Immunoglobulin G response of periodontitis patients to Porphyromonas gingivalis capsular carbohydrate and lipopolysaccharide antigens

A Novel Regulation of K-antigen Capsule Synthesis in Porphyromonas gingivalis Is Driven by the Response Regulator PG0720-Directed Antisense RNA

The periodontal pathogen Porphyromonas gingivalis strain W83 displays at least three different surface glycans, specifically two types of lipopolysaccharides (O-LPS and A-LPS) and K-antigen capsule. Despite the importance of K-antigen capsule to the virulence of P. gingivalis, little is known as to how expression of genes involved in the synthesis of this surface glycan is regulated. The genes required for K-antigen capsule synthesis are located in a locus that encodes a number of transcripts, including an operon (PG0104 to PG0121, generating ~19.4-kb transcript) which contains a non-coding 77-bp inverted repeat (77 bpIR) region near the 5'-end. Previously, we identified a 550-nucleotide antisense RNA molecule (designated asSuGR for antisense Surface Glycan Regulator) encoded within the 77-bpIR element that influences the synthesis of surface glycans. In this study, we demonstrate that the DNA-binding response regulator PG0720 can bind the promoter region of asSuGR and activate expression of asSuGR, indicating that PG0720 may indirectly influence transcript levels of the K-antigen capsule operon expressed from the sense strand. The data show that deletion of the PG0720 gene confers a defect in the presentation of surface polysaccharides compared with the parent strain and quantitative RT-PCR (qPCR) analysis determined that the overall expression of genes involved in K-antigen capsule synthesis were down-regulated in the PG0720 mutant. Furthermore, the defects of the PG0720 deletion mutant were restored by complementation. Importantly, the PG0720 deletion mutant showed reduced virulence. Altogether, our data show that the response regulator PG0720 regulates expression of asSuGR, a trans-acting antisense RNA molecule involved in modulating the production of surface polysaccharides in P. gingivalis strain W83. The data provide further evidence that surface glycans are key virulence determinants and significantly advances our understanding of the molecular mechanisms controlling the synthesis of P. gingivalis K-antigen capsule, a key virulence determinant.

A Porphyromonas gingivalis Capsule-Conjugate Vaccine Protects From Experimental Oral Bone Loss

Periodontal diseases are chronic inflammatory diseases of the periodontium that result in progressive destruction of the soft and hard tissues supporting the teeth, and it is the most common cause of tooth loss among adults. In the US alone, over 100 million individuals are estimated to have periodontal disease. Subgingival bacteria initiate and sustain inflammation, and, although several bacteria have been associated with periodontitis, Porphyromonas gingivalis has emerged as the key etiological organism significantly contributing to the disease. Currently, intensive clinical maintenance strategies are deployed to mitigate the further progression of disease in afflicted individuals; however, these treatments often fail to stop disease progression, and, as such, the development of an effective vaccine for periodontal disease is highly desirable. We generated a conjugate vaccine, comprising of the purified capsular polysaccharide of P. gingivalis conjugated to eCRM®, a proprietary and enhanced version of the CRM197 carrier protein with predetermined conjugation sites (Pg-CV). Mice immunized with alum adjuvanted Pg-CV developed robust serum levels of whole organism-specific IgG in comparison to animals immunized with unconjugated capsular polysaccharide alone. Using the murine oral bone loss model, we observed that mice immunized with the capsule-conjugate vaccine were significantly protected from the effects of P. gingivalis-elicited oral bone loss. Employing a preclinical model of infection-elicited oral bone loss, our data support that a conjugate vaccine incorporating capsular polysaccharide antigen is effective in reducing the main clinical endpoint of periodontal disease-oral bone destruction. Further development of a P. gingivalis capsule-based conjugate vaccine for preventing periodontal diseases is supported.

Alzheimer's Disease-Like Pathology Triggered by Porphyromonas gingivalis in Wild Type Rats Is Serotype Dependent

Periodontal disease is a disease of tooth-supporting tissues. It is a chronic disease with inflammatory nature and infectious etiology produced by a dysbiotic subgingival microbiota that colonizes the gingivodental sulcus. Among several periodontal bacteria, Porphyromonas gingivalis (P. gingivalis) highlights as a keystone pathogen. Previous reports have implied that chronic inflammatory response and measurable bone resorption are observed in young mice, even after a short period of periodontal infection with P. gingivalis, which has been considered as a suitable model of experimental periodontitis. Also, encapsulated P. gingivalis strains are more virulent than capsular-defective mutants, causing an increased immune response, augmented osteoclastic activity, and accrued alveolar bone resorption in these rodent experimental models of periodontitis. Recently, P. gingivalis has been associated with Alzheimer’s disease (AD) pathogenesis, either by worsening brain pathology in AD-transgenic mice or by inducing memory impairment and age-dependent neuroinflammation middle-aged wild type animals. We hypothesized here that the more virulent encapsulated P. gingivalis strains could trigger the appearance of brain AD-markers, neuroinflammation, and cognitive decline even in young rats subjected to a short periodontal infection exposure, due to their higher capacity of activating brain inflammatory responses. To test this hypothesis, we periodontally inoculated 4-week-old male Sprague-Dawley rats with K1, K2, or K4 P. gingivalis serotypes and the K1-isogenic non-encapsulated mutant (GPA), used as a control. 45-days after periodontal inoculations with P. gingivalis serotypes, rat´s spatial memory was evaluated for six consecutive days in the Oasis maze task. Following functional testing, the animals were sacrificed, and various tissues were removed to analyze alveolar bone resorption, cytokine production, and detect AD-specific biomarkers. Strikingly, only K1 or K2 P. gingivalis-infected rats displayed memory deficits, increased alveolar bone resorption, pro-inflammatory cytokine production, changes in astrocytic morphology, increased Aβ1-42 levels, and Tau hyperphosphorylation in the hippocampus. None of these effects were observed in rats infected with the non-encapsulated bacterial strains. Based on these results, we propose that the bacterial virulence factors constituted by capsular polysaccharides play a central role in activating innate immunity and inflammation in the AD-like pathology triggered by P. gingivalis in young rats subjected to an acute experimental infection episode.

Changes in lipopolysaccharide profile of Porphyromonas gingivalis clinical isolates correlate with changes in colony morphology and polymyxin B resistance

Virulence factors on the surface of Porphyromonas gingivalis constitute the first line of interaction with host cells and contribute to immune modulation and periodontitis progression. In order to characterize surface virulence factors present on P. gingivalis, we obtained clinical isolates from healthy and periodontitis subjects and compared them with reference strains. Colony morphology, aggregation in liquid medium, surface charge, membrane permeability to bactericidal compounds, novobiocin and polymyxin B resistance, capsule presence and lipopolysaccharide (LPS) profiles were evaluated. By comparing isolates from healthy and periodontitis subjects, differences in colony morphology and aggregation in liquid culture were found; the latter being similar to two reference strains. These differences were not a consequence of variations in bacterial surface charge. Furthermore, isolates also presented differences in polymyxin B and novobiocin resistance; isolates from healthy subjects were susceptible to polymyxin B and resistant to novobiocin and, in contrast, isolates from periodontitis subjects were resistant to polymyxin B and susceptible to novobiocin. These changes in antimicrobial resistance levels correlate with variations in LPS profiles, since -unlike periodontitis isolates-isolates from healthy samples synthesize LPS molecules lacking both O-antigen moieties and anionic polysaccharide. Additionally, this phenotype correlated with the absence of O-antigen ligase activity. Altogether, our results reveal novel variations on surface components of P. gingivalis isolates obtained from healthy and periodontitis subjects that could be associated with differences in bacterial virulence and periodontitis progression.

Deletion of a 77-base-pair inverted repeat element alters the synthesis of surface polysaccharides in Porphyromonas gingivalis

Bacterial cell surface glycans, such as capsular polysaccharides and lipopolysaccharides (LPS), influence host recognition and are considered key virulence determinants. The periodontal pathogen Porphyromonas gingivalis is known to display at least three different types of surface glycans: O-LPS, A-LPS, and K-antigen capsule. We have shown that PG0121 (in strain W83) encodes a DNABII histone-like protein and that this gene is transcriptionally linked to the K-antigen capsule synthesis genes, generating a large ∼19.4-kb transcript (PG0104-PG0121). Furthermore, production of capsule is deficient in a PG0121 mutant strain. In this study, we report on the identification of an antisense RNA (asRNA) molecule located within a 77-bp inverted repeat (77bpIR) element located near the 5' end of the locus. We show that overexpression of this asRNA decreases the amount of capsule produced, indicating that this asRNA can impact capsule synthesis in trans. We also demonstrate that deletion of the 77bpIR element and thereby synthesis of the large 19.4-kb transcript also diminishes, but does not eliminate, capsule synthesis. Surprisingly, LPS structures were also altered by deletion of the 77bpIR element, and reactivity to monoclonal antibodies specific to both O-LPS and A-LPS was eliminated. Additionally, reduced reactivity to these antibodies was also observed in a PG0106 mutant, indicating that this putative glycosyltransferase, which is required for capsule synthesis, is also involved in LPS synthesis in strain W83. We discuss our finding in the context of how DNABII proteins, an antisense RNA molecule, and the 77bpIR element may modulate expression of surface polysaccharides in P. gingivalis.

IMPORTANCE

The periodontal pathogen Porphyromonas gingivalis displays at least three different types of cell surface glycans: O-LPS, A-LPS, and K-antigen capsule. We have shown using Northern analysis that the K-antigen capsule locus encodes a large transcript (∼19.4 kb), encompassing a 77-bp inverted repeat (77bpIR) element near the 5' end. Here, we report on the identification of an antisense RNA (asRNA) encoded within the 77bpIR. We show that overexpression of this asRNA or deletion of the element decreases the amount of capsule. LPS structures were also altered by deletion of the 77bpIR, and reactivity to monoclonal antibodies to both O-LPS and A-LPS was eliminated. Our data indicate that the 77bpIR element is involved in modulating both LPS and capsule synthesis in P. gingivalis.

Can the oral microflora affect oral ulcerative mucositis?

PURPOSE OF REVIEW

Oral mucositis is one of the most prevalent toxicities after hematopoietic stem cell transplantation. Mucositis is initiated by the chemotherapy or radiotherapy preceding the transplantation. It is commonly accepted that microorganisms play a role in the process of oral mucositis. Despite the upcoming techniques to determine the whole oral bacterial ecosystem, the exact role of the microflora in mucositis is not yet understood. This article provides an overview of the state-of-the-art research on the oral microflora and mucositis.

RECENT FINDINGS

A shift in microflora, in both the intestine and the oral cavity, can be found after chemotherapy or radiation therapy. The presence of oral ulcerative mucositis coincides with the presence of periodontitis-associated bacteria, in particular Porphyromonas gingivalis. Moreover, this bacterium can inhibit wound healing processes in an in-vitro model.

SUMMARY

We come to realize that some diseases are associated with a shift in the microflora. The role of the microflora in oral and intestinal mucositis is gaining more attention in recent literature. In the oral cavity, periodontitis-associated bacteria may influence the healing of ulcerations and the role they play in mucositis may be more subtle and complicated than was previously thought.

In vitro invasion and survival of Porphyromonas gingivalis in gingival fibroblasts; role of the capsule

Porphyromonas gingivalis is a Gram-negative, anaerobic bacterium involved in periodontitis and peri-implantitis that can invade and survive inside host cells in vitro. P. gingivalis can invade human gingival fibroblasts (GF), but no data are available about the role of P. gingivalis' capsule in GF invasion. In the current study, we aimed to determine the ability of three strains of P. gingivalis (encapsulated wild type W83, non-encapsulated HG91 and the non-encapsulated insertional isogenic knockout mutant of W83, ΔEpsC) to invade GF and the ability of internalized P. gingivalis to survive in vitro antibiotic treatment. The ability of P. gingivalis strains to invade GF was tested using an antibiotic protection assay at multiplicity of infection (MOI) 100 and 1000. The survival of internalized P. gingivalis cells was further analyzed by subsequent in vitro treatment with either metronidazole or amoxicillin alone or a combination of metronidazole and amoxicillin and anaerobic culture viability counts. All strains of P. gingivalis used in this study were able to invade GFs. The non-encapsulated mutant of W83 (ΔEpsC mutant) was significantly more invasive than the wild type W83 at MOI 100 (p value 0.025) and MOI 1000 (p value 0.038). Furthermore, internalized P. gingivalis was able to resist in vitro antibiotic treatment. As demonstrated by the differences in invasion efficiencies of P. gingivalis strain W83 and its isogenic mutant ΔEpsC, the capsule of P. gingivalis makes it less efficient in invading gingival fibroblasts. Moreover, internalized P. gingivalis can survive antibiotic treatment in vitro.

Relationship between periodontitis-related antibody and frequent exacerbations in chronic obstructive pulmonary disease

Background

To identify patients with chronic obstructive pulmonary disease (COPD) who are susceptible to frequent exacerbations is important. Although periodontitis aggravated by poor oral hygiene might increase the risk of lower respiratory tract infection, the relationship between periodontitis and COPD exacerbations remains unknown. This prospective cohort study investigates the relationship between periodontitis-related antibody and exacerbation frequency over a one-year period.

Methods

We assessed an IgG antibody titer against Porphyromonas gingivalis, which is a major pathogen of periodontitis, and then prospectively followed up 93 individuals over one year to detect exacerbations.

Results

The numbers of exacerbations and the rate of individuals with frequent exacerbations (at least two per year) were significantly lower in patients with higher IgG titer than those with normal IgG titer (0.8 vs. 1.2 per year, p  = 0.045 and 14.3 vs. 38.6%, p  = 0.009, respectively). Multivariate logistic regression analysis showed that being normal-IgG titer for periodontitis-related antibody significantly increased the risk of frequent exacerbations (relative risk, 5.27, 95% confidence interval, 1.30–25.7; p  = 0.019) after adjusting for other possible confounders, such as a history of exacerbations in the past year, disease severity, COPD medication and smoking status.

Conclusions

Normal-IgG titer for periodontitis-related antibody can be an independent predictor of frequent exacerbations. Measuring periodontitis-related antibody titers might be useful to identify patients with susceptibility to frequent exacerbations so that an aggressive prevention strategy can be designed.

Porphyromonas gingivalis: an invasive and evasive opportunistic oral pathogen

Porphyromonas gingivalis is a Gram-negative oral anaerobe that is involved in the pathogenesis of periodontitis, an inflammatory disease that destroys the tissues supporting the tooth, eventually leading to tooth loss. Porphyromonas gingivalis has can locally invade periodontal tissues and evade the host defence mechanisms. In doing so, it utilizes a panel of virulence factors that cause deregulation of the innate immune and inflammatory responses. The present review discusses the invasive and evasive strategies of P. gingivalis and the role of its major virulence factors in these, namely lipopolysaccharide, capsule, gingipains and fimbriae. Moreover, the role of P. gingivalis as a 'keystone' biofilm species in orchestrating a host response, is highlighted.

Relationship between serum antibody titres to Porphyromonas gingivalis and hs-CRP levels as inflammatory markers of periodontitis

OBJECTIVE

The present study was designed to investigate whether titres of antibody to two strains of Porphyromonas gingivalis, FDC381 and SU63, are associated with serum high-sensitivity C-reactive protein (hs-CRP) levels in Japanese periodontitis patients.

DESIGN

Forty-nine patients with moderate to advanced periodontitis and 40 periodontally healthy control subjects were included in this study. hs-CRP levels and antibody titres to P. gingivalis were measured at baseline and reassessment 3-4 months after periodontal treatment in periodontitis patients as well as at the time of examination in the periodontally healthy subjects. Further, the effect of periodontal therapy, including surgical treatment and use of antibacterials on both markers, was analysed in patients.

RESULTS

hs-CRP levels and antibody titres to P. gingivalis were higher in periodontitis patients than in control subjects, and they significantly decreased following periodontal treatment (p < 0.005). Also, a significant decrease in hs-CRP levels as a result of periodontal treatment was found in patients with hs-CRP levels >1 mgl(-1) at baseline (p < 0.005). Probing depth, clinical attachment level, and alveolar bone loss in patients were significantly associated with a higher antibody titre to both strains of P. gingivalis (p < 0.05), but were not related to hs-CRP levels. No relationship was observed between hs-CRP levels and tertiles as defined by titres of antibody to P. gingivalis strains FDC381 and SU63.

CONCLUSIONS

Our data indicate that hs-CRP levels were independent of antibody titres to P. gingivalis in Japanese periodontitis patients.

Prognosis of periodontitis recurrence after intensive periodontal treatment using examination of serum IgG antibody titer against periodontal bacteria

Chronic periodontitis is associated with systemic diseases such as atherosclerosis. In this study, we evaluated the efficacy of serum IgG antibody titer to periodontal bacteria for prognosis of periodontitis recurrence during supportive periodontal therapy (SPT) phase. The 139 patients during SPT phase were selected and divided to two groups as follows: "Stable" and "Recurrence" group at SPT phase for case-control study: "High IgG titer" and "Normal IgG titer" group before transition to SPT phase for cohort study. We examined whether clinical findings or serum IgG antibody titers to periodontal bacteria are risk factors for the development of periodontitis recurrence. Case-control study showed that there were significant differences between the stable and recurrence groups in age and number of teeth. The serum IgG antibody titer to Eikenella corrodens FDC1073, Porphyromonas gingivalis SU63, and Campylobacter rectus ATCC33238 was significantly higher in the recurrence group. Next, we found, that the recurrence ratio in the high IgG titer group to Gram-negative obligate anaerobe, Prevotella intermedia, Treponema denticola, and C. rectus was significantly higher than that of the normal IgG titer group. Taken together, serum IgG antibody titer test is useful in the prognosis of periodontitis recurrence during the SPT phase.

Feasibility and therapeutic strategies of vaccines against Porphyromonas gingivalis

Periodontitis is a chronic infectious disease that is highly prevalent worldwide and is characterized by inflammation of the gums, and loss of connective tissue and bone support. The Gram-negative anerobic bacterium Porphyromonas gingivalis is generally accepted as the main etiological agent for chronic periodontitis. The objective of this paper is to elucidate the feasibility of achieving protection against periodontitis though immunization against P. gingivalis. Until now, animal studies have showed no complete protection against P. gingivalis. However, current knowledge about P. gingivalis structures could be applicable for further research to develop a successful licensed vaccine and alternative therapeutic strategies. This review reveals that a multicomponent vaccine against P. gingivalis, which includes structures shared among P. gingivalis serotypes, will be feasible to induce broad and complete protection.

Immunoglobulin G (IgG) class, but Not IgA or IgM, antibodies to peptides of the Porphyromonas gingivalis chaperone HtpG predict health in subjects with periodontitis by a fluorescence enzyme-linked immunosorbent assay

Chaperones are molecules found in all cells and are critical in stabilization of synthesized proteins, in repair/removal of defective proteins, and as immunodominant antigens in innate and adaptive immunity. Subjects with gingivitis colonized by the oral pathogen Porphyromonas gingivalis previously demonstrated levels of anti-human chaperone Hsp90 that were highest in individuals with the best oral health. We hypothesized that similar antibodies to pathogen chaperones might be protective in periodontitis. This study examined the relationship between antibodies to P. gingivalis HtpG and clinical statuses of healthy and periodontitis-susceptible subjects. We measured the humoral responses (immunoglobulin G [IgG], IgA, and IgM) to peptides of a unique insert (P18) found in Bacteroidaceae HtpG by using a high-throughput, quantitative fluorescence enzyme-linked immunosorbent assay. Indeed, higher levels of IgG class anti-P. gingivalis HtpG P18 peptide (P < 0.05) and P18alpha, consisting of the N-terminal 16 amino acids of P18 (P < 0.05), were associated with better oral health; these results were opposite of those found with anti-P. gingivalis whole-cell antibodies and levels of the bacterium in the subgingival biofilm. When we examined the same sera for IgA and IgM class antibodies, we found no significant relationship to subject clinical status. The relationship between anti-P18 levels and clinical populations and individual subjects was found to be improved when we normalized the anti-P18alpha values to those for anti-P18gamma (the central 16 amino acids of P18). That same ratio correlated with the improvement in tissue attachment gain after treatment (P < 0.05). We suggest that anti-P. gingivalis HtpG P18alpha antibodies are protective in periodontal disease and may have prognostic value for guidance of individual patient treatment.

Immunization of Macaca fascicularis against experimental periodontitis using a vaccine containing cysteine proteases purified from Porphyromonas gingivalis

INTRODUCTION

Periodontitis is a common infectious disease to which Porphyromonas gingivalis has been closely linked, in which the attachment tissues of the teeth and their alveolar bone housing are destroyed. We conducted a study to determine if immunization using a purified antigen could alter the onset and progression of the disease.

METHODS

Using the ligature-induced model of periodontitis in Macaca fascicularis, we immunized five animals with cysteine protease purified from P. gingivalis and used an additional five animals as controls. Alveolar bone loss was measured by digital subtraction radiography.

RESULTS

Immunization induced high titers of specific immunoglobuin G serum antibodies that were opsonic. Total bacterial load, levels of P. gingivalis in subgingival plaque and levels of prostaglandin E(2) in gingival crevicular fluid were significantly reduced. Onset and progression of alveolar bone loss was inhibited by approximately 50%. No manifestations of toxicity were observed.

CONCLUSIONS

Immunization using a purified protein antigen from P. gingivalis inhibits alveolar bone destruction in a ligature-induced periodontitis model in M. fascicularis.

Differential interactions of fimbriae and lipopolysaccharide from Porphyromonas gingivalis with the Toll-like receptor 2-centred pattern recognition apparatus

The lipopolysaccharide (LPS) and fimbriae of Porphyromonas gingivalis play important roles in periodontal inflammation and pathogenesis. We investigated fimbriae and LPS from several P. gingivalis strains in terms of relative dependence on Toll-like receptor (TLR) signalling partners or accessory pattern-recognition molecules mediating ligand transfer to TLRs, and determined induced assembly of receptor complexes in lipid rafts. Fimbriae could utilize TLR1 or TLR6 for cooperative TLR2-dependent activation of transfected cell lines, in contrast to LPS and a mutant version of fimbriae which displayed preference for TLR1. Whether used to activate human cell lines or mouse macrophages, fimbriae exhibited strong dependence on membrane-expressed CD14 (mCD14), which could not be substituted for by soluble CD14 (sCD14). In contrast, sCD14 efficiently substituted for mCD14 in LPS-induced cellular activation. LPS-binding protein was more important for LPS- than for fimbria-induced cell activation, whereas the converse was true for CD11b/CD18. Cell activation by LPS or fimbriae required lipid raft function and formation of heterotypic receptor complexes (TLR1-2/CD14/CD11b/CD18), although wild-type fimbriae additionally recruited TLR6. In summary, TLR2 activation by P. gingivalis LPS or fimbriae involves differential dependence on accessory signalling or ligand-binding receptors, which may differentially influence innate immune responses.

The K1 serotype capsular polysaccharide of Porphyromonas gingivalis elicits chemokine production from murine macrophages that facilitates cell migration

Porphyromonas gingivalis is the principal organism associated with aggressive forms of generalized periodontal disease. Previous reports have suggested that encapsulated P. gingivalis strains are more virulent than unencapsulated strains; however, the contribution of capsular polysaccharide (CPS) to the virulence of this organism is poorly understood. Since periodontal disease presents with a complex inflammatory cell lesion comprised of neutrophils and monocytes, we cultured murine peritoneal macrophages with heat-killed P. gingivalis W83, CPS purified from P. gingivalis strain W83, and the seven known serotype-specific P. gingivalis CPS and assessed the ability of supernatant fluids produced by challenged macrophages to attract naïve inflammatory cells. We also defined JE/MCP-1, KC, MIP-2, and RANTES production in response to the P. gingivalis CPS antigens. We observed that supernatant fluids collected from macrophages incubated with P. gingivalis W83 and serotype K1 CPS stimulated the migration of naïve murine bone marrow-derived polymorphonuclear leukocytes in an in vitro cell migration chamber. CPS from W83 and the K1 serotype elicited potent chemokine secretion patterns for macrophages, while those specific to serotypes K2 to K7 were significantly less stimulatory. Reverse transcription-PCR and enzyme-linked immunosorbent assay revealed JE/MCP-1, KC, MIP-2, and RANTES expression from murine macrophages which had been challenged with purified P. gingivalis W83 CPS. Chemokine production appeared to be dependent on both the dose of and time of exposure to P. gingivalis W83 CPS. These data demonstrate that the P. gingivalis serotype K1 CPS elicits chemokine production from phagocytic cells. Furthermore, these data suggest that the host response to this antigen may contribute to the formation of the inflammatory cell lesion observed during P. gingivalis-elicited periodontal disease.

Coaggregation of Porphyromonas gingivalis and Fusobacterium nucleatum PK 1594 is mediated by capsular polysaccharide and lipopolysaccharide

Previous reports have shown that coaggregation between Porphyromonas gingivalis and Fusobacterium nucleatum, two important periodontopathogens, is mediated by a galactoside on the surface of P. gingivalis and a lectin on F. nucleatum. In the present study, purified capsular polysaccharide (CPS) and lipopolysaccharide (LPS) of P. gingivalis PK 1924 (serotype K5) were found to be able to bind to F. nucleatum cells and to inhibit binding of F. nucleatum to P. gingivalis serotype K5. Sugar binding studies showed that the requirements for binding of P. gingivalis serotype K5 CPS and LPS to the F. nucleatum lectin are: the presence of a metal divalent ion, an axial free hydroxyl group at position 4 and free equatorial hydroxyl groups at position 3 and 6 of d-galactose. These data suggest that P. gingivalis serotype K5- CPS and LPS act as receptors mediating coaggregation between P. gingivalis and fusobacteria.

Identification and characterization of the capsular polysaccharide (K-antigen) locus of Porphyromonas gingivalis

Capsular polysaccharides of gram-negative bacteria play an important role in maintaining the structural integrity of the cell in hostile environments and, because of their diversity within a given species, can act as useful taxonomic aids. In order to characterize the genetic locus for capsule biosynthesis in the oral gram-negative bacterium Porphyromonas gingivalis, we analyzed the genome of P. gingivalis W83 which revealed two candidate loci at PG0106-PG0120 and PG1135-PG1142 with sufficient coding capacity and appropriate gene functions based on comparisons with capsule-coding loci in other bacteria. Insertion and deletion mutants were prepared at PG0106-PG0120 in P. gingivalis W50-a K1 serotype. Deletion of PG0109-PG0118 and PG0116-PG0120 both yielded mutants which no longer reacted with antisera to K1 serotypes. Restriction fragment length polymorphism analysis of the locus in strains representing all six K-antigen serotypes and K(-) strains demonstrated significant variation between serotypes and limited conservation within serotypes. In contrast, PG1135-PG1142 was highly conserved in this collection of strains. Sequence analysis of the capsule locus in strain 381 (K(-) strain) demonstrated synteny with the W83 locus but also significant differences including replacement of PG0109-PG0110 with three unique open reading frames, deletion of PG0112-PG0114, and an internal termination codon within PG0106, each of which could contribute to the absence of capsule expression in this strain. Analysis of the Arg-gingipains in the capsule mutants of strain W50 revealed no significant changes to the glycan modifications of these enzymes, which indicates that the glycosylation apparatus in P. gingivalis is independent of the capsule biosynthetic machinery.

Critical pathways in microbial virulence

The virulence of a microbe represents a combination of complex factors including the agent's transmissibility and the severity of the disease associated with infection and is also significantly influenced by the susceptibility of the colonized host. Virulence factors may be defined as those products of the organism which are required to complete the various stages of the life cycle leading to pathology in the host. In this review, we examine some of the approaches which have been adopted in other fields of infectious disease in order to categorically identify virulence factors using a classical genetics approach with relevant models or human subjects. The absence of an accurate experimental model for periodontal disease means that our understanding of the microbial virulence determinants and pathways in this disease remains hypothetical and based largely on observations in vitro. However, factors which enable the organism to persist in spite of the elevated immune and inflammatory pressure at sites of disease are liable to be critical. Periodontal bacterial genomics is liable to make a significant impact on the field through an increased appreciation of the role of gene acquisition and gene loss in the evolution of periodontal bacteria and of the consequences of strain variation in gene content on virulence potential.

Major outer membrane proteins from Porphyromonas gingivalis: strain variation, distribution, and clinical significance in periradicular lesions

Porphyromonas gingivalis has been implicated in both marginal periodontitis and periapical infection. This study examined the major outer membrane proteins, from P. gingivalis, which related to periradicular lesions. Outer membrane protein profiles of P. gingivalis ATCC 33277 and W83 were compared by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and N-terminal amino acid analysis. Most outer membrane proteins, such as RagA, gingipains, and OmpA-like proteins, were found in both strains in a similar distribution pattern; however, the migration positions of Lys-gingipain and RagB were inverted in SDS-PAGE. Western blot analysis showed that RagA, RagB, and OmpA-like proteins were found in all of the P. gingivalis strains tested. The antiserum of W83 against RagB reacted poorly to some strains, such as ATCC 33277. When strains phylogenetically related to P. gingivalis were examined, RagA and OmpA homologs were immunologically detected in several strains. However, none of the RagB homologs were detected in any strain analyzed, suggesting that RagB is unique to P. gingivalis. To examine immunoreactive antigens in P. gingivalis, sera from patients with periradicular lesions were used. More than half of the sera showed strong reactions to P. gingivalis cell components, especially RagB. Our results indicate that a major outer membrane protein, RagB, is a possible virulence factor in periradicular lesions.

Structural analysis of a novel anionic polysaccharide fromPorphyromonas gingivalisstrain W50 related to Arg-gingipain glycans

The Arg-gingipains (RgpsA and B) of Porphyromonas gingivalis are a family of extracellular cysteine proteases and are important virulence determinants of this periodontal bacterium. A monoclonal antibody, MAb1B5, which recognizes an epitope on glycosylated monomeric RgpAs also cross-reacts with a cell-surface polysaccharide of P. gingivalis W50 suggesting that the maturation pathway of the Arg-gingipains may be linked to the biosynthesis of a surface carbohydrate. We report the purification and structural characterization of the cross-reacting anionic polysaccharide (APS), which is distinct from both the lipopolysaccharide and serotype capsule polysaccharide of P. gingivalis W50. The structure of APS was determined by 1D and 2D NMR spectroscopy and methylation analysis, which showed it to be a phosphorylated branched mannan. The backbone is built up of alpha-1,6-linked mannose residues and the side-chains contain alpha-1,2-linked mannose oligosaccharides of different lengths (one to two sugar residues) attached to the backbone via 1,2-linkage. One of the side-chains in the repeating unit contains Manalpha1-2Manalpha1-phosphate linked via phosphorus to a backbone mannose at position 2. De-O-phosphorylation of APS abolished cross-reactivity suggesting that Manalpha1-2Manalpha1-phosphate fragment forms part of the epitope recognized by MAb1B5. This phosphorylated branched mannan represents a novel polysaccharide that is immunologically related to the post-translational additions of Arg-gingipains.

Humoral responses to Porphyromonas gingivalis gingipain adhesin domains in subjects with chronic periodontitis

The gingipains have been implicated in the pathogenicity of Porphyromonas gingivalis, a major etiologic agent of chronic periodontitis. Mature gingipains often present as a membrane-bound glycosylated proteinase-adhesin complex comprising multiple adhesin domains (HA1 to -4) and a catalytic domain. Using recombinant adhesin domains, we were able to show that patients with chronic periodontitis produce significantly more immunoglobulin G reactive with gingipain domains than a corresponding group with healthy periodontium. Titers were predominantly directed toward the carbohydrate epitopes shared between the gingipains and the lipopolysaccharide of P. gingivalis with little recognition of the peptide backbone of the catalytic domains. Distribution of titers to peptide epitopes of the adhesin domains was as follows: HA4 approximately HA1 > HA3 >> HA2. No correlation was observed between markers of disease severity and titers to individual adhesins within the disease group. Posttreatment titers showed no change or a decrease in titers for the majority of patients except for titers to the HA2 domain which showed marked increases in a few responding patients. Since the HA2 domain is important in hemoglobin binding and acquisition of essential porphyrin, boosting titers of antibodies to this domain may have the potential to control the growth of this organism.

Immunization with Porphyromonas gingivalis capsular polysaccharide prevents P. gingivalis-elicited oral bone loss in a murine model

The capsular polysaccharide (CPS) of the periodontal pathogen Porphyromonas gingivalis is an important virulence factor for this organism. We purified P. gingivalis CPS, immunized mice with this antigen, and assessed the vaccine potential of P. gingivalis CPS by using the murine oral challenge model. Animals immunized with P. gingivalis CPS developed elevated levels of immunoglobulin M (IgM) and IgG in serum that reacted with whole P. gingivalis organisms. The mice immunized with P. gingivalis CPS were protected from P. gingivalis-elicited oral bone loss. These data demonstrate that P. gingivalis CPS is a vaccine candidate for prevention of P. gingivalis-elicited oral bone loss.

Induction of monocyte chemoattractant protein-1 by Porphyromonas gingivalis in human endothelial cells

The association between periodontal and cardiovascular diseases could be mediated by direct interaction of periodontal pathogens with cardiac tissue. In order to explore this possibility, the effect of the periodontal pathogen Porphyromonas gingivalis on monocyte chemoattractant protein-1 (MCP-1) production by endothelial cells was investigated. When incubated with live P. gingivalis 381, MCP-1 production by human umbilical vein endothelial cells (HUVEC) was potently increased. Compared to the type strain 381, non-adhesive/invasive strains (W50 and DPG3) did not increase MCP-1 production, which was also demonstrated at the mRNA level. Killed P. gingivalis 381 was much less effective than live bacteria for MCP-1 induction. Treatment of HUVEC with cytochalasin D, an inhibitor of endocytosis, prevented MCP-1 mRNA up-regulation by P. gingivalis 381, suggesting that internalization of P. gingivalis is necessary for MCP-1 induction. In conclusion, the secretion of high levels of MCP-1 resulting from interactions of P. gingivalis with endothelial cells could enhance atherosclerosis progression by contributing to the recruitment of monocytes.