Objective: Previous reports showed that periodontopathic bacteria induce epithelial–mesenchymal transition (EMT) in oral squamous cell carcinoma (OSCC). Fisetin, a foodborne flavonoid, is reportedly associated with anticancer potential in various carcinogenic processes. This study aimed to elucidate the effects of fisetin on Fusobacterium nucleatum- and Porphyromonas gingivalis-induced EMT in OSCC cells. Methods: OSCC cells were co-cultured with live and heat-killed forms of F. nucleatum and P. gingivalis. The concentration of fisetin was set at 10 μM. Morphological changes in the OSCC cells were observed under a light microscope. Cell viability was measured using the Cell Counting Kit-8 assay, whereas migration was examined via wound healing. The mRNA expression of EMT-related markers was quantified using quantitative real-time polymerase chain reaction (PCR), and the expression of EMT-related markers and Wnt pathway-associated proteins was examined via Western blotting. Results: At a multiplicity of infection (MOI) of 300:1 for F. nucleatum and 100:1 for P. gingivalis, OSCC cell viability remained unchanged; however, wound closure rates increased significantly relative to the control. Likewise, treatment with fisetin (10 µM) did not materially alter viability; nevertheless, it attenuated promigratory effects induced by heat-killed periodontal pathogens at 3 h and 6 h. The OSCC cells exhibited EMT-like morphological changes after 6 h of co-culture with heat-killed pathogens. Consistently, reverse-transcriptase quantitative PCR and Western blot analyses showed increased expression of TWIST, ZEB1, and N-cadherin, accompanied by decreased E-cadherin expression, which was more pronounced in F. nucleatum than in P. gingivalis. However, fisetin reversed these trends. Moreover, co-culture with heat-killed pathogens markedly elevated β-catenin protein levels. In line with modulation of canonical Wnt/β-catenin signaling, fisetin and a Wnt inhibitor reduced β-catenin expression, whereas co-treatment with a Wnt agonist restored β-catenin levels in the presence of fisetin. Conclusions: Heat-killed F. nucleatum and P. gingivalis induced EMT in OSCC cells, with F. nucleatum exerting the strongest effect. Fisetin suppressed pathogen-driven EMT, at least partly via canonical Wnt/β-catenin signaling, highlighting its potential therapeutic value and warranting further investigation.

Background:Circadian rhythm disruption is an underlying cause of metabolic syndrome (MetS) and is associated with the development of periodontitis. Circadian syndrome (CircS) is an emerging measure of circadian rhythm disruption based on MetS. We aimed to explore the cross-sectional association between CircS and periodontitis through the National Health and Nutrition Examination Survey 2009-2014. Methods:We included 7,555 eligible participants. CircS was assessed by the five components of the MetS, depression, and short sleep duration, with fulfillment of ≥4 of the 7 components indicating the presence of CircS. Periodontitis was evaluated according to the Centers for Disease Control and Prevention-American Academy of Periodontology criteria. Multivariable logistic regression analysis was used to explore the association between CircS and periodontitis. In addition, restrictive cubic spline analysis, mediation analysis, and stratified analysis were used to comprehensively evaluate these associations. Results:After adjusting for all confounders, CircS was significantly associated with periodontitis (odds ratio 1.509, 95% CI 1.326-1.716, p < 0.0001). Similar findings were found for CircS components. A higher number of components was associated with increased odds of periodontitis compared to participants without any components. However, among CircS participants, higher components were not associated with the odds of periodontitis. The number of CircS components was nonlinearly associated with periodontitis, and a positive association existed only when the number of components was <4. Mediation analyses suggested that several serum lipids, oxidative stress, and systemic inflammation markers mediated the association of CircS with periodontitis. This association was more pronounced in participants <60 years of age, income-poverty ratio >3, and non-vigorous physical activity. Conclusion:The presence of CircS was significantly associated with increased odds of periodontitis, serum lipids, oxidative stress, and systemic inflammation may mediate this association. These findings emphasize that CircS may serve as an independent risk factor for periodontitis and provide insights for individualized prevention of periodontitis.

Background In dentistry, instruments, appliances, and body fluids such as saliva or blood are possible sources of infection. Although conventional antiseptic procedures effectively prevent infection, spittoons cannot be sanitized between each treated patient and are usually washed only with running water. However, there is currently no fast and efficient disinfection method that can be implemented between treatments. An optically filtered krypton chloride excimer lamp using ultraviolet light (Far UV-C) in the 200-230 nm wavelength range (innocuous to humans) has been recently used as a virus- and bacteria-inactivating technology. This study aimed to identify the bioburden of a dental spittoon and examine the susceptibility of two oral Streptococcus and two Enterococci to 222-nm Far UV-C by irradiating the spittoon with 222 nm Far UV-C for 5 min before evaluating the disinfection effect. Methods Bacterial analysis and real-time polymerase-chain reaction testing was used to confirm the spittoon's biological contamination. Bacterial susceptibility to a 222-nm Far UV-C was determined with a graded dose irradiation test. After each treatment, the spittoon was irradiated with 222-nm Far UV-C for 5 min, and the disinfecting effect was evaluated. Microbial analysis of the spittoon's surface was performed using the Silva database. Results We found that > 97% of the microbes consisted of six bacterial phyla, whereas no viruses were found. Pseudomonas aeruginosa was frequently detected. The 1-log reduction value of two oral-derived Streptococci and two Enterococci species at 222-nm Far UV-C was 4.5-7.3 mJ/cm(2). Exposure of the spittoon to 222-nm Far UV-C at 3.6-13.5 mJ/cm(2) significantly decreased bacterial counts (p < 0.001). Conclusions Irradiation with 222-nm Far UV-C at 3.6-13.5 mJ/cm(2) significantly eliminates bacteria in spittoons, even when they are only rinsed with water. Hence, 222-nm Far UV-C irradiation may inhibit the risk of bacterial transmission from droplets in sink surfaces.

Objective: Resveratrol is a natural phytoalexin that has anti-inflammatory properties, reverses doxorubicin resistance, and inhibits epithelial-mesenchymal transition (EMT) in many types of cancer cells. Fusobacterium nucleatum is reportedly enriched in oral squamous cell carcinoma (OSCC) tissues compared to adjacent normal tissues, sparking interest in the relationship between F. nucleatum and OSCC. Recently, F. nucleatum was shown to be associated with EMT in OSCC. In the present study, we aimed to investigate the effects of the natural plant compound resveratrol on F. nucleatum-induced EMT in OSCC. Design: F. nucleatum was co-cultured with OSCC cells, with a multiplicity of infection (MOI) of 300:1. Resveratrol was used at a concentration of 10 mu M. Cell Counting Kit-8 and wound healing assays were performed to examine the viability and migratory ability of OSCC cells. Subsequently, real-time RT-PCR was performed to investigate the gene expression of EMT-related markers. Western blotting and immunofluorescence analyses were used to further analyze the expression of the epithelial marker E-cadherin and the EMT transcription factor SNAI1. Results: Co-cultivation with F. nucleatum did not significantly enhance cell viability. The co-cultured cells displayed similarities to the positive control of EMT, exhibiting enhanced migration and expression changes in EMTrelated markers. SNAI1 was significantly upregulated, whereas E-cadherin, was significantly downregulated. Notably, resveratrol inhibited F. nucleatum-induced cell migration, decreasing the expression of SNAI1. Conclusions: Resveratrol inhibited F. nucleatum-induced EMT by downregulating SNAI1, which may provide a target for OSCC treatment.

ObjectivesRothia spp. are emerging as significant bacteria associated with oral health, with Rothia dentocariosa being one of the most prevalent species. However, there is a lack of studies examining these properties at the genetic level. This study aimed to establish a genetic modification platform for R. dentocariosa.MethodsRothia spp. were isolated from saliva samples collected from healthy volunteers. Subsequently, R. dentocariosa strains were identified through colony morphology, species-specific polymerase chain reaction (PCR), and 16S ribosomal RNA gene sequencing. The identified strains were then transformed with plasmid pJRD215, and the most efficient strain was selected. Transposon insertion mutagenesis was performed to investigate the possibility of genetic modifications.ResultsA strain demonstrating high transforming ability, designated as R. dentocariosa LX16, was identified. This strain underwent transposon insertion mutagenesis and was screened for 5-fluoroorotic acid-resistant transposants. The insertion sites were confirmed using arbitrary primed PCR, gene-specific PCR, and Sanger sequencing.ConclusionThis study marks the first successful genetic modification of R. dentocariosa. Investigating R. dentocariosa at the genetic level can provide insights into its role within the oral microbiome.

Fusobacterium nucleatum (F. nucleatum), a key pathogen implicated in periodontal disease, contributes to oral biofilm maturation and is linked to development of systemic diseases like colorectal cancer and liver cirrhosis. Photodynamic therapy (PDT) combined with 5-aminolevulinic acid (5-ALA) treatment (ALA-PDT) selectively targets F. nucleatum by inducing porphyrin accumulation. The bactericidal effect of red light-based PDT on F. nucleatum has not been evaluated previously. This study investigates the effect of ALA-PDT using red light-emitting diode (LED) light on F. nucleatum subspecies and their porphyrin accumulation. F. nucleatum subspecies were cultured with varying concentrations of 5-ALA under anaerobic conditions. Porphyrin accumulation was measured via fluorescence spectroscopy, and colony-forming units were measured to determine bacterial viability post-treatment. Additionally, other subspecies responded well to 0.01% 5-ALA, and uroporphyrin I accumulation correlated with bacterial death, revealing optimal bactericidal conditions. These results suggest that optimizing light intensity and 5-ALA concentration can significantly enhance the therapeutic potential of ALA-PDT in oral healthcare.

In the immune system, the detection of pathogens through various mechanisms triggers immune responses. Several types of specific programmed cell deaths play a role in the inflammatory reaction. This study emphasizes the inflammatory response induced by Actinomycetes. Actinomyces spp. are resident bacteria in human oral plaque and often serve as a bridge for pathogenic bacteria, which lack affinity to the tooth surface, aiding their colonization of the plaque. We aim to investigate the potential role of Actinomyces oris in the early stages of oral diseases from a new perspective. Actinomyces oris MG-1 (A. oris) was chosen for this research. Differentiated THP-1 (dTHP-1) cells were transiently treated with A. oris to model the inflammatory reaction. Cell viability, as well as relative gene and protein expression levels of dTHP-1 cells, were assessed using CCK-8, quantitative real-time polymerase chain reaction (RT-qPCR), enzyme-linked immunosorbent assay (ELISA), and Western blot assay. The treatment decreased cell viability and increased the expression of inflammatory genes such as IL-1R1 and NLRP3. It was also observed to significantly enhance the release of IL-1β/IL-18 into the supernatant. Immunoblot analysis revealed a notable increase in the expression of N-gasdermin D persisting up to 24 h. Conversely, in models pre-treated with TLR2 inhibitors, N-gasdermin D was detectable only 12 h post-treatment and absent at 24 h. These results suggest that Actinomyces oris MG-1 induces pyroptosis in dTHP-1 cells via TLR2, but the process is not solely dependent on TLR2.

Periodontitis, a chronic infectious disease leading to gingival atrophy and potential tooth loss through alveolar bone resorption, is closely linked to the oral microbiome. Fusobacterium nucleatum, known to facilitate late-stage bacterial colonization in the oral microbiome, plays a crucial role in the onset of periodontitis. Controlling F. nucleatum abundance is vital for preventing and treating periodontal disease. Photodynamic therapy combined with 5-aminolevulinic acid (ALA-PDT) has been reported to be bactericidal against Pseudomonas aeruginosa and Staphylococcus aureus. We aimed to investigate the bactericidal potential of ALA-PDT against F. nucleatum, which was evaluated by examining the impact of varying 5-ALA concentrations, culture time, and light intensity. After ALA-PDT treatment, DNA was extracted from interdental plaque samples collected from 10 volunteers and sequenced using the Illumina MiSeq platform. To further elucidate the bactericidal mechanism of ALA-PDT, porphyrins were extracted from F. nucleatum following cultivation with 5-ALA and subsequently analyzed using fluorescence spectra. ALA-PDT showed a significant bactericidal effect against F. nucleatum. Its bactericidal activity demonstrated a positive correlation with culture time and light intensity. Microbiota analysis revealed no significant alteration in α-diversity within the ALA-PDT group, although there was a noteworthy reduction in the proportion of the genus Fusobacterium. Furthermore, fluorescence spectral analysis indicated that F. nucleatum produced an excitable photosensitive substance following the addition of 5-ALA. Overall, if further studies confirm these results, this combined therapy could be an effective strategy for reducing the prevalence of periodontitis.

Although in vivo studies have explored the relationship between oral environment and microbial communities, a precise analysis of the effects of environmental pH on oral microbiota remains challenging owing to their complexity and external influences. This study aimed to investigate the effect of environmental pH on the structure and diversity of oral microbiota in vitro. Tongue coating samples from ten participants were cultured anaerobically at six pH levels (5.5–8.0) using adjusted media. After DNA extraction, high-throughput sequencing of the 16s rRNA V3–V4 region was performed. Microbial diversity was analyzed using alpha and beta diversity indices, and differential taxa were identified using linear discriminant analysis effect size (LEfSe). Alpha diversity analysis revealed reduced diversity at pH 5.5 and 8.0. Beta diversity revealed that microbial communities at pH 5.5, 7.5, and 8.0 were separated from those at pH 7.0. LEfSe identified bacterial species that were significantly altered at pH 5.5 and 8.0. Environmental pH significantly influences the diversity and composition of microbial communities, with substantial changes occurring under acidic or alkaline conditions. These findings provide deeper insight into how oral biofilms respond to pH variations, underscoring the critical role of pH in oral microbiota dynamics.

Abstract Background Periodontitis is the most common oral disease in dogs, and its progression and severity are influenced by risk factors, such as age and body size. Recent studies have assessed the canine oral microbiota in relation to different stages of periodontitis and niches within the oral cavity. However, knowledge of the bacterial composition at different ages and body sizes, especially in puppies, is limited. This study aimed to characterize the oral microbiota in the healthy gingiva of small breed puppies using next-generation sequencing. Additionally, we assessed the impact of dental care practices and the presence of retained deciduous teeth on the oral microbiota. Results In this study, plaque samples were collected from the gingival margin of 20 small breed puppies (age, 6.9 ± 0.6 months). The plaque samples were subjected to next-generation sequencing targeting the V3-V4 region of the 16 S rRNA. The microbiota of the plaque samples was composed mostly of gram-negative bacteria, primarily Proteobacteria (54.12%), Bacteroidetes (28.79%), and Fusobacteria (5.11%). Moraxella sp. COT-017, Capnocytophaga cynodegmi COT-254, and Bergeyella zoohelcum COT-186 were abundant in the oral cavity of the puppies. In contrast, Neisseria animaloris were not detected. The high abundance of Pasteurellaceae suggests that this genus is characteristic of the oral microbiota in puppies. Dental care practices and the presence of retained deciduous teeth showed no effects on the oral microbiota. Conclusions In this study, many bacterial species previously reported to be detected in the normal oral cavity of adult dogs were also detected in 6–8-month-old small breed dogs. On the other hand, some bacterial species were not detected at all, while others were detected in high abundance. These data indicate that the oral microbiota of 6–8-month-old small breed dogs is in the process of maturating in to the adult microbiota and may also have characteristics of the small dog oral microbiota.

Abstract Microbial current production (MCP) coupled with fermentation metabolism emerges as critical for microbial electrochemical technologies. Unlike MCP associated with anaerobic respiration, a low amount of electron flux via MCP can impact the fermentation pathway and product yield. However, understanding the machinery for such an intriguing impact of MCP on fermentation remains unclear. Here, we report that the redox regulator protein (Rex), found in many Gram-positive bacteria, was activated by a low microbial current generation and affected the fermentation balance via pyruvate dehydrogenase upregulation in Streptococcus mutans. Although the coulombic efficiency of MCP was less than 0.02%, a significant shift in fermentation balance from ethanol to lactate production occurred in association with MCP to an electrode and with the reduction of a soluble electron acceptor flavin. Modeling metabolic flux in the wild type and the Δrex strains based on transcriptomics suggested that Rex protein was responsible for the shift in fermentation pathway through pyruvate dehydrogenase modification, resulting in increased ethanol concentration in the absence of MCP. Accordingly, deletion of the rex gene resulted in the loss of MCP-alteration of fermentation metabolic switch. Given that the rex gene is widely distributed in electrogenic bacteria, gene upregulation by MCP might be a prevalent mechanism.

Actinomyces oris strain K20 was isolated from oral apical lesions. Here, we report the complete circular genome sequence of this strain, obtained by means of hybrid assembly using two next-generation sequencing datasets. The strain has a 3.1-Mb genome with 2,636 coding sequences.

Porphyromonas gingivalis, known as an anaerobic gram-negative bacteria, is associated with the progress of a periodontitis. Since gingipain (gp), a specific protease secreted from its bacteria, is its main pathogenicity, gp has been utilized as a marker of the periodontitis. Here, an electrochemical protease assay using a ferrocenylpeptide probes was applied to the detection of gp activity; the probe was cleaved with its protease activity and current peak decreased by the released ferrocene part to balk solution. A series of ferrocenylpeptides as specific substrates of Arg-gp (Rgp) and Lys-gp (Kgp) was synthesized: FRC and FKC having cysteine residue; FRSS and FKSS having lipoic acid; FRpra and FKpra having propargylglycine; FRDE and FRDK having cysteine and D-type amino acid. The electron transfer rate constant of all of ferrocenylpeptide immobilized on a gold electrode were estimated by Lavirons analysis. The obtained electron transfer rate constant were 400-3500 s(-1), where fastest one of 3500 s(-1) was obtained from FRC immobilized electrode. Peak currents of these electrodes were decreased after the treatment of a sample containing Porphyromonas gingivalis The detection limits of Porphyromonas gingivalis were 1.0 x 10(7) , 5.0 x 10(6) , 3.3 x 10(6) , 5.0 x 10(6) , and 5.0 x 10(6) cells, for FRPra- FKPra-, FRG, FRDE-, and FRDK-immobilized electrodes, respectively. FRDE- and FRDK-immobilized electrodes were applied for patients suffering from periodontitis. It was successfully classified between the patients and healthy peoples using the FRDK-immobilized electrode. These results suggest that gp activity is connected with a clinical condition of periodontitis, and it is expected to be applied to a periodontal disease screening.

Comparative structural/molecular biology by single-molecule analyses combined with single-cell dissection, mass spectroscopy, and biochemical reconstitution have been powerful tools for elucidating the mechanisms underlying genome DNA folding. All genomes in the three domains of life undergo stepwise folding from DNA to 30–40 nm fibers. Major protein players are histone (Eukarya and Archaea), Alba (Archaea), and HU (Bacteria) for fundamental structural units of the genome. In Euryarchaeota, a major archaeal phylum, either histone or HTa (the bacterial HU homolog) were found to wrap DNA. This finding divides archaea into two groups: those that use DNA-wrapping as the fundamental step in genome folding and those that do not. Archaeal transcription factor-like protein TrmBL2 has been suggested to be involved in genome folding and repression of horizontally acquired genes, similar to bacterial H-NS protein. Evolutionarily divergent SMC proteins contribute to the establishment of higher-order structures. Recent results are presented, including the use of Hi-C technology to reveal that archaeal SMC proteins are involved in higher-order genome folding, and the use of single-molecule tracking to reveal the detailed functions of bacterial and eukaryotic SMC proteins. Here, we highlight the similarities and differences in the DNA-folding mechanisms in the three domains of life.

Oral microbiome dysbiosis has important links to human health and disease. Although photodynamic therapy influences microbiome diversity, the specific effect of violet light irradiation remains largely unknown. In this study, we analyzed the effect of violet light-emitting diode (LED) irradiation on interdental plaque microbiota. Interdental plaque was collected from 12 human subjects, exposed to violet LED irradiation, and cultured in a specialized growth medium. Next-generation sequencing of the 16S ribosomal RNA genes revealed that α-diversity decreased, whereas β-diversity exhibited a continuous change with violet LED irradiation doses. In addition, we identified several operational taxonomic units that exhibited significant shifts during violet LED irradiation. Specifically, violet LED irradiation led to a significant reduction in the relative abundance of Fusobacterium species, but a significant increase in several species of oral bacteria, such as Veillonella and Campylobacter. Our study provides an overview of oral plaque microbiota changes under violet LED irradiation, and highlights the potential of this method for adjusting the balance of the oral microbiome without inducing antibiotic resistance.

Archaeal species encode a variety of distinct lineage-specific chromosomal proteins. We have previously shown that inThermococcus kodakarensis, histone, Alba, and TrmBL2 play distinct roles in chromosome organization. Although our understanding of individual archaeal chromosomal proteins has been advancing, how archaeal chromosomes are folded into higher-order structures and how they are regulated are largely unknown. Here, we investigated the primary and higher-order structures of archaeal chromosomes from different archaeal lineages. Atomic force microscopy of chromosome spreads out ofThermoplasma acidophilumandPyrobaculum calidifontiscells revealed 10-nm fibers and 30-40-nm globular structures, suggesting the occurrence of higher-order chromosomal folding. Our results also indicated that chromosome compaction occurs toward the stationary phase. Micrococcal nuclease digestion indicated that fundamental structural units of the chromosome exist inT. acidophilumandT. kodakarensisbut not inP. calidifontisorSulfolobus solfataricus. In vitroreconstitution showed that, inT. acidophilum, the bacterial HU protein homolog HTa formed a 6-nm fiber by wrapping DNA, and that Alba was responsible for the formation of the 10-nm fiber by binding along the DNA without wrapping. Remarkably, Alba could form different higher-order complexes with histone or HTa on DNAin vitro. Mass spectrometry detected HTa and Rad50 in theT. acidophilumchromosome but not in other species. A putative transcriptional regulator of the AsnC/Lrp family (Pcal_1183) was detected on theP. calidifontischromosome, but not on that of other species studied. Putative membrane-associated proteins were detected in the chromosomes of the three archaeal species studied, includingT. acidophilum,P. calidifontis, andT. kodakarensis. Collectively, our data show that Archaea use different combinations of proteins to achieve chromosomal architecture and functional regulation.

The Cover Feature illustrates the current production capability, that is, electron transport from the cell inside to the extracellular electrode surface in two periodontal pathogens. More information can be found in the Article by D. Naradasu et al.

Background: Oral microbiota has been linked to both health and diseases. Specifically, tongue-coating microbiota has been implicated in aspiration pneumonia and halitosis. Approaches altering one's oral microbiota have the potential to improve oral health and prevent diseases. Methods: Here, we designed a study that allows simultaneous monitoring of the salivary and tongue microbiomes during an intervention on the oral microbiota. We applied this study design to evaluate the effect of single-day use of oral care tablets on the oral microbiome of 10 healthy individuals. Tablets with or without actinidin, a protease that reduces biofilm formation in vitro, were tested. Results: Alpha diversity of the tongue microbiome was significantly lower than that of the salivary microbiome, using both the number of observed amplicon sequence variants (254 ± 53 in saliva and 175 ± 37 in tongue; P = 8.9e-7, Kruskal–Wallis test) and Shannon index (6.0 ± 0.4 in saliva and 5.4 ± 0.3 in tongue; P = 2.0e-7, Kruskal–Wallis test). Fusobacterium periodonticum, Saccharibacteria sp. 352, Streptococcus oralis subsp. dentisani, Prevotella melaninogenica, Granulicatella adiacens, Campylobacter concisus, and Haemophilus parainfluenzae were the core operational taxonomic units (OTUs) common to both sites. The salivary and tongue microbiomes of one individual tended to be more similar to one another than to those of other individuals. The tablets did not affect the alpha or beta diversity of the oral microbiome, nor the abundance of specific bacterial species. Conclusions: While the salivary and tongue microbiomes differed significantly in terms of bacterial composition, they showed inter- rather than intra-individual diversity. A one-day usage of oral care tablets did not alter the salivary or tongue microbiomes of healthy adults. Whether the use of oral tablets for a longer period on healthy people or people with greater tongue coating accumulation shifts their oral microbiome needs to be investigated.

Extracellular electron transfer (EET) via cell-bound redox enzymes and/or redox shuttles is extensively studied in environmental bacteria. Meanwhile, EET capable pathogens have been identified in the human gut. However, other EET-capable bacterial niches where possible biofilm infections are prominent have scarcely been explored. Herein, we electrochemically characterized human oral biofilm pathogens, Aggregatibacter actinomycetemcomitans and Porphyromonas gingivalis, to examine their EET capability. Both strains showed current production with the electrode poised at +0.4 V vs. a standard hydrogen electrode, which was associated with a decrease in electron-donor concentration, coupled with the appearance of oxidative peaks in differential pulse (DP) and cyclic voltammograms (CV). Addition of antibiotics that suppress the biosynthesis of membrane or protein showed a significant current decrease, demonstrating that current production reflects the cellular activity in these pathogens. DPV- and CV-based kinetic analyses supported by transmission electron microscopy of the cells stained for transition metals suggest a potential EET mechanism associated with the presence of redox enzymes on the cell membrane. These results could be the basis to reevaluate human oral pathogens from an electroactive point of view. The identified electrochemical activity of the two strains can be an effective test for assessing the impact of antibacterial compounds on the pathogen cellular activity on an electrode.