC. Remarkably, K⁺, Cl^-, NH₄⁺, Na⁺, SO₄^2-, Ca²⁺, Mg²⁺, and Br^- were enriched while pH and NO₃^- were depleted in ECC. Moreover, the dmft index (ECC severity) positively correlated with Cl^-, NH₄⁺, Ca²⁺, Mg²⁺, Br^-, while negatively with pH and NO₃^-. Furthermore, machine-learning classification models were constructed based on these biomarkers from saliva microbiota, or electrolytes (and pH). Unexpectedly, the electrolyte-based classifier (AUROC = 0.94) outperformed microbiome-based (AUROC = 0.70) one and the composite-based one (with both microbial and biochemical data; AUC = 0.89) in predicting ECC. Collectively, these findings indicate ECC-associated alterations and interplays in the oral microbiota, electrolytes and pH, underscoring the necessity of developing diagnostic models with predictors from salivary electrolytes.

A Novel Competence Pathway in the Oral Pathogen Streptococcus sobrinus

Streptococcus sobrinus is an etiologic cause of dental caries (tooth decay) in humans. Our knowledge of S. sobrinus is scant despite the organism's important role in oral health. It is widely believed that S. sobrinus lacks the natural competence pathways that are used by other streptococci to regulate growth, virulence, and quorum sensing. The lack of natural competence has also prevented genetic manipulation of S. sobrinus, limiting our knowledge of its pathogenicity. We discovered that most strains of S. sobrinus contain a new class of the ComRS competence system. Although S. sobrinus is typically placed among the mutans group streptococci, the S. sobrinus ComRS system is most similar to the competence pathways in the salivarius group. Unlike all other ComRS systems, the S. sobrinus pathway contains 2 copies of the transcriptional regulator ComR and has a peptide pheromone (XIP) that lacks any aromatic amino acids. Synthetic XIP enables transformation of S. sobrinus with plasmid or linear DNA, and we leverage this newfound genetic tractability to confirm that only 1 of the ComR homologs is required for induced competence while the other appears to suppress competence. Exogenous XIP increases the expression of bacteriocin gene clusters and produces an antimicrobial response that inhibits growth of S. mutans. We also identified 2 strains of S. sobrinus that appear to be "cheaters" by either not responding to or not producing XIP. We show how a recombination event in the nonresponsive strain could restore function of the ComRS pathway but delete the gene encoding XIP. Thus, the S. sobrinus ComRS pathway provides new tools for studying this pathogen and offers a lens into the evolution of ecological cheaters.

Core Microbiota Promotes the Development of Dental Caries

A previous longitudinal study about using microbiome as a caries indicator has successfully predicted early childhood caries (ECC) in healthy individuals, but there is no evidence to verify the composition of core microbiota and its pathogenicity in vitro and in vivo. Biofilm acidogenicity, S. mutans count, and biofilm composition were estimated by pH evaluation, colony-forming unit, and quantitative PCR, respectively. Extracellular polysaccharide production and enamel demineralization were observed by confocal laser scanning microscopy (CLSM) and transverse microradiography (TMR), respectively. A rat caries model was established for dental caries formation in vivo, and caries lesions were quantified by Keyes Scoring. We put forward that microbiota including Veillonella parvula, Fusobacterium nucleatum, Prevotella denticola, and Leptotrichia wadei served as the predictors for ECC may be the core microbiota in ECC. This study found that the core microbiota of ECC produced limited acid, but promoted growth and acidogenic ability of S. mutans. Besides, core microbiota could help to promote the development of biofilms. Moreover, the core microbiota enhanced the enamel demineralization in vitro and increased cariogenic potential in vivo. These results proved that core microbiota could promote the development of dental caries and plays an important role in the development of ECC.

Effect of HIV/HAART and Other Clinical Variables on the Oral Mycobiome Using Multivariate Analyses

The oral microbiome is likely a key element of homeostasis in the oral cavity. With >600 bacterial species and >160 fungal species comprising the oral microbiome, influences on its composition can have an impact on both local and systemic health.

The oral microbiome is considered an important factor in health and disease. We recently reported significant effects of HIV and several other clinical variables on the oral bacterial communities in a large cohort of HIV-positive and -negative individuals. The purpose of the present study was to similarly analyze the oral mycobiome in the same cohort. To identify fungi, the internal transcribed spacer 2 (ITS2) of the fungal rRNA genes was sequenced using oral rinse samples from 149 HIV-positive and 88 HIV-negative subjects that had previously undergone bacterial amplicon sequencing. Quantitative PCR was performed for total fungal content and total bacterial content. Interestingly, samples often showed predominance of a single fungal species with four major clusters predominated by Candida albicans, Candida dubliniensis, Malassezia restricta, or Saccharomyces cerevisiae. Quantitative PCR analysis showed the Candida-dominated sample clusters had significantly higher total fungal abundance than the Malassezia or Saccharomyces species. Of the 25 clinical variables evaluated for potential influences on the oral mycobiome, significant effects were associated with caries status, geographical site of sampling, sex, HIV under highly active antiretroviral therapy (HAART), and missing teeth, in rank order of statistical significance. Investigating specific interactions between fungi and bacteria in the samples often showed Candida species positively correlated with Firmicutes or Actinobacteria and negatively correlated with Fusobacteria, Proteobacteria, and Bacteroidetes. Our data suggest that the oral mycobiome, while diverse, is often dominated by a limited number of species per individual; is affected by several clinical variables, including HIV positivity and HAART; and shows genera-specific associations with bacterial groups.

Biocultural Drivers of Salivary Microbiota in Australian Aboriginal and Torres Strait Islander Children

Australian Aboriginal and Torres Strait Islander children experience unacceptably high rates of dental caries compared to their non-Indigenous Australian counterparts. Dental caries significantly impacts the quality of life of children and their families, particularly in remote communities. While many socioeconomic and lifestyle factors impact caries risk, the central role of the oral microbiota in mediating dental caries has not been extensively investigated in these communities. Here, we examine factors that shape diversity and composition of the salivary microbiota in Aboriginal and Torres Strait Islander children and adolescents living in the remote Northern Peninsula Area (NPA) of Far North Queensland. We employed 16S ribosomal RNA amplicon sequencing to profile bacteria present in saliva collected from 205 individuals aged 4–17 years from the NPA. Higher average microbial diversity was generally linked to increased age and salivary pH, less frequent toothbrushing, and proxies for lower socioeconomic status (SES). Differences in microbial composition were significantly related to age, salivary pH, SES proxies, and active dental caries. Notably, a feature classified as Streptococcus sobrinus increased in abundance in children who reported less frequent tooth brushing. A specific Veillonella feature was associated with caries presence, while features classified as Actinobacillus/Haemophilus and Leptotrichia were associated with absence of caries; a Lactobacillus gasseri feature increased in abundance in severe caries. Finally, we statistically assessed the interplay between dental caries and caries risk factors in shaping the oral microbiota. These data provide a detailed understanding of biological, behavioral, and socioeconomic factors that shape the oral microbiota and may underpin caries development in this group. This information can be used in the future to improve tailored caries prevention and management options for Australian Aboriginal and Torres Strait Islander children and communities.

Quorum Sensing in Streptococcus mutans Regulates Production of Tryglysin, a Novel RaS-RiPP Antimicrobial Compound

Bacteria interact and compete with a large community of organisms in their natural environment. Streptococcus mutans is one such organism, and it is an important member of the oral microbiota. We found that S. mutans uses a quorum-sensing system to regulate production of a novel posttranslationally modified peptide capable of inhibiting growth of several streptococcal species.

The genus Streptococcus encompasses a large bacterial taxon that commonly colonizes mucosal surfaces of vertebrates and is capable of disease etiologies originating from diverse body sites, including the respiratory, digestive, and reproductive tracts. Identifying new modes of treating infections is of increasing importance, as antibiotic resistance has escalated. Streptococcus mutans is an important opportunistic pathogen that is an agent of dental caries and is capable of systemic diseases such as endocarditis. As such, understanding how it regulates virulence and competes in the oral niche is a priority in developing strategies to defend from these pathogens. We determined that S. mutans UA159 possesses a bona fide short hydrophobic peptide (SHP)/Rgg quorum-sensing system that regulates a specialized biosynthetic operon featuring a radical-SAM (S-adenosyl-l-methionine) (RaS) enzyme and produces a ribosomally synthesized and posttranslationally modified peptide (RiPP). The pairing of SHP/Rgg regulatory systems with RaS biosynthetic operons is conserved across streptococci, and a locus similar to that in S. mutans is found in Streptococcus ferus, an oral streptococcus isolated from wild rats. We identified the RaS-RiPP product from this operon and solved its structure using a combination of analytical methods; we term these RiPPs tryglysin A and B for the unusual Trp-Gly-Lys linkage. We report that tryglysins specifically inhibit the growth of other streptococci, but not other Gram-positive bacteria such as Enterococcus faecalis or Lactococcus lactis. We predict that tryglysin is produced by S. mutans in its oral niche, thus inhibiting the growth of competing species, including several medically relevant streptococci.

Microbial population shift and metabolic characterization of silver diamine fluoride treatment failure on dental caries

The objective of this pilot study was to describe the microbial profiles present in the plaque and saliva of children who continued to develop new carious lesions following treatment with silver diamine fluoride ("nonresponders") compared to caries active, caries-free, and children immediately receiving SDF treatment for untreated caries in order to identify potential microbial differences that may relate to a re-incidence of caries. Saliva and plaque samples from infected and contralateral sites were obtained from twenty children who were either caries free, had active carious lesions, were caries active and received SDF treatment immediately before sampling, or had previously received SDF treatment and developed new caries. In total, 8,057,899 Illumina-generated sequence reads from 60 samples were obtained. Reads were processed using the Quantitative Insights Into Microbial Ecology pipeline. Group differences were assessed using Analysis of Variance Models and Tukey Honest Significant Differences. To identify significant taxa between treatment groups, Linear discriminant analysis Effect Size (LefSe) and Analysis of Differential Abundance Taking Sample Variation Into Account were used. Differential abundant analysis indicated that members of the Lachnospiraceae family were significantly enriched in non-responders and the genus Tannerella and species Granulicatella adiances were also highly abundant in this group. LefSe analysis between non-responders and SDF-treated groups revealed that genera Leptotrichia and Granulicatella were enriched in non-responders. We observed the highest abundance of phosphotransferase system and lowest abundance of lipopolysaccharide synthesis in non-responders. The microbiome in dental biofilms is responsible for initiation and progression of dental caries. SDF has been shown to be effective in arresting the progression carious lesions, in part due to its antimicrobial properties. Findings suggest that the differential abundance of select microbiota and specific pathway functioning in individuals that present with recurrent decay after SDF treatment may contribute to a potential failure of silver diamine fluoride to arrest dental caries. However, the short duration of sample collection following SDF application and the small sample size emphasize the need for further data and additional analysis.

Acquisition and establishment of the oral microbiota

Acquisition and establishment of the oral microbiota occur in a dynamic process over various stages and involve close and continuous interactions with the host and its environment. In the present review, we discuss the stages of this process in chronological order. We start with the prenatal period and address the following questions: ‘Is the fetus exposed to maternal microbiota during pregnancy?’ and ‘If so, what is the potential role of this exposure?’ We comment on recent reports of finding bacterial DNA in placenta during pregnancies, and provide current views on the potential functions of prenatal microbial encounters. Next, we discuss the physiological adaptations that take place in the newborn during the birth process and the effect of this phase of life on the acquisition of the oral microbiota. Is it really just exposure to maternal vaginal microbes that results in the difference between vaginally and Cesarian section‐born infants? Then, we review the postnatal phase, in which we focus on transmission of microbes, the intraoral niche specificity, the effects of the host behavior and environment, as well as the role of genetic background of the host on shaping the oral microbial ecosystem. We discuss the changes in oral microbiota during the transition from deciduous to permanent dentition and during puberty. We also address the finite knowledge on colonization of the oral cavity by microbes other than the bacterial component. Finally, we identify the main outstanding questions that limit our understanding of the acquisition and establishment of a healthy microbiome at an individual level.

Identification of unknown acid-resistant genes of oral microbiotas in patients with dental caries using metagenomics analysis

Acid resistance is critical for the survival of bacteria in the dental caries oral micro-environment. However, there are few acid-resistant genes of microbiomes obtained through traditional molecular biology experimental techniques. This study aims to try macrogenomics technologies to efficiently identify acid-resistant genes in oral microbes of patients with dental caries. Total DNA was extracted from oral microbiota obtained from thirty dental caries patients and subjected to high-throughput sequencing. This data was used to build a metagenomic library, which was compared to the sequences of two Streptococcus mutant known acid-resistant genes, danK and uvrA, using a BLAST search. A total of 19 and 35 unknown gene sequences showed similarities with S. mutans uvrA and dnaK in the metagenomic library, respectively. Two unknown genes, mo-dnaK and mo-uvrA, were selected for primer design and bioinformatic analysis based on their sequences. Bioinformatics analysis predicted them encoding of a human heat-shock protein (HSP) 70 and an ATP-dependent DNA repair enzyme, respectively, closely related with the acid resistance mechanism. After cloning, these genes were transferred into competent Escherichia coli for acid resistance experiments. E. coli transformed with both genes demonstrated acid resistance, while the survival rate of E. coli transformed with mo-uvrA was significantly higher in an acidic environment (pH = 3). Through this experiment we found that identify unknown acid-resistant genes in oral microbes of patients with caries by establishing a metagenomic library is very efficient. Our results provide an insight into the mechanisms and pathogenesis of dental caries for their treatment without affecting oral probiotics.

Antibiofilm effects of Thymus vulgaris and Hyptis spicigera essential oils on cariogenic bacteria

Aim: The inhibitory and antibiofilm effects of Thymus vulgaris (EOTv) and Hyptis spicigera essential oils (EOHs) on cariogenic microorganisms were evaluated. Materials & methods: The chemical characterization of EOTv was performed by gas chromatography/mass spectrometry. Streptococcus mutans, Streptococcus gordonii, Streptococcus sanguinis, Streptococcus mitis, Streptococcus sobrinus, Lactobacillus acidophilus and Actinomyces naeslundii were used for agar diffusion assays and determination of minimal inhibitory and minimal bactericide concentrations. In addition, 20 streptococci and lactobacilli clinical isolates were also tested. The effects of essential oil on microbial initial biofilm formation and on preformed microcosm biofilm formed from human saliva were studied. Results & conclusion: Both essential oils had inhibitory effects on the cariogenic species and reduced the bacterial adherence to dental enamel. Essential oils were able to disrupt preformed microcosm biofilms. Thymus vulgaris and Hyptis spicigera essential oils have potential to be used in the development of formulations to the control of cariogenic biofilms.

In Vitro Anti-Biofilm and Antibacterial Properties of Streptococcus downii sp. nov

The aim of this study was to evaluate the potential anti-biofilm and antibacterial activities of Streptococcus downii sp. nov. To test anti-biofilm properties, Streptococcus mutans, Actinomyces naeslundii, Veillonella parvula, Fusobacterium nucleatum, Porphyromonas gingivalis, and Aggregatibacter actinomycetemcomitans were grown in a biofilm model in the presence or not of S. downii sp. nov. for up to 120 h. For the potential antibacterial activity, 24 h-biofilms were exposed to S. downii sp. nov for 24 and 48 h. Biofilms structures and bacterial viability were studied by microscopy, and the effect in bacterial load by quantitative polymerase chain reaction. A generalized linear model was constructed, and results were considered as statistically significant at p < 0.05. The presence of S. downii sp. nov. during biofilm development did not affect the structure of the community, but an anti-biofilm effect against S. mutans was observed (p < 0.001, after 96 and 120 h). For antibacterial activity, after 24 h of exposure to S. downii sp. nov., counts of S. mutans (p = 0.019) and A. actinomycetemcomitans (p = 0.020) were significantly reduced in well-structured biofilms. Although moderate, anti-biofilm and antibacterial activities of S. downii sp. nov. against oral bacteria, including some periodontal pathogens, were demonstrated in an in vitro biofilm model.

Understanding Human Microbiota Offers Novel and Promising Therapeutic Options against Candida Infections

Human fungal pathogens particularly of Candida species are one of the major causes of hospital acquired infections in immunocompromised patients. The limited arsenal of antifungal drugs to treat Candida infections with concomitant evolution of multidrug resistant strains further complicates the management of these infections. Therefore, deployment of novel strategies to surmount the Candida infections requires immediate attention. The human body is a dynamic ecosystem having microbiota usually involving symbionts that benefit from the host, but in turn may act as commensal organisms or affect positively (mutualism) or negatively (pathogenic) the physiology and nourishment of the host. The composition of human microbiota has garnered a lot of recent attention, and despite the common occurrence of Candida spp. within the microbiota, there is still an incomplete picture of relationships between Candida spp. and other microorganism, as well as how such associations are governed. These relationships could be important to have a more holistic understanding of the human microbiota and its connection to Candida infections. Understanding the mechanisms behind commensalism and pathogenesis is vital for the development of efficient therapeutic strategies for these Candida infections. The concept of host-microbiota crosstalk plays critical roles in human health and microbiota dysbiosis and is responsible for various pathologies. Through this review, we attempted to analyze the types of human microbiota and provide an update on the current understanding in the context of health and Candida infections. The information in this article will help as a resource for development of targeted microbial therapies such as pre-/pro-biotics and microbiota transplant that has gained advantage in recent times over antibiotics and established as novel therapeutic strategy.

Structural changes in the oral microbiome of the adolescent patients with moderate or severe dental fluorosis

Dental fluorosis is a very prevalent endemic disease. Although oral microbiome has been reported to correlate with different oral diseases, there appears to be an absence of research recognizing any relationship between the severity of dental fluorosis and the oral microbiome. To this end, we investigated the changes in oral microbial community structure and identified bacterial species associated with moderate and severe dental fluorosis. Salivary samples of 42 individuals, assigned into Healthy (N = 9), Mild (N = 14) and Moderate/Severe (M&S, N = 19), were investigated using the V4 region of 16S rRNA gene. The oral microbial community structure based on Bray Curtis and Weighted Unifrac were significantly changed in the M&S group compared with both of Healthy and Mild. As the predominant phyla, Firmicutes and Bacteroidetes showed variation in the relative abundance among groups. The Firmicutes/Bacteroidetes (F/B) ratio was significantly higher in the M&S group. LEfSe analysis was used to identify differentially represented taxa at the species level. Several genera such as Streptococcus mitis, Gemella parahaemolysans, Lactococcus lactis, and Fusobacterium nucleatum, were significantly more abundant in patients with moderate/severe dental fluorosis, while Prevotella melaninogenica and Schaalia odontolytica were enriched in the Healthy group. In conclusion, our study indicates oral microbiome shift in patients with moderate/severe dental fluorosis. We identified several differentially represented bacterial species enriched in moderate and severe fluorosis. Findings from this study suggests that the roles of these bacteria in oral health and related diseases warrant more consideration in patients with moderate and severe fluorosis.

In Vivo Colonization with Candidate Oral Probiotics Attenuates Colonization and Virulence of Streptococcus mutans

A collection of 113 Streptococcus strains from supragingival dental plaque of caries-free individuals were recently tested in vitro for direct antagonism of the dental caries pathogen Streptococcus mutans, and for their capacity for arginine catabolism via the arginine deiminase system (ADS). To advance their evaluation as potential probiotics, twelve strains of commensal oral streptococci with various antagonistic and ADS potentials were assessed in a mouse model for oral (i.e., oral mucosal pellicles and saliva) and dental colonization under four diets (healthy or high-sucrose, with or without prebiotic arginine). Colonization by autochthonous bacteria was also monitored. One strain failed to colonize, whereas oral colonization by the other eleven strains varied by 3 log units. Dental colonization was high for five strains regardless of diet, six strains increased colonization with at least one high-sucrose diet, and added dietary arginine decreased dental colonization of two strains. Streptococcus sp. A12 (high in vitro ADS activity and antagonism) and two engineered mutants lacking the ADS (ΔarcADS) or pyruvate oxidase-mediated H₂O₂ production (ΔspxB) were tested for competition against S. mutans UA159. A12 wild type and ΔarcADS colonized only transiently, whereas ΔspxB persisted, but without altering oral or dental colonization by S. mutans In testing four additional candidates, S. sanguinis BCC23 markedly attenuated S. mutans' oral and dental colonization, enhanced colonization of autochthonous bacteria, and decreased severity of smooth surface caries under highly cariogenic conditions. Results demonstrate the utility of the mouse model to evaluate potential probiotics, revealing little correlation between in vitro antagonism and competitiveness against S. mutans in vivo IMPORTANCE Our results demonstrate in vivo testing of potential oral probiotics can be accomplished and can yield information to facilitate the ultimate design and optimization of novel anti-caries probiotics. We show human oral commensals associated with dental health are an important source of potential probiotics that may be used to colonize patients under dietary conditions of highly varying cariogenicity. Assessment of competitiveness against dental caries pathogen Streptococcus mutans and impact on caries identified strains or genetic elements for further study. Results also uncovered strains that enhanced oral and dental colonization by autochthonous bacteria when challenged with S. mutans, suggesting cooperative interactions for future elucidation. Distinguishing a rare strain that effectively compete with S. mutans under conditions that promote caries further validates our systematic approach to more critically evaluate probiotics for use in humans.

Casein phosphopeptide-amorphous calcium phosphate fluoride treatment enriches the symbiotic dental plaque microbiome in children

OBJECTIVES

The dysbiotic oral microbiome plays a key role in the pathogenesis of caries in children. Topical application of casein phosphopeptide-amorphous calcium phosphate containing fluoride (CPP-ACP/F) is an effective treatment modality for children with caries (CC). Hitherto the mechanism by which CPP-ACP/F modules the oral microbiome in CC has not been investigated. The study aimed to examine the CPP-ACP/F effect on the dental plaque microbiome of children group with caries.

METHODS

This preliminary prospective clinical cohort included 10 children with caries. The children received topical fluoride CPP-ACP/F once-a-week for one month. Plaque samples were collected before and after treatment and subjected to 16S rDNA-based next-generation-sequencing. Microbial composition, diversity and functional roles were analyzed in comparison to the clinical characteristics of cohort using standard bioinformatics tools.

RESULTS

CPP-ACP/F treatment modulated dysbiotic oral microbiome towards healthier community as the higher proportion of Proteobacteria and certain microbial protective species were enriched following CPP-ACP/F treatment. Despite overall uniformity of community structure in children with caries between the groups, some bacterial species were differentially represented in a statistically significant manner between pre- and post- treatments. Three bacterial species were found to be predictive of strongly sensitive to the CPP-ACP/F treatment, marked by decreased abundance of Lautropia mirabalis and increased abundance of Gemella haemolysans and Schwartzia succinivorans.

CONCLUSION

Within the limits of the current study, it could be concluded that the CPP-ACP/F varnish treatment modulated the microbial composition of the dental plaque microbiome towards symbiosis. These symbiotic changes may demonstrate the potential clinical significance of CPP-ACP/F varnish treatment.

Streptococcus mutans and Streptococcus sobrinus distribution in the saliva and plaque of Iranian population: Higher prevalence of S. mutans serotypes f and k

OBJECTIVE

This study aimed to find the relation of the MS co-existence with the decayed, missing (Extracted) and filled teeth (DMFT) score and the prevalence of Streptococcus mutans serotypes in the Iranian population.

METHODS

In this cross-sectional research conducted in 2018, volunteers aged 10-60< years were measured by population selection criteria. PCR technique was used to screen MS serotypes in the homogenized saliva and plaque samples.

RESULTS

499 subjects met the selection criteria of the study population. Out of 499 samples, 448 samples were finalized for serotype determination and DMFT relation evaluation. From 448, 348 (77.6%) samples harboured only S. mutans, 44 (9.8%) had both S. mutans and S. sobrinus, 6 (1.3%) were positive for S. sobrinus alone, and 94 (20.9%) were free of both specious. The mean DMFT score in people with S. mutans (6.7) was higher than S. mutans negative (4.6) participants (p < 0.05). In people with both S. mutans and S. sobrinus, the mean DMFT did not change significantly. The frequency of c, e, f and k serotypes was 47.7, 22.7, 27.5 and 22.1%, respectively. The mean DMFT score in participants with serotype e was significantly higher than others (p < .05).

CONCLUSIONS

People can acquire different S. mutans serotypes over a lifetime. The high prevalence rate of serotype k, a systemic S. mutans serotype, calls worldwide studies on the prevalence of serotype k strains.

Candida albicans as an Essential "Keystone" Component within Polymicrobial Oral Biofilm Models?

Background: Existing standardized biofilm assays focus on simple mono-species or bacterial-only models. Incorporating Candida albicans into complex biofilm models can offer a more appropriate and relevant polymicrobial biofilm for the development of oral health products. Aims: This study aimed to assess the importance of interkingdom interactions in polymicrobial oral biofilm systems with or without C. albicans, and test how these models respond to oral therapeutic challenges in vitro. Materials and Methods: Polymicrobial biofilms (two models containing 5 and 10 bacterial species, respectively) were created in parallel in the presence and absence of C. albicans and challenged using clinically relevant antimicrobials. The metabolic profiles and biomasses of these complex biofilms were estimated using resazurin dye and crystal violet stain, respectively. Quantitative PCR was utilized to assess compositional changes in microbial load. Additional assays, for measurements of pH and lactate, were included to monitor fluctuations in virulence "biomarkers." Results: An increased level of metabolic activity and biomass in the presence of C. albicans was observed. Bacterial load was increased by more than a factor of 10 in the presence of C. albicans. Assays showed inclusion of C. albicans impacted the biofilm virulence profiles. C. albicans did not affect the biofilms' responses to the short-term incubations with different treatments. Conclusions: The interkingdom biofilms described herein are structurally robust and exhibit all the hallmarks of a reproducible model. To our knowledge, these data are the first to test the hypothesis that yeasts may act as potential "keystone" components of oral biofilms.

The pH-Responsive Property of Antimicrobial Peptide GH12 Enhances Its Anticaries Effects at Acidic pH

Dental caries is closely related to the acidification of the biofilms on the tooth surface, in which cariogenic bacteria bring about a dramatic pH decrease and disrupt remineralisation equilibrium upon the fermentation of dietary sugars. Thus, approaches targeting the acidified niches with enhanced anticaries activities at acidic pH are highly desirable. In our previous study, a cationic amphipathic α-helical antimicrobial peptide GH12 (Gly-Leu-Leu-Trp-His-Leu-Leu-His-His-Leu-Leu-His-NH2) was designed with good stability, low cytotoxicity, and excellent antibacterial effects. Considering its potent antibacterial activity against the acidogenic bacteria and its histidine-rich sequence, it was speculated that GH12 might show enhanced antimicrobial effects at an acidic pH. In this study, the pH-responsive property of GH12 was determined to evaluate its potential as a smart acid-activated anticaries agent. GH12 possessed much lower minimal inhibitory concentrations and minimal bactericidal concentrations against various kinds of bacteria at pH 5.5 than at pH 7.2. Employing Streptococcus mutans, the principal caries pathogen, as the model system, it was found that GH12 showed much stronger bactericidal effects on both planktonic S. mutans and S. mutans embedded in the biofilm at pH 5.5. In addition, short-term treatment with GH12 showed much more effective inhibitory effects on water-insoluble exopolysaccharides synthesis and lactic acid production of the preformed S. mutans biofilm at pH 5.5. As for the mechanism exploration, it was found that the net positive charge of GH12 increased and the tryptophan fluorescence intensity heightened with the peak shifting towards the short wavelength at pH 5.5, which demonstrated that GH12 could be more easily attracted to the anionic microbial cell membranes and that GH12 showed stronger interactions with the lipid membranes. In conclusion, acidic pH enhanced the antibacterial and antibiofilm activities of GH12, and GH12 is a potential smart anticaries agent targeting the cariogenic acidic microenvironment.

Flavorless vs. Flavored Electronic Cigarette-Generated Aerosol and E-Liquid on the Growth of Common Oral Commensal Streptococci

Introduction

Electronic cigarette (ECIG) use or vaping has become popular globally. While the question “Is vaping safer than smoking?” continues, it is becoming clearer that one of the most dangerous components of E-liquids are the flavorings. Since the oral cavity is the first anatomical site to be assaulted by ECIG aerosol, the aim of this study is to test the hypothesis that flavored ECIG aerosols or E-liquids pose a more detrimental effect on the growth of commensal oral streptococcal bacteria compared to flavorless aerosols or E-liquids.

Methods

Kirby Bauer assays and 24-h planktonic growth curves were used to compare the effects of flavorless vs. flavored (tobacco, menthol, cinnamon, strawberry and blueberry) ECIG-generated aerosols and E-liquids on the growth of four common strains of oral commensal bacteria (Streptococcus gordonii, Streptococcus intermedius, Streptococcus mitis and Streptococcus oralis).

Results

Kirby Bauer assays revealed inhibition of growth for all bacteria tested when exposed to 100% menthol, cinnamon or strawberry flavors. In contrast, 5% flavor in E-liquid had no effect. When exposed to 100 puffs of ECIG-generated aerosol ± flavors (≈ 0.05% flavor in brain heart infusion media) or an equivalent amount of E-liquid ± flavors, twenty-four hour planktonic growth curves indicated no effect on growth for all streptococci tested. Subsequent twenty-four hour planktonic growth curves testing the effects of E-liquid ± flavors (0.0625, 0.125, 0.25, 0.3125, 0.625, and 1.25% flavor in brain heart infusion media) revealed dose-dependent inhibition of growth, particularly for menthol, cinnamon and strawberry), for all bacteria tested.

Conclusion

These results support the hypothesis that flavored E-liquids are more detrimental to the growth of oral commensal bacteria than unflavored E-liquids. The streptococci tested in this study are early colonizers and part of the foundation of oral biofilms and dental plaque. Disturbances in the composition and growth of these primary colonizers is crucial to the development of a healthy dental plaque and host-bacteria interactions. E-liquids and their aerosols containing flavoring agents alter the growth of these bacteria. Such perturbations of pioneering oral communities pose a potential risk to the health of the oral cavity and, ultimately, health in general.

The Oral Host-Microbial Interactome: An Ecological Chronometer of Health?

An increasing number of studies reveal that host-microbial interactome networks are coordinated, impacting human health and disease. Recently, several lines of evidence have revealed associations between the acquisition of a complex microbiota and adaptive immunity, supporting that host-microbiota symbiotic relationships have evolved as a means to maintain homeostasis where the role of the microbiota is to promote and educate the immune system. Here, we hypothesize an oral host-microbial interactome that could serve as an ecological chronometer of health and disease, with specific focus on caries, periodontal diseases, and cancer. We also review the current state of the art on the human oral microbiome and its correlations with host innate immunity, and host cytokine control, with the goal of using this information for disease prediction and designing novel treatments for local and systemic dysbiosis. In addition, we discuss new insights into the role of novel host-microbial signals as potential biomarkers, and their relevance for the future of precision dentistry and medicine.

Evaluation of the antimicrobial activity and compressive strength of a dental cement modified using plant extract mixture

Literature lacks sufficient data regarding addition of natural antibacterial agents to glass ionomer cement (GICs). Hence, the aim of the study was to increase the antimicrobial properties of GICs through its modification with mixture of plant extracts to be evaluated along with an 0.5% chlorohexidine-modified GIC (CHX-GIC) with regard to biological and compressive strength properties. Conventional GIC (freeze-dried version) and CHX were used. Alcoholic extract of Salvadora persica, Olea europaea, and Ficus carcia leaves were prepared using a Soxhlet extractor for 12 h. The plant extract mixture (PE) was added in three different proportions to the water used for preparation of the dental cement (Group 1:1 PE, 2:1 PE, and 1:2 PE). Specimens were then prepared and tested against the unmodified GIC (control) and the 0.5% CHX-GIC. Chemical analysis of the extract mixture was performed using Gas chromatography-mass spectrometry. Antimicrobial activity was evaluated using agar diffusion assay against Micrococcus luteus and Streptoccocus mutans. Compressive strength was evaluated according to ISO 9917-1:2007 using a Zwick testing machine at a crosshead speed of 0.5 mm/min. Antimicrobial activity against Streptoccocus mutans was significantly increased for all the extract-modified materials compared to the unmodified cement, and the highest concentration was comparable to the CHX-GIC mixture. The activity against Micrococcus luteus was also significantly increased, but only for the material with the highest extract concentration, and here the CHX-GIC group showed statistically the highest antimicrobial activity. Compressive strength results revealed that there was no statistically significant difference between the different mixtures and the control except for the highest tested concentration that showed the highest mean values. The plant extracts (PEs) enhanced the antimicrobial activity against S. mutans and also against M. luteus in the higher concentration while compressive strength was improved by addition of the PE at higher concentrations.

Dental plaque microbiota profiles of children with caries-free and caries-active dentition

OBJECTIVE

Microbiota comparisons between healthy and diseased dental tissues have accentuated the importance of cultivating and identifying bacterial species that play a role in the initiation and progression of dental caries. The objective of this study was to evaluate the bacterial community composition in caries-active and caries-free children.

METHODS

Supragingival plaque samples were collected from 64 caries-active and 64 caries-free Middle Eastern children. The hypervariable V3-V4 of the bacterial 16S rRNA gene was sequenced with Human Oral Microbe Identification using Next Generation Sequencing. Microbial community structure and composition analyses were performed by processing operational taxonomic units. Bioinformatic analyses, including analysis of similarity, alpha and beta diversities, and principal coordinate analysis, were carried out.

RESULTS

Diversity indices did not find differences between the caries-active and caries-free groups (p > 0.05). Similarity analysis demonstrated that the microbiota composition did not differ between the two groups. Comparative analysis at the species level revealed a significantly higher relative abundance of Leptotrichia shahii, Prevotella melaninogenica, Veillonella dispar, Leptotrichia HOT 498, and Streptococcus mutans in caries-active children (p < 0.05). Corynebacterium matruchotii, Lautropia mirabilis, Neisseria elongata, and Corynebacterium durum were relatively more abundant in the caries-free group (p < 0.05). Species belonging to the Leptotrichia, Prevotella, and Veillonella genera were significantly predominant in the caries-active subjects.

CONCLUSION

In view of the lack of a clear association between Corynebacterium spp. and dental caries status in the literature, the predominance of these species in caries-free children warrants further research to understand their possible role in a health-associated microbial community.

CLINICAL SIGNIFICANCE

Understanding the relationship between specific bacteria present in dental biofilms and health and disease is essential for preventing and combating dental caries. Using advanced next generation sequencing techniques, the present study demonstrated the complexity of the caries microbiome and identified species/genera whose virulence or protective properties should be further explored.

Deep metagenomics examines the oral microbiome during dental caries, revealing novel taxa and co-occurrences with host molecules

Dental caries, the most common chronic infectious disease worldwide, has a complex etiology involving the interplay of microbial and host factors that are not completely understood. In this study, the oral microbiome and 38 host cytokines and chemokines were analyzed across 23 children with caries and 24 children with healthy dentition. De novo assembly of metagenomic sequencing obtained 527 metagenome-assembled genomes (MAGs), representing 150 bacterial species. Forty-two of these species had no genomes in public repositories, thereby representing novel taxa. These new genomes greatly expanded the known pangenomes of many oral clades, including the enigmatic Saccharibacteria clades G3 and G6, which had distinct functional repertoires compared to other oral Saccharibacteria. Saccharibacteria are understood to be obligate epibionts, which are dependent on host bacteria. These data suggest that the various Saccharibacteria clades may rely on their hosts for highly distinct metabolic requirements, which would have significant evolutionary and ecological implications. Across the study group, Rothia, Neisseria, and Haemophilus spp. were associated with good dental health, whereas Prevotella spp., Streptococcus mutans, and Human herpesvirus 4 (Epstein-Barr virus [EBV]) were more prevalent in children with caries. Finally, 10 of the host immunological markers were significantly elevated in the caries group, and co-occurrence analysis provided an atlas of potential relationships between microbes and host immunological molecules. Overall, this study illustrated the oral microbiome at an unprecedented resolution and contributed several leads for further study that will increase the understanding of caries pathogenesis and guide therapeutic development.

Analysis of relative bacterial activity and lactate dehydrogenase gene expression of caries-associated bacteria in a site-specific natural biofilm: an ex vivo study

Objectives

Detecting bacterial activity is considered a promising approach to monitor shifts from symbiosis to dysbiosis in oral microbiome. The present study aimed at investigating both the relative bacterial activity and the lactate dehydrogenase (ldh) gene expression of caries-associated bacteria in a site-specific natural biofilm.

Material and methods

Sixty subjects (age, mean ± SE: 30.1 ± 1.4) were allocated to two groups: caries-free subjects (CF) or caries-active subjects (CA). CF presented one sound surface (CFS, n = 30). CA presented two donor sites: a cavitated caries lesion (CAC, n = 30) and a sound reference surface (CAS, n = 30). Real-time quantitative PCR (q-PCR) on species or genus level and total bacteria was performed targeting the 16S gene, the 16S rRNA, the ldh gene, and the ldh mRNA (increasing 16S ribosomal RNA copy numbers can function as an indicator of increased energy metabolism). As the 16S rRNA abundance represents the number of ribosomes, while the 16S gene abundance represents the number of genomes, the quotient of the relative abundances functions as a measure for the relative bacterial activity (%).

Results

Both lactobacilli and S. mutans showed the highest relative bacterial activity in CAC ((mean ± SE) 218 ± 60% and 61 ± 16%, respectively) and the lowest values for both sound reference surfaces (69 ± 48%; 8 ± 3%). Significant differences were found between CAC and CAS as well as between CAC and CFS for both lactobacilli and S. mutans (p < 0.05). The ldh gene expression of lactobacilli and S. mutans only showed moderate values in CAC (1.90E+03 ± 2.11E+03; 2.08E+04 ± 4.44E+04 transcripts/μl) and CFS (2.04E+03 ± 2.74E+03; 8.16E+03 ± 6.64E+03 transcripts/μl); consequently no significant differences were detected.

Conclusion and clinical relevance

Caries-associated bacteria (lactobacilli and S. mutans) showed the highest relative bacterial activity in plaque of cavitated lesions, the lowest in sound surfaces, allowing the detection of a significant activity shift in health and disease for caries-active patients. However, no significant differences in ldh gene expression could be determined.

The role of the oral microbiota in chronic non-communicable disease and its relevance to the Indigenous health gap in Australia

BACKGROUND

Aboriginal Australians and Torres Strait Islanders (hereafter respectfully referred to as Indigenous Australians) experience disproportionately poor health and low life expectancy compared to non-Indigenous Australians. Poor oral health is a critical, but understudied, contributor to this health gap. A considerable body of evidence links poor oral health to increased risks of other chronic non-communicable conditions, such as diabetes, cardiovascular disease, chronic kidney disease, and poor emotional wellbeing.  MAIN: The oral microbiota is indisputably associated with several oral diseases that disproportionately affect Indigenous Australians. Furthermore, a growing literature suggests direct and indirect links between the oral microbiota and systemic chronic non-communicable diseases that underpin much of the Indigenous health gap in Australia. Recent research indicates that oral microbial communities are shaped by a combination of cultural and lifestyle factors and are inherited from caregivers to children. Systematic differences in oral microbiota diversity and composition have been identified between Indigenous and non-Indigenous individuals in Australia and elsewhere, suggesting that microbiota-related diseases may be distinct in Indigenous Australians.  CONCLUSION: Oral microbiota research involving Indigenous Australians is a promising new area that could benefit Indigenous communities in numerous ways. These potential benefits include: (1) ensuring equity and access for Indigenous Australians in microbiota-related therapies; (2) opportunities for knowledge-sharing and collaborative research between scientists and Indigenous communities; and (3) using knowledge about the oral microbiota and chronic disease to help close the gaps in Indigenous oral and systemic health.

Manganese Depletion Leads to Multisystem Changes in the Transcriptome of the Opportunistic Pathogen Streptococcus sanguinis

Streptococcus sanguinis is a primary colonizer of teeth and is typically considered beneficial due to its antagonistic relationship with the cariogenic pathogen Streptococcus mutans. However, S. sanguinis can also act as an opportunistic pathogen should it enter the bloodstream and colonize a damaged heart valve, leading to infective endocarditis. Studies have implicated manganese acquisition as an important virulence determinant in streptococcal endocarditis. A knockout mutant lacking the primary manganese import system in S. sanguinis, SsaACB, is severely attenuated for virulence in an in vivo rabbit model. Manganese is a known cofactor for several important enzymes in S. sanguinis, including superoxide dismutase, SodA, and the aerobic ribonucleotide reductase, NrdEF. To determine the effect of manganese depletion on S. sanguinis, we performed transcriptomic analysis on a ΔssaACB mutant grown in aerobic fermentor conditions after the addition of the metal chelator EDTA. Despite the broad specificity of EDTA, analysis of cellular metal content revealed a decrease in manganese, but not in other metals, that coincided with a drop in growth rate. Subsequent supplementation with manganese, but not iron, zinc, or magnesium, restored growth in the fermentor post-EDTA. Reduced activity of Mn-dependent SodA and NrdEF likely contributed to the decreased growth rate post-EDTA, but did not appear entirely responsible. With the exception of the Dps-like peroxide resistance gene, dpr, manganese depletion did not induce stress response systems. By comparing the transcriptome of ΔssaACB cells pre- and post-EDTA, we determined that manganese deprivation led to altered expression of diverse systems. Manganese depletion also led to an apparent induction of carbon catabolite repression in a glucose-independent manner. The combined results suggest that manganese limitation produces effects in S. sanguinis that are diverse and complex, with no single protein or system appearing entirely responsible for the observed growth rate decrease. This study provides further evidence for the importance of this trace element in streptococcal biology. Future studies will focus on determining mechanisms for regulation, as the multitude of changes observed in this study indicate that multiple regulators may respond to manganese levels.

Effects of xylitol and erythritol consumption on mutans streptococci and the oral microbiota: a systematic review

OBJECTIVE

A systematic review of published data was conducted with the aim of assessing effects of xylitol and erythritol consumption on levels of mutans streptococci (MS) and the oral microbiota.

MATERIALS AND METHODS

Electronic and hand searches were performed to find clinical microbiological studies concerning the consumption of xylitol and erythritol chewing gum or candies, and published between 2000 and 2019. Prospective randomized controlled clinical trials conducted in healthy subjects were included in the review.

RESULTS

The initial search identified 561 xylitol and 83 erythritol studies. After applying inclusion and exclusion criteria, 21 xylitol studies and one erythritol study were reviewed. The review identified nine xylitol studies with a fair or high quality, four conducted in children and five in adults, all demonstrating a decrease in MS levels in association with habitual consumption of xylitol. The three microbiota studies employing multispecies probe approaches revealed no effects for xylitol on the microbiota. The only erythritol study fulfilling the inclusion criteria showed no consistent effects on MS levels.

CONCLUSIONS

Xylitol consumption is likely to decrease MS counts but it may not change the overall microbiota. Xylitol shows thus properties of an oral prebiotic. More studies are needed to demonstrate the effects of erythritol on MS.

Enhanced biofilm formation of Streptococcus gordonii with lipoprotein deficiency

Streptococcus gordonii is a commensal Gram-positive bacterium that acts as an opportunistic pathogen that can cause apical periodontitis, endocarditis, and pneumonia. Biofilm formation of bacteria is important for the initiation and progression of such diseases. Although lipoproteins play key roles in physiological functions, the role of lipoproteins of S. gordonii in its biofilm formation has not been clearly understood. In this study, we investigated the role of lipoproteins of S. gordonii in the bacterial biofilm formation using its lipoprotein-deficient strain (Δlgt). The S. gordonii Δlgt exhibited increased biofilm formation on the human dentin slices or on the polystyrene surfaces compared to the wild-type strain, while its growth rate did not differ from that of the wild-type. In addition, the S. gordonii Δlgt strain exhibited the enhanced LuxS mRNA expression and AI-2 production, which is known to be a positive regulator of biofilm formation, compared to the wild-type. Concordantly, the augmented biofilm formation of S. gordonii Δlgt was attenuated by an AI-2 inhibitor, D-ribose. In addition, lipoproteins from purified S. gordonii inhibited the biofilm formation of S. gordonii wild-type and Δlgt. Taken together, these results suggest that lipoprotein-deficient S. gordonii form biofilms more effectively than the wild-type strain, which might be related to the AI-2 quorum-sensing system.

Isolation and Identification of Potentially Pathogenic Microorganisms Associated with Dental Caries in Human Teeth Biofilms

Dental caries is attributed to the predominance of cariogenic microorganisms. Cariogenic microorganisms are pathological factors leading to acidification of the oral microenvironment, which is related to the initiation and progression of caries. The accepted cariogenic microorganism is Streptococcus mutans (S. mutans). However, studies have found that caries could occur in the absence of S. mutans. This study aimed to assess the presence of potentially cariogenic microorganisms in human teeth biofilm. The microorganisms were isolated from human mouth and freshly extracted human maxillary incisors extracted for reasons of caries. The isolates were sorted based on their acidogenic and aciduric properties, and the S. mutans was used as the reference strain. Four potentially cariogenic strains were selected. The selected strains were identified as Streptococcus salivarius (S. salivarius), Streptococcus anginosus (S. anginosus), Leuconostoc mesenteroides (L. mesenteroides), and Lactobacillus sakei (L. sakei) through morphological analysis followed by 16S rRNA gene sequence analysis. The cariogenicity of isolates was analyzed. We show, for the first time, an association between L. sakei (present in fermented food) and dental caries. The data provide useful information on the role of lactic acid bacteria from fermented foods and oral commensal streptococci in dental caries.

Oral microbiota and dental caries data from monozygotic and dizygotic twin children

There are recent studies which aimed to detect the inheritance on the etiology of dental caries exploring oral composition. We present data on the oral microbiota and its relation with dental caries and other factors in monozygotic (MZ) and dizygotic (DZ) twin children. Following clinical investigation, DNA samples were collected and isolated from saliva of 198 patients (49 MZ and 50 DZ twins) with an average age of 9.7 ± 2.7 years. Salivary bacterial microbiota analysis was performed using high throughput amplicon sequencing method targeting V3-V4 region of the 16S rRNA gene. A total of 8,297,859 raw reads corresponding to 41,908 reads per sample were obtained on average. The QIIME2-deblur workflow was used for 16S rRNA amplicon analysis. Microbiome similarity analyses between twins (based on Bray-Curtis dissimilarity, weighted and unweighted Unifrac distances) showed that monozygotic twins share more bacterial microbial content compared to dizygotic twins. This is a large microbial community dataset of MZ and DZ twins with or without dental findings which can be further used for children oral microbiome profile explorations.

Measurement(s)	Oral Microbiome • DNA • dental health
Technology Type(s)	twin design • amplicon sequencing • Examination
Factor Type(s)	zygosity status • age • sex
Sample Characteristic - Organism	Microbiota • Homo sapiens
Sample Characteristic - Environment	saliva

Machine-accessible metadata file describing the reported data: 10.6084/m9.figshare.12987797

Nitrite-producing oral microbiome in adults and children

Recently, it was suggested that the nitrite (NO₂^-) produced from NO₃^- by oral bacteria might contribute to oral and general health. Therefore, we aimed to clarify the detailed information about the bacterial NO₂-production in the oral biofilm. Dental plaque and tongue-coating samples were collected, then the NO₂-producing activity was measured. Furthermore, the composition of the NO₂^--producing bacterial population were identified using the Griess reagent-containing agar overlay method and molecular biological method. NO₂^--producing activity per mg wet weight varied among individuals but was higher in dental plaque. Additionally, anaerobic bacteria exhibited higher numbers of NO₂^--producing bacteria, except in the adults' dental plaque. The proportion of NO₂^--producing bacteria also varied among individuals, but a positive correlation was found between NO₂^--producing activity and the number of NO₂^--producing bacteria, especially in dental plaque. Overall, the major NO₂^--producing bacteria were identified as Actinomyces, Schaalia, Veillonella and Neisseria. Furthermore, Rothia was specifically detected in the tongue coatings of children. These results suggest that dental plaque has higher NO₂^--producing activity and that this activity depends not on the presence of specific bacteria or the bacterial compositions, but on the number of NO₂^--producing bacteria, although interindividual differences were detected.

Propolis nanoparticle enhances the potency of antimicrobial photodynamic therapy against Streptococcus mutans in a synergistic manner

Less invasive removal approaches have been recommended for deep caries lesions. Antimicrobial photodynamic therapy (aPDT) and propolis nanoparticle (PNP) are highlighted for the caries management plan. Evidence is lacking for an additive effect of combination PNP with photosensitizer (PS) in aPDT. This study aimed to investigate the individual and synergistic effects of chlorophyllin-phycocyanin mixture (PhotoActive⁺) and toluidine blue O (TBO) as PSs in combination with PNP in the aPDT process (aPDT^plus) against major important virulence factors of Streptococcus mutans. Following characterization, biocompatibility of the PSs alone, or in combination with PNP were investigated on human gingival fibroblast cell. The in vitro synergy of PhotoActive⁺ or TBO and PNP was evaluated by the checkerboard method. The bacteria's virulence properties were surveyed in the presence of the PSs, individually as well as in combination. When the PSs were examined in combination (synergistic effect, FIC Index < 0.5), a stronger growth inhibitory activity was exhibited than the individual PSs. The biofilm formation, as well as genes involved in biofilm formation, showed greater suppression when the PSs were employed in combination. Overall, the results of this study suggest that the combination of PhotoActive⁺ or TBO with PNP with the least cytotoxicity effects and the highest antimicrobial activites would improve aPDT outcomes, leading to synergistic effects and impairing the virulence of S. mutans.

Microbial Analysis of Saliva to Identify Oral Diseases Using a Point-of-Care Compatible qPCR Assay

Oral health is maintained by a healthy microbiome, which can be monitored by state-of-the art diagnostics. Therefore, this study evaluated the presence and quantity of ten oral disease-associated taxa (P. gingivalis, T. forsythia, T. denticola, F. nucleatum, C. rectus, P. intermedia, A. actinomycetemcomitans, S. mutans, S. sobrinus, oral associated Lactobacilli) in saliva and their clinical status association in 214 individuals. Upon clinical examination, study subjects were grouped into healthy, caries and periodontitis and their saliva was collected. A highly specific point-of-care compatible dual color qPCR assay was developed and used to study the above-mentioned bacteria of interest in the collected saliva. Assay performance was compared to a commercially available microbial reference test. Eight out of ten taxa that were investigated during this study were strong discriminators between the periodontitis and healthy groups: C. rectus, T. forsythia, P. gingivalis, S. mutans, F. nucleatum, T. denticola, P. intermedia and oral Lactobacilli (p < 0.05). Significant differentiation between the periodontitis and caries group microbiome was only shown for S. mutans (p < 0.05). A clear distinction between oral health and disease was enabled by the analysis of quantitative qPCR data of target taxa levels in saliva.

Low levels of salivary metals, oral microbiome composition and dental decay

Salivary microbiome composition can change following exposure to environmental toxicants, e.g., heavy metals. We hypothesized that levels of salivary nutrients and metals would correlate with salivary microbiome composition and be associated with dental decay. Here we assess the salivary concentrations of 5 essential minerals (cobalt, copper, manganese, molybdenum, and zinc), 4 metals with some evidence of normal physiological function (chromium, nickel, tungsten, and vanadium), and 12 with known toxicity (antimony, arsenic, barium, beryllium, cadmium, cesium, lead, mercury, platinum, thallium, tin, and uranium), and their associations with salivary microbiome composition and dental decay in 61 children and adults. 16 metals were detected in 54% of participants; 8 were found in all. Marked differences in salivary bacterial taxa were associated with levels of antimony, arsenic, and mercury, after adjusting for multiple testing. Further, antimony levels were associated with the presence of decayed teeth. Thus, salivary metal levels, even at low concentrations, may impact oral health.

Saliva proteomics from children with caries at different severity stages

OBJECTIVE

To perform a comparative analysis of saliva protein profile of patients with early childhood caries at different levels of severity and caries-free individuals.

MATERIALS AND METHODS

Stimulated saliva samples were collected from 126 children (2-6 years old), classified according to the ICDAS II, and divided into 3 groups (n = 42): caries-free (CF), enamel caries (EC), and dentine caries (DC). Samples were digested and analyzed by nanoUPLC coupled with a mass spectrometry. Data analyses were conducted with Progenesis QI for Proteomics Software v2.0. Gene Ontology (GO) terms and protein-protein interaction analysis were obtained.

RESULTS

A total of 306 proteins (≈6 peptides) were identified. Among them, 122 were differentially expressed in comparisons among children with different caries status. Out of the 122 proteins, the proteins E2AK4 and SH3L2 were exclusively present in groups CF and EC, respectively, and 8 proteins (HAUS4, CAH1, IL36A, IL36G, AIMP1, KLHL8, KLH13, and SAA1) were considered caries-related proteins when compared to caries-free children; they were up-regulated proteins in the caries groups (EC and DC).

CONCLUSION

The identification of exclusive proteins for caries-free or carious-related conditions may help in understanding the mechanisms of caries and predicting risk as well as advancing in caries control or anti-caries approaches.

Antibacterial Effect of Caffeic Acid Phenethyl Ester on Cariogenic Bacteria and Streptococcus mutans Biofilms

Dental caries is the most common disease in the human mouth. Streptococcus mutans is the primary cariogenic bacterium. Propolis is a nontoxic natural product with a strong inhibitory effect on oral cariogenic bacteria. The polyphenol-rich extract from propolis inhibits S. mutans growth and biofilm formation, as well as the genes involved in virulence and adherence, through the inhibition of glucosyltransferases (GTF). However, because the chemical composition of propolis is highly variable and complex, the mechanism of its antimicrobial action and the active compound are controversial and not completely understood. Caffeic acid phenethyl ester (CAPE) is abundant in the polyphenolic compounds from propolis, and it has many pharmacological effects. In this study, we investigated the antibacterial effects of CAPE on common oral cariogenic bacteria (Streptococcus mutans, Streptococcus sobrinus, Actinomyces viscosus, and Lactobacillus acidophilus) and its effects on the biofilm-forming and cariogenic abilities of S. mutans CAPE shows remarkable antimicrobial activity against cariogenic bacteria. Moreover, CAPE also inhibits the formation of S. mutans biofilms and their metabolic activity in mature biofilms. Furthermore, CAPE can inhibit the key virulence factors of S. mutans associated with cariogenicity, including acid production, acid tolerance, and the bacterium's ability to produce extracellular polysaccharides (EPS), without affecting bacterial viability at subinhibitory levels. In conclusion, CAPE appears to be a new agent with anticariogenic potential, not only via inhibition of the growth of cariogenic bacteria.

Investigation on the effect of vitamin C on growth & biofilm-forming potential of Streptococcus mutans isolated from patients with dental caries

BACKGROUND

Streptococcus mutans is a major cause of dental caries. Its capacity to produce biofilm is fundamental in the pathogenesis of this ubiquitous condition. As maintaining a healthy dentition is a genuine goal given the contemporary advance in caries control, researchers are striving to achieve a breakthrough in caries therapy. We are taking the anti-cariogenic properties of vitamin C a step-further, considering the well-known evidence of the inversely proportionate relationship between salivary levels of vitamin C and dental caries. The aim of this study was to determine MIC, MBC, biofilm prevention concentration (BPC), and derivative measures of vitamin C against fresh clinical isolates of S. mutans to evaluate its efficacy as an anti-cariogenic agent.

RESULTS

Based on the data of four independent experiments done in quadruplicates, we found a concentration-dependent inhibitory effect of vitamin C on all S. mutans strains tested. The average MBC, MIC, and BPC of vitamin C were found to be 10.16, 9.38, and 5.61 mg/ml, respectively. Spectrophotometric quantitation of crystal violet showed diminished biofilm formation in the presence of vitamin C (p < 0.05). When compared with gentamicin, vitamin C produced a zone of inhibition that was three times as large against the clinical isolates.

CONCLUSION

Our results show that vitamin C has a negative effect on S. mutans growth and biofilm formation. Being the first to meticulously utilize BPC to explore a well-known effect of vitamin C, this report aims to help in the instigation of trials of higher evidence that will ultimately culminate in repurposing vitamin C as a novel anti-cariogenic agent, albeit further studies are required to provide auxiliary evidence in this context.

In vitro Synergy of Polyphenolic Extracts From Honey, Myrtle and Pomegranate Against Oral Pathogens, S. mutans and R. dentocariosa

The increasing incidence rate of oral diseases, the wide spread of antimicrobial resistance, and the adverse effects of conventional antibiotics mean alternative prevention and treatment options are needed to counteract oral pathogens. In this regard, our study aims to evaluate the antibacterial activity of polyphenolic extracts prepared from acacia honey, myrtle leaves, and pomegranate peel against cariogenic bacteria, such as Streptococcus mutans and Rothia dentocariosa. The chemical-physical parameters of acacia honey and the RP-HPLC polyphenolic profile of pomegranate peel extract have been previously described in our studies, while the characterization of myrtle extract, performed by HPLC analysis, is reported here. All the extracts were used singly and in binary combinations to highlight any synergistic effects. Moreover, the extracts were tested in association with amoxicillin to evaluate their ability to reduce the effective dose of this drug in vitro. The values of minimal inhibitory concentrations and minimal bactericidal concentrations have been used to quantitatively measure the antibacterial activity of the single extracts, while the fractional inhibitory concentration index has been considered as predictor of in vitro anticariogenic synergistic effects. Finally, a time-kill curve method allowed for the evaluation of the bactericidal efficacy of the combined extracts. The microbiological tests suggest that acacia honey, myrtle, and pomegranate extracts are able to inhibit the cariogenic bacteria, also with synergistic effects. This study provides useful and encouraging results for the use of natural extract combinations alone or in association with antibiotics (adjuvant therapy) as a valid alternative for the prevention and treatment of oral infectious diseases.

The role of the microbiota in periodontal disease

The last decade has witnessed unparalleled advances in our understanding of the complexity of the oral microbiome and the compositional changes that occur in subgingival biofilms in the transition from health to gingivitis and to destructive periodontal disease. The traditional view, which has held sway for the last 2 decades, that disease is characterized by the outgrowth of a consortium, or consortia, of a limited number of potentially pathogenic organisms, has given way to an alternative paradigm. In this new view, the microbiological changes associated with disease represent whole-scale alterations to the overall microbial population structure and to the functional properties of the entire community. Thus, and in common with other microbially mediated diseases of the gastrointestinal tract, the normally balanced, symbiotic, and generally benign commensal microbiome of the tooth-associated biofilm undergoes dysbiosis to a potentially deleterious microbiota. Coincident with progress in defining the microbiology of these diseases, there have been equally important advances in our understanding of the inflammatory systems of the periodontal tissues, their control, and how inflammation may contribute both to the development of dysbiosis and, in a deregulated state, the destructive disease process. One can therefore speculate that the inflammatory response and the periodontal microbiome are in a bidirectional balance in oral health and a bidirectional imbalance in periodontitis. However, despite these clear insights into both sides of the host/microbe balance in periodontal disease, there remain several unresolved issues concerning the role of the microbiota in disease. These include, but are not limited to, the factors which determine progression from gingivitis to periodontitis in a proportion of the population, whether dysbiosis causes disease or results from disease, and the molecular details of the microbial stimulus responsible for driving the destructive inflammatory response. Further progress in resolving these issues may provide significant benefit to diagnosis, treatment, and prevention.

Antimicrobial Peptide GH12 Prevents Dental Caries by Regulating Dental Plaque Microbiota

Due to the complex microecology and microenvironment of dental plaque, novel caries prevention strategies require modulating the microbial communities ecologically and reducing the cariogenic properties effectively. Antimicrobial peptide GH12 reduced the lactic acid production and exopolysaccharide (EPS) synthesis of a Streptococcus mutans biofilm and a three-species biofilm in vitro in previous studies. However, the anticaries effects and microecological effects of GH12 remained to be investigated in a complex biofilm model in vitro and an animal caries model in vivo In the present study, GH12 at 64 mg/liter showed the most effective inhibition of lactic acid production, EPS synthesis, pH decline, and biofilm integrity of human dental plaque-derived multispecies biofilms in vitro, and GH12 at 64 mg/liter was therefore chosen for use in subsequent in vitro and in vivo assays. When treated with 64-mg/liter GH12, the dental plaque-derived multispecies biofilms sampled from healthy volunteers maintained its microbial diversity and showed a microbial community structure similar to that of the control group. In the rat caries model with a caries-promoting diet, 64-mg/liter GH12 regulated the microbiota of dental plaque, in which the abundance of caries-associated bacteria was decreased and the abundance of commensal bacteria was increased. In addition, 64-mg/liter GH12 significantly reduced the caries scores of sulcal and smooth surface caries in all locations. In conclusion, GH12 inhibited the cariogenic properties of dental plaque without perturbing the dental plaque microbiota of healthy individuals and GH12 regulated the dysbiotic microbial ecology and arrested caries development under cariogenic conditions.IMPORTANCE The anticaries effects and microecological regulation effects of the antimicrobial peptide GH12 were evaluated systematically in vitro and in vivo GH12 inhibited the cariogenic virulence of dental plaque without overintervening in the microbial ecology of healthy individuals in vitro GH12 regulated the microbial ecology of dental plaque to a certain extent in vivo under cariogenic conditions, increased the proportion of commensal bacteria, and decreased the abundance of caries-associated bacteria. GH12 significantly suppressed the incidence and severity of dental caries in vivo This study thus describes an alternative antimicrobial therapy for dental caries.