Gingival epithelial cell signalling and cytoskeletal responses to Porphyromonas gingivalis invasion

Role of fimbriae variations in Porphyromonas gulae biofilm formation

OBJECTIVES

Porphyromonas gulae is a major causative agent of periodontal disease in companion animals that possesses various virulence factors, including fimbriae, lipopolysaccharides, and proteases. P. gulae fimbriae are classified into three genotypes (A, B, and C) based on their nucleotide sequences. Type C fimbrial isolates have been reported to be more virulent than other fimA types, suggesting that different fimA types may aid in the regulation of periodontal pathogenesis. Detailed findings regarding the ability of P. gulae to form biofilms have yet to be reported. Here, we investigated the contributions of fimbrial genotypes in P. gulae biofilm formation.

METHODS

P. gulae and P. gingivalis biofilms were generated on plates and analyzed using confocal laser microscopy. Additionally, the biofilms formed were assessed by staining with crystal violet. Furthermore, the physical strength of P. gulae biofilms was examined by ultrasonication.

RESULTS

Biofilms formed by P. gulae type C were denser than those formed by types A and B. Moreover, the amount of biofilm formed by type C strains was significantly greater than that formed by type A and B strains, which was similar to the biofilms formed by P. gingivalis with type II fimbriae. Additionally, the physical strength of the type C biofilm was significantly greater than that of the other strains.

CONCLUSIONS

These results suggest that FimA variation may coordinate for biofilm formation. This is the first report on the observation and characterization of P. gulae biofilm formation.

Opportunistic pathogen Porphyromonas gingivalis targets the LC3B-ceramide complex and mediates lethal mitophagy resistance in oral tumors

Mechanisms by which Porphyromonas gingivalis (P. gingivalis) infection enhances oral tumor growth or resistance to cell death remain elusive. Here, we determined that P. gingivalis infection mediates therapeutic resistance via inhibiting lethal mitophagy in cancer cells and tumors. Mechanistically, P. gingivalis targets the LC3B-ceramide complex by associating with LC3B via bacterial major fimbriae (FimA) protein, preventing ceramide-dependent mitophagy in response to various therapeutic agents. Moreover, ceramide-mediated mitophagy is induced by Annexin A2 (ANXA2)-ceramide association involving the E142 residue of ANXA2. Inhibition of ANXA2-ceramide-LC3B complex formation by wild-type P. gingivalis prevented ceramide-dependent mitophagy. Moreover, a FimA-deletion mutant P. gingivalis variant had no inhibitory effects on ceramide-dependent mitophagy. Further, 16S rRNA sequencing of oral tumors indicated that P. gingivalis infection altered the microbiome of the tumor macroenvironment in response to ceramide analog treatment in mice. Thus, these data provide a mechanism describing the pro-survival roles of P. gingivalis in oral tumors.

Frankincense (Boswellia serrata) Extract Effects on Growth and Biofilm Formation of Porphyromonas gingivalis, and Its Intracellular Infection in Human Gingival Epithelial Cells

Frankincense is produced by Boswellia trees, which can be found throughout the Middle East and parts of Africa and Asia. Boswellia serrata extract has been shown to have anti-cancer, anti-inflammatory, and antimicrobial effects. Periodontitis is an oral chronic inflammatory disease that affects nearly half of the US population. We investigated the antimicrobial effects of B. serrata extract on two oral pathogens associated with periodontitis. Using the minimum inhibitory concentration and crystal violet staining methods, we demonstrated that Porphyromonas gingivalis growth and biofilm formation were impaired by treatment with B. serrata extracts. However, the effects on Fusobacterium nucleatum growth and biofilm formation were not significant. Using quantification of colony-forming units and microscopy techniques, we also showed that concentrations of B. serrata that were not toxic for host cells decreased intracellular P. gingivalis infection in human gingival epithelial cells. Our results show antimicrobial activity of a natural product extracted from Boswellia trees (B. serrata) against periodontopathogens. Thus, B. serrata has the potential for preventing and/or treating periodontal diseases. Future studies will identify the molecular components of B. serrata extracts responsible for the beneficial effects.

Crosstalk between integrin/FAK and Crk/Vps25 governs invasion of bovine mammary epithelial cells by S. agalactiae

Streptococcus agalactiae (S. agalactiae) is a contagious obligate parasite of the udder in dairy cows. Here, we examined S. agalactiae-host interactions in bovine mammary epithelial cells (BMECs) in vitro. We found that S. agalactiae infected BMECs through laminin β2 and integrin. Crk, Vps25, and RhoA were differentially expressed in S. agalactiae-infected cells. S. agalactiae infection activated FAK and Crk. FAK deficiency decreased the number of intracellular S. agalactiae and Crk activation. Knockdown of Crk or Vps25 increased the level of intracellular S. agalactiae, whereas its overexpression had the opposite effect. RhoA expression and actin cytoskeleton were altered in S. agalactiae-infected BMECs. Crk and Vps25 interact in cells, and invaded S. agalactiae also activates Crk, allowing it to cooperate with Vps25 to defend against intracellular infection by S. agalactiae. This study provides insights into the mechanism by which intracellular infection by S. agalactiae is regulated in BMECs.

The presence of intratumoral Porphyromonas gingivalis correlates with a previously defined pancreatic adenocarcinoma, immune cell expression phenotype and with tumor resident, adaptive immune receptor features

The association between pancreatic adenocarcinoma (PAAD) and the pancreatic microbiome is not fully understood, although bacteria may decrease the effectiveness of chemotherapy and lead to anti-apoptotic, pro-inflammatory microenvironments. To better understand the relationship between the PAAD microbiome and the microenvironment, we identified Porphyromonas gingivalis-positive PAAD samples and found a strong association between intratumoral P. gingivalis and: (i) an immune cell gene expression phenotype previously defined by others as gene program 7; and (ii) recovery of immunoglobulin recombination, sequencing reads. We applied a novel chemical complementarity scoring algorithm, suitable for a big data setting, and determined that the previously established P. gingivalis antigen, rpgB had a reduced chemical complementarity with T-cell receptor (TCR) complementarity-determining region-3 amino acid sequences recovered from PAAD samples with P. gingivalis in comparison to TCR-rpgB chemical complementarity represented by the PAAD samples that lacked P. gingivalis. This finding strengthens the existing body of evidence correlating P. gingivalis with PAAD, which may have implications for the treatment and prognosis of patients. Furthermore, demonstrating the correlation of P. gingivalis and gene program 7 raises the question of whether P. gingivalis infection is responsible for the gene program 7 subdivision of PAAD?

Illuminating the oral microbiome: cellular microbiology

Epithelial cells line mucosal surfaces such as in the gingival crevice and provide a barrier to the ingress of colonizing microorganisms. However, epithelial cells are more than a passive barrier to microbial intrusion, and rather constitute an interactive interface with colonizing organisms which senses the composition of the microbiome and communicates this information to the underlying cells of the innate immune system. Microorganisms, for their part, have devised means to manipulate host cell signal transduction pathways to favor their colonization and survival. Study of this field, which has become known as cellular microbiology, has revealed much about epithelial cell physiology, bacterial colonization and pathogenic strategies, and innate host responses.

Influence of Surface Characteristics of TiO2 Coatings on the Response of Gingival Cells: A Systematic Review of In Vitro Studies

The soft tissue-implant interface requires the formation of epithelium and connective tissue seal to hinder microbial infiltration and prevent epithelial down growth. Nanoporous titanium dioxide (TiO₂) surface coatings have shown good potential for promoting soft tissue attachment to implant surfaces. However, the impact of their surface properties on the biological response of gingival cells needs further investigation. This systematic review aimed to investigate the cellular behavior of gingival cells on TiO₂-implant abutment coatings based on in vitro studies. The review was performed to answer the question: "How does the surface characteristic of TiO₂ coatings influence the gingival cell response in in vitro studies?". A search in MEDLINE/PubMed and the web of science databases from 1990 to 2022 was performed using keywords. A quality assessment of the studies selected was performed using the SciRAP method. A total of 11 publications were selected from the 289 studies that fulfilled the inclusion criteria. The mean reporting and methodologic quality SciRAP scores were 82.7 ± 6.4/100 and 87 ± 4.2/100, respectively. Within the limitations of this in vitro systematic review, it can be concluded that the TiO₂ coatings with smooth nano-structured surface topography and good wettability improve gingival cell response compared to non-coated surfaces.

Local and Systemic Effects of Porphyromonas gingivalis Infection

Porphyromonas gingivalis, a gram-negative anaerobe, is a leading etiological agent in periodontitis. This infectious pathogen can induce a dysbiotic, proinflammatory state within the oral cavity by disrupting commensal interactions between the host and oral microbiota. It is advantageous for P. gingivalis to avoid complete host immunosuppression, as inflammation-induced tissue damage provides essential nutrients necessary for robust bacterial proliferation. In this context, P. gingivalis can gain access to the systemic circulation, where it can promote a prothrombotic state. P. gingivalis expresses a number of virulence factors, which aid this pathogen toward infection of a variety of host cells, evasion of detection by the host immune system, subversion of the host immune responses, and activation of several humoral and cellular hemostatic factors.

Alzheimer's Disease: A Systems View Provides a Unifying Explanation of Its Development

Alzheimer's disease (AD) is a debilitating neurodegenerative disorder affecting 50 million people globally. It is characterized by the presence of extracellular senile plaques and intracellular neurofibrillary tangles, consisting of amyloid-β and hyperphosphorylated tau proteins, respectively. Despite global research efforts, there is currently no cure available, due in part to an incomplete understanding of the disease pathogenesis. Numerous possible mechanisms, or hypotheses, explaining the origins of sporadic or late-onset AD have been proposed, including the amyloid-β, inflammatory, vascular, and infectious hypotheses. However, despite ample evidence, the failure of multiple trial drugs at the clinical stage illuminates the possible pitfalls of these hypotheses. Systems biology is a strategy which aims to elucidate the interactions between parts of a whole. Using this approach, the current paper shows how the four previously mentioned hypotheses of AD pathogenesis can be intricately connected. This approach allows for seemingly contradictory evidence to be unified in a system-focused explanation of sporadic AD development. Within this view, it is seen that infectious agents, such as P. gingivalis, may play a central role. The data presented here shows that when present, P. gingivalis or its virulence factors, such as gingipains, may induce or exacerbate pathologies underlying sporadic AD. This evidence supports the view that infectious agents, and specifically P. gingivalis, may be suitable treatment targets in AD.

Mechanisms of Porphyromonas gingivalis to translocate over the oral mucosa and other tissue barriers

Introduction

The oral pathogen Porphyromonas gingivalis is not only associated with periodontitis but also with systemic diseases elsewhere in the body. The mechanisms by which P. gingivalis travels from the oral cavity to other organs in the body are largely unknown. This review describes the four putative mechanisms supported by experimental evidence, which enable translocation of P. gingivalis over the oral mucosa, endothelial barriers and subsequent dissemination into the bloodstream.

Mechanisms

The first mechanism: proteolytic enzymes secreted by P. gingivalis degrade adhesion molecules between tissue cells, and the extracellular matrix. This weakens the structural integrity of the mucosa and allows P. gingivalis to penetrate the tissue. The second is transcytosis: bacteria actively enter tissue cells and transfer to the next layer or the extracellular space. By travelling from cell to cell, P. gingivalis reaches deeper structures. Thirdly, professional phagocytes take up P. gingivalis and travel to the bloodstream where P. gingivalis is released. Lastly, P. gingivalis can adhere to the hyphae forming Candida albicans. These hyphae can penetrate the mucosal tissue, which may allow P. gingivalis to reach deeper structures.

Conclusion

More research could elucidate targets to inhibit P. gingivalis dissemination and prevent the onset of various systemic diseases.

Effects of green tea extract epigallocatechin-3-gallate (EGCG) on oral disease-associated microbes: a review

For thousands of years, caries, periodontitis and mucosal diseases, which are closely related to oral microorganisms, have always affected human health and quality of life. These complex microbiota present in different parts of the mouth can cause chronic infections in the oral cavity under certain conditions, some of which can also lead to acute and systemic diseases. With the mutation of related microorganisms and the continuous emergence of drug-resistant strains, in order to prevent and treat related diseases, in addition to the innovation of diagnosis and treatment technology, the development of new antimicrobial drugs is also important. Catechins are polyphenolic compounds in green tea, some of which are reported to provide health benefits for a variety of diseases. Studies have shown that epigallocatechin-3-gallate (EGCG) is the most abundant and effective active ingredient in green tea catechins, which acts against a variety of gram-positive and negative bacteria, as well as some fungi and viruses. This review aims to summarize the research progress on the activity of EGCG against common oral disease-associated organisms and discuss the mechanisms of these actions, hoping to provide new medication strategies for the prevention and treatment of oral infectious diseases, the future research of EGCG and its translation into clinical practice are also discussed.

Engineering a 3D In Vitro Model of Human Gingival Tissue Equivalent with Genipin/Cytochalasin D

Although three-dimensional (3D) co-culture of gingival keratinocytes and fibroblasts-populated collagen gel can mimic 3D structure of in vivo tissue, the uncontrolled contraction of collagen gel restricts its application in clinical and experimental practices. We here established a stable 3D gingival tissue equivalent (GTE) using hTERT-immortalized gingival fibroblasts (hGFBs)-populated collagen gel directly crosslinked with genipin/cytochalasin D and seeding hTERT-immortalized gingival keratinocytes (TIGKs) on the upper surface for a 2-week air–liquid interface co-culture. MTT assay was used to measure the cell viability of GTEs. GTE size was monitored following culture period, and the contraction was analyzed. Immunohistochemical assay was used to analyze GTE structure. qRT-PCR was conducted to examine the mRNA expression of keratinocyte-specific genes. Fifty µM genipin (G50) or combination (G + C) of G50 and 100 nM cytochalasin D significantly inhibited GTE contraction. Additionally, a higher cell viability appeared in GTEs crosslinked with G50 or G + C. GTEs crosslinked with genipin/cytochalasin D showed a distinct multilayered stratified epithelium that expressed keratinocyte-specific genes similar to native gingiva. Collagen directly crosslinked with G50 or G + C significantly reduced GTE contraction without damaging the epithelium. In summary, the TIGKs and hGFBs can successfully form organotypic multilayered cultures, which can be a valuable tool in the research regarding periodontal disease as well as oral mucosa disease. We conclude that genipin is a promising crosslinker with the ability to reduce collagen contraction while maintaining normal cell function in collagen-based oral tissue engineering.

Epithelial cell attachment and adhesion protein expression on novel in sol TiO2 coated zirconia and titanium alloy surfaces

An adequate mucosal attachment is important when it comes to preventing peri-implant inflammation. The aim of this study was to compare epithelial cell adhesion and adhesion protein expression on in sol TiO₂ -coated and non-coated zirconia and titanium alloy surfaces. Fifty-six zirconia and titanium discs were cut, and half of them were coated with bioactive TiO₂ -coating. To study the epithelial cell attachment, human gingival keratinocytes were cultivated on discs for 1, 3, 6, and 24 h. The cell proliferation was detected by cultivating cells for 1, 3, and 7 days. In addition, the levels of adhesion proteins laminin y2, integrin α6, β4, vinculin, and paxillin were detected with Western Blot method. Furthermore, high-resolution imaging of the actin cytoskeleton and focal adhesion proteins was established. Longer-term cell culture (1-7 days) revealed higher cell numbers on the coated zirconia and titanium discs compared to non-coated discs. The difference was statistically significant (p < .05) after 24 h on coated zirconia and after 3 and 7 days on coated titanium discs compared to non-coated discs. Clear induction in the protein levels of laminin y2 and integrin α6 were detected on both coated samples, meanwhile integrin β4 were clearly induced on coated titanium alloy. The microscope evaluation showed significantly increased cell spreading on the coated discs. According to this study, the in sol induced TiO₂ -coating increases keratinocyte attachment and the expression of adhesion proteins on coated zirconia and titanium in vitro. Consequently, the coating has potential to enhance the mucosal attachment on implant surfaces.

Associations of Porphyromonas gingivalis Infection and Low Beclin1 Expression With Clinicopathological Parameters and Survival of Esophageal Squamous Cell Carcinoma Patients

Purpose: The present study focused on exploring the associations of Porphyromonas gingivalis (P. gingivalis) infection and low Beclin1 expression with clinicopathological parameters and survival of esophageal squamous cell carcinoma (ESCC) patients, so as to illustrate its clinical significance and prognostic value. Methods: Immunohistochemistry (IHC) was used to detect P. gingivalis infection status and Beclin1 expression in 370 ESCC patients. The chi-square test was adopted to illustrate the relationship between categorical variables, and Cohen's kappa coefficient was used for correlation analysis. Kaplan-Meier survival curves with the log-rank test were used to analyse the correlation of P. gingivalis infection and low Beclin1 expression with survival time. The effects of P. gingivalis infection and Beclin1 downregulation on the proliferation, migration and antiapoptotic abilities of ESCC cells in vitro were detected by Cell Counting Kit-8, wound healing and flow cytometry assays. For P. gingivalis infection of ESCC cells, cell culture medium was replaced with antibiotic-free medium when the density of ESCC cells was 70-80%, cells were inoculated with P. gingivalis at a multiplicity of infection (MOI) of 10. Result: P. gingivalis infection was negatively correlated with Beclin1 expression in ESCC tissues, and P. gingivalis infection and low Beclin1 expression were associated with differentiation status, tumor invasion depth, lymph node metastasis, clinical stage and prognosis in ESCC patients. In vitro experiments confirmed that P. gingivalis infection and Beclin1 downregulation potentiate the proliferation, migration and antiapoptotic abilities of ESCC cells (KYSE150 and KYSE30). Our results provide evidence that P. gingivalis infection and low Beclin1 expression were associated with the development and progression of ESCC. Conclusion: Long-term smoking and alcohol consumption causes poor oral and esophageal microenvironments and ESCC patients with these features were more susceptible to P. gingivalis infection and persistent colonization, and exhibited lower Beclin1 expression, worse prognosis and more advanced clinicopathological features. Our findings indicate that effectively eliminating P. gingivalis colonization and restoring Beclin1 expression in ESCC patients may contribute to preventation and targeted treatment, and yield new insights into the aetiological research on ESCC.

Vegetal Compounds as Sources of Prophylactic and Therapeutic Agents in Dentistry

Dental pathology remains a global health problem affecting both children and adults. The most important dental diseases are dental caries and periodontal pathologies. The main cause of oral health problems is overpopulation with pathogenic bacteria and for this reason, conventional therapy can often be ineffective due to bacterial resistance or may have unpleasant side effects. For that reason, studies in the field have focused on finding new therapeutic alternatives. Special attention is paid to the plant kingdom, which offers a wide range of plants and active compounds in various pathologies. This review focused on the most used plants in the dental field, especially on active phytocompounds, both in terms of chemical structure and in terms of mechanism of action. It also approached the in vitro study of active compounds and the main types of cell lines used to elucidate the effect and mechanism of action. Thus, medicinal plants and their compounds represent a promising and interesting alternative to conventional therapy.

Porphyromonas gingivalis survival skills: Immune evasion

Periodontitis is a chronic inflammatory condition that destroys the tooth-supporting tissues and eventually leads to tooth loss. As one of the most prevalent oral conditions, periodontitis endangers the oral health of 70% of people throughout the world. Periodontitis is also related to various systemic diseases, such as diabetes mellitus, atherosclerosis, and rheumatoid arthritis, which not only has a great impact on population health status and the quality of life but also increases the social burden. Porphyromonas gingivalis (P. gingivalis) is a gram-negative oral anaerobic bacterium that plays a key role in the pathogenesis of periodontitis. Porphyromonas gingivalis can express various of virulence factors to overturn innate and adaptive immunities, which makes P. gingivalis survive and propagate in the host, destroy periodontal tissues, and have connection to systemic diseases. Porphyromonas gingivalis can invade into and survive in host tissues by destructing the gingival epithelial barrier, internalizing into the epithelial cells, and enhancing autophagy in epithelial cells. Deregulation of complement system, degradation of antibacterial peptides, and destruction of phagocyte functions facilitate the evasion of P. gingivalis. Porphyromonas gingivalis can also suppress adaptive immunity, which allows P. gingivalis to exist in the host tissues and cause the inflammatory response persistently. Here, we review studies devoted to understanding the strategies utilized by P. gingivalis to escape host immunity. Methods for impairing P. gingivalis immune evasion are also mentioned.

Treponema denticola-Induced RASA4 Upregulation Mediates Cytoskeletal Dysfunction and MMP-2 Activity in Periodontal Fibroblasts

The periodontal complex consists of the periodontal ligament (PDL), alveolar bone, and cementum, which work together to turn mechanical load into biological responses that are responsible for maintaining a homeostatic environment. However oral microbes, under conditions of dysbiosis, may challenge the actin dynamic properties of the PDL in the context of periodontal disease. To study this process, we examined host-microbial interactions in the context of the periodontium via molecular and functional cell assays and showed that human PDL cell interactions with Treponema denticola induce actin depolymerization through a novel actin reorganization signaling mechanism. This actin reorganization mechanism and loss of cell adhesion is a pathological response characterized by an initial upregulation of RASA4 mRNA expression resulting in an increase in matrix metalloproteinase-2 activity. This mechanism is specific to the T. denticola effector protein, dentilisin, thereby uncovering a novel effect for Treponema denticola-mediated RASA4 transcriptional activation and actin depolymerization in primary human PDL cells.

Frequencies of Porphyromonas gingivalis Detection in Oral-Digestive Tract Tumors

Mounting evidence suggests a causal relationship between specific bacterial infections and the development of certain malignancies. In this study, we examined the presence of Porphyromonas gingivalis (P. gingivalis) in oral-digestive tract tumors by immunohistochemistry (IHC) and PCR and analyzed the correlation between P. gingivalis detection and clinicopathological characteristics and prognosis of oral and esophageal carcinoma. The IHC results showed that the positive rates of P. gingivalis were 60.00, 46.00, 20.00, 6.67, and 2.86% in oral, esophagus, cardiac, stomach, and colorectal cancer tissues, respectively. Likewise, PCR results showed rates of 56.00, 42.00, 16.67, 3.33, and 2.86%, respectively. The two methods were consistent, and the kappa value was 0.806, P < 0.001. In addition, P. gingivalis expression was significantly correlated with lymph node metastasis and the clinical stages of oral and esophageal cancer (P < 0.05). The overall survival rate of the P. gingivalis undetected group (86, 50%) was significantly higher than that of the P. gingivalis detected group (57, 14%) for oral and esophageal cancer, respectively. In conclusion, the detection rate of P. gingivalis showed a decreasing trend in oral-digestive tract tumors. Detection with P. gingivalis was associated with poor prognosis for oral and esophageal cancer.

Porphyromonas gingivalis Outer Membrane Vesicles as the Major Driver of and Explanation for Neuropathogenesis, the Cholinergic Hypothesis, Iron Dyshomeostasis, and Salivary Lactoferrin in Alzheimer's Disease

Porphyromonas gingivalis (Pg) is a primary oral pathogen in the widespread biofilm-induced "chronic" multi-systems inflammatory disease(s) including Alzheimer's disease (AD). It is possibly the only second identified unique example of a biological extremophile in the human body. Having a better understanding of the key microbiological and genetic mechanisms of its pathogenesis and disease induction are central to its future diagnosis, treatment, and possible prevention. The published literature around the role of Pg in AD highlights the bacteria's direct role within the brain to cause disease. The available evidence, although somewhat adopted, does not fully support this as the major process. There are alternative pathogenic/virulence features associated with Pg that have been overlooked and may better explain the pathogenic processes found in the "infection hypothesis" of AD. A better explanation is offered here for the discrepancy in the relatively low amounts of "Pg bacteria" residing in the brain compared to the rather florid amounts and broad distribution of one or more of its major bacterial protein toxins. Related to this, the "Gingipains Hypothesis", AD-related iron dyshomeostasis, and the early reduced salivary lactoferrin, along with the resurrection of the Cholinergic Hypothesis may now be integrated into one working model. The current paper suggests the highly evolved and developed Type IX secretory cargo system of Pg producing outer membrane vesicles may better explain the observed diseases. Thus it is hoped this paper can provide a unifying model for the sporadic form of AD and guide the direction of research, treatment, and possible prevention.

Clinical significance and prognostic value of Porphyromonas gingivalis infection in lung cancer

A variety of pathogenic microorganisms can promote the occurrence and development of malignant tumors by colonizing in the body. It has been shown that Porphyromonas gingivalis (P. gingivalis) can be colonized for a long time in upper gastrointestinal tumors and is closely related to the occurrence and development of esophageal cancer in previous studies of our team. Because the esophagus and trachea are closely adjacent and P. gingivalis can instantly enter and colonize in cells, we speculate that P. gingivalis may be colonized in lung cancer cells through oral or blood, promoting the malignant progression of lung cancer. In this study, we investigated P. gingivalis infection in lung carcinoma tissues and adjacent lung tissues, and found that the colonization rate of P. gingivalis in carcinoma tissues was significantly higher than that in adjacent lung tissues. Therefore, we propose that the microenvironment of cancer cells is more conducive to the survival of P. gingivalis. Then, we analyzed the correlation between P. gingivalis infection and clinicopathological features and survival prognosis of patients with lung cancer. It was found that P. gingivalis infection was closely related to smoking, drinking, lymph node metastasis and clinical stage. Moreover, the survival rate and median survival time of patients with P. gingivalis infection were significantly shortened. Therefore, we put forward the view that long term smoking and drinking will cause a bad oral environment, increasing the risk of P. gingivalis infection, then P. gingivalis infection will promote the malignant progression of lung cancer.

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.

A review of co-culture models to study the oral microenvironment and disease

Co-cultures allow for the study of cell-cell interactions between different eukaryotic species or with bacteria. Such an approach has enabled researchers to more closely mimic complex tissue structures. This review is focused on co-culture systems modelling the oral cavity, which have been used to evaluate this unique cellular environment and understand disease progression. Over time, these systems have developed significantly from simple 2D eukaryotic cultures and planktonic bacteria to more complex 3D tissue engineered structures and biofilms. Careful selection and design of the co-culture along with critical parameters, such as seeding density and choice of analysis method, have resulted in several advances. This review provides a comparison of existing co-culture systems for the oral environment, with emphasis on progression of 3D models and the opportunity to harness techniques from other fields to improve current methods. While filling a gap in navigating this literature, this review ultimately supports the development of this vital technique in the field of oral biology.

In Situ Intraepithelial Localizations of Opportunistic Pathogens, Porphyromonas gingivalis and Filifactor alocis, in Human Gingiva

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The gingival epithelium serves as a growth reservoir for opportunistic bacteria.

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Intraepithelial P. gingivalis and F. alocis colonies are detected together in dysbiotic mucosa.

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Increased metabolically active dual species can lead to higher microvasculature.

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Invasion of intraepithelial microvessels leads to systemic pathogen dissemination.

Porphyromonas gingivalis and Filifactor alocis are fastidious oral pathogens and etiological agents associated with chronic periodontitis. Although previous studies showed increased levels of the two obligate anaerobic species in periodontitis patients, methodologies for this knowledge were primarily limited to sampling subgingival plaque, saliva, or gingival crevicular fluid. To evaluate the extent to which P. gingivalis and F. alocis may invade the periodontal tissues, an in situ cross-sectional study was comparatively conducted on the gingival biopsy specimens of patients diagnosed with periodontal health or chronic periodontitis. Immunostained tissue sections for each organism were imaged by Super-Resolution Confocal Scanning Microscopy to determine the relative presence and localization of target bacterial species. Fluorescence-in-situ-hybridization (FISH) coupled with species specific 16S rRNA method was utilized to confirm whether detected bacteria were live within the tissue. In periodontitis, P. gingivalis and F. alocis revealed similarly concentrated localization near the basement membrane or external basal lamina of the gingival epithelium. The presence of both bacteria was significantly increased in periodontitis vs. healthy tissue. However, P. gingivalis was still detected to an extent in health tissue, while only minimal levels of F. alocis were spotted in health. Additionally, the micrographic analyses displayed heightened formation of epithelial microvasculature containing significantly co-localized and metabolically active dual species within periodontitis tissue. Thus, this study demonstrates, for the first-time, spatial arrangements of P. gingivalis and F. alocis in both single and co-localized forms within the complex fabric of human gingiva during health and disease. It also exhibits critical visualizations of co-invaded microvascularized epithelial layer of the tissue by metabolically active P. gingivalis and F. alocis from patients with severe periodontitis. These findings collectively uncover novel visual evidence of a potential starting point for systemic spread of opportunistic bacteria during their chronic colonization in gingival epithelium.

Chemical constituents of Streptomyces sp. strain Al-Dhabi-97 isolated from the marine region of Saudi Arabia with antibacterial and anticancer properties

BACKGROUND

Unlike the terrestrial region, the microorganisms especially actinomycetes groups existing in the marine environment are important sources for the medically important drugs and other active compounds. Considering the importance of natural compounds from the marine actinomycetes, the present study proceeded to identify and characterize promising antibacterial and anticancer actinomycetes from the marine region of Saudi Arabia and to profile the individual chemical components.

METHODS

Antimicrobial, anticancer and chemical profiling were performed by broth microdilution, mitochondrial membrane potential assays and GC-MS analysis. Investigations were directed towards the isolation and characterization of active Streptomyces sp. strain Al-Dhabi-97.

RESULTS

The obtained results of the morphological, biochemical, physiological and molecular level studies of the isolate Al-Dhabi-97 showed similarity towards the species of Streptomyces. Gram positive bacteria such as Bacillus subtilis, Enterococcus faecalis, Staphylococcus epidermidis and Staphylococcus aureus showed MIC values of 500, 250, 125 and 62.5μg/ml and Gram negative bacteria such as Pseudomonas aeruginosa, Klebsiella pneumonia, Escherichia coli and Salmonella paratyphi reported MIC values of 500, 500, 250 and >250μg/ml in the antimicrobial studies. The results of anticancer studies showed that at 100μg/ml, the extract showed maximum cell growth inhibition and exhibited 2.5% necrosis, 62.2% late apoptosis and 20.8% early apoptosis in COLO 320 DM and VERO cell lines respectively. Chemical profiling of the extract authenticated the presence of constituents such as 1-phenanthrenemethanol (46.64%), phthalic acid, di(2-propylpentyl) ester (26.97%), benzenebutanoic acid (3.37%), podocarp-7-en-3-one (2.68%), and indole-3-carboxaldehyde (1.11%) respectively.

CONCLUSION

The present study concluded that Saudi Arabian marine region was a promising area for the identification of medically important natural products producing actinomycetes for antibacterial and anticancer drugs.

The prevalence rate of periodontal pathogens and its association with oral squamous cell carcinoma

Mounting evidence suggests a causal relationship between specific bacterial infections or microbial compositions and the development of certain malignant neoplasms. In this study, we performed research through 16S rRNA amplicon sequencing, qPCR and fluorescence in situ hybridization to certify the relationship between periodontal pathogens and oral squamous cell carcinoma (OSCC). Subgingival plaque, cancer and paracancerous tissues from 6 patients with OSCC were selected for mapping bacterial profiles by 16S rRNA amplicon sequencing. The research showed that periodontal pathogens were enriched in cancer and paracancerous tissues, while the bacterial profiles were similar between the cancer tissues and subgingival plaque. Furthermore, the relative abundance of Porphyromonas gingivalis, Fusobacterium nucleatum and Streptococcus sanguinis was detected in 61 cancer tissues, paracancerous tissues and subgingival plaque samples and in 30 normal tissues by qPCR. The results revealed that P. gingivalis and F. nucleatum existed at higher levels in cancer tissue than in normal tissues and were correlated with subgingival plaques. P. gingivalis was detected using a special oligonucleotide probe in 60.7% of OSCC tissues, 32.8% of paracancerous tissues and 13.3% of normal tissues. Relevance analysis showed that P. gingivalis infection was positively associated with late clinical staging, low differentiation and lymph node metastasis in patients with OSCC, which was accompanied by deeper periodontal pockets, severe clinical attachment loss and loss of teeth. This study revealed that there might be a close relationship between oral microorganisms, particularly periodontal pathogens, and OSCC, which might enrich the pathogenesis of oral squamous carcinoma.

Porphyromonas gingivalis traffics into endoplasmic reticulum-rich-autophagosomes for successful survival in human gingival epithelial cells

Porphyromonas gingivalis, an opportunistic pathogen usurps gingival epithelial cells (GECs) as primary intracellular niche for its colonization in the oral mucosa. However, the precise characterization of the intracellular trafficking and fate of P. gingivalis in GECs remains incomplete. Therefore, we employed high-resolution three-dimensional-transmission-electron-microscopy to determine the subcellular location of P. gingivalis in human primary GECs upon invasion. Serial sections of infected-GECs and their tomographic reconstruction depicted ER-rich-double-membrane autophagosomal-vacuoles harboring P. gingivalis. Western-blotting and fluorescence confocal microscopy showed that P. gingivalis significantly induces LC3-lipidation in a time-dependent-manner and co-localizes with LC3, ER-lumen-protein Bip, or ER-tracker, which are major components of the phagophore membrane. Furthermore, GECs that were infected with FMN-green-fluorescent transformant-strain (PgFbFP) and selectively permeabilized by digitonin showed rapidly increasing large numbers of double-membrane-vacuolar-P. gingivalis over 24 hours of infection with a low-ratio of cytosolically free-bacteria. Moreover, inhibition of autophagy using 3-methyladenine or ATG5 siRNA significantly reduced the viability of intracellular P. gingivalis in GECs as determined by an antibiotic-protection-assay. Lysosomal marker, LAMP-1, showed a low-degree colocalization with P. gingivalis (∼20%). PgFbFP was used to investigate the fate of vacuolar- versus cytosolic-P. gingivalis by their association with ubiquitin-binding-adaptor-proteins, NDP52 and p62. Only cytosolic-P. gingivalis had a significant association with both markers, which suggests cytosolically-free bacteria are likely destined to the lysosomal-degradation pathway whereas the vacuolar-P. gingivalis survives. Therefore, the results reveal a novel mechanism for P. gingivalis survival in GECs by harnessing host autophagy machinery to establish a successful replicative niche and persistence in the oral mucosa.

Identification of novel genes involved in gingival epithelial cells responding to Aggregatibacter actinomycetemcomitans and Porphyromonas gingivalis infections

OBJECTIVE

This study aimed to identify the differentially expressed genes (DEGs) in gingiva epithelial cells responding to Aggregatibacter actinomycetemcomitans and Porphyromonas gingivalis infections using bioinformatics method.

STUDY DESIGN

GSE9723 dataset was downloaded from Gene Expression Omnibus, and DEGs between the infected cells and controls were identified using unpaired t-test. Overlapping DEGs in responding to Aggregatibacter actinomycetemcomitans and Porphyromonas gingivalis infections were extracted. Protein-protein interaction networks were constructed and functional modules were isolated using Molecular Complex Detection algorithm. Key genes in protein-protein interaction network and Molecular Complex Detection modules were subjected to functional enrichment analyses. In addition, the transcriptional factors were predicted.

RESULTS

A total of 533 co-up-regulated and 202 co-down-regulated genes were identified. The up-regulated genes, including IL6, CCL19, EDN1, ADCY9, and BCL2 and the down-regulated genes, including CCNB1, PLK1, and CCNA2 were the key genes in the protein-protein interaction network and modules. They were intensively enriched in chemokine signaling pathway, calcium signaling pathway and cell cycle. Finally, two transcriptional factors, E12 and NRSF, targeting to the up-regulated genes and one transcriptional factor, NRP1, targeting the down-regulated genes, were predicted.

CONCLUSIONS

CCNB1, PLK1, and CCNA2 might play important roles in the response of host epithelial cells to Aggregatibacter actinomycetemcomitans and Porphyromonas gingivalis.

Identification of key determinants in Porphyromonas gingivalis host-cell invasion assays

The periodontal pathogen Porphyromonas gingivalis can invade host cells, a virulence trait which may contribute to the persistence of infection at subgingival sites. Whilst the antibiotic protection assay has been commonly employed to investigate and quantify P. gingivalis invasion, data obtained have varied widely and a thorough investigation of the factors influencing this is lacking. We investigated the role of a number of bacterial and host-cell factors and report that the growth phase of P. gingivalis, source (laboratory strain vs. clinical strain), host-cell identity (cell line vs. primary), host-cell lysis method, and host-cell passage number had no significant effect on bacterial invasion. However, incubation time, host-cell seeding density, method of quantification (viable count vs. DNA), and whether host cells were plated or in suspension, were shown to influence invasion. Also, cells isolated by rapid adhesion to fibronectin exhibited higher levels of P. gingivalis invasion, possibly as a result of increased levels of active α5β1 integrin. Interestingly, this may represent a population of cells with stem cell-like properties. This study provides important new information by identifying the most important factors that influence P. gingivalis invasion assays and may help to explain variations in the levels previously reported.

Extracellular galectin-1 enhances adhesion to and invasion of oral epithelial cells by Porphyromonas gingivalis

Galectin-1 and galectin-3 are C-type lectin receptors that bind to lipopolysaccharide in the cell wall of gram-negative bacteria. In this study, we investigated the effects of galectin-1 and galectin-3 on adhesion to and invasion of the human gingival epithelial cell line Ca9-22 by Porphyromonas gingivalis, a periodontal pathogenic gram-negative bacterium. Recombinant galectin-1, but not galectin-3, enhanced P. gingivalis adhesion and invasion, although both galectins bound similarly to P. gingivalis. Flow cytometry also revealed that Ca9-22 cells express low levels of galectin-1 and moderate levels of galectin-3. Ca9-22 cells in which galectin-3 was knocked-down did not exhibit enhanced P. gingivalis adhesion and invasion. Similarly, specific antibodies to galectin-1 and galectin-3 did not inhibit P. gingivalis adhesion and invasion. These results suggest that soluble galectin-1, but not galectin-3, may exacerbate periodontal disease by enhancing the adhesion to and invasion of host cells by periodontal pathogenic bacteria.

Human Primary Epithelial Cells Acquire an Epithelial-Mesenchymal-Transition Phenotype during Long-Term Infection by the Oral Opportunistic Pathogen, Porphyromonas gingivalis

Porphyromonas gingivalis is a host-adapted oral pathogen associated with chronic periodontitis that successfully survives and persists in the oral epithelium. Recent studies have positively correlated periodontitis with increased risk and severity of oral squamous cell carcinoma (OSCC). Intriguingly, the presence of P. gingivalis enhances tumorigenic properties independently of periodontitis and has therefore been proposed as a potential etiological agent for OSCC. However, the initial host molecular changes induced by P. gingivalis infection which promote predisposition to cancerous transformation through EMT (epithelial-mesenchymal-transition), has never been studied in human primary cells which more closely mimic the physiological state of cells in vivo. In this study, we examine for the first time in primary oral epithelial cells (OECs) the expression and activation of key EMT mediators during long-term P. gingivalis infection in vitro. We examined the inactive phosphorylated state of glycogen synthase kinase-3 beta (p-GSK3β) over 120 h P. gingivalis infection and found p-GSK3β, an important EMT regulator, significantly increases over the course of infection (p < 0.01). Furthermore, we examined the expression of EMT-associated transcription factors, Slug, Snail, and Zeb1 and found significant increases (p < 0.01) over long-term P. gingivalis infection in protein and mRNA expression. Additionally, the protein expression of mesenchymal intermediate filament, Vimentin, was substantially increased over 120 h of P. gingivalis infection. Analysis of adhesion molecule E-cadherin showed a significant decrease (p < 0.05) in expression and a loss of membrane localization along with β-catenin in OECs. Matrix metalloproteinases (MMPs) 2, 7, and 9 are all markedly increased with long-term P. gingivalis infection. Finally, migration of P. gingivalis infected cells was evaluated using scratch assay in which primary OEC monolayers were wounded and treated with proliferation inhibitor, Mitomycin C. The cellular movement was determined by microscopy. Results displayed P. gingivalis infection promoted cell migration which was slightly enhanced by co-infection with Fusobacterium nucleatum, another oral opportunistic pathogen. Therefore, this study demonstrates human primary OECs acquire initial molecular/cellular changes that are consistent with EMT induction during long-term infection by P. gingivalis and provides a critically novel framework for future mechanistic studies.

Genes Contributing to Porphyromonas gingivalis Fitness in Abscess and Epithelial Cell Colonization Environments

Porphyromonas gingivalis is an important cause of serious periodontal diseases, and is emerging as a pathogen in several systemic conditions including some forms of cancer. Initial colonization by P. gingivalis involves interaction with gingival epithelial cells, and the organism can also access host tissues and spread haematogenously. To better understand the mechanisms underlying these properties, we utilized a highly saturated transposon insertion library of P. gingivalis, and assessed the fitness of mutants during epithelial cell colonization and survival in a murine abscess model by high-throughput sequencing (Tn-Seq). Transposon insertions in many genes previously suspected as contributing to virulence showed significant fitness defects in both screening assays. In addition, a number of genes not previously associated with P. gingivalis virulence were identified as important for fitness. We further examined fitness defects of four such genes by generating defined mutations. Genes encoding a carbamoyl phosphate synthetase, a replication-associated recombination protein, a nitrosative stress responsive HcpR transcription regulator, and RNase Z, a zinc phosphodiesterase, showed a fitness phenotype in epithelial cell colonization and in a competitive abscess infection. This study verifies the importance of several well-characterized putative virulence factors of P. gingivalis and identifies novel fitness determinants of the organism.

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.

Opportunistic Pathogen Porphyromonas gingivalis Modulates Danger Signal ATP-Mediated Antibacterial NOX2 Pathways in Primary Epithelial Cells

Porphyromonas gingivalis, a major opportunistic pathogen in the etiology of chronic periodontitis, successfully survives in human gingival epithelial cells (GECs). P. gingivalis abrogates the effects of a host danger molecule, extracellular ATP (eATP)/P2X₇ signaling, such as the generation of reactive oxygen species (ROS) via the mitochondria and NADPH oxidases (NOX) from primary GECs. However, antimicrobial functions of ROS production are thoroughly investigated in myeloid-lineage immune cells and have not been well-understood in epithelial cells. Therefore, this study characterizes antibacterial NOX2 generated ROS and host downstream effects in P. gingivalis infected human primary GECs. We examined the expression of NOX isoforms in the GECs and demonstrate eATP stimulation increased the mRNA expression of NOX2 (p < 0.05). Specific peptide inhibition of NOX2 significantly reduced eATP-mediated ROS as detected by DCFDA probe. The results also showed P. gingivalis infection can temporally modulate NOX2 pathway by reorganizing the localization and activation of cytosolic molecules (p47phox, p67phox, and Rac1) during 24 h of infection. Investigation into downstream biocidal factors of NOX2 revealed an eATP-induced increase in hypochlorous acid (HOCl) in GECs detected by R19-S fluorescent probe, which is significantly reduced by a myeloperoxidase (MPO) inhibitor. MPO activity of the host cells was assayed and found to be positively affected by eATP treatment and/or infection. However, P. gingivalis significantly reduced the MPO product, bactericidal HOCl, in early times of infection upon eATP stimulation. Analysis of the intracellular levels of a major host-antioxidant, glutathione during early infection revealed a substantial decrease (p < 0.05) in reduced glutathione indicative of scavenging of HOCl by P. gingivalis infection and eATP treatment. Examination of the mRNA expression of key enzymes in the glutathione synthesis pathway displayed a marked increase (p < 0.05) in glutamate cysteine ligase (GCL) subunits GCLc and GCLm, glutathione synthetase, and glutathione reductase during the infection. These suggest P. gingivalis modulates the danger signal eATP-induced NOX2 signaling and also induces host glutathione synthesis to likely avoid HOCl mediated clearance. Thus, we characterize for the first time in epithelial cells, an eATP/NOX2-ROS-antibacterial pathway and demonstrate P. gingivalis can circumvent this important antimicrobial defense system potentially for successful persistence in human epithelial tissues.

Nucleoside-Diphosphate-Kinase of P. gingivalis is Secreted from Epithelial Cells In the Absence of a Leader Sequence Through a Pannexin-1 Interactome

Nucleoside-diphosphate-kinases (NDKs) are leaderless, multifunctional enzymes. The mode(s) of NDK secretion is currently undefined, while extracellular translocation of bacterial NDKs is critical for avoidance of host pathogen clearance by opportunistic pathogens such as Porphyromonas gingivalis. P. gingivalis-NDK during infection inhibits extracellular-ATP (eATP)/P2X₇-receptor mediated cell death in gingival epithelial cells (GECs) via eATP hydrolysis. Furthermore, depletion of pannexin-1-hemichannel (PNX1) coupled with P2X₇-receptor blocks the infection-induced eATP release in GECs, and P. gingivalis-NDK impacts this pathway. Ultrastructural and confocal microscopy of P. gingivalis-co-cultured GECs or green-fluorescent-protein (GFP)-P. gingivalis-NDK transfected GECs revealed a perinuclear/cytoplasmic localization of NDK. eATP stimulation induced NDK recruitment to the cell periphery. Depletion of PNX1 by siRNA or inhibition by probenecid resulted in significant blocking of extracellular NDK activity and secretion using ATPase and ELISA assays. Co-immunoprecipitation-coupled Mass-spectrometry method revealed association of P. gingivalis-NDK to the myosin-9 motor molecule. Interestingly, inhibition of myosin-9, actin, and lipid-rafts, shown to be involved in PNX1-hemichannel function, resulted in marked intracellular accumulation of NDK and decreased NDK secretion from infected GECs. These results elucidate for the first time PNX1-hemichannels as potentially main extracellular translocation pathway for NDKs from an intracellular pathogen, suggesting that PNX1-hemichannels may represent a therapeutic target for chronic opportunistic infections.

Role of OmpA2 surface regions of Porphyromonas gingivalis in host-pathogen interactions with oral epithelial cells

Outer membrane protein A (OmpA) is a key outer membrane protein found in Gram‐negative bacteria that contributes to several crucial processes in bacterial virulence. In Porphyromonas gingivalis, OmpA is predicted as a heterotrimer of OmpA1 and OmpA2 subunits encoded by adjacent genes. Here we describe the role of OmpA and its individual subunits in the interaction of P. gingivalis with oral cells. Using knockout mutagenesis, we show that OmpA2 plays a significant role in biofilm formation and interaction with human epithelial cells. We used protein structure prediction software to identify extracellular loops of OmpA2, and determined these are involved in interactions with epithelial cells as evidenced by inhibition of adherence and invasion of P. gingivalis by synthetic extracellular loop peptides and the ability of the peptides to mediate interaction of latex beads with human cells. In particular, we observe that OmpA2‐loop 4 plays an important role in the interaction with host cells. These data demonstrate for the first time the important role of P. gingivalis OmpA2 extracellular loops in interaction with epithelial cells, which may help design novel peptide‐based antimicrobial therapies for periodontal disease.

Porphyromonas gingivalis fimbriae are pro-inflammatory but do not play a prominent role in the innate immune response to P. gingivalis

The fimA gene encodes the major fimbrial protein of Porphyromonas gingivalis. It has been shown to stimulate adhesion to salivary proteins and other bacteria. It is also thought to play a major role in invading and stimulating host cells. To determine whether the fimA gene represents one of the principal molecules of P. gingivalis that induces inflammation, we tested purified FimA protein and a mutant P. gingivalis (DPG3) that lacks the fimA gene versus wild-type (WT) P. gingivalis. When injected into connective tissue of the scalp, purified FimA protein induced TNF-α and MIP-2 expression confirming that it is pro-inflammatory. WT P. gingivalis induced TNF-α expression and recruitment of PMNs in the same model. However, DPG3 P. gingivalis stimulated TNF expression and PMN recruitment to the same extent. The latter was consistent with similar induction of the chemokine MIP-2. Similar results were obtained with diabetic mice that have a more prolonged inflammatory response to bacterial stimulation. These results indicate that FimA is a potent inducer of inflammatory cytokine expression but, in the context of P. gingivalis infection, it is not a principal stimulator of the innate host response.

The M. tuberculosis HAD phosphatase (Rv3042c) interacts with host proteins and is inhibited by Clofazimine

Mycobacterium tuberculosis codes for a HAD-phosphatase, Rv3042c (MtSerB2), that has earlier been characterized as a metabolic enzyme. Here we demonstrate that MtSerB2 is secreted into the cytosol of infected macrophages and is found in bronchoalveolar lavage samples of tuberculosis patients. MtSerB2 induces significant cytoskeleton rearrangements through cofilin activation and affects the expression of genes that regulate actin dynamics. It specifically interacts with HSP90, HSP70 and HSP27 that block apoptotic pathways and not with other HSPs. It actively dephosphorylates MAPK-p38 and NF-kappa B p65 that play crucial roles in inflammatory and immune responses. This in turn leads to down-regulation of Interleukin 8, a chemotactic and inflammatory cytokine. Finally, during evaluation of inhibitors against MtSerB2 we found that Clofazimine, a drug being evaluated for XDR and MDR tuberculosis, inhibits MtSerB2 phosphatase activity and reverses the above effects and interactions with host proteins. Overall, the study identifies that MtSerB2 has new functions that might help the pathogen to evade the host's immune response.

Two Small Molecules Block Oral Epithelial Cell Invasion by Porphyromons gingivalis

Porphyromonas gingivalis is a keystone pathogen of periodontitis. One of its bacterial characteristics is the ability to invade various host cells, including nonphagocytic epithelial cells and fibroblasts, which is known to facilitate P. gingivalis adaptation and survival in the gingival environment. In this study, we investigated two small compounds, Alop1 and dynasore, for their role in inhibition of P. gingivalis invasion. Using confocal microscopy, we showed that these two compounds significantly reduced invasion of P. gingivalis and its outer membrane vesicles into human oral keratinocytes in a dose-dependent manner. The inhibitory effects of dynasore, a dynamin inhibitor, on the bacterial entry is consistent with the notion that P. gingivalis invasion is mediated by a clathrin-mediated endocytic machinery. We also observed that microtubule arrangement, but not actin, was altered in the host cells treated with Alop1 or dynasore, suggesting an involvement of microtubule in this inhibitory activity. This work provides an opportunity to develop compounds against P. gingivalis infection.

Presence of Porphyromonas gingivalis in esophagus and its association with the clinicopathological characteristics and survival in patients with esophageal cancer

Background

Mounting evidence suggests a causal relationship between specific bacterial infections and the development of certain malignancies. However, the possible role of the keystone periodontal pathogen, Porphyromonas gingivalis, in esophageal squamous cell carcinoma (ESCC) remains unknown. Therefore, we examined the presence of P. gingivalis in esophageal mucosa, and the relationship between P. gingivalis infection and the diagnosis and prognosis of ESCC.

Methods

The presence of P. gingivalis in the esophageal tissues from ESCC patients and normal controls was examined by immunohistochemistry using antibodies targeting whole bacteria and its unique secreted protease, the gingipain Kgp. qRT-PCR was used as a confirmatory approach to detect P. gingivalis 16S rDNA. Clinicopathologic characteristics were collected to analyze the relationship between P. gingivalis infection and development of ESCC.

Results

P. gingivalis was detected immunohistochemically in 61 % of cancerous tissues, 12 % of adjacent tissues and was undetected in normal esophageal mucosa. A similar distribution of lysine-specific gingipain, a catalytic endoprotease uniquely secreted by P. gingivalis, and P. gingivalis 16S rDNA was also observed. Moreover, statistic correlations showed P. gingivalis infection was positively associated with multiple clinicopathologic characteristics, including differentiation status, metastasis, and overall survival rate.

Conclusion

These findings demonstrate for the first time that P. gingivalis infects the epithelium of the esophagus of ESCC patients, establish an association between infection with P. gingivalis and the progression of ESCC, and suggest P. gingivalis infection could be a biomarker for this disease. More importantly, these data, if confirmed, indicate that eradication of a common oral pathogen could potentially contribute to a reduction in the overall ESCC burden.

Electronic supplementary material

The online version of this article (doi:10.1186/s13027-016-0049-x) contains supplementary material, which is available to authorized users.

Dynamics of Fluoride Bioavailability in the Biofilms of Different Oral Surfaces after Amine Fluoride and Sodium Fluoride Application

It was the aim of this study to investigate differences in fluoride bioavailability in different oral areas after the application of amine fluoride (AmF) and sodium fluoride (NaF). The null hypothesis suggested no differences in the fluoride bioavailability. The tongue coating was removed and biofilm samples from the palate, oral floor and cheeks were collected. All subjects brushed their teeth with toothpaste containing AmF or NaF. Specimens were collected before, as well as immediately after and at 30 and 120 minutes after tooth brushing. The fluoride concentration was determined. The area under the curve was calculated for each location and compared statistically. In the tongue coating, fluoride concentration increased faster after NaF application than after AmF application. After 30 minutes, the fluoride concentration decreased and remained stable until 120 minutes after AmF application and returned to baseline after NaF application. The difference between the baseline and the endpoint measurements was statistically significant. The fluoride concentration in the tongue coating remained at a higher level compared with the baseline for up to 120 minutes post-brushing. This may indicate that the tongue coating is a major reservoir for fluoride bioavailability. The results also indicate an unequal fluoride distribution in the oral cavity.

Patho-epigenetics of Infectious Diseases Caused by Intracellular Bacteria

In multicellular eukaryotes including plants, animals and humans, epigenetic reprogramming may play a role in the pathogenesis of a wide variety of diseases. Recent studies revealed that in addition to viruses, pathogenic bacteria are also capable to dysregulate the epigenetic machinery of their target cells. In this chapter we focus on epigenetic alterations induced by bacteria infecting humans. Most of them are obligate or facultative intracellular bacteria that produce either bacterial toxins and surface proteins targeting the host cell membrane, or synthesise effector proteins entering the host cell nucleus. These bacterial products typically elicit histone modifications, i.e. alter the "histone code". Bacterial pathogens are capable to induce alterations of host cell DNA methylation patterns, too. Such changes in the host cell epigenotype and gene expression pattern may hinder the antibacterial immune response and create favourable conditions for bacterial colonization, growth, or spread. Epigenetic dysregulation mediated by bacterial products may also facilitate the production of inflammatory cytokines and other inflammatory mediators affecting the epigenotype of their target cells. Such indirect epigenetic changes as well as direct interference with the epigenetic machinery of the host cells may contribute to the initiation and progression of malignant tumors associated with distinct bacterial infections.

The Porphyromonas gingivalis O antigen is required for inhibition of apoptosis in gingival epithelial cells following bacterial infection

BACKGROUND AND OBJECTIVE

Porphyromonas gingivalis infection induces apoptosis inhibition in gingival epithelial cells; however, it is not fully understood which bacterial effectors are involved in this process. The aim of this study is to evaluate whether the P. gingivalis lipopolysaccharide (LPS), specifically the O-antigen region, affects adherence, invasion, viability and apoptosis of gingival epithelial cells.

MATERIAL AND METHODS

Gingival epithelial cells (OKF6/TERT2 line) were infected by different freshly prepared P. gingivalis clinical isolates, obtained from subjects with chronic periodontitis (CP3 and CP4) and healthy individuals (H1 and H3). Periodontitis and healthy isolates show differences in O-antigen production, as healthy isolates lack the O-antigen region. In addition, cells were infected by a site-specific mutant lacking the O-antigen portion. After 24 h postinfection, cell proliferation, viability and apoptosis were evaluated by Trypan blue, MTS and annexin V assays, respectively. Bacterial invasion, adhesion and proliferation were measured by gentamicin/metronidazole protection assays. Finally, toll-like receptor (TLR)2 and TLR4 mRNA expression was evaluated by quantitative reverse transcription-polymerase chain reaction. Statistical analysis was performed using ANOVA, Tukey's or Dunnett's tests (p < 0.05).

RESULTS

At 24 h postinfection, strains lacking the O-antigen region (healthy isolates and O-antigen ligase-deficient strain) were unable to increase proliferation and viability, or decrease apoptosis as compared with strains producing intact LPS (periodontitis isolates and reference strain). However, the presence of the O-antigen neither contributed to changes in the ability of the bacteria to adhere to or invade cells, nor to intracellular survival. The presence of O-antigen also increased the expression of TLR4 (nearly sixfold), which correlated with inhibition of apoptosis.

CONCLUSION

The O-antigen region of P. gingivalis LPS is required to increase gingival epithelial cell viability upon infection by bacteria and this increase is attributable to a reduction in apoptosis. Moreover, although bacterial internalization is required, the effects observed are not due to alterations in P. gingivalis adherence, invasion or intracellular survival. Interestingly, inhibition of apoptosis correlates with increased TLR4 expression, suggesting a role for TLR4 in this process.

Invasion of Porphyromonas gingivalis strains into vascular cells and tissue

Porphyromonas gingivalis is considered a major pathogen in adult periodontitis and is also associated with multiple systemic diseases, for example, cardiovascular diseases. One of its most important virulence factors is invasion of host cells. The invasion process includes attachment, entry/internalization, trafficking, persistence, and exit. The present review discusses these processes related to P. gingivalis in cardiovascular cells and tissue. Although most P. gingivalis strains invade, the invasion capacity of strains and the mechanisms of invasion including intracellular trafficking among them differ. This is consistent with the fact that there are significant differences in the pathogenicity of P. gingivalis strains. P. gingivalis invasion mechanisms are also dependent on types of host cells. Although much is known about the invasion process of P. gingivalis, we still have little knowledge of its exit mechanisms. Nevertheless, it is intriguing that P. gingivalis can remain viable in human cardiovascular cells and atherosclerotic plaque and later exit and re-enter previously uninfected host cells.

Porphyromonas gingivalis attenuates ATP-mediated inflammasome activation and HMGB1 release through expression of a nucleoside-diphosphate kinase

Many intracellular pathogens evade the innate immune response in order to survive and proliferate within infected cells. We show that Porphyromonas gingivalis, an intracellular opportunistic pathogen, uses a nucleoside-diphosphate kinase (NDK) homolog to inhibit innate immune responses due to stimulation by extracellular ATP, which acts as a danger signal that binds to P2X7 receptors and induces activation of an inflammasome and caspase-1. Thus, infection of gingival epithelial cells (GECs) with wild-type P. gingivalis results in inhibition of ATP-induced caspase-1 activation. However, ndk-deficient P. gingivalis is less effective than wild-type P. gingivalis in reducing ATP-mediated caspase-1 activation and secretion of the pro-inflammatory cytokine, IL-1β, from infected GECs. Furthermore, P. gingivalis NDK modulates release of high-mobility group protein B1 (HMGB1), a pro-inflammatory danger signal, which remains associated with chromatin in healthy cells. Unexpectedly, infection with either wild-type or ndk-deficient P. gingivalis causes release of HMGB1 from the nucleus to the cytosol. But HMGB1 is released to the extracellular space when uninfected GECs are further stimulated with ATP, and there is more HMGB1 released from the cells when ATP-treated cells are infected with ndk-deficient mutant than wild-type P. gingivalis. Our results reveal that NDK plays a significant role in inhibiting P2X7-dependent inflammasome activation and HMGB1 release from infected GECs.

Secretome of gingival epithelium in response to subgingival biofilms

Periodontitis is the chronic inflammatory destruction of periodontal tissues as a result of bacterial biofilm formation on the tooth surface. Proteins secreted by the gingival epithelium challenged by subgingival biofilms represent an important initial response for periodontal inflammation. The aim of this in vitro study was to characterize the whole secreted proteome of gingival epithelial tissue challenged by subgingival biofilms, and to evaluate the differential effects of the presence of the red-complex species in the biofilm. Multi-layered human gingival epithelial cultures were challenged with a 10-species in vitro biofilm model or its seven-species variant excluding the red complex. Liquid chromatography-tandem mass spectrometry for label-free quantitative proteomics was applied to identify and quantify the secreted epithelial proteins in the culture supernatant. A total of 192 proteins were identified and quantified. The biofilm challenge resulted in more secreted proteins being downregulated than upregulated. Even so, presence of the red complex in the biofilm was responsible for much of this downregulatory effect. Over 24 h, the upregulated biological processes were associated with inflammation and apoptosis, whereas the downregulated processes were associated with the disruption of epithelial tissue integrity and impairment of tissue turnover. Over 48 h, negative regulation of several metabolic processes and degradation of various molecular complexes was further intensified. Again, many of these biological regulations were attributed to the presence of the red complex. In conclusion, the present study provides the secreted proteome profile of gingival epithelial tissue to subgingival biofilms, and identifies a significant role for the red-complex species in the observed effects.

Proteome analysis of coinfection of epithelial cells with Filifactor alocis and Porphyromonas gingivalis shows modulation of pathogen and host regulatory pathways

Changes in periodontal status are associated with shifts in the composition of the bacterial community in the periodontal pocket. The relative abundances of several newly recognized microbial species, including Filifactor alocis, as-yet-unculturable organisms, and other fastidious organisms have raised questions on their impact on disease development. We have previously reported that the virulence attributes of F. alocis are enhanced in coculture with Porphyromonas gingivalis. We have evaluated the proteome of host cells and F. alocis during a polymicrobial infection. Coinfection of epithelial cells with F. alocis and P. gingivalis strains showed approximately 20% to 30% more proteins than a monoinfection. Unlike F. alocis ATCC 35896, the D-62D strain expressed more proteins during coculture with P. gingivalis W83 than with P. gingivalis 33277. Proteins designated microbial surface component-recognizing adhesion matrix molecules (MSCRAMMs) and cell wall anchor proteins were highly upregulated during the polymicrobial infection. Ultrastructural analysis of the epithelial cells showed formation of membrane microdomains only during coinfection. The proteome profile of epithelial cells showed proteins related to cytoskeletal organization and gene expression and epigenetic modification to be in high abundance. Modulation of proteins involved in apoptotic and cell signaling pathways was noted during coinfection. The enhanced virulence potential of F. alocis may be related to the differential expression levels of several putative virulence factors and their effects on specific host cell pathways.

Breaking bad: manipulation of the host response by Porphyromonas gingivalis

Recent metagenomic and mechanistic studies are consistent with a new model of periodontal pathogenesis. This model proposes that periodontal disease is initiated by a synergistic and dysbiotic microbial community rather than by a select few bacteria traditionally known as "periopathogens." Low-abundance bacteria with community-wide effects that are critical for the development of dysbiosis are now known as keystone pathogens, the best-documented example of which is Porphyromonas gingivalis. Here, we review established mechanisms by which P. gingivalis interferes with host immunity and enables the emergence of dysbiotic communities. We integrate the role of P. gingivalis with that of other bacteria acting upstream and downstream in pathogenesis. Accessory pathogens act upstream to facilitate P. gingivalis colonization and co-ordinate metabolic activities, whereas commensals-turned pathobionts act downstream and contribute to destructive inflammation. The recent concepts of keystone pathogens, along with polymicrobial synergy and dysbiosis, have profound implications for the development of therapeutic options for periodontal disease.

Transglutaminase 2 is essential for adherence of Porphyromonas gingivalis to host cells

Porphyromonas gingivalis is the major causative agent of periodontitis, and it may also be involved in the development of systemic diseases (atherosclerosis, rheumatoid arthritis). P. gingivalis is found on and within oral and gingival epithelial cells following binding to surface components of host cells, which serve as receptors for the bacterium. Evidence is presented in this study that shows that transglutaminase 2 (TG2) plays a critical role in the adherence of P. gingivalis to host cells. Studies of confocal microscopy indicate colocalization of P. gingivalis with TG2 on the surface of HEp-2 epithelial cells, with clusters of TG2 seen at bacterial attachment sites. By silencing the expression of TG2 with siRNA in HEp-2 cells, P. gingivalis association was greatly diminished. The bacterium does not bind well to a mouse fibroblast cell line that produces low amounts of surface TG2, but binding can be restored by introduction of TG2 expressed on a plasmid. TG2 can form very tight complexes with fibronectin (FN), and the complementary binding sites of the two proteins are known. A synthetic peptide that mimics the main FN-binding sequence of TG2 blocks the formation of TG2-FN complexes and is highly effective in inhibiting adherence of P. gingivalis to host cells. These findings provide evidence of a role for cell-surface TG2 in bacterial attachment and subsequent internalization.