Bacterial invasion of periodontal tissues in advanced periodontitis in humans

Matrix Metalloproteinases in the Periodontium-Vital in Tissue Turnover and Unfortunate in Periodontitis

The extracellular matrix (ECM) is a complex non-cellular three-dimensional macromolecular network present within all tissues and organs, forming the foundation on which cells sit, and composed of proteins (such as collagen), glycosaminoglycans, proteoglycans, minerals, and water. The ECM provides a fundamental framework for the cellular constituents of tissue and biochemical support to surrounding cells. The ECM is a highly dynamic structure that is constantly being remodeled. Matrix metalloproteinases (MMPs) are among the most important proteolytic enzymes of the ECM and are capable of degrading all ECM molecules. MMPs play a relevant role in physiological as well as pathological processes; MMPs participate in embryogenesis, morphogenesis, wound healing, and tissue remodeling, and therefore, their impaired activity may result in several problems. MMP activity is also associated with chronic inflammation, tissue breakdown, fibrosis, and cancer invasion and metastasis. The periodontium is a unique anatomical site, composed of a variety of connective tissues, created by the ECM. During periodontitis, a chronic inflammation affecting the periodontium, increased presence and activity of MMPs is observed, resulting in irreversible losses of periodontal tissues. MMP expression and activity may be controlled in various ways, one of which is the inhibition of their activity by an endogenous group of tissue inhibitors of metalloproteinases (TIMPs), as well as reversion-inducing cysteine-rich protein with Kazal motifs (RECK).

Treponema denticola invasion into human gingival epithelial cells

Host cell invasion is important for periodontal pathogens in evading host defenses and spreading into deeper areas of the periodontal tissue. Treponema denticola has been implicated in a number of potentially pathogenic processes, including periodontal tissue penetration. Here we tested the ability of T. denticola strains to invade human gingival epithelial cells (HGEC). After 2 h infection, intracellular location of T. denticola cells was confirmed by confocal laser scanning microscopy (CLSM). Results from an antibiotic protection assay following [(3)H]uridine labeling indicated that invasion efficiency reached a maximum at 2 h after infection. Internalized T. denticola cells were still observed in HGEC at 24 h by CLSM. A dentilisin deficient mutant exhibited significantly decreased invasion (p < 0.05) compared with the wild-type strain. In inhibition assays, phenylmethylsulfonyl fluoride and metabolic inhibitors such as methyl-β-cyclodextrin and staurosporine significantly reduced T. denticola invasion. Under CLSM, T. denticola colocalized with GM-1 ganglioside-containing membrane microdomains in a cholesterol-dependent manner. These results indicated that T. denticola has the ability to invade into and survive within HGECs. Dentilisin activity of T. denticola and lipid rafts on HGEC appear to play important roles in this process.

Relationship between invasion of the periodontium by periodontal pathogens and periodontal disease: a systematic review

Bacterial invasion of the periodontal tissues has been suggested as a relevant step in the etiopathogenesis of periodontal disease. However, its exact importance remains to be defined. The present systematic review assessed the scientific evidence concerning the relationship between the quality or quantity of periodontal microbiota in periodontal tissues and development of periodontal disease. The databases Medline-PubMed, Cochrane-CENTRAL, ISI Web of Knowledge and SCOPUS were searched, up to January 2014. Studies that reported evaluation of periodontal pathogens invasion on human tissues were selected. The screening of 440 title/abstracts elected 26 papers for full-text reading. Twenty three papers were subsequently excluded because of insufficient data or a study protocol not related to the objectives of this systematic review. All included studies were case-control studies that evaluated intracellular or adherent bacteria to epithelial cells from periodontal pockets versus healthy sulci. Study protocols presented heterogeneity regarding case and control definitions and methodological approaches for microbial identification. No consistent significant differences were found related to the presence/absence or proportion of specific periopathogens across the studies, as only one study found statistically significant differences regarding the presence of A. actinomycetemcomitans (p = 0.043), T. forsythia (P < 0.001), P. intermedia (P < 0.001), C. ochracea (P < 0.001) and C. rectus (P = 0.003) in epithelial cells from periodontal pockets vs. healthy sulci. All studies reported a larger unspecific bacterial load in or on the epithelial cells taken from a diseased site compared to a healthy sulcus. The current available data is of low to moderate quality and inconsistent mainly due to study design, poor reporting and methodological diversity. As so, there is insufficient evidence to support or exclude the invasion by periodontal pathogens as a key step in the etiopathogenesis of periodontal disease. Further research is needed.

Porphyromonas gingivalis infection increases osteoclastic bone resorption and osteoblastic bone formation in a periodontitis mouse model

Background

Porphyromonas gingivalis has been shown to invade osteoblasts and inhibit their differentiation and mineralization in vitro. However, it is unclear if P. gingivalis can invade osteoblasts in vivo and how this would affect alveolar osteoblast/osteoclast dynamics. This study aims to answer these questions using a periodontitis mouse model under repetitive P. gingivalis inoculations.

Methods

For 3-month-old BALB/cByJ female mice, 10⁹ CFU of P. gingivalis were inoculated onto the gingival margin of maxillary molars 4 times at 2-day intervals. After 2 weeks, another 4 inoculations at 2-day intervals were applied. Calcein was injected 7 and 2 days before sacrificing animals to label the newly formed bone. Four weeks after final inoculation, mice were sacrificed and maxilla collected. Immunohistochemistry, micro-CT, and bone histomorphometry were performed on the specimens. Sham infection with only vehicle was the control.

Results

P. gingivalis was found to invade gingival epithelia, periodontal ligament fibroblasts, and alveolar osteoblasts. Micro-CT showed alveolar bone resorption and significant reduction of bone mineral density and content in the infected mice compared to the controls. Bone histomorphometry showed a decrease in osteoblasts, an increase in osteoclasts and bone resorption, and a surprisingly increased osteoblastic bone formation in the infected mice compared to the controls.

Conclusions

P. gingivalis invades alveolar osteoblasts in the periodontitis mouse model and cause alveolar bone loss. Although P. gingivalis appears to suppress osteoblast pool and enhance osteoclastic bone resorption, the bone formation capacity is temporarily elevated in the infected mice, possibly via some anti-microbial compensational mechanisms.

Periodontitis: a host-mediated disruption of microbial homeostasis. Unlearning learned concepts

New concepts evolve when existing ones fail to address known factors adequately or are invalidated by new evidence. For decades periodontitis has been considered to be caused by specific bacteria or groups of bacteria and, accordingly, treatment protocols have largely been based on anti-infective therapies. However, close inspection of current data leads one to question whether these bacteria are the cause or the result of periodontitis. Good evidence is emerging to suggest that it is indeed the host response to oral bacteria that leads to the tissue changes noted in gingivitis. These changes lead to an altered subgingival environment that favors the emergence of 'periodontal pathogens' and the subsequent development of periodontitis if the genetic and external environmental conditions are favorable for disease development. Thus, it seems that it is indeed the initial early host-inflammatory and immune responses occurring during the development of gingivitis, and not specific bacteria or their so-called virulence factors, which determine whether periodontitis develops and progresses. In this review we consider these concepts and their potential to change the way in which we view and manage the inflammatory periodontal diseases.

Porphyromonas gingivalis invades osteoblasts and inhibits bone formation

Porphyromonas gingivalis is etiologically associated with adult periodontitis, but it is unclear how P. gingivalis long-term interactions with bone cells contribute to this disease. This study investigates P. gingivalis interactions with osteoblasts over an extended time course. A primary mouse calvarial osteoblast culture was established and inoculated with P. gingivalis 33277 repeatedly every other day for up to four weeks. Invasion of osteoblasts by P. gingivalis, and the resulting effects on the proliferation, differentiation, and mineralization of osteoblasts were evaluated. P. gingivalis was found to invade osteoblasts in a dose-dependent manner, and repetitive inoculation increased the percentage of osteoblasts with internalized P. gingivalis. P. gingivalis did not affect osteoblast proliferation, but inhibited their differentiation and mineralization, partially via an inhibition of the differentiation regulatory transcription factors Cbfa-1 and osterix. In conclusion, P. gingivalis invades osteoblasts and inhibits bone formation, which likely contributes to alveolar bone loss in chronic periodontitis.

Presence of bacteria in dentinal tubules

This study demonstrated that a significant number of bacteria is present in the radicular dentinal tubules of periodontally diseased human teeth. Ten periodontally diseased teeth were prepared and stained by Brown and Brenn technique for histological examination. Bacteria were detected in all teeth. It is suggested that bacteria may invade dentinal tubules exposed to periodontal pocket and are very hard to be eliminated by conventional mechanical and chemical periodontal therapy. Contaminated dentinal tubules of periodontally diseased teeth can thus act as active bacterial reservoirs to promote recolonization of mechanically treated root surfaces, which could interfere with the periodontal healing and progression of the disease.

Identification of periodontopathic bacteria in gingival tissue of Japanese periodontitis patients

INTRODUCTION

The identification of invading periodontopathic bacteria in tissues is important to determine their role in the pathogenesis of periodontal disease. The objective of this study was to identify periodontopathic bacteria in diseased gingival tissue of periodontitis patients.

METHODS

Subgingival plaque and gingival tissue were collected from 32 generalized chronic periodontitis (CP), 16 generalized aggressive periodontitis (GAgP) and eight localized aggressive periodontitis (LAgP) patients. Detection frequencies and quantities of Porphyromonas gingivalis, Actinobacillus actinomycetemcomitans and Tannerella forsythensis were investigated by polymerase chain reaction. The prevalences of Streptococcus oralis and Streptococcus sobrinus were also examined and the distribution of A. actinomycetemcomitans serotypes was observed.

RESULTS

P. gingivalis and T. forsythensis were detected in approximately 70% of tissue samples and 50% of plaque samples in the three periodontitis groups. Prevalence of A. actinomycetemcomitans in tissue samples was higher in the LAgP (63%) group than in either the CP (16%) or the GAgP (38%) group. A. actinomycetemcomitans serotype c was detected in 50% of LAgP patients. Detection frequencies of S. oralis and S. sobrinus were markedly low in both plaque and tissue samples from all three periodontitis groups. Amounts of P. gingivalis, A. actinomycetemcomitans and T. forsythensis in the tissue samples were not different among the three periodontitis groups.

CONCLUSION

P. gingivalis, A. actinomycetemcomitans and T. forsythensis can localize in diseased gingival tissue and may be involved in periodontal tissue destruction. Serotype c is the predominant serotype of A. actinomycetemcomitans in Japanese LAgP patients.

IL-8 and IDO expression by human gingival fibroblasts via TLRs

Human gingival fibroblasts (HGFs), a predominant cell type in tooth-supporting structure, are presently recognized for their active role in the innate immune response. They produce a variety of inflammatory cytokines in response to microbial components such as LPS from the key periodontal pathogen, Porphyromonas gingivalis. In this study, we demonstrated that HGFs expressed mRNA of TLRs 1, 2, 3, 4, 5, 6, and 9, but not TLRs 7, 8, and 10. Stimulation of HGFs with highly purified TLR2 ligand (P. gingivalis LPS), TLR3 ligand (poly(I:C)), TLR4 ligand (Escherichia coli LPS), and TLR5 ligand (Salmonella typhimurium flagellin) led to expression of IL-8 and IDO. A potent TLR 9 ligand, CpG oligodeoxynucleotide 2006 had no effect, although HGFs showed a detectable TLR9 mRNA expression. No significant enhancement on IL-8 or IDO expression was observed when HGFs were stimulated with various combinations of TLR ligands. Surprisingly, the TLR9 ligand CpG oligodeoxynucleotide 2006 was able to specifically inhibit poly(I:C)-induced IL-8 and IDO expression. TNF-alpha enhanced TLR ligand-induced IL-8 production in HGFs, whereas IFN-gamma enhanced TLR ligand-induced IDO expression. HGF production of IDO in response to P. gingivalis LPS, IFN-gamma, or the two in combination inhibited T cell proliferation in MLRs. The observed T cell inhibition could be reversed by addition of either 1-methyl-dl-tryptophan or l-tryptophan. Our results suggest an important role of HGFs not only in orchestrating the innate immune response, but also in dampening potentially harmful hyperactive inflammation in periodontal tissue.

The hemoglobin receptor protein of porphyromonas gingivalis inhibits receptor activator NF-kappaB ligand-induced osteoclastogenesis from bone marrow macrophages

Extracellular proteinaceous factors of Porphyromonas gingivalis, a periodontal pathogen, that influence receptor activator of nuclear factor-kappaB (NF-kappaB) ligand (RANKL)-induced osteoclastogenesis from bone marrow macrophages were investigated. The culture supernatant of P. gingivalis had the ability to inhibit RANKL-induced in vitro osteoclastogenesis. A major protein of the culture supernatant, hemoglobin receptor protein (HbR), suppressed RANKL-induced osteoclastogenesis in a dose-dependent fashion. HbR markedly inhibited RANKL-induced osteoclastogenesis when present in the culture for the first 24 h after addition of RANKL, whereas no significant inhibition was observed when HbR was added after 24 h or later, implying that HbR might interfere with only the initial stage of RANKL-mediated differentiation. HbR tightly bound to bone marrow macrophages and had the ability to induce phosphorylation of ERK, p38, NF-kappaB, and Akt. RANKL-induced phosphorylation of ERK, p38, and NF-kappaB was not suppressed by HbR, but that of Akt was markedly suppressed. HbR inhibited RANKL-mediated induction of c-Fos and NFATc1. HbR could induce beta interferon (IFN-beta) from bone marrow macrophages, but the induction level of IFN-beta might not be sufficient to suppress RANKL-mediated osteoclastogenesis, implying presence of an IFN-beta-independent pathway in HbR-mediated inhibition of osteoclastogenesis. Since rapid and extensive destruction of the alveolar bone causes tooth loss, resulting in loss of the gingival crevice that is an anatomical niche for periodontal pathogens such as P. gingivalis, the suppressive effect of HbR on osteoclastogenesis may help the microorganism exist long in the niche.

Proinflammatory gene expression in mouse ST2 cell line in response to infection by Porphyromonas gingivalis

Porphyromonas gingivalis is a predominant periodontal pathogen, whose infection causes inflammatory responses in periodontal tissue and alveolar bone resorption. Various virulence factors of this pathogen modulate host innate immune responses. It has been reported that gingipains degrade a wide variety of host cell proteins, and fimbriae are involved in bacterial adhesion to and invasion of host cells. In the present study, we profiled ST2 stromal cell gene expression following infection with the viable P. gingivalis strain ATCC33277 as well as with its gingipain- and fimbriae-deficient mutants, using microarray technology and quantitative real-time polymerase chain reaction. Using a mouse array of about 20,000 genes, we found that infection with the wild strain elicited a significant upregulation (greater than 2-fold) of expression of about 360 genes in ST2 cells, which included the chemokines CCL2, CCL5, and CXCL10, and other proinflammatory proteins such as interleukin-6 (IL-6) and matrix metalloproteinase-13 (MMP-13). Further, infection with the gingipain-deficient mutant elicited a reduced expression of the CXCL10, IL-6 and MMP-13 genes, suggesting that gingipains play an important role in inducing the expression of those genes following P. gingivalis infection. On the other hand, the pattern of global gene expression induced by the fimbriae-deficient mutant was similar to that by the wild strain. These results suggest that P. gingivalis infection induces gene expression of a wide variety of proinflammatory proteins in stromal cells/osteoblasts, and gingipains may be involved in inducing several of the proinflammatory factors.

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.

Biological activities of Bacteroides forsythus lipoproteins and their possible pathological roles in periodontal disease

Bacteroides forsythus is a gram-negative, anaerobic, fusiform bacterium and is considered to be an etiological agent in periodontal disease. A lipoprotein fraction prepared from B. forsythus cells by Triton X-114 phase separation (BfLP) activated human gingival fibroblasts and a human monocytic cell line, THP-1, to induce interleukin-6 production and tumor necrosis factor alpha production. BfLP was found to be capable of inducing nuclear factor-kappaB translocation in human gingival fibroblasts and THP-1 cells. By using Chinese hamster ovary K1 cells transfected with Toll-like receptor genes together with a nuclear factor-kappaB-dependent CD25 reporter plasmid, it was found that signaling by BfLP was mediated by Toll-like receptor 2 but not by CD14 or Toll-like receptor 4. BfLP induced apoptotic cell death in human gingival fibroblasts, KB cells (an oral epithelial cell line), HL-60 cells (a human myeloid leukemia cell line), and THP-1 cells but not in MOLT4 cells (a T-cell leukemia cell line). Caspase-8, an initiator caspase in apoptosis, was found to be activated in these cells in response to BfLP stimulation. Thus, this study suggested that BfLP plays some etiological roles in oral infections, especially periodontal disease, by induction of cell activation or apoptosis.

Two epithelial cell invasion-related loci of the oral pathogen Actinobacillus actinomycetemcomitans

Two invasion-related loci, apiA and the two-gene operon apiBC, were isolated from the oral pathogen Actinobacillus actinomycetemcomitans UT32. apiA encodes a 32.5 kDa protein that migrates on SDS-PAGE as a 101 kDa protein as detected by Western blot analysis or silver staining of an outer membrane-enriched fraction of Escherichia coli transformants. E. coli expressing ApiA have a different phenotype than the host vector, in broth and on solid media, and a colony morphology that resembles that of fresh A. actinomycetemcomitans isolates. These E. coli transformants bound to chicken collagen type II, human collagen type II, III, V and fibronectin. apiB and apiC encode proteins of 130.1 and 70.6 kDa, respectively. ApiBC conferred on E. coli a slightly enhanced ability to bind to collagen type III. ApiA- and ApiB-deficient mutants were constructed in A. actinomycetemcomitans. The ApiB-mutant had 4-fold diminished invasion of KB cells; the ApiA-mutant had increased invasion. Both loci were found in all A. actinomycetemcomitans strains, although polymorphism was detected only for apiBC. The deduced sequences of these invasion-related proteins are homologous to members of the YadA adhesin/invasin family.

Role of dentilisin in Treponema denticola epithelial cell layer penetration

Treponema denticola is an oral anaerobic spirochete implicated in periodontal diseases. The chymotrypsin-like protease, dentilisin (PrtP), has been suggested to be an important virulence factor of T. denticola. In this study, we examined the role of dentilisin in T. denticola epithelial monolayer penetration by comparing the wild type and prtP mutant. Wild-type T. denticola can disrupt transepithelial resistance (TER) and substantially penetrate the HEp-2 cell layer. The prtP mutant altered the monolayer only slightly and penetrated the Hep-2 layer in very low numbers. The membrane fraction of wild-type T. denticola is able to complement the prtP mutant in monolayer penetration, while the comparable fraction from the mutant has no such effect. Immunofluorescence studies suggested that wild-type T. denticola altered the TER by likely degrading the tight junctional proteins such as ZO-1. Cytotoxicity was not a major factor in the disruption of TER. The outer membrane vesicles (OMVs) of wild-type T. denticola also disrupted epithelial barrier function and penetrated the epithelial layers. Taken together, these results suggest that T. denticola penetrates the epithelial cell monolayers by altering cellular tight junctions.

Interactions between periodontal bacteria and human oral epithelial cells: Fusobacterium nucleatum adheres to and invades epithelial cells

Bacteria are causative agents of periodontal diseases. Interactions between oral bacteria and gingival epithelial cells are essential aspects of periodontal infections. Using an in vitro tissue culture model, a selected group of gram-negative anaerobic bacteria frequently associated with periodontal diseases, including Bacteroides forsythus, Campylobacter curvus, Eikenella corrodens, Fusobacterium nucleatum, Porphyromonas gingivalis, and Prevotella intermedia, were examined for their ability to adhere to and invade primary cultures of human gingival epithelial cells (HGEC). The effects of these bacteria on the production of interleukin-8 (IL-8), a proinflammatory chemokine, were also measured. These studies provided an initial demonstration that F. nucleatum adhered to and invaded HGEC and that this was accompanied by high levels of IL-8 secretion from the epithelial cells. The attachment and invasion characteristics of F. nucleatum were also tested using KB cells, an oral epithelial cell line. The invasion was verified by transmission electron microscopy and with metabolic inhibitors. Invasion appeared to occur via a "zipping" mechanism and required the involvement of actins, microtubules, signal transduction, protein synthesis, and energy metabolism of the epithelial cell, as well as protein synthesis by F. nucleatum. A spontaneous mutant, lam, of F. nucleatum, isolated as defective in autoagglutination, was unable to attach to or invade HGEC or KB cells, further indicating the requirement of bacterial components in these processes. Sugar inhibition assays indicated that lectin-like interactions were involved in the attachment of F. nucleatum to KB cells. Investigation of these new virulence phenotypes should improve our understanding of the role of F. nucleatum in periodontal infections.

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.

A comparison of IgG antibody reactive with Bacteroides forsythus and Porphyromonas gingivalis in adult and early-onset periodontitis

Recent work has indicated that Bacteroides forsythus and Porphyromonas gingivalis are significant local risk factors for periodontitis. Several reports find that both organisms are frequently associated with periodontitis lesions and often are present together. We have previously shown that early-onset periodontitis patients seropositive for P. gingivalis have less attachment loss than seronegative patients. In this study, we determined serum IgG antibody concentrations reactive with B. forsythus in adult and early-onset periodontitis patients using an ELISA and used P. gingivalis in the same populations as a positive control. The results for P. gingivalis were consistent with previous work and indicated that 47%, 36%, and 33% of adult, generalized early-onset, and localized juvenile patients were seropositive, respectively. Mean serum IgG concentrations for the three groups were 5.36 microg/ml, 5.65 microg/ml, and 5.44 microg/ml for adult, generalized early-onset, and localized juvenile patients, respectively. In contrast, for B. forsythus only 11%, 14%, and 10% of adult, generalized early-onset, and localized juvenile patients were seropositive, with mean serum IgG concentrations of 0.46 microg/ml, 0.46 microg/ml, and 0.47 microg/ml, respectively. This suggests that B. forsythus is either poorly immunogenic or less invasive than P. gingivalis. If most patients fail to mount an immune response to B. forsythus and it is invasive, it may explain why this organism is a risk factor for disease.

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.

Topographic distribution of subgingival plaque along root surfaces of human periodontally diseased teeth. A descriptive study

The purpose of this study was to characterize the topographical distribution and organization of subgingival plaque in periodontally diseased teeth. 26 extracted teeth were fixed and processed for undecalcified histological evaluation. The sections were cut perpendicular to the long axis of the tooth and analyzed by phase-contrast microscopy. The coronal portion of the analyzed roots showed a dense accumulation of filamentous forms, fusiform rods, coccoid forms and loosely aggregated spirochetes. The middle and apical portions showed a non-uniform distribution of the microflora, with microorganisms representing all the known morphotypes. Furthermore, plaque was detected below undisturbed periodontal fibers, indicating that plaque not only forms apically, but also in a lateral direction, penetrating and colonizing below areas where periodontal fibers are inserted into the root surface.

Production of inflammatory mediators and cytokines by human gingival fibroblasts following bacterial challenge

Bacteria can indirectly affect the course of periodontal diseases by activating host cells to produce and release inflammatory mediators and cytokines. These mediators and cytokines manifest potent proinflammatory and catabolic activity and may play key roles in local amplification of the immune response as well as in periodontal tissue breakdown. This study tested the effect of Actinobacillus actinomycetemcomitans (Aa) and Campylobacter rectus (Cr) challenge on PGE2, IL-1 beta, IL-6 and IL-8 production by human gingival fibroblasts (HGF). Contact-inhibited HGF were prepared and formalin-killed bacterial cells (Aa JP2, ATCC 29523 & 33384 and Cr ATCC 33238) at 10(6)-10(9) were added to the HGF. Culture supernatants were collected at varying time intervals and analyzed for cytokine and mediator content. All concentrations of Aa JP2 and Cr ATCC 33238 suppressed IL-1 beta production up to approximately 50% during the initial 3-12-h period. No bacterial concentration tested was able to increase IL-1 beta production above the maximum basal levels. Both bacterial species stimulated production of IL-6 and IL-8. Aa JP2 did not affect PGE2 levels significantly, whereas Cr ATCC 33238 was stimulatory only at the highest concentration tested (10(9)). There were no significant differences among the three Aa strains with respect to IL-1 beta production. However, Aa ATCC 29523 and ATCC 33384 were less capable of stimulating IL-6 secretion and more efficient in stimulating IL-8 production than Aa JP2. In general, Cr was the most potent enhancer of cytokine and mediator production by HGF. In conclusion, Aa and Cr are capable of amplifying the local immune response and promoting periodontal tissue inflammation by stimulating HGF to secrete mainly IL-6 and IL-8.

Evidence for two distinct locomotory phenotypes of Treponema denticola ATCC 35405

Using a two-layer system, a bottom layer containing treponema cells suspended in NOS (New Oral Spirochete)-Noble agar medium or NOS-Bacto agar medium and overlaid with cell-free NOS-agarose medium resulted in the spirochete cells migrating into the top layer. However, if the positions of the medium layers were reversed with the cells inoculated into the bottom layer containing NOS-agarose, there was no migration into the upper layer. This suggests migration of the spirochetes away from Bacto and Noble agars. Using a 3-layer system in which cells were inoculated into a middle layer consisting of NOS-agarose medium and sandwiched between cell-free NOS-agarose medium layers, cells remained within the middle layer. If the cells were inoculated into a middle layer consisting of NOS-Bacto agar medium while the upper and lower layers remained unchanged, cells migrated into both upper and lower layers. If cells that had migrated into the upper layer were transferred into a middle layer, they virtually all migrated into the upper layer repeatedly. Cells that had migrated into the lower layer and transferred to the middle layer migrated repeatedly into the lower layer. These results suggest the possible existence of two distinct locomotory phenotypes within this strain of treponeme.

Viscosity-dependent locomotion of oral spirochetes

Spirochetes are thought to remain motile in environments (such as intercellular spaces) that immobilize extracellularly flagellated eubacteria. This attribute suggests that the viscosity of the milieu is of importance to locomotion. We sought to determine the interdependence of oral spirochete locomotion with media viscosity. Video time-lapse microscopy using darkfield optics was used. The motility of the spirochetes in media of different viscosities (various concentrations of Noble agar) was measured. Treponema denticola exhibited the fastest speed (18.7 +/- 4.4 microns/min) at a viscosity of 30 mPa.s. The highest speeds for Treponema vincentii and Treponema socranskii were 41.9 +/- 14.9 and 33.4 +/- 13.2 microns/min, respectively, at 88 mPa.s. These data show that optimal migration of spirochetes is viscosity-dependent. The results support the hypothesis that such viscosity-dependent locomotion could be a virulence factor that enables oral spirochetes to initiate and sustain periodontal disease.

The periodontally-involved root surface

Recent years have seen much research on the periodontally-involved root surface. Many of these studies have produced results which suggest that plaque contaminants of the root surface are only superficially placed, and capable of being removed by gentle means. Further research has attested to the difficulties in rendering periodontally-involved root surfaces free of calculus deposits by instrumentation, yet clinical studies show that periodontal disease can be managed by root planing. It is concluded that root surface debridement is best assessed on the basis of the healing response and that it should aim to disrupt plaque on and remove plaque from the periodontally-involved root surface rather than to remove part of the root surface itself.

Pathogen-related oral spirochetes from dental plaque are invasive

Spirochetes that share pathogen-restricted antigens with Treponema pallidum subsp. pallidum have been identified in dental plaque and diseased gingival tissues, but it is not known whether these spirochetes possess virulence characteristics. In this study, plaque spirochetes were able to transmigrate a tissue barrier in vitro and were identified on the other side by using monoclonal antibodies specific for pathogen-restricted determinants from T. pallidum subsp. pallidum. This invasive capability is shared with T. pallidum subsp. pallidum, but cultured oral and intestinal treponemes did not perforate the tissue barrier. Cocultures indicated that invasive treponemes do not create opportunities for cultivable oral treponemes to cross the barrier. These findings indicate that gingival tissues may be a port of entry for previously unrecognized invasive spirochetes in humans.

Single-dose concentrations of tinidazole in gingival crevicular fluid, serum, and gingival tissue in adults with periodontitis

Previous studies have shown that metronidazole is effective in the treatment of subgingival microflora associated with destructive periodontitis. The aim of this study was to determine whether tinidazole, a close analogue of metronidazole, would reach sufficient concentrations in serum, gingival crevicular fluid, and gingival tissue, to inhibit putative periodontopathic bacteria. Ten adult patients with moderate to advanced periodontitis took a single 2-g dose of tinidazole orally. Samples were assayed by high-performance liquid chromatography. The concentrations of tinidazole in serum and GCF were in a similar range (3.2-46.5 micrograms/mL). Tinidazole was not detected in the GCF in three of the patients. The drug was found in gingival tissue obtained at two h (0.17 +/- 0.14 micrograms/mg) and six h (0.15 +/- 0.18 micrograms/mg) after oral administration. The mean concentration of tinidazole in serum at 24 h (13 +/- 3.0 micrograms/mL) is greater than the minimum inhibitory concentration for anaerobic bacteria as reported by others. The present data suggest that a single 2-g oral dose of tinidazole may lead to the presence of potentially bactericidal levels of tinidazole for up to 24 h in the periodontal pockets of some patients with periodontitis.

Effect of infection with Eikenella corrodens on the progression of ligature-induced periodontitis in rats

The periodontopathic ability of Eikenella corrodens 1073-R (EcR) on ligature-induced periodontal defects in immunosuppressed and non-immunosuppressed rats was studied bacteriologically and histologically. Silk ligatures were placed around the maxillary second molars of rats, and the rats were divided into eight groups. Four groups received cyclophosphamide (CY), an immunosuppressive agent, the day after ligature placement. On days 3 and 4, the oral cavities of the rats in all four groups were inoculated with 8 x 10(8) cells of live EcR. Rats were sacrificed on d 1, 3, 5, 8, 11 and 18. Alveolar bone resorption of ligated rats was enhanced by the implantation of EcR, although the number of total cultivable bacterial cells from ligated sites was not changed by the implantation of EcR. CY suppressed the number of white blood cells, inflammatory cellular infiltrates in gingival tissue, and repair of periodontal tissue, and enhanced bone destruction. The implantation of EcR in the ligature- and CY-treated rats also enhanced osteoclastic bone resorption. Without ligatures, high doses of CY or EcR inoculum did not result in periodontal destruction. These results indicate that it is possible to establish EcR in conventional rat flora with a ligature and that EcR causes osteoclastic bone resorption in this model.

Bacterial penetration of gingiva in the adult beagle dog with periodontitis

Invasion of gingival tissues by bacteria is thought to be a major factor in development of periodontal lesions. Morphologic studies have revealed bacteria within the pocket epithelium, gingival connective tissues, alveolar bone, and oral epithelium. The current studies are intended to determine whether they are present in healthy and diseased tissues and to identify the microbial source. Five beagle dogs with naturally occurring periodontitis were fed a soft diet. Two quadrants of the dentition of each dog were cleaned regularly and health maintained while others were allowed to develop further disease. After 4 weeks, samples of gingiva were removed both prior to and after the animals were sacrificed by perfusion fixation attempting not to introduce microorganisms. The identical samples were examined by light and scanning electron microscopy for numbers and location of organisms. Their numbers were greater in diseased than in healthy tissues. Furthermore, the quantity was greater in samples taken prior to perfusion fixation than after such treatment, especially in the oral epithelium. The results suggest that normally there are some microorganisms present within the periodontal tissues and that their numbers are greater in diseased tissues. However, the data also indicated that significant numbers may be introduced into the tissues during sampling of unfixed tissues.

Direct and immune-cell-mediated effects of Bacteroides gingivalis on bone metabolism in vitro

We investigated direct and immune-cell-mediated effects of Bacteroides gingivalis on bone metabolism in vitro. Fetal mouse long-bone rudiments were cultured under aerobic conditions in the presence of (a) intact bacteria, (b) low molecular weight (MW less than 1000) metabolic products of the bacteria, or (c) conditioned media of mouse spleen cells activated by whole bacteria. A suspension of intact bacteria, added directly to the bone culture, had no effect on bone resorption or bone formation. Low molecular weight (MW less than 1000) excretion products of the bacteria inhibited bone resorption and transiently reduced mineralization of the diaphysis, while the growth in length of the bones was not affected. However, conditioned media of bacteria-activated spleen cells strongly enhanced bone resorption and increased osteoclast numbers in the bone culture, while inhibiting mineral formation in the diaphysis. This led to a strongly negative mineral balance. These data do not support a direct effect of either bacteria or bacterial products on bone tissue as a likely explanation for bone loss in periodontal disease. Rather, they favour the concept that the loss of bone in this disease is an indirect effect of the host response, resulting from the contact of immune cells with the bacteria. This implies that bacterial invasion of the connective tissue of the gingiva may not be a prerequisite for alveolar bone loss.

Influence of granulation tissue, dental calculus and contaminated root cementum on periodontal wound healing. An experimental study in monkeys

The rôle of gingival granulation tissue, dental calculus and contaminated root cementum in marginal periodontal formation of new attachment was studied experimentally after chemical conditioning of the root surfaces of premolars and molars in 8 monkeys. Each treatment procedure was carried out in 4 monkeys. The other 4 monkeys served as controls. A morphometrical method was used to evaluate the results. It was concluded that a significant amount of new attachment including formation of new adhering cementum will result only on chemically-conditioned cementum surfaces. Small amounts of calculus or granulation tissue left in situ do not seem to influence healing, provided the cementum is left intact after chemical cleansing.

Quantification of bacterial penetration in spontaneous periodontal disease in beagle dogs

The role of bacteria in the pathogenesis of periodontal disease is controversial. Although bacterial penetration has been demonstrated in human periodontitis, relationships of bacteria to varying levels of periodontal health in other animals has not been well documented. In this study of beagle dog periodontium, bacteria were counted within the various tissue regions of sites which exhibited periodontal health, gingivitis, or periodontitis. Affected sites within whole block sections from two aged beagle dogs were prepared for investigation by light (LM) and scanning electron microscopy (SEM), and bacterial counts were subjected to statistical analysis for differences. Periodontitis sites viewed with LM had more bacteria than healthy sites. Neither LM nor SEM observations yielded any other differences in bacterial counts between the levels of periodontal health. When viewed using SEM, the sulcular epithelium had more bacteria than the other tissue regions in diseased sites. Relative to the number of bacteria in plaque, however, counts from all microscopic observations were very low. These findings indicate that the presence of bacteria within the periodontium is of questionable significance in the pathogenesis of spontaneous periodontal disease in beagle dogs.

Bacterial penetration of the pocket tissues in juvenile/postjuvenile periodontitis after the presurgical oral hygiene phase

Previous ultrastructural investigations of untreated sites of both adult and juvenile periodontitis have shown bacteria within the periodontal soft tissues. In the present study biopsies of the soft tissue walls of deep pockets from seven patients with juvenile (JP) or postjuvenile periodontitis (PJP) were removed at the end of the presurgical oral hygiene phase of treatment and examined in the transmission electron microscope. Bacteria were sparse, regardless of the level of tissue breakdown, both on the surface and within the superficial layers of the epithelium, deep to the basement membrane and throughout the underlying connective tissue. Of the 140 blocks from 20 biopsies, only two revealed intratissue accumulations of microorganisms. The organisms observed were gram-positive or gram-negative and appeared to be exclusively coccoid or rod-shaped. It is suggested that the reduced tissue content of bacteria reflects the establishment of adequate oral hygiene. Evidently either the tissue content of bacteria is less than has been reported previously or the host response is able to cope with residual bacteria that have penetrated the soft tissue.

Attachment of oral bacteria to a basement-membrane-like matrix and to purified matrix proteins

The purpose of this study was to investigate the adherence of oral bacteria to an in vitro basement-membrane-like matrix and to selected individual macromolecular constituents of this matrix. Radiolabeled bacteria were incubated with basement-membrane-like matrices isolated from PF HR-9 cells. Bacteroides gingivalis 33277, Fusobacterium nucleatum FN-2, and Actinobacillus actinomycetemcomitans GA3(A) bound to the matrix in the range of 44 to 70%, considerably higher than the ranges of A. actinomycetemcomitans GA3(NA) and SUNY AB67 (range, 20 to 25%). The attachment of selected strains of gram-positive bacteria such as Streptococcus and Actinomyces spp. was much less frequent (range, 6 to 25%). Competitive inhibition studies demonstrated that preincubating the bacteria with fibronectin significantly decreased the binding of B. gingivalis by 51% but increased the binding of other gram-negative and gram-positive organisms tested. Similarly, preincubating the matrices with antifibronectin antibodies decreased the binding of B. gingivalis by 31%, whereas the other bacteria tested were either unaffected or binding was increased. The adherence of bacteria to purified basement membrane proteins was also investigated. Strain and species differences were seen in binding, but no clear relationship emerged between binding to an intact matrix and binding to isolated matrix proteins. The results of this study suggest that some gram-negative oral bacteria commonly associated with periodontal disease, such as B. gingivalis, A. actinomycetemcomitans, and F. nucleatum, bound in high numbers to basement-membrane-like matrices in vitro. On the other hand, the gram-positive strains tested bound in much fewer numbers. The results suggest that further studies with this in vitro model may aid in understanding the mechanisms by which oral bacteria adhere to basement membranes.

Tissue localization of Actinobacillus actinomycetemcomitans in human periodontitis. II. Correlation between immunofluorescence and culture techniques

Recent immunohistological studies have suggested that Actinobacillus actinomycetemcomitans is present in the gingival tissues in juvenile periodontitis lesions. The present study examined tissue bound A. actinomycetemcomitans by bacterial culture and immunohistological demonstration of antigen in tissue. A total of 14 periodontitis lesions were examined. Eleven biopsies were obtained from gingiva adjacent to A. actinomycetemcomitans infected pockets, while the remaining three control biopsies were obtained from gingiva adjacent to pockets where subgingival A. actinomycetemcomitans infection could not be detected. Each biopsy was hemisected, one half was used for immunofluorescence microscopic examination while the other half was processed for culture of A. actinomycetemcomitans. The latter section was surface-disinfected, repeatedly washed and then minced to release bacteria from within the tissues. Aliquots from the serial washings and the minced tissue suspension were cultured on medium selective for A. actinomycetemcomitans. Surface disinfection and serial washings gradually decreased cultivable A. actinomycetemcomitans in the washings aliquots. Following tissue disruption, an increase in colony-forming units of A. actinomycetemcomitans was seen from eight of the 11 test biopsies. This bacterium could not be detected in washings or minced tissue suspensions from the control biopsies obtained from lesions in which subgingival A. actinomycetemcomitans was previously not detected. A positive correlation was seen between the presence of A. actinomycetemcomitans antigens in the gingival biopsies and; (1) A. actinomycetemcomitans colony-forming units released from the minced tissues (r = 0.90, p = 0.000), as well as; (2) the colony-forming units from the periodontal pocket (r = 0.62, P = 0.017).(ABSTRACT TRUNCATED AT 250 WORDS)

Bacterial penetration of pocket soft tissues in chronic adult and juvenile periodontitis cases. An ultrastructural study

This study investigates bacterial invasion of the soft tissue walls of deep pockets from cases with adult (AP) and juvenile periodontitis (JP). Transmission electron microscopy was used to examine pocket soft tissue walls removed from extracted teeth from 5 patients with AP and 2 patients with JP. Bacteria were sparse throughout the epithelium and connective tissue, regardless of the level of tissue breakdown. However many inflammatory cells were seen, and these did appear to be located in regions of marked collagen loss. Accumulations of large numbers of bacteria were extremely rare and found only on the epithelial surface or in artefactual spaces within the deeper tissues. The findings indicate that the tissue destruction associated with periodontitis is not directly related to bacterial invasion. The sparse organisms within the pocket tissues probably result from passive entry rather than an invasive action. Under these circumstances, it would seem reasonable to suggest that bacterial metabolic products rather than the micro-organisms themselves penetrate the tissues in periodontitis.

The non-specific theory in microbial etiology of inflammatory periodontal diseases

In the absence of toothbrushing, the gingival crevice is colonized by a complex indigenous microflora causing gingivitis, a non-specific inflammation. Subgingival plaque may develop by downgrowth into the inflamed pocket of those micro-organisms from supragingival plaque which can multiply there. By direct microscopy, increased proportions of motile rods and spirochetes have been found in diseased pockets. Cultures on selective media have demonstrated increased prevalence of various gram-negative rods. Cultures on non-selective media have revealed the complexity and variability of the subgingival microflora, comprising more than 200 species. Destructive periodontitis is the result of subgingival colonization, which is favored by such ecological changes as plaque accumulation, gingivitis, and gingival exudate. These changes increase the numbers of micro-organisms and alter their proportions, but no single species appears in active sites which is not also commonly present in inactive sites. The subgingival micro-organisms have several virulence factors which promote colonization of the pockets, destroy host defense mechanisms, and provoke inflammation. It appears that different combinations of indigenous bacteria, rather than just a single species, can produce the pathogenic potential necessary to cause progression from gingivitis to destructive periodontitis.

Pathogenesis of periodontitis

Periodontitis is an inflammatory disease of the periodontium which is characterized by a progressive destruction of the tissues supporting the tooth. Its primary etiology is an ill-defined series of microbial infections which may be composed of only some of the more than 300 species of bacteria currently recognized in the oral cavity. The disease is currently considered to progress as periodic, relatively short episodes of rapid tissue destruction followed by some repair, and prolonged intervening periods of disease remission. Despite the apparent random distribution of episodes of disease activity, the resulting tissue breakdown exhibits a symmetrical pattern of alveolar bone loss and pocket formation which is common to several forms of periodontitis, although the distribution of the most affected teeth and surfaces may vary among diseases (e.g., juvenile periodontitis versus adult periodontitis or rapidly progressive periodontitis). Several reports have indicated that bacterial cells can be found in the pocket wall of periodontitis lesions. The translocation of bacteria into the tissues from the pocket environment is quite common, as evidenced by the common occurrence of bacteremias in patients with periodontitis following relatively minor events such as chewing and oral hygiene procedures. However, it is important to distinguish between the passive introduction of bacteria into periodontal tissues and frank invasion as might occur in an acute infection, since the pathological implications may be quite different.

Immunohistochemical localization of transferrin receptors in junctional and sulcular epithelium of human gingiva

Transferrin receptors were found on the apical cells of the junctional epithelium and on the basal and adjacent suprabasal cells of the sulcular epithelium, consistent with the rapidly renewing character of these tissues. High density of receptors was found in the coronal portion of the junctional epithelium and on the sulcular cells adjacent to the tooth surface. This may indicate the proliferative potential of such cells rather than their actual division. An inert substratum, stimulating the tooth surface in vitro caused positive expression of the transferrin receptor, but not so extensively as in vivo. Thus factors not present in culture may normally activate the distinct non-differentiating junctional and sulcular cells to express the receptor.

Bacteroides intermedius binds fibrinogen

The binding of Bacteroides intermedius VPI 8944 to human fibrinogen has been characterized. The binding is time dependent, at least partially reversible, saturable, and specific. On an average, a maximum of 3,500 fibrinogen molecules bind per bacterial cell, with a dissociation constant of 1.7 X 10(-11) M. These bacteria also exhibit a fibrinogenolytic activity which can be partially inhibited by protease inhibitors. Bacteria release fibrinogenolytic activity into the surrounding medium without loss of binding activity, but more pronounced fibrinogen breakdown occurs when 125I-labeled fibrinogen is associated with the bacteria, suggesting that fibrinogen is degraded at the cell surface. Fibrinogen binding by B. intermedius might represent a mechanism of bacterial tissue adherence.