Porphyromonas gingivalis invades oral epithelial cells in vitro

Role of helper T cells in the humoral immune responses against 53-kDa outer membrane protein from Porphyromonas gingivalis

Outer membrane protein with a 53-kDa molecular weight (Ag53) isolated from Porphyromonas gingivalis evokes strong humoral immune responses in many periodontitis patients. To examine the effects of cytokines produced by Ag53-specific Th cells on the IgG production against Ag53, we established Ag53-specific Th-cell lines from patients with early onset periodontitis and from healthy volunteers. We then developed a mixed lymphocyte culture system between Ag53-specific Th cells and auto- or allo-derived T-cell-depleted leukocytes produced from the subjects whose HLA class II haplotypes were completely matched. Interferon-gamma production was observed in all Th cell lines from patients and healthy subjects. As for Th2 type cytokines, interleukin (IL)-4, IL-5, IL-6 and IL-10 production varied greatly in Th cells regardless of the periodontal condition of the donor. Only Th cell lines with a high Th2/Th1 ratio induced Ag53-specific IgG production when cocultured with T-cell-depleted leukocytes. Thus, the difference in Th2/Th1 balance may regulate the Ag53-specific IgG production.

Porphyromonas gingivalis induces its uptake by human macrophages and promotes foam cell formation in vitro

Porphyromonas gingivalis is an etiologic agent of periodontal disease in humans, which has been linked to an increased risk for atherosclerosis-related events. In this study, we examined the effect of P. gingivalis infection on human macrophages with respect to foam cell formation, the hallmark of early atherogenesis, and the potential of P. gingivalis to induce its uptake by these cells. Human monocyte-derived macrophages were incubated with low density lipoprotein and infected with P. gingivalis FDC381 or its fimbriae deficient mutant, DPG3. Consistent with a role for fimbriae in this process, strain 381 significantly increased foam cell formation as compared to DPG3. Recovery of viable P. gingivalis in antibiotic protection experiments was significantly higher for strain 381 than for DPG3. By transmission electron microscopy, the wild-type strain was shown to adhere to and enter THP-1 cells. These results suggest that properties of P. gingivalis which render it capable of adhering to/invading other cell types may also be operative in macrophages and play an important role in its atherogenic potential.

Porphyromonas gingivalis strain-dependent activation of human endothelial cells

Porphyromonas gingivalis is an important bacterium involved in periodontal diseases. Colonization by periodontopathogens has been associated with severe local inflammatory reactions in the connective tissue. In this study we characterized P. gingivalis-mediated infection and activation of human umbilical vein endothelial cells by using two strains of different virulence capacities, strains ATCC 53977 and DSMZ 20709. Both strains were able to adhere to and infect endothelial cells with an infection rate of 0.48% for ATCC 53977 and 0.007% for DSMZ 20709. The triggering of two signal transduction pathways in P. gingivalis-infected endothelial cells was demonstrated for both strains, with a rapid increase of p38 mitogen-activated protein kinase phosphorylation and a more delayed degradation of IkappaBalpha, followed by nuclear translocation of NF-kappaB. In addition, both strains induced enhanced expression of endothelial adhesion molecules E-selectin and intracellular adhesion molecule 1 (ICAM-1). Target cell activation was independent of bacterial fimbriae expression since the fimA knockout strain A7436 DeltafimA induced the same level of ICAM-1 as the corresponding wild type (A7436-WT). Thus, two P. gingivalis strains, ATCC 53799 and DSMZ 20709, infect endothelial cells and trigger signaling cascades leading to endothelial activation, which in turn may result in or promote severe local and systemic inflammation.

Intracellular localization of Porphyromonas gingivalis thiol proteinase in periodontal tissues of chronic periodontitis patients

OBJECTIVES

Porphyromonas gingivalis is a significant periodontal pathogen that has been shown in vitro to be able to invade gingival epithelial cells and grow intracellularly. The aim of the present study was to detect P. gingivalis in gingival tissues from chronic periodontitis (CP) patients.

MATERIALS AND METHODS

Monoclonal antibodies specific to a cell membrane-bound thiol proteinase of P. gingivalis were used to detect the microbe in gingival tissues of CP patients (n = 13) by immunohistochemistry. The presence of P. gingivalis was also analysed by polymerase chain reaction (PCR).

RESULTS

Immunohistochemical analysis of the periodontal tissues revealed positive staining for P. gingivalis thiol proteinase in 11 of the 13 patients. Positive staining was mainly located intracellularly in the perinuclear region of the cytoplasm in the periodontal epithelial cells and it could be detected throughout the whole depth of both pocket and oral epithelium. The sensitivity of immunohistochemistry was found to be comparable with that of PCR.

CONCLUSIONS

Our results provide in vivo evidence of the ability of P. gingivalis to enter human gingival epithelial cells. Intracellular localization of P. gingivalis contributes to its evasion of the host immune surveillance and eventually increases its resistance to conventional treatments of periodontal diseases.

Porphyromonas gingivalis induces receptor activator of NF-kappaB ligand expression in osteoblasts through the activator protein 1 pathway

Porphyromonas gingivalis, an important periodontal pathogen, is closely associated with inflammatory alveolar bone resorption, and several components of the organism such as lipopolysaccharides have been reported to stimulate production of cytokines that promote inflammatory bone destruction. We investigated the effect of infection with viable P. gingivalis on cytokine production by osteoblasts. Reverse transcription-PCR and real-time PCR analyses revealed that infection with P. gingivalis induced receptor activator of nuclear factor kappaB (NF-kappaB) ligand (RANKL) mRNA expression in mouse primary osteoblasts. Production of interleukin-6 was also stimulated; however, osteoprotegerin was not. SB20350 (an inhibitor of p38 mitogen-activated protein kinase), PD98059 (an inhibitor of classic mitogen-activated protein kinase kinase, MEK1/2), wortmannin (an inhibitor of phosphatidylinositol 3 kinase), and carbobenzoxyl-leucinyl-leucinyl-leucinal (an inhibitor of NF-kappaB) did not prevent the RANKL expression induced by P. gingivalis. Degradation of inhibitor of NF-kappaB-alpha was not detectable; however, curcumin, an inhibitor of activator protein 1 (AP-1), prevented the RANKL production induced by P. gingivalis infection. Western blot analysis revealed that phosphorylation of c-Jun, a component of AP-1, occurred in the infected cells, and an analysis of c-Fos binding to an oligonucleotide containing an AP-1 consensus site also demonstrated AP-1 activation in infected osteoblasts. Infection with P. gingivalis KDP136, an isogenic deficient mutant of arginine- and lysine-specific cysteine proteinases, did not stimulate RANKL production. These results suggest that P. gingivalis infection induces RANKL expression in osteoblasts through AP-1 signaling pathways and cysteine proteases of the organism are involved in RANKL production.

ANTI-PHAGOCYTIC ROLE OF SURFACE FIBROUS STRUCTURE OF AN INVASIVE PORPHYROMONAS GINGIVALIS STRAIN

Recent studies have shown that invasive and non-invasive strains of Porphyromonas gingivalis can both be isolated from patients with periodontitis. We examined the interaction between an invasive 16-1 P. gingivalis strain and phagocytes obtained from human peripheral blood and guinea pig peritoneal cavity. Phagocytes from human peripheral blood, mainly polymorphonuclear leukocytes (PMNs) isolated by centrifugation in Ficoll Hypaque, and macrophages collected from the peritoneal cavity of guinea pigs, were exposed to P. gingivalis cells. After this exposure, greater numbers of the non-invasive P. gingivalis ATCC 33277 were observed in human PMNs and guinea pig macrophages compared with the invasive P. gingivalis 16-1. Electron microscopic observations showed that invasive 16-1 within phagosomes in human PMNs and guinea pig macrophages retained their surface fibrous structures as well as their outer membranes. Electron microscopic examination showed that destruction and damage to the cell membranes and inner structures were clear in human PMNs and guinea pig macrophages after exposure to invasive 16-1 for 6 and 24 hours; this was a clear difference from exposure to the non-invasive ATCC 33277. Release of lactate dehydrogenase (LDH) activities into the culture supernatant of PMNs after exposure to the invasive 16-1 for 4 and 6 hours was significantly greater than that after exposure to the non-invasive ATCC 33277 (p<0.05). On the other hand, the LDH activity after exposure for 21 hours to the invasive 16-1 was significantly lower than that of untreated cells and cells after exposure to the non-invasive ATCC 33277 strain (p<0.05). The PMN viabilities after exposure to cells of the invasive 16-1 for 3, 4, and 6 hours as evaluated by trypan blue staining were similar to those after exposure to cells of the non-invasive ATCC 33277, but that after exposure to the invasive 16-1 strain for 21 hours was significantly lower than that after exposure to cells of the non-invasive ATCC 33277 strain.

Adhesion of Porphyromonas gingivalis to cultured pocket epithelium: mono- and multi-layered

Adhesion of bacteria to epithelial cells might be influenced by the degree of cell differentiation, as observed in the multi-layering process of epithelial cells. In the present study, the adhesion of a large group of clinical Porphyromonas gingivalis strains (n=11) to in vitro cultured mono- and multi-layers of epithelial cells was examined and compared. The tissue samples originated from 6 patients with chronic adult periodontitis. Porphyromonas gingivalis bacteria adhered more to mono-layers as opposed to the more differentiated multi-layers. Differences between the clinical P. gingivalis strains, however, became obvious only on multi-layers. These partially differentiated cells may also better represent the individual subject variations. Mono-layer cultures, which are simpler to obtain, seem to be less precise. The importance of cell differentiation on bacterial adhesion needs more attention.

Molecular interaction of Porphyromonas gingivalis with host cells: implication for the microbial pathogenesis of periodontal disease

Porphyromonas gingivalis is a predominant periodontal pathogen, which expresses a number of potential virulence factors involved in the pathogenesis of periodontitis. Among them, fimbriae are a critical factor to mediate the bacterial interaction with host tissues, which promotes the bacterial adhesion to and invasion of the targeted sites. Fimbriae are capable of binding to human salivary components, commensal bacteria, and a variety of host cells including macrophages, epithelial cells, and fibroblasts. Human extracellular matrix (ECM) proteins such as vitronectin and fibronectin play important roles in cellular signal transduction via binding to receptor integrins. Fimbriae showed significant binding affinity to ECM proteins and clearly inhibited the molecular interactions between vitronectin/fibronectin and their receptor alphavbeta3 and alpha5beta1 integrins overexpressed on Chinese hamster ovary (CHO) cell strain. P. gingivalis fimbriae are likely to interrupt the cellular signaling via ECM proteins/integrins in periodontal regions. Fimbriae are also thought to be critically important in invasive events of the organism to host cells. The fimA genes, encoding FimA (a subunit of fimbriae), of P. gingivalis strains are classified into 5 types, I to V. Recent clinical investigations demonstrated the close relationship between the organisms with type II fimA and periodontitis development. Recombinant FimA (rFimA) proteins of types I to V were generated to compare their adhesion/invasion abilities to human gingival fibroblasts (HGF) and a human epithelial cell line (HEp-2 cells), respectively. There were no significant differences in the adhesion ability of microspheres (MS) coated with these rFimAs to HGF; however, the adhesion of type II rFimA-MS to HEp-2 cells was significantly greater than that of other rFimA types. It was also observed that the type II rFimA-MS markedly invaded the epithelial cells and accumulated around the nuclei. Collectively, these findings suggest that fimbriae of P. gingivalis, especially type II, are involved in the initiation and progression of human periodontitis.

Viability of cultured periodontal pocket epithelium cells and Porphyromonas gingivalis association

OBJECTIVES

Porphyromonas gingivalis, one of the key pathogens in the development of periodontitis, produces a number of virulence factors that might explain its pathogenicity. One of them is the ability to adhere and invade pocket epithelium. The aim of this study was to follow, over time, the association of P. gingivalis and consequent morphological changes of the pocket epithelium cells.

MATERIAL AND METHODS

The association capacity of four P. gingivalis serotypes [K1, K2, K4, K- (nonencapsulated)] with in vitro cultured mono-layers from periodontal pocket epithelial cells of patients with periodontitis, was followed by fluorescence microscopy and bacterial culture. The contact time between bacteria and epithelium cells ranged from 45 min to 8 h. The microscopic evaluation allowed differentiation between dead and living cells (bacteria as well as epithelium) and description of the morphological changes after association.

RESULTS

A highly significant difference in the number of associating bacteria was found between dead and living epithelium cells, and between non-capsulated and capsulated strains. A significant increase in the proportion of dead pocket epithelium cells was found with prolonged association time. The morphological changes (rounding of the epithelial cell, detachment from the glass cover-slip and loss of intercellular contact) occurred faster for mono-layers inoculated with the non-encapsulated P. gingivalis strain.

CONCLUSIONS

This study indicates that dead pocket epithelium cells harbor more P. gingivalis cells, and that a positive correlation exists between contact time and cell death. For the P. ginigvalis species, non-encapsulated strains associate in higher number. As a result, the damage they cause to the host cell seems to occur faster than occurs in encapsulated strains. As such, cell death can be seen as the end-result of bacterial association.

Roles for Arg- and Lys-gingipains in the disruption of cytokine responses and loss of viability of human endothelial cells by Porphyromonas gingivalis infection

Accumulating evidence indicates that periodontal disease is associated with human cardiovascular diseases. The periodontal pathogen Porphyromonas gingivalis was shown to be present in atherosclerotic plaques in addition to periodontal pockets. This bacterium is known to produce two individual cysteine proteinases, Arg-gingipain (Rgp) and Lys-gingipain (Kgp). Here we show that these two enzymes are responsible for either the disruption of cytokine responses in human umbilical vein endothelial cells (HUVEC) to the bacterium infection or the loss of cell viability. The expression of interleukin-8 and monocyte chemoattractant protein-1 mRNA in HUVEC was greatly induced when infected with the wild-type strain, nevertheless, their protein levels in the culture medium were markedly decreased. This decrease was completely abolished in the cells infected with the Rgp/Kgp-null mutant, but not in either the Rgp- or Kgp-null mutants. Loss of the adhesion activity and viability of HUVEC were greatly induced by the culture supernatant of the wild-type strain and strongly inhibited by either a combination of the Rgp- and the Kgp-specific inhibitors or the deficiency of the Rgp- and Kgp-encoding genes. These findings indicate that P. gingivalis modulates the cytokine response in the cells and disrupts the adhesion activity and the viability through the cooperative action of Rgp and Kgp and thereby may contribute to pathogenesis of cardiovascular diseases as well as periodontal disease.

Hydrolysis of epithelial junctional proteins by Porphyromonas gingivalis gingipains

Porphyromonas gingivalis has been implicated as an etiologic agent of adult periodontitis. We have previously shown that P. gingivalis can degrade the epithelial cell-cell junction complexes, thus suggesting that this bacterium can invade the underlying connective tissues via a paracellular pathway. However, the precise mechanism(s) involved in this process has not been elucidated. The purpose of this study was to determine if the arginine- and lysine-specific gingipains of P. gingivalis (i.e., HRgpA and RgpB, and Kgp, respectively) were responsible for the degradation of E-cadherin, the cell-cell adhesion protein in the adherens junctions. In addition, we compared the degradative abilities of the whole gingipains HRgpA and Kgp to those of their catalytic domains alone. In these studies, immunoprecipitated E-cadherin as well as monolayers of polarized Madin-Darby canine kidney (MDCK) epithelial cell cultures were incubated with the gingipains and hydrolysis of E-cadherin was assessed by Western blot analysis. Incubation of P. gingivalis cells with immunoprecipitated E-cadherin resulted in degradation, whereas prior exposure of P. gingivalis cells to leupeptin and especially acetyl-Leu-Val-Lys-aldehyde (which are arginine- and lysine-specific inhibitors, respectively) reduced this activity. Furthermore, incubation of E-cadherin immunoprecipitates with the different gingipains resulted in an effective and similar hydrolysis of the protein. However, when monolayers of MDCK cells were exposed to the gingipains, Kgp was most effective in hydrolyzing the E-cadherin molecules in the adherens junction. Kgp was more effective than its catalytic domain in degrading E-cadherin at 500 nM but not at a lower concentration (250 nM). These results suggest that the hemagglutinin domain of Kgp plays a role in degradation and that there is a critical threshold concentration for this activity. Taken together, these results provide evidence that the gingipains, especially Kgp, are involved in the degradation of the adherens junction of epithelial cells, which may be important in the invasion of periodontal connective tissue by P. gingivalis.

Functional differences among FimA variants of Porphyromonas gingivalis and their effects on adhesion to and invasion of human epithelial cells

Fimbriae of Porphyromonas gingivalis, a periodontopathogen, play an important role in its adhesion to and invasion of host cells. The fimA genes encoding fimbrillin (FimA), a subunit protein of fimbriae, have been classified into five types, types I to V, based on nucleotide sequences. We previously reported that P. gingivalis with type II fimA was strongly associated with adult periodontitis. In the present study, we compared the abilities of recombinant FimA (rFimA) types I to V to adhere to and invade human gingival fibroblasts (HGF) and a human epithelial cell line (HEp-2 cells) by using rFimA-conjugated microspheres (rFimA-MS). There were no significant differences in the abilities of the rFimA-MS to adhere to HGF; however, the adhesion of type II rFimA-MS to HEp-2 cells was significantly greater than those of other types of rFimA-MS. We also observed that type II rFimA-MS invaded epithelial cells and accumulated around the nuclei. These adhesion and invasion characteristics were eliminated by the addition of antibodies to type II rFimA and alpha5beta1-integrin. In contrast, Arg-Gly-Asp-Ser peptide and a synthetic peptide of proline-rich protein C had negligible inhibitory effects. Furthermore, P. gingivalis strain HW24D1 with type II fimA adhered to cells and invaded them more than strains with other fimA genotypes. These results suggest that type II FimA can bind to epithelial cells most efficiently through specific host receptors.

Porphyromonas gingivalis fimbriae bind to cytokeratin of epithelial cells

The adherence of Porphyromonas gingivalis to host cells is likely a prerequisite step in the pathogenesis of P. gingivalis-induced periodontal disease. P. gingivalis binds to and invades epithelial cells, and fimbriae are shown to be involved in this process. Little is known regarding epithelial receptor(s) involved in binding of P. gingivalis fimbriae. Using an overlay assay with purified P. gingivalis fimbriae as a probe, two major epithelial cell proteins with masses of 50 and 40 kDa were identified by immunoblotting with fimbria-specific antibodies. Iodinated purified fimbriae also bound to the same two epithelial cell proteins. An affinity chromatography technique was utilized to isolate and purify the epithelial components to which P. gingivalis fimbriae bind. Purified fimbriae were coupled to CNBr-activated Sepharose-4B, and the solubilized epithelial cell extract proteins bound to the immobilized fimbriae were isolated from the column. A major 50-kDa component and a minor 40-kDa component were purified and could be digested with trypsin, suggesting that they were proteins. These affinity-eluted 50- and 40-kDa proteins were then subjected to amino-terminal sequencing, and no sequence could be determined, suggesting that these proteins have blocked amino-terminal residues. CNBr digestion of the 50-kDa component resulted in an internal sequence homologous to that of Keratin I molecules. Further evidence that P. gingivalis fimbriae bind to cytokeratin molecule(s) comes from studies showing that multicytokeratin rabbit polyclonal antibodies cross-react with the affinity-purified 50-kDa epithelial cell surface component. Also, binding of purified P. gingivalis fimbriae to epithelial components can be inhibited in an overlay assay by multicytokeratin rabbit polyclonal antibodies. Furthermore, we showed that biotinylated purified fimbriae bind to purified human epidermal keratin in an overlay assay. These studies suggest that the surface-accessible epithelial cytokeratins may act as receptor(s) for P. gingivalis fimbriae. We hypothesize that adherence of P. gingivalis fimbriae to cytokeratin may be important for colonization of oral mucous membranes and possibly also for activation of epithelial cells.

Porphyromonas gingivalis traffics to autophagosomes in human coronary artery endothelial cells

Porphyromonas gingivalis is a periodontal pathogen that also localizes to atherosclerotic plaques. Our previous studies demonstrated that P. gingivalis is capable of invading endothelial cells and that intracellular bacteria are contained in vacuoles that resemble autophagosomes. In this study, we have examined the trafficking of P. gingivalis 381 to the autophagic pathway. P. gingivalis 381 internalized by human coronary artery endothelial (HCAE) cells is located within vacuoles morphologically identical to autophagosomes. The progression of P. gingivalis 381 through intracellular vacuoles was analyzed by immunofluorescence microscopy. Vacuoles containing P. gingivalis colocalize with Rab5 and HsGsa7p early after internalization. At later times, P. gingivalis colocalizes with BiP and then progresses to a vacuole that contains BiP and lysosomal glycoprotein 120. Late endosomal markers and the lysosomal cathepsin L do not colocalize with P. gingivalis 381. The intracellular survival of P. gingivalis 381 decreases over 8 h in HCAE cells pretreated with the autophagy inhibitors 3-methyladenine and wortmannin. In addition, the vacuole containing P. gingivalis 381 lacks BiP but contains cathepsin L in the presence of wortmannin. These results suggest that P. gingivalis 381 evades the endocytic pathway to lysosomes and instead traffics to the autophagosome.

Calprotectin expression in vitro by oral epithelial cells confers resistance to infection by Porphyromonas gingivalis

Calprotectin, an S100 calcium-binding protein with broad-spectrum antimicrobial activity in vitro, is expressed in neutrophils, monocytes, and gingival keratinocytes. In periodontitis, calprotectin appears upregulated and is detected at higher levels in gingival crevicular fluid and tissue specimens. How calprotectin contributes to the pathogenesis of periodontal diseases is unknown. To isolate the effects of calprotectin, a calprotectin-negative oral epithelial cell line was transfected with calprotectin genes to enable expression. Porphyromonas gingivalis was permitted to bind and invade transfected cells expressing calprotectin and sham transfectants. Rates of invasion into both cell lines were compared using the antibiotic protection assay. Transfected cells expressing calprotectin showed 40 to 50% fewer internalized P. gingivalis than sham transfectants. Similarly, binding to calprotectin expressing cells was reduced approximately twofold at all time points (15, 30, 45, and 60 min) as estimated by immunofluorescence analysis. Independent of invasion, however, prolonged exposure to P. gingivalis induced epithelial cell rounding and detachment from the substratum. These morphological changes were delayed, however, in cells expressing calprotectin. Using P. gingivalis protease-deficient mutants, we found that Arg-gingipain and Lys-gingipain contributed to epithelial cell rounding and detachment. In conclusion, expression of calprotectin appears to protect epithelial cells in culture against binding and invasion by P. gingivalis. In addition, cells expressing calprotectin are more resistant to detachment mediated by Arg-gingipain and Lys-gingipain. In periodontal disease, calprotectin may augment both the barrier protection and innate immune functions of the gingival epithelium to promote resistance to P. gingivalis infection.

Adhesion of Porphyromonas gingivalis strains to cultured epithelial cells from patients with a history of chronic adult periodontitis or from patients less susceptible to periodontitis

BACKGROUND

The present study aimed to explain the interindividual variation in periodontitis susceptibility by differences in the initial adhesion rate of Porphyromonas gingivalis to the pocket epithelium of these individuals, and/or by inter-P. gingivalis strain differences in association capacity (adhesion and internalization).

METHODS

Adhesion assays were performed on epithelial monolayers (cultured in vitro from pocket epithelium belonging to patients who were less or more susceptible to chronic adult periodontitis) using 11 genetically different clinical strains of P. gingivalis.

RESULTS

Both the disease category (less susceptible versus susceptible) and the interstrain variation were found to have a significant effect (both P <0.05) on the initial bacterial association. The chronic adult periodontitis group showed significantly more association of P. gingivalis when compared to less susceptible patients (4.2 x 10(6) versus 3.5 x 10(6)). Also, the interstrain variation was significant, with strains Pg 4 and 5 representing the least and best associating bacteria (1.8 x 10(6) colony forming units for Pg 4, 9 x 10(6) for Pg 5).

CONCLUSIONS

These results indicate that periodontitis susceptibility is influenced by both the interindividual differences in pocket epithelium (allowing more adhesion of P. gingivalis) or by the strain type by which the patient is infected (intra-species differences in adhesion capacity).

Interleukin-8 and intercellular adhesion molecule 1 regulation in oral epithelial cells by selected periodontal bacteria: multiple effects of Porphyromonas gingivalis via antagonistic mechanisms

Interaction of bacteria with mucosal surfaces can modulate the production of proinflammatory cytokines and adhesion molecules produced by epithelial cells. Previously, we showed that expression of interleukin-8 (IL-8) and intercellular adhesion molecule 1 (ICAM-1) by gingival epithelial cells increases following interaction with several putative periodontal pathogens. In contrast, expression of IL-8 and ICAM-1 is reduced after Porphyromonas gingivalis ATCC 33277 challenge. In the present study, we investigated the mechanisms that govern the regulation of these two molecules in bacterially infected gingival epithelial cells. Experimental approaches included bacterial stimulation of gingival epithelial cells by either a brief challenge (1.5 to 2 h) or a continuous coculture throughout the incubation period. The kinetics of IL-8 and ICAM-1 expression following brief challenge were such that (i) secretion of IL-8 by gingival epithelial cells reached its peak 2 h following Fusobacterium nucleatum infection whereas it rapidly decreased within 2 h after P. gingivalis infection and remained decreased up to 30 h and (ii) IL-8 and ICAM-1 mRNA levels were up-regulated rapidly 2 to 4 h postinfection and then decreased to basal levels 8 to 20 h after infection with either Actinobacillus actinomycetemcomitans, F. nucleatum, or P. gingivalis. Attenuation of IL-8 secretion was facilitated by adherent P. gingivalis strains. The IL-8 secreted from epithelial cells after F. nucleatum stimulation could be down-regulated by subsequent infection with P. gingivalis or its culture supernatant. Although these results suggested that IL-8 attenuation at the protein level might be associated with P. gingivalis proteases, the Arg- and Lys-gingipain proteases did not appear to be solely responsible for IL-8 attenuation. In addition, while P. gingivalis up-regulated IL-8 mRNA expression, this effect was overridden when the bacteria were continuously cocultured with the epithelial cells. The IL-8 mRNA levels in epithelial cells following sequential challenge with P. gingivalis and F. nucleatum and vice versa were approximately identical and were lower than those following F. nucleatum challenge alone and higher than control levels or those following P. gingivalis challenge alone. Thus, together with the protease effect, P. gingivalis possesses a powerful strategy to ensure the down-regulation of IL-8 and ICAM-1.

Cytokine responses of oral epithelial cells to Porphyromonas gingivalis infection

Accumulating evidence indicates that epithelia are not merely mechanical barriers but also important elements of the innate immune system. The present study was performed to examine cytokine responses of oral epithelial cells after infection with the periodontal pathogen Porphyromonas gingivalis. The KB-cell line and primary cultures of periodontal pocket epithelium were infected with P. gingivalis for assessment of bacterial invasion by an antibiotic protection assay, and examination of expression of interleukin-1 beta, interleukin-6, interleukin-8, and tumor necrosis factor-alpha by in situ hybridization and immunohistochemistry. We observed that P. gingivalis induces a strong cytokine response, positively correlated with the adhesive/invasive potential of the infecting strain, in both KB cells and primary cultures. These findings indicate that the epithelial cells of the periodontal pocket are an integral part of the immune system, eliciting cytokine responses to a bacterial challenge. In this context, the adhesive/invasive phenotype of P. gingivalis appears to contribute to pathogenicity.

Characterization of Porphyromonas gingivalis-induced degradation of epithelial cell junctional complexes

Porphyromonas gingivalis is considered among the etiological agents of human adult periodontitis. Although in vitro studies have shown that P. gingivalis has the ability to invade epithelial cell lines, its effect on the epithelial barrier junctions is not known. Immunofluorescence analysis of human gingival epithelial cells confirmed the presence of tight-junction (occludin), adherens junction (E-cadherin), and cell-extracellular matrix junction (beta1-integrin) transmembrane proteins. These transmembrane proteins are expressed in Madin-Darby canine kidney (MDCK) cells. In addition, MDCK cells polarize and therefore serve as a useful in vitro model for studies on the epithelial cell barrier. Using the MDCK cell system, we examined the effect of P. gingivalis on epithelial barrier function. Exposure of the basolateral surfaces of MDCK cells to P. gingivalis (>10(9) bacteria/ml) resulted in a decrease in transepithelial resistance. Immunofluorescence microscopy demonstrated decreases in the amounts of immunoreactive occludin, E-cadherin, and beta1-integrin at specific times which were related to a disruption of cell-cell junctions in MDCK cells exposed to basolateral P. gingivalis. Disruption of cell-cell junctions was also observed upon apical exposure to bacteria; however, the effects took longer than those seen upon basolateral exposure. Cell viability was not affected by either basolateral or apical exposure to P. gingivalis. Western blot analysis demonstrated hydrolysis of occludin, E-cadherin, and beta1-integrin in lysates derived from MDCK cells exposed to P. gingivalis. Immunoprecipitated occludin and E-cadherin molecules from MDCK cell lysates were also degraded by P. gingivalis, suggesting a bacterial protease(s) capable of cleaving these epithelial junction transmembrane proteins. Collectively, these data suggest that P. gingivalis is able to invade the deeper structures of connective tissues via a paracellular pathway by degrading epithelial cell-cell junction complexes, thus allowing the spread of the bacterium. These results also indicate the importance of a critical threshold concentration of P. gingivalis to initiate epithelial barrier destruction.

Invasion of human coronary artery cells by periodontal pathogens

There is an emerging paradigm shift from coronary heart disease having a purely hereditary and nutritional causation to possibly having an infectious etiology. Recent epidemiological studies have shown a correlation between periodontal disease and coronary heart disease. However, to date, there is minimal information as to the possible disease mechanisms of this association. It is our hypothesis that invasion of the coronary artery cells by oral bacteria may start and/or exacerbate the inflammatory response in atherosclerosis. Since a few periodontal pathogens have been reported to invade oral epithelial tissues, we tested the ability of three putative periodontal pathogens-Eikenella corrodens, Porphyromonas gingivalis, and Prevotella intermedia-to invade human coronary artery endothelial cells and coronary artery smooth muscle cells. In this study we demonstrate by an antibiotic protection assay and electron microscopy that specific species and strains invade coronary artery cells at a significant level. Actin polymerization and eukaryotic protein synthesis in metabolically active cells were required since the corresponding inhibitors nearly abrogated invasion. Many intracellular P. gingivalis organisms were seen to be present in multimembranous vacuoles resembling autophagosomes by morphological analysis. This is the first report of oral microorganisms invading human primary cell cultures of the vasculature.

Comparison of fluorescence microscopy and culture assays to quantitate adhesion of Porphyromonas gingivalis to mono- and multi-layered pocket epithelium cultures

BACKGROUND

The present study compared 2 different methods (direct versus indirect evaluation) for the quantification of the adhesion of Porphyromonas gingivalis strains to in vitro cultured mono-layers of pocket epithelium.

METHODS

The indirect culture viability assay (calculation of colony forming units) was compared to a direct microscopic evaluation using a novel fluorescent stain. The fluorescent kit was found to stain both bacteria and epithelial cells and enabled a differentiation between dead and living cells.

RESULTS

Comparing the visual to the culture data, a high and significant correlation was found (Pearson's correlation = 0.75; P <0.001). The adhesion capacity was in general higher for dead epithelial cells than for living cells (P <0.01). Although comparable numbers of bacteria of 2 P. gingivalis strains (Pg 4 and Pg 5) were applied, Pg 4 showed a significantly lower adhesion capacity. This intra-strain variability was observed by the culture assay (2.3 x 10(6) versus 7.8 x 10(6)+/-2.7 x 10(6); P <0.01) and by the direct microscopy (P <0.01) for both live and dead epithelial cells. A second goal was to see whether there was a difference in the amount of bacterial adherence to mono- and multi-layers of in vitro cultured epithelium. No significant differences were found for the 5 examined P. gingivalis strains. However, interstrain differences in adhesion capacity were evident for both tissues.

CONCLUSIONS

This study highlights the reproducibility of a direct microscopic evaluation of bacterial adhesion to in vitro cultured epithelial cells, and suggests both intrastrain (P. gingivalis) and inter-cell (live versus dead) variation in adhesion capacity. Studies are needed to determine the extent to which P. gingivalis strain variation is reflected in variation of other strains in humans.

Multi-layered periodontal pocket epithelium reconstituted in vitro: histology and cytokeratin profiles

BACKGROUND

In order to study inter-individual differences in bacterial adhesion/invasion of periodontal tissues, an in vitro model for culturing multi-layered pocket epithelium without feeder layers or stromal equivalents (including the evaluation of their cytokeratin profiles) was developed.

METHODS

Pocket epithelium was collected and grown until confluent in Falcon flasks using keratinocyte-serum free medium (KSFM), without a feeder layer. In the second passage, oral keratinocytes were re-grown in a 2 compartment system using either a clear polyester (transwell-clear [TCL]) or a collagen (transwell-col [TCO]) membrane as culture surface. After the first week, the calcium concentration was raised to 1.2 mM and in half the wells, the KSFM was supplemented with 10% fetal calf serum (FCS). Histology and immunohistochemistry were performed after 1, 2, and 3 weeks of additional growth.

RESULTS

In general, all conditions resulted in a structured epithelium consisting of 3 to 5 layers, but important differences were observed between the membrane types and between the media. CK4 was rarely and only lightly expressed while CK18 and 19 (characteristic of junctional epithelium) were very strongly expressed in the older (2 and 3 weeks) cultures. CK13 and 14 (characteristic of any stratifiable epithelial cell) also tended to increase over time; CK13 seemed to be stronger in KSFM with FCS while the contrary was true for CK14. The multi-layer created by the combination TCL/KSFM + 10% FCS resembled a junctional epithelium most, while that grown on TCO without FCS mimicked the sulcular epithelium.

CONCLUSIONS

It seems possible to create a histiotypic culture resembling either periodontal pocket or junctional epithelium without the use of stromal equivalents or feeder layers which make this approach more cumbersome. This multi-layered culture offers a model to investigate the permeability of pocket epithelium and the adhesion and penetration of bacteria under well-defined environmental conditions.

Relationship between herpesviruses and adult periodontitis and periodontopathic bacteria

BACKGROUND

Various mammalian viruses and specific bacteria seem to play important roles in the pathogenesis of human periodontitis. This study examined the relationship between subgingival herpesviruses and periodontal disease and potential periodontopathic bacteria in 140 adults exhibiting either periodontitis or gingivitis.

METHODS

A nested-polymerase chain reaction (PCR) method determined the presence of Epstein-Barr virus type 1 and type 2 (EBV-1, EBV-2), human cytomegalovirus (HCMV), and herpes simplex virus (HSV) and a 16S rRNA PCR detection method identified Actinobacillus actinomycetemcomitans, Porphyromonas gingivalis, Bacteroides forsythus, Prevotella intermedia, Prevotella nigrescens, and Treponema denticola.

RESULTS

Using a logistic analysis, EBV-1 showed significant positive association with P. gingivalis (odds ratio [OR] 3.37), and with coinfections of P. gingivalis and P. intermedia (OR 4.03); P. gingivalis and B. forsythus (OR 3.84); P. gingivalis and T. denticola (OR 4.17); P. gingivalis, B. forsythus, and T. denticola (OR 4.06); and P. gingivalis, P. nigrescens, and T. denticola (OR 3.29). EBV-1 also showed positive association with severe periodontitis (OR 5.09), with increasing age (OR 1.03), and with periodontal probing depth at the sample sites (OR 1.77). HCMV was positively associated with coinfections of P. gingivalis and P. nigrescens (OR 3.23); P. gingivalis, B. forsythus, and P. nigrescens (OR 3.23); and P. gingivalis, P. nigrescens, and T. denticola (OR 2.59); with severe periodontitis (OR 4.65); and with age (OR 1.03). Patients with mixed viral infections revealed significant associations with P. gingivalis (OR 2.27), and with coinfections of P. gingivalis and B. forsythus (OR 2.06); P. gingivalis and P. nigrescens (OR 2.91); P. gingivalis, B. forsythus, and P. nigrescens (OR 2.91); and P. gingivalis, P. nigrescens, and T. denticola (OR 2.70) with the clinical diagnosis of slight (OR 3.73), moderate (OR 3.82), or severe periodontitis (OR 4.36), and with probing depth at the sample sites (OR 1.39). HSV and EBV-2 showed no significant associations with any of the variables tested.

CONCLUSIONS

The results indicate that subgingival EBV-1, HCMV, and viral coinfections are associated with the subgingival presence of some periodontal pathogens and periodontitis. Herpesviruses may exert periodontopathic potential by decreasing the host resistance against subgingival colonization and multiplication of periodontal pathogens.

Adherence of Peptostreptococcus micros morphotypes to epithelial cells in vitro

Peptostreptococcus micros, which is associated with oral and non-oral mixed anaerobic infections, occurs in three colony morphotypes, the smooth type, the rough type and the smooth variant of the rough type. These types differ in surface structures; the rough type expresses large fibrillar surface appendages, which are absent on the surface of both the smooth and the smooth variant of the rough type. To determine the role of these surface structures in adherence we characterized the adherence of the three morphotypes of P. micros to epithelial cells in vitro. Although all three types adhered well to epithelial cells, adhering numbers of the rough type were significantly lower than those of the smooth and the smooth variant of the rough type. Protease treatment increased the adherence of the rough type of the level of the two other types. The adherence of all three types was reduced more than 85% by treatment with 10 mM sodium periodate. Furthermore, the adherence was pH independent and could not be blocked by incubation with antisera to the bacteria. In addition, we determined the capacity to invade epithelial cells by P. micros. In an acridine orange assay such invasion could not be detected. Our results suggest that the adherence of P. micros to epithelial cells is mediated by periodate-sensitive extracellular polysaccharides and that the protruding fibril-like protein surface structures of the rough type have an obstructive effect on the adherence.

Invasion of human oral epithelial cells by Prevotella intermedia

Invasion of oral epithelial cells by pathogenic oral bacteria may represent an important virulence factor in the progression of periodontal disease. Here we report that a clinical isolate of Prevotella intermedia, strain 17, was found to invade a human oral epithelial cell line (KB), whereas P. intermedia 27, another clinical isolate, and P. intermedia 25611, the type strain, were not found to invade the cell line. Invasion was quantified by the recovery of viable bacteria following a standard antibiotic protection assay and observed by electron microscopy. Cytochalasin D, cycloheximide, monodansylcadaverine, and low temperature (4 degreesC) inhibited the internalization of P. intermedia 17. Antibodies raised against P. intermedia type C fimbriae and against whole cells inhibited invasion, but the anti-type-C-fimbria antibody inhibited invasion to a greater extent than the anti-whole-cell antibody. This work provides evidence that at least one strain of P. intermedia can invade an oral epithelial cell line and that the type C fimbriae and a cytoskeletal rearrangement are required for this invasion.

Differential expression of interleukin-8 and intercellular adhesion molecule-1 by human gingival epithelial cells in response to Actinobacillus actinomycetemcomitans or Porphyromonas gingivalis infection

Little is known regarding the molecules expressed by gingival epithelial cells that are involved in initiating and maintaining inflammation following the interaction with periodontal pathogens. Thus, we investigated the effect of Actinobacillus actinomycetemcomitans and Porphyromonas gingivalis infection on the expression of neutrophil chemoattractant interleukin 8 (IL-8) and the adhesion molecule intercellular adhesion molecule-1 by gingival epithelial cells. The data revealed that both IL-8 and intercellular adhesion molecule-1 expression increased after infection with A. actinomycetemcomitans (IL-8: 2- to 7-fold; intercellular adhesion molecule-1: 2.5- to 3.7-fold). IL-8 secretion reached a maximal level 6 h after the infection and the expression subsequently decreased to basal level. The increased cell surface intercellular adhesion molecule-1 expression started at 4 h after infection and reached a maximal level 14 h after the infection. In contrast, the expression of both molecules rapidly decreased 2 h after challenge with P. gingivalis. This opposite influence of A. actinomycetemcomitans and P. gingivalis infection on the expression of IL-8 and intercellular adhesion molecule-1 by gingival epithelial cells suggests that A. actinomycetemcomitans infection may initiate the recruitment of neutrophils, whereas the P. gingivalis infection may retard this process and therefore demonstrate a distinct perspective of virulence.

Subgingival microbiota in healthy, well-maintained elder and periodontitis subjects

This investigation compared the site prevalence of 40 subgingival species in 30 periodontally healthy (mean age 36+/-9 years), 35 elders with a well-maintained periodontium (mean age 77+/-5) and 138 adult periodontitis subjects (mean age 46+/-11). Subgingival plaque samples were taken from the mesial aspect of each tooth (up to 28 samples) in the 203 subjects at baseline. The presence and levels of 40 subgingival taxa were determined in 5003 plaque samples using whole genomic DNA probes and checkerboard DNA-DNA hybridization. Clinical assessments including dichotomous measures of gingival redness, bleeding on probing, plaque accumulation and suppuration, as well as duplicate measures of pocket depth and attachment level, were made at 6 sites per tooth. The % of sites colonized by each species (prevalence) was computed for each subject. Differences in prevalence and levels among groups were sought using the Kruskal-Wallis test. Commonly detected species, such as Actinomyces naeslundii genospecies 2, Streptococcus sanguis and Streptococcus oralis did not differ significantly among subject groups. After adjusting for multiple comparisons, 4 species were significantly elevated and at greater prevalence in the periodontitis group. Mean % of sites (+/-SEM) colonized by Bacteroides forsythus was 10+/-3, 12+/-2 and 40+/-2 (p<0.001) for healthy, elder and periodontitis groups respectively. The odds ratio was 14.4:1 that a subject had periodontitis when B. forsythus was detected at > or = 5% of sampled sites. Mean prevalence for Porphyromonas gingivalis in healthy, elder and periodontitis subjects was 4+/-2, 5+/-2 and 23+/-2 respectively (p<0.001); for Treponema denticola 12+/-4, 10+/-3 and 30+/-2 (p<0.001) and for Selenomonas noxia 6+/-2, 7+/-2 and 19+/-2 (p<0.01). Similar differences among subject groups were observed when only sites with PD 0-4 mm were analyzed. The data suggest an etiologic role for B. forsythus, P. gingivalis, T. denticola and S. noxia in adult periodontitis.

Oral pathogens: from dental plaque to cardiac disease

Oral bacteria exhibit highly specific adherence mechanisms and as a result they colonize and cause disease principally in the oral cavity. Oral pathogens, however, can produce systemic disease and are known causative agents of infective endocarditis. Recent studies have revealed that periodontal disease per se is also a statistically significant risk factor for cardiovascular disease. A link between the two diseases is the secretion and systemic appearance in periodontitis of pro-inflammatory cytokines capable of eliciting effects associated with atherosclerosis and coronary heart disease.

Histopathological investigation of gingival tissue from patients with rapidly progressive periodontitis

In this study, fine structural features of the pocket walls in rapidly progressive periodontitis (RPP) and adult periodontitis (AP) in 20 cases were compared using light and transmission electron microscopy. Gingiva was also obtained from a control group of periodontally healthy teeth. Clinical parameters were assessed in both RPP and AP patients and in controls. Bone destruction and attachment loss were more marked in RPP than in AP. Light microscopical observations of inflamed RPP tissue as compared to AP showed gross histological distortions in the pocket walls. Micro-ridges within the epithelium and large intercellular spaces between the epithelial cells were observed in most RPP biopsies. Epithelial cells surrounding the microclefts and adjacent keratinocytes were found to produce interleukin-1beta (IL-1beta). Prevotella intermedia and Porphyromonas gingivalis were identified in the RPP biopsies using immunohistological methods. These microorganisms were localized outside the epithelium and inside intercellular spaces. Furthermore, the effect of inflammation on the distribution of collagen types I, III, IV, V, and VI in the human gingiva was studied after staining them with antibodies to these proteins. In RPP and AP tissues, the staining was sparse in areas of inflammation and leukocytic infiltration. Collagen type I and III were almost entirely lost at sites of inflammation. Type V and VI collagen antibodies were retained in inflamed areas. Type IV collagen was restricted to basement membrane structures. These observations demonstrated numerous structural features indicative of more pronounced degenerative changes in RPP than in AP.

Models of invasion of enteric and periodontal pathogens into epithelial cells: a comparative analysis

Bacterial invasion of epithelial cells is associated with the initiation of infection by many bacteria. To carry out this action, bacteria have developed remarkable processes and mechanisms that co-opt host cell function and stimulate their own uptake and adaptation to the environment of the host cell. Two general types of invasion processes have been observed. In one type, the pathogens (e.g., Salmonella and Yersinia spp.) remain in the vacuole in which they are internalized and replicate within the vacuole. In the other type, the organism (e.g., Actinobacillus actinomycetemcomitans, Shigella flexneri, and Listeria monocytogenes) is able to escape from the vacuole, replicate in the host cell cytoplasm, and spread to adjacent host cells. The much-studied enteropathogenic bacteria usurp primarily host cell microfilaments for entry. Those organisms which can escape from the vacuole do so by means of hemolytic factors and C type phospholipases. The cell-to-cell spread of these organisms is mediated by microfilaments. The investigation of invasion by periodontopathogens is in its infancy in comparison with that of the enteric pathogens. However, studies to date on two invasive periodontopathogens. A actinomycetemcomitans and Porphyromonas (Bacteroides) gingivalis, reveal that these bacteria have developed invasion strategies and mechanisms similar to those of the enteropathogens. Entry of A. actinomycetemcomitans is mediated by microfilaments, whereas entry of P. gingivalis is mediated by both microfilaments and microtubules. A. actinomycetemcomitans, like Shigella and Listeria, can escape from the vacuole and spread to adjacent cells. However, the spread of A. actinomycetemcomitans is linked to host cell microtubules, not microfilaments. The paradigms presented establish that bacteria which cause chronic infections, such as periodontitis, and bacteria which cause acute diseases, such as dysentery, have developed similar invasion strategies.

Porphyromonas gingivalis infection of oral epithelium inhibits neutrophil transepithelial migration

Periodontal diseases are inflammatory disorders caused by microorganisms of dental plaque that colonize the gingival sulcus and, subsequently, the periodontal pocket. As in other mucosal infections, the host response to plaque bacteria is characterized by an influx of polymorphonuclear leukocytes (PMNs) to the gingival crevice. Neutrophil migration through the epithelial lining of the gingival pocket is thought to be the first line of defense against plaque bacteria. In order to model this phenomenon in vitro, we used the oral epithelial cell line KB and human PMNs in the Transwell system and examined the impact of Porphyromonas gingivalis-epithelial cell interactions on subsequent PMN transepithelial migration. We demonstrate here that P. gingivalis infection of oral epithelial cells failed to trigger transmigration of PMNs. Furthermore, it significantly inhibited neutrophil transmigration actively induced by stimuli such as N-formylmethionyl leucyl phenylalanine, interleukin-8 (IL-8), and the intestinal pathogen enterotoxigenic Escherichia coli. The ability of P. gingivalis to block PMN transmigration was strongly positively correlated with the ability to adhere to and invade epithelial cells. In addition, P. gingivalis attenuated the production of IL-8 and the expression of intercellular adhesion molecule 1 by epithelial cells. The ability of P. gingivalis to block neutrophil migration across an intact epithelial barrier may critically impair the potential of the host to confront the bacterial challenge and thus may play an important role in the pathogenesis of periodontal disease.

Fimbriae and the hemagglutinating adhesin HA-Ag2 mediate adhesion of Porphyromonas gingivalis to epithelial cells

The mechanisms by which Porphyromonas gingivalis, a gram-negative anaerobic bacterium, is pathogenic for the periodontium remain largely hypothetical. Invasion of host tissues by P. gingivalis is believed to require adhesion of the bacterium to host cells. The aim of this study was to use monoclonal antibodies (MAbs) to characterize the bacterial cell surface component(s) acting as a ligand binding to a receptor on epithelial cells. Surface antigens of P. gingivalis ATCC 33277 were obtained as a glass bead-EDTA extract (GBE), and antiserum against the GBE was produced in rabbits. Epithelial cell membrane proteins (ECMP) were prepared from a homogenate of the SK-MES-1 cell line with Triton X-100. The antigen/ligand profile of GBE was resolved by crossed immunoaffinity electrophoresis by using ECMP in the first-dimension gel. The migration of one immunoprecipitate (IP) was retarded, indicating a ligand-receptor interaction between a surface antigen of P. gingivalis and a complementary binding site on the epithelial cell membrane. The corresponding IP in the GBE/anti-GBE immunoelectrophoresis profile was excised from replicate gels to immunize mice for production of MAbs specific for the bacterial ligand. Five MAbs were obtained and tested for reactivity with GBE in immunoblots and for inhibition of the interaction between GBE and ECMP. Immunoblots revealed polypeptides at 28, 42, 43, and 49 kDa. Inhibition tests were positive for all five MAbs. These results are conclusive evidence that the MAbs recognize functional epitopes involved in the adherence of P. gingivalis to epithelial cells and that the adhesins are likely associated with fimbriae and the hemagglutinating adhesin HA-Ag2.

Occurrence of invading bacteria in radicular dentin of periodontally diseased teeth: microbiological findings

Bacterial invasion in roots of periodontally diseased teeth, which has been recently documented using cultural and microscopic techniques, may be important in the pathogenesis of periodontal disease. The purpose of this investigation was to determine the occurrence and the species of invading bacteria in radicular dentin of periodontally diseased teeth. Samples were taken from the middle layer of radicular dentin of 26 periodontally diseased teeth. 14 healthy teeth were used as controls. Dentin samples were cultured anaerobically. The chosen methodology allowed the determination of the numbers of bacteria present in both deeper and outer part of dentinal tubules, and the bacterial concentration in dentin samples, expressed as colony forming units per mg of tissue (CFU/mg). Invading bacteria was detected in 14 (53.8%) samples from periodontally diseased teeth. The bacterial concentration ranged from 831.84 to 11971.3 CFU/mg (mean+/-standard deviation: 3043.15+/-2763.13). Micro-organisms identified included putative periodontal pathogens such as Prevotella intermedia, Porphyromonas gingivalis, Fusobacterium nucleatum, Bacteroides forsythus, Peptostreptococcus micros and Streptococcus intermedius. These findings suggest that radicular dentin could act as bacterial reservoir from which periodontal pathogens can recolonize treated periodontal pockets, contributing to the failure of therapy and recurrence of disease.

A role for fimbriae in Porphyromonas gingivalis invasion of oral epithelial cells

Isogenic mutants of Porphyromonas gingivalis which differ in the expression of fimbriae were used to examine the contribution of fimbriae in invasion of a human oral epithelial cell line (KB). At a multiplicity of infection of 100, the wild-type P. gingivalis strains 33277, 381, and A7436 exhibited adherence efficiencies of 5.5, 0.11, and 5.0%, respectively, and invasion efficiencies of 0.15, 0.03, and 0.10%, respectively. However, adherence to and invasion of KB cells was not detected with the P. gingivalis fimA mutants, DPG3 and MPG1. Adherence of P. gingivalis wild-type strains to KB cells was completely inhibited by the addition of hyperimmune sera raised to the major fimbriae. Examination by electron microscopy of invasion of epithelial cells by the P. gingivalis wild-type strain 381 revealed microvillus-like extensions around adherent bacteria; this was not observed with P. gingivalis fim mutants. Taken together, these results indicate that the P. gingivalis major fimbriae are required for adherence to and invasion of oral epithelial cells.

Mechanisms of adhesion by oral bacteria

Adherence to a surface is a key element for colonization of the human oral cavity by the more than 500 bacterial taxa recorded from oral samples. Three surfaces are available: teeth, epithelial mucosa, and the nascent surface created as each new bacterial cell binds to existing dental plaque. Oral bacteria exhibit specificity for their respective colonization sites. Such specificity is directed by adhesin-receptor cognate pairs on genetically distinct cells. Colonization is successful when adherent cells grow and metabolically participate in the oral bacterial community. The potential roles of adherence-relevant molecules are discussed in the context of the dynamic nature of the oral econiche.

Comparison of 3 periodontal local antibiotic therapies in persistent periodontal pockets

The aim of this study was to evaluate the efficacy of 3 commercially available periodontal systems for local delivery of antibiotics as adjuncts to scaling and root planing in treatment of sites with persistent periodontal lesions following a course of scaling and root planing. Fifty-four patients with 4 pockets > or = 5 mm and bleeding on probing and/or suppuration were randomized in 4 treatment groups including: scaling and root planing plus application of 25% tetracycline fiber (S + Tet) (13 patients), scaling and root planing plus application of 2% minocycline gel (S + Min) (14 patients), scaling and root planing plus application of 25% metronidazole gel (S + Met) (14 patients), and scaling and root planing alone (S) (13 patients). Clinical measurements were taken at baseline and 6 weeks after the end of treatment periods. All treatments were applied using the distributors' recommended protocols and resulted in significant improvement in probing depth, attachment level, bleeding on probing and the modified gingival index (MGI) scores. The improvements in clinical parameters were greater in all three adjunctive treatment groups than scaling and root planing alone. The mean probing depth reductions were: S + Tet = 1.35 mm, S + Met = 0.95 mm, S + Min = 0.87 mm and S = 0.60 mm. The probing depth reduction was significantly greater in the scaling plus tetracycline fiber group than the scaling and root planing alone group (P = 0.002). The difference between groups in improvement of attachment level or bleeding on probing was not significant Scaling plus tetracycline fiber treatment resulted in the greatest reduction in the MGI scores which was significantly greater than all other groups. While the frequency of sites with suppuration was markedly reduced following all treatments, it reached zero in the scaling plus tetracycline fiber group. No serious adverse effects were observed or reported for any treatment. While all three locally applied antimicrobial systems seem to offer some benefit over scaling and root planing alone, a treatment regimen of scaling and root planing plus tetracycline fiber replacement gave the greatest advantage in the treatment of persistent periodontal lesions at least during the 6-week period following treatment.

Porphyromonas gingivalis genes isolated by screening for epithelial cell attachment

Porphyromonas gingivalis is associated with chronic and severe periodontitis in adults. P. gingivalis and the other periodontal pathogens colonize and interact with gingival epithelial cells, but the genes and molecular mechanisms involved are unknown. To dissect the first steps in these interactions, a P. gingivalis expression library was screened for clones which bound human oral epithelial cells. Insert DNA from the recombinant clones did not contain homology to the P. gingivalis fimA gene, encoding fimbrillin, the subunit protein of fimbriae, but showed various degrees of homology to certain cysteine protease-hemagglutinin genes. The DNA sequence of one insert revealed three putative open reading frames which appeared to be in an operon. The relationship between P. gingivalis attachment to epithelial cells and the activities identified by the screen is discussed.

Cellular events concurrent with Porphyromonas gingivalis invasion of oral epithelium in vitro

The aim of the present study was to elucidate events related to receptor function, signal transmission and cytoskeletal rearrangements concurrent with Porphyromonas gingivalis invasion of oral epithelial cells in vitro. Porphyromonas gingivalis strain FDC 381 and the KB cell line (ATCC CCL 17) were used in a previously described antibiotic protection assay. The involvement of a receptor-mediated endocytosis pathway in the internalization process was demonstrated after treatment of the epithelial cells with monodansylcadaverine and ouabain, substances that inhibit formation of coated pits, resulting in reduction in the number of invading P. gingivalis: Treatment of the epithelial cells with the protein kinase (PK) inhibitor staurosporine and the tyrosine-specific PK inhibitor genistein was also found to significantly decrease the number of invading bacteria, suggesting involvement of tyrosine phosphorylation in signal transduction during invasion. This was further supported by the identification of a 43 kD protein acting as a substrate for tyrosine phosphorylation subsequent to the microbial-host cell interaction. Tyrosine phosphorylation of the 43 kD protein was strongly reduced by treatment with PK inhibitors. The decrease in invasion observed after treatment of epithelial cells with colchicine and nocodazole, inhibitors of microtubuli polymerization, suggested that the bacterial-receptor interaction and the phosphotyrosine-dependent intracellular signalling trigger an internalization process involving rearrangements of cytoskeletal microtubuli.

Porphyromonas gingivalis FDC381 multiplies and persists within human oral epithelial cells in vitro

Porphyromonas gingivalis FDC381 replication and persistence within KB epithelial cells in vitro were studied by means of an antibiotic protection assay and electron microscopy. Intracellular counts decreased during the first 24 h; showed a threefold increase during the second day, indicating intracellular multiplication; and after 8 days declined to levels approximating 40% of the initial invasion. The ability of P. gingivalis to persist and multiply within epithelial cells may constitute a pathogenic mechanism in periodontal disease.