Development of a multispecies oral bacterial community in a saliva-conditioned flow cell

Comprehensive strategies for overcoming dental biofilms: Microbial dynamics and innovative methods

Dental biofilm develops through a complex process initiated by the attachment of early colonising bacteria to the surface of teeth. These bacteria use specific adhesion molecules to bind to the enamel, after which they proliferate and secrete an extracellular polymeric substance. As a result, the early colonisers eventually form a resilient, multispecies community encased in an extracellular polymeric matrix, reinforcing the biofilm structure. This matrix enables microbes to withstand the mechanical disruption, evade host immune defences and resist many antimicrobials. Diseases associated with dental biofilm are among the most prevalent oral health issues, highlighting the importance of effective biofilm management in maintaining oral health. This review explores the progression of biofilm development and evaluates various strategies, from conventional antibiotics and herbal medicine to advanced strategies like antimicrobial peptides, nanoparticles, probiotics, cold atmospheric plasma, quorum sensing inhibitors and enzymes. In particular, enzymatic agents such as Dispersin B, DNAases, and glucanohydrolases, including mutanase and dextranase, have shown promise in disrupting the biofilm structure, thereby offering potential avenues for managing dental biofilm.

When oral health affects overall health: biofilms, dental infections, and emerging antimicrobial strategies

Dental health is a crucial component of overall health, yet it is frequently overlooked in discussions about well-being. This article explores the multifaceted aspects of dental infections, primarily focusing on biofilms formed by pathogenic bacteria such as Streptococcus mutans and Porphyromonas gingivalis. These biofilms contribute to dental caries and periodontal disease, conditions that affect oral health and have systemic consequences. Recent advancements in understanding biofilm formation and interactions have led to novel strategies for prevention and treatment, including using nanoparticles and smart hydrogels designed to disrupt biofilm integrity while promoting biocompatibility with human tissues. Furthermore, the article highlights the potential of natural remedies, including herbal extracts, as adjuncts in maintaining oral hygiene and combating microbial infections. A comprehensive overview of biofilm dynamics, including adhesion, maturation, and dispersion, is presented, alongside discussions on innovative therapeutic approaches addressing the limitations of conventional treatments. Ultimately, this article emphasizes the importance of maintaining dental health in preventing a wide spectrum of health issues, reinforcing that the mouth is a gateway to the body.

Advances in modeling periodontal host-microbe interactions: insights from organotypic and organ-on-chip systems

Periodontal disease, a chronic inflammatory condition affecting the supporting structures of teeth, is driven by an imbalanced interaction between the periodontal microbiota and the host inflammatory response. Beyond its local impact, periodontal disease is associated with systemic conditions such as diabetes mellitus, cardiovascular disease, and inflammatory bowel disease, emphasizing the importance of understanding its mechanisms. Traditional pre-clinical models, such as monolayer cultures and animal studies, have provided foundational insights but are limited by their physiological relevance and ethical concerns. Recent advancements in tissue engineering and microfluidic technologies have led to the development of three-dimensional (3D) organotypic culture models and organ-on-chip systems that more closely mimic native tissue microenvironments. This review provides an overview of the evolution of methods to study periodontal host-microbe interactions, from simple 2D monolayer cultures to complex 3D organotypic and microfluidic organ-on-chip (OoC) models. We discuss various fabrication strategies, host-microbe co-culture techniques, and methods for evaluating outcomes in these advanced models. Additionally, we highlight insights gained from gut-on-chip platforms and their potential applications in periodontal research and understanding oral-systemic links of periodontal disease. Through a comprehensive overview of current advancements and future directions, this review provides insights on the transformative potential of OoC technology in periodontal research, offering new avenues for studying disease mechanisms and developing therapeutic strategies.

Disentangling the feedback loops driving spatial patterning in microbial communities

The properties of multispecies biofilms are determined by how species are arranged in space. How these patterns emerge is a complex and largely unsolved problem. Here, we synthesize the known factors affecting pattern formation, identify the interdependencies and feedback loops coupling them, and discuss approaches to disentangle their effects. Finally, we propose an interdisciplinary research program that could create a predictive understanding of pattern formation in microbial communities.

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

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

Antibiofilm activity of Clitoria ternatea flowers anthocyanin fraction against biofilm-forming oral bacteria

This study investigated the antibiofilm effects of Clitoria ternatea flowers anthocyanin fraction (AF) on Streptococcus mutans, Actinomyces viscosus, and Aggregatibacter actinomycetemcomitans. AF was obtained using column chromatography, and liquid chromatography-mass spectrometry was employed for its characterization and identification. The crystal violet assay and scanning electron microscopy analysis revealed significant inhibition of early biofilm formation and destruction of preformed biofilms after AF treatment (0.94-15 mg ml-1). Antiadhesion assay on acrylic teeth demonstrated that AF effectively hampered sucrose dependent and independent attachment. Importantly, growth curve and pH drop assays showed that AF inhibited pH reduction for all bacteria tested without hindering bacterial growth. Furthermore, the tetrazolium-based cytotoxicity assay indicated no toxicity towards normal human gingival fibroblasts at 0.78-12.5 mg ml-1. These findings suggest C. ternatea anthocyanins are promising antibiofilm agents for oral biofilm control, acting during both initial formation and on mature biofilms.

Microfluidic organ-on-chip systems for periodontal research: advances and future directions

Advances in tissue engineering and microfluidic technologies have enabled the development of sophisticated in vitro models known as organ-on-a-chip (OoC) or microphysiological systems. These systems enable to potential to simulate the dynamic interactions between host tissues and their microenvironment including microbes, biomaterials, mechanical forces, pharmaceutical, and consumer-care products. These fluidic technologies are increasingly being utilized to investigate host-microbe and host-material interactions in oral health and disease. Of interest is their application in understanding periodontal disease, a chronic inflammatory condition marked by the progressive destruction of periodontal tissues, including gingiva, periodontal ligament, and alveolar bone. The pathogenesis of periodontal disease involves a complex interplay between microbial dysbiosis and host immune responses, which can lead to a loss of dental support structures and contribute to systemic conditions such as cardiovascular disease, diabetes, and inflammatory bowel disease. This provides a comprehensive overview of the latest developments in millifluidic and microfluidic systems designed to emulate periodontal host-microbe and host-material interactions. We discuss the critical engineering and biological considerations in designing these platforms, their applications in studying oral biofilms, periodontal tissue responses, and their potential to unravel disease mechanisms and therapeutic targets in periodontal disease.

The Bacterial Biofilms: Formation, Impacts, and Possible Management Targets in the Healthcare System

Introduction: The persistent increase in multidrug-resistant pathogens has catalyzed the creation of novel strategies to address antivirulence and anti-infective elements. Such methodologies aim to diminish the selective pressure exerted on bacterial populations, decreasing the likelihood of resistance emergence. This review explores the role of biofilm formation as a significant virulence factor and its impact on the development of antimicrobial resistance (AMR). Case Presentation: The ability of bacteria to form a superstructure-biofilm-has made resistance cases in the microbial world a big concern to public health and other sectors as it is a crucial virulence factor that causes difficulties in the management of infections, hence enhancing chronic infection occurrence. Biofilm formation dates to about 3.4 billion years when prokaryotes were discovered to be forming them and since then due to evolution and growth in science, they are more understood. Management and Outcome: The unique microenvironments within bacterial biofilms diminish antibiotic effectiveness and help bacteria evade the host immune system. Biofilm production is a widespread capability among diverse bacterial species. Biofilm formation is enhanced by quorum sensing (QS), reduction of nutrients, or harsh environments for the bacteria. Conclusion: The rise of severe, treatment-resistant biofilm infections poses major challenges in medicine and agriculture, yet much about how these biofilms form remains unknown.

Mechanisms of antimicrobial resistance in biofilms

Most bacteria in nature exist in aggregated communities known as biofilms, and cells within a biofilm demonstrate major physiological changes compared to their planktonic counterparts. Biofilms are associated with many different types of infections which can have severe impacts on patients. Infections involving a biofilm component are often chronic and highly recalcitrant to antibiotic therapy as a result of intrinsic physical factors including extracellular matrix production, low growth rates, altered antibiotic target production and efficient exchange of resistance genes. This review describes the biofilm lifecycle, phenotypic characteristics of a biofilm, and contribution of matrix and persister cells to biofilms intrinsic tolerance to antimicrobials. We also describe how biofilms can evolve antibiotic resistance and transfer resistance genes within biofilms. Multispecies biofilms and the impacts of various interactions, including cooperation and competition, between species on tolerance to antimicrobials in polymicrobial biofilm communities are also discussed.

Difference in formation of a dental multi-species biofilm according to substratum direction

OBJECTIVES

The aim of this study was to investigate the difference in dental biofilm formation according to substratum direction, using an artificial biofilm model.

METHODS

A three-species biofilm, consisting of Streptococcus mutans, Streptococcus oralis, and Actinomyces naeslundii, was formed on saliva-coated hydroxyapatite (sHA) discs oriented in three directions: downward (the discs placed in the direction of gravity), vertical (the discs placed parallel to the direction of gravity), and upward (the discs placed in opposite direction of gravity). The biofilms at 22 h and 46 h of age were analyzed using microbiological and biochemical methods, fluorescence-based assays, and scanning electron microscopy to investigate difference in bacterial adhesion, early and mature biofilm formation.

RESULTS

The biofilms formed in the upward direction displayed the most complex structure, with the highest number and biovolume of bacteria, as well as the lowest pH conditions at both time points. The vertical and downward directions, however, had only scattered and small bacterial colonies. In the 22-h-old biofilms, the proportion of S. oralis was similar to, or slightly higher than, that of S. mutans in all directions of substratum surfaces. However, in the 46-h-old biofilms, S. mutans became the dominant bacteria in all directions, especially in the vertical and upward directions.

CONCLUSIONS

The direction of the substratum surface could impact the proportion of bacteria and cariogenic properties of the multi-species biofilm. Biofilms in an upward direction may exhibit a higher cariogenic potential, followed by those in the vertical and downward directions, which could be related to gravity.

Development of an in vitro biofilm model of the human supra-gingival microbiome for Oral microbiome transplantation

The high prevalence of dental caries and periodontal disease place a significant burden on society, both socially and economically. Recent advances in genomic technologies have linked both diseases to shifts in the oral microbiota - a community of >700 bacterial species that live within the mouth. The development of oral microbiome transplantation draws on the success of fecal microbiome transplantation for the treatment of gut pathologies associated with disease. Many current in vitro oral biofilm models have been developed but do not fully capture the complexity of the oral microbiome which is required for successful OMT. To address this, we developed an in vitro biofilm system that maintained an oral microbiome with 252 species on average over 14 days. Six human plaque samples were grown in 3D printed flow cells on hydroxyapatite discs using artificial saliva medium (ASM). Biofilm composition and growth were monitored by high throughput sequencing and confocal microscopy/SEM, respectively. While a significant drop in bacterial diversity occurred, up to 291 species were maintained in some flow cells over 14 days with 70% viability grown with ASM. This novel in vitro biofilm model represents a marked improvement on existing oral biofilm systems and provides new opportunities to develop oral microbiome transplant therapies.

Staphylococcus epidermidis biofilm assembly and self-dispersion: bacteria and matrix dynamics

Staphylococcus epidermidis, despite being a commensal of human skin and mucosa, is a major nosocomial pathogen implicated in device-associated infections. The dissemination of infection to other body sites is related to biofilm dispersal. This study focused on the dispersion stage of S. epidermidis CIP 444 biofilm, with the assessment of biofilm matrix composition in a time-dependent experiment (7 days extended) with 3 independent repetitions, using confocal laser scanning microcopy (CLSM) in association with ZEN 3.4 blue edition, COMSTAT, and ImageJ software. SYTO-9, propidium iodide (PI), DID'OIL, FITC, and calcofluor white M2R (CFW) were used to stain biofilm components. The results indicated that the biomass of dead cells increased from 15.18 ± 1.81 µm3/µm2 (day 3) to 23.15 ± 6.075 µm3/µm2 (day 4), along with a decrease in alive cells' biomass from 22.75 ± 2.968 µm3/µm2 (day 3) to 18.95 ± 5.713 µm3/µm2 (day 4). When the intensities were measured after marking the biofilm components, in a 24-h-old biofilm, polysaccharide made up the majority of the investigated components (52%), followed by protein (18.9%). Lipids make up just 11.6% of the mature biofilm. Protein makes up the largest portion (48%) of a 4-day-old biofilm, followed by polysaccharides (37.8%) and lipids (7.27%). According to our findings, S. epidermidis CIP 444 dispersion occurred on day 4 of incubation, and new establishment of the biofilm occurred on day 7. Remarkable changes in biofilm composition will pave the way for a new approach to understanding bacterial strategies inside biofilms and finding solutions to their impacts in the medical field.

Patent Mining on the Use of Antioxidant Phytochemicals in the Technological Development for the Prevention and Treatment of Periodontitis

Periodontal disease is an inflammatory condition characterized by an aberrant immune response against a dysbiotic dental biofilm, with oxidative stress performing an essential role in its pathogenesis. This paper presents a patent mining, performed in the Orbit Intelligence patent database, related to antioxidant phytochemicals in the technological developments that are working to prevent and treat periodontal disease. To access the documents, the descriptors "PERIODONTAL" and "ANTIOXIDANT" were typed in the title, abstract, and claim search fields. A total of 322 patents demonstrate the growing interest in researching natural antioxidants for scientific and technological purposes. The top ten countries regarding the number of family patents produced were the United States, the European Office, Japan, South Korea, China, India, Mexico, Denmark, Canada, and Great Britain. The most cited compounds were vitamin C, green tea, quercetin, melatonin, lycopene, resveratrol, and curcumin. These compounds have been used for the technological development of gels, membranes, dentifrices, chewing gum, orally disintegrating film, mouthwash, mouth spray, and mouth massage cream and exhibit the ability to neutralize free radicals and reduce oxidative stress, a critical factor in the development and progression of periodontal diseases. The patent documents have shown that using antioxidant compounds in conjunction with traditional periodontal treatments is a promising area of interest in periodontal therapy.

Interactions and effects of a stannous-containing sodium fluoride dentifrice on oral pathogens and the oral microbiome

Numerous studies have investigated the effects of stannous ions on specific microbes and their efficacy in reducing dental plaque. Nonetheless, our understanding of their impact on the oral microbiome is still a subject of ongoing exploration. Therefore, this study sought to evaluate the effects of a stannous-containing sodium fluoride dentifrice in comparison to a zinc-containing sodium fluoride dentifrice and a control group on intact, healthy oral biofilms. Utilizing the novel 2bRAD-M approach for species-resolved metagenomics, and FISH/CLSM with probes targeting periodontal and caries associated species alongside Sn2+ and Zn2+ ions, we collected and analyzed in situ biofilms from 15 generally healthy individuals with measurable dental plaque and treated the biofilms with dentifrices to elucidate variations in microbial distribution. Although significant shifts in the microbiome upon treatment were not observed, the use of a stannous-containing sodium fluoride dentifrice primarily led to an increase in health-associated commensal species and decrease in pathogenic species. Notably, FISH/CLSM analysis highlighted a marked reduction in representative species associated with periodontitis and caries following treatment with the use of a stannous-containing sodium fluoride dentifrice, as opposed to a zinc-containing sodium fluoride dentifrice and the control group. Additionally, Sn2+ specific intracellular imaging reflected the colocalization of Sn2+ ions with P. gingivalis but not with other species. In contrast, Zn2+ ions exhibited non-specific binding, thus suggesting that Sn2+ could exhibit selective binding toward pathogenic species. Altogether, our results demonstrate that stannous ions could help to maintain a healthy oral microbiome by preferentially targeting certain pathogenic bacteria to reverse dysbiosis and underscores the importance of the continual usage of such products as a preventive measure for oral diseases and the maintenance of health.

Bacterial multispecies interaction mechanisms dictate biogeographic arrangement between the oral commensals Corynebacterium matruchotii and Streptococcus mitis

IMPORTANCE

As the microbiome era matures, the need for mechanistic interaction data between species is crucial to understand how stable microbiomes are preserved, especially in healthy conditions where the microbiota could help resist opportunistic or exogenous pathogens. Here we reveal multiple mechanisms of interaction between two commensals that dictate their biogeographic relationship to each other in previously described structures in human supragingival plaque. Using a novel variation for chemical detection, we observed metabolite exchange between individual bacterial cells in real time validating the ability of these organisms to carry out metabolic crossfeeding at distal and temporal scales observed in vivo. These findings reveal one way by which these interactions are both favorable to the interacting commensals and potentially the host.

Microbiologically influenced corrosion-more than just microorganisms

Microbiologically influenced corrosion (MIC) is a phenomenon of increasing concern that affects various materials and sectors of society. MIC describes the effects, often negative, that a material can experience due to the presence of microorganisms. Unfortunately, although several research groups and industrial actors worldwide have already addressed MIC, discussions are fragmented, while information sharing and willingness to reach out to other disciplines are limited. A truly interdisciplinary approach, which would be logical for this material/biology/chemistry-related challenge, is rarely taken. In this review, we highlight critical non-biological aspects of MIC that can sometimes be overlooked by microbiologists working on MIC but are highly relevant for an overall understanding of this phenomenon. Here, we identify gaps, methods, and approaches to help solve MIC-related challenges, with an emphasis on the MIC of metals. We also discuss the application of existing tools and approaches for managing MIC and propose ideas to promote an improved understanding of MIC. Furthermore, we highlight areas where the insights and expertise of microbiologists are needed to help progress this field.

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

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

Current concepts in the pathogenesis of periodontitis: from symbiosis to dysbiosis

The primary etiological agent for the initiation and progression of periodontal disease is the dental plaque biofilm which is an organized aggregation of microorganisms residing within a complex intercellular matrix. The non-specific plaque hypothesis was the first attempt to explain the role of the dental biofilm in the pathogenesis of periodontal diseases. However, the introduction of sophisticated diagnostic and laboratory assays has led to the realisation that the development of periodontitis requires more than a mere increase in the biomass of dental plaque. Indeed, multispecies biofilms exhibit complex interactions between the bacteria and the host. In addition, not all resident microorganisms within the biofilm are pathogenic, since beneficial bacteria exist that serve to maintain a symbiotic relationship between the plaque microbiome and the host's immune-inflammatory response, preventing the emergence of pathogenic microorganisms and the development of dysbiosis. This review aims to highlight the development and structure of the dental plaque biofilm and to explore current literature on the transition from a healthy (symbiotic) to a diseased (dysbiotic) biofilm in periodontitis and the associated immune-inflammatory responses that drive periodontal tissue destruction and form mechanistic pathways that impact other systemic non-communicable diseases.

Fernandez de Henestrosa A, Furmanczyk M, Trullàs C, Jourdan E, López-López J, Jorba M. Substantivity of mouth-rinse formulations containing cetylpyridinium chloride and O-cymen-5-ol: a randomized-crossover trial

BACKGROUND

The efficacy of mouth-rinses strongly depends upon their substantivity. The use of natural and non-toxic products that avoid secondary effects is gaining interest in preventive dentistry. The purpose of this study was to evaluate the substantivity of two formulations of mouth-washing solutions based on cetylpyridinium (CPC) and O-cymen-5-ol.

METHODS

This was a randomized, double-blind, crossover trial conducted at the Faculty of Medicine and Health Sciences of the University of Barcelona. Bacterial re-colonization was followed by live/dead (SYTO^TM9 + propidium iodide) bacterial staining and measured by confocal laser scanning microscopy and fluorometry. Unstimulated saliva samples were collected from 16 healthy individuals at baseline saliva and then, at 15 min, 30 min and 1, 2, 3, and 4 h after the following mouth-rinses: (i) a single, 1-min mouth-rinse with 15 ml of placebo (negative control); (ii) a single, 1-min mouth-rinse with 15 ml of CPC (0.05%) ; (iii) a single, 1-min mouth-rinse with 15 ml of O-cymen-5-ol (0.09%); (iv) a single, 1-min mouth-rinse with 15 ml of CPC (0.05%) + O-cymen-5-ol (0.09%).

RESULTS

Proportion of dead bacteria was significantly higher for all mouthrinses during the first 15 min compared to baseline (CPC = 48.0 ± 13.9; 95% CI 40.98-56.99; p < 0.001, O-cymen-5-ol = 79.8 ± 21.0; 95% CI 67.71-91.90; p < 0.05, CPC + O-cymen-5-ol = 49.4 ± 14; 95% CI 40.98-56.99; p < 0.001 by fluorometry and 54.8 ± 23.0; 95% CI 41.50-68.06; p < 0.001, 76.3 ± 17.1; 95% CI 66.36-86.14; p < 0.001, 47.4 ± 11.9; 95% CI 40.49-54.30; p < 0.001 by confocal laser scanning microscopy, respectively). Nevertheless, after 4 h, CPC + O-cymen-5-ol was the only one that obtained significant values as measured by the two quantification methods used (80.3 ± 22.8; 95% CI 67.15-93.50; p < 0.05 and 81.4 ± 13.8; 95% CI 73.45-89.43; p < 0.05). The combined use of CPC + O-cymen-5-ol increased the substantivity of the mouthrinse with respect to mouthrinses prepared with either of the two active products alone.

CONCLUSION

The synergistic interaction of CPC and O-cymen-5-ol prolongs their substantivity. The resulting formulation may be as effective as other antimicrobials, such as triclosan or chlorhexidine, but without their undesirable secondary effects. Thus, mouthrinsing products based on Combinations of CPC and O-cymen-5-ol may replace in the near future Triclosan and Chlorhexidine-based mouthrinses.

Application of Fluorescence In Situ Hybridization (FISH) in Oral Microbial Detection

Varieties of microorganisms reside in the oral cavity contributing to the occurrence and development of microbes associated with oral diseases; however, the distribution and in situ abundance in the biofilm are still unclear. In order to promote the understanding of the ecosystem of oral microbiota and the diagnosis of oral diseases, it is necessary to monitor and compare the oral microorganisms from different niches of the oral cavity in situ. The fluorescence in situ hybridization (FISH) has proven to be a powerful tool for representing the status of oral microorganisms in the oral cavity. FISH is one of the most routinely used cytochemical techniques for genetic detection, identification, and localization by a fluorescently labeled nucleic acid probe, which can hybridize with targeted nucleic acid sequences. It has the advantages of rapidity, safety, high sensitivity, and specificity. FISH allows the identification and quantification of different oral microorganisms simultaneously. It can also visualize microorganisms by combining with other molecular biology technologies to represent the distribution of each microbial community in the oral biofilm. In this review, we summarized and discussed the development of FISH technology and the application of FISH in oral disease diagnosis and oral ecosystem research, highlighted its advantages in oral microbiology, listed the existing problems, and provided suggestions for future development..

Nutritional factors influencing microbiota-mediated colonization resistance of the oral cavity: A literature review

The oral cavity is a key biocenosis for many distinct microbial communities that interact with both the external environment and internal body systems. The oral microbiota is a vital part of the human microbiome. It has been developed through mutual interactions among the environment, host physiological state, and microbial community composition. Indigenious microbiota of the oral cavity is one of the factors that prevent adhesion and invasion of pathogens on the mucous membrane, i.e., the development of the infectious process and thereby participating in the implementation of one of the mechanisms of local immunity-colonization resistance. The balance between bacterial symbiosis, microbial virulence, and host resistance ensures the integrity of the oral cavity. In this review we have tried to address how nutritional factors influence integrity of the oral indigenous microbiota and its involvement in colonization resistance.

Targeting the succinate receptor effectively inhibits periodontitis

Periodontal disease (PD) is one of the most common inflammatory diseases in humans and is initiated by an oral microbial dysbiosis that stimulates inflammation and bone loss. Here, we report an abnormal elevation of succinate in the subgingival plaque of subjects with severe PD. Succinate activates succinate receptor-1 (SUCNR1) and stimulates inflammation. We detected SUCNR1 expression in the human and mouse periodontium and hypothesize that succinate activates SUCNR1 to accelerate periodontitis through the inflammatory response. Administration of exogenous succinate enhanced periodontal disease, whereas SUCNR1 knockout mice were protected from inflammation, oral dysbiosis, and subsequent periodontal bone loss in two different models of periodontitis. Therapeutic studies demonstrated that a SUCNR1 antagonist inhibited inflammatory events and osteoclastogenesis in vitro and reduced periodontal bone loss in vivo. Our study reveals succinate’s effect on periodontitis pathogenesis and provides a topical treatment for this disease.

Periodontitis is the most prevalent adult oral disease. Guo et al. show elevation of succinate in periodontitis, which aggravates the disease through the succinate receptor (SUCNR1). They developed a gel formulation of a small compound specifically blocking SUCNR1 to prevent and treat periodontitis by inhibiting dysbiosis, inflammation, and bone loss.

Emerging microfluidic technologies for microbiome research

The importance of the microbiome is increasingly prominent. For example, the human microbiome has been proven to be strongly associated with health conditions, while the environmental microbiome is recognized to have a profound influence on agriculture and even the global climate. Furthermore, the microbiome can serve as a fascinating reservoir of genes that encode tremendously valuable compounds for industrial and medical applications. In the past decades, various technologies have been developed to better understand and exploit the microbiome. In particular, microfluidics has demonstrated its strength and prominence in the microbiome research. By taking advantage of microfluidic technologies, inherited shortcomings of traditional methods such as low throughput, labor-consuming, and high-cost are being compensated or bypassed. In this review, we will summarize a broad spectrum of microfluidic technologies that have addressed various needs in the field of microbiome research, as well as the achievements that were enabled by the microfluidics (or technological advances). Finally, how microfluidics overcomes the limitations of conventional methods by technology integration will also be discussed.

Evaluation of photosensitizer-containing superhydrophobic surfaces for the antibacterial treatment of periodontal biofilms

Antimicrobial photodynamic therapy (aPDT) is a promising approach to control biofilms involved in periodontal diseases. However, certain challenges, such as staining of teeth, preferential interaction of photosensitizer (PS) with Gram-positive versus Gram-negative bacteria, and insufficient oxygen in hypoxic periodontal pockets have presented barriers to its use in the clinic. To overcome these challenges, a novel superhydrophobic (SH) film that generates airborne singlet oxygen has been developed. The SH-aPDT approach isolates the PS onto a topologically rough solid SH film on which channels allow air to diffuse to the PS surface, thus ensuring sufficient oxygen supply. Upon illumination, gas phase singlet oxygen (¹O₂) is produced and diffuses from the SH surface to the underlying biofilm. The killing efficacy was assessed as a function of transmitted fluence (17.9-89.5 J/cm²) and chorin e6 loading (96-1110 nmol/cm²) by counting of colony forming units, biofilm metabolism by XTT and confocal microscopy. The decrease in viability of both Gram-positive and Gram-negative bacteria in a multi-species biofilm was found to be linearly dependent on the fluence as well as the loading of the PS up to 71.6 J/cm² when 1110 nmols/cm² of chlorin e6 was used. A > 4.6 log bacterial reduction was observed under these conditions (p < 0.05). This novel SH-aPDT approach shows promise as an effective method to disinfect multi-species bacterial biofilms associated with periodontal disease and will be evaluated in animal models in future studies.

Light-Propelled Nanorobots for Facial Titanium Implants Biofilms Removal

Titanium miniplates are biocompatible materials used in modern oral and maxillofacial surgery to treat facial bone fractures. However, plate removal is often required due to implant complications. Among them, a biofilm formation on an infected miniplate is associated with severe inflammation, which frequently results in implant failure. In light of this, new strategies to control or treat oral bacterial biofilm are of high interest. Herein, the authors exploit the ability of nanorobots against multispecies bacterial biofilm grown onto facial commercial titanium miniplate implants to simulate pathogenic conditions of the oral microenvironment. The strategy is based on the use of light-driven self-propelled tubular black-TiO₂ /Ag nanorobots, that unlike traditional ones, exhibit an extended absorption and motion actuation from UV to the visible-light range. The motion analysis is performed separately over UV, blue, and green light irradiation and shows different motion behaviors, including a fast rotational motion that decreases with increasing wavelengths. The biomass reduction is monitored by evaluating LIVE/DEAD fluorescent and digital microscope images of bacterial biofilm treated with the nanorobots under motion/no-motion conditions. The current study and the obtained results can bring significant improvements for effective therapy of infected metallic miniplates by biofilm.

Mechanistic Effects of E-Liquids on Biofilm Formation and Growth of Oral Commensal Streptococcal Communities: Effect of Flavoring Agents

Background: Vaping has become a global health concern. As research continues, more studies are beginning to question the relative safety of E-liquid flavoring additives. The oral cavity is the first site of exposure to E-liquid aerosol, making it critical for investigation. Because of the importance of commensal bacterial biofilms for oral health, we sought to explore the effects of E-liquids ± flavors on the formation and growth of single- and multi-species biofilms and to investigate the mechanism of inhibition. Methods: Quantitative and confocal biofilm analysis, death curves, and colony-forming units (CFU) were evaluated with flavorless and flavored (tobacco, menthol, cinnamon, strawberry, blueberry) E-liquids using four strains of oral commensal bacteria (Streptococcus gordonii, Streptococcus intermedius, Streptococcus mitis, and Streptococcus oralis). Results: All flavoring agents show a dose-dependent inhibition in the growth of single-species and multi-species biofilms. Furthermore, CFUs, death curves, and light microscopy show that flavoring agents have a bactericidal mode of inhibition on the growth of these oral streptococci. Conclusions: These results show that flavored, rather than unflavored, E-liquids are more detrimental to biofilm formation and growth of oral commensal bacteria. Consequently, E-liquid flavorings agents could pose risks to the oral microenvironment, and by extension, to systemic health.

Characteristics of Clinical Isolates of Streptococcus mutans

Dental caries is an infectious disease which remains a significant health problem all over the world. The purpose of the study was to characterise a collection of 60 clinical isolates of S. mutans from adults’ and children’s dental plaque (natural biofilm). The paper describes the process of isolation, identification, analysis of biofilm formation and collection testing for the presence of 13 two-component systems (TCS) identified earlier in reference strain ATCC 700610 (UA159). In the case of S. mutans strains, plaque formation is specifically influenced by binary systems. All isolated strains of S. mutans form biofilm at high levels and possess a set of 26 genes forming TSC binary systems, which have an important role in plaque formation.

Biofilm reactor calibration for in vitro investigation of composite biodegradation

Introduction: The majority of biodegradation studies of composite materials use simplified models of microbial biofilm despite the apparent diversity of the oral microbiota. The use of in vitro systems of “artificial mouth” design is a step towards clarifying the synergistic effect that microbial plaque and human saliva have on composite degradation.

Aim: Establishment of functional parameters for in vitro reproduction of oral biofilms via biofilm reactor systems.

Materials and methods: The CDC Biofilm Reactor system consists of eight polypropylene sticks. The rod cover and the retaining plates are mounted in a 1-dm glass cylinder with an outlet side opening. The laboratory bioreactor has a working volume of 340 ml. The device is equipped with a four-blade magnetic stirrer. The system also includes gauging appliances and executive mechanisms for controlling and adjusting the basic parameters of the process.

Results: Determination of the operating volume of the reactor is performed prior to the experiment along with the time of reach and stabilization of the set temperature in the design which is 60 min at 120 rpm. A mathematical model is used to calculate the rate of delivery of growth medium - 11 millilitres per minute. The bioreactor is sterilized by 0.3% neomycin solution for 24 hours. Prior to the experiment the system is cleansed (via passage) with sterile water for 60 minutes.

Conclusions: The pre-calibration of a bioreactor system allows specification and refinement of its working parameters, thus engaging for accurate reproduction of the environmental conditions in the oral cavity.

Polymicrobial Aggregates in Human Saliva Build the Oral Biofilm

Biofilm community development has been established as a sequential process starting from the attachment of single cells on a surface. However, microorganisms are often found as aggregates in the environment and in biological fluids. Here, we conduct a comprehensive analysis of the native structure and composition of aggregated microbial assemblages in human saliva and investigate their spatiotemporal attachment and biofilm community development. Using multiscale imaging, cell sorting, and computational approaches combined with sequencing analysis, a diverse mixture of aggregates varying in size, structure, and microbial composition, including bacteria associated with host epithelial cells, can be found in saliva in addition to a few single-cell forms. Phylogenetic analysis reveals a mixture of complex consortia of aerobes and anaerobes in which bacteria traditionally considered early and late colonizers are found mixed together. When individually tracked during colonization and biofilm initiation, aggregates rapidly proliferate and expand tridimensionally, modulating population growth, spatial organization, and community scaffolding. In contrast, most single cells remain static or are incorporated by actively growing aggregates. These results suggest an alternative biofilm development process whereby aggregates containing different species or associated with human cells collectively adhere to the surface as "growth nuclei" to build the biofilm and shape polymicrobial communities at various spatial and taxonomic scales. IMPORTANCE Microbes in biological fluids can be found as aggregates. How these multicellular structures bind to surfaces and initiate the biofilm life cycle remains understudied. Here, we investigate the structural organization of microbial aggregates in human saliva and their role in biofilm formation. We found diverse mixtures of aggregates with different sizes, structures, and compositions in addition to free-living cells. When individually tracked during binding and growth on tooth-like surfaces, most aggregates developed into structured biofilm communities, whereas most single cells remained static or were engulfed by the growing aggregates. Our results reveal that preformed microbial consortia adhere as "buds of growth," governing biofilm initiation without specific taxonomic order or cell-by-cell succession, which provide new insights into spatial and population heterogeneity development in complex ecosystems.

In vitro model systems for exploring oral biofilms: From single-species populations to complex multi-species communities

Numerous in vitro biofilm model systems are available to study oral biofilms. Over the past several decades, increased understanding of oral biology and advances in technology have facilitated more accurate simulation of intraoral conditions and have allowed for the increased generalizability of in vitro oral biofilm studies. The integration of contemporary systems with confocal microscopy and 16S rRNA community profiling has enhanced the capabilities of in vitro biofilm model systems to quantify biofilm architecture and analyse microbial community composition. In this review, we describe several model systems relevant to modern in vitro oral biofilm studies: the constant depth film fermenter, Sorbarod perfusion system, drip-flow reactor, modified Robbins device, flowcells and microfluidic systems. We highlight how combining these systems with confocal microscopy and community composition analysis tools aids exploration of oral biofilm development under different conditions and in response to antimicrobial/anti-biofilm agents. The review closes with a discussion of future directions for the field of in vitro oral biofilm imaging and analysis.

Veillonellae: Beyond Bridging Species in Oral Biofilm Ecology

The genus Veillonella comprises 16 characterized species, among which eight are commonly found in the human oral cavity. The high abundance of Veillonella species in the microbiome of both supra- and sub-gingival biofilms, and their interdependent relationship with a multitude of other bacterial species, suggest veillonellae to play an important role in oral biofilm ecology. Development of oral biofilms relies on an incremental coaggregation process between early, bridging and later bacterial colonizers, ultimately forming multispecies communities. As early colonizer and bridging species, veillonellae are critical in guiding the development of multispecies communities in the human oral microenvironment. Their ability to establish mutualistic relationships with other members of the oral microbiome has emerged as a crucial factor that may contribute to health equilibrium. Here, we review the general characteristics, taxonomy, physiology, genomic and genetics of veillonellae, as well as their bridging role in the development of oral biofilms. We further discuss the role of Veillonella spp. as potential “accessory pathogens” in the human oral cavity, capable of supporting colonization by other, more pathogenic species. The relationship between Veillonella spp. and dental caries, periodontitis, and peri-implantitis is also recapitulated in this review. We finally highlight areas of future research required to better understand the intergeneric signaling employed by veillonellae during their bridging activities and interspecies mutualism. With the recent discoveries of large species and strain-specific variation within the genus in biological and virulence characteristics, the study of Veillonella as an example of highly adaptive microorganisms that indirectly participates in dysbiosis holds great promise for broadening our understanding of polymicrobial disease pathogenesis.

An in vitro biofilm model system to facilitate study of microbial communities of the human oral cavity

The human oral cavity is host to a diverse microbiota. Much of what is known about the behaviour of oral microbes derives from studies of individual or several cultivated species, situations which do not totally reflect the function of organisms within more complex microbiota or multispecies biofilms. The number of validated models that allow examination of the role that biofilms play during oral cavity colonization is also limited. The CDC biofilm reactor is a standard method that has been deployed to study interactions between members of human microbiotas allowing studies to be completed during an extended period under conditions where nutrient availability, and washout of waste products are controlled. The objective of this work was to develop a robust in vitro biofilm-model system from a pooled saliva inoculum to study the development, reproducibility and stability of the oral microbiota. By employing deep sequencing of the variable regions of the 16S rRNA gene, we found that the CDC biofilm reactor could be used to efficiently cultivate microbiota containing all six major phyla previously identified as the core saliva microbiota. After an acclimatisation period, communities in each reactor stabilised. Replicate reactors were predominately populated by a shared core microbiota; variation between replicate reactors was primarily driven by shifts in abundance of shared operational taxonomic units. We conclude that the CDC biofilm reactor can be used to cultivate communities that replicate key features of the human oral cavity and is a useful tool to facilitate studies of the dynamics of these communities.

Water in bacterial biofilms: pores and channels, storage and transport functions

Bacterial biofilms occur in many natural and industrial environments. Besides bacteria, biofilms comprise over 70 wt% water. Water in biofilms occurs as bound- or free-water. Bound-water is adsorbed to bacterial surfaces or biofilm (matrix) structures and possesses different Infra-red and Nuclear-Magnetic-Resonance signatures than free-water. Bound-water is different from intra-cellularly confined-water or water confined within biofilm structures and bacteria are actively involved in building water-filled structures by bacterial swimmers, dispersion or lytic self-sacrifice. Water-filled structures can be transient due to blocking, resulting from bacterial growth, compression or additional matrix formation and are generally referred to as "channels and pores." Channels and pores can be distinguished based on mechanism of formation, function and dimension. Channels allow transport of nutrients, waste-products, signalling molecules and antibiotics through a biofilm provided the cargo does not adsorb to channel walls and channels have a large length/width ratio. Pores serve a storage function for nutrients and dilute waste-products or antimicrobials and thus should have a length/width ratio close to unity. The understanding provided here on the role of water in biofilms, can be employed to artificially engineer by-pass channels or additional pores in industrial and environmental biofilms to increase production yields or enhance antimicrobial penetration in infectious biofilms.

Polymeric nano- and microparticulate drug delivery systems for treatment of biofilms

Now-a-days healthcare systems face great challenges with antibiotic resistance and low efficacy of antibiotics when combating pathogenic bacteria and bacterial biofilms. Administration of an antibiotic in its free form is often ineffective due to lack of selectivity to the infectious site and breakdown of the antibiotic before it exerts its effect. Therefore, polymeric delivery systems, where the antibiotic is encapsulated into a formulation, have shown great promise, facilitating a high local drug concentration at the site of infection, a controlled drug release and less drug degradation. All this leads to improved therapeutic effects and fewer systemic side effects together with a lower risk of developing antibiotic resistance. Here, we review and provide a comprehensive overview of polymer-based nano- and microparticles as carriers for antimicrobial agents and their effect on eradicating bacterial biofilms. We have a main focus on polymeric particulates containing poly(lactic-co-glycolic acid), chitosan and polycaprolactone, but also strategies involving combinations of these polymers are included. Different production techniques are reviewed and important parameters for biofilm treatment are discussed such as drug loading capacity, control of drug release, influence of particle size and mobility in biofilms. Additionally, we reflect on other promising future strategies for combating biofilms such as lipid-polymer hybrid particles, enzymatic biofilm degradation, targeted/triggered antibiotic delivery and future alternatives to the conventional particles.

Relationship between sucrose concentration and bacteria proportion in a multispecies biofilm: : Sucrose challenges to a multispecies biofilm

Objective: The aim of this study was to evaluate the relationship between sucrose concentration and bacteria proportion in a multispecies biofilm model. Methods: Streptococcus mutans (S. mutans), Streptococcus oralis (S. oralis), and Actinomyces naeslundii (A. naeslundii) were chose to form a multispecies biofilm. Different concentration (0-40%) of sucrose was introduced to the multispecies biofilm 3 times per day (30 min per time). And then the bacteria proportion and acid production of the biofilms were analyzed. Results: Increasing sucrose level increased CFU count of S. mutans up to a certain concentration (5% sucrose), after which the number of S. mutans slightly decreased, but the CFU counts of S. oralis and A. naeslundii continually decreased with sucrose concentration increase, especially, from 5% sucrose, the reduction was significant, and S. mutans became the dominant species in the biofilms. Furthermore, the acid production ability of the multispecies biofilm gradually increased and slightly decreased with sucrose concentration increased, and the turning concentration was 5%. Conclusion: Our findings suggest that increasing sucrose level could increase the competitiveness of S. mutans in the multispecies biofilm, which may shift the biofilm to a more cariogenic one, and 5% sucrose formed a most cariogenic biofilm in this study.

Community-wide changes reflecting bacterial interspecific interactions in multispecies biofilms

Existence of most bacterial species, in natural, industrial, and clinical settings in the form of surface-adhered communities or biofilms has been well acknowledged for decades. Research predominantly focusses on single-species biofilms as these are relatively easy to study. However, microbiologists are now interested in studying multispecies biofilms and revealing interspecific interactions in these communities because of the existence of a plethora of different bacterial species together in almost all natural settings. Multispecies biofilms-led emergent properties are triggered by bacterial social interactions which have huge implication for research and practical knowledge useful for the control and manipulation of these microbial communities. Here, we discuss some important bacterial interactions that take place in multispecies biofilm communities and provide insights into community-wide changes that indicate bacterial interactions and elucidate underlying mechanisms.

We Are One: Multispecies Metabolism of a Biofilm Consortium and Their Treatment Strategies

The ecological and medical significance of bacterial biofilms have been well recognized. Biofilms are harder to control than their planktonic free-living counterparts and quite recently, the focus of the study has shifted to the multispecies consortia, which represent the vast majority of real-case infection scenarios. Studies have begun to explore the complex interspecies interactions within these biofilms. However, only little attention is currently given to the role of cellular metabolites in the cell-to-cell communication. The concentration gradients of metabolic substrates and products affect the spatial growth of bacteria in multispecies biofilm. This, if looked into more deeply, can lead to identification of potential therapies targeting the specific metabolites and hence the coordinated protection in the bacterial community. Herein, we review the interspecies communications, including their metabolic cross-talking, in multispecies biofilm, to signify the importance of such interactions on the initial formation and subsequent growth of these biofilms. Multispecies biofilms with their species heterogeneity are more resilient to antimicrobial agents than their single species biofilm counterparts and this characteristic is of particular interest when dealing with pathogenic bacteria. In this Review, we also discuss the treatment options available, to include current and emerging avenues to combat pathogenic multispecies biofilms in the clinical, environmental, as well as industrial settings.

Modification of in situ Biofilm Formation on Titanium by a Hydroxyapatite Nanoparticle-Based Solution

Oral biofilms play an essential role on peri-implant disease development. Synthetic hydroxyapatite nanoparticles (nHAP) are a bioinspired material that has structural and functional similarities to dental enamel apatite and may provide preventive properties against biofilm formation. This study aimed to investigate the effects of an experimental nHAP solution on biofilm formation on polished and non-polished titanium under oral conditions. Five volunteers carried maxillary splints with non-polished and polished titanium and followed a 48 h rinsing protocol with the proposed nHAP solution, and with chlorhexidine 0.2% (CHX) and water, as controls. Samples were analyzed by fluorescence microscopy (FM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). FM showed a significant reduction of biofilms on polished samples treated with nHAP (p = 0.0485) compared with water, without differences between nHAP and CHX (p > 0.9999). Analyzing biofilm viability, polished samples rinsed with nHAP showed significantly fewer dead bacteria than CHX (p = 0.0079), but there was no significant difference in viability between polished samples rinsed with water and nHAP (p = 0.9268). A significantly higher biofilm coverage was observed on the non-polished surfaces compared to the polished surfaces when nHAP was applied (p = 0.0317). This difference between polished and non-polished surfaces was not significant when water (p = 0.1587) or CHX (p = 0.3413) rinsing were applied. SEM and TEM analysis supported the FM findings, that polished samples rinsed with nHAP presented fewer biofilm coverage compared to samples rinsed with water. In conclusion, the nHAP solution reduced the biofilm formation on polished Ti surfaces without altering bacterial viability, providing a novel approach for the management of biofilm formation on biomaterials.

Evaluating the Effects of Disinfectants on Bacterial Biofilms Using a Microfluidics Flow Cell and Time-Lapse Fluorescence Microscopy

A commercially available microfluidics flow cell was utilized together with widefield fluorescence microscopy to evaluate the effects of disinfectants on bacterial strains. The flow cell’s inner surface supports the formation of biofilms of numerous bacterial species. The modular setup of the flow cell accessories allows connection to syringes, pumps and collection vials, facilitating aseptic experiments in a controlled fluidics environment which can be documented with precisely timed microscopy imaging. The flow cell is inoculated with a suspension of bacteria in a nutrient medium and incubated for several days allowing bacterial cells to form a biofilm. Shortly before performing an assay, the biofilm is labelled with a dual-fluorescent DNA probe which distinguishes unharmed and damaged bacteria. Then a disinfectant sample (or control) is gently injected and time-lapse imaging is used for quantifying the course of bacterial biomass response. We use a simplified widefield microscopy method that allows intensive recording and quantification of time series of two-dimensional frames for tracking the course of disinfectant action on a variety of microbial strains. This procedure has potential for the rapid evaluation of novel products.

Oral Microbiota Display Profound Differential Metabolic Kinetics and Community Shifts upon Incubation with Sucrose, Trehalose, Kojibiose, and Xylitol

This study compares the metabolic properties of kojibiose, trehalose, sucrose, and xylitol upon incubation with representative oral bacteria as monocultures or synthetic communities or with human salivary bacteria in a defined medium. Compared to sucrose and trehalose, kojibiose resisted metabolism during a 48-h incubation with monocultures, except for Actinomyces viscosus Incubations with Lactobacillus-based communities, as well as salivary bacteria, displayed kojibiose metabolism, yet to a lesser extent than sucrose and trehalose. Concurring with our in vitro findings, screening for carbohydrate-active enzymes revealed that only Lactobacillus spp. and A. viscosus possess enzymes from glycohydrolase (GH) families GH65 and GH15, respectively, which are associated with kojibiose metabolism. Donor-dependent differences in salivary microbiome composition were noted, and differences in pH drop during incubation indicated different rates of sugar metabolism. However, functional analysis indicated that lactate, acetate, and formate evenly dominated the metabolic profile for all sugars except for xylitol. 16S rRNA gene sequencing analysis and α-diversity markers revealed that a significant shift of the microbiome community by sugars was more pronounced in sucrose and trehalose than in kojibiose and xylitol. In Streptococcus spp., a taxon linked to cariogenesis dominated in sucrose (mean ± standard deviation, 91.8 ± 6.4%) and trehalose (55.9 ± 38.6%), representing a high diversity loss. In contrast, Streptococcus (5.1 ± 3.7%) was less abundant in kojibiose, which instead was dominated by Veillonella (26.8 ± 19.6%), while for xylitol, Neisseria (29.4 ± 19.1%) was most abundant. Overall, kojibiose and xylitol incubations stimulated cariogenic species less yet closely maintained an abundance of key phyla and genera of the salivary microbiome, suggesting that kojibiose has low cariogenic properties.IMPORTANCE This study provides a detailed scientific insight on the metabolism of a rare disaccharide, kojibiose, whose mass production has recently been made possible. While the resistance of kojibiose was established with monocultures, delayed utilization of kojibiose was observed with communities containing lactobacilli and A. viscosus as well as with complex communities of bacteria from human saliva. Kojibiose is, therefore, less metabolizable than sucrose and trehalose. Moreover, although conventional sugars cause distinct shifts in salivary microbial communities, our study has revealed that kojibiose is able to closely maintain the salivary microbiome composition, suggesting its low cariogenic properties. This study furthermore underscores the importance and relevance of microbial culture and ex vivo mixed cultures to study cariogenicity and substrate utilization; this is in sharp contrast with tests that solely rely on monocultures such as Streptococcus mutans, which clearly fail to capture complex interactions between oral microbiota.

Antibacterial Effect of Cupral® on Oral Biofilms - An In-Vitro Study

Objective:

This study aimed to assess the efficacy of Cupral^®, a Ca(OH)₂ and Cu²⁺ based materials used in endodontics, against biofilms of the oral species Streptococcus oralis, Streptococcus gordonii and Aggregatibacter actinomycetemcomitans at different maturation stages.

Methods:

Biofilms of the bacterial target species were grown in brain heart infusion (BHI) medium for 1 and 5 days on titanium disks (titanium, grade 4) to collect microbial communities at different stages of biofilm maturation. Biofilms were subjected to different Cupral^® concentrations (4-, 15- and 50-fold dilution) to assess the antimicrobial- and biofilm dissolving effect. 0.2% chlorhexidine gluconate (CHX) solution was used as a positive control. Biovolume and antibacterial efficacy were analyzed by live/dead staining in combination with confocal laser scanning microscopy (CLSM) to quantify biofilm detachment and antibacterial efficacy.

Results:

All tested Cupral^® concentration showed a strong antibacterial effect on tested bacterial species at all biofilm maturation stages. Efficacy of biofilms detachment was concentration dependent, i.e. higher Cupral^® concentrations generally led to increased biofilm detachment. The antibacterial efficacy of tested Cupral^® concentration was at least equal to CHX treatment (P=0.03).

Conclusion:

Cupral^® shows a strong anti-biofilm efficacy and may be applied for oral biofilm treatment and control in dental disciplines other than endodontics.

Fusobacterium Species and Subspecies Differentially Affect the Composition and Architecture of Supra- and Subgingival Biofilms Models

Fusobacteria are common obligately anaerobic Gram-negative bacteria of the oral cavity that may act as a bridge between early and late colonizing bacteria in dental plaque and have a role in oral and extra-oral infections. Fusobacterium nucleatum has a crucial role in oral biofilm structure and ecology, as revealed in experimental and clinical biofilm models. The aim of this study was to investigate the impact of various Fusobacterium species on in vitro biofilm formation and structure in three different oral biofilm models namely a supragingival, a supragingival “feeding”, and a subgingival biofilm model. The standard six-species supragingival and “feeding” biofilm models employed contained Actinomyces oris, Candida albicans, Streptococcus mutans, Streptococcus oralis, Veillonella dispar, and Fusobacterium sp. The subgingival biofilm model contained 10 species (A. oris, Campylobacter rectus, F. nucleatum ssp. nucleatum, Porphyromonas gingivalis, Prevotella intermedia, Streptococcus anginosus, S. oralis, Tannerella forsythia, Treponema denticola, and V. dispar). Six different Fusobacterium species or subspecies, respectively, were tested namely F. nucleatum ssp. fusiforme, F. nucleatum ssp. nucleatum, F. nucleatum ssp. polymorphum, F. nucleatum ssp. vincentii, F. naviforme, and F. periodonticum). Biofilms were grown anaerobically on hydroxyapatite disks in 24-well culture dishes. After 64 h, biofilms were either harvested and quantified by culture analysis or proceeded to fluorescent in situ hybridization (FISH) and confocal laser scanning microscopy (CLSM). All Fusobacterium species tested established well in the biofilms, with CFUs ranging from 1.4E+04 (F. nucleatum ssp. fusiforme) to 5.6E+06 (F. nucleatum ssp. nucleatum). The presence of specific Fusobacterium sp./ssp. induced a significant decrease in C. albicans levels in the supragingival model and in V. dispar levels in the “feeding” supragingival model. In the subgingival model, the counts of A. oris, S. oralis, P. intermedia, P. gingivalis, and C. rectus significantly decreased in the presence of specific Fusobacterium sp./ssp. Collectively, this study showed variations in the growing capacities of different fusobacteria within biofilms, affecting the growth of surrounding species and potentially the biofilm architecture. Hence, clinical or experimental studies need to differentiate between Fusobacterium sp./ssp., as their biological properties may well vary.

A Multispecies Biofilm In Vitro Screening Model of Dental Caries for High-Throughput Susceptibility Testing

There is a current need to develop and optimize new therapeutics for the treatment of dental caries, but these efforts are limited by the relatively low throughput of relevant in vitro models. The aim of this work was to bridge the 96-well microtiter plate system with a relevant multispecies dental caries model that could be reproducibly grown to allow for the high-throughput screening of anti-biofilm therapies. Various media and inoculum concentrations were assessed using metabolic activity, biomass, viability, and acidity assays to determine the optimal laboratory-controlled conditions for a multispecies biofilm composed of Streptococcus gordonii, Streptococcus mutans, and Candida albicans. The selected model encompasses several of the known fundamental characteristics of dental caries-associated biofilms. The 1:1 RPMI:TSBYE 0.6% media supported the viability and biomass production of mono- and multispecies biofilms best. Kinetic studies over 48 h in 1:1 RPMI:TSBYE 0.6% demonstrated a stable biofilm phase between 10 and 48 h for all mono- and multispecies biofilms. The 1:1:0.1 S. gordonii: S. mutans: C. albicans multispecies biofilm in 1:1 RPMI:TSBYE 0.6% is an excellent choice for a high-throughput multispecies model of dental caries. This high-throughput multispecies model can be used for screening novel therapies and for better understanding the treatment effects on biofilm interactions and stability.

Development of an in vitro system to study oral biofilms in real time through impedance technology: validation and potential applications

Background and objectives: We have developed a standardized, easy-to-use in vitro model to study single- and multiple-species oral biofilms in real time through impedance technology, which elucidates the kinetics of biofilm formation in 96-well plates, without the requirement for any further manipulation.

Design and Results: Using this system, biofilms of Streptococcus mutans appear to be sugar-dependent and highly resistant to amoxicilin, an antibiotic to which this oral pathogen is highly sensitive in a planktonic state. Saliva, tongue and dental plaque samples were also used as inocula to form multiple-species biofilms. DNA isolation and Illumina sequencing of the biofilms showed that the multi-species biofilms were formed by tens or hundreds of species, had a similar composition to the original inoculum, and included fastidious microorganisms which are important for oral health and disease. As an example of the potential applications of the model, we show that oral biofilms can be inhibited by amoxicilin, but in some cases they are induced by the antibiotic, suggesting the existence of responders and non-responders to a given antibiotic.

Conclusions: We therefore propose the system as a valid in vitro model to study oral biofilm dynamics, including their susceptibility to antibiotics, antiseptics or anti-adhesive compounds.

Amino Sugars Modify Antagonistic Interactions between Commensal Oral Streptococci and Streptococcus mutans

N-Acetylglucosamine (GlcNAc) and glucosamine (GlcN) enhance the competitiveness of the laboratory strain DL1 of Streptococcus gordonii against the caries pathogen Streptococcus mutans Here, we examine how amino sugars affect the interaction of five low-passage-number clinical isolates of abundant commensal streptococci with S. mutans by utilizing a dual-species biofilm model. Compared to that for glucose, growth on GlcN or GlcNAc significantly reduced the viability of S. mutans in cocultures with most commensals, shifting the proportions of species. Consistent with these results, production of H₂O₂ was increased in most commensals when growing on amino sugars, and inhibition of S. mutans by Streptococcus cristatus, Streptococcus oralis, or S. gordonii was enhanced by amino sugars on agar plates. All commensals except S. oralis had higher arginine deiminase activities when grown on GlcN and, in some cases, GlcNAc. In ex vivo biofilms formed using pooled cell-containing saliva (CCS), the proportions of S. mutans were drastically diminished when GlcNAc was the primary carbohydrate. Increased production of H₂O₂ could account in large part for the inhibitory effects of CCS biofilms. Surprisingly, amino sugars appeared to improve mutacin production by S. mutans on agar plates, suggesting that the commensals have mechanisms to actively subvert antagonism by S. mutans in cocultures. Collectively, these findings demonstrate that amino sugars can enhance the beneficial properties of low-passage-number commensal oral streptococci and highlight their potential for moderating the cariogenicity of oral biofilms.IMPORTANCE Dental caries is driven by dysbiosis of oral biofilms in which dominance by acid-producing and acid-tolerant bacteria results in loss of tooth mineral. Our previous work demonstrated the beneficial effects of amino sugars GlcNAc and GlcN in promoting the antagonistic properties of a health-associated oral bacterium, Streptococcus gordonii, in competition with the major caries pathogen Streptococcus mutans Here, we investigated 5 low-passage-number clinical isolates of the most common streptococcal species to establish how amino sugars may influence the ecology and virulence of oral biofilms. Using multiple in vitro models, including a human saliva-derived microcosm biofilm, experiments showed significant enhancement by at least one amino sugar in the ability of most of these bacteria to suppress the caries pathogen. Therefore, our findings demonstrated the mechanism of action by which amino sugars may affect human oral biofilms to promote health.

Role of Dilution Rate and Nutrient Availability in the Formation of Microbial Biofilms

We revisited the mathematical model of the chemostat and examined consequences of considerably decreasing the concentration of limiting nutrient in the inflow for the growth of both the planktonic and biofilm cells in the chemostat tank (fermenter). The model predicts a substantially lower steady-state biomass of planktonic cells in response to decreasing inflowing nutrient concentration. Contrarily, the steady-state concentration of nutrient inside the fermenter is expected to remain the same, as long as the inflowing concentration does not fall below its value. This allows the biofilm cells to grow at a rate regulated only by the exchange rate of the medium (dilution rate). We maintained a strain of Enterococcus faecalis in a chemostat of our own design with limiting nutrient in the inflow set near saturation constant at three dilution rates (0.09, 0.28, and 0.81 h-1). The highest dilution rate was near the critical rate calculated by the model. The one-day total biofilm buildup was 21× larger and its estimated growth rate 2.4× higher at highest dilution rate than at the lowest one. This increased biofilm formation with increased dilution rates is in agreement with previously published data on pure and mixed continuous flow cultures.

An experimental murine model to study periodontitis

Periodontal disease (PD) is a common dental disease associated with the interaction between dysbiotic oral microbiota and host immunity. It is a prevalent disease, resulting in loss of gingival tissue, periodontal ligament, cementum and alveolar bone. PD is a major form of tooth loss in the adult population. Experimental animal models have enabled the study of PD pathogenesis and are used to test new therapeutic approaches for treating the disease. The ligature-induced periodontitis model has several advantages as compared with other models, including rapid disease induction, predictable bone loss and the capacity to study periodontal tissue and alveolar bone regeneration because the model is established within the periodontal apparatus. Although mice are the most convenient and versatile animal models used in research, ligature-induced periodontitis has been more frequently used in large animals. This is mostly due to the technical challenges involved in consistently placing ligatures around murine teeth. To reduce the technical challenge associated with the traditional ligature model, we previously developed a simplified method to easily install a bacterially retentive ligature between two molars for inducing periodontitis. In this protocol, we provide detailed instructions for placement of the ligature and demonstrate how the model can be used to evaluate gingival tissue inflammation and alveolar bone loss over a period of 18 d after ligature placement. This model can also be used on germ-free mice to investigate the role of human oral bacteria in periodontitis in vivo. In conclusion, this protocol enables the mechanistic study of the pathogenesis of periodontitis in vivo.

Saliva-coated titanium biosensor detects specific bacterial adhesion and bactericide caused mass loading upon cell death

Bacteria adhering to implanted medical devices can cause invasive microbial infections, of e.g. skin, lung or blood. In dentistry, Streptococcus gordonii is an early oral colonizer initiating dental biofilm formation and also being involved in life-threatening infective endocarditis. To treat oral biofilms, antibacterial mouth rinses are commonly used. Such initial biomaterial-bacteria interactions and the influence of antibacterial treatments are poorly understood and investigated here in situ by quartz crystal microbalance with dissipation monitoring (QCM-D). A saliva-coated titanium (Ti) biosensor is applied to analyze possible specific signal patterns indicating microbial binding mechanisms and bactericide-caused changes in bacterial film rigidity or cell leakage caused by a clinically relevant antibacterial agent (ABA), i.e., a mouth rinse comprising chlorhexidine (CHX) and cetylpyridinium chloride (CPC). Apparent missing mass effects during the formation of microscopically proven dense and vital bacterial films indicate punctual, specific binding of S. gordonii to the saliva-coated biosensor, compared to unspecific adhesion to pure Ti. Coincidentally to ABA-induced killing of surface-adhered bacteria, an increase of adsorbed dissipative mass can be sensed, contrary to the prior mass-loss. This suggests the acoustic sensing of the leakage of cellular content caused by bacterial cell wall rupturing and membrane damage upon the bactericidal attack. The results have significant implications for testing bacterial adhesion mechanisms and cellular integrity during interaction with antibacterial agents.

Potential role for Streptococcus gordonii-derived hydrogen peroxide in heme acquisition by Porphyromonas gingivalis

Streptococcus gordonii, an accessory pathogen and early colonizer of plaque, co-aggregates with many oral species including Porphyromonas gingivalis. It causes α-hemolysis on blood agar, a process mediated by H₂ O₂ and thought to involve concomitant oxidation of hemoglobin (Hb). Porphyromonas gingivalis has a growth requirement for heme, which is acquired mainly from Hb. The paradigm for Hb heme acquisition involves the initial oxidation of oxyhemoglobin (oxyHb) to methemoglobin (metHb), followed by heme release and extraction through the actions of K-gingipain protease and/or the HmuY hemophore-like protein. The ability of S. gordonii to mediate Hb oxidation may potentially aid heme capture during co-aggregation with P. gingivalis. Hemoglobin derived from zones of S. gordonii α-hemolysis was found to be metHb. Generation of metHb from oxyHb by S. gordonii cells was inhibited by catalase, and correlated with levels of cellular H₂ O₂ production. Generation of metHb by S. gordonii occurred through the higher Hb oxidation state of ferrylhemoglobin. Heme complexation by the P. gingivalis HmuY was employed as a measure of the ease of heme capture from metHb. HmuY was able to extract iron(III)protoporphyrin IX from metHb derived from zones of S. gordonii α-hemolysis and from metHb generated by the action of S. gordonii cells on isolated oxyHb. The rate of HmuY-Fe(III)heme complex formation from S. gordonii-mediated metHb was greater than from an equivalent concentration of auto-oxidized metHb. It is concluded that S. gordonii may potentially aid heme acquisition by P. gingivalis by facilitating metHb formation in the presence of oxyHb.