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

Dual Antibacterial and Soft-Tissue-Integrative Effect of Combined Strontium Acetate and Silver Nitrate on Peri-Implant Environment: Insights from Multispecies Biofilms and a 3D Coculture Model

Creation of a biological seal and efficient antibacterial qualities in the peri-implant environment is essential for the success of dental implants. Therefore, novel multifunctional strategies are being developed to address these issues, aiming at the simultaneous improvement of tissue integration and hindering pathological biofilm formation. In this study, we investigated the effect of tissue-promotive strontium acetate (SrAc), antibacterial silver nitrate (AgNO3), and their combination on oral soft tissue cells and an oral multispecies biofilm not only in monoculture setups but also in a three-dimensional (3D) implant-tissue-oral bacterial-biofilm model (INTERbACT model) that takes the naturally occurring interactions into account. Application of SrAc led to improved fibroblast migration in the monoculture setting, without impairment of metabolic activity, even upon additional AgNO3 administration. Notably, the combined treatment of SrAc and AgNO3 resulted in a synergistic antibacterial effect during biofilm formation as well as on early matured biofilms. Most interestingly, the antibacterial effect of the combined treatment was even further enhanced within the coculture setup leading to increased bacterial death and decreased biofilm volume. The 3D tissue in the coculture setup underwent the combined treatment with a notable rise in CCL20 and IL-1β levels. Histologically, only the AgNO3-treated groups exhibited damage to the integrity of the epithelial barrier. Therefore, the results of this study demonstrated promising dual antibacterial and tissue-integrative characteristics of combined AgNO3 and SrAc in the dental implant environment. Additionally, the study emphasizes the importance of considering naturally occurring tissue-bacteria interactions for reliable in vitro testing of novel implant materials.

Effects of Porphyromonas gingivalis and Aggregatibacter actinomycetemcomitans on Modeling Subgingival Microbiome and Impairment of Oral Epithelial Barrier

Periodontitis is an exemplar of dysbiosis associated with the coordinated action of multiple members within the microbial consortium. The polymicrobial synergy and dysbiosis hypothesis proposes a dynamic host-microbiome balance, with certain modulators capable of disrupting eubiosis and driving shifts towards dysbiosis within the community. However, these factors remain to be explored. We established a Porphyromonas gingivalis- or Aggregatibacter actinomycetemcomitans-modified subgingival microbiome model and 16S rRNA sequencing revealed that P. gingivalis and A. actinomycetemcomitans altered the microbiome structure and composition indicated by α and β diversity metrics. P. gingivalis increased the subgingival dysbiosis index (SDI), while A. actinomycetemcomitans resulted in a lower SDI. Furthermore, P. gingivalis-stimulated microbiomes compromised epithelium function and reduced expression of tight junction proteins, whereas A. actinomycetemcomitans yielded mild effects. In conclusion, by inoculating P. gingivalis, we created dysbiotic microcosm biofilms in vitro resembling periodontitis-related subgingival microbiota, exhibiting enhanced dysbiosis and impaired epithelium integrity.

The Regulatory Effect of Coaggregation Between Fusobacterium nucleatum and Streptococcus gordonii on the Synergistic Virulence to Human Gingival Epithelial Cells

In subgingival plaque biofilms, Fusobacterium nucleatum is closely related to the occurrence and development of periodontitis. Streptococcus gordonii, as an accessory pathogen, can coaggregate with periodontal pathogens, facilitating the subgingival colonization of periodontal pathogens. Studies have shown that F. nucleatum can coaggregate with S. gordonii and colonize the subgingival plaque. However, most studies have focused on monocultures or coinfection of species and the potential impact of coaggregation between the two species on periodontal interactions to human gingival epithelial cells (hGECs) remains poorly understood. The present study explored the effect of coaggregation between F. nucleatum and S. gordonii on subgingival synergistic virulence to hGECs. The results showed that coaggregation inhibited the adhesion and invasion of F. nucleatum to hGECs compared with that in the F. nucleatum monoculture and coinfection group. Coaggregation and coinfection with F. nucleatum both enhanced S. gordonii adhesion to hGECs, but neither of the two groups affected S. gordonii invasion to hGECs compared with S. gordonii monoculture. The gene expression levels of TLR2 and TLR4 in hGECs in the coaggregation group were higher than those in the monoculture groups but lower than those in the coinfection group. Compared with coinfection, the coaggregation inhibited apoptosis of hGECs and promoted the secretion of the proinflammatory cytokines TNF-α and IL-6 by hGECs, showed a synergistic inflammatory effect, while coaggregation inhibited the secretion of the anti-inflammatory cytokine TGF-β1. Coaggregation enhanced the phosphorylation of p65, p38, and JNK proteins and therefore activated the NF-κB and MAPK signaling pathways. Pretreatment with a pathway antagonist/inhibitor decreased the phosphorylation levels of proteins and the secretion of TNF-α and IL-6. In conclusion, coaggregation inhibited the adhesion and invasion of F. nucleatum to hGECs. However, it enhanced the adhesion of S. gordonii to hGECs. Compared with coinfection, coaggregation inhibited the apoptosis of hGECs. The coaggregation coordinately promoted the secretion of TNF-α and IL-6 by hGECs through the TLR/NF-κB and TLR/MAPK signaling pathways while inhibiting the secretion of TGF-β1, thus aggravating the inflammatory response of hGECs.

Generation and functional characterization of recombinant Porphyromonas gingivalis W83 FimA

Porphyromonas gingivalis (P. gingivalis) is regarded as a keystone pathogen in destructive periodontal diseases. It expresses a variety of virulence factors, amongst them fimbriae that are involved in colonization, invasion, establishment and persistence of the bacteria inside the host cells. The fimbriae also were demonstrated to affect the host immune-response mechanisms. The major fimbriae are able to bind specifically to different host cells, amongst them peripheral blood monocytes. The interaction of these cells with fimbriae induces release of cytokines such as interleukin-1 (IL-1), IL-6, and tumor necrosis factor-α (TNF-α). The aim of this study was to generate recombinant major FimA protein from P. gingivalis W83 fimbriae and to prove its biological activity. FimA of P. gingivalis W83 was amplified from chromosomal DNA, cloned in a vector and transferred into Listeria innocua. (L. innocua).The expressed protein was harvested and purified using FPLC via a His trap HP column. The identity and purity was demonstrated by gel-electrophoresis and mass-spectrometry. The biological activity was assessed by stimulation of human oral epithelial cells and peripheral blood monocytes with the protein and afterwards cytokines in the supernatants were quantified by enzyme linked immunosorbent assay (ELISA) and cytometric bead array. Recombinant FimA could successfully be generated and purified. Gel-electrophoresis and mass-spectrometry confirmed that the detected sequences are identical with FimA. Stimulation of human monocytes induced the release of high concentrations of IL-1β, IL-6, IL-10 and TNF-α by these cells. In conclusion, a recombinant FimA protein was established and its biological activity was proven. This protein may serve as a promising agent for further investigation of its role in periodontitis and possible new therapeutic approaches.

Effects of 2% sodium fluoride solution on the prevention of streptococcal adhesion to titanium and zirconia surfaces

Streptococci are associated with dental plaque formation as the early-colonizing bacteria that adhere to titanium (CpTi) and zirconia (TZP) implant abutment surfaces. Effective prevention of peri-implantitis may be possible by removing streptococci as target. This study aimed to evaluate the effects of 2% NaF on the prevention of streptococcal adhesion to CpTi and TZP. After immersion in 2% NaF for 90 min, surface characterization of mirror-polished CpTi and TZP disks were assesed using XPS, EPMA, and SEM. S. sanguinis, S. gordonii, and S. oralis were used as the streptococcal bacterial strains. After 24 h culture, bacterial adhesion was evaluated using an ATP-bioluminescent assay and SEM. In XPS, EPMA, and SEM analyses, fluoride was detected on the CpTi and TZP surfaces after 2% NaF immersion with no signs of localization, and no corrosion on the CpTi disks. Based on the adhesion assay, the adherences of S. sanguinis, S. gordonii, and S. oralis were significantly lower with NaF than without NaF in CpTi (p = 0.005, 0.001, and 0.001, respectively) and TZP (p = 0.003, 0.002, and 0.001). This was also confirmed by SEM. In conclusion, 2% NaF reduced the adhesion of streptococci to the CpTi and TZP surfaces.

Adhesion of streptococci to titanium and zirconia

The purpose of this study was to evaluate the adherence of streptococci to disks of titanium (commercially pure titanium: CpTi) and zirconia (tetragonal zirconia polycrystals: TZP). CpTi and yttria-stabilized TZP disks with a mirror-polished surface were used as specimens. The arithmetic mean surface roughness (Ra and Sa) and the surface wettability of the experimental specimens were measured. For analyzing the outermost layer of the experimental specimens, X-ray photoelectron spectroscopy (XPS) analysis was performed. Streptococcus sanguinis, S. gordonii, S. oralis, and S. mutans were used as streptococcal bacterial strains. These bacterial cultures were grown for 24 h on CpTi and TZP. The number of bacterial adhesions was estimated using an ATP-bioluminescent assay, and scanning electron microscope (SEM) observation of the adhered bacterial specimens was performed. No significant differences in surface roughness or wettability were found between CpTi and TZP. In XPS analyses, outermost layer of CpTi included Ti0 and Ti⁴⁺, and outermost layer of TZP included Zr⁴⁺. In the cell adhesion assay, the adherences of S. sanguinis, S. gordonii, and S. oralis to TZP were significantly lower than those to CpTi (p < 0.05); however, significant difference was not observed for S. mutans among the specimens. The adherence to CpTi and TZP of S. mutans was significantly lower than that of S. sanguinis, S. gordonii, and S. oralis. These results were confirmed by SEM. S. sanguinis, S. gordonii, and S. oralis adhered less to TZP than to CpTi, but the adherence of S. mutans was similar to both surfaces. S. mutans was less adherent compare with the other streptococci tested in those specimens.

Commensal and pathogenic biofilms differently modulate peri-implant oral mucosa in an organotypic model

The impact of oral commensal and pathogenic bacteria on peri-implant mucosa is not well understood, despite the high prevalence of peri-implant infections. Hence, we investigated responses of the peri-implant mucosa to Streptococcus oralis or Aggregatibacter actinomycetemcomitans biofilms using a novel in vitro peri-implant mucosa-biofilm model. Our 3D model combined three components, organotypic oral mucosa, implant material, and oral biofilm, with structural assembly close to native situation. S. oralis induced a protective stress response in the peri-implant mucosa through upregulation of heat shock protein (HSP70) genes. Attenuated inflammatory response was indicated by reduced cytokine levels of interleukin-6 (IL-6), interleukin-8 (CXCL8), and monocyte chemoattractant protein-1 (CCL2). The inflammatory balance was preserved through increased levels of tumor necrosis factor-alpha (TNF-α). A. actinomycetemcomitans induced downregulation of genes important for cell survival and host inflammatory response. The reduced cytokine levels of chemokine ligand 1 (CXCL1), CXCL8, and CCL2 also indicated a diminished inflammatory response. The induced immune balance by S. oralis may support oral health, whereas the reduced inflammatory response to A. actinomycetemcomitans may provide colonisation advantage and facilitate later tissue invasion. The comprehensive characterisation of peri-implant mucosa-biofilm interactions using our 3D model can provide new knowledge to improve strategies for prevention and therapy of peri-implant disease.

Time-Course Transcriptome Analysis for Drug Repositioning in Fusobacterium nucleatum-Infected Human Gingival Fibroblasts

Fusobacterium nucleatum (F. nucleatum) is a crucial periodontal pathogen and human gingival fibroblasts (GFs) are the first line of defense against oral pathogens. However, the research on potential molecular mechanisms of host defense and effective treatment of F. nucleatum infection in GFs remains scarce. In this study, we undertook a time-series experiment and performed an RNA-seq analysis to explore gene expression profiles during the process of F. nucleatum infection in GFs. Differentially expressed genes (DEGs) could be divided into three coexpression clusters. Functional analysis revealed that the immune-related signaling pathways were more overrepresented at the early stage, while metabolic pathways were mainly enriched at the late stage. We computationally identified several U.S. Food and Drug Administration (FDA)-approved drugs that could protect the F. nucleatum infected GFs via a coexpression-based drug repositioning approach. Biologically, we confirmed that six drugs (etravirine, zalcitabine, wortmannin, calcium D-pantothenate, ellipticine, and tanespimycin) could significantly decrease F. nucleatum-induced reactive oxygen species (ROS) generation and block the Protein Kinase B (PKB/AKT)/mitogen-activated protein kinase signaling pathways. Our study provides more detailed molecular mechanisms of the process by which F. nucleatum infects GFs and illustrates the value of the cogena-based drug repositioning method and the potential therapeutic application of these tested drugs in the treatment of F. nucleatum infection.

Prolyl hydroxylase inhibitor DMOG suppressed inflammatory cytokine production in human gingival fibroblasts stimulated with Fusobacterium nucleatum

OBJECTIVE

Fusobacterium nucleatum (F. nucleatum) is one of the most common bacteria involved in the initiation and progression of periodontal diseases. Pharmacological inhibitor of prolyl hydroxylases (PHDs), dimethyloxallyl glycine (DMOG), has been reported to exert anti-inflammatory effects. The aim of this investigation was to evaluate the role of DMOG in inflammatory cytokine production of human gingival fibroblasts (HGFs) stimulated with F. nucleatum.

MATERIAL AND METHODS

HGFs were pretreated with 10, 50, and 100 μM DMOG for 24 h before infected with F. nucleatum (MOI = 100). Cell morphology and survival after infection with F. nucleatum were determined by crystal violet staining assay. The mRNA levels of interleukin (IL)-6, IL-8, tumor necrosis factor (TNF)-α, and IL-1β were evaluated by quantitative real-time polymerase chain reaction (qRT-PCR). The production of IL-6, IL-8, TNF-α, and IL-1β was assessed by enzyme-linked immunosorbent assay (ELISA).

RESULTS

F. nucleatum did not affect the morphology and survival of HGFs by the concentrations of MOI (multiplicity of infection) = 10, 50, and 100. The mRNA levels of IL-6, IL-8, TNF-α, and IL-1β were significantly enhanced with the stimulation of F. nucleatum, and the maximal effect reached at 6 h. The secretion of IL-6, IL-8, and TNF-α was significantly upregulated by the infection of F. nucleatum while the production of IL-1β was nearly unchanged. Above all, DMOG suppressed F. nucleatum-stimulated IL-6, IL-8, TNF-α, and IL-1β expressions.

CONCLUSIONS

These data indicate that prolyl hydroxylase inhibitor DMOG partly downregulates inflammatory cytokine expression in F. nucleatum-infected HGFs.

CLINICAL RELEVANCE

DMOG may provide a novel strategy for the therapy of periodontitis.

Structural properties of a haemophore facilitate targeted elimination of the pathogen Porphyromonas gingivalis

Porphyromonas gingivalis is a keystone bacterial pathogen of chronic periodontitis. P. gingivalis is unable to synthesise the porphyrin macrocycle and relies on exogenous porphyrin, including haem or haem biosynthesis intermediates from host sources. We show that under the iron-limited conditions prevailing in tissue environments, P. gingivalis expresses a haemophore-like protein, HusA, to mediate the uptake of essential porphyrin and support pathogen survival within epithelial cells. The structure of HusA, together with titration studies, mutagenesis and in silico docking, show that haem binds in a hydrophobic groove on the α-helical structure without the typical iron coordination seen in other haemophores. This mode of interaction allows HusA to bind to a variety of abiotic and metal-free porphyrins with higher affinities than to haem. We exploit this unusual porphyrin-binding activity of HusA to target a prototypic deuteroporphyrin-metronidazole conjugate with restricted antimicrobial specificity in a Trojan horse strategy that effectively kills intracellular P. gingivalis.

Transcriptome profiling analysis of senescent gingival fibroblasts in response to Fusobacterium nucleatum infection

Periodontal disease is caused by dental plaque biofilms. Fusobacterium nucleatum is an important periodontal pathogen involved in the development of bacterial complexity in dental plaque biofilms. Human gingival fibroblasts (GFs) act as the first line of defense against oral microorganisms and locally orchestrate immune responses by triggering the production of reactive oxygen species and pro-inflammatory cytokines (IL-6 and IL-8). The frequency and severity of periodontal diseases is known to increase in elderly subjects. However, despite several studies exploring the effects of aging in periodontal disease, the underlying mechanisms through which aging affects the interaction between F. nucleatum and human GFs remain unclear. To identify genes affected by infection, aging, or both, we performed an RNA-Seq analysis using GFs isolated from a single healthy donor that were passaged for a short period of time (P4) 'young GFs' or for longer period of time (P22) 'old GFs', and infected or not with F. nucleatum. Comparing F. nucleatum-infected and uninfected GF(P4) cells the differentially expressed genes (DEGs) were involved in host defense mechanisms (i.e., immune responses and defense responses), whereas comparing F. nucleatum-infected and uninfected GF(P22) cells the DEGs were involved in cell maintenance (i.e., TGF-β signaling, skeletal development). Most DEGs in F. nucleatum-infected GF(P22) cells were downregulated (85%) and were significantly associated with host defense responses such as inflammatory responses, when compared to the DEGs in F. nucleatum-infected GF(P4) cells. Five genes (GADD45b, KLF10, CSRNP1, ID1, and TM4SF1) were upregulated in response to F. nucleatum infection; however, this effect was only seen in GF(P22) cells. The genes identified here appear to interact with each other in a network associated with free radical scavenging, cell cycle, and cancer; therefore, they could be potential candidates involved in the aged GF's response to F. nucleatum infection. Further studies are needed to confirm these observations.

LRLSHMDA: Laplacian Regularized Least Squares for Human Microbe-Disease Association prediction

An increasing number of evidences indicate microbes are implicated in human physiological mechanisms, including complicated disease pathology. Some microbes have been demonstrated to be associated with diverse important human diseases or disorders. Through investigating these disease-related microbes, we can obtain a better understanding of human disease mechanisms for advancing medical scientific progress in terms of disease diagnosis, treatment, prevention, prognosis and drug discovery. Based on the known microbe-disease association network, we developed a semi-supervised computational model of Laplacian Regularized Least Squares for Human Microbe-Disease Association (LRLSHMDA) by introducing Gaussian interaction profile kernel similarity calculation and Laplacian regularized least squares classifier. LRLSHMDA reached the reliable AUCs of 0.8909 and 0.7657 based on the global and local leave-one-out cross validations, respectively. In the framework of 5-fold cross validation, average AUC value of 0.8794 +/-0.0029 further demonstrated its promising prediction ability. In case studies, 9, 9 and 8 of top-10 predicted microbes have been manually certified to be associated with asthma, colorectal carcinoma and chronic obstructive pulmonary disease by published literature evidence. Our proposed model achieves better prediction performance relative to the previous model. We expect that LRLSHMDA could offer insights into identifying more promising human microbe-disease associations in the future.

Polymicrobial Biofilm Studies: From Basic Science to Biofilm Control

Microbes rarely exist as single species planktonic forms as they have been commonly studied in the laboratory. Instead, the vast majority exists as part of complex polymicrobial biofilm communities attached to host and environmental surfaces. The oral cavity represents one of the most diverse and well-studied polymicrobial consortia. Despite a burgeoning field of mechanistic biofilm research within the past decades, our understanding of interactions that occur between microbial members within oral biofilms is still limited. Thus, the primary objective of this review is to focus on polymicrobial biofilm formation, microbial interactions and signaling events that mediate oral biofilm development, consequences of oral hygiene on both local and systemic disease, and potential therapeutic strategies to limit oral dysbiosis.

Polymicrobial synergy and dysbiosis in inflammatory disease

Uncontrolled inflammation of the periodontal area may arise when complex microbial communities transition from a commensal to a pathogenic entity. Communication among constituent species leads to polymicrobial synergy between metabolically compatible organisms that acquire functional specialization within the developing community. Keystone pathogens, even at low abundance, elevate community virulence, and the resulting dysbiotic community targets specific aspects of host immunity to further disable immune surveillance while promoting an overall inflammatory response. Inflammophilic organisms benefit from proteinaceous substrates derived from inflammatory tissue breakdown. Inflammation and dysbiosis reinforce each other, and the escalating environmental changes further select for a pathobiotic community. We have synthesized the polymicrobial synergy and dysbiotic components of the process into a new model for inflammatory diseases.

[Periodontal disease in pediatric rheumatic diseases]

Gingivitis and periodontitis are immunoinflammatory periodontal diseases characterized by chronic localized infections usually associated with insidious inflammation This narrative review discusses periodontal diseases and mechanisms influencing the immune response and autoimmunity in pediatric rheumatic diseases (PRD), particularly juvenile idiopathic arthritis (JIA), childhood-onset systemic lupus erythematosus (C-SLE) and juvenile dermatomyositis (JDM). Gingivitis was more frequently observed in these diseases compared to health controls, whereas periodontitis was a rare finding. In JIA patients, gingivitis and periodontitis were related to mechanical factors, chronic arthritis with functional disability, dysregulation of the immunoinflammatory response, diet and drugs, mainly corticosteroids and cyclosporine. In C-SLE, gingivitis was associated with longer disease period, high doses of corticosteroids, B-cell hyperactivation and immunoglobulin G elevation. There are scarce data on periodontal diseases in JDM population, and a unique gingival pattern, characterized by gingival erythema, capillary dilation and bush-loop formation, was observed in active patients. In conclusion, gingivitis was the most common periodontal disease in PRD. The observed association with disease activity reinforces the need for future studies to determine if resolution of this complication will influence disease course or severity.

Porphyromonas gingivalis-induced reactive oxygen species activate JAK2 and regulate production of inflammatory cytokines through c-Jun

Pathogen-induced reactive oxygen species (ROS) play a crucial role in host innate immune responses through regulating the quality and quantity of inflammatory mediators. However, the underlying molecular mechanisms of this effect have yet to be clarified. In this study, we examined the mechanism of action of ROS stimulated by Porphyromonas gingivalis in gingival epithelial cells. P. gingivalis induced the rapid production of ROS, which lead to the phosphorylation of JAK2 and increased levels of secreted proinflammatory cytokines interleukin-6 (IL-6) and IL-1β. Neutralization of ROS by N-acetyl-l-cysteine (NAC) abrogated the phosphorylation of JAK2 and suppressed the production of IL-6 and IL-1β. ROS-mediated phosphorylation of JAK2 induced the phosphoactivation of c-Jun amino-terminal protein kinase (JNK) and the downstream transcriptional regulator c-Jun. Inhibition of JAK2, either pharmacologically or by small interfering RNA (siRNA), reduced both the phosphorylation of these molecules and the production of proinflammatory cytokines in response to P. gingivalis. Furthermore, pharmacological inhibition or siRNA-mediated gene silencing of JNK or c-Jun mimicked the effect of JAK2 inhibition to suppress P. gingivalis-induced IL-6 and IL-1β levels. The results show that ROS-mediated activation of JAK2 is required for P. gingivalis-induced inflammatory cytokine production and that the JNK/c-Jun signaling axis is involved in the ROS-dependent regulation of IL-1β and IL-6 production.

Breaking the Gingival Epithelial Barrier: Role of the Aggregatibacter actinomycetemcomitans Cytolethal Distending Toxin in Oral Infectious Disease

The Gram-negative bacterium Aggregatibacter actinomycetemcomitans is part of the HACEK group that causes infective endocarditis, a constituent of the oral flora that promotes some forms of periodontal disease and a member of the family of species that secrete a cytolethal distending toxin (Cdt). The family of bacteria that express the cdt genes participate in diseases that involve the disruption of a mucosal or epithelial layer. In vitro studies have shown that human gingival epithelial cells (HGEC) are native targets of the Cdt that typically induces DNA damage that signals growth arrest at the G₂/M interphase of the cell cycle. The gingival epithelium is an early line of defense in the oral cavity against microbial assault. When damaged, bacteria collectively gain entry into the underlying connective tissue where microbial products can affect processes and pathways in infiltrating inflammatory cells culminating in the destruction of the attachment apparatus of the tooth. One approach has been the use of an ex vivo gingival explant model to assess the effects of the Cdt on the morphology and integrity of the tissue. The goal of this review is to provide an overview of these studies and to critically examine the potential contribution of the Cdt to the breakdown of the protective gingival barrier.

Predictive modeling of gingivitis severity and susceptibility via oral microbiota

Predictive modeling of human disease based on the microbiota holds great potential yet remains challenging. Here, 50 adults underwent controlled transitions from naturally occurring gingivitis, to healthy gingivae (baseline), and to experimental gingivitis (EG). In diseased plaque microbiota, 27 bacterial genera changed in relative abundance and functional genes including 33 flagellar biosynthesis-related groups were enriched. Plaque microbiota structure exhibited a continuous gradient along the first principal component, reflecting transition from healthy to diseased states, which correlated with Mazza Gingival Index. We identified two host types with distinct gingivitis sensitivity. Our proposed microbial indices of gingivitis classified host types with 74% reliability, and, when tested on another 41-member cohort, distinguished healthy from diseased individuals with 95% accuracy. Furthermore, the state of the microbiota in naturally occurring gingivitis predicted the microbiota state and severity of subsequent EG (but not the state of the microbiota during the healthy baseline period). Because the effect of disease is greater than interpersonal variation in plaque, in contrast to the gut, plaque microbiota may provide advantages in predictive modeling of oral diseases.

Genetic exchange of fimbrial alleles exemplifies the adaptive virulence strategy of Porphyromonas gingivalis

Porphyromonas gingivalis is a gram–negative anaerobic bacterium, a member of the human oral microbiome, and a proposed “keystone” pathogen in the development of chronic periodontitis, an inflammatory disease of the gingiva. P. gingivalis is a genetically diverse species, and is able to exchange chromosomal DNA between strains by natural competence and conjugation. In this study, we investigate the role of horizontal DNA transfer as an adaptive process to modify behavior, using the major fimbriae as our model system, due to their critical role in mediating interactions with the host environment. We show that P. gingivalis is able to exchange fimbrial allele types I and IV into four distinct strain backgrounds via natural competence. In all recombinants, we detected a complete exchange of the entire fimA allele, and the rate of exchange varies between the different strain backgrounds. In addition, gene exchange within other regions of the fimbrial genetic locus was identified. To measure the biological implications of these allele swaps we compared three genotypes of fimA in an isogenic background, strain ATCC 33277. We demonstrate that exchange of fimbrial allele type results in profound phenotypic changes, including the quantity of fimbriae elaborated, membrane blebbing, auto-aggregation and other virulence-associated phenotypes. Replacement of the type I allele with either the type III or IV allele resulted in increased invasion of gingival fibroblast cells relative to the isogenic parent strain. While genetic variability is known to impact host-microbiome interactions, this is the first study to quantitatively assess the adaptive effect of exchanging genes within the pan genome cloud. This is significant as it presents a potential mechanism by which opportunistic pathogens may acquire the traits necessary to modify host-microbial interactions.

Genetic diversity in the oral pathogen Porphyromonas gingivalis: molecular mechanisms and biological consequences

Porphyromonas gingivalis is a Gram-negative anaerobic bacterium that colonizes the human oral cavity. It is implicated in the development of periodontitis, a chronic periodontal disease affecting half of the adult population in the USA. To survive in the oral cavity, these bacteria must colonize dental plaque biofilms in competition with other bacterial species. Long-term survival requires P. gingivalis to evade host immune responses, while simultaneously adapting to the changing physiology of the host and to alterations in the plaque biofilm. In reflection of this highly variable niche, P. gingivalis is a genetically diverse species and in this review the authors summarize genetic diversity as it relates to pathogenicity in P. gingivalis. Recent studies revealing a variety of mechanisms by which adaptive changes in genetic content can occur are also reviewed. Understanding the genetic plasticity of P. gingivalis will provide a better framework for understanding the host-microbe interactions associated with periodontal disease.

Suppression of T-cell chemokines by Porphyromonas gingivalis

Porphyromonas gingivalis is a major pathogen in periodontal disease and is associated with immune dysbiosis. In this study, we found that P. gingivalis did not induce the expression of the T-cell chemokine IP-10 (CXCL10) from neutrophils, peripheral blood mononuclear cells (PBMCs), or gingival epithelial cells. Furthermore, P. gingivalis suppressed gamma interferon (IFN-γ)-stimulated release of IP-10, ITAC (CXCL11), and Mig (CXCL9) from epithelial cells and inhibited IP-10 secretion in a mixed infection with the otherwise stimulatory Fusobacterium nucleatum. Inhibition of chemokine expression occurred at the level of gene transcription and was associated with downregulation of interferon regulatory factor 1 (IRF-1) and decreased levels of Stat1. Ectopic expression of IRF-1 in epithelial cells relieved P. gingivalis-induced inhibition of IP-10 release. Direct contact between P. gingivalis and epithelial cells was not required for IP-10 inhibition. These results highlight the immune-disruptive potential of P. gingivalis. Suppression of IP-10 and other Th1-biasing chemokines by P. gingivalis may perturb the balance of protective and destructive immunity in the periodontal tissues and facilitate the pathogenicity of oral microbial communities.

Proteomic and bioinformatic profile of primary human oral epithelial cells

Wounding of the oral mucosa occurs frequently in a highly septic environment. Remarkably, these wounds heal quickly and the oral cavity, for the most part, remains healthy. Deciphering the normal human oral epithelial cell (NHOEC) proteome is critical for understanding the mechanism(s) of protection elicited when the mucosal barrier is intact, as well as when it is breached. Combining 2D gel electrophoresis with shotgun proteomics resulted in identification of 1662 NHOEC proteins. Proteome annotations were performed based on protein classes, molecular functions, disease association and membership in canonical and metabolic signaling pathways. Comparing the NHOEC proteome with a database of innate immunity-relevant interactions (InnateDB) identified 64 common proteins associated with innate immunity. Comparison with published salivary proteomes revealed that 738/1662 NHOEC proteins were common, suggesting that significant numbers of salivary proteins are of epithelial origin. Gene ontology analysis showed similarities in the distributions of NHOEC and saliva proteomes with regard to biological processes, and molecular functions. We also assessed the interindividual variability of the NHOEC proteome and observed it to be comparable with other primary cells. The baseline proteome described in this study should serve as a resource for proteome studies of the oral mucosa, especially in relation to disease processes.

MAPK usage in periodontal disease progression

In periodontal disease, host recognition of bacterial constituents, including lipopolysaccharide (LPS), induces p38 MAPK activation and subsequent inflammatory cytokine expression, favoring osteoclastogenesis and increased net bone resorption in the local periodontal environment. In this paper, we discuss evidence that the p38/MAPK-activated protein kinase-2 (MK2) signaling axis is needed for periodontal disease progression: an orally administered p38α inhibitor reduced the progression of experimental periodontal bone loss by reducing inflammation and cytokine expression. Subsequently, the significance of p38 signaling was confirmed with RNA interference to attenuate MK2-reduced cytokine expression and LPS-induced alveolar bone loss. MAPK phosphatase-1 (MKP-1), a negative regulator of MAPK activation, was also critical for periodontal disease progression. In MPK-1-deficient mice, p38-sustained activation increased osteoclast formation and bone loss, whereas MKP-1 overexpression dampened p38 signaling and subsequent cytokine expression. Finally, overexpression of the p38/MK2 target RNA-binding tristetraprolin (TTP) decreased mRNA stability of key inflammatory cytokines at the posttranscriptional level, thereby protecting against periodontal inflammation. Collectively, these studies highlight the importance of p38 MAPK signaling in immune cytokine production and periodontal disease progression.

Preliminary characterization of the oral microbiota of Chinese adults with and without gingivitis

BACKGROUND

Microbial communities inhabiting human mouth are associated with oral health and disease. Previous studies have indicated the general prevalence of adult gingivitis in China to be high. The aim of this study was to characterize in depth the oral microbiota of Chinese adults with or without gingivitis, by defining the microbial phylogenetic diversity and community-structure using highly paralleled pyrosequencing.

METHODS

Six non-smoking Chinese, three with and three without gingivitis (age range 21-39 years, 4 females and 2 males) were enrolled in the present cross-sectional study. Gingival parameters of inflammation and bleeding on probing were characterized by a clinician using the Mazza Gingival Index (MGI). Plaque (sampled separately from four different oral sites) and salivary samples were obtained from each subject. Sequences and relative abundance of the bacterial 16 S rDNA PCR-amplicons were determined via pyrosequencing that produced 400 bp-long reads. The sequence data were analyzed via a computational pipeline customized for human oral microbiome analyses. Furthermore, the relative abundances of selected microbial groups were validated using quantitative PCR.

RESULTS

The oral microbiomes from gingivitis and healthy subjects could be distinguished based on the distinct community structures of plaque microbiomes, but not the salivary microbiomes. Contributions of community members to community structure divergence were statistically accessed at the phylum, genus and species-like levels. Eight predominant taxa were found associated with gingivitis: TM7, Leptotrichia, Selenomonas, Streptococcus, Veillonella, Prevotella, Lautropia, and Haemophilus. Furthermore, 98 species-level OTUs were identified to be gingivitis-associated, which provided microbial features of gingivitis at a species resolution. Finally, for the two selected genera Streptococcus and Fusobacterium, Real-Time PCR based quantification of relative bacterial abundance validated the pyrosequencing-based results.

CONCLUSIONS

This methods study suggests that oral samples from this patient population of gingivitis can be characterized via plaque microbiome by pyrosequencing the 16 S rDNA genes. Further studies that characterize serial samples from subjects (longitudinal study design) with a larger population size may provide insight into the temporal and ecological features of oral microbial communities in clinically-defined states of gingivitis.

Epithelial cell innate response to Candida albicans

With the advent of treatments and diseases such as AIDS resulting in increasing numbers of patients with suppressed immune systems, fungal diseases are an escalating problem. Candida albicans is the most common of these fungal pathogens, causing infections in many of these patients. It is therefore important to understand how immunity to this fungus is regulated and how it might be manipulated. Although work has been done to identify the receptors, fungal moieties, and responses involved in anti-Candida immunity, most studies have investigated interactions with myeloid or lymphoid cells. Given that the first site of contact of C. albicans with its host is the mucosal epithelial surface, recent studies have begun to focus on interactions of C. albicans with this site. The results are startling yet in retrospect obvious, indicating that epithelial cells play an important role in these interactions, initiating responses and even providing a level of protection. These findings have obvious implications, not just for fungal pathogens, but also for identifying how host organisms can distinguish between commensal and pathogenic microbes. This review highlights some of these recent findings and discusses their importance in the wider context of infection and immunity.

Prevention of aspiration pneumonia (AP) with oral care

AP is a major cause of morbidity and mortality in elderly patients, especially frail elderly patients. The aim of this article is to review effect of oral care, including oral hygiene and improvement of oral function, on the prevention of AP among elderly people in hospitals and nursing homes. There is now a substantial body of work studying the effect of oral care on the prevention of respiratory diseases. Oral hygiene, consisting of oral decontamination and mechanical cleaning by dental professionals, has resulted in significant clinical effects (decreased incidence of pneumonia and decreased mortality from respiratory diseases) in clinical randomized trials. Moreover, studies examining oral colonization by pneumonia pathogens have shown the effect of oral hygiene on eliminating these pathogens. In addition, swallowing training has been shown to improve the movement and function of swallowing-related muscles, also resulting in decreased incidence of pneumonia. These findings support the contention that oral care is effective in the prevention of AP.

Mucosal immunity and Candida albicans infection

Interactions between mucosal surfaces and microbial microbiota are key to host defense, health, and disease. These surfaces are exposed to high numbers of microbes and must be capable of distinguishing between those that are beneficial or avirulent and those that will invade and cause disease. Our understanding of the mechanisms involved in these discriminatory processes has recently begun to expand as new studies bring to light the importance of epithelial cells and novel immune cell subsets such as T(h)17 T cells in these processes. Elucidating how these mechanisms function will improve our understanding of many diverse diseases and improve our ability to treat patients suffering from these conditions. In our voyage to discover these mechanisms, mucosal interactions with opportunistic commensal organisms such as the fungus Candida albicans provide insights that are invaluable. Here, we review current knowledge of the interactions between C. albicans and epithelial surfaces and how this may shape our understanding of microbial-mucosal interactions.

Interaction of oral bacteria with gingival epithelial cell multilayers

Primary gingival epithelial cells were cultured in multilayers as a model for the study of interactions with oral bacteria associated with health and periodontal disease. Multilayers maintained at an air-liquid interface in low-calcium medium displayed differentiation and cytokeratin properties characteristic of junctional epithelium. Multilayers were infected with fluorescently labeled Porphyromonas gingivalis, Aggregatibacter actinomycetemcomitans, Fusobacterium nucleatum or Streptococcus gordonii, and bacterial association was determined by confocal microscopy and quantitative image analysis. Porphyromonas gingivalis invaded intracellularly and spread from cell to cell; A. actinomycetemcomitans and F. nucleatum remained extracellular and showed intercellular movement through the multilayer; whereas S. gordonii remained extracellular and predominantly associated with the superficial cell layer. None of the bacterial species disrupted barrier function as measured by transepithelial electrical resistance. P. gingivalis did not elicit secretion of proinflammatory cytokines. However, A. actinomycetemcomitans and S. gordonii induced interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α), IL-6 and IL-8 secretion; and F. nucleatum stimulated production of IL-1β and TNF-α. Aggregatibacter actinomycetemcomitans, F. nucleatum and S. gordonii, but not P. gingivalis, increased levels of apoptosis after 24 h infection. The results indicate that the organisms with pathogenic potential were able to traverse the epithelium, whereas the commensal bacteria did not. In addition, distinct host responses characterized the interaction between the junctional epithelium and oral bacteria.

Tannerella forsythia infection-induced calvarial bone and soft tissue transcriptional profiles

Tannerella forsythia is associated with subgingival biofilms in adult periodontitis, although the molecular mechanisms contributing to chronic inflammation and loss of periodontal bone remain unclear. We examined changes in the host transcriptional profiles during a T. forsythia infection using a murine calvarial model of inflammation and bone resorption. Tannerella forsythia was injected into the subcutaneous soft tissue over calvariae of BALB/c mice for 3 days, after which the soft tissues and calvarial bones were excised. RNA was isolated and Murine GeneChip (Affymetrix, Santa Clara, CA) array analysis of transcript profiles showed that 3226 genes were differentially expressed in the infected soft tissues (P < 0.05) and 2586 genes were differentially transcribed in calvarial bones after infection. Quantitative real-time reverse transcription-polymerase chain reaction analysis of transcription levels of selected genes corresponded well with the microarray results. Biological pathways significantly impacted by T. forsythia infection in calvarial bone and soft tissue included leukocyte transendothelial migration, cell adhesion molecules (immune system), extracellular matrix-receptor interaction, adherens junction, and antigen processing and presentation. Histologic examination revealed intense inflammation and increased osteoclasts in calvariae compared with controls. In conclusion, localized T. forsythia infection differentially induces transcription of a broad array of host genes, and the profiles differ between inflamed soft tissues and calvarial bone.

Inflammation and uncoupling as mechanisms of periodontal bone loss

Periodontal disease is characterized by both inflammation and bone loss. Advances in research in both these areas have led to a new appreciation of not only each field but also the intimate relationship between inflammation and bone loss. This relationship has resulted in a new field of science called osteoimmunology and provides a context for better understanding the pathogenesis of periodontal disease. In this review, we discuss several aspects of the immuno-inflammatory host response that ultimately results in loss of alveolar bone. A proposal is made that periodontal inflammation not only stimulates osteoclastogenesis but also interferes with the uncoupling of bone formation and bone resorption, consistent with a pathologic process. Furthermore, arguments based on experimental animal models suggest a critical role of the spatial and temporal aspects of inflammation in the periodontium. A review of these findings leads to a new paradigm to help explain more fully the impact of inflammation on alveolar bone in periodontal disease so that it includes the effects of inflammation on uncoupling of bone formation from resorption.

The role of Desulfovibrio desulfuricans lipopolysaccharides in modulation of periodontal inflammation through stimulation of human gingival fibroblasts

OBJECTIVE

Periodontitis is a destructive disease which is likely to be the result of the activities of different microbial complexes. Recently, sulphate-reducing bacteria (SRB) have been detected in the oral cavity, and they have been found to be common inhabitants of sites showing periodontal destruction. The aim of study was to evaluate the influence of endotoxins of Desulfovibrio desulfuricans bacteria on human gingival fibroblast HGF-1 line.

METHODS

The immunological response of gingival fibroblasts was evaluated by determination of their IL-6 and IL-8 secretion upon treatment with D. desulfuricans intestinal and type strain LPS, sodium butyrate (NaB) and IL-1beta. The amounts of cytokines were estimated by ELISA immunoassay. The influence of LPS and NaB on fibroblast proliferation was determined using the CyQUANT Cell Proliferation Assay Kit.

RESULTS

No significant growth inhibition of cells exposed to LPS was observed, except for the culture growing in the presence of intestinal strain endotoxin at the highest concentration (100 microg/ml). The secretion of IL-6 and IL-8 by fibroblasts was increased by D. desulfuricans endotoxins. Cells stimulated with proinflammatory cytokine 1L-1beta showed very high levels of both cytokines secretion. The release of IL-6 and IL-8 by cells in response to LPS and 1L-1beta was modulated by butyric acid.

CONCLUSIONS

The observed response of gingival fibroblasts to stimulation by endotoxin suggests that D. desulfuricans can be involved in the pathogenesis of periodontitis. Moreover, butyrate present in the oral cavity seems to have immunoregulatory effect on cytokine production by gingival fibroblasts under physiological conditions and during microbe-induced inflammation.

The Hpk2-Rrp2 two-component regulatory system of Treponema denticola: a potential regulator of environmental and adaptive responses

Treponema denticola levels in the gingival crevice become elevated as periodontal disease develops. Oral treponemes may account for as much as 40% of the total bacterial population in the periodontal pocket. The stimuli that trigger enhanced growth of T. denticola, and the mechanisms associated with the transmission of these signals, remain to be defined. We hypothesize that the T. denticola open reading frames tde1970 (histidine kinase) and tde1969 (response regulator) constitute a functional two-component regulatory system that regulates, at least in part, responses to the changing environmental conditions associated with the development of periodontal disease. The results presented demonstrate that tde1970 and tde1969 are conserved, universal among T. denticola isolates and transcribed as part of a seven-gene operon in a growth-phase-dependent manner. tde1970 undergoes autophosphorylation and transfers phosphate to tde1969. Henceforth, the proteins encoded by these open reading frames are designated as Hpk2 and Rrp2 respectively. Hpk2 autophosphorylation kinetics were influenced by environmental conditions and by the presence or absence of a PAS domain. It can be concluded that Hpk2 and Rrp2 constitute a functional two-component system that contributes to environmental sensing.

Human trophoblast responses to Porphyromonas gingivalis infection

Porphyromonas gingivalis is a periodontal pathogen that is also associated with preterm low-birthweight delivery. We investigated the transcriptional responses of human extravillous trophoblasts (HTR-8) to infection with P. gingivalis. Over 2000 genes were differentially regulated in HTR-8 cells by P. gingivalis. In ontology analyses of regulated genes, overpopulated biological pathways included mitogen-activated protein (MAP) kinase signaling and cytokine production. Immunoblots confirmed overexpression of the MAP kinase pathway components MEK3, p38 and Max. Furthermore, P. gingivalis infection induced phosphorylation and activation of MEK3 and p38. Increased production of interleukin (IL)-1beta and IL-8 by HTR-8 cells was demonstrated phenotypically by enzyme-linked immunosorbent assay of HTR-8 cell lysates and culture supernatants. Hence, infection of trophoblasts by P. gingivalis can impact signal transduction pathways and modulate cytokine expression, outcomes that could disrupt the maintenance of pregnancy.

Molecular characterization of Treponema denticola infection-induced bone and soft tissue transcriptional profiles

Treponema denticola is associated with subgingival biofilms in adult periodontitis and with acute necrotizing ulcerative gingivitis. However, the molecular mechanisms by which T. denticola impacts periodontal inflammation and alveolar bone resorption remain unclear. Here, we examined changes in the host transcriptional profiles during a T. denticola infection using a murine calvarial model of inflammation and bone resorption. T. denticola was injected into the subcutaneous soft tissue over the calvaria of BALB/c mice for 3 days, after which the soft tissues and the calvarial bones were excised. RNA was isolated and analysed for transcript profiling using Murine GeneChip arrays. Following T. denticola infection, 2905 and 1234 genes in the infected calvarial bones and soft tissues, respectively, were differentially expressed (P <or= 0.05). Biological pathways significantly impacted by T. denticola infection in calvarial bone and calvarial tissue included leukocyte transendothelial migration, cell adhesion (immune system) molecules, cell cycle, extracellular matrix-receptor interaction, focal adhesion, B-cell receptor signaling and transforming growth factor-beta signaling pathways resulting in proinflammatory, chemotactic effects, and T-cell stimulation. In conclusion, localized T. denticola infection differentially induces transcription of a broad array of host genes, the profiles of which differed between inflamed calvarial bone and soft tissues.

Porphyromonas gingivalis infection-induced tissue and bone transcriptional profiles

Porphyromonas gingivalis has been associated with subgingival biofilms in adult periodontitis. However, the molecular mechanisms of its contribution to chronic gingival inflammation and loss of periodontal structural integrity remain unclear. This investigation aimed to examine changes in the host transcriptional profiles during a P. gingivalis infection using a murine calvarial model of inflammation and bone resorption. P. gingivalis FDC 381 was injected into the subcutaneous soft tissue over the calvaria of BALB/c mice for 3 days, after which the soft tissues and calvarial bones were excised. RNA was isolated from infected soft tissues and calvarial bones and was analysed for transcript profiles using Murine GeneChip((R)) arrays to provide a molecular profile of the events that occur following infection of these tissues. After P. gingivalis infection, 6452 and 2341 probe sets in the infected soft tissues and calvarial bone, respectively, were differentially expressed (P </= 0.05). Biological pathways significantly impacted by P. gingivalis infection in tissues and calvarial bone included cell adhesion (immune system) molecules, Toll-like receptors, B-cell receptor signaling, transforming growth factor-beta cytokine family receptor signaling, and major histocompatibility complex class II antigen processing pathways resulting in proinflammatory, chemotactic effects, T-cell stimulation, and downregulation of antiviral and T-cell chemotactic effects. P. gingivalis-induced inflammation activated osteoclasts, leading to local bone resorption. This is the first in vivo evidence that localized P. gingivalis infection differentially induces transcription of a broad array of host genes, the profiles of which differed between inflamed soft tissues and calvarial bone.

Lung infections in cystic fibrosis: deriving clinical insight from microbial complexity

Lower respiratory tract bacterial infections, such as those associated with cystic fibrosis lung disease, represent a major healthcare burden. Treatment strategies are currently informed by culture-based routine diagnostics whose limitations, including an inability to isolate all potentially clinically significant bacterial species present in a sample, are well documented. Some advances have resulted from the introduction of culture-independent molecular assays for the detection of specific pathogens. However, the application of bacterial community profiling techniques to the characterization of these infections has revealed much higher levels of microbial diversity than previously recognized. These findings are leading to a fundamental shift in the way such infections are considered. Increasingly, polymicrobial infections are being viewed as complex communities of interacting organisms, with dynamic processes key to their pathogenicity. Such a model requires an analytical strategy that provides insight into the interactions of all members of the infective community. The rapid advance in sequencing technology, along with protocols that limit analysis to viable bacterial cells, are for the first time providing an opportunity to gain such insight.

Epithelial cell pro-inflammatory cytokine response differs across dental plaque bacterial species

AIM

The dental plaque is comprised of numerous bacterial species, which may or may not be pathogenic. Human gingival epithelial cells (HGECs) respond to perturbation by various bacteria of the dental plaque by production of different levels of inflammatory cytokines, which is a putative reflection of their virulence. The aim of the current study was to determine responses in terms of interleukin (IL)-1beta, IL-6, IL-8 and IL-10 secretion induced by Porphyromonas gingivalis, Aggregatibacter actinomycetemcomitans, Fusobacterium nucleatum and Streptococcus gordonii in order to gauge their virulence potential.

MATERIALS AND METHODS

HGECs were challenged with the four bacterial species, live or heat killed, at various multiplicity of infections and the elicited IL-1beta, IL-6, IL-8 and IL-10 responses were assayed by enzyme-linked immunosorbent assay.

RESULTS

Primary HGECs challenged with live P. gingivalis produced high levels of IL-1beta, while challenge with live A. actinomycetemcomitans gave high levels of IL-8. The opportunistic pathogen F. nucleatum induces the highest levels of pro-inflammatory cytokines, while the commensal S. gordonii is the least stimulatory.

CONCLUSION

We conclude that various dental plaque biofilm bacteria induce different cytokine response profiles in primary HGECs that may reflect their individual virulence or commensal status.

Subgingival bacterial colonization profiles correlate with gingival tissue gene expression

Background

Periodontitis is a chronic inflammatory disease caused by the microbiota of the periodontal pocket. We investigated the association between subgingival bacterial profiles and gene expression patterns in gingival tissues of patients with periodontitis. A total of 120 patients undergoing periodontal surgery contributed with a minimum of two interproximal gingival papillae (range 2-4) from a maxillary posterior region. Prior to tissue harvesting, subgingival plaque samples were collected from the mesial and distal aspects of each tissue sample. Gingival tissue RNA was extracted, reverse-transcribed, labeled, and hybridized with whole-genome microarrays (310 in total). Plaque samples were analyzed using checkerboard DNA-DNA hybridizations with respect to 11 bacterial species. Random effects linear regression models considered bacterial levels as exposure and expression profiles as outcome variables. Gene Ontology analyses summarized the expression patterns into biologically relevant categories.

Results

Wide inter-species variation was noted in the number of differentially expressed gingival tissue genes according to subgingival bacterial levels: Using a Bonferroni correction (p < 9.15 × 10^-7), 9,392 probe sets were differentially associated with levels of Tannerella forsythia, 8,537 with Porphyromonas gingivalis, 6,460 with Aggregatibacter actinomycetemcomitans, 506 with Eikenella corrodens and only 8 with Actinomyces naeslundii. Cluster analysis identified commonalities and differences among tissue gene expression patterns differentially regulated according to bacterial levels.

Conclusion

Our findings suggest that the microbial content of the periodontal pocket is a determinant of gene expression in the gingival tissues and provide new insights into the differential ability of periodontal species to elicit a local host response.

The degree of microbiome complexity influences the epithelial response to infection

Background

The human microflora is known to be extremely complex, yet most pathogenesis research is conducted in mono-species models of infection. Consequently, it remains unclear whether the level of complexity of a host's indigenous flora can affect the virulence potential of pathogenic species. Furthermore, it remains unclear whether the colonization by commensal species affects a host cell's response to pathogenic species beyond the direct physical saturation of surface receptors, the sequestration of nutrients, the modulation of the physico-chemical environment in the oral cavity, or the production of bacteriocins. Using oral epithelial cells as a model, we hypothesized that the virulence of pathogenic species may vary depending on the complexity of the flora that interacts with host cells.

Results

This is the first report that determines the global epithelial transcriptional response to co-culture with defined complex microbiota. In our model, human immortalized gingival keratinocytes (HIGK) were infected with mono- and mixed cultures of commensal and pathogenic species. The global transcriptional response of infected cells was validated and confirmed phenotypically. In our model, commensal species were able to modulate the expression of host genes with a broad diversity of physiological functions and antagonize the effect of pathogenic species at the cellular level. Unexpectedly, the inhibitory effect of commensal species was not correlated with its ability to inhibit adhesion or invasion by pathogenic species.

Conclusion

Studying the global transcriptome of epithelial cells to single and complex microbial challenges offers clues towards a better understanding of how bacteria-bacteria interactions and bacteria-host interactions impact the overall host response. This work provides evidence that the degree of complexity of a mixed microbiota does influence the transcriptional response to infection of host epithelial cells, and challenges the current dogma regarding the potential versus the actual pathogenicity of bacterial species. These findings support the concept that members of the commensal oral flora have evolved cellular mechanisms that directly modulate the host cell's response to pathogenic species and dampen their relative pathogenicity.

The host cytokine response to Porphyromonas gingivalis is modified by gingipains

BACKGROUND/AIMS

Clinical studies indicate that primary proinflammatory cytokines, such as interleukin-1beta (IL-1beta) are elevated in the gingival crevice around teeth with periodontitis but the secondary cytokines and chemokines, IL-6 and IL-8, are not. The human gingival epithelial cells (HGECs) lining the gingival sulcus respond to perturbation by microbes of dental plaque by releasing a wide range of cytokines. Porphyromonas gingivalis, a putative periodontal pathogen, possesses numerous virulence factors some of which directly impact on the host response. In the present study, we sought to determine how P. gingivalis influences the inflammatory cytokine responses.

METHODS

HGECs were challenged with P. gingivalis and other putative periodontal pathogens, and the resultant production of IL-1beta, IL-6, and IL-8 was assayed by enzyme-linked immunosorbent assay (ELISA). Culture supernatants and recombinant human cytokines were challenged with live P. gingivalis wild-type and gingipain-deficient strains and the resultant cytokine profile was assessed by ELISA and Western blot.

RESULTS

We show here that primary HGECs challenged with live P. gingivalis result in high levels of IL-1beta but not the related secondary cytokines IL-6 and IL-8. We further demonstrate that cytokine response differences are the result of the action of P. gingivalis proteases, with lysine gingipain being the most effective.

CONCLUSION

We conclude that P. gingivalis, through lysine gingipain, can subvert the protective host proinflammatory response by direct cytokine degradation. Changes in the crevicular cytokine profile have consequences in periodontal disease pathogenesis that should be considered in the development of diagnostic and therapeutic modalities.

Transcriptomes in healthy and diseased gingival tissues

BACKGROUND

Clinical and radiographic measures are gold standards for diagnosing periodontitis but offer little information regarding the pathogenesis of the disease. We hypothesized that a comparison of gene expression signatures between healthy and diseased gingival tissues would provide novel insights in the pathobiology of periodontitis and would inform the design of future studies.

METHODS

Ninety systemically healthy non-smokers with moderate to advanced periodontitis (63 with chronic periodontitis and 27 with aggressive periodontitis) each contributed at least two diseased interproximal papillae (with bleeding on probing [BOP], probing depth [PD] > or =4 mm, and attachment loss [AL] > or =3 mm) and a healthy papilla, if available (no BOP, PD < or =4 mm, and AL < or =2 mm). RNA was extracted, amplified, reverse-transcribed, labeled, and hybridized with whole genome microarrays. Differential expression was assayed in 247 individual tissue samples (183 from diseased sites and 64 from healthy sites) using a standard mixed-effects linear model approach, with patient effects considered random with a normal distribution and gingival tissue status considered a two-level fixed effect. Gene ontology analysis classified the expression patterns into biologically relevant categories.

RESULTS

Transcriptome analysis revealed that 12,744 probe sets were differentially expressed after adjusting for multiple comparisons (P <9.15 x 10(7)). Of those, 5,295 were upregulated and 7,449 were downregulated in disease compared to health. Gene ontology analysis identified 61 differentially expressed groups (adjusted P <0.05), including apoptosis, antimicrobial humoral response, antigen presentation, regulation of metabolic processes, signal transduction, and angiogenesis.

CONCLUSION

Gingival tissue transcriptomes provide a valuable scientific tool for further hypothesis-driven studies of the pathobiology of periodontitis.

Analysis of a band 7/MEC-2 family gene of Porphyromonas gingivalis

In vivo-induced antigen technology has previously been used to identify 115 genes induced in Porphyromonas gingivalis W83 during human infection. The aim of this study was to determine if one of these genes, PG1334, was important for the virulence of P. gingivalis. Analysis of plaque samples from persons with periodontitis revealed that PG1334 was expressed in 88.0% of diseased sites, compared with 42.1% of healthy sites, even though P. gingivalis was detected in equal numbers from both sites. A mutant of PG1334 was found to adhere to and to invade better than the parent strain, but did not persist as well in human coronary artery endothelial cells. Additionally, the mutant did not persist as well in a mouse abscess model. This gene appears to be important for the virulence of P. gingivalis, both in vivo and in vitro.