Synergistic biofilm formation byTreponema denticolaandPorphyromonas gingivalis

A new class of protein sensor links spirochete pleomorphism, persistence, and chemotaxis

IMPORTANCE

A new class of bacterial protein sensors monitors intracellular levels of S-adenosylmethionine to modulate cell morphology, chemotaxis, and biofilm formation. Simultaneous regulation of these behaviors enables bacterial pathogens to survive within their niche. This sensor, exemplified by Treponema denticola CheWS, is anchored to the chemotaxis array and its sensor domain is located below the chemotaxis rings. This position may allow the sensor to directly interact with the chemotaxis histidine kinase CheA. Collectively, these data establish a critical role of CheWS in pathogenesis and further illustrate the impact of studying non-canonical chemotaxis proteins.

Phylogenomic analysis of the Porphyromonas gingivalis - Porphyromonas gulae duo: approaches to the origin of periodontitis

Porphyromonas gingivalis is an oral human pathogen associated with the onset and progression of periodontitis, a chronic immune-inflammatory disease characterized by the destruction of the teeth-supporting tissue. P. gingivalis belongs to the genus Porphyromonas, which is characterized by being composed of Gram-negative, asaccharolytic, non-spore-forming, non-motile, obligatory anaerobic species, inhabiting niches such as the oral cavity, urogenital tract, gastrointestinal tract and infected wound from different mammals including humans. Among the Porphyromonas genus, P. gingivalis stands out for its specificity in colonizing the human oral cavity and its keystone pathogen role in periodontitis pathogenesis. To understand the evolutionary process behind P. gingivalis in the context of the Pophyoromonas genus, in this study, we performed a comparative genomics study with publicly available Porphyromonas genomes, focused on four main objectives: (A) to confirm the phylogenetic position of P. gingivalis in the Porphyromonas genus by phylogenomic analysis; (B) the definition and comparison of the pangenomes of P. gingivalis and its relative P. gulae; and (C) the evaluation of the gene family gain/loss events during the divergence of P. gingivalis and P. gulae; (D) the evaluation of the evolutionary pressure (represented by the calculation of Tajima-D values and dN/dS ratios) comparing gene families of P. gingivalis and P. gulae. Our analysis found 84 high-quality assemblies representing P. gingivalis and 14 P. gulae strains (from a total of 233 Porphyromonas genomes). Phylogenomic analysis confirmed that P. gingivalis and P. gulae are highly related lineages, close to P. loveana. Both organisms harbored open pangenomes, with a strong core-to-accessory ratio for housekeeping genes and a negative ratio for unknown function genes. Our analyses also characterized the gene set differentiating P. gulae from P. gingivalis, mainly associated with unknown functions. Relevant virulence factors, such as the FimA, Mfa1, and the hemagglutinins, are conserved in P. gulae, P. gingivalis, and P. loveana, suggesting that the origin of those factors occurred previous to the P. gulae - P. gingivalis divergence. These results suggest an unexpected evolutionary relationship between the P. gulae - P. gingivalis duo and P. loveana, showing more clues about the origin of the role of those organisms in periodontitis.

Oral-Gut Microbiota, Periodontal Diseases, and Arthritis: Literature Overview on the Role of Probiotics

Periodontal diseases are oral inflammatory diseases affecting the tissues supporting and surrounding the teeth and include gingivitis and periodontitis. Oral pathogens may lead to microbial products spreading into the systemic circulation and reaching distant organs, while periodontal diseases have been related to low-grade systemic inflammation. Gut and oral microbiota alterations might play a role in the pathogenesis of several autoimmune and inflammatory diseases including arthritis, considering the role of the gut-joint axis in the regulation of molecular pathways involved in the pathogenesis of these conditions. In this scenario, it is hypothesized that probiotics might contribute to the oral and intestinal micro-ecological balance and could reduce low-grade inflammation typical of periodontal diseases and arthritis. This literature overview aims to summarize state-of-the-art ideas about linkages among oral-gut microbiota, periodontal diseases, and arthritis, while investigating the role of probiotics as a potential therapeutic intervention for the management of both oral diseases and musculoskeletal disorders.

Targeted Anti-Biofilm Therapy: Dissecting Targets in the Biofilm Life Cycle

Biofilm is a crucial virulence factor for microorganisms that causes chronic infection. After biofilm formation, the bacteria present improve drug tolerance and multifactorial defense mechanisms, which impose significant challenges for the use of antimicrobials. This indicates the urgent need for new targeted technologies and emerging therapeutic strategies. In this review, we focus on the current biofilm-targeting strategies and those under development, including targeting persistent cells, quorum quenching, and phage therapy. We emphasize biofilm-targeting technologies that are supported by blocking the biofilm life cycle, providing a theoretical basis for design of targeting technology that disrupts the biofilm and promotes practical application of antibacterial materials.

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.

The Mechanistic Pathways of Periodontal Pathogens Entering the Brain: The Potential Role of Treponema denticola in Tracing Alzheimer’s Disease Pathology

Alzheimer’s Disease (AD) is a complex neurodegenerative disease and remains the most common form of dementia. The pathological features include amyloid (Aβ) accumulation, neurofibrillary tangles (NFTs), neural and synaptic loss, microglial cell activation, and an increased blood–brain barrier permeability. One longstanding hypothesis suggests that a microbial etiology is key to AD initiation. Among the various periodontal microorganisms, Porphyromonas gingivalis has been considered the keystone agent to potentially correlate with AD, due to its influence on systemic inflammation. P. gingivalis together with Treponema denticola and Tannerella forsythia belong to the red complex consortium of bacteria advocated to sustain periodontitis within a local dysbiosis and a host response alteration. Since the implication of P. gingivalis in the pathogenesis of AD, evidence has emerged of T. denticola clusters in some AD brain tissue sections. This narrative review explored the potential mode of spirochetes entry into the AD brain for tracing pathology. Spirochetes are slow-growing bacteria, which can hide within ganglia for many years. It is this feature in combination with the ability of these bacteria to evade the hosts’ immune responses that may account for a long lag phase between infection and plausible AD disease symptoms. As the locus coeruleus has direct connection between the trigeminal nuclei to periodontal free nerve endings and proprioceptors with the central nervous system, it is plausible that they could initiate AD pathology from this anatomical region.

Fracture Related Infections and Their Risk Factors for Treatment Failure—A Major Trauma Centre Perspective

Fracture related infections (FRI) are debilitating and costly complications of musculoskeletal trauma surgery that can result in permanent functional loss or amputation. Surgical treatment can be unsuccessful, and it is necessary to determine the predictive variables associated with FRI treatment failure, allowing one to optimise them prior to treatment and identify patients at higher risk. The clinical database at a major trauma centre was retrospectively reviewed between January 2015 and January 2021. FRI treatment failure was defined by infection recurrence or amputation. A univariable logistic regression analysis was performed, followed by a multivariable regression analysis for significant outcomes between groups on univariable analysis, to determine risk factors for treatment failure. In total, 102 patients were identified with a FRI (35 open, 67 closed fractures). FRI treatment failure occurred in 24 patients (23.5%). Risk factors determined by our multivariate logistic regression model were obesity (OR 2.522; 95% CI, 0.259–4.816; p = 0.006), Gustilo Anderson type 3c (OR 4.683; 95% CI, 2.037–9.784; p = 0.004), and implant retention (OR 2.818; 95% CI, 1.588–7.928; p = 0.041). Given that FRI treatment in 24 patients (23.5%) ended up in failure, future management need to take into account the predictive variables analysed in this study, redirect efforts to improve management and incorporate adjuvant technologies for patients at higher risk of failure, and implement a multidisciplinary team approach to optimise risk factors such as diabetes and obesity.

Potential Treponema denticola-based periodontal vaccine to resolve a global public health challenge: a narrative literature review

INTRODUCTION

Periodontitis is a diseased condition of the gum which imposes considerable costs on healthcare systems. It progresses further beyond the inflammation of supportive tissues of the teeth, and the collateral damages are closely associated with Alzheimer's disease, cardiovascular disease, and diabetes mellitus.

AREAS COVERED

A comprehensive literature review was performed to summarize published studies in English during the period of 1990-2021 to discuss the rationales for developing periodontal vaccine, cost-effectiveness analyses on the prevention of periodontitis, Treponema denticola-based vaccine candidates, as well as immunological mechanisms in animal models.

EXPERT OPINION

Preventive strategies against periodontitis may halt the onset of gum inflammation itself and the consequent chronic diseases. Considering the multi-microbial condition of periodontitis, an ideal periodontal vaccine should target multiple pathological pathways. Preventive approaches compared to surgical treatments evidently have significant impact on the healthcare budget and long-term health of the individuals in different communities. Despite many advances in periodontal vaccine research, there are still significant hurdles to overcome in developing a vaccine. Investment in research and development activities on key periodontal pathogens including Treponema denticola and Porphyromonas gingivalis in the foreseeable future is a worthy and cost-effective approach for the policymakers to prevent deleterious impacts of periodontitis.

An Association of Pathogens and Biofilms with Alzheimer's Disease

As one of the leading causes of dementia, Alzheimer's disease (AD) is a condition in which individuals experience progressive cognitive decline. Although it is known that beta-amyloid (Aβ) deposits and neurofibrillary tangles (NFT) of tau fibrils are hallmark characteristics of AD, the exact causes of these pathologies are still mostly unknown. Evidence that infectious diseases may cause AD pathology has been accumulating for decades. The association between microbial pathogens and AD is widely studied, and there are noticeable correlations between some bacterial species and AD pathologies, especially spirochetes and some of the oral microbes. Borrelia burgdorferi has been seen to correlate with Aβ plaques and NFTs in infected cells. Because of the evidence of spirochetes in AD patients, Treponema pallidum and other oral treponemes are speculated to be a potential cause of AD. T. pallidum has been seen to form aggregates in the brain when the disease disseminates to the brain that closely resemble the Aβ plaques of AD patients. This review examines the evidence as to whether pathogens could be the cause of AD and its pathology. It offers novel speculations that treponemes may be able to induce or correlate with Alzheimer's disease.

Antibiotic susceptibility pattern of fish pathogens: A new approach of emerging the bacterial resistance through biofilm formation in in-vitro condition

•

Different fishes were collected and were subjected to form an in vitro biofilm.

•

Huge array (up to 10⁷ cfu/ml or g) of pathogenic bacteria.

•

Few of the isolates were sensitive and few were resistant against the antibiotics but after bio-film formation all the species acquired resistance.

Background

The ability of many bacteria to adhere on the host surfaces and forming biofilms has major implications in a wide variety of industries including the food industry, where biofilms may create a persistent source of contamination. In the same environmental condition, the multiple bacterial species can closely interact with each other and may easily enhance their drug resistance capability, which finally increases the multi-drug resistant (MDR) attribute of the species.

Objective

The present study examined whether the mixed-species biofilm possesses any impact on the enhancement of the antibiotic resistance of the planktonic or single-cell bacterial isolates present in the fish samples.

Methods

In this regard, Cyprinus rubrofuscus (Koi), Heteropneustes fossilis (Shing) and Mystus vittatus (Tengra) fishes were collected and subjected to form an in vitro biofilm by shaking condition into the wise bath. The drug-resistant pattern was determined by the Kirby Bauer technique.

Results

All the samples exhibited a huge array (up to 10⁷ cfu/ml or g) of bacteria such as E. coli, Klebsiella spp., Vibrio spp., Salmonella spp., Proteus spp. and Staphylococcus spp. The isolates from both the bulk samples and their corresponding biofilms were subjected to antibiogram assay using antibiotics such as Ampicillin (10 µg), Erythromycin (15 μg), Streptomycin (STP 10 μg), Oxacillin (10 µg), Nalidixic acid (30 µg). Before biofilm formation, few of the isolates were found to be sensitive and few were resistant against the antibiotics. But when the species were isolated from the biofilm the sensitive one acquired drug resistance and resistant strain unveiled more resistance towards the same antibiotics. The present study revealed extensive bacterial contamination in fish samples among those some were resistant against the supplied drugs.

Conclusion

After the formation of multi-species biofilm, the isolates became more resistant against the same drugs that is alarming for consumers and major obstacles to maintain sustainable health.

Periodontal Disease: The Good, The Bad, and The Unknown

Periodontal disease is classically characterized by progressive destruction of the soft and hard tissues of the periodontal complex, mediated by an interplay between dysbiotic microbial communities and aberrant immune responses within gingival and periodontal tissues. Putative periodontal pathogens are enriched as the resident oral microbiota becomes dysbiotic and inflammatory responses evoke tissue destruction, thus inducing an unremitting positive feedback loop of proteolysis, inflammation, and enrichment for periodontal pathogens. Keystone microbial pathogens and sustained gingival inflammation are critical to periodontal disease progression. However, recent studies have revealed the importance of previously unidentified microbes involved in disease progression, including various viruses, phages and bacterial species. Moreover, newly identified immunological and genetic mechanisms, as well as environmental host factors, including diet and lifestyle, have been discerned in recent years as further contributory factors in periodontitis. These factors have collectively expanded the established narrative of periodontal disease progression. In line with this, new ideologies related to maintaining periodontal health and treating existing disease have been explored, such as the application of oral probiotics, to limit and attenuate disease progression. The role of systemic host pathologies, such as autoimmune disorders and diabetes, in periodontal disease pathogenesis has been well noted. Recent studies have additionally identified the reciprocated importance of periodontal disease in potentiating systemic disease states at distal sites, such as in Alzheimer's disease, inflammatory bowel diseases, and oral cancer, further highlighting the importance of the oral cavity in systemic health. Here we review long-standing knowledge of periodontal disease progression while integrating novel research concepts that have broadened our understanding of periodontal health and disease. Further, we delve into innovative hypotheses that may evolve to address significant gaps in the foundational knowledge of periodontal disease.

Porphyromonas gingivalis FimA and Mfa1 fimbriae: Current insights on localization, function, biogenesis, and genotype

In general, the periodontal pathogen Porphyromonas gingivalis expresses distinct FimA and Mfa1 fimbriae. Each of these consists of five FimA–E and five Mfa1–5 proteins encoded by the fim and mfa gene clusters, respectively. The main shaft portion comprises FimA and Mfa1, whereas FimB and Mfa2 are localized on the basal portion and function as anchors and elongation terminators. FimC–E and Mfa3–5 participate in the assembly of an accessory protein complex on the tips of each fimbria. Hence, they serve as ligands for the receptors on host cells and other oral bacterial species. The crystal structures of FimA and Mfa1 fimbrial proteins were recently elucidated and new insights into the localization, function, and biogenesis of these proteins have been reported. Several studies indicated a correlation between P. gingivalis pathogenicity and the fimA genotype but not the mfa1 genotype. We recently revealed polymorphisms of all genes in the fim and mfa gene clusters. Intriguingly, mfa5 occurred in numerous different forms and underwent duplication. Detailed structural and functional knowledge of the fimbrial proteins in the context of the entire filament could facilitate the development of innovative therapeutic strategies for structure-based drug design.

Contributions of Escherichia coli and Its Motility to the Formation of Dual-Species Biofilms with Vibrio cholerae

Biofilm formation is important in both the environmental and intestinal phases of the Vibrio cholerae life cycle. Nevertheless, most studies of V. cholerae biofilm formation focus on monospecies cultures, whereas nearly all biofilm communities found in nature consist of a variety of microorganisms. Multispecies biofilms formed between V. cholerae and other bacteria in the environment and the interactions that exist between these species are still poorly understood. In this study, the influence of Escherichia coli on the biofilm formation of V. cholerae was studied in the context of both in vitro coculture and in vivo coinfection. To understand the underlying synergistic mechanisms between these two species and to investigate the role of E. coli in V. cholerae biofilm formation, different pathotypes of E. coli and corresponding deletion mutants lacking genes that influence flagellar motility, curli fibers, or type I pili were cocultured with V. cholerae. Our findings demonstrate that the presence of commensal E. coli increases biofilm formation at the air-liquid interface in vitro and the generation of biofilm-like multicellular clumps in mouse feces. Examination of laboratory E. coli flagellar-motility ΔfliC and ΔmotA mutants in dual-species biofilm formation suggests that flagellar motility plays an important role in the synergistic interaction and coaggregation formation between V. cholerae and E. coli. This study facilitates a better understanding of how V. cholerae resides in harsh environments and colonizes the intestine. IMPORTANCE Biofilms play an important role in the V. cholerae life cycle. Until now, only monospecies biofilm formation of V. cholerae has been well studied. However, in nature, bacteria live in complex microbial communities, where biofilm is mostly composed of multiple microbial species that interact to cooperate with or compete against each other. Uncovering how V. cholerae forms multispecies biofilms is critical for furthering our understanding of how V. cholerae survives in the environment and transitions to infecting the human host. In this work, the dual-species biofilm containing V. cholerae and Escherichia coli was investigated. We demonstrate that the presence of commensal E. coli increased overall biofilm formation. Furthermore, we demonstrate that the motility of E. coli flagella is important for V. cholerae and E. coli to form coaggregation clumps in a dual-species biofilm. These results shed light on a new mechanism for understanding the survival and pathogenesis of V. cholerae.

Treponema denticola-Induced RASA4 Upregulation Mediates Cytoskeletal Dysfunction and MMP-2 Activity in Periodontal Fibroblasts

The periodontal complex consists of the periodontal ligament (PDL), alveolar bone, and cementum, which work together to turn mechanical load into biological responses that are responsible for maintaining a homeostatic environment. However oral microbes, under conditions of dysbiosis, may challenge the actin dynamic properties of the PDL in the context of periodontal disease. To study this process, we examined host-microbial interactions in the context of the periodontium via molecular and functional cell assays and showed that human PDL cell interactions with Treponema denticola induce actin depolymerization through a novel actin reorganization signaling mechanism. This actin reorganization mechanism and loss of cell adhesion is a pathological response characterized by an initial upregulation of RASA4 mRNA expression resulting in an increase in matrix metalloproteinase-2 activity. This mechanism is specific to the T. denticola effector protein, dentilisin, thereby uncovering a novel effect for Treponema denticola-mediated RASA4 transcriptional activation and actin depolymerization in primary human PDL cells.

Influence of interspecies interactions on the spatial organization of dual species bacterial communities

Interspecies interactions in bacterial biofilms have important impacts on the composition and function of communities in natural and engineered systems. To investigate these interactions, synthetic communities provide experimentally tractable systems. Biofilms grown on agar-surfaces have been used for investigating the eco-evolutionary and biophysical forces that determine community composition and spatial distribution of bacteria. Prior studies have used genetically identical bacterial strains and strains with specific mutations, that express different fluorescent proteins, to investigate intraspecies interactions. Here, we investigated interspecies interactions and, specifically, determined the community composition and spatial distribution in synthetic communities of Pseudomonas aeruginosa, Pseudomonas protegens and Klebsiella pneumoniae. Using quantitative microscopic imaging, we found that interspecies interactions in multispecies colonies were influenced by type IV pilus mediated motility, extracellular matrix secretion, environmental parameters, and these effects were also influenced by the specific partner in the dual species combinations. These results indicate that the patterns observable in mixed species colonies can be used to understand the mechanisms that drive interspecies interactions, which are dependent on the interplay between specific species’ physiology and environmental conditions.

•

Spatial patterns in bacterial colonies are species and interaction dependent.

•

Surface motility and extracellar matrix production affect interspecies interactions.

•

Agar surface colonies show how bacteria interact in biofilms.

Treponema spp. Isolated from Bovine Digital Dermatitis Display Different Pathogenicity in a Murine Abscess Model

Digital dermatitis (DD) causes lameness in cattle with substantial negative impact on sustainability and animal welfare. Although several species of Treponema bacteria have been isolated from various DD stages, their individual or synergistic roles in the initiation or development of lesions remain largely unknown. The objective of this study was to compare effects of the three most common Treponema species isolated from DD lesions in cattle (T. phagedenis, T. medium and T. pedis), both as individual and as mixed inoculations, in a murine abscess model. A total of 109 or 5 × 108Treponema spp. were inoculated subcutaneously, and produced abscess was studied after 7 days post infection. There were no synergistic effects when two or three species were inoculated together; however, T. medium produced the largest abscesses, whereas those produced by T. phagedenis were the smallest and least severe. Treponema species were cultured from skin lesions at 7 days post infection and, additionally, from the kidneys of some mice (2/5), confirming systemic infection may occur. Taken together, these findings suggest that T. medium and T. pedis may have more important roles in DD lesion initiation and development than T. phagedenis.

Elevated Baseline Salivary Protease Activity May Predict the Steadiness of Gingival Inflammation During Periodontal Healing: A 12-Week Follow-Up Study on Adults

Aim was to profile salivary total protease, Porphyromonas gingivalis gingipain, and neutrophil elastase activities in relation to the resolution of periodontal inflammation, salivary macrophage-derived chemokine (MDC), and macrophage inflammatory protein-1α concentrations. Nonsurgical periodontal treatment was performed in 24 periodontitis patients in a prospective interventional study design. Periodontal clinical parameters were recorded, and stimulated saliva samples were collected at baseline and 2, 6, and 12 weeks after treatment. Salivary total protease and gingipain activities were determined using fluorogenic substrates, elastase activity by chromogenic substrates, and cytokine concentrations by Luminex immunoassay. For statistical analyses, generalized linear mixed models for repeated measures were used. Salivary total protease activity elevated, while gingival inflammation and plaque accumulation decreased 2 and 6 weeks after periodontal therapy. Salivary MDC concentration was elevated 12 weeks after periodontal treatment. Patients with elevated protease activities at baseline in comparison to patients with low baseline total protease activities, had higher levels of gingival inflammation before and after periodontal treatment. In conclusion, elevations in salivary total protease activity seem to be part of periodontal healing at its early phases. Higher levels of salivary total protease activities before periodontal treatment may predict the severity and steadiness of unresolved gingival inflammation.

In vitro corrosion studies of stainless-steel dental substrates during Porphyromonas gingivalis biofilm growth in artificial saliva solutions: providing insights into the role of resident oral bacterium

Stainless-steel AISI 321 is an effective material for fabricating dental crowns and other implants utilized dental restorative protocols for elderly and pediatric populations. This unique clinical application is possible through the mechanical stability and corrosion-resistance properties of this metallic material. However, stainless-steel dental implants eventually fail, leading to the creation of surface cavities and cracks within their microstructures during persistent mechanical stresses and biocorrosion. In this study, the in vitro corrosion behaviour of a medical-grade stainless-steel dental substrate was investigated during Porphyromonas gingivalis biofilm growth process in artificial saliva culture suspension (ASCS). Among the causative bioagents of corrosion, P. gingivalis was chosen for this study since it is also responsible for oral periodontitis and a major contributing factor to corrosion in most dental implants. Increased P. gingivalis growth was observed within the incubation period under study as compact cellular clusters fouled the metal surfaces in ASCS media. This led to the corrosion of steel substrates after bacterial growth maturity within 90 days. Corrosion rate increased with higher CFU and bacterial incubation period for all test substrates due to biocorrosion incited by the volatile sulphide products of P. gingivalis metabolism. The presence of some of these volatile compounds has been observed from experimental evidences. Significant anodic degradation in the forms of localized pitting were also recorded by surface analytical techniques. Residual fluorinated ions within the ASCS media also increased the rate of anodic dissolution due to media acidity. This study has provided extensive insights into the fate of stainless-steel dental crown in oral environments infected by a resident oral bacterium. Influences of oral conditions similar to fluoride-enriched mouthwashes were reflected in a view to understanding the corrosion patterns of stainless-steel dental substrates.

A stainless-steel 321 dental substrate significantly corroded within Porphyromonas gingivalis growth culture in artificial saliva culture suspension, with and without NaF additive.

Salivary Total Protease Activity Based on a Broad-Spectrum Fluorescence Resonance Energy Transfer Approach to Monitor Induction and Resolution of Gingival Inflammation

OBJECTIVE

Salivary total protease and chitinase activities were measured by a broad-spectrum fluorescence resonance energy transfer approach as predictors of induction and resolution of gingival inflammation in healthy individuals by applying an experimental human gingivitis model.

METHODS

Dental biofilm accumulated (21 days, Induction Phase) by omitting oral hygiene practices followed by a 2-week Resolution Phase to restore gingival health in an experimental gingivitis study. Plaque accumulation, as assessed by the Turesky Modification of the Quigley-Hein Plaque Index (TQHPI), and gingival inflammation, assessed using the Modified Gingival Index (MGI), scores were recorded and unstimulated saliva was collected weekly. Saliva was analysed for total protein, albumin, total protease activity and chitinase activity (n = 18).

RESULTS

The TQHPI and MGI scores, as well as total protease activity, increased until day 21. After re-establishment of oral hygiene, gingival inflammation levels returned to values similar to baseline (day 0). Levels of protease activity decreased significantly, but not to baseline values. Furthermore, 'fast' responders, who responded immediately to plaque, exhibited significantly higher proteolytic activity throughout the experimental course than 'slow' responders, who showed a lagged inflammatory response.

CONCLUSION

The results indicate that differential inflammatory responses encompass inherent variations in total salivary proteolytic activities, which could be further utilised in contemporary diagnostic, prognostic and treatment modalities for periodontal diseases.

Endodontic-Like Oral Biofilms as Models for Multispecies Interactions in Endodontic Diseases

Oral bacteria possess the ability to form biofilms on solid surfaces. After the penetration of oral bacteria into the pulp, the contact between biofilms and pulp tissue may result in pulpitis, pulp necrosis and/or periapical lesion. Depending on the environmental conditions and the availability of nutrients in the pulp chamber and root canals, mainly Gram-negative anaerobic microorganisms predominate and form the intracanal endodontic biofilm. The objective of the present study was to investigate the role of different substrates on biofilm formation as well as the separate and collective incorporation of six endodontic pathogens, namely Enterococcus faecalis, Staphylococcus aureus, Prevotella nigrescens, Selenomonas sputigena, Parvimonas micra and Treponema denticola into a nine-species "basic biofilm". This biofilm was formed in vitro as a standard subgingival biofilm, comprising Actinomyces oris, Veillonella dispar, Fusobacterium nucleatum, Streptococcus anginosus, Streptococcus oralis, Prevotella intermedia, Campylobacter rectus, Porphyromonas gingivalis, and Tannerella forsythia. The resulting endodontic-like biofilms were grown 64 h under the same conditions on hydroxyapatite and dentin discs. After harvesting the endodontic-like biofilms, the bacterial growth was determined using quantitative real-time PCR, were labeled using fluorescence in situ hybridization (FISH) and analyzed by confocal laser scanning microscopy (CLSM). The addition of six endodontic pathogens to the "basic biofilm" induced a decrease in the cell number of the "basic" species. Interestingly, C. rectus counts increased in biofilms containing E. faecalis, S. aureus, P. nigrescens and S. sputigena, respectively, both on hydroxyapatite and on dentin discs, whereas P. intermedia counts increased only on dentin discs by addition of E. faecalis. The growth of E. faecalis on hydroxyapatite discs and of E. faecalis and S. aureus on dentin discs were significantly higher in the biofilm containing all species than in the "basic biofilm". Contrarily, the counts of P. nigrescens, S. sputigena and P. micra on hydroxyapatite discs as well as counts of P. micra and T. denticola on dentin discs decreased in the all-species biofilm. Overall, all bacterial species associated with endodontic infections were successfully incorporated into the standard multispecies biofilm model both on hydroxyapatite and dentin discs. Thus, future investigations on endodontic infections can rely on this newly established endodontic-like multispecies biofilm model.

The Role of Treponema denticola Motility in Synergistic Biofilm Formation With Porphyromonas gingivalis

Chronic periodontitis has a polymicrobial biofilm etiology and interactions between key oral bacterial species, such as Porphyromonas gingivalis and Treponema denticola contribute to disease progression. P. gingivalis and T. denticola are co-localized in subgingival plaque and have been previously shown to exhibit strong synergy in growth, biofilm formation and virulence in an animal model of disease. The motility of T. denticola, although not considered as a classic virulence factor, may be involved in synergistic biofilm development between P. gingivalis and T. denticola. We determined the role of T. denticola motility in polymicrobial biofilm development using an optimized transformation protocol to produce two T. denticola mutants targeting the motility machinery. These deletion mutants were non-motile and lacked the gene encoding the flagellar hook protein of the periplasmic flagella (ΔflgE) or a component of the stator motor that drives the flagella (ΔmotB). The specificity of these gene deletions was determined by whole genome sequencing. Quantitative proteomic analyses of mutant strains revealed that the specific inactivation of the motility-associated gene, motB, had effects beyond motility. There were 64 and 326 proteins that changed in abundance in the ΔflgE and ΔmotB mutants, respectively. In the ΔflgE mutant, motility-associated proteins showed the most significant change in abundance confirming the phenotype change for the mutant was related to motility. However, the inactivation of motB as well as stopping motility also upregulated cellular stress responses in the mutant indicating pleiotropic effects of the mutation. T. denticola wild-type and P. gingivalis displayed synergistic biofilm development with a 2-fold higher biomass of the dual-species biofilms than the sum of the monospecies biofilms. Inactivation of T. denticola flgE and motB reduced this synergy. A 5-fold reduction in dual-species biofilm biomass was found with the motility-specific ΔflgE mutant suggesting that T. denticola periplasmic flagella are essential in synergistic biofilm formation with P. gingivalis.

Calibrated interdental brushing for the prevention of periodontal pathogens infection in young adults - a randomized controlled clinical trial

Periodontal disease is clearly correlated with systemic disease. The presence of periodontal pathogens in interdental spaces in young, healthy adults is a strong indicator of the need to introduce daily interdental prophylaxis. Twenty-five subjects (aged 18–35 years), diagnosticated clinically as periodontally healthy, were enrolled in this study. One hundred interdental sites were included. Among these sites, 50 “test” sites were cleaned daily with calibrated interdental brushes (IDBs), whereas the other 50 sites were not cleaned and considered “controls”. The interdental biofilm at these interdental sites was collected at the beginning of the study (basal) and at 1 week, 2 weeks, 3 weeks, 4 weeks, and 3 months. Real-time polymerase chain reaction (PCR) methodology was used to quantify (i) 19 periodontal bacteria, including Porphyromonas gingivalis, Treponema denticola, and Tannerella forsythia, and (ii) total bacteria. In the test sites, the quantity of total bacteria decreased over time with the use of IDBs. The bacteria from the red and orange Socransky complexes, which are associated with periodontal disease, significantly decreased in the test sites but not in the control sites. Bacteria from the yellow, and purple Socransky complexes, which are associated with periodontal health, increased significantly in both groups whereas bacteria from the blue Socransky complex increased significantly only in the test sites. Furthermore, at basal, 66% of test sites and 68% of control sites bled during interdental brushing. These percentages decreased by 85% in 3 months for the test sites and by 27% in the control sites. In conclusion, the daily use of calibrated IDBs can reduce periodontal pathogens, reestablish symbiotic microbiota and, decrease interdental inflammation in interdental sites of healthy young adults.

Fluorescent Pseudomonas -FAP2 and Bacillus licheniformis interact positively in biofilm mode enhancing plant growth and photosynthetic attributes

Compatible interaction between commonly used plant growth promoting rhizobacteria (PGPR) in biofilm mode in vitro and in the rhizosphere is expected to provide better understanding for the development of effective consortium. With the above hypothesis, the present study evaluated two characterized PGPR (Pseudomonas fluorescens FAP2 and Bacillus licheniformis B642) for their biofilm-related functions using standard protocols. The interaction between the FAP2 and B642 in planktonic mode was studied by plate spot/overlay method and competitive growth assessment. Biofilm development on a microtitre plate and a glass surface was studied by standard methods. Biofilm formation was characterized by SEM. Rhizosphere and rhizoplane colonization of wheat seedlings by both isolates individually and by co-inoculation was studied by determining CFU/g of soil/root samples. Biofilm development on the root surface was further analyzed by SEM. Both isolates demonstrated multiple plant growth promoting (PGP) traits (production of IAA, siderophore, and ammonia; phosphate solubilization) and biofilm-related functions such as production of EPS, alginate, cell surface hydrophobicity and swarming motility. Both strains formed strong biofilms on a glass cover slip in vitro. Interaction between the two strains under the planktonic mode revealed no antagonism in terms of growth inhibition and competitive growth kinetics. Similarly, FAP2 and B642 strains formed a mixed biofilm on a glass cover slip as well as on seedling roots. Wheat rhizosphere and rhizoplane were colonized by both isolates as evidenced from their viable counts in single and co-inoculation. The effect of single and co inoculation revealed the significant enhancement of vegetative growth and photosynthetic parameters such as chlorophyll content, transpiration rate (E), internal CO₂ concentration (Ci), stomatal conductance (g_s), and net photosynthetic rate (P_N) and leaf water potential (LWP) as compared to uninoculated control. Indigenous Pseudomonas fluorescens FAP2 strain and Bacillus licheniformis B642 are compatible PGPR in both planktonic and biofilm modes of growth and threfore could be developed effective consortium of PGPR. Further indepth investigation is required to understand molecular mechanism of the interaction in biofilm mode of growth under natural condition.

Signaling Systems in Oral Bacteria

The supra- and subgingival plaque biofilm communities of plaque are composed of hundreds of different microbes. These communities are spatially and temporally structured, largely due to cell-cell communications that coordinate synergistic interactions, and intracellular signaling systems to sense changes in the surrounding environment. Homeostasis is maintained through metabolic communication, mutualistic cross-feeding, and cross-respiration. These nutritional symbioses can reciprocally influence the local microenvironments by altering the pH and by detoxifying oxidative compounds. Signal transduction mechanisms include two-component systems, tyrosine phosphorelays, quorum sensing systems, and cyclic nucleotide secondary messengers. Signaling converges on transcriptional programs and can result in synergistic or antagonistic interbacterial interactions that sculpt community development. The sum of all these interactions can be a well-organized polymicrobial community that remains in homeostasis with the host, or a dysbiotic community that provokes pathogenic responses in the host.

Confocal fluorescence imaging to evaluate the effect of antimicrobial photodynamic therapy depth on P. gingivalis and T. denticola biofilms

BACKGROUND

Porphyromonas gingivalis and Treponema denticola are both principally implicated in the incidence of both periodontal disease and peri-implantitis. Recent studies have demonstrated that these bacteria exhibit symbiotic growth in vitro and a synergistic virulence in co-infection of animal models. Found at varying depths throughout the biofilm, these bacteria present a significant challenge to traditional antimicrobial treatment modalities. Antimicrobial photodynamic therapy (aPDT) has yielded high success against bacterial biofilms, namely those found in the oral cavity. Data on the use of aPDT against these particular periodontal pathogens is, however, scarce. Here, we studied the qualitative killing efficacy and depth of drug and laser penetration into defined P. gingivalis and T. denticola biofilms.

METHODS

P. gingivalis and T. denticola were incubated under anaerobic (10%CO2, 10%H2, 80%N2) conditions for two days in diluted TSB with PBS (TYGVS for T. denticola maintenance) to elicit biofilm growth on coverslip-modified polystyrene dishes. Treated biofilms were exposed to a purpurin-based sensitizer (25 μg/mL in DMSO) for 30 min, and then aPDT was carried out using a diode laser at 664 nm. Light doses of 15 and 45 J/cm2 were used. All biofilms were then exposed to Filmtracer™ LIVE/DEAD® Biofilm Viability Kit (Cat No. L10316). Qualitative analysis was performed using a Zeiss LSM 510 Meta NLO Confocal Microscope with attached Zeiss Axioimager Z1 and Axiovert 200 M for visual data collection, and images were processed using the ZEN Digital Imaging for Light Microscopy software suite. Analysis was performed in 2 × 3 stacks to assess the entire depth of both the biofilm and presumed drug/laser penetration.

RESULTS

Initial planktonic studies confirmed that the bacteria in question were present in the grown cultures and susceptible to aPDT exposure. Biofilm control groups were found to have significant levels of surviving bacterial colonies. Both treatment groups featured complete bacterial kill throughout the entirety of the biofilm (average: 23.17 μm; range: 18.13-27.20 μm).

CONCLUSIONS

The efficacy of the purpurin-based PS and aPDT is demonstrated to be effective at both high and low light doses. Bacterial kill was fully efficacious at each visualized biofilm layer (1.01 μm/z-level). This study serves as a proof of concept for future studies that must consider appropriate treatment parameters, including the amount of applied PS, and laser dose. These findings indicate that aPDT is a method that can be used to eliminate microorganisms associated with biofilms implicated in the etiology of peri-implantitis and periodontitis at large.

The evolution of ecological facilitation within mixed-species biofilms in the mouse gastrointestinal tract

The eco-evolutionary interactions among members of the vertebrate gut microbiota that ultimately result in host-specific communities are poorly understood. Here we show that Lactobacillus reuteri coexists with  species that belong to the Lactobacillus johnsonii cluster (L. johnsonii, L. gasseri, and L taiwanensis) in a taxonomically wide range of rodents, suggesting cohabitation over evolutionary times. The two dominant Lactobacillus species found in wild mice establish a commensalistic relationship in gastric biofilms when introduced together into germ-free mice in which L. reuteri facilitates colonization of L. taiwanensis. Genomic analysis revealed allopatric diversification in strains of both species that originated from geographically separated locations (Scotland and France). Allopatry of the strains resulted in reduced formation of mixed biofilms in vitro, indicating that interspecies interactions in gastric Lactobacillus-biofilms are the result of an adaptive evolutionary process that occurred in a biogeographical context. In summary, these findings suggest that members within the vertebrate gut microbiota can evolve inter-dependencies through ecological facilitation, which could represent one mechanism by which host-specific bacterial communities assemble across vertebrate species and an explanation for their spatial and biogeographic patterns.

Identification of a specific domain of Porphyromonas gingivalis Hgp44 responsible for adhesion to Treponema denticola

Interaction between two periodontal pathogens, Porphyromonas gingivalis and Treponema denticola, contributes to plaque biofilm formation. Porphyromonas gingivalis forms aggregates with T. denticola through its adhesion/hemagglutinin domain (Hgp44). In this study, we investigated the specific domain of P. gingivalis Hgp44 responsible for adhesion to T. denticola using expression vectors harboring P. gingivalis Hgp44 DNA sequences encoding amino acid residues 1-419. Six plasmids harboring fragments in this region were generated by PCR amplification and self-ligation, and recombinant proteins r-Hgp44 (residues 1-419), r-Hgp441 (residues 1-124), r-Hgp442 (1-199), r-Hgp443 (1-316), r-Hgp444 (199-419), r-Hgp445 (124-198) and r-Hgp446 (199-316) were produced, as confirmed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblotting. r-Hgp44, r-Hgp443 and r-Hgp446 showed greater adhesion to T. denticola sonicates than the control, as determined by enzyme-linked immunosorbent assay. r-Hgp446 reduced the coaggregation of P. gingivalis and T. denticola. Scanning electron and confocal laser scanning microscopy analyses revealed that r-Hgp446 reduced dual-species biofilm formation. Our results indicate that residues 199-316 of P. gingivalis Hgp44 are mainly responsible for adhesion to T. denticola; inhibiting this domain could potentially disrupt periodontopathic biofilm formation and maturation.

Effect of azithromycin on a red complex polymicrobial biofilm

Azithromycin has recently gained popularity for the treatment of periodontal disease, despite sparse literature supporting efficiency in treating periodontal bacterial biofilms. The aim of this study was to evaluate the effect of azithromycin on biofilms comprised of Porphyromonas gingivalis, Treponema denticola, and Tannerella forsythia in comparison to an amoxicillin and metronidazole combination. P. gingivalis W50, T. denticola ATCC35405, and T. forsythia ATCC43037 grown under anaerobic conditions at 37°C were aliquoted into 96-well flat-bottom plates in different combinations with addition of azithromycin or amoxicillin + metronidazole at various concentrations. For the biofilm assay, the plates were incubated at 37°C anaerobically for 48 h, after which the biofilms were stained with crystal violet and measured for absorbance at AU₆₂₀. In this model, polymicrobial biofilms of P. gingivalis + T. denticola, P. gingivalis + T. forsythia, and T. denticola + T. forsythia were cultured. Combination of all three bacteria enhanced biofilm biomass. Azithromycin demonstrated a minimal biofilm inhibitory concentration (MBIC) of 10.6 mg/L, while the amoxicillin + metronidazole combination was more effective in inhibiting biofilm formation with a MBIC of 1.63 mg/L. Polymicrobial biofilm formation was demonstrated by combination of all three red complex bacteria. Azithromycin was ineffective in preventing biofilm formation within a clinically achievable concentration, whereas the combination of amoxicillin and metronidazole was more effective for this purpose.

New approaches to combat Porphyromonas gingivalis biofilms

In nature, bacteria predominantly reside in structured, surface-attached communities embedded in a self-produced, extracellular matrix. These so-called biofilms play an important role in the development and pathogenesis of many infections, as they are difficult to eradicate due to their resistance to antimicrobials and host defense mechanisms. This review focusses on the biofilm-forming periodontal bacterium Porphyromonas gingivalis. Current knowledge on the virulence mechanisms underlying P. gingivalis biofilm formation is presented. In addition, oral infectious diseases in which P. gingivalis plays a key role are described, and an overview of conventional and new therapies for combating P. gingivalis biofilms is given. More insight into this intriguing pathogen might direct the development of better strategies to combat oral infections.

Modulation of the Substitution Pattern of 5-Aryl-2-Aminoimidazoles Allows Fine-Tuning of Their Antibiofilm Activity Spectrum and Toxicity

We previously synthesized several series of compounds, based on the 5-aryl-2-aminoimidazole scaffold, that showed activity preventing the formation of Salmonella enterica serovar Typhimurium and Pseudomonas aeruginosa biofilms. Here, we further studied the activity spectrum of a number of the most active N1- and 2N-substituted 5-aryl-2-aminoimidazoles against a broad panel of biofilms formed by monospecies and mixed species of bacteria and fungi. An N1-substituted compound showed very strong activity against the biofilms formed by Gram-negative and Gram-positive bacteria and the fungus Candida albicans but was previously shown to be toxic against various eukaryotic cell lines. In contrast, 2N-substituted compounds were nontoxic and active against biofilms formed by Gram-negative bacteria and C. albicans but had reduced activity against biofilms formed by Gram-positive bacteria. In an attempt to develop nontoxic compounds with potent activity against biofilms formed by Gram-positive bacteria for application in antibiofilm coatings for medical implants, we synthesized novel compounds with substituents at both the N1 and 2N positions and tested these compounds for antibiofilm activity and toxicity. Interestingly, most of these N1-,2N-disubstituted 5-aryl-2-aminoimidazoles showed very strong activity against biofilms formed by Gram-positive bacteria and C. albicans in various setups with biofilms formed by monospecies and mixed species but lost activity against biofilms formed by Gram-negative bacteria. In light of application of these compounds as anti-infective coatings on orthopedic implants, toxicity against two bone cell lines and the functionality of these cells were tested. The N1-,2N-disubstituted 5-aryl-2-aminoimidazoles in general did not affect the viability of bone cells and even induced calcium deposition. This indicates that modulating the substitution pattern on positions N1 and 2N of the 5-aryl-2-aminoimidazole scaffold allows fine-tuning of both the antibiofilm activity spectrum and toxicity.

Role of OmpA2 surface regions of Porphyromonas gingivalis in host-pathogen interactions with oral epithelial cells

Outer membrane protein A (OmpA) is a key outer membrane protein found in Gram‐negative bacteria that contributes to several crucial processes in bacterial virulence. In Porphyromonas gingivalis, OmpA is predicted as a heterotrimer of OmpA1 and OmpA2 subunits encoded by adjacent genes. Here we describe the role of OmpA and its individual subunits in the interaction of P. gingivalis with oral cells. Using knockout mutagenesis, we show that OmpA2 plays a significant role in biofilm formation and interaction with human epithelial cells. We used protein structure prediction software to identify extracellular loops of OmpA2, and determined these are involved in interactions with epithelial cells as evidenced by inhibition of adherence and invasion of P. gingivalis by synthetic extracellular loop peptides and the ability of the peptides to mediate interaction of latex beads with human cells. In particular, we observe that OmpA2‐loop 4 plays an important role in the interaction with host cells. These data demonstrate for the first time the important role of P. gingivalis OmpA2 extracellular loops in interaction with epithelial cells, which may help design novel peptide‐based antimicrobial therapies for periodontal disease.

Coexistence facilitates interspecific biofilm formation in complex microbial communities

Social interactions in which bacteria respond to one another by modifying their phenotype are central determinants of microbial communities. It is known that interspecific interactions influence the biofilm phenotype of bacteria; a phenotype that is central to the fitness of bacteria. However, the underlying role of fundamental ecological factors, specifically coexistence and phylogenetic history, in biofilm formation remains unclear. This study examines how social interactions affect biofilm formation in multi-species co-cultures from five diverse environments. We found prevalence of increased biofilm formation among co-cultured bacteria that have coexisted in their original environment. Conversely, when randomly co-culturing bacteria across these five consortia, we found less biofilm induction and a prevalence of biofilm reduction. Reduction in biofilm formation was even more predominant when co-culturing bacteria from environments where long-term coexistence was unlikely to have occurred. Phylogenetic diversity was not found to be a strong underlying factor but a relation between biofilm induction and phylogenetic history was found. The data indicates that biofilm reduction is typically correlated with an increase in planktonic cell numbers, thus implying a behavioral response rather than mere growth competition. Our findings suggest that an increase in biofilm formation is a common adaptive response to long-term coexistence.

Polymicrobial biofilm formation by Candida albicans, Actinomyces naeslundii, and Streptococcus mutans is Candida albicans strain and medium dependent

Oral biofilms comprise of extracellular polysaccharides and polymicrobial microorganisms. The objective of this study was to determine the effect of polymicrobial interactions of Candida albicans, Actinomyces naeslundii, and Streptococcus mutans on biofilm formation with the hypotheses that biofilm biomass and metabolic activity are both C. albicans strain and growth medium dependent. To study monospecific biofilms, C. albicans, A. naeslundii, and S. mutans were inoculated into artificial saliva medium (ASM) and RPMI-1640 in separate vials, whereas to study polymicrobial biofilm formation, the inoculum containing microorganisms was prepared in the same vial prior inoculation into a 96-well plate followed by 72 hours incubation. Finally, biofilm biomass and metabolic activity were measured using crystal violet and XTT assays, respectively. Our results showed variability of monospecies and polymicrobial biofilm biomass between C. albicans strains and growth medium. Based on cut-offs, out of 32, seven RPMI-grown biofilms had high biofilm biomass (HBB), whereas, in ASM-grown biofilms, 14 out of 32 were HBB. Of the 32 biofilms grown in RPMI-1640, 21 were high metabolic activity (HMA), whereas in ASM, there was no biofilm had HMA. Significant differences were observed between ASM and RPMI-grown biofilms with respect to metabolic activity (P <01). In conclusion, biofilm biomass and metabolic activity were both C. albicans strain and growth medium dependent.

Dual lifestyle of Porphyromonas gingivalis in biofilm and gingival cells

Porphyromonas gingivalis is deeply involved in the pathogenesis of marginal periodontitis, and recent findings have consolidated its role as an important and unique pathogen. This bacterium has a unique dual lifestyle in periodontal sites including subgingival dental plaque (biofilm) and gingival cells, as it has been clearly shown that P. gingivalis is able to exert virulence using completely different tactics in each environment. Inter-bacterial cross-feeding enhances the virulence of periodontal microflora, and such metabolic and adhesive interplay creates a supportive environment for P. gingivalis and other species. Human oral epithelial cells harbor a large intracellular bacterial load, resembling the polymicrobial nature of periodontal biofilm. P. gingivalis can enter gingival epithelial cells and pass through the epithelial barrier into deeper tissues. Subsequently, from its intracellular position, the pathogen exploits cellular recycling pathways to exit invaded cells, by which it is able to control its population in infected tissues, allowing for persistent infection in gingival tissues. Here, we outline the dual lifestyle of P. gingivalis in subgingival areas and its effects on the pathogenesis of periodontitis.

Role of Porphyromonas gingivalis gingipains in multi-species biofilm formation

Background

Periodontal diseases are polymicrobial diseases that cause the inflammatory destruction of the tooth-supporting (periodontal) tissues. Their initiation is attributed to the formation of subgingival biofilms that stimulate a cascade of chronic inflammatory reactions by the affected tissue. The Gram-negative anaerobes Porphyromonas gingivalis, Tannerella forsythia and Treponema denticola are commonly found as part of the microbiota of subgingival biofilms, and they are associated with the occurrence and severity of the disease. P. gingivalis expresses several virulence factors that may support its survival, regulate its communication with other species in the biofilm, or modulate the inflammatory response of the colonized host tissue. The most prominent of these virulence factors are the gingipains, which are a set of cysteine proteinases (either Arg-specific or Lys-specific). The role of gingipains in the biofilm-forming capacity of P. gingivalis is barely investigated. Hence, this in vitro study employed a biofilm model consisting of 10 “subgingival” bacterial species, incorporating either a wild-type P. gingivalis strain or its derivative Lys-gingipain and Arg-gingipan isogenic mutants, in order to evaluate quantitative and qualitative changes in biofilm composition.

Results

Following 64 h of biofilm growth, the levels of all 10 species were quantified by fluorescence in situ hybridization or immunofluorescence. The wild-type and the two gingipain-deficient P. gingivalis strains exhibited similar growth in their corresponding biofilms. Among the remaining nine species, only the numbers of T. forsythia were significantly reduced, and only when the Lys-gingipain mutant was present in the biofilm. When evaluating the structure of the biofilm by confocal laser scanning microscopy, the most prominent observation was a shift in the spatial arrangement of T. denticola, in the presence of P. gingivalis Arg-gingipain mutant.

Conclusions

The gingipains of P. gingivalis may qualitatively and quantitatively affect composition of polymicrobial biofilms. The present experimental model reveals interdependency between the gingipains of P. gingivalis and T. forsythia or T. denticola.

High prevalence of biofilm synergy among bacterial soil isolates in cocultures indicates bacterial interspecific cooperation

Biofilms that form on roots, litter and soil particles typically contain multiple bacterial species. Currently, little is known about multispecies biofilm interactions and few studies have been based on environmental isolates. Here, the prevalence of synergistic effects in biofilm formation among seven different soil isolates, cocultured in combinations of four species, was investigated. We observed greater biofilm biomass production in 63% of the four-species culture combinations tested than in biofilm formed by single-species cultures, demonstrating a high prevalence of synergism in multispecies biofilm formation. One four-species consortium, composed of Stenotrophomonas rhizophila, Xanthomonas retroflexus, Microbacterium oxydans and Paenibacillus amylolyticus, exhibited strong synergy in biofilm formation and was selected for further study. Of the four strains, X. retroflexus was the only one capable of forming abundant biofilm in isolation, under the in vitro conditions investigated. In accordance, strain-specific quantitative PCR revealed that X. retroflexus was predominant within the four-species consortium (>97% of total biofilm cell number). Despite low relative abundance of all the remaining strains, all were indispensable for the strong synergistic effect to occur within the four-species biofilm. Moreover, absolute individual strain cell numbers were significantly enhanced when compared with those of single-species biofilms, indicating that all the individual strains benefit from inclusion in the multispecies community. Our results show a high prevalence of synergy in biofilm formation in multispecies consortia isolated from a natural bacterial habitat and suggest that interspecific cooperation occurs.

Life in a Diverse Oral Community - Strategies for Oxidative Stress Survival

BACKGROUND

While the oral cavity harbors more than 680 bacterial species, the interaction and association of selected bacterial species play a role in periodontal diseases. Bacterial species including Porphyromonas gingivalis, Treponema denticola and Tannerella forsythia, a consortium previously designated as the "red complex" is now being expanded to include other new emerging pathogens that are significantly associated with periodontal disease.

HIGHLIGHT

In addition to novel mechanisms for oxidative resistance of individual species, community dynamics may lead to an overall strategy for survival in the inflammatory environment of the periodontal pocket. Complex systems controlled by response regulators protect against oxidative and nitrosative stress.

CONCLUSION

The combination of these multifaceted strategies would provide a comprehensive defense and support system against the repetitive host immune response to promote microbial persistence and disease.

Porphyromonas gingivalis gingipain is involved in the detachment and aggregation of Aggregatibacter actinomycetemcomitans biofilm

Porphyromonas gingivalis and Aggregatibacter actinomycetemcomitans are major periodontal pathogens that cause several types of periodontal disease. Our previous study suggested that P. gingivalis gingipains secreted in the subgingival environment are related to the detachment of A.actinomycetemcomitans biofilms. However, it remains unclear whether arginine-specific cysteine proteinase (Rgp) and lysine-specific proteinase (Kgp) play different roles in the detachment of A. actinomycetemcomitans biofilm. The aim of this study was to investigate possible disruptive roles of Kgp and Rgp in the aggregation and attachment of A. actinomycetemcomitans. While P. gingivalis ATCC33277 culture supernatant has an ability to decrease autoaggregation and coaggregation of A. actinomycetemcomitans cells, neither the boiled culture supernatant of ATCC33277 nor the culture supernatant of KDP136 showed this ability. The addition of KYT-1 and KYT-36, specific inhibitors of Rgp and Kgp, respectively, showed no influence on the ability of P. gingivalis culture supernatant. The result of gelatin zymography suggested that other proteases processed by gingipains mediated the decrease of A. actinomycetemcomitans aggregations. We also examined the biofilm-destructive effect of gingipains by assessing the detachment of A. actinomycetemcomitans from polystyrene surfaces. Scanning electron microscope analysis indicated that A. actinomycetemcomitans cells were detached by P. gingivalis Kgp. The quantity of A. actinomycetemcomitans in biofilm was decreased in co-culture with P. gingivalis. However, this was not found after the addition of KYT-36. These findings suggest that Kgp is a critical component for the detachment and decrease of A. actinomycetemcomitans biofilms.

Porphyromonas gingivalis and Treponema denticola exhibit metabolic symbioses

Porphyromonas gingivalis and Treponema denticola are strongly associated with chronic periodontitis. These bacteria have been co-localized in subgingival plaque and demonstrated to exhibit symbiosis in growth in vitro and synergistic virulence upon co-infection in animal models of disease. Here we show that during continuous co-culture a P. gingivalis:T. denticola cell ratio of 6∶1 was maintained with a respective increase of 54% and 30% in cell numbers when compared with mono-culture. Co-culture caused significant changes in global gene expression in both species with altered expression of 184 T. denticola and 134 P. gingivalis genes. P. gingivalis genes encoding a predicted thiamine biosynthesis pathway were up-regulated whilst genes involved in fatty acid biosynthesis were down-regulated. T. denticola genes encoding virulence factors including dentilisin and glycine catabolic pathways were significantly up-regulated during co-culture. Metabolic labeling using ¹³C-glycine showed that T. denticola rapidly metabolized this amino acid resulting in the production of acetate and lactate. P. gingivalis may be an important source of free glycine for T. denticola as mono-cultures of P. gingivalis and T. denticola were found to produce and consume free glycine, respectively; free glycine production by P. gingivalis was stimulated by T. denticola conditioned medium and glycine supplementation of T. denticola medium increased final cell density 1.7-fold. Collectively these data show P. gingivalis and T. denticola respond metabolically to the presence of each other with T. denticola displaying responses that help explain enhanced virulence of co-infections.

Unlike the traditional view that most diseases are caused by infection with a single bacterial species, some chronic diseases including periodontitis result from the perturbation of the natural microbiota and the proliferation of a number of opportunistic pathogens. Both Porphyromonas gingivalis and Treponema denticola have been associated with the progression and severity of chronic periodontitis and have been shown to display synergistic virulence in animal models. However, the underlying mechanisms to these observations are unclear. Here we demonstrate that these two bacteria grow synergistically in continuous co-culture and modify their gene expression. The expression of T. denticola genes encoding known virulence factors and enzymes involved in the uptake and metabolism of the amino acid glycine was up-regulated in co-culture. T. denticola stimulated the proteolytic P. gingivalis to produce free glycine, which T. denticola used as a major carbon source. Our study shows P. gingivalis and T. denticola co-operate metabolically and this helps to explain their synergistic virulence in animal models and their intimate association in vivo.

Mechanisms of synergy in polymicrobial infections

Communities of microbes can live almost anywhere and contain many different species. Interactions between members of these communities often determine the state of the habitat in which they live. When these habitats include sites on the human body, these interactions can affect health and disease. Polymicrobial synergy can occur during infection, in which the combined effect of two or more microbes on disease is worse than seen with any of the individuals alone. Powerful genomic methods are increasingly used to study microbial communities, including metagenomics to reveal the members and genetic content of a community and metatranscriptomics to describe the activities of community members. Recent efforts focused toward a mechanistic understanding of these interactions have led to a better appreciation of the precise bases of polymicrobial synergy in communities containing bacteria, eukaryotic microbes, and/or viruses. These studies have benefited from advances in the development of in vivo models of polymicrobial infection and modern techniques to profile the spatial and chemical bases of intermicrobial communication. This review describes the breadth of mechanisms microbes use to interact in ways that impact pathogenesis and techniques to study polymicrobial communities.

Transcriptional responses of Treponema denticola to other oral bacterial species

The classic organization by Socransky and coworkers categorized the oral bacteria of the subgingival plaque into different complexes. Treponema denticola, Porphyromonas gingivalis and Tannerella forsythia are grouped into the red complex that is highly correlated with periodontal disease. Socransky's work closely associates red with orange complex species such as Fusobacterium nucleatum and Prevotella intermedia but not with members of the other complexes. While the relationship between species contained by these complexes is in part supported by their ability to physically attach to each other, the physiological consequences of these interactions and associations are less clear. In this study, we employed T. denticola as a model organism to analyze contact-dependent responses to interactions with species belonging to the same complex (P. gingivalis and T. forsythia), the closely associated orange complex (using F. nucleatum and P. intermedia as representatives) and the unconnected yellow complex (using Streptococcus sanguinis and S. gordonii as representatives). RNA was extracted from T. denticola alone as well as after pairwise co-incubation for 5 hrs with representatives of the different complexes, and the respective gene expression profiles were determined using microarrays. Numerous genes related to motility, metabolism, transport, outer membrane and hypothetical proteins were differentially regulated in T. denticola in the presence of the tested partner species. Further analysis revealed a significant overlap in the affected genes and we identified a general response to the presence of other species, those specific to two of the three complexes as well as individual complexes. Most interestingly, many predicted major antigens (e.g. flagella, Msp, CTLP) were suppressed in responses that included red complex species indicating that the presence of the most closely associated species induces immune-evasive strategies. In summary, the data presented here provide an in-depth understanding of the transcriptional responses triggered by contact-dependent interactions between microorganisms inhabiting the periodontal pocket.

Oxantel disrupts polymicrobial biofilm development of periodontal pathogens

Bacterial pathogens commonly associated with chronic periodontitis are the spirochete Treponema denticola and the Gram-negative, proteolytic species Porphyromonas gingivalis and Tannerella forsythia. These species rely on complex anaerobic respiration of amino acids, and the anthelmintic drug oxantel has been shown to inhibit fumarate reductase (Frd) activity in some pathogenic bacteria and inhibit P. gingivalis homotypic biofilm formation. Here, we demonstrate that oxantel inhibited P. gingivalis Frd activity with a 50% inhibitory concentration (IC50) of 2.2 μM and planktonic growth of T. forsythia with a MIC of 295 μM, but it had no effect on the growth of T. denticola. Oxantel treatment caused the downregulation of six P. gingivalis gene products and the upregulation of 22 gene products. All of these genes are part of a regulon controlled by heme availability. There was no large-scale change in the expression of genes encoding metabolic enzymes, indicating that P. gingivalis may be unable to overcome Frd inhibition. Oxantel disrupted the development of polymicrobial biofilms composed of P. gingivalis, T. forsythia, and T. denticola in a concentration-dependent manner. In these biofilms, all three species were inhibited to a similar degree, demonstrating the synergistic nature of biofilm formation by these species and the dependence of T. denticola on the other two species. In a murine alveolar bone loss model of periodontitis oxantel addition to the drinking water of P. gingivalis-infected mice reduced bone loss to the same level as the uninfected control.

Porphyromonas gingivalis and Treponema denticola synergistic polymicrobial biofilm development

Chronic periodontitis has a polymicrobial biofilm aetiology and interactions between key bacterial species are strongly implicated as contributing to disease progression. Porphyromonas gingivalis, Treponema denticola and Tannerella forsythia have all been implicated as playing roles in disease progression. P. gingivalis cell-surface-located protease/adhesins, the gingipains, have been suggested to be involved in its interactions with several other bacterial species. The aims of this study were to determine polymicrobial biofilm formation by P. gingivalis, T. denticola and T. forsythia, as well as the role of P. gingivalis gingipains in biofilm formation by using a gingipain null triple mutant. To determine homotypic and polymicrobial biofilm formation a flow cell system was employed and the biofilms imaged and quantified by fluorescent in situ hybridization using DNA species-specific probes and confocal scanning laser microscopy imaging. Of the three species, only P. gingivalis and T. denticola formed mature, homotypic biofilms, and a strong synergy was observed between P. gingivalis and T. denticola in polymicrobial biofilm formation. This synergy was demonstrated by significant increases in biovolume, average biofilm thickness and maximum biofilm thickness of both species. In addition there was a morphological change of T. denticola in polymicrobial biofilms when compared with homotypic biofilms, suggesting reduced motility in homotypic biofilms. P. gingivalis gingipains were shown to play an essential role in synergistic polymicrobial biofilm formation with T. denticola.

Mixed red-complex bacterial infection in periodontitis

The red complex, which includes Porphyromonas gingivalis, Treponema denticola, and Tannerella forsythia (formerly Bacteroides forsythus), are recognized as the most important pathogens in adult periodontal disease. These bacteria are usually found together in periodontal pockets, suggesting that they may cause destruction of the periodontal tissue in a cooperative manner. This article discusses the interspecies pathogenic interactions within the red complex.

Treponema denticola improves adhesive capacities of Porphyromonas gingivalis

Porphyromonas gingivalis, an important etiological agent of periodontal disease, is frequently found associated with Treponema denticola, an anaerobic spirochete, in pathogenic biofilms. However, interactions between these two bacteria are not well understood at the molecular level. In this study, we seek to link the influence of T. denticola on the expression of P. gingivalis proteases with its capacities to adhere and to form biofilms. The P. gingivalis genes encoding Arg-gingipain A (RgpA), Lys-gingipain (Kgp), and hemagglutinin A (HagA) were more strongly expressed after incubation with T. denticola compared with P. gingivalis alone. The amounts of the three resulting proteins, all of which contain hemagglutinin adhesion domains, were increased in culture supernatants. Moreover, incubation of P. gingivalis with T. denticola promoted static and dynamic biofilm formation, primarily via a time-dependent enhancement of P. gingivalis adhesion capacities on bacterial partners such as Streptococcus gordonii. Adhesion of P. gingivalis to human cells was also increased. These results showed that interactions of P. gingivalis with other bacterial species, such as T. denticola, induce increased adhesive capacities on various substrata by hemagglutinin adhesion domain-containing proteins.