Episymbiotic Saccharibacteria TM7x modulates the susceptibility of its host bacteria to phage infection and promotes their coexistence.

Bacteriophages (phages) play critical roles in modulating microbial ecology. Within the human microbiome, the factors influencing the long-term coexistence of phages and bacteria remain poorly investigated. Saccharibacteria (formerly TM7) are ubiquitous members of the human oral microbiome. These ultrasmall bacteria form episymbiotic relationships with their host bacteria and impact their physiology. Here, we showed that during surface-associated growth, a human oral Saccharibacteria isolate (named TM7x) protects its host bacterium, a Schaalia odontolytica strain (named XH001) against lytic phage LC001 predation. RNA-Sequencing analysis identified in XH001 a gene cluster with predicted functions involved in the biogenesis of cell wall polysaccharides (CWP), whose expression is significantly down-regulated when forming a symbiosis with TM7x. Through genetic work, we experimentally demonstrated the impact of the expression of this CWP gene cluster on bacterial-phage interaction by affecting phage binding. In vitro coevolution experiments further showed that the heterogeneous populations of TM7x-associated and TM7x-free XH001, which display differential susceptibility to LC001 predation, promote bacteria and phage coexistence. Our study highlights the tripartite interaction between the bacterium, episymbiont, and phage. More importantly, we present a mechanism, i.e., episymbiont-mediated modulation of gene expression in host bacteria, which impacts their susceptibility to phage predation and contributes to the formation of "source-sink" dynamics between phage and bacteria in biofilm, promoting their long-term coexistence within the human microbiome.

Acquisition of the arginine deiminase system benefits epiparasitic Saccharibacteria and their host bacteria in a mammalian niche environment.

Saccharibacteria are a group of widespread and genetically diverse ultrasmall bacteria with highly reduced genomes that belong to the Candidate Phyla Radiation. Comparative genomic analyses suggest convergent evolution of key functions enabling the adaptation of environmental Saccharibacteria to mammalian microbiomes. Currently, our understanding of this environment-to-mammal niche transition within Saccharibacteria and their obligate episymbiotic association with host bacteria is limited. Here, we identified a complete arginine deiminase system (ADS), found in further genome streamlined mammal-associated Saccharibacteria but missing in their environmental counterparts, suggesting acquisition during environment-to-mammal niche transition. Using TM7x, the first cultured Saccharibacteria strain from the human oral microbiome and its host bacterium Actinomyces odontolyticus, we experimentally tested the function and impact of the ADS. We demonstrated that by catabolizing arginine and generating adenosine triphosphate, the ADS allows metabolically restrained TM7x to maintain higher viability and infectivity when disassociated from the host bacterium. Furthermore, the ADS protects TM7x and its host bacterium from acid stress, a condition frequently encountered within the human oral cavity due to bacterial metabolism of dietary carbohydrates. Intriguingly, with a restricted host range, TM7x forms obligate associations with Actinomyces spp. lacking the ADS but not those carrying the ADS, suggesting the acquired ADS may also contribute to partner selection for cooperative episymbiosis within a mammalian microbiome. These data present experimental characterization of a mutualistic interaction between TM7x and their host bacteria, and illustrate the benefits of acquiring a novel pathway in the transition of Saccharibacteria to mammalian microbiomes.

Transcriptome of Epibiont Saccharibacteria Nanosynbacter lyticus Strain TM7x During the Establishment of Symbiosis.

Saccharibacteria Nanosynbacter lyticus strain TM7x is a member of the broadly distributed candidate phylum radiation. These bacteria have ultrasmall cell sizes, have reduced genomes, and live as epibionts on the surfaces of other bacteria. The mechanisms by which they establish and maintain this relationship are not yet fully understood. The transcriptomes of the epibiont TM7x and its host bacteria Schaalia odontolytica strain XH001 were captured across the establishment of symbiosis during both the initial interaction and stable symbiosis. The results showed a dynamic interaction with large shifts in gene expression for both species between the initial encounter and stable symbiosis, notably in transporter genes. During stable symbiosis, the host XH001 showed higher gene expression for peptidoglycan biosynthesis, mannosylation, cell cycle and stress-related genes, whereas it showed lower expression of chromosomal partitioning genes. This was consistent with the elongated cell shape seen in XH001 infected with TM7x and our discovery that infection resulted in thickened cell walls. Within TM7x, increased pili, type IV effector genes, and arginine catabolism/biosynthesis gene expression during stable symbiosis implied a key role for these functions in the interaction. Consistent with its survival and persistence in the human microbiome as an obligate epibiont with reduced de novo biosynthetic capacities, TM7x also showed higher levels of energy production and peptidoglycan biosynthesis, but lower expression of stress-related genes, during stable symbiosis. These results imply that TM7x and its host bacteria keep a delicate balance in order to sustain an episymbiotic lifestyle. IMPORTANCE Nanosynbacter lyticus type strain TM7x is the first cultivated member of the Saccharibacteria and the candidate phyla radiation (CPR). It was discovered to be ultrasmall in cell size with a highly reduced genome that establishes an obligate epibiotic relationship with its host bacterium. The CPR is a large, monophyletic radiation of bacteria with reduced genomes that includes Saccharibacteria. The vast majority of the CPR have yet to be cultivated, and our insights into these unique organisms to date have been derived from only a few Saccharibacteria species. Being obligate parasites, it is unknown how these ultrasmall Saccharibacteria, which are missing many de novo biosynthetic pathways, are maintained at a high prevalence within the human microbiome as well as in the environment.

Klebsiella and Providencia emerge as lone survivors following long-term starvation of oral microbiota.

It is well-understood that many bacteria have evolved to survive catastrophic events using a variety of mechanisms, which include expression of stress-response genes, quiescence, necrotrophy, and metabolic advantages obtained through mutation. However, the dynamics of individuals leveraging these abilities to gain a competitive advantage in an ecologically complex setting remain unstudied. In this study, we observed the saliva microbiome throughout the ecological perturbation of long-term starvation, allowing only the species best equipped to access and use the limited resources to survive. During the first several days, the community underwent a death phase that resulted in a ∼50-100-fold reduction in the number of viable cells. Interestingly, after this death phase, only three species, Klebsiella pneumoniae, Klebsiella oxytoca, and Providencia alcalifaciens, all members of the family Enterobacteriaceae, appeared to be transcriptionally active and recoverable. Klebsiella are significant human pathogens, frequently resistant to multiple antibiotics, and recently, ectopic colonization of the gut by oral Klebsiella was documented to induce dysbiosis and inflammation. MetaOmics analyses provided several leads for further investigation regarding the ecological success of the Enterobacteriaceae. The isolates accumulated single nucleotide polymorphisms in known growth advantage in stationary phase alleles and produced natural products closely resembling antimicrobial cyclic depsipeptides. The results presented in this study suggest that pathogenic Enterobacteriaceae persist much longer than their more benign neighbors in the salivary microbiome when faced with starvation. This is particularly significant, given that hospital surfaces contaminated with oral fluids, especially sinks and drains, are well-established sources of outbreaks of drug-resistant Enterobacteriaceae.

Rapid evolution of decreased host susceptibility drives a stable relationship between ultrasmall parasite TM7x and its bacterial host.

Around one-quarter of bacterial diversity comprises a single radiation with reduced genomes, known collectively as the Candidate Phyla Radiation. Recently, we coisolated TM7x, an ultrasmall strain of the Candidate Phyla Radiation phylum Saccharibacteria, with its bacterial host Actinomyces odontolyticus strain XH001 from human oral cavity and stably maintained as a coculture. Our current work demonstrates that within the coculture, TM7x cells establish a long-term parasitic association with host cells by infecting only a subset of the population, which stay viable yet exhibit severely inhibited cell division. In contrast, exposure of a naïve A. odontolyticus isolate, XH001n, to TM7x cells leads to high numbers of TM7x cells binding to each host cell, massive host cell death, and a host population crash. However, further passaging reveals that XH001n becomes less susceptible to TM7x over time and enters a long-term stable relationship similar to that of XH001. We show that this reduced susceptibility is driven by rapid host evolution that, in contrast to many forms of phage resistance, offers only partial protection. The result is a stalemate where infected hosts cannot shed their parasites; nevertheless, parasite load is sufficiently low that the host population persists. Finally, we show that TM7x can infect and form stable long-term relationships with other species in a single clade of Actinomyces, displaying a narrow host range. This system serves as a model to understand how parasitic bacteria with reduced genomes such as those of the Candidate Phyla Radiation have persisted with their hosts and ultimately expanded in their diversity.

Prolonged oral ingestion of microplastics induced inflammation in the liver tissues of C57BL/6J mice through polarization of macrophages and increased infiltration of natural killer cells.

Microplastics (< 5 mm diameter) are one of most important environmental pollutants and contaminants worldwide. However, how microplastics affect liver immune microenvironment in not well understood. Microplastics (0.5 µm) were administered orally to C57BL/6J mice for 4 consecutive weeks at the rate of 0.5 mg/day. Non-parenchymal cells were isolated from of the mice through fractionation of fresh hepatic tissues. The immune landscape for four cell populations of B cells, T cells, NK cells and macrophages in the liver tissues was then evaluated using flow cytometry. The secretion level of inflammatory cytokines and associated signaling pathway were investigated using quantitative real-time polymerase chain reaction and western blot. Oral ingestion of microplastics increases liver weight, general liver index as well as expression of serum, liver function-related indicators. Microplastics also increased the infiltration of natural killer cells and macrophages to non-parenchymal liver cells, but reduced that of B cells to the same tissues. However, microplastics had no effect on the infiltration of T cell to non-parenchymal liver cells. Ingestion of MPs also up-regulated the expression of IFN-γ, TNF-α, IL-1ß, IL-6 and IL-33 mRNA, but down-regulated that of IL-4, IL-5, IL-10, IL-18 and TGF-ß1. Overall, the aforementioned processes were regulated via the NF-κB pathway in the hepatic non-parenchymal cells. Microplastics disrupts inflammatory process in liver tissues via the NF-κB signaling pathway. These findings provide a strong foundation on immune processes in hepatic tissues following prolonged ingestion of microplastics.

A Linear Plasmid-Like Prophage of Actinomyces odontolyticus Promotes Biofilm Assembly.

The human oral cavity is home to a large number of bacteria and bacteriophages (phages). However, the biology of oral phages as members of the human microbiome is not well understood. Recently, we isolated Actinomyces odontolyticus subsp. actinosynbacter strain XH001 from the human oral cavity, and genomic analysis revealed the presence of an intact prophage named xhp1. Here, we demonstrated that xhp1 is a linear plasmid-like prophage, which is a newly identified phage of A. odontolyticus The prophage xhp1 genome is a 35-kb linear double-stranded DNA with 10-bp single-stranded, 3' cohesive ends. xhp1 exists extrachromosomally, with an estimated copy number of 5. Annotation of xhp1 revealed 54 open reading frames, while phylogenetic analysis suggests that it has limited similarity with other phages. xhp1 phage particles can be induced by mitomycin C and belong to the Siphoviridae family, according to transmission electron microscopic examination. The released xhp1 particles can reinfect the xhp1-cured XH001 strain and result in tiny blurry plaques. Moreover, xhp1 promotes XH001 biofilm formation through spontaneous induction and the release of host extracellular DNA (eDNA). In conclusion, we identified a linear plasmid-like prophage of A. odontolyticus, which enhances bacterial host biofilm assembly and could be beneficial to the host for its persistence in the oral cavity.IMPORTANCE The biology of phages as members of the human oral microbiome is understudied. Here, we report the characterization of xhp1, a novel linear plasmid-like prophage identified from a human oral isolate, Actinomyces odontolyticus subsp. actinosynbacter strain XH001. xhp1 can be induced and reinfect xhp1-cured XH001. The spontaneous induction of xhp1 leads to the lysis of a subpopulation of bacterial hosts and the release of eDNA that promotes biofilm assembly, thus potentially contributing to the persistence of A. odontolyticus within the oral cavity.

Precision-guided antimicrobial peptide as a targeted modulator of human microbial ecology.

One major challenge to studying human microbiome and its associated diseases is the lack of effective tools to achieve targeted modulation of individual species and study its ecological function within multispecies communities. Here, we show that C16G2, a specifically targeted antimicrobial peptide, was able to selectively kill cariogenic pathogen Streptococcus mutans with high efficacy within a human saliva-derived in vitro oral multispecies community. Importantly, a significant shift in the overall microbial structure of the C16G2-treated community was revealed after a 24-h recovery period: several bacterial species with metabolic dependency or physical interactions with S. mutans suffered drastic reduction in their abundance, whereas S. mutans' natural competitors, including health-associated Streptococci, became dominant. This study demonstrates the use of targeted antimicrobials to modulate the microbiome structure allowing insights into the key community role of specific bacterial species and also indicates the therapeutic potential of C16G2 to achieve a healthy oral microbiome.

Cultivation of a human-associated TM7 phylotype reveals a reduced genome and epibiotic parasitic lifestyle.

The candidate phylum TM7 is globally distributed and often associated with human inflammatory mucosal diseases. Despite its prevalence, the TM7 phylum remains recalcitrant to cultivation, making it one of the most enigmatic phyla known. In this study, we cultivated a TM7 phylotype (TM7x) from the human oral cavity. This extremely small coccus (200-300 nm) has a distinctive lifestyle not previously observed in human-associated microbes. It is an obligate epibiont of an Actinomyces odontolyticus strain (XH001) yet also has a parasitic phase, thereby killing its host. This first completed genome (705 kb) for a human-associated TM7 phylotype revealed a complete lack of amino acid biosynthetic capacity. Comparative genomics analyses with uncultivated environmental TM7 assemblies show remarkable conserved gene synteny and only minimal gene loss/gain that may have occurred as TM7x adapted to conditions within the human host. Transcriptomic and metabolomic profiles provided the first indications, to our knowledge, that there is signaling interaction between TM7x and XH001. Furthermore, the induction of TNF-α production in macrophages by XH001 was repressed in the presence of TM7x, suggesting its potential immune suppression ability. Overall, our data provide intriguing insights into the uncultivability, pathogenicity, and unique lifestyle of this previously uncharacterized oral TM7 phylotype.

Effect of titanium and zirconia dental implant abutments on a cultivable polymicrobial saliva community.

STATEMENT OF PROBLEM: Peri-implantitis is considered the most important biological complication responsible for late implant failure. The physical chemical properties intrinsic to each material can affect the first step to biofilm development and is an important precursor to the adaptive behavior of pathogenic bacteria species. PURPOSE: The purpose of this in vitro study was to evaluate the effect of 2 commercially available implant abutment materials on the adhesion phase and biofilm formation. MATERIAL AND METHODS: Disks (8 mm in diameter, 2 mm thick) of machined pure titanium (Ti) and yttrium-stabilized zirconia (ZrO2) materials were used to mimic implant abutments. The physical chemical surface properties were investigated using different approaches. Initial adherent bacteria and biofilm formation were evaluated after 16 and 48 hours by incubating the disks in a rich medium containing representative saliva-derived oral microbial community. Unpaired t test, 2 tailed, was used to compare the groups. RESULTS: Ti presented lower hydrophobicity and surface free energy values than the ZrO2, and 6.1-fold fewer bacteria adhered to the Ti. After 48 hours, detailed quantitative analysis showed that biofilm biomass and biofilm density were lower on the Ti disks than on ZrO2. The quantity of phylotypes on the Ti and ZrO2 surfaces was relatively similar during the attachment and early biofilm formation periods. CONCLUSIONS: Although no difference in the bacteria profile was observed between both materials independent of the time point, the highest level of colonization was on ZrO2.

Phenotypic and Physiological Characterization of the Epibiotic Interaction Between TM7x and Its Basibiont Actinomyces.

Despite many examples of obligate epibiotic symbiosis (one organism living on the surface of another) in nature, such an interaction has rarely been observed between two bacteria. Here, we further characterize a newly reported interaction between a human oral obligate parasitic bacterium TM7x (cultivated member of Candidatus Saccharimonas formerly Candidate Phylum TM7), and its basibiont Actinomyces odontolyticus species (XH001), providing a model system to study epiparasitic symbiosis in the domain Bacteria. Detailed microscopic studies indicate that both partners display extensive morphological changes during symbiotic growth. XH001 cells manifested as short rods in monoculture, but displayed elongated and hyphal morphology when physically associated with TM7x. Interestingly, these dramatic morphological changes in XH001 were also induced in oxygen-depleted conditions, even in the absence of TM7x. Targeted quantitative real-time PCR (qRT-PCR) analyses revealed that both the physical association with TM7x as well as oxygen depletion triggered up-regulation of key stress response genes in XH001, and in combination, these conditions act in an additive manner. TM7x and XH001 co-exist with relatively uniform cell morphologies under nutrient-replete conditions. However, upon nutrient depletion, TM7x-associated XH001 displayed a variety of cell morphologies, including swollen cell body, clubbed-ends, and even cell lysis, and a large portion of TM7x cells transformed from ultrasmall cocci into elongated cells. Our study demonstrates a highly dynamic interaction between epibiont TM7x and its basibiont XH001 in response to physical association or environmental cues such as oxygen level and nutritional status, as reflected by their morphological and physiological changes during symbiotic growth.

Synergistic Inhibition of Enamel Demineralization by Peptide 8DSS and Fluoride.

The biomimetic peptide 8DSS has shown beneficial effects in promoting remineralization of demineralized enamel in vitro. Here we examined the ability of 8DSS alone and in combination with fluoride to inhibit enamel demineralization during pH-cycling mimicking intraoral conditions. Enamel blocks were subjected to 9 days of pH-cycling in the presence of 1,000 ppm NaF (positive control), distilled-deionized water (DDW; negative control), 25 µM 8DSS alone, 25 µM 8DSS with 500 ppm NaF (8DSS-FL) or 25 µM 8DSS with 1,000 ppm NaF (8DSS-FH) twice daily for 1 min each time. The blocks were analyzed in terms of surface microhardness (SMH), fluoride uptake and mineral content. The 8DSS-treated blocks showed significantly lower mineral loss, shallower lesions and higher SMH than the DDW-treated blocks. No significant differences were observed between the blocks treated with 8DSS alone or fluoride alone. The blocks treated with 8DSS alone or DDW showed similar amounts of fluoride uptake, which was the lowest of all the treatment groups. The blocks treated with 8DSS-FL or 8DSS-FH did not differ significantly, and both groups showed significantly greater SMH and fluoride uptake as well as significantly lower mineral loss and shallower lesions than the NaF-treated blocks. Mineral content was significantly higher in the 8DSS-treated blocks than in the DDW-treated blocks from the surface layer (10 µm) to the lesion depth (110 µm), and it was significantly higher in the blocks treated with 8DSS-FL or 8DSS-FH than in the NaF-treated blocks from 10 to 90 µm. These findings illustrate the potential of 8DSS for inhibiting enamel demineralization and for enhancing the anticaries effect of NaF.

Oral cavity contains distinct niches with dynamic microbial communities.

Microbes colonize human oral surfaces within hours after delivery. During postnatal development, physiological changes, such as the eruption of primary teeth and replacement of the primary dentition with permanent dentition, greatly alter the microbial habitats, which, in return, may lead to community composition shifts at different phases in people's lives. By profiling saliva, supragingival and mucosal plaque samples from healthy volunteers at different ages and dentition stages, we observed that the oral cavity is a highly heterogeneous ecological system containing distinct niches with significantly different microbial communities. More importantly, the phylogenetic microbial structure varies with ageing. In addition, only a few taxa were present across the whole populations, indicating a core oral microbiome should be defined based on age and oral niches.

Nanoscale characterization of effect of L-arginine on Streptococcus mutans biofilm adhesion by atomic force microscopy.

A major aetiological factor of dental caries is the pathology of the dental plaque biofilms. The amino acid L-arginine (Arg) is found naturally in saliva as a free molecule or as a part of salivary peptides and proteins. Plaque bacteria metabolize Arg to produce alkali and neutralize glycolytic acids, promoting a less cariogenous oral microbiome. Here, we explored an alternative and complementary mechanism of action of Arg using atomic force microscopy. The nanomechanical properties of Streptococcus mutans biofilm extracellular matrix were characterized under physiological buffer conditions. We report the effect of Arg on the adhesive behaviour and structural properties of extracellular polysaccharides in S. mutans biofilms. High-resolution imaging of biofilm surfaces can reveal additional structural information on bacterial cells embedded within the surrounding extracellular matrix. A dense extracellular matrix was observed in biofilms without Arg compared to those grown in the presence of Arg. S. mutans biofilms grown in the presence of Arg could influence the production and/or composition of extracellular membrane glucans and thereby affect their adhesion properties. Our results suggest that the presence of Arg in the oral cavity could influence the adhesion properties of S. mutans to the tooth surface.

Ultrasmall epibiont Nanosynbacter lyticus strain TM7x and host bacteria transcriptional activity after initial host parasitism.

Background: Oral Saccharibacteria Nanosynbacter lyticus strain TM7× lives as an ultrasmall epibiont on the surface of its host, Schaalia odontolytica strain XH001. Establishing this interaction is a poorly understood multi-step process. The recovery phase marks a shift in the TM7×/host interaction, switching from the early killing phase, with extensive host cell death, to a stable symbiosis phase where the host and epibiont can grow together. Results: Transcriptomes of TM7× and host, XH001, were captured during the recovery phase and compared to uninfected host and the early host/epibiont interaction (initial encounter). XH001 showed increased expression for rhamnose cell wall components and for the precursor to peptidoglycan while TM7× showed increases in the peptidoglycan pathway. Transporter expression was generally increased for both organisms during recovery compared to the initial encounter, though, XH001 showed lower amino acid transporter expression. Consistent with host parasitism, XH001 showed increased expression of various stress-related genes during recovery while TM7× showed reduced stress. TM7× displayed higher expression of type IV pili, consistent with increased attachment to new hosts. Conclusion: As TM7× is a member of the broadly distributed Candidate Phyla Radiation with small genomes lacking numerous biosynthetic pathways, this study provides further insights into how these epibionts interact and modulate their host bacteria.

Episymbiotic Saccharibacteria induce intracellular lipid droplet production in their host bacteria.

Saccharibacteria (formerly TM7) are a group of widespread and genetically diverse ultrasmall bacteria with highly reduced genomes that belong to Candidate Phyla Radiation, a large monophyletic lineage with poorly understood biology. Nanosynbacter lyticus type strain TM7x is the first Saccharibacteria member isolated from the human oral microbiome. With restrained metabolic capacities, TM7x lives on the surface of, and forms an obligate episymbiotic relationship with its bacterial host, Schaalia odontolytica strain XH001. The symbiosis allows TM7x to propagate but presents a burden to host bacteria by inducing stress response. Here, we employed super-resolution fluorescence imaging to investigate the physical association between TM7x and XH001. We showed that the binding with TM7x led to a substantial alteration in the membrane fluidity of XH001. We also revealed the formation of intracellular lipid droplets in XH001 when forming episymbiosis with TM7x, a feature that has not been reported in oral bacteria. The TM7x-induced lipid droplets accumulation in XH001 was confirmed by label-free Raman spectroscopy, which also unveiled additional phenotypical features when XH001 cells are physically associated with TM7x. Further exploration through culturing XH001 under various stress conditions showed that lipid droplets accumulation was a general response to stress. A survival assay demonstrated that the presence of lipid droplets plays a protective role in XH001, enhancing its survival under adverse conditions. In conclusion, our study sheds new light on the intricate interaction between Saccharibacteria and their host bacteria, highlighting the potential benefit conferred by TM7x to its host and further emphasizing the context-dependent nature of symbiotic relationships.

Development of a new model system to study microbial colonization on dentures.

PURPOSE: Dentures are often colonized with a variety of microorganisms, including Candida albicans, that contribute to denture stomatitis. Several in vitro models have been previously established to study denture-related microbial colonization and evaluate treatment efficacy of denture cleansers; however, those models typically fail to appreciate the complex topology and heterogeneity of denture surfaces and lack effective ways to accurately measure microbial colonization. The purpose of this study was to study microbial colonization with a new model system based on real dentures, to more realistically mimic in vivo conditions. MATERIALS AND METHODS: Scanning electron microscopy was used to observe topological structures among surfaces from different parts of the denture. Employing C. albicans as a model microorganism, we established microbial colonization on different denture surfaces. Moreover, we applied a modified MTT (3-(4,5-dimethylthiazol-2-yl)-2, 5-diphenyl tetrazolium bromide) colorimetric assay to quantify C. albicans colonization on dentures without the necessity of biofilm removal and to evaluate treatment efficacy of denture cleansers. RESULTS: There were significant variations in topological structures among surfaces from different parts of the denture, with the unpolished side having the highest amounts of indentations and pores. The distinct denture surfaces support microbial colonization differently, with the unpolished side containing the highest level of microbial colonization and biofilm formation. Furthermore, the modified MTT colorimetric assay proved to be an accurate assay to measure biofilm formation on dentures and evaluate treatment efficacy of denture cleansers. CONCLUSION: This new denture model system in conjunction with the MTT colorimetric assay is a valuable tool to study denture-related microbiology and treatment approaches.

Salivary biomarkers for caries risk assessment.

Saliva contains various microbes and host biological components that could be used for caries risk assessment. This review focuses on the research topics that connect dental caries with saliva, including both the microbial and host components within saliva.

Classification specific lymphatic malformations management on head and neck in children.

OBJECTIVE: The aim of this study was to retrospectively analyze the outcomes from surgical and nonsurgical treatments for head and neck lymphatic malformations (LMs) in children. STUDY DESIGN: Fifty-eight patients were divided into a surgical group (22) and a nonsurgical group (36). The surgical group contained microcystic LMs in the tongue treated by surgery or with sclerotherapy. The nonsurgical group contained macrocystic and mixed LMs in floor of the mouth, neck, face, submandibular region, maxillofacial region and neck treated by sclerotherapy or with microwave ablation (MWA). RESULTS: In the surgical group, the mean follow-up time was 44 ± 15.3 months. At last follow-up, 15 LMs (68.2%) were completely controlled, 3 LMs (13.6%) were stable without need for further treatment, and 4 LMs (18.2%) were persistent. In the nonsurgical group, the median follow-up time was 23.5 months (13.0, 32.8). At last follow-up, 28 LMs (77.8%,) have a volume reduction rate of >50%, and 6 LMs (16.7%.) have the complication. CONCLUSIONS: Surgery is suitable for microcystic LMs in the early stage with clear boundary and becomes limited for them in the late stages due to diffuse lesions. Sclerotherapy is effective for macrocystic and mixed LMs. Sclerotherapy with MWA is exceptionally effective for large cystic LMs with multiple compartments.

Antagonistic interaction between two key endodontic pathogens Enterococcus faecalis and Fusobacterium nucleatum.

Background: Endodontic infections are known to be caused by pathogenic bacteria. Numerous previous studies found that both Fusobacterium nucleatum and Enterococcus faecalis are associated with endodontic infections, with Fusobacterium nucleatum more abundant in primary infection while Enterococcus faecalis more abundant in secondary infection. Little is known about the potential interactions between different endodontic pathogens. Objective: This study aims to investigate the potential interaction between F. nucleatum and E. faecalis via phenotypical and genetic approaches. Methods: Physical and physiological interactions of F. nucleatum and E. faecalis under both planktonic and biofilm conditions were measured with co-aggregation and competition assays. The mechanisms behind these interactions were revealed with genetic screening and biochemical measurements. Results: E. faecalis was found to physically bind to F. nucleatum under both in vitro planktonic and biofilm conditions, and this interaction requires F. nucleatum fap2, a galactose-inhibitable adhesin-encoding gene. Under our experimental conditions, E. faecalis exhibits a strong killing ability against F. nucleatum by generating an acidic micro-environment and producing hydrogen peroxide (H2O2). Finally, the binding and killing capacities of E. faecalis were found to be necessary to invade and dominate a pre-established in vitro F. nucleatum biofilm. Conclusions: This study reveals multifaceted mechanisms underlying the physical binding and antagonistic interaction between F. nucleatum and E. faecalis, which could play a potential role in the shift of microbial composition in primary and secondary endodontic infections.