Heterogeneity of virulence among strains of Bacteroides gingivalis

Defining Porphyromonas gingivalis strains associated with periodontal disease

Porphyromonas gingivalis, a Gram-negative anaerobic bacterium commonly found in human subgingival plaque, is a major etiologic agent for periodontitis and has been associated with multiple systemic pathologies. Many P. gingivalis strains have been identified and different strains possess different virulence factors. Current oral microbiome approaches (16S or shotgun) have been unable to differentiate P. gingivalis strains. This study presents a new approach that aims to improve the accuracy of strain identification, using a detection method based on sequencing of the intergenic spacer region (ISR) which is variable between P. gingivalis strains. Our approach uses two-step PCR to amplify only the P. gingivalis ISR region. Samples are then sequenced with an Illumina sequencer and mapped to specific strains. Our approach was validated by examining subgingival plaque from 153 participants with and without periodontal disease. We identified the avirulent strain ATCC33277/381 as the most abundant strain across all sample types. The W83/W50 strain was significantly enriched in periodontitis, with 13% of participants harboring that strain. Overall, this approach can have significant implications not only for the diagnosis and treatment of periodontal disease but also for other diseases where P. gingivalis or its toxins have been implicated, such as Alzheimer's disease.

Organotypic model of the gingiva for studying bacterial and viral pathogens implicated in periodontitis

Background

Three-dimensional (3D) tissue models bridge the gap between conventional two-dimensional cell cultures and animal models. The aim of this study was to develop an organotypic 3D gingival (OTG) model to provide a tool to investigate bacterial and viral pathogens in periodontitis.

Methods

The OTG model composed of gingival fibroblasts (GFs) and telomerase-immortalized gingival keratinocytes (TIGKs) was constructed and applied to study infections by Porphyromonas gingivalis and herpes simplex virus 1 (HSV-1). Immunohistochemical staining, confocal microscopy, qPCR, titration techniques, and colony-forming unit counts were applied to interrogate epithelial markers expression, monitor P. gingivalis and HSV-1 presence, and evaluate the immune response along with the efficiency of antimicrobial drugs.

Results

The OTG model resembled the morphology of the human gingiva. During infection, both pathogens penetrated deep into the tissue and persisted for a few days with P. gingivalis also forming a biofilm on the cell surface. The infection triggered the expression of inflammatory mediators in cells and both pathogens were efficiently eliminated by specific antimicrobials.

Conclusions

Presented OTG model constitutes a simple and convenient tool to study the interaction between bacterial and viral pathogens within the gingival tissue, including penetration, persistence and biofilm formation. It is also suitable to examine the efficiency of antimicrobial drugs.

Mirdza E. Neiders: A pioneer in oral pathology, oral health science research, and education

Over her near 60-year career, Mirdza E. (Mitzi) Neiders has served as a teacher, dentist, researcher, mentor, role-model, friend, and critic for thousands of faculty, students, and patients of the University at Buffalo School of Dental Medicine. One of the first women to serve on the dental school faculty, this article describes her journey and the great impact that she has made on dentistry and her community on the occasion of her retirement.

A Tale of Two Fimbriae: How Invasion of Dendritic Cells by Porphyromonas gingivalis Disrupts DC Maturation and Depolarizes the T-Cell-Mediated Immune Response

Porphyromonas gingivalis (P. gingivalis) is a unique pathogen implicated in severe forms of periodontitis (PD), a disease that affects around 50% of the US population. P. gingivalis is equipped with a plethora of virulence factors that it uses to exploit its environment and survive. These include distinct fimbrial adhesins that enable it to bind to other microbes, colonize inflamed tissues, acquire nutrients, and invade cells of the stroma and immune system. Most notable for this review is its ability to invade dendritic cells (DCs), which bridge the innate and adaptive immune systems. This invasion process is tightly linked to the bridging functions of resultant DCs, in that it can disable (or stimulate) the maturation function of DCs and cytokines that are secreted. Maturation molecules (e.g., MHCII, CD80/CD86, CD40) and inflammatory cytokines (e.g., IL-1b, TNFa, IL-6) are essential signals for antigen presentation and for proliferation of effector T-cells such as Th17 cells. In this regard, the ability of P. gingivalis to coordinately regulate its expression of major (fimA) and minor (mfa-1) fimbriae under different environmental influences becomes highly relevant. This review will, therefore, focus on the immunoregulatory role of P. gingivalis fimbriae in the invasion of DCs, intracellular signaling, and functional outcomes such as alveolar bone loss and immune senescence.

A PorX/PorY and σP Feedforward Regulatory Loop Controls Gene Expression Essential for Porphyromonas gingivalis Virulence

The PorX/PorY two-component system in the periodontal pathogen Porphyromonas gingivalis controls the expression of the por genes, encoding a type IX secretion system, and the sigP gene, encoding sigma factor σ^P. Previous results implied that PorX/PorY and σ^P formed a regulatory cascade because the PorX/PorY-activated σ^P enhanced the por genes, including porT, via binding to their promoters. We recently showed that PorX also binds to the por promoters, thus suggesting that an alternative mechanism is required for the PorX/PorY- and σ^P-governed expression. Here, our in vitro assays show the PorX response regulator binds to the sigP promoter at a sequence shared with the porT promoter and enhances its transcription, mediated by a reconstituted P. gingivalis RNA polymerase holoenzyme. Merely producing σ^P in trans fails to reverse the porT transcription in a porX mutant, which further argues against the action of the proposed regulatory cascade. An in vitro transcription assay using a reconstituted RNA polymerase-σ^P holoenzyme verifies the direct role of PorX in porT transcription, since transcription is enhanced by a pure PorX protein. Accordingly, we propose that the PorX/PorY system coordinates with σ^P to construct a coherent regulatory mechanism, known as the feedforward loop. Specifically, PorX will not only bind to the sigP promoter to stimulate the expression of σ^P, but also bind to the porT promoter to facilitate the RNA polymerase-σ^P-dependent transcription. Importantly, mutations at the porX and sigP genes attenuate bacterial virulence in a mouse model, demonstrating that this regulatory mechanism is essential for P. gingivalis pathogenesis. IMPORTANCE The anaerobic bacterium Porphyromonas gingivalis is not only the major etiologic agent for chronic periodontitis, but also prevalent in some common noncommunicable diseases such as cardiovascular disease, Alzheimer's disease, and rheumatoid arthritis. We present genetic, biochemical, and biological results to demonstrate that the PorX/PorY two-component system and sigma factor σ^P build a specific regulatory network to coordinately control transcription of the genes encoding the type IX secretion system, and perhaps also other virulence factors. Results in this study verify that the response regulator PorX stimulates the expression of the genes encoding both σ^P and the type IX secretion system by binding to their promoters. This study also provides evidence that σ^P, like the PorX/PorY system, contributes to P. gingivalis virulence in a mouse model.

The PorX/PorY system is a virulence factor of Porphyromonas gingivalis and mediates the activation of the type IX secretion system

PorX/PorY is a two-component system (TCS) of Porphyromonas gingivalis that governs transcription of numerous genes including those encoding a type IX secretion system (T9SS) for gingipain secretion and heme accumulation. Here, an in vitro analysis showed that the response regulator PorX specifically bound to two regions in the promoter of porT, a known PorX-regulated T9SS gene, thus demonstrating that PorX/PorY can directly regulate specific target genes. A truncated PorX protein containing the N-terminal receiver and effector domains retained a wild-type ability in both transcription regulation and heme accumulation, ruling out the role of the C-terminal ALP domain in gene regulation. The PorX/PorY system was the only TCS essential for heme accumulation and concomitantly responded to hemin to stimulate transcription of several known PorX-dependent genes in a concentration-dependent manner. We found that PorX/PorY activated the sigH gene, which encodes a sigma factor known for P. gingivalis adaptation to hydrogen peroxide (H₂O₂). Consistently, both ΔporX and ΔsigH mutants were susceptible to H₂O₂, suggesting a PorX/PorY-σ^H regulatory cascade to confer resistance to oxidative stress. Furthermore, the ΔporX mutant became susceptible to high hemin levels that could induce oxidative stress. Therefore, a possible reason why hemin activates PorX/PorY is to confer resistance to hemin-induced oxidative stress. We also demonstrated that PorX/PorY was essential for P. gingivalis virulence because the ΔporX mutant was avirulent in a mouse model. Specifically, this TCS was required for the repression of proinflammatory cytokines secreted by dendritic cells and T cells in the P. gingivalis–infected mice.

Porphyromonas gingivalis laboratory strains and clinical isolates exhibit different distribution of cell surface and secreted gingipains

Background: The cell-surface cysteine proteinases RgpA, RgpB (Arg-gingipain), and Kgp (Lys-gingipain) are major virulence factors of P. gingivalis, a keystone pathogen in the development of destructive periodontal disease. The gingipains function as proteinases and transpeptidases utilising small peptides such as glycylglycine as acceptor molecules. However, the characteristics of the gingipains from most P. gingivalis strains have not been determined.

Methods: We determined the phenotypes of a panel of P. gingivalis laboratory strains and global clinical isolates with respect to growth on blood agar plus whole-cell and vesicle-free culture supernatant (VFSN) Arg- and Lys-specific proteinase activities.

Results: The P. gingivalis isolates exhibited different growth characteristics and hydrolysis of haemoglobin in solid media. Whole-cell Arg-gingipain Vmax varied 5.8-fold and the whole cell Lys-gingipain V_max varied 2.1-fold across the strains. Furthermore, the P. gingivalis strains showed more than 107-fold variance in soluble Arg-gingipain activity in VFSN and more than 371-fold variance in soluble Lys-gingipain activity in VFSN. Glycylglycine and cysteine stimulated Arg- and Lys-specific cleavage activities of all strains. The stimulation by cysteine was in addition to its redox effect consistent with both glycylglycine and cysteine promoting transpeptidation.

Conclusion: The global P. gingivalis clinical isolates exhibit different Arg- and Lys‑gingipain activities with substantial variability in the level of soluble proteinases released into the environment.

Immunological Pathways Triggered by Porphyromonas gingivalis and Fusobacterium nucleatum: Therapeutic Possibilities?

Porphyromonas gingivalis (P. gingivalis) and Fusobacterium nucleatum (F. nucleatum) are Gram-negative anaerobic bacteria possessing several virulence factors that make them potential pathogens associated with periodontal disease. Periodontal diseases are chronic inflammatory diseases of the oral cavity, including gingivitis and periodontitis. Periodontitis can lead to tooth loss and is considered one of the most prevalent diseases worldwide. P. gingivalis and F. nucleatum possess virulence factors that allow them to survive in hostile environments by selectively modulating the host's immune-inflammatory response, thereby creating major challenges to host cell survival. Studies have demonstrated that bacterial infection and the host immune responses are involved in the induction of periodontitis. The NLRP3 inflammasome and its effector molecules (IL-1β and caspase-1) play roles in the development of periodontitis. We and others have reported that the purinergic P2X7 receptor plays a role in the modulation of periodontal disease and intracellular pathogen control. Caspase-4/5 (in humans) and caspase-11 (in mice) are important effectors for combating bacterial pathogens via mediation of cell death and IL-1β release. The exact molecular events of the host's response to these bacteria are not fully understood. Here, we review innate and adaptive immune responses induced by P. gingivalis and F. nucleatum infections and discuss the possibility of manipulations of the immune response as therapeutic strategies. Given the global burden of periodontitis, it is important to develop therapeutic targets for the prophylaxis of periodontopathogen infections.

Capsular-defective Porphyromonas gingivalis mutant strains induce less alveolar bone resorption than W50 wild-type strain due to a decreased Th1/Th17 immune response and less osteoclast activity

BACKGROUND

Encapsulation of Porphyromonas gingivalis has been demonstrated as responsible of several host immunological changes, which have been associated with the pathogenesis of periodontitis. Using a murine model of periodontitis and two isogenic non-capsulated mutants of P. gingivalis, this study aimed to analyze whether P. gingivalis encapsulation induces more severe alveolar bone resorption, and whether this bone loss is associated with a T-helper (Th)1 and Th17-pattern of immune response.

METHODS

Experimental periodontal infections were generated by oral inoculation with the encapsulated W50 wild-type strain or isogenic non-encapsulated ΔPG0116-PG0120 (GPA) and ΔPG0109-PG0118 (GPC) mutants of P. gingivalis. Periodontal infections induced with the encapsulated HG184 or non-encapsulated ATCC 33277 strains of P. gingivalis were used as controls. Alveolar bone resorption was analyzed using microcomputed tomography and scanning electron microscopy. The expression levels of Th1, Th2, Th17, or T regulatory-associated cytokines and RANKL, as well as the periodontal bacterial load, were quantified by quantitative polymerase chain reaction. The detection of Th1 and Th17 lymphocytes was analyzed by flow cytometry.

RESULTS

In the periodontal lesions, both capsular-defective knockout mutant strains of P. gingivalis induced less alveolar bone resorption than the encapsulated W50 wild-type strain. This decreased bone loss was associated with a dismissed RANKL expression, decreased Th1- and Th17-type of cytokine expression, reduced Th1 and Th17 lymphocyte detection, and low osteoclast finding.

CONCLUSION

These data demonstrate that encapsulation of P. gingivalis plays a key role in the alveolar bone resorption induced during periodontitis, and this bone loss is associated with a Th1- and Th17-pattern of immune response triggered in the periodontal lesions.

A Secreted Bacterial Peptidylarginine Deiminase Can Neutralize Human Innate Immune Defenses

The keystone oral pathogen Porphyromonas gingivalis is associated with severe periodontitis. Intriguingly, this bacterium is known to secrete large amounts of an enzyme that converts peptidylarginine into citrulline residues. The present study was aimed at identifying possible functions of this citrullinating enzyme, named Porphyromonas peptidylarginine deiminase (PPAD), in the periodontal environment. The results show that PPAD is detectable in the gingiva of patients with periodontitis, and that it literally neutralizes human innate immune defenses at three distinct levels, namely bacterial phagocytosis, capture in neutrophil extracellular traps (NETs), and killing by the lysozyme-derived cationic antimicrobial peptide LP9. As shown by mass spectrometry, exposure of neutrophils to PPAD-proficient bacteria reduces the levels of neutrophil proteins involved in phagocytosis and the bactericidal histone H2. Further, PPAD is shown to citrullinate the histone H3, thereby facilitating the bacterial escape from NETs. Last, PPAD is shown to citrullinate LP9, thereby restricting its antimicrobial activity. The importance of PPAD for immune evasion is corroborated in the infection model Galleria mellonella, which only possesses an innate immune system. Together, the present observations show that PPAD-catalyzed protein citrullination defuses innate immune responses in the oral cavity, and that the citrullinating enzyme of P. gingivalis represents a new type of bacterial immune evasion factor.IMPORTANCE Bacterial pathogens do not only succeed in breaking the barriers that protect humans from infection, but they also manage to evade insults from the human immune system. The importance of the present study resides in the fact that protein citrullination is shown to represent a new bacterial mechanism for immune evasion. In particular, the oral pathogen P. gingivalis employs this mechanism to defuse innate immune responses by secreting a protein-citrullinating enzyme. Of note, this finding impacts not only the global health problem of periodontitis, but it also extends to the prevalent autoimmune disease rheumatoid arthritis, which has been strongly associated with periodontitis, PPAD activity, and loss of tolerance against citrullinated proteins, such as the histone H3.

Involvement of PorK, a component of the type IX secretion system, in Prevotella melaninogenica pathogenicity

Prevotella melaninogenica is a gram-negative anaerobic commensal bacterium that resides in the human oral cavity and is isolated as a pathogen of suppurative diseases both inside and outside the mouth. However, little is known about the pathogenic factors of P. melaninogenica. The periodontal pathogens Porphyromonas gingivalis and Tanerella forsythia secrete virulence factors such as protease and bacterial cell surface proteins via a type IX secretion system (T9SS) that are involved in pathogenicity. P. melaninogenica also possesses all known orthologs of T9SS. In this study, a P. melaninogenica GAI 07411 mutant deficient in the orthologue of the T9SS-encoding gene, porK, was constructed. Hemagglutination and biofilm formation were decreased in the porK mutant. Furthermore, following growth on skim milk-containing medium, the diameters of the halos surrounding the porK mutant were smaller than those of the wild-type strain, suggesting a decrease in secretion of proteases outside the bacterium. To investigate this in detail, culture supernatants of wild-type and porK mutant strains were purified and compared by two-dimensional electrophoresis. In the mutant strain, fewer spots were detected, indicating fewer secreted proteins. In infection experiments, the mortality rate of mice inoculated with the porK mutant strain was significantly lower than in the wild-type strain. These results suggest that P. melaninogenica secretes potent virulence factors via the T9SS that contribute to its pathogenic ability.

Molecular mechanisms of Porphyromonas gingivalis-host cell interaction on periodontal diseases

Porphyromonas gingivalis (P. gingivalis) is a major oral pathogen and associated with periodontal diseases including periodontitis and alveolar bone loss. In this review, we indicate that two virulence factors, which are hemoglobin receptor protein (HbR) and cysteine proteases “gingipains”, expressed by P. gingivalis have novel functions on the pathogenicity of P. gingivalis. P. gingivalis produces three types of gingipains and concomitantly several adhesin domains. Among the adhesin domains, hemoglobin receptor protein (HbR), also called HGP15, has the function of induction of interleukin-8 (IL-8) expression in human gingival epithelial cells, indicating the possibility that HbR is associated with P. gingivalis-induced periodontal inflammation. On bacteria-host cells contact, P. gingivalis induces cellular signaling alteration in host cells. Phosphatidylinositol 3-kinase (PI3K) and Akt are well known to play a pivotal role in various cellular physiological functions including cell survival and glucose metabolism in mammalian cells. Recently, we demonstrated that gingipains attenuate the activity of PI3K and Akt, which might have a causal influence on periodontal diseases by chronic infection to the host cells from the speculation of molecular analysis. In this review, we discuss new molecular and biological characterization of the virulence factors from P. gingivalis.

Restriction Fragment Length Polymorphism Analysis of the Fimbrillin Locus, fimA, of Porphyromonas gingivalis

With hybridization probes derived from the fimbrial locus of Porphyromonas gingivalis strain 381, fimA381' restriction fragment length polymorphisms (RFLPs) were examined at the fimbrillin locus in 39 human and animal strains of this species. The 39 strains were subdivided into nine RFLP groups (I-IX) after genomic digests were probed with the internal coding sequence of the fimA381 gene. Thirty-three strains showed one or more AluI fragments of moderate-to-high homology (≥77%) with the internal coding sequence of fimA381. These strains were distributed into the first seven RFLP groups, based solely on the size of the major hybridizing AluI fragment. Five human strains (RFLP Group VIII) had only one Alu I fragment that hybridized very poorly with this probe. One animal strain did not have homology at all (RFLP Group IX). When all AluI fragments that hybridized with fimA381 were analyzed, RFLP groups I-VIII were further differentiated into 25 distinct RFLP patterns. Hybridizations were also performed with the internal coding sequence of fimA381 to probe PstI genomic digests of selected strains that appeared to have lesser homology with fimA381. These hybridizations were performed to determine the level and location of the region of poor homology within the fimA genes of these strains. The results suggested that fimbrial coding sequences are more commonly conserved between these strains in the 5'-region of the fimA locus (≥92% sequence homology). However, the five human strains of RFLP Group VIII had only one PstI fragment that hybridized very poorly with a probe derived from fimA381 coding sequence, and this sequence homology (only > 66%) was located in the central or 3'-end of the fimA gene. The 5'-region of the fimA allele in Group VIII strains did not have any detectable sequence homology. In contrast, the Group VIII strains were highly homologous with the sequences flanking the fimA381 gene. This indicates that these strains do possess a fimA allele at the same chromosomal location as fimA381.

Characterization of Fusobacterium nucleatum ATCC 23726 adhesins involved in strain-specific attachment to Porphyromonas gingivalis

Bacterial adherence is an essential virulence factor in pathogenesis and infection. Fusobacterium nucleatum has a central role in oral biofilm architecture by acting as a bridge between early Gram-positive and late Gram-negative colonizers that do not otherwise adhere to each other. In this study, we survey a key adherence interaction of F. nucleatum with Porphyromonas gingivalis, and present evidence that multiple fusobacterial adhesins have a role in the attachment of F. nucleatum ATCC 23726 to P. gingivalis in a highly strain-dependent manner. Interaction between these species displayed varying sensitivities to arginine, galactose and lactose. Arginine was found to hamper coaggregation by at least 62% and up to 89% with several P. gingivalis strains and galactose inhibition ranged from no inhibition up to 58% with the same P. gingivalis strains. Lactose consistently inhibited F. nucleatum interaction with these P. gingivalis strains ranging from 40% to 56% decrease in coaggregation. Among the adhesins involved are the previously described Fap2 and surprisingly, RadD, which was described in an earlier study for its function in attachment of F. nucleatum to Gram-positive species. We also provide evidence for the presence of at least one additional adhesin that is sensitive to arginine but unlike Fap2 and RadD, is not a member of the autotransporter family type of fusobacterial large outer membrane proteins. The strain-specific binding profile of multiple fusobacterial adhesins to P. gingivalis highlights the heterogeneity and complexity of interspecies interactions in the oral cavity.

Involvement of an Skp-Like Protein, PGN_0300, in the Type IX Secretion System of Porphyromonas gingivalis

The oral Gram-negative anaerobic bacterium Porphyromonas gingivalis is an important pathogen involved in chronic periodontitis. Among its virulence factors, the major extracellular proteinases, Arg-gingipain and Lys-gingipain, are of interest given their abilities to degrade host proteins and process other virulence factors. Gingipains possess C-terminal domains (CTDs) and are translocated to the cell surface or into the extracellular milieu by the type IX secretion system (T9SS). Gingipains contribute to the colonial pigmentation of the bacterium on blood agar. In this study, Omp17, the PGN_0300 gene product, was found in the outer membrane fraction. A mutant lacking Omp17 did not show pigmentation on blood agar and showed reduced proteolytic activity of the gingipains. CTD-containing proteins were released from bacterial cells without cleavage of the CTDs in the omp17 mutant. Although synthesis of the anionic polysaccharide (A-LPS) was not affected in the omp17 mutant, the processing of and A-LPS modification of CTD-containing proteins was defective. PorU, a C-terminal signal peptidase that cleaves the CTDs of other CTD-containing proteins, was not detected in any membrane fraction of the omp17 mutant, suggesting that the defective maturation of CTD-containing proteins by impairment of Omp17 is partly due to loss of function of PorU. In the mouse subcutaneous infection experiment, the omp17 mutant was less virulent than the wild type. These results suggested that Omp17 is involved in P. gingivalis virulence.

Evolutionary Divergence of Aggregatibacter actinomycetemcomitans

Gram-negative facultative Aggregatibacter actinomycetemcomitans is an oral pathogen associated with periodontitis. The genetic heterogeneity among A. actinomycetemcomitans strains has been long recognized. This study provides a comprehensive genomic analysis of A. actinomycetemcomitans and the closely related nonpathogenic Aggregatibacter aphrophilus. Whole genome sequencing by Illumina MiSeq platform was performed for 31 A. actinomycetemcomitans and 2 A. aphrophilus strains. Sequence similarity analysis shows a total of 3,220 unique genes across the 2 species, where 1,550 are core genes present in all genomes and 1,670 are variable genes (accessory genes) missing in at least 1 genome. Phylogenetic analysis based on 397 concatenated core genes distinguished A. aphrophilus and A. actinomycetemcomitans. The latter was in turn divided into 5 clades: clade b (serotype b), clade c (serotype c), clade e/f (serotypes e and f), clade a/d (serotypes a and d), and clade e' (serotype e strains). Accessory genes accounted for 14.1% to 23.2% of the A. actinomycetemcomitans genomes, with a majority belonging to the category of poorly characterized by Cluster of Orthologous Groups classification. These accessory genes were often organized into genomic islands (n = 387) with base composition biases, suggesting their acquisitions via horizontal gene transfer. There was a greater degree of similarity in gene content and genomic islands among strains within clades than between clades. Strains of clade e' isolated from human were found to be missing the genomic island that carries genes encoding cytolethal distending toxins. Taken together, the results suggest a pattern of sequential divergence, starting from the separation of A. aphrophilus and A. actinomycetemcomitans through gain and loss of genes and ending with the divergence of the latter species into distinct clades and serotypes. With differing constellations of genes, the A. actinomycetemcomitans clades may have evolved distinct adaptation strategies to the human oral cavity.

Porphyromonas gingivalis evasion of autophagy and intracellular killing by human myeloid dendritic cells involves DC-SIGN-TLR2 crosstalk

Signaling via pattern recognition receptors (PRRs) expressed on professional antigen presenting cells, such as dendritic cells (DCs), is crucial to the fate of engulfed microbes. Among the many PRRs expressed by DCs are Toll-like receptors (TLRs) and C-type lectins such as DC-SIGN. DC-SIGN is targeted by several major human pathogens for immune-evasion, although its role in intracellular routing of pathogens to autophagosomes is poorly understood. Here we examined the role of DC-SIGN and TLRs in evasion of autophagy and survival of Porphyromonas gingivalis in human monocyte-derived DCs (MoDCs). We employed a panel of P. gingivalis isogenic fimbriae deficient strains with defined defects in Mfa-1 fimbriae, a DC-SIGN ligand, and FimA fimbriae, a TLR2 agonist. Our results show that DC-SIGN dependent uptake of Mfa1+P. gingivalis strains by MoDCs resulted in lower intracellular killing and higher intracellular content of P. gingivalis. Moreover, Mfa1+P. gingivalis was mostly contained within single membrane vesicles, where it survived intracellularly. Survival was decreased by activation of TLR2 and/or autophagy. Mfa1+P. gingivalis strain did not induce significant levels of Rab5, LC3-II, and LAMP1. In contrast, P. gingivalis uptake through a DC-SIGN independent manner was associated with early endosomal routing through Rab5, increased LC3-II and LAMP-1, as well as the formation of double membrane intracellular phagophores, a characteristic feature of autophagy. These results suggest that selective engagement of DC-SIGN by Mfa-1+P. gingivalis promotes evasion of antibacterial autophagy and lysosome fusion, resulting in intracellular persistence in myeloid DCs; however TLR2 activation can overcome autophagy evasion and pathogen persistence in DCs.

Among the most successful of human microbes are intracellular pathogens. By entering the intracellular milieu, these pathogens are protected from harsh environmental factors in the host, including the humoral and cellular immune responses. Porphyromonas gingivalis is an opportunistic pathogen that colonizes the oral mucosa and accesses the bloodstream and distant sites such as the blood vessel walls, brain, placenta and other organs. Still unclear is how P. gingivalis traverses from oral mucosa to these distant sites. Dendritic cells are highly migratory antigen presenting cells that “patrol” the blood, skin, mucosa and all the major organ systems. Capture of microbes by dendritic cells activates a tightly regulated series of events, including directed migration towards the secondary lymphoid organs, where processed antigens are ostensibly presented to T cells. Autophagy is now recognized as an integral component of microbial clearance, antigen processing and presentation by dendritic cells. We report here that P. gingivalis is able to subvert autophagic destruction within dendritic cells. This occurs through its glycoprotein fimbriae, called Mfa-1, which targets the C-type lectin DC-SIGN on dendritic cells. The other major fimbriae on P. gingivalis, FimA, targets TLR2, which promotes autophagic destruction of P. gingivalis. We conclude that DC-SIGN-TLR2 crosstalk determines the intracellular fate of this pathogen within dendritic cells, and may have profound implications for the treatment of many chronic diseases involving low-grade infections.

The role of Porphyromonas gingivalis gingipains in platelet activation and innate immune modulation

Platelets are considered to have important functions in inflammatory processes and as actors in the innate immunity. Several studies have shown associations between cardiovascular disease and periodontitis, where the oral anaerobic pathogen Porphyromonas gingivalis has a prominent role in modulating the immune response. Porphyromonas gingivalis has been found in atherosclerotic plaques, indicating spreading of the pathogen via the circulation, with an ability to interact with and activate platelets via e.g. Toll-like receptors (TLR) and protease-activated receptors. We aimed to evaluate how the cysteine proteases, gingipains, of P. gingivalis affect platelets in terms of activation and chemokine secretion, and to further investigate the mechanisms of platelet-bacteria interaction. This study shows that primary features of platelet activation, i.e. changes in intracellular free calcium and aggregation, are affected by P. gingivalis and that arg-gingipains are of great importance for the ability of the bacterium to activate platelets. The P. gingivalis induced a release of the chemokine RANTES, however, to a much lower extent compared with the TLR2/1-agonist Pam3 CSK4 , which evoked a time-dependent release of the chemokine. Interestingly, the TLR2/1-evoked response was abolished by a following addition of viable P. gingivalis wild-types and gingipain mutants, showing that both Rgp and Kgp cleave the secreted chemokine. We also demonstrate that Pam3 CSK4 -stimulated platelets release migration inhibitory factor and plasminogen activator inhibitor-1, and that also these responses were antagonized by P. gingivalis. These results supports immune-modulatory activities of P. gingivalis and further clarify platelets as active players in innate immunity and in sensing bacterial infections, and as target cells in inflammatory reactions induced by P. gingivalis infection.

Immunization with malondialdehyde-modified low-density lipoprotein (LDL) reduces atherosclerosis in LDL receptor-deficient mice challenged with Porphyromonas gingivalis

Periodontal infections increase the risk of atherosclerotic vascular disease via partly unresolved mechanisms. Of the natural IgM Abs that recognize molecular mimicry on bacterial epitopes and modified lipid and protein structures, IgM directed against oxidized low-density lipoprotein (LDL) is associated with atheroprotective properties. Here, the effect of natural immune responses to malondialdehyde-modified LDL (MDA-LDL) in conferring protection against atherosclerosis, which was accelerated by the major periodontopathogen Porphyromonas gingivalis, was investigated. LDL receptor-deficient (LDLR(-/-)) mice were immunized with mouse MDA-LDL without adjuvant before topical application challenge with live P. gingivalis. Atherosclerosis was analyzed after a high-fat diet, and plasma IgG and IgM Ab levels were measured throughout the study, and the secretion of IL-5, IL-10 and IFN-γ in splenocytes stimulated with MDA-LDL was determined. LDLR(-/-) mice immunized with MDA-LDL had elevated IgM and IgG levels to MDA-LDL compared with saline-treated controls. MDA-LDL immunization diminished aortic lipid depositions after challenge with P. gingivalis compared with mice receiving only P. gingivalis challenge. Immunization of LDLR(-/-) mice with homologous MDA-LDL stimulated the production of IL-5, implicating general activation of B-1 cells. Immune responses to MDA-LDL protected from the P. gingivalis-accelerated atherosclerosis. Thus, the linkage between bacterial infectious burden and atherogenesis is suggested to be modulated via natural IgM directed against cross-reactive epitopes on bacteria and modified LDL.

The unique hmuY gene sequence as a specific marker of Porphyromonas gingivalis

Porphyromonas gingivalis, a major etiological agent of chronic periodontitis, acquires heme from host hemoproteins using the HmuY hemophore. The aim of this study was to develop a specific P. gingivalis marker based on a hmuY gene sequence. Subgingival samples were collected from 66 patients with chronic periodontitis and 40 healthy subjects and the entire hmuY gene was analyzed in positive samples. Phylogenetic analyses demonstrated that both the amino acid sequence of the HmuY protein and the nucleotide sequence of the hmuY gene are unique among P. gingivalis strains/isolates and show low identity to sequences found in other species (below 50 and 56%, respectively). In agreement with these findings, a set of hmuY gene-based primers and standard/real-time PCR with SYBR Green chemistry allowed us to specifically detect P. gingivalis in patients with chronic periodontitis (77.3%) and healthy subjects (20%), the latter possessing lower number of P. gingivalis cells and total bacterial cells. Isolates from healthy subjects possess the hmuY gene-based nucleotide sequence pattern occurring in W83/W50/A7436 (n = 4), 381/ATCC 33277 (n = 3) or TDC60 (n = 1) strains, whereas those from patients typically have TDC60 (n = 21), W83/W50/A7436 (n = 17) and 381/ATCC 33277 (n = 13) strains. We observed a significant correlation between periodontal index of risk of infectiousness (PIRI) and the presence/absence of P. gingivalis (regardless of the hmuY gene-based sequence pattern of the isolate identified [r = 0.43; P = 0.0002] and considering particular isolate pattern [r = 0.38; P = 0.0012]). In conclusion, we demonstrated that the hmuY gene sequence or its fragments may be used as one of the molecular markers of P. gingivalis.

Porphyromonas gingivalis fimbriae

Marginal periodontitis is not a homogeneous disease but is rather influenced by an intricate set of host susceptibility differences as well as diversities in virulence among the harbored organisms. It is likely that clonal heterogeneity of subpopulations with both high and low levels of pathogenicity exists among organisms harbored by individuals with negligible, slight, or even severe periodontal destruction. Therefore, specific virulent clones of periodontal pathogens may cause advanced and/or aggressive periodontitis. Porphyromonas gingivalis is a predominant periodontal pathogen that expresses a number of potential virulence factors involved in the pathogenesis of periodontitis, and accumulated evidence shows that its expression of heterogenic virulence properties is dependent on clonal diversity. Fimbriae are considered to be critical factors that mediate bacterial interactions with and invasion of host tissues, with P. gingivalis shown to express two distinct fimbria-molecules, long and short fimbriae, on the cell surface, both of which seem to be involved in development of periodontitis. Long fimbriae are classified into six types (I to V and Ib) based on the diversity of fimA genes encoding FimA (a subunit of long fimbriae). Studies of clones with type II fimA have revealed their significantly greater adhesive and invasive capabilities as compared to other fimA type clones. Long and short fimbriae induce various cytokine expressions such as IL-1α, IL-β, IL-6, and TNF-α, which result in alveolar bone resorption. Although the clonal diversity of short fimbriae is unclear, distinct short fimbria-molecules have been found in different strains. These fimbriae variations likely influence the development of periodontal disease.

Experimental periodontitis induced by Porphyromonas gingivalis does not alter the onset or severity of diabetes in mice

BACKGROUND AND OBJECTIVE

Diabetes mellitus is believed to increase the risk and severity of periodontitis. However, less evidence is available on the converse effects of periodontitis on diabetes. The objective of the study was to investigate to what degree experimental periodontitis induced by Porphyromonas gingivalis might influence the onset and severity of diabetes in different mouse models.

MATERIAL AND METHODS

Twenty-eight male Tallyho/JngJ mice (type 2 diabetes), 20 male streptozotocin-induced diabetes C57BL/6J mice (type 1 diabetes) and 20 male C57BL/6J mice at 4 wks of age were evenly divided into two groups: periodontal infection and sham infection. Periodontitis was induced by Porphyromonas gingivalis W50 (P. gingivalis) oral inoculation before the development of diabetes. Sham-infected mice received vehicle as control. P. gingivalis in the oral cavity were identified by quantitative polymerase chain reaction. Fasting glucose, body weight and food intake levels were monitored and glucose tolerance tests were performed to assess glucose homeostasis for the onset and progression of diabetes. The level of alveolar bone loss and tumor necrosis factor-alpha were determined in week 20 when mice were killed.

RESULTS

Mice in the infection groups developed more alveolar bone loss than those in sham-infection groups (Tallyho p = 0.021; C57-STZ p = 0.014; C57 p = 0.035). Hyperglycemic mice exhibited significantly more bone loss compared to those normal glucose mice (Tallyho vs. C57 p = 0.029; C57-STZ vs. C57 p = 0.024). The level of tumor necrosis factor-alpha was consistent with that of periodontal bone loss and hyperglycemia. There was no significant effect of mouse species on the amount of bone loss at the same level of blood glucose. No statistically significant difference or trend in glucose metabolism was found between the infection and sham-infection group.

CONCLUSION

Diabetes enhanced the risk for periodontal disease induced by P. gingivalis. However, no converse impact was found between this periodontal infection and onset and severity of diabetes in both type 1 and 2 diabetes mice.

Divergence of the systemic immune response following oral infection with distinct strains of Porphyromonas gingivalis

Periodontitis is a polymicrobial oral infection characterized by the destruction of tooth-supporting structures that can be linked to systemic diseases such as cardiovascular disease, diabetes or rheumatoid arthritis. Porphyromonas gingivalis, a bacterium implicated in the etiology of periodontitis, has shown variation in inducing T-cell responses among different strains. Therefore, in this study we investigated the strain-specific immune response using a murine experimental model of periodontitis. Periodontitis was induced by P. gingivalis strains A7A1-28, W83 and W50, and later confirmed by the presence of P. gingivalis in the oral microflora and by alveolar bone resorption. Splenocytes were evaluated for gene expression, cellular proteins and cytokine expression. Dendritic cells were stimulated in vitro for T helper cell-cytokine profiling. Results showed that P. gingivalis had the ability to alter the systemic immune response after bacterial exposure. Strains W50 and W83 were shown to induce alveolar bone loss, whereas the A7A1-28 strain did not significantly promote bone resorption in mice. Splenocytes derived from mice infected with strains W50 and W83 induced expression of high levels of interleukin-4 (IL-4) but A7A1-28 stimulated increased IL-10. Stimulation of dendritic cells in vitro showed a similar pattern of cytokine expression of IL-12p40, IL-6 and transforming growth factor-β among strains. A distinct systemic response in vivo was observed among different strains of P. gingivalis, with IL-10 associated with the least amount of alveolar bone loss. Evaluation of pathogen-driven systemic immune responses associated with periodontal disease pathogenesis may assist in defining how periodontitis may impact other diseases.

Strain-specific colonization patterns and serum modulation of multi-species oral biofilm development

Periodontitis results from an ecological shift in the composition of subgingival biofilms. Subgingival community maturation is modulated by inter-organismal interactions and the relationship of communities with the host. In an effort to better understand this process, we evaluated biofilm formation, with oral commensal species, by three strains of the subgingivally prevalent microorganism Fusobacterium nucleatum and four strains of the periodontopathogen Porphyromonas gingivalis. We also tested the effect of serum, which resembles gingival exudates, on subgingival biofilms. Biofilms were allowed to develop in flow cells using salivary medium. We found that although not all strains of F. nucleatum were able to grow in mono-species biofilms, forming a community with health-associated partners Actinomyces oris and Veillonella parvula promoted biofilm growth of all F. nucleatum strains. Strains of P. gingivalis also showed variable ability to form mono-species biofilms. P. gingivalis W50 and W83 did not form biofilms, while ATCC 33277 and 381 formed biofilm structures, but only strain ATCC 33277 grew over time. Unlike the enhanced growth of F. nucleatum with the two health-associated species, no strain of P. gingivalis grew in three-species communities with A. oris and V. parvula. However, addition of F. nucleatum facilitated growth of P. gingivalis ATCC 33277 with health-associated partners. Importantly, serum negatively affected the adhesion of F. nucleatum, while it favored biofilm growth by P. gingivalis. This work highlights strain specificity in subgingival biofilm formation. Environmental factors such as serum alter the colonization patterns of oral microorganisms and could impact subgingival biofilms by selectively promoting pathogenic species.

Natural competence is a major mechanism for horizontal DNA transfer in the oral pathogen Porphyromonas gingivalis

Porphyromonas gingivalis is a Gram-negative anaerobe that resides exclusively in the human oral cavity. Long-term colonization by P. gingivalis requires the bacteria to evade host immune responses while adapting to the changing host physiology and alterations in the composition of the oral microflora. The genetic diversity of P. gingivalis appears to reflect the variability of its habitat; however, little is known about the molecular mechanisms generating this diversity. Previously, our research group established that chromosomal DNA transfer occurs between P. gingivalis strains. In this study, we examine the role of putative DNA transfer genes in conjugation and transformation and demonstrate that natural competence mediated by comF is the dominant form of chromosomal DNA transfer, with transfer by a conjugation-like mechanism playing a minor role. Our results reveal that natural competence mechanisms are present in multiple strains of P. gingivalis, and DNA uptake is not sensitive to DNA source or modification status. Furthermore, extracellular DNA was observed for the first time in P. gingivalis biofilms and is predicted to be the major DNA source for horizontal transfer and allelic exchange between strains. We propose that exchange of DNA in plaque biofilms by a transformation-like process is of major ecological importance in the survival and persistence of P. gingivalis in the challenging oral environment.

P. gingivalis colonizes the oral cavities of humans worldwide. The long-term persistence of these bacteria can lead to the development of chronic periodontitis and host morbidity associated with tooth loss. P. gingivalis is a genetically diverse species, and this variability is believed to contribute to its successful colonization and survival in diverse human hosts, as well as evasion of host immune defenses and immunization strategies. We establish here that natural competence is the major driving force behind P. gingivalis DNA exchange and that conjugative DNA transfer plays a minor role. Furthermore, we reveal for the first time the presence of extracellular DNA in P. gingivalis biofilms, which is most likely the source of DNA exchanged between strains within dental plaque. These studies expand our understanding of the mechanisms used by this important member of the human oral flora to transition its relationship with the host from a commensal to a pathogenic relationship.

Porphyromonas gingivalis: a clonal pathogen?: Diversities in housekeeping genes and the major fimbriae gene

The introduction of multilocus sequence typing (MLST) in infectious disease research has allowed standardized typing of bacterial clones. Through multiple markers around the genome, it is possible to determine the sequence type (ST) of bacterial isolates to establish the population structure of a species. For the periodontal pathogen, Porphyromonas gingivalis, the MLST scheme has been established at www.pubmlst.org/pgingivalis, and data from the database indicate a high degree of genetic diversity and a weakly clonal population structure comparable with Neisseria menigitidis. The major fimbriae (FimA) have been held responsible for the adhesive properties of P. gingivalis and represent an important virulence factor. The fimA genotyping method (PCR based) indicate that fimA genotype II, IV and Ib are associated with diseased sites in periodontitis and tissue specimens from cardiovascular disease. fimA genotyping of the isolates in the MLST database supports the association of genotypes II and IV with periodontitis. As a result of multiple positive PCR reactions in the fimA genotyping, sequencing of the fimA gene revealed only minor nucleotide variation between isolates of the same and different genotypes, suggesting that the method should be redesigned or re-evaluated. Results from several investigations indicate a higher intraindividual heterogeneity of P. gingivalis than found earlier. Detection of multiple STs from one site in several patients with "refractory" periodontitis, showed allelic variation in two housekeeping genes indicating recombination between different clones within the periodontal pocket.

The capsule of Porphyromonas gingivalis leads to a reduction in the host inflammatory response, evasion of phagocytosis, and increase in virulence

Periodontal disease is a chronic oral inflammatory disease that is triggered by bacteria such as Porphyromonas gingivalis. P. gingivalis strains exhibit great heterogeneity, with some strains being encapsulated while others are nonencapsulated. Although the encapsulated strains have been shown to be more virulent in a mouse abscess model, so far the role of the capsule in P. gingivalis interactions with host cells is not well understood and its role in virulence has not been defined. Here, we investigated the contribution of the capsule to triggering a host response following microbial infection, as well as its protective role following bacterial internalization by host phagocytic cells with subsequent killing, using the encapsulated P. gingivalis strain W50 and its isogenic nonencapsulated mutant, PgC. Our study shows significant time-dependent upregulation of the expression of various groups of genes in macrophages challenged with both the encapsulated and nonencapsulated P. gingivalis strains. However, cells infected with the nonencapsulated strain showed significantly higher upregulation of 9 and 29 genes at 1 h and 8 h postinfection, respectively, than cells infected with the encapsulated strain. Among the genes highly upregulated by the nonencapsulated PgC strain were ones coding for cytokines and chemokines. Maturation markers were induced at a 2-fold higher rate in dendritic cells challenged with the nonencapsulated strain for 4 h than in dendritic cells challenged with the encapsulated strain. The rates of phagocytosis of the nonencapsulated P. gingivalis strain by both macrophages and dendritic cells were 4.5-fold and 7-fold higher, respectively, than the rates of phagocytosis of the encapsulated strain. On the contrary, the survival of the nonencapsulated P. gingivalis strain was drastically reduced compared to the survival of the encapsulated strain. Finally, the encapsulated strain exhibited greater virulence in a mouse abscess model. Our results indicate that the P. gingivalis capsule plays an important role in aiding evasion of host immune system activation, promoting survival of the bacterium within host cells, and increasing virulence. As such, it is a major virulence determinant of P. gingivalis.

Comparison of the virulence of exopolysaccharide-producing Prevotella intermedia to exopolysaccharide non-producing periodontopathic organisms

BACKGROUND

Evidence in the literature suggests that exopolysaccharides (EPS) produced by bacterial cells are essential for the expression of virulence in these organisms. Secreted EPSs form the framework in which microbial biofilms are built.

METHODS

This study evaluates the role of EPS in Prevotella intermedia for the expression of virulence. This evaluation was accomplished by comparing EPS-producing P. intermedia strains 17 and OD1-16 with non-producing P. intermedia ATCC 25611 and Porphyromonas gingivalis strains ATCC 33277, 381 and W83 for their ability to induce abscess formation in mice and evade phagocytosis.

RESULTS

EPS-producing P. intermedia strains 17 and OD1-16 induced highly noticeable abscess lesions in mice at 107 colony-forming units (CFU). In comparison, P. intermedia ATCC 25611 and P. gingivalis ATCC 33277, 381 and W83, which all lacked the ability to produce viscous materials, required 100-fold more bacteria (109 CFU) in order to induce detectable abscess lesions in mice. Regarding antiphagocytic activity, P. intermedia strains 17 and OD1-16 were rarely internalized by human polymorphonuclear leukocytes, but other strains were readily engulfed and detected in the phagosomes of these phagocytes.

CONCLUSIONS

These results demonstrate that the production of EPS by P. intermedia strains 17 and OD1-16 could contribute to the pathogenicity of this organism by conferring their ability to evade the host's innate defence response.

Porphyromonas gingivalis virulence in a Drosophila melanogaster model

Porphyromonas gingivalis has been implicated in the etiology of adult periodontitis. In this study, we examined the viability of Drosophila melanogaster as a new model for examining P. gingivalis-host interactions. P. gingivalis (W83) infection of Drosophila resulted in a systemic infection that killed in a dose-dependent manner. Differences in the virulence of several clinically prevalent P. gingivalis strains were observed in the Drosophila killing model, and the results correlated well with studies in mammalian infection models and human epidemiologic studies. P. gingivalis pathobiology in Drosophila did not result from uncontrolled growth of the bacterium in the Drosophila hemolymph (blood) or overt damage to Drosophila tissues. P. gingivalis killing of Drosophila was multifactorial, involving several bacterial factors that are also involved in virulence in mammals. The results from this study suggest that many aspects of P. gingivalis pathogenesis in mammals are conserved in Drosophila, and thus the Drosophila killing model should be useful for characterizing P. gingivalis-host interactions and, potentially, polymicrobe-host interactions.

Tetratricopeptide repeat protein-associated proteins contribute to the virulence of Porphyromonas gingivalis

Porphyromonas gingivalis is one of the most etiologically important microorganisms in periodontal disease. We found in a previous study that PG1385 (TprA) protein, a tetratricopeptide repeat (TPR) protein, was upregulated in P. gingivalis wild-type cells placed in a mouse subcutaneous chamber and that a tprA mutant was clearly less virulent in the mouse subcutaneous abscess model (M. Yoshimura et al., Oral Microbiol. Immunol. 23:413-418, 2008). In the present study, we investigated the gene expression profile of tprA mutant cells placed in a mouse subcutaneous chamber and found that 9 genes, including PG2102 (tapA), PG2101 (tapB), and PG2100 (tapC) genes, were downregulated in the tprA mutant compared with those in the wild type. Expression of a cluster of tapA, tapB, and tapC genes of the mutant was also downregulated in an in vitro culture with enriched brain heart infusion medium. The TprA protein has three TPR motifs known as a protein-protein interaction module. Yeast two-hybrid system analysis and in vitro protein binding assays with immunoprecipitation and surface plasmon resonance detection revealed that the TprA protein could bind to TapA and TapB proteins. TprA and TapB proteins were located in the periplasmic space, whereas TapA, which appeared to be one of the C-terminal domain family proteins, was located at the outer membrane. We constructed tapA, tapB, and tapC single mutants and a tapA-tapB-tapC deletion mutant. In the mouse subcutaneous infection experiment, all of the mutants were less virulent than the wild type. These results suggest that TprA, TapA, TapB, and TapC are cooperatively involved in P. gingivalis virulence.

The capsule of Porphyromonas gingivalis reduces the immune response of human gingival fibroblasts

BACKGROUND

Periodontitis is a bacterial infection of the periodontal tissues. The Gram-negative anaerobic bacterium Porphyromonas gingivalis is considered a major causative agent. One of the virulence factors of P. gingivalis is capsular polysaccharide (CPS). Non-encapsulated strains have been shown to be less virulent in mouse models than encapsulated strains.

RESULTS

To examine the role of the CPS in host-pathogen interactions we constructed an insertional isogenic P. gingivalis knockout in the epimerase-coding gene epsC that is located at the end of the CPS biosynthesis locus. This mutant was subsequently shown to be non-encapsulated. K1 capsule biosynthesis could be restored by in trans expression of an intact epsC gene. We used the epsC mutant, the W83 wild type strain and the complemented mutant to challenge human gingival fibroblasts to examine the immune response by quantification of IL-1beta, IL-6 and IL-8 transcription levels. For each of the cytokines significantly higher expression levels were found when fibroblasts were challenged with the epsC mutant compared to those challenged with the W83 wild type, ranging from two times higher for IL-1beta to five times higher for IL-8.

CONCLUSIONS

These experiments provide the first evidence that P. gingivalis CPS acts as an interface between the pathogen and the host that may reduce the host's pro-inflammatory immune response. The higher virulence of encapsulated strains may be caused by this phenomenon which enables the bacteria to evade the immune system.

NOD1 and NOD2 mediate sensing of periodontal pathogens

In bacterial infection, Nucleotide-binding Oligomerization Domain (NOD) 1 and NOD2 induce innate immune responses by recognizing fragments of the bacterial component peptidoglycan (PGN). To determine the roles of these receptors in detection of periodontal pathogens, we stimulated human embryonic kidney cells expressing NOD1 or NOD2 with heat-killed Porphyromonas gingivalis, Aggregatibacter actinomycetemcomitans, and Fusobacterium nucleatum or their soluble PGNs (sPGNs). All bacteria and their sPGNs could stimulate activation of NF-kappaB. However, there were differences in NOD1- and NOD2-stimulatory activities among the species of bacteria. P. gingivalis showed weaker NOD1- and NOD2-stimulatory activities than did other bacteria. These differences in activities were confirmed by production of interleukin-8 from oral epithelial cells stimulated with sPGNs. These findings indicate that both NOD1 and NOD2 might be involved in the recognition of periodontal pathogens, and that the weak NOD-stimulatory property of P. gingivalis might be helpful for survival in the periodontal pocket.

Porphyromonas gingivalis strain diversity

Porphyromonas gingivalis is implicated in the etiology of chronic periodontitis. Genotyping studies suggest that genetic variability exists among P. gingivalis strains; however, the extent of variability remains unclear and regions of variability remain largely unidentified. To assess P. gingivalis strain diversity, we previously used heteroduplex analysis of the ribosomal operon intergenic spacer region (ISR) to type strains in clinical samples and identified 22 heteroduplex types. Additionally, we used ISR sequence analysis to determine the relatedness of P. gingivalis strains to one another and demonstrated a link between ISR sequence phylogeny and the disease-associated phenotype of the strains. In the current study, heteroduplex analysis of the ISR was used to determine the worldwide genetic variability and distribution of P. gingivalis, and microarray-based comparative genomic hybridization (CGH) analysis was used to more comprehensively examine the variability of major heteroduplex type strains by using the entire genome. Heteroduplex analysis of clinical samples from geographically diverse populations identified 6 predominant geographically widespread heteroduplex types (prevalence, > or = 5%) and 14 rare heteroduplex types (prevalence, <2%) which are found in one or a few locations. CGH analysis of the genomes of seven clinically prevalent heteroduplex type strains identified 133 genes from strain W83 that were divergent in at least one of the other strains. The relatedness of the strains to one another determined on the basis of genome content (microarray) analysis was highly similar to their relatedness determined on the basis of ISR sequence analysis, and a striking correlation between the genome contents and disease-associated phenotypes of the strains was observed.

Fusobacterium nucleatum enhances invasion of human gingival epithelial and aortic endothelial cells by Porphyromonas gingivalis

Invasion by Porphyromonas gingivalis has been proposed as a possible mechanism of pathogenesis in periodontal and cardiovascular diseases. Porphyromonas gingivalis have direct access to the systemic circulation and endothelium in periodontitis patients by transient bacteremia. Periodontitis can be described as one of the predominant polymicrobial infections of humans. In the present study, P. gingivalis strains were tested for their ability to invade a human gingival epithelial cell line (Ca9-22) and human aortic endothelial cells in coinfection with Fusobacterium nucleatum using antibiotic protection assays. Coinfection with F. nucleatum resulted in 2-20-fold increase in the invasion of host cells by P. gingivalis strains. The invasive abilities of P. gingivalis strains were significantly greater when incubated with a F. nucleatum clinical isolate (which possesses strong biofilm-forming ability), than when incubated with a F. nucleatum-type strain. In inhibition assays with metabolic inhibitors, a difference in inhibition profiles was observed between mono- and polymicrobial infections. Collectively, our results suggest that F. nucleatum facilitates invasion of host cells by P. gingivalis. Investigations of polymicrobial infection of host cells should improve our understanding of the role of P. gingivalis in periodontal infection and proatherogenic mechanisms.

Proteome analysis of Porphyromonas gingivalis cells placed in a subcutaneous chamber of mice

INTRODUCTION

Porphyromonas gingivalis, an oral anaerobic bacterium, is considered a major pathogen for chronic periodontitis. Pathogenic bacteria usually upregulate or downregulate gene expression to combat the protective responses of their hosts.

METHODS

To determine what protein is regulated when P. gingivalis cells invade host tissues, we analyzed the proteome of P. gingivalis cells that were placed in a mouse subcutaneous chamber by two-dimensional gel electrophoresis and mass spectrometry.

RESULTS

Fourteen proteins were upregulated, while four proteins were downregulated. We focused on three upregulated proteins, PG1089 (DNA-binding response regulator RprY), PG1385 (TPR domain protein), and PG2102 (immunoreactive 61-kDa antigen), and constructed mutant strains that were defective in these proteins. Mouse abscess model experiments revealed that the mutant strain defective in PG1385 was clearly less virulent than the wild-type parent strain.

CONCLUSION

These results indicate that the PG1385 protein is involved in P. gingivalis virulence and that the method used here is useful when investigating the P. gingivalis proteins responsible for virulence.

Porphyromonas gingivalis RgpA-Kgp proteinase-adhesin complexes penetrate gingival tissue and induce proinflammatory cytokines or apoptosis in a concentration-dependent manner

The RgpA-Kgp proteinase-adhesin complexes of Porphyromonas gingivalis were observed, using immunostaining, in human gingival tissue associated with periodontitis but not in healthy tissue. The staining pattern suggested a concentration gradient from the subgingival plaque into the subjacent gingival connective tissue. Intense immunostaining was observed in areas displaying gross disturbance of tissue architecture. P. gingivalis cells and the RgpA-Kgp complexes at low concentrations were shown to stimulate secretory intercellular adhesion molecule 1, interleukin-8 (IL-8), IL-6, and macrophage chemoattractant protein secretion from cultured human epithelial (KB) and fibroblast (MRC-5) cells. However, at high concentrations a reduction in the level of these mediators was observed. In contrast, macrophage inflammatory protein 1alpha and IL-1alpha were stimulated only at high P. gingivalis cell concentrations. P. gingivalis cells and the RgpA-Kgp complexes were shown to induce apoptosis in KB and MRC-5 cells in a time- and dose-dependent manner. These data suggest that the RgpA-Kgp complexes penetrate the gingival connective tissue; at low concentrations distal from the plaque the complexes stimulate the secretion of proinflammatory mediators, while at high concentrations proximal to the plaque they induce apoptosis and attenuate the secretion of proinflammatory mediators.

The role of the RgpA-Kgp proteinase-adhesin complexes in the adherence of Porphyromonas gingivalis to fibroblasts

Porphyromonas gingivalis strains W50 and ATCC 33277 were shown to bind to cultured human fibroblast (MRC-5) cells using flow cytometry. As the concentration of P. gingivalis strain W50 cells was increased relative to the concentration of MRC-5 cells, the number of W50 cells bound per MRC-5 cell increased, as did the percentage of MRC-5 cells with bacteria bound. However, this relationship was only seen for P. gingivalis strain ATCC 33277 at low cell concentrations: at high bacterial cell concentrations strain ATCC 33277 auto-aggregated and binding to the MRC-5 cells decreased. Strain W50 was therefore chosen to study the role of the surface proteinase-adhesin complexes (RgpA-Kgp complexes) in binding to MRC-5 cells. P. gingivalis W50 cells treated with an inhibitor of the RgpA-Kgp complexes exhibited reduced binding to MRC-5 cells. The purified active and proteinase-inactive RgpA-Kgp complexes competitively inhibited binding of W50 to MRC-5 cells, and isogenic mutants of W50 lacking RgpA/B and Kgp displayed reduced binding. P. gingivalis W50 mutant cells lacking Kgp exhibited the lowest binding to MRC-5 cells, suggesting an important role for this proteinase and its associated adhesins in binding to fibroblasts.

Prevalence and clonal analysis of Porphyromonas gingivalis in primary endodontic infections

This study investigated the prevalence of Porphyromonas gingivalis in 62 teeth with primary endodontic infections by using a species-specific 16S rRNA gene-based nested polymerase chain reaction assay. P. gingivalis isolates recovered from 2 infected root canals were also analyzed for clonal diversity by using arbitrarily primed PCR. Overall, P. gingivalis was found in 48% of the samples. This species was specifically detected in 36% of canals of teeth with chronic apical periodontitis, in 46% of the cases of acute apical periodontitis, and in 67% of acute apical abscesses. P. gingivalis was significantly more frequent in abscess aspirates than in canals of teeth with chronic apical periodontitis (P < .05). Typing of colonies retrieved from 2 infected canals revealed 2 clones per individual. These findings confirmed that P. gingivalis can be an important endodontic pathogen, mostly associated with acute abscesses, and demonstrated that different clonal types of this species can colonize the root canal in the same individual.

Genetic diversity of Porphyromonas gingivalis isolates recovered from single "refractory" periodontitis sites

Multilocus sequence typing and fimA genotyping were performed on Porphyromonas gingivalis isolates from 15 subjects with "refractory" periodontitis. Several sequence types were detected for most individual pockets. The variation indicated recombination at the recA and pepO genes. The prevalence of fimA genotypes II and IV confirmed their association with periodontitis.

Invasive differences among Porphyromonas gingivalis strains from healthy and diseased periodontal sites

BACKGROUND AND OBJECTIVE

The purpose of this study was to determine any difference between Porphyromonas gingivalis isolates from periodontally healthy sites as compared to those from diseased sites with respect to the ability to invade host cells.

MATERIAL AND METHODS

Subgingival plaque samples were obtained from periodontally healthy and diseased sites using paper points. P. gingivalis colonies were isolated and tested, using an antibiotic protection assay, for their ability to invade KB cells. P. gingivalis 381 and Escherichia coli MC1061 were used as controls.

RESULTS

Mean values of 16.79 +/- 0.86 x 10(3) colony-forming units/mL and 26.14 +/- 2.11 x 10(3) colony-forming units/mL were observed in invasion assays for isolates from periodontally healthy and diseased sites, respectively. P. gingivalis present in diseased sites had significantly greater invasive abilities than strains isolated from healthy sites. No statistical difference was noted between male or female subjects concerning the degree of invasion; isolates from diseased sites from both genders had significantly greater invasion abilities than those from healthy sites. A significant correlation was found between the increased invasive capabilities of P. gingivalis isolates vs. an increased probing depth.

CONCLUSION

The increased invasion noted with P. gingivalis isolates from diseased sites vs. healthy sites, and the increased invasive capabilities with increasing probing depth, indicate that P. gingivalis isolates have a varying ability to invade host cells in the periodontal pocket.

Application of 16O/18O reverse proteolytic labeling to determine the effect of biofilm culture on the cell envelope proteome of Porphyromonas gingivalis W50

Porphyromonas gingivalis is an oral pathogen linked to chronic periodontitis. The bacterium exists as part of a polymicrobial biofilm accreted onto the tooth surface. An understanding of the changes to the proteome especially of the cell envelope of biofilm cells compared with planktonic cells could provide valuable insight into the molecular processes of biofilm formation. To establish which proteins changed in abundance between the planktonic and biofilm growth states, the cell envelope fractions of two biological replicates of P. gingivalis cultivated in a chemostat were analysed. Proteins were separated by 1-D SDS-PAGE, in-gel digested with trypsin in the presence of H216O or H218O and identified and quantified by LC-MALDI TOF/TOF-MS. Using a reverse labeling strategy we identified and quantified the changes in abundance of 81 P. gingivalis cell envelope proteins. No form of bias between the labels was observed. Twenty four proteins increased in abundance and 18 decreased in abundance in the biofilm state. A group of cell-surface located C-Terminal Domain family proteins including RgpA, HagA, CPG70 and PG99 increased in abundance in the biofilm cells. Other proteins that exhibited significant changes in abundance included transport related proteins (HmuY and IhtB), metabolic enzymes (FrdAB) and immunogenic proteins.

Identification of the genes associated with a virulent strain of Porphyromonas gingivalis using the subtractive hybridization technique

BACKGROUND/AIMS

Porphyromonas gingivalis, a major etiological organism implicated in periodontal disease, can be classified into virulent and avirulent strains. Our aim was to identify a gene for the virulence of P. gingivalis.

METHODS

The subtractive hybridization technique was employed to identify the genes specific to P. gingivalis W83, a virulent strain. In this study, P. gingivalis W83 was used as the tester strain, and P. gingivalis ATCC 33277 was the driver strain. The prevalence of W83-specific genes was determined by Southern blot analysis of several P. gingivalis strains.

RESULTS

We obtained 575 colonies using the subtractive hybridization technique. From among these, 26 DNA fragments were subjected to a homology search using the BLAST program. Compared with strain ATCC 33277, strain W83 contained 12 unique clones. The specificities of the isolated DNA fragments were analyzed among four P. gingivalis strains by Southern blot analysis. Five genes showed specificity for strain W83 compared with strain ATCC 33277. All five genes were also identified in strain W50.

CONCLUSIONS

The subtractive hybridization technique was effective in screening the two strains for specific DNA sequences, some of which might be responsible for determining virulence. The results suggested that several genes specific to strain W83 were associated with its virulence. Further analysis of these DNA fragments will provide important information on the pathogenesis of virulent P. gingivalis strains.

fimA genotypes and multilocus sequence types of Porphyromonas gingivalis from patients with periodontitis

Fimbriae are important virulence factors of pathogenic bacteria, facilitating their attachment to host and bacterial cells. In the periodontal pathogen Porphyromonas gingivalis, the fimA gene is classified into six types (genotypes I, Ib, II, III, IV, and V) on the basis of different nucleotide sequences, with fimA genotypes II and IV being prevalent in isolates from patients with periodontitis. The aims of this study were to examine the distribution of fimA genotypes in a collection of 82 P. gingivalis isolates from adult periodontitis patients of worldwide origin and to investigate the relationship between the fimA genotypes and the sequence types (STs), as determined by multilocus sequence typing (MLST), of the isolates. The fimA gene was amplified by PCR with primer sets specific for each genotype. The STs of all strains were assigned according to the MLST database for P. gingivalis (www.pubmlst.org/pgingivalis). The 82 strains showed extensive genetic diversity and were assigned to 69 STs. Only isolates with closely related STs harbored the same fimA genotype. Twenty-eight (34.1%) strains harbored fimA genotype II, while only the reference strain for fimA genotype V reacted with the primers specific for this genotype. Twenty-one isolates (25.6%) were positive by more than one of the fimA PCR assays; the most frequent combinations were genotypes I, Ib, and II (eight isolates) and genotypes I and II (four isolates). Sequencing of the fimA gene from selected isolates did not support the observed specific fimA genotype combinations, suggesting that the genotyping method used for the major fimbriae in P. gingivalis should be reevaluated.