Association of a high-molecular weight arginine-binding protein of Fusobacterium nucleatum ATCC 10953 with adhesion to secretory immunoglobulin A and coaggregation with Streptococcus cristatus

Surface adherence and vacuolar internalization of bacterial pathogens to the Candida spp. cells: Mechanism of persistence and propagation

BACKGROUND

The co-existence of Candida albicans with the bacteria in the host tissues and organs displays interactions at competitive, antagonistic, and synergistic levels. Several pathogenic bacteria take advantage of such types of interaction for their survival and proliferation. The chemical interaction involves the signaling molecules produced by the bacteria or Candida spp., whereas the physical attachment occurs by involving the surface proteins of the bacteria and Candida. In addition, bacterial pathogens have emerged to internalize inside the C. albicans vacuole, which is one of the inherent properties of the endosymbiotic relationship between the bacteria and the eukaryotic host.

AIM OF REVIEW

The interaction occurring by the involvement of surface protein from diverse bacterial species with Candida species has been discussed in detail in this paper. An in silico molecular docking study was performed between the surface proteins of different bacterial species and Als3P of C. albicans to explain the molecular mechanism involved in the Als3P-dependent interaction. Furthermore, in order to understand the specificity of C. albicans interaction with Als3P, the evolutionary relatedness of several bacterial surface proteins has been investigated. Furthermore, the environmental factors that influence bacterial pathogen internalization into the Candida vacuole have been addressed. Moreover, the review presented future perspectives for disrupting the cross-kingdom interaction and eradicating the endosymbiotic bacterial pathogens.

KEY SCIENTIFIC CONCEPTS OF REVIEW

With the involvement of cross-kingdom interactions and endosymbiotic relationships, the bacterial pathogens escape from the environmental stresses and the antimicrobial activity of the host immune system. Thus, the study of interactions between Candida and bacterial pathogens is of high clinical significance.

Fusobacterium nucleatum: The Opportunistic Pathogen of Periodontal and Peri-Implant Diseases

Peri-implant diseases are considered to be a chronic destructive inflammatory destruction/damage occurring in soft and hard peri-implant tissues during the patient’s perennial use after implant restoration and have attracted much attention because of their high incidence. Although most studies seem to suggest that the pathogenesis of peri-implant diseases is similar to that of periodontal diseases and that both begin with microbial infection, the specific mechanism of peri-implant diseases remains unclear. As an oral opportunistic pathogen, Fusobacterium nucleatum (F. nucleatum) has been demonstrated to be vital for the occurrence and development of many oral infectious diseases, especially periodontal diseases. More notably, the latest relevant studies suggest that F. nucleatum may contribute to the occurrence and development of peri-implant diseases. Considering the close connection between peri-implant diseases and periodontal diseases, a summary of the role of Fusobacterium nucleatum in periodontal diseases may provide more research directions and ideas for the peri-implantation mechanism. In this review, we summarize the effects of F. nucleatum on periodontal diseases by biofilm formation, host infection, and host response, and then we establish the relationship between periodontal and peri-implant diseases. Based on the above aspects, we discuss the importance and potential value of F. nucleatum in peri-implant diseases.

Spatial scale in analysis of the dental plaque microbiome

Ecologists have long recognized the importance of spatial scale in understanding structure-function relationships among communities of organisms within their environment. Here, we review historical and contemporary studies of dental plaque community structure in the context of three distinct scales: the micro (1-10 µm), meso (10-100 µm) and macroscale (100 µm to ≥1 cm). Within this framework, we analyze the compositional nature of dental plaque at the macroscale, the molecular interactions of microbes at the microscale, and the emergent properties of dental plaque biofilms at the mesoscale. Throughout our analysis of dental plaque across spatial scales, we draw attention to disease and health-associated structure-function relationships and include a discussion of host immune involvement in the mesoscale structure of periodontal disease-associated biofilms. We end with a discussion of two filamentous organisms, Fusobacterium nucleatum and Corynebacterium matruchotii, and their relevant contributions in structuring dental plaque biofilms.

Glutathione-Stabilized Silver Nanoparticles: Antibacterial Activity against Periodontal Bacteria, and Cytotoxicity and Inflammatory Response in Oral Cells

Silver nanoparticles (AgNPs) have been proposed as new alternatives to limit bacterial dental plaque because of their antimicrobial activity. Novel glutathione-stabilized silver nanoparticles (GSH-AgNPs) have proven powerful antibacterial properties in food manufacturing processes. Therefore, this study aimed to evaluate the potentiality of GSH-AgNPs for the prevention/treatment of oral infectious diseases. First, the antimicrobial activity of GSH-AgNPs against three oral pathogens (Porphyromonas gingivalis, Fusobacterium nucleatum, and Streptococcus mutans) was evaluated. Results demonstrated the efficiency of GSH-AgNPs in inhibiting the growth of all bacteria, especially S. mutans (IC50 = 23.64 μg/mL, Ag concentration). Second, GSH-AgNPs were assayed for their cytotoxicity (i.e., cell viability) toward a human gingival fibroblast cell line (HGF-1), as an oral epithelial model. Results indicated no toxic effects of GSH-AgNPs at low concentrations (≤6.16 µg/mL, Ag concentration). Higher concentrations resulted in losing cell viability, which followed the Ag accumulation in cells. Finally, the inflammatory response in the HGF-1 cells after their exposure to GSH-AgNPs was measured as the production of immune markers (interleukins 6 and 8 (IL-6 and IL-8) and tumor necrosis factor-alpha (TNF-α)). GSH-AgNPs activates the inflammatory response in human gingival fibroblasts, increasing the production of cytokines. These findings provide new insights for the use of GSH-AgNPs in dental care and encourage further studies for their application.

The Oral Bacterium Fusobacterium nucleatum Binds Staphylococcus aureus and Alters Expression of the Staphylococcal Accessory Regulator sarA

Staphylococcus aureus, an opportunistic pathogen member of the nasal and skin microbiota, can also be found in human oral samples and has been linked to infectious diseases of the oral cavity. As the nasal and oral cavities are anatomically connected, it is currently unclear whether S. aureus can colonize the oral cavity and become part of the oral microbiota, or if its presence in the oral cavity is simply transient. To start addressing this question, we assessed S. aureus ability to directly bind selected members of the oral microbiota as well as its ability to integrate into a human-derived complex oral microbial community in vitro. Our data show that S. aureus forms aggregates with Fusobacterium nucleatum and Porphyromonas gingivalis and that it can incorporate into the human-derived in vitro oral community. Further analysis of the F. nucleatum-S. aureus interaction revealed that the outer-membrane adhesin RadD is partially involved in aggregate formation and that the RadD-mediated interaction leads to an increase in expression of the staphylococcal global regulator gene sarA. Our findings lend support to the notion that S. aureus can become part of the complex microbiota of the human mouth, which could serve as a reservoir for S. aureus. Furthermore, direct interaction with key members of the oral microbiota could affect S. aureus pathogenicity contributing to the development of several S. aureus associated oral infections.

Salivary calculi microbiota: new insights into microbial networks and pathogens reservoir

Sialolithiasis represents the most common disorders of salivary glands in middle-aged patients. It has been hypothesized that the retrograde migration of bacteria from the oral cavity to gland ducts may facilitate the formation of stones. Thus, in the present study, a microbiome characterization of salivary calculi was performed to evaluate the abundance and the potential correlations between microorganisms constituting the salivary calculi microbiota. Our data supported the presence of a core microbiota of sialoliths constituted principally by Streptococcus spp., Fusobacterium spp. and Eikenella spp., along with the presence of important pathogens commonly involved in infective sialoadenitis.

Cellular Components Mediating Coadherence of Candida albicans and Fusobacterium nucleatum

Candida albicans is an opportunistic fungal pathogen found as part of the normal oral flora. It can be coisolated with Fusobacterium nucleatum, an opportunistic bacterial pathogen, from oral disease sites, such as those involved in refractory periodontitis and pulp necrosis. The physical coadherence between these 2 clinically important microbes has been well documented and suggested to play a role in facilitating their oral colonization and colocalization and contributing to polymicrobial pathogenesis. Previous studies indicated that the physical interaction between C. albicans and F. nucleatum was mediated by the carbohydrate components on the surface of C. albicans and the protein components on the Fusobaterium cell surface. However, the identities of the components involved still remain elusive. This study was aimed at identifying the genetic determinants involved in coaggregation between the 2 species. By screening a C. albicans SN152 mutant library and a panel of F. nucleatum 23726 outer membrane protein mutants, we identified FLO9, which encodes a putative adhesin-like cell wall mannoprotein of C. albicans and radD, an arginine-inhibitable adhesin-encoding gene in F. nucleatum that is involved in interspecies coadherence. Consistent with these findings, we demonstrated that the strong coaggregation between wild-type F. nucleatum 23726 and C. albicans SN152 in an in vitro assay could be greatly inhibited by arginine and mannose. Our study also suggested a complex multifaceted mechanism underlying physical interaction between C. albicans and F. nucleatum and for the first time revealed the identity of major genetic components involved in mediating the coaggregation. These observations provide useful knowledge for developing new targeted treatments for disrupting interactions between these 2 clinically relevant pathogens.

L-arginine destabilizes oral multi-species biofilm communities developed in human saliva

The amino acid L-arginine inhibits bacterial coaggregation, is involved in cell-cell signaling, and alters bacterial metabolism in a broad range of species present in the human oral cavity. Given the range of effects of L-arginine on bacteria, we hypothesized that L-arginine might alter multi-species oral biofilm development and cause developed multi-species biofilms to disassemble. Because of these potential biofilm-destabilizing effects, we also hypothesized that L-arginine might enhance the efficacy of antimicrobials that normally cannot rapidly penetrate biofilms. A static microplate biofilm system and a controlled-flow microfluidic system were used to develop multi-species oral biofilms derived from pooled unfiltered cell-containing saliva (CCS) in pooled filter-sterilized cell-free saliva (CFS) at 37^oC. The addition of pH neutral L-arginine monohydrochloride (LAHCl) to CFS was found to exert negligible antimicrobial effects but significantly altered biofilm architecture in a concentration-dependent manner. Under controlled flow, the biovolume of biofilms (μm³/μm²) developed in saliva containing 100-500 mM LAHCl were up to two orders of magnitude less than when developed without LAHCI. Culture-independent community analysis demonstrated that 500 mM LAHCl substantially altered biofilm species composition: the proportion of Streptococcus and Veillonella species increased and the proportion of Gram-negative bacteria such as Neisseria and Aggregatibacter species was reduced. Adding LAHCl to pre-formed biofilms also reduced biovolume, presumably by altering cell-cell interactions and causing cell detachment. Furthermore, supplementing 0.01% cetylpyridinium chloride (CPC), an antimicrobial commonly used for the treatment of dental plaque, with 500 mM LAHCl resulted in greater penetration of CPC into the biofilms and significantly greater killing compared to a non-supplemented 0.01% CPC solution. Collectively, this work demonstrates that LAHCl moderates multi-species oral biofilm development and community composition and enhances the activity of CPC. The incorporation of LAHCl into oral healthcare products may be useful for enhanced biofilm control.

Fap2 of Fusobacterium nucleatum is a galactose-inhibitable adhesin involved in coaggregation, cell adhesion, and preterm birth

Fusobacterium nucleatum is a common oral anaerobe involved in periodontitis that is known to translocate and cause intrauterine infections. In the oral environment, F. nucleatum adheres to a large diversity of species, facilitating their colonization and creating biological bridges that stabilize the multispecies dental biofilm. Many of these interactions (called coadherences or coaggregations) are galactose sensitive. Galactose-sensitive interactions are also involved in the binding of F. nucleatum to host cells. Hemagglutination of some F. nucleatum strains is also galactose sensitive, suggesting that a single galactose-sensitive adhesin might mediate the interaction of fusobacteria with many partners and targets. In order to identify the fusobacterial galactose-sensitive adhesin, a system for transposon mutagenesis in fusobacteria was created. The mutant library was screened for hemagglutination deficiency, and three clones were isolated. All three clones were found to harbor the transposon in the gene coding for the Fap2 outer membrane autotransporter. The three fap2 mutants failed to show galactose-inhibitable coaggregation with Porphyromonas gingivalis and were defective in cell binding. A fap2 mutant also showed a 2-log reduction in murine placental colonization compared to that of the wild type. Our results suggest that Fap2 is a galactose-sensitive hemagglutinin and adhesin that is likely to play a role in the virulence of fusobacteria.

Physiological adaptations of key oral bacteria

Oral colonising bacteria are highly adapted to the various environmental niches harboured within the mouth, whether that means while contributing to one of the major oral diseases of caries, pulp infections, or gingival/periodontal disease or as part of a commensal lifestyle. Key to these infections is the ability to adhere to surfaces via a range of specialised adhesins targeted at both salivary and epithelial proteins, their glycans and to form biofilm. They must also resist the various physical stressors they are subjected to, including pH and oxidative stress. Possibly most strikingly, they have developed the ability to harvest both nutrient sources provided by the diet and those derived from the host, such as protein and surface glycans. We have attempted to review recent developments that have revealed much about the molecular mechanisms at work in shaping the physiology of oral bacteria and how we might use this information to design and implement new treatment strategies.

Ubiquitous sialometabolism present among oral fusobacteria

Fusobacterium nucleatum is a ubiquitous member of the human oral flora and is associated with the development of periodontitis and a variety of other types of polymicrobial infections of the mucosa. In the oral cavity, this species is one of the few that is prevalent in both healthy and diseased subgingival plaque. Using microarray analysis, we examined the transcriptional response of F. nucleatum subspecies nucleatum to whole blood in order to identify some of the genetic responses that might occur during the transition from health to disease. From these studies, we identified a sialic acid catabolism operon that was induced by the presence of blood. We subsequently confirmed that this operon was inducible by the presence of synthetic sialic acid, but we found no evidence suggesting sialic acid was used as a major carbon source. However, this organism was found to possess a de novo synthesized surface sialylation ability that is widely conserved among the various F. nucleatum subspecies as well as in F. periodonticum. We provide evidence that fusobacterial sialylation does occur in the oral cavity irrespective of health status. Interestingly, only a minority of fusobacterial cells exhibit surface sialylation within dental plaque, whereas most cells are uniformly sialylated when grown in pure culture. The implications of these results are discussed.

A proteomic investigation of Fusobacterium nucleatum alkaline-induced biofilms

Background

The Gram negative anaerobe Fusobacterium nucleatum has been implicated in the aetiology of periodontal diseases. Although frequently isolated from healthy dental plaque, its numbers and proportion increase in plaque associated with disease. One of the significant physico-chemical changes in the diseased gingival sulcus is increased environmental pH. When grown under controlled conditions in our laboratory, F. nucleatum subspecies polymorphum formed mono-culture biofilms when cultured at pH 8.2. Biofilm formation is a survival strategy for bacteria, often associated with altered physiology and increased virulence. A proteomic approach was used to understand the phenotypic changes in F. nucleatum cells associated with alkaline induced biofilms. The proteomic based identification of significantly altered proteins was verified where possible using additional methods including quantitative real-time PCR (qRT-PCR), enzyme assay, acidic end-product analysis, intracellular polyglucose assay and Western blotting.

Results

Of 421 proteins detected on two-dimensional electrophoresis gels, spot densities of 54 proteins varied significantly (p < 0.05) in F. nucleatum cultured at pH 8.2 compared to growth at pH 7.4. Proteins that were differentially produced in biofilm cells were associated with the functional classes; metabolic enzymes, transport, stress response and hypothetical proteins. Our results suggest that biofilm cells were more metabolically efficient than planktonic cells as changes to amino acid and glucose metabolism generated additional energy needed for survival in a sub-optimal environment. The intracellular concentration of stress response proteins including heat shock protein GroEL and recombinational protein RecA increased markedly in the alkaline environment. A significant finding was the increased abundance of an adhesin, Fusobacterial outer membrane protein A (FomA). This surface protein is known for its capacity to bind to a vast number of bacterial species and human epithelial cells and its increased abundance was associated with biofilm formation.

Conclusion

This investigation identified a number of proteins that were significantly altered by F. nucleatum in response to alkaline conditions similar to those reported in diseased periodontal pockets. The results provide insight into the adaptive mechanisms used by F. nucleatum biofilms in response to pH increase in the host environment.

Effect of a self-etching adhesive containing an antibacterial monomer on clinical periodontal parameters and subgingival microbiologic composition in orthodontic patients

INTRODUCTION

The aims of this study were to evaluate the effect of a self-etching adhesive system containing an antibacterial monomer on periodontal health and subgingival microbiologic composition in orthodontic patients and to compare it with a conventional adhesive system.

METHODS

A split-mouth design was chosen, and 15 patients were included in the study. Brackets in contralateral quadrants were bonded with either a conventional adhesive system (control) or a self-etching adhesive system that contained an antibacterial monomer. Clinical periodontal parameters including plaque index, gingival index, probing depths, and bleeding on probing were determined. Subgingival plaque samples were collected before bracket placement (T0) and at the 6-month follow-up (T1). The real-time TaqMan polymerase chain reaction assay was used to determine the subgingival counts of Porphyromonas gingivalis, Tannerella forsythensis, Prevotella intermedia, Aggregatibacter actinomycetemcomitans, Fusobacterium nucleatum, and Campylobacter rectus. For clinical periodontal parameters, analysis of covariance (ANCOVA) and, for bacterial counts, Wilcoxon tests were used for statistical comparisons at the P <0.05 level.

RESULTS

Clinical periodontal parameters were not changed, and they were not different between the groups from T0 to T1. T forsythensis and F nucleatum increased during the treatment period in both groups (P <0.05). The majority of the bacteria were T nucleatum at T0 and T1 in both groups. Changes in bacterial load from T0 to T1 were not different between groups except for T forsythensis and F nucleatum (P <0.05).

CONCLUSIONS

The use of an antibacterial monomer did not have an additional positive effect on clinical periodontal parameters. When used in bonding orthodontic brackets, the antibacterial monomer failed to reduce periodontopathogenic bacteria when compared with the conventional adhesive system during a 6-month treatment period.

Stick to your gums: mechanisms of oral microbial adherence

Studies on the adherence properties of oral bacteria have been a major focus in microbiology research for several decades. The ability of bacteria to adhere to the variety of surfaces present in the oral cavity, and to become integrated within the resident microbial communities, confers growth and survival properties. Molecular analyses have revealed several families of Gram-positive bacterial surface proteins, including serine-rich repeat, antigen I/II, and pilus families, that mediate adherence to a variety of salivary and oral bacterial receptors. In Gram-negative bacteria, pili, auto-transporters, and extracellular matrix-binding proteins provide components for host tissue recognition and building of complex microbial communities. Future studies will reveal in greater detail the binding pockets for these adhesin families and their receptors. This information will be crucial for the development of new inhibitors or vaccines that target the functional regions of bacterial proteins that are involved in colonization and pathogenesis.

Bacterial and host interactions of oral streptococci

The oral microbial flora comprises one of the most diverse human-associated biofilms. Its development is heavily influenced by oral streptococci, which are considered the main group of early colonizers. Their initial attachment determines the composition of later colonizers in the oral biofilm and impacts the health or disease status of the host. Thus, the role of streptococci in the development of oral diseases is best described in the context of bacterial ecology, which itself is further influenced by interactions with host epithelial cells, the immune system, and salivary components. The tractability of the oral biofilm makes it an excellent model system for studies of complex, biofilm-associated polymicrobial diseases. Using this system, numerous cooperative and antagonistic bacterial interactions have been demonstrated to occur within the community and with the host. In this review, several recent identified interactions are presented.

The oral microbiota: living with a permanent guest

The oral cavity of healthy individuals contains hundreds of different bacterial, viral, and fungal species. Many of these can associate to form biofilms, which are resistant to mechanical stress or antibiotic treatment. Most are also commensal species, but they can become pathogenic in responses to changes in the environment or other triggers in the oral cavity, including the quality of an individual's personal hygiene. The complexity of the oral microbiome is being characterized through the newly developed tools of metagenomics. How the microbiome of the oral cavity contributes to health and disease is attracting the interest of a growing number of cell biologists, microbiologists, and immunologists.

The Fusobacterium nucleatum outer membrane protein RadD is an arginine-inhibitable adhesin required for inter-species adherence and the structured architecture of multispecies biofilm

A defining characteristic of the suspected periodontal pathogen Fusobacterium nucleatum is its ability to adhere to a plethora of oral bacteria. This distinguishing feature is suggested to play an important role in oral biofilm formation and pathogenesis, with fusobacteria proposed to serve as central 'bridging organisms' in the architecture of the oral biofilm bringing together species which would not interact otherwise. Previous studies indicate that these bacterial interactions are mediated by galactose- or arginine-inhibitable adhesins although genetic evidence for the role and nature of these proposed adhesins remains elusive. To characterize these adhesins at the molecular level, the genetically transformable F. nucleatum strain ATCC 23726 was screened for adherence properties, and arginine-inhibitable adhesion was evident, while galactose-inhibitable adhesion was not detected. Six potential arginine-binding proteins were isolated from the membrane fraction of F. nucleatum ATCC 23726 and identified via mass spectroscopy as members of the outer membrane family of proteins in F. nucleatum. Inactivation of the genes encoding these six candidates for arginine-inhibitable adhesion and two additional homologues revealed that only a mutant derivative carrying an insertion in Fn1526 (now designated as radD) demonstrated significantly decreased co-aggregation with representatives of the gram-positive 'early oral colonizers'. Lack of the 350 kDa outer membrane protein encoded by radD resulted in the failure to form the extensive structured biofilm observed with the parent strain when grown in the presence of Streptococcus sanguinis ATCC 10556. These findings indicate that radD is responsible for arginine-inhibitable adherence of F. nucleatum and provides definitive molecular evidence that F. nucleatum adhesins play a vital role in inter-species adherence and multispecies biofilm formation.