Host modulation of tissue destruction caused by periodontopathogens: effects on a mixed microbial infection composed of Porphyromonas gingivalis and Fusobacterium nucleatum

Porphyromonas gingivalis Tyrosine Kinase Is a Fitness Determinant in Polymicrobial Infections

Many pathogenic microbial ecosystems are polymicrobial, and community function can be shaped by interbacterial interactions. Little is known, however, regarding the genetic determinants required for fitness in heterotypic community environments. In periodontal diseases, Porphyromonas gingivalis is a primary pathogen, but only within polymicrobial communities. Here, we used a transposon sequencing (Tn-Seq) library of P. gingivalis to screen for genes that influence fitness of the organism in a coinfection murine abscess model with the oral partner species Streptococcus gordonii and Fusobacterium nucleatum. Genes impacting fitness with either organism were involved in diverse processes, including metabolism and energy production, along with cell wall and membrane biogenesis. Despite the overall similarity of function, the majority of identified genes were specific to the partner species, indicating that synergistic mechanisms of P. gingivalis vary to a large extent according to community composition. Only two genes were identified as essential for P. gingivalis fitness in abscess development with both S. gordonii and F. nucleatum: ptk1, encoding a tyrosine kinase, and inlJ, encoding an internalin family surface protein. Ptk1, but not InlJ, is required for community development with S. gordonii, and we found that the action of this kinase is similarly required for P. gingivalis to accumulate in a community with F. nucleatum. A limited number of P. gingivalis genes are therefore required for species-independent synergy, and the Ptk1 tyrosine kinase network may integrate and coordinate input from multiple organisms.

Regulation of olfactomedin 4 by Porphyromonas gingivalis in a community context

At mucosal barriers, the virulence of microbial communities reflects the outcome of both dysbiotic and eubiotic interactions with the host, with commensal species mitigating or potentiating the action of pathogens. We examined epithelial responses to the oral pathogen Porphyromonas gingivalis as a monoinfection and in association with a community partner, Streptococcus gordonii. RNA-Seq of oral epithelial cells showed that the Notch signaling pathway, including the downstream effector olfactomedin 4 (OLFM4), was differentially regulated by P. gingivalis alone; however, regulation was overridden by S. gordonii. OLFM4 was required for epithelial cell migratory, proliferative and inflammatory responses to P. gingivalis. Activation of Notch signaling was induced through increased expression of the Notch1 receptor and the Jagged1 (Jag1) agonist. In addition, Jag1 was released in response to P. gingivalis, leading to paracrine activation. Following Jag1-Notch1 engagement, the Notch1 extracellular domain was cleaved by P. gingivalis gingipain proteases. Antagonism by S. gordonii involved inhibition of gingipain activity by secreted hydrogen peroxide. The results establish a novel mechanism by which P. gingivalis modulates epithelial cell function which is dependent on community context. These interrelationships have relevance for innate inflammatory responses and epithelial cell fate decisions in oral health and disease.

Non-Invasive Luciferase Imaging of Type I Interferon Induction in a Transgenic Mouse Model of Biomaterial Associated Bacterial Infections: Microbial Specificity and Inter-Bacterial Species Interactions

The performance of biomaterials is often compromised by bacterial infections and subsequent inflammation. So far, the conventional analysis of inflammatory processes in vivo involves time-consuming histology and biochemical assays. The present study employed a mouse model where interferon beta (IFN-β) is monitored as a marker for non-invasive rapid detection of inflammation in implant-related infections. The mouse model comprises subcutaneous implantation of morphologically modified titanium, followed by experimental infections with four taxonomically diverse oral bacteria: Streptococcus oralis, Aggregatibacter actinomycetemcomitans, Porphyromonas gingivalis and Treponema denticola (as mono culture or selected mixed-culture). IFN-β expression increased upon infections depending on the type of pathogen and was prolonged by the presence of the implant. IFN-β expression kinetics reduced with two mixed species infections when compared with the single species. Histological and confocal microscopy confirmed pathogen-specific infiltration of inflammatory cells at the implant-tissue interface. This was observed mainly in the vicinity of infected implants and was, in contrast to interferon expression, higher in infections with dual species. In summary, this non-invasive mouse model can be used to quantify longitudinally host inflammation in real time and suggests that the polymicrobial character of infection, highly relevant to clinical situations, has complex effects on host immunity.

Porphyromonas gingivalis adopts intricate and unique molecular mechanisms to survive and persist within the host: a critical update

is an obligate, asaccharolytic, gram-negative bacteria commonly associated with increased periodontal and systemic inflammation. P. gingivalis is known to survive and persist within the host tissues as it modulates the entire ecosystem by either engineering its environment or modifying the host's immune response. It interacts with various host receptors and alters signaling pathways of inflammation, complement system, cell cycle, and apoptosis. P. gingivalis is even known to induce suicidal cell death of the host and other microbes in its vicinity with the emergence of pathobiont species. Recently, new molecular and immunological mechanisms and virulence factors of P. gingivalis that increase its chance of survival and immune evasion within the host have been discovered. Thus, the present paper aims to provide a consolidated update on the new intricate and unique molecular mechanisms and virulence factors of P. gingivalis associated with its survival, persistence, and immune evasion within the host.

Discovery of a Novel Periodontal Disease-Associated Bacterium

One of the world's most common infectious disease, periodontitis (PD), derives from largely uncharacterized communities of oral bacteria growing as biofilms (a.k.a. plaque) on teeth and gum surfaces in periodontal pockets. Bacteria associated with periodontal disease trigger inflammatory responses in immune cells, which in later stages of the disease cause loss of both soft and hard tissue structures supporting teeth. Thus far, only a handful of bacteria have been characterized as infectious agents of PD. Although deep sequencing technologies, such as whole community shotgun sequencing have the potential to capture a detailed picture of highly complex bacterial communities in any given environment, we still lack major reference genomes for the oral microbiome associated with PD and other diseases. In recent work, by using a combination of supervised machine learning and genome assembly, we identified a genome from a novel member of the Bacteroidetes phylum in periodontal samples. Here, by applying a comparative metagenomics read-classification approach, including 272 metagenomes from various human body sites, and our previously assembled draft genome of the uncultivated Candidatus Bacteroides periocalifornicus (CBP) bacterium, we show CBP's ubiquitous distribution in dental plaque, as well as its strong association with the well-known pathogenic "red complex" that resides in deep periodontal pockets.

An in vitro model of Fusobacterium nucleatum and Porphyromonas gingivalis in single- and dual-species biofilms

Purpose

The goal of this study was to develop and validate a standardized in vitro pathogenic biofilm attached onto saliva-coated surfaces.

Methods

Fusobacterium nucleatum (F. nucleatum) and Porphyromonas gingivalis (P. gingivalis) strains were grown under anaerobic conditions as single species and in dual-species cultures. Initially, the bacterial biomass was evaluated at 24 and 48 hours to determine the optimal timing for the adhesion phase onto saliva-coated polystyrene surfaces. Thereafter, biofilm development was assessed over time by crystal violet staining and scanning electron microscopy.

Results

The data showed no significant difference in the overall biomass after 48 hours for P. gingivalis in single- and dual-species conditions. After adhesion, P. gingivalis in single- and dual-species biofilms accumulated a substantially higher biomass after 7 days of incubation than after 3 days, but no significant difference was found between 5 and 7 days. Although the biomass of the F. nucleatum biofilm was higher at 3 days, no difference was found at 3, 5, or 7 days of incubation.

Conclusions

Polystyrene substrates from well plates work as a standard surface and provide reproducible results for in vitro biofilm models. Our biofilm model could serve as a reference point for studies investigating biofilms on different surfaces.

Different frequencies of Porphyromonas gingivalis infection in cancers of the upper digestive tract

The high incidence rate of multiple carcinomas in the upper digestive tract is often explained in terms of involvement of the same underlying risk factors. It has been reported that the oral bacterium Streptococcus anginosus is associated with esophageal, gastric, and pharyngeal cancers. We previously reported occurrence of Porphyromonas gingivalis (P. gingivalis) DNA in esophagus cancer. In this study, the presence of P. gingivalis in specimens of various types of cancer from the upper digestive tract was investigated. Here we report that P. gingivalis was preferentially and frequently present in specimens of esophageal cancer as well as in those from dysplasia of the esophagus but rarely in matched noncancerous portions and are quite low or absent in cancers from the cardia or stomach. Therefore, it led us to propose that, the microorganism does not survive in conditions of high acidity. We then investigate the pH dependence of survival of P. gingivalis as well as the acid tolerance of it. We found that, exposure to acidic buffers of a wide range of pH values led to a decline in colony forming units of P. gingivalis, thus, providing a possible explanation for variations in frequencies of P. gingivalis infection in this study.

Modulation of inflammasome activity by Porphyromonas gingivalis in periodontitis and associated systemic diseases

Inflammasomes are large multiprotein complexes localized in the cytoplasm of the cell. They are responsible for the maturation of pro-inflammatory cytokines such as interleukin-1β (IL-1β) and IL-18 as well as for the activation of inflammatory cell death, the so-called pyroptosis. Inflammasomes assemble in response to cellular infection, cellular stress, or tissue damage; promote inflammatory responses and are of great importance in regulating the innate immune system in chronic inflammatory diseases such as periodontitis and several chronic systemic diseases. In addition to sensing cellular integrity, inflammasomes are involved in the homeostatic mutualism between the indigenous microbiota and the host. There are several types of inflammasomes of which NLRP3 is best characterized in microbial pathogenesis. Many opportunistic bacteria try to evade the innate immune system in order to survive in the host cells. One of these is the periodontopathogen Porphyromonas gingivalis which has been shown to have several mechanisms of modulating innate immunity by limiting the activation of the NLRP3 inflammasome. Among them, ATP-/P2X₇- signaling is recently associated not only with periodontitis but also with development of several systemic diseases. The present paper reviews multiple mechanisms through which P. gingivalis can modify innate immunity by affecting inflammasome activity.

Fusobacterium nucleatum Alters Atherosclerosis Risk Factors and Enhances Inflammatory Markers with an Atheroprotective Immune Response in ApoE(null) Mice

The American Heart Association supports an association between periodontal disease (PD) and atherosclerotic vascular disease (ASVD) but does not as of yet support a causal relationship. Recently, we have shown that major periodontal pathogens Porphyromonas gingivalis and Treponema denticola are causally associated with acceleration of aortic atherosclerosis in ApoEnull hyperlipidemic mice. The aim of this study was to determine if oral infection with another significant periodontal pathogen Fusobacterium nucleatum can accelerate aortic inflammation and atherosclerosis in the aortic artery of ApoEnull mice. ApoEnull mice (n = 23) were orally infected with F. nucleatum ATCC 49256 and euthanized at 12 and 24 weeks. Periodontal disease assessments including F. nucleatum oral colonization, gingival inflammation, immune response, intrabony defects, and alveolar bone resorption were evaluated. Systemic organs were evaluated for infection, aortic sections were examined for atherosclerosis, and inflammatory markers were measured. Chronic oral infection established F. nucleatum colonization in the oral cavity, induced significant humoral IgG (P=0.0001) and IgM (P=0.001) antibody response (12 and 24 weeks), and resulted in significant (P=0.0001) alveolar bone resorption and intrabony defects. F. nucleatum genomic DNA was detected in systemic organs (heart, aorta, liver, kidney, lung) indicating bacteremia. Aortic atherosclerotic plaque area was measured and showed a local inflammatory infiltrate revealed the presence of F4/80+ macrophages and CD3+ T cells. Vascular inflammation was detected by enhanced systemic cytokines (CD30L, IL-4, IL-12), oxidized LDL and serum amyloid A, as well as altered serum lipid profile (cholesterol, triglycerides, chylomicrons, VLDL, LDL, HDL), in infected mice and altered aortic gene expression in infected mice. Despite evidence for systemic infection in several organs and modulation of known atherosclerosis risk factors, aortic atherosclerotic lesions were significantly reduced after F. nucleatum infection suggesting a potential protective function for this member of the oral microbiota.

Experimental Abscess Formation Caused by Human Dental Plaque

Human dental plaque consists of a wide variety of microorganisms, some of which are believed to cause systemic infections, including abscesses, at various sites in the body. To confirm this hypothesis experimentally, we examined the abscess-forming ability of native dental plaque in mice, the microbial features of the infectious locus produced by the plaque, and the anti-phagocytic property of microbial isolates. Aliquots of a suspension of supragingival dental plaque containing 6 x 10(6) colony-forming unit of bacteria were injected subcutaneously into the dorsa of mice. Abscess formation was induced in 76 of 85 mice using ten different plaque samples. Thirteen microorganisms were isolated from pus samples aspirated from abscess lesions. The microbial composition of pus, examined in 17 of 76 abscesses, was very simple compared to that of the plaque sample that had induced the abscess. The majority of the isolates belonged to the Streptococcus anginosus group, normally a minor component of plaque samples. S. anginosus was the most frequently detected organism and the most prevalent in seven abscesses, and Streptococcus intermedius and Streptococcus constellatus were predominant in one and three abscess samples, respectively. Each isolate of S. anginosus group produced abscesses in mice, and heat-treated supragingival dental plaque influenced the abscess-forming ability of S. anginosus isolate. These isolates possessed a high antiphagocytic capacity against human polymorphonuclear leukocytes. Our results suggest that human supragingival dental plaque itself is a source of the infectious pathogens that cause abscess formation.

Mixed red-complex bacterial infection in periodontitis

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

Porphyromonas gingivalis entry into gingival epithelial cells modulated by Fusobacterium nucleatum is dependent on lipid rafts

Host cell invasion by a major periodontal pathogen, Porphyromonas gingivalis, has been proposed as an important mechanism involved in host-pathogen interactions in periodontal and cardiovascular diseases. The present study sought to gain insight into the underlying mechanism(s) involved in previously demonstrated fusobacterial modulation of host cell invasion by P. gingivalis. An immortalized human gingival cell line Ca9-22 was dually infected with P. gingivalis ATCC 33277 and Fusobacterium nucleatum TDC 100, and intracellular invasion was assessed by scanning electron microscopy (SEM) and confocal scanning laser microscopy (CSLM). SEM observation showed that P. gingivalis and F. nucleatum formed consortia and were in the process of penetrating into Ca9-22 by 30-60 min after infection. In CSLM, Ca9-22 cells that contained both P. gingivalis and F. nucleatum were frequently observed after 2 h, although cells that contained exclusively P. gingivalis were also found. Infection by P. gingivalis and/or F. nucleatum revealed evident colocalization with a lipid raft marker, GM1-containing membrane microdomains. In an antibiotic protection assay, depletion of epithelial plasma membrane cholesterol resulted in a significant reduction of recovered P. gingivalis or F. nucleatum (∼33% of untreated control; p < 0.001). This inhibition was also confirmed by CSLM. Sequential infection experiments showed that timing of infection by each species could critically influence the invasion profile. Co-infection with F. nucleatum significantly enhanced host cell invasion by P. gingivalis 33277, its serine phophatase SerB mutant and complemented strains, suggesting that the SerB does not play a major role in this fusobacterial enhancement of P. gingivalis invasion. Thus, the interaction between F. nucleatum and host cells may be important in the fusobacterial enhancement of P. gingivalis invasion. Collectively, these results suggest that lipid raft-mediated process is at least one of the potential mechanisms involved in fusobacterium-modulated host cell invasion by P. gingivalis.

Porphyromonas gingivalis mediates inflammasome repression in polymicrobial cultures through a novel mechanism involving reduced endocytosis

The interleukin (IL)-1β-processing inflammasome has recently been identified as a target for pathogenic evasion of the inflammatory response by a number of bacteria and viruses. We postulated that the periodontal pathogen, Porphyromonas gingivalis may suppress the inflammasome as a mechanism for its low immunogenicity and pathogenic synergy with other, more highly immunogenic periodontal bacteria. Our results show that P. gingivalis lacks signaling capability for the activation of the inflammasome in mouse macrophages. Furthermore, P. gingivalis can suppress inflammasome activation by another periodontal bacterium, Fusobacterium nucleatum. This repression affects IL-1β processing, as well as other inflammasome-mediated processes, including IL-18 processing and cell death, in both human and mouse macrophages. F. nucleatum activates IL-1β processing through the Nlrp3 inflammasome; however, P. gingivalis repression is not mediated through reduced levels of inflammasome components. P. gingivalis can repress Nlrp3 inflammasome activation by Escherichia coli, and by danger-associated molecular patterns and pattern-associated molecular patterns that mediate activation through endocytosis. However, P. gingivalis does not suppress Nlrp3 inflammasome activation by ATP or nigericin. This suggests that P. gingivalis may preferentially suppress endocytic pathways toward inflammasome activation. To directly test whether P. gingivalis infection affects endocytosis, we assessed the uptake of fluorescent particles in the presence or absence of P. gingivalis. Our results show that P. gingivalis limits both the number of cells taking up beads and the number of beads taken up for bead-positive cells. These results provide a novel mechanism of pathogen-mediated inflammasome inhibition through the suppression of endocytosis.

The role of coaggregation between Porphyromonas gingivalis and Fusobacterium nucleatum on the host response to mixed infection

AIM

To evaluate the role of coaggregation between Porphyromonas gingivalis and Fusobacterium nucleatum on the virulence of the mixed infection in mice.

MATERIALS AND METHODS

Inhibition of coaggregation was carried out using lactose. In vitro, inhibition of coaggregation was verified using a coaggregation assay. In vivo, the virulence of the mixed infection, with and without coaggregation, was examined in a model of experimental periodontitis in mice. The local host response to the mixed infection, with or without coaggregation, was examined using the subcutaneous chamber model of infection.

RESULTS

Lactose inhibited the coaggregation between P. gingivalis and F. nucleatum at all the tested concentrations (1-0.0625 M). Surprisingly, the addition of lactose to the mixed infection increased the severity of experimental periodontitis (as measured by alveolar bone loss) compared with mixed infection with coaggregating bacteria. The addition of lactose to the mixed infection resulted in mild attenuation of TNFα and IL-1β levels. In addition, inhibition of coaggregation resulted in inhibition of the phagocytosis of F. nucleatum and augmentation of the phagocytosis of P. gingivalis.

CONCLUSIONS

The ability of P. gingivalis and F. nucleatum to coaggregate may limit their ability to induce experimental periodontitis in a mixed infection model. Moreover, there is a shift in the phagocytosis pattern of the bacteria with the annulment of coaggregeaiton, with a reduction in F. nucleatum phagocytosis and amplification of P. gingivalis phagocytosis. The increased virulence of the mixed infection without coaggregation may surprisingly lay in the sustention of F. nucleatum in the infected sites.

Porphyromonas gingivalis and Treponema denticola Mixed Microbial Infection in a Rat Model of Periodontal Disease

Porphyromonas gingivalis and Treponema denticola are periodontal pathogens that express virulence factors associated with the pathogenesis of periodontitis. In this paper we tested the hypothesis that P. gingivalis and T. denticola are synergistic in terms of virulence; using a model of mixed microbial infection in rats. Groups of rats were orally infected with either P. gingivalis or T. denticola or mixed microbial infections for 7 and 12 weeks. P. gingivalis genomic DNA was detected more frequently by PCR than T. denticola. Both bacteria induced significantly high IgG, IgG2b, IgG1, IgG2a antibody levels indicating a stimulation of Th1 and Th2 immune response. Radiographic and morphometric measurements demonstrated that rats infected with the mixed infection exhibited significantly more alveolar bone loss than shaminfected control rats. Histology revealed apical migration of junctional epithelium, rete ridge elongation, and crestal alveolar bone resorption; resembling periodontal disease lesion. These results showed that P. gingivalis and T. denticola exhibit no synergistic virulence in a rat model of periodontal disease.

Mouse model of experimental periodontitis induced by Porphyromonas gingivalis/Fusobacterium nucleatum infection: bone loss and host response

AIM

To compare the effect of oral infection with Porphyromonas gingivalis or Fusobacterium nucleatum versus infection with both bacteria on mouse periodontal tissues, and to characterize the inflammatory response.

MATERIALS AND METHODS

Mice were orally infected with P. gingivalis, F. nucleatum or both. At 42 days post-infection, alveolar bone loss was quantified using micro-computerized tomography. Tumour necrosis factor-alpha (TNF-alpha) and interleukin (IL)-1beta levels induced by the infection were quantified using the subcutaneous chamber model.

RESULTS

Mice orally infected with F. nucleatum/P. gingivalis exhibited significantly more bone loss compared with that of mono-infected and sham-infected mice. F. nucleatum/P. gingivalis infection also increased the levels of TNF-alpha and IL1beta compared with the levels found in the mono-infected groups.

CONCLUSIONS

Polymicrobial infection with P. gingivalis/F. nucleatum aggravates alveolar bone loss and induces a stronger inflammatory response compared with that observed upon infection with either bacterium alone. The results suggest that oral infection of mice with a mixture of P. gingivalis and F. nucleatum may be superior to mono-infection models of experimental periodontitis.

Proteomics of Porphyromonas gingivalis within a model oral microbial community

BACKGROUND

Porphyromonas gingivalis is a periodontal pathogen that resides in a complex multispecies microbial biofilm community known as dental plaque. Confocal laser scanning microscopy showed that P. gingivalis can assemble into communities in vitro with Streptococcus gordonii and Fusobacterium nucleatum, common constituents of dental plaque. Whole cell quantitative proteomics, along with mutant construction and analysis, were conducted to investigate how P. gingivalis adapts to this three species community.

RESULTS

1156 P. gingivalis proteins were detected qualitatively during comparison of the three species model community with P. gingivalis incubated alone under the same conditions. Integration of spectral counting and summed signal intensity analyses of the dataset showed that 403 proteins were down-regulated and 89 proteins up-regulated. The proteomics results were inspected manually and an ontology analysis conducted using DAVID. Significant decreases were seen in proteins involved in cell shape and the formation of the cell envelope, as well as thiamine, cobalamin, and pyrimidine synthesis and DNA repair. An overall increase was seen in proteins involved in protein synthesis. HmuR, a TonB dependent outer membrane receptor, was up-regulated in the community and an hmuR deficient mutant was deficient in three species community formation, but was unimpaired in its ability to form mono- or dual-species biofilms.

CONCLUSION

Collectively, these results indicate that P. gingivalis can assemble into a heterotypic community with F. nucleatum and S. gordonii, and that a community lifestyle provides physiologic support for P. gingivalis. Proteins such as HmuR, that are up-regulated, can be necessary for community structure.

Synergistic pathogenicity of Porphyromonas gingivalis and Fusobacterium nucleatum in the mouse subcutaneous chamber model

Porphyromonas gingivalis and Fusobacterium nucleatum are often coisolated from sites of infection, such as suppurative apical periodontitis. The synergistic pathogenicity of mixed infection of P. gingivalis HG 405 with F. nucleatum PK 1594 was studied in the mouse subcutaneous chamber model in groups of seven animals. The minimal dose for P. gingivalis HG 405 that was required to infect 100% of the chambers was reduced by 1,000-fold when animals were inoculated in the same chamber with 1 x 10(9)F. nucleatum PK 1594 (p < 0.001). To benefit from the presence of the fusobacteria, P. gingivalis HG 405 had to be coinoculated; inoculation in separate chambers for the same animal had no such effect (p < 0.001). Subinfective F. nucleatum inocula also benefited from the association with P. gingivalis HG 405 and uniformly established an infection when this partner was present (p < 0.001). These results suggest that the frequent and natural coexistence of P. gingivalis and F. nucleatum in diseased sites may express such a synergism in successful establishment and survival of small inocula.

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.

Beyond good and evil in the oral cavity: insights into host-microbe relationships derived from transcriptional profiling of gingival cells

In many instances, the encounter between host and microbial cells, through a long-standing evolutionary association, can be a balanced interaction whereby both cell types co-exist and inflict a minimal degree of harm on each other. In the oral cavity, despite the presence of large numbers of diverse organisms, health is the most frequent status. Disease will ensue only when the host-microbe balance is disrupted on a cellular and molecular level. With the advent of microarrays, it is now possible to monitor the responses of host cells to bacterial challenge on a global scale. However, microarray data are known to be inherently noisy, which is caused in part by their great sensitivity. Hence, we will address several important general considerations required to maximize the significance of microarray analysis in depicting relevant host-microbe interactions faithfully. Several advantages and limitations of microarray analysis that may have a direct impact on the significance of array data are highlighted and discussed. Further, this review revisits and contextualizes recent transcriptional profiles that were originally generated for the specific study of intricate cellular interactions between gingival cells and 4 important plaque micro-organisms. To our knowledge, this is the first report that systematically investigates the cellular responses of a cell line to challenge by 4 different micro-organisms. Of particular relevance to the oral cavity, the model bacteria span the entire spectrum of documented pathogenic potential, from commensal to opportunistic to overtly pathogenic. These studies provide a molecular basis for the complex and dynamic interaction between the oral microflora and its host, which may lead, ultimately, to the development of novel, rational, and practical therapeutic, prophylactic, and diagnostic applications.

Interspecies interactions within oral microbial communities

While reductionism has greatly advanced microbiology in the past 400 years, assembly of smaller pieces just could not explain the whole! Modern microbiologists are learning "system thinking" and "holism." Such an approach is changing our understanding of microbial physiology and our ability to diagnose/treat microbial infections. This review uses oral microbial communities as a focal point to describe this new trend. With the common name "dental plaque," oral microbial communities are some of the most complex microbial floras in the human body, consisting of more than 700 different bacterial species. For a very long time, oral microbiologists endeavored to use reductionism to identify the key genes or key pathogens responsible for oral microbial pathogenesis. The limitations of reductionism forced scientists to begin adopting new strategies using emerging concepts such as interspecies interaction, microbial community, biofilms, polymicrobial disease, etc. These new research directions indicate that the whole is much more than the simple sum of its parts, since the interactions between different parts resulted in many new physiological functions which cannot be observed with individual components. This review describes some of these interesting interspecies-interaction scenarios.

Destructive periodontitis lesions are determined by the nature of the lymphocytic response

It is now 35 years since Brandtzaeg and Kraus (1965) published their seminal work entitled "Autoimmunity and periodontal disease". Initially, this work led to the concept that destructive periodontitis was a localized hypersensitivity reaction involving immune complex formation within the tissues. In 1970, Ivanyi and Lehner highlighted a possible role for cell-mediated immunity, which stimulated a flurry of activity centered on the role of lymphokines such as osteoclast-activating factor (OAF), macrophage-activating factor (MAF), macrophage migration inhibition factor (MIF), and myriad others. In the late 1970s and early 1980s, attention focused on the role of polymorphonuclear neutrophils, and it was thought that periodontal destruction occurred as a series of acute exacerbations. As well, at this stage doubt was being cast on the concept that there was a neutrophil chemotactic defect in periodontitis patients. Once it was realized that neutrophils were primarily protective and that severe periodontal destruction occurred in the absence of these cells, attention swung back to the role of lymphocytes and in particular the regulatory role of T-cells. By this time in the early 1990s, while the roles of interleukin (IL)-1, prostaglandin (PG) E(2), and metalloproteinases as the destructive mediators in periodontal disease were largely understood, the control and regulation of these cytokines remained controversial. With the widespread acceptance of the Th1/Th2 paradigm, the regulatory role of T-cells became the main focus of attention. Two apparently conflicting theories have emerged. One is based on direct observations of human lesions, while the other is based on animal model experiments and the inability to demonstrate IL-4 mRNA in gingival extracts. As part of the "Controversy" series, this review is intended to stimulate debate and hence may appear in some places provocative. In this context, this review will present the case that destructive periodontitis is due to the nature of the lymphocytic infiltrate and is not due to periodic acute exacerbations, nor is it due to the so-called virulence factors of putative periodontal pathogens.

Genome sequence of Fusobacterium nucleatum subspecies polymorphum - a genetically tractable fusobacterium

Fusobacterium nucleatum is a prominent member of the oral microbiota and is a common cause of human infection. F. nucleatum includes five subspecies: polymorphum, nucleatum, vincentii, fusiforme, and animalis. F. nucleatum subsp. polymorphum ATCC 10953 has been well characterized phenotypically and, in contrast to previously sequenced strains, is amenable to gene transfer. We sequenced and annotated the 2,429,698 bp genome of F. nucleatum subsp. polymorphum ATCC 10953. Plasmid pFN3 from the strain was also sequenced and analyzed. When compared to the other two available fusobacterial genomes (F. nucleatum subsp. nucleatum, and F. nucleatum subsp. vincentii) 627 open reading frames unique to F. nucleatum subsp. polymorphum ATCC 10953 were identified. A large percentage of these mapped within one of 28 regions or islands containing five or more genes. Seventeen percent of the clustered proteins that demonstrated similarity were most similar to proteins from the clostridia, with others being most similar to proteins from other gram-positive organisms such as Bacillus and Streptococcus. A ten kilobase region homologous to the Salmonella typhimurium propanediol utilization locus was identified, as was a prophage and integrated conjugal plasmid. The genome contains five composite ribozyme/transposons, similar to the CdISt IStrons described in Clostridium difficile. IStrons are not present in the other fusobacterial genomes. These findings indicate that F. nucleatum subsp. polymorphum is proficient at horizontal gene transfer and that exchange with the Firmicutes, particularly the Clostridia, is common.

Actinobacillus actinomycetemcomitans and Porphyromonas gingivalis subgingival presence, species-specific serum immunoglobulin G antibody levels, and periodontitis disease recurrence

BACKGROUND AND OBJECTIVE

The biological and clinical effects of antibody against periodontal pathogenic bacteria are incompletely understood. This study evaluated the inter-relationships among periodontal levels of cultivable Actinobacillus actinomycetemcomitans and Porphyromonas gingivalis, species-specific serum immunoglobulin G (IgG) antibody levels, and periodontitis disease activity.

MATERIAL AND METHODS

Forty-three adults who had previously been treated for periodontitis and who also harbored cultivable A. actinomycetemcomitans or P. gingivalis were evaluated semiannually for clinical disease recurrence over a 36-month period. Each patient provided subgingival microbial samples, for the recovery of A. actinomycetemcomitans and P. gingivalis, from the two deepest pockets in each dentition sextant. A. actinomycetemcomitans and P. gingivalis serum IgG antibody levels were assessed using enzyme-linked immunosorbent assay (ELISA), together with whole-cell sonicate extracts from A. actinomycetemcomitans serotypes a-c and P. gingivalis ATCC 33277. Data were analyzed using the Mantel-Haenszel chi-square and Fisher exact two-tailed tests.

RESULTS

Eighteen (60.0%) of 30 A. actinomycetemcomitans-positive subjects, and 10 (76.9%) of 13 P. gingivalis-positive subjects, exhibited recurrent periodontal breakdown within 36 months of periodontal therapy. Nineteen (67.9%) of the 28 patients with active periodontitis had A. actinomycetemcomitans or P. gingivalis serum antibody levels below designated threshold values. In comparison, 10 (66.7%) of 15 culture-positive clinically stable subjects showed A. actinomycetemcomitans or P. gingivalis serum antibody levels above threshold values. The difference between specific antibody levels in periodontitis-active and periodontitis-stable patients was statistically significant (p = 0.032).

CONCLUSIONS

Serum levels of IgG antibodies against A. actinomycetemcomitans or P. gingivalis in periodontitis-stable patients were higher than those in patients with active periodontitis. The results suggest that elevated levels of IgG antibody against A. actinomycetemcomitans and P. gingivalis have a detectable protective effect against periodontal infections with these microorganisms.

Enhanced pathogenicity of Fusobacterium nucleatum adapted to oxidative stress

Fusobacterium nucleatum is an obligate anaerobic bacterium found in the indigenous human microbiota but also recovered from several anaerobic infections. Considering the biological and medical relevance of F. nucleatum, the characterization of its response to oxidative stress is needed in order to understand how this anaerobic bacterium survives during an invasive process of oxygenated tissues. Influence of oxidative stress by atmospheric oxygen exposure on cellular morphology and pathogenicity of F. nucleatum were investigated. The wild-type F. nucleatum ATCC 25586 (wt-strain) was exposed to oxidative stress to select an adapted strain (aero-strain). Conventional NIH Swiss mice were split in two experimental groups which were challenged intraperitoneally with wt-strain and aero-strain, respectively, and a control group, unchallenged. Histopathological and hyperemia analysis were performed by day 30 after infection. Gram stain of aero-strain showed drastic changes in cellular morphology when compared to wt-strain. A significant increase of liver weight/body weight ratio (P < 0.05) as well as a tendency (P = 0.16) to higher spleen weight/body weight ratio were observed for the mice challenged with aero-strain when compared to the two other animal groups. Additionally, these animals also showed hyperemia in the spleen and liver as well as an increased number of inflammatory cells and steatosis in the liver. The results showed that, in addition to extensive changes in cell morphology, the adaptation to oxidative stress might also influence the pathogenicity of F. nucleatum. These findings have clinical implications since in the host tissues this indigenous putative pathogen is exposed to more or less oxygenated environments found on the different anatomic sites invaded by the bacterium.

Stimulation of growth of Porphyromonas gingivalis by cell extracts from Tannerella forsythia

OBJECTIVE

In order to examine if Tannerella forsythia stimulates the growth of Porphyromonas gingivalis, an in vitro study was performed.

BACKGROUND

P. gingivalis and T. forsythia are often isolated simultaneously from active periodontitis sites, indicating that these bacteria somewhat interact in the periodontal environment. We reported previously that mixed infection of P. gingivalis and T. forsythia synergistically induced lesion formation in a murine abscess model, and gingipains of P. gingivalis played an important role in this synergism. One of the possible mechanisms of this synergism is growth promotion by coinfection of the two bacteria.

METHODS

Cell extracts of T. forsythia were added to the nutrition-decreased medium and the promotion of growth of P. gingivalis was examined.

RESULTS

Sonicated extract of T. forsythia stimulated growth of P. gingivalis in nutrition-decreased medium in a dose-dependent manner. Proteins appeared to be the nature of growth-promoting factor, and the cell extract of T. forsythia had no stimulating effect on the growth of P. gingivalis strain devoid of gingipain activities.

CONCLUSION

A product or a component of T. forsythia seemed to stimulate growth of P. gingivalis under nutrition-limited conditions. Gingipains are considered to play an important role in digestion or uptake of this growth-promoting factor. The interaction between T. forsythia and P. gingivalis in growth may be in part related with the synergistic virulence in a murine model.

Modulation of the antibody response by Porphyromonas gingivalis and Fusobacterium nucleatum in a mouse model

Successive immunization of mice with Fusobacterium nucleatum and Porphyromonas gingivalis has been shown to modulate the specific serum IgG responses to these organisms. The aim of this study was to investigate these antibody responses further by examining the IgG subclasses induced as well as the opsonizing properties of the specific antibodies. Serum samples from BALB/c mice immunized with F. nucleatum (gp1-F), P. gingivalis (gp2-P), P. gingivalis followed by F. nucleatum (gp3-PF) F. nucleatum followed by P. gingivalis (gp4-FP) or saline alone (gp5-S) were examined for specific IgG1 (Th2) and IgG2a (Th1) antibody levels using an ELISA and the opsonizing properties measured using a neutrophil chemiluminescence assay. While IgG1 and IgG2a subclasses were induced in all immunized groups, there was a tendency towards an IgG1 response in mice immunized with P. gingivalis alone, while immunization with F. nucleatum followed by P. gingivalis induced significantly higher anti-P. gingivalis IgG2a levels than IgG1. The maximum light output due to neutrophil phagocytosis of P. gingivalis occurred at 10 min using nonopsonized bacteria. Chemiluminescence was reduced using serum-opsonized P. gingivalis and, in particular, sera from P. gingivalis-immunized mice (gp2-P), with maximum responses occurring at 40 min. In contrast, phagocytosis of immune serum-opsonized F. nucleatum demonstrated peak light output at 10 min, while that of F. nucleatum opsonized with sera from saline injected mice (gp5-S) and control nonopsonized bacteria showed peak responses at 40 min. The lowest phagocytic response occurred using gp4-FP serum-opsonized F. nucleatum. In conclusion, the results of the present study have demonstrated a systemic Th1/Th2 response in mice immunized with P. gingivalis and/or F. nucleatum with a trend towards a Th2 response in P. gingivalis-immunized mice and a significantly increased anti-P. gingivalis IgG2a (Th1) response in mice immunized with F. nucleatum prior to P. gingivalis. Further, the inhibition of neutrophil phagocytosis of immune serum-opsonized P. gingivalis was modulated by the presence of anti-F. nucleatum antibodies, while anti-P. gingivalis antibodies induced an inhibitory effect on the phagocytic response to F. nucleatum.

The microbial synergy of Peptostreptococcus micros and Prevotella intermedia in a murine abscess model

This study characterized the microbial interaction of Peptostreptococcus micros and Prevotella intermedia, the major pathogens of dentoalveolar infection, using a murine model. Subcutaneous injection of P. micros cells in the dorsum of the mouse together with living cells of P. intermedia resulted in a significantly larger abscess when compared with single injection of the organisms (P < 0.02). The abscess size was also significantly increased (P < 0.05) when the plate-cultured cell suspension of P. micros was injected into mouse with the culture filtrate of P. intermedia. The heat-treated culture filtrate of P. intermedia also enhanced the virulence of P. micros. P. micros culture filtrate did not affect the virulence of P. intermedia. Interestingly, the virulence of P. micros appeared to be enhanced even when the culture filtrate of P. intermedia was injected at separate sites in the mouse. These results suggest that a heat-stable product or products of P. intermedia increase the virulence of P. micros indirectly by altering the host condition, whereas living cells of P. micros can directly enhance virulence of P. intermedia.

In vitro environmental regulation of Porphyromonas gingivalis growth and virulence

Porphyromonas gingivalis appears to be a major contributor to periodontal disease, especially soft tissue destruction, which is reflected by the ability to cause invasive, spreading lesions, and tissue inflammation in a murine abscess model. This study investigated the role of hemin on the regulation of growth and virulence of P. gingivalis strains. P. gingivalis strains W50, A7A1-28, 3079, 381, W50/BEI, and NG4B19 were grown in broth and on blood agar plates. P. gingivalis cells grown under iron-depleted conditions for multiple passages showed significantly decreased lesion size in mice, in contrast to cells grown under iron-normal (5 microg/ml) and iron-elevated conditions. Statistically significant (P < 0.01) decreases in gingipain enzyme activity were found among the strains grown under iron-depleted conditions. P. gingivalis grown in the presence of blood induced significantly different lesion type, lesion size, lesion onset, and mortality. Elevated hemin resulted in increased cell-associated iron in P. gingivalis, which increased the capacity of the microorganism to survive at times of iron deprivation. These results indicate that hemin or iron availability regulates multiple aspects related to P. gingivalis virulence, including growth, survival, gingipain levels, and iron accumulation.

Communication among oral bacteria

Human oral bacteria interact with their environment by attaching to surfaces and establishing mixed-species communities. As each bacterial cell attaches, it forms a new surface to which other cells can adhere. Adherence and community development are spatiotemporal; such order requires communication. The discovery of soluble signals, such as autoinducer-2, that may be exchanged within multispecies communities to convey information between organisms has emerged as a new research direction. Direct-contact signals, such as adhesins and receptors, that elicit changes in gene expression after cell-cell contact and biofilm growth are also an active research area. Considering that the majority of oral bacteria are organized in dense three-dimensional biofilms on teeth, confocal microscopy and fluorescently labeled probes provide valuable approaches for investigating the architecture of these organized communities in situ. Oral biofilms are readily accessible to microbiologists and are excellent model systems for studies of microbial communication. One attractive model system is a saliva-coated flowcell with oral bacterial biofilms growing on saliva as the sole nutrient source; an intergeneric mutualism is discussed. Several oral bacterial species are amenable to genetic manipulation for molecular characterization of communication both among bacteria and between bacteria and the host. A successful search for genes critical for mixed-species community organization will be accomplished only when it is conducted with mixed-species communities.

Effect of Fusobacterium nucleatum on the T and B cell responses to Porphyromonas gingivalis in a mouse model

T cell cytokine profiles and specific serum antibody levels in five groups of BALB/c mice immunized with saline alone, viable Fusobacterium nucleatum ATCC 25586, viable Porphyromonas gingivalis ATCC 33277, F. nucleatum followed by P. gingivalis and P. gingivalis followed by F. nucleatum were determined. Splenic CD4 and CD8 cells were examined for intracytoplasmic interleukin (IL)-4, interferon (IFN)-gamma and IL-10 by dual colour flow cytometry and the levels of serum anti-F. nucleatum and anti-P. gingivalis antibodies determined by an ELISA. Both Th1 and Th2 responses were demonstrated by all groups, and while there were slightly lower percentages of cytokine positive T cells in mice injected with F. nucleatum alone compared with the other groups immunized with bacteria, F. nucleatum had no effect on the T cell production of cytokines induced by P. gingivalis in the two groups immunized with both organisms. However, the percentages of cytokine positive CD8 cells were generally significantly higher than those of the CD4 cells. Mice immunized with F. nucleatum alone had high levels of serum anti-F. nucleatum antibodies with very low levels of P. gingivalis antibodies, whereas mice injected with P. gingivalis alone produced anti-P. gingivalis antibodies predominantly. Although the levels of anti-F. nucleatum antibodies in mice injected with F. nucleatum followed by P. gingivalis were the same as in mice immunized with F. nucleatum alone, antibody levels to P. gingivalis were very low. In contrast, mice injected with P. gingivalis followed by F. nucleatum produced equal levels of both anti-P. gingivalis and anti-F. nucleatum antibodies, although at lower levels than the other three groups immunized with bacteria, respectively. Anti-Actinobacillus actinomycetemcomitans, Bacteroides forsythus and Prevotella intermedia serum antibody levels were also determined and found to be negligible. In conclusion, F. nucleatum immunization does not affect the splenic T cell cytokine response to P. gingivalis. However, F. nucleatum immunization prior to that of P. gingivalis almost completely inhibited the production of anti-P. gingivalis antibodies while P. gingivalis injection before F. nucleatum demonstrated a partial inhibitory effect by P. gingivalis on antibody production to F. nucleatum. The significance of these results with respect to human periodontal disease is difficult to determine. However, they may explain in part differing responses to P. gingivalis in different individuals who may or may not have had prior exposure to F. nucleatum. Finally, the results suggested that P. gingivalis and F. nucleatum do not induce the production of cross-reactive antibodies to other oral microorganisms.

Prior exposure of mice to Fusobacterium nucleatum modulates host response to Porphyromonas gingivalis

Multiple periodontal pathogens sequentially colonize the subgingival niche during the conversion from gingivitis to destructive periodontal disease. An animal model of sequential immunization with key periodontal pathogens has been developed to determine whether T- and B-lymphocyte effector functions are skewed and fail to protect the host from pathogenic challenge. The present study was performed to evaluate the immunomodulatory effect of exposure to Fusobacterium nucleatum prior to Porphyromonas gingivalis. Group 1 (control) mice were immunized with phosphate-buffered saline, group 2 were immunized with F. nucleatum prior to P. gingivalis and group 3 were immunized with P. gingivalis alone. All the T-cell clones derived from group 2 demonstrated type 2 helper T-cell clone (Th2 subsets), whereas those from group 3 mice demonstrated Th1 subsets. Exposure of mice to F. nucleatum prior to P. gingivalis interfered with the opsonophagocytosis function of sera against P. gingivalis. In adoptive T-cell transfer experiments, in vivo protective capacity of type 2 helper T-cell clones (Th2) from group 2 was significantly lower than type 1 helper T-cell clones (Th1) from group 3 against the lethal dose infection of P. gingivalis. Western blot analysis indicated a different pattern of recognition of P. gingivalis fimbrial proteins between sera from group 2 and group 3. In conclusion, these studies suggest that exposure of a host to F. nucleatum prior to the periodontal pathogen P. gingivalis modulates the host immune responses to P. gingivalis at the humoral, cellular and molecular levels.

The virulence of mixed infection with Streptococcus constellatus and Fusobacterium nucleatum in a murine orofacial infection model

Orofacial infections are usually polymicrobial, and it is the microbial interactions of pathogenic species that cause tissue destruction. In this study, the microbial interaction between Streptococcus constellatus and Fusobacterium nucleatum was characterized using a murine orofacial infection model. A mixture of viable S. constellatus and F. nucleatum cells (both 2 x 10(8) CFU/mouse) was injected into the submandible; as a result, all of the test mice died. In contrast, none of the experimental animals monoinjected with either S. constellatus or F. nucleatum died (P<0.001), indicating that the synergism between the two resulted in the virulence. When a mixture of viable S. constellatus cells and a culture filtrate of F. nucleatum was tested, lethality and the bacterial cell count per lesion were significantly enhanced as compared with monoinjections (P<0.02). However, the virulence of F. nucleatum was not enhanced by infection of a culture filtrate of S. constellatus. The enhancement of virulence was observed even when viable S. constellatus cells and the culture filtrate of F. nucleatum were injected at separate sites. Heat treatment of the culture filtrate of F. nucleatum did not affect the enhancement. These results indicate that a heat-stable substance(s) produced by F. nucleatum contributes to the microbial synergy of S. constellatus and F. nucleatum in orofacial infections.

B-Cell deficiency predisposes mice to disseminating anaerobic infections: protection by passive antibody transfer

We have previously demonstrated that a high proportion of RAG-2 SCID knockout mice, which lack T and B cells, develop orofacial abscesses and disseminated infections following pulpal infection, whereas immunocompetent control mice do not. In the present study, we sought to identify the components of the adaptive immune response which contribute to protection against disseminating anaerobic infections and sepsis. For this purpose, various genetically engineered immunodeficient mice were employed, including RAG-2 SCID, Igh-6 (B-cell deficient), Tcrb Tcrd (T-cell deficient) and Hc(0) (C5 deficient). For abscess induction, the mandibular first molars were subjected to pulp exposure on day 0. Teeth were infected with a mixture of four anaerobic pathogens, including Prevotella intermedia, Streptococcus intermedius, Fusobacterium nucleatum, and Peptostreptococcus micros, and teeth were sealed to prevent communication with the oral cavity. The findings demonstrate that both RAG-2 SCID and B-cell-deficient mice, but not T-cell- or C5-deficient mice, have increased susceptibility to the development of disseminating anaerobic infections. Abscess-susceptible RAG-2 SCID and B-cell-deficient mice also showed a significant loss of body weight, splenomegaly, and absent antibacterial antibody production. Furthermore, dissemination was significantly reduced, from 74 to 25%, in susceptible RAG-2 mice by passively transferred antibody, predominantly immunoglobulin G2b (IgG2b) and IgM, against the infecting bacterial innoculum. Fractionated IgG-enriched preparations were more efficient in transferring protection than IgM preparations. We conclude that an antibody-mediated mechanism(s), most likely bacterial opsonization, is of importance in localizing anaerobic root canal infections and in preventing their systemic spread.

Polarization of Porphyromonas gingivalis-specific helper T-cell subsets by prior immunization with Fusobacterium nucleatum

Antigen-specific T-cell clones were obtained from mice immunized with Fusobacterium nucleatum ATCC 10953 and/or Porphyromonas gingivalis 381. 10 BALB/c mice per group were immunized with F. nucleatum followed by P. gingivalis, or with P. gingivalis alone by intraperitoneal injection of viable microorganisms. Spleen T cells were isolated and stimulated in vitro with viable P. gingivalis cells to establish P. gingivalis-specific T-cell clones. T-cell phenotypes and cytokine profiles were determined along with T-cell responsiveness to F. nucleatum or P. gingivalis. Serum immunoglobulin G antibody titers to F. nucleatum or P. gingivalis were also determined by enzyme-linked immunosorbent assay. All the T-cell clones derived from mice immunized with F. nucleatum followed by P. gingivalis demonstrated Th2 subsets, while those from mice immunized with P. gingivalis alone demonstrated Th1 subsets based on the flow cytometric analysis and cytokine profiles. All T-cell clones from both groups were cross-reactive to both P. gingivalis and F. nucleatum antigens. Phenotypes of T-cell clones were all positive for CD4. Mean post-immune serum IgG antibody levels to F. nucleatum or P. gingivalis were significantly higher than the pre-immune levels (P < 0.05, P < 0.01, respectively). There were no significant differences in the antibody titers between the two groups. It was concluded that P. gingivalis-specific T cells initially primed by cross-reactive F. nucleatum antigens were polarized to Th2 subset, while T cells stimulated with P. gingivalis alone maintained the profile of Th1 subset.

Virulence of a polymicrobic complex, Treponema denticola and Porphyromonas gingivalis, in a murine model

The effect of a polymicrobic infection employing Treponema denticola and Porphyromonas gingivalis in the murine lesion model was used to determine the synergistic virulence of these two periodontopathic bacteria. At high doses of P. gingivalis W50, addition of T. denticola in the infection mixture had no effect on the formation and size of the spreading lesion caused by this microorganism. However, at low P. gingivalis challenge doses, T. denticola significantly enhanced the virulence of P. gingivalis compared with monoinfection of this microorganism. A potential role of the trypsin-like protease enzyme activity of P. gingivalis in this synergistic virulence was tested using P. gingivalis mutants deficient (i.e., BEI) or devoid (i.e., NG4B19) of this protease activity. These findings demonstrated that T. denticola-P. gingivalis complexes exhibit enhanced virulence in this model and that even using a polymicrobic challenge infection, the trypsin-like protease activity was important to P. gingivalis virulence expression.