Bacteroides gingivalis vesicles mediate attachment of streptococci to serum-coated hydroxyapatite

Bacterial Membrane Vesicles as Mediators of Microbe - Microbe and Microbe - Host Community Interactions

Bacterial membrane vesicles are proteoliposomal nanoparticles produced by both Gram-negative and Gram-positive bacteria. As they originate from the outer surface of the bacteria, their composition and content is generally similar to the parent bacterium’s membrane and cytoplasm. However, there is ample evidence that preferential packaging of proteins, metabolites, and toxins into vesicles does occur. Incorporation into vesicles imparts a number of benefits to the cargo, including protection from degradation by other bacteria, the host organism, or environmental factors, maintenance of a favorable microenvironment for enzymatic activity, and increased potential for long-distance movement. This enables vesicles to serve specialized functions tailored to changing or challenging environments, particularly in regard to microbial community interactions including quorum sensing, biofilm formation, antibiotic resistance, antimicrobial peptide expression and deployment, and nutrient acquisition. Additionally, based on their contents, vesicles play crucial roles in host-microbe interactions as carriers of virulence factors and other modulators of host cell function. Here, we discuss recent advances in our understanding of how vesicles function as signals both within microbial communities and between pathogenic or commensal microbes and their mammalian hosts. We also highlight a few areas that are currently ripe for additional research, including the mechanisms of selective cargo packaging into membrane vesicles and of cargo processing once it enters mammalian host cells, the function of vesicles in transfer of nucleic acids among bacteria, and the possibility of engineering commensal bacteria to deliver cargo of interest to mammalian hosts in a controlled manner.

Composition and immuno-stimulatory properties of extracellular DNA from mouse gut flora

AIM

To demonstrate that specific bacteria might release bacterial extracellular DNA (eDNA) to exert immunomodulatory functions in the mouse small intestine.

METHODS

Extracellular DNA was extracted using phosphate buffered saline with 0.5 mmol/L dithiothreitol combined with two phenol extractions. TOTO-1 iodide, a cell-impermeant and high-affinity nucleic acid stain, was used to confirm the existence of eDNA in the mucus layers of the small intestine and colon in healthy Male C57BL/6 mice. Composition difference of eDNA and intracellular DNA (iDNA) of the small intestinal mucus was studied by Illumina sequencing and terminal restriction fragment length polymorphism (T-RFLP). Stimulation of cytokine production by eDNA was studied in RAW264.7 cells in vitro.

RESULTS

TOTO-1 iodide staining confirmed existence of eDNA in loose mucus layer of the mouse colon and thin surface mucus layer of the small intestine. Illumina sequencing analysis and T-RFLP revealed that the composition of the eDNA in the small intestinal mucus was significantly different from that of the iDNA of the small intestinal mucus bacteria. Illumina Miseq sequencing showed that the eDNA sequences came mainly from Gram-negative bacteria of Bacteroidales S24-7. By contrast, predominant bacteria of the small intestinal flora comprised Gram-positive bacteria. Both eDNA and iDNA were added to native or lipopolysaccharide-stimulated Raw267.4 macrophages, respectively. The eDNA induced significantly lower tumor necrosis factor-α/interleukin-10 (IL-10) and IL-6/IL-10 ratios than iDNA, suggesting the predominance for maintaining immune homeostasis of the gut.

CONCLUSION

Our results indicated that degraded bacterial genomic DNA was mainly released by Gram-negative bacteria, especially Bacteroidales-S24-7 and Stenotrophomonas genus in gut mucus of mice. They decreased pro-inflammatory activity compared to total gut flora genomic DNA.

Heterogeneity of Surfaces of Subgingival Bacteria as Detected by Zeta Potential Measurements

Porphyromonasgingivalis, Prevotella intermedia, and Actinobacillus actinomycetemcomitans (A.a.) are Gram-negative bacteria which are implicated in various forms of periodontal disease. The Gram-positive Peptostreptococcus micros may also play an important role. For investigation of the possible adhesion and colonization mechanisms of these organisms, the charge properties of the outermost layers of bacterial cell surfaces were studied through the measurement of zeta potentials at various pH values. Eleven fresh clinical isolates, representing the four species, and one laboratory strain, P. gingivalis W83, were examined. Eleven of the 12 strains displayed heterogeneity with respect to pH-dependent zeta potentials. Within single cultures of each of these strains, two distinct populations of cells were found, one which was more negatively charged than the other. For the Gram-negative strains, the more negatively charged subpopulation was in the majority, while the P. micros strains appeared to be composed mainly of a less-negatively-charged subpopulation. Vesicles prepared from two strains displayed the same pH dependence and heterogeneity of zeta potentials as the parent cells. An A.a. strain which was passaged several times in fluid medium had lost its fimbriae and became homogeneous with respect to charge.

Outer membrane vesicles - offensive weapons or good Samaritans?

Outer membrane vesicles (OMVs) from Gram-negative bacteria were first considered as artifacts and were followed with disbelief and bad reputation. Later, their existence was accepted and they became characterized as bacterial bombs, virulence bullets, and even decoys. Today, we know that OMVs also can be involved in cell-cell signaling/communication and be mediators of immune regulation and cause disease protection. Furthermore, OMVs represent a distinct bacterial secretion pathway selecting and protecting their cargo, and they can even be good Samaritans providing nutrients to the gut microbiota maintaining commensal homeostasis beneficial to the host. The versatility in functions of these nanostructures is remarkable and includes both defense and offense. The broad spectrum of usability does not stop with that, as it now seems that OMVs can be used as vaccines and adjuvants or vehicles engineered for drug treatment of emerging and new diseases not only caused by bacteria but also by virus. They may even represent new ways of selective drug treatment.

Analysis of Major Virulence Factors inPorphyromonas gingivalisunder Various Culture Temperatures Using Specific Antibodies

Porphyromonas gingivalis is implicated in the occurrence of adult periodontitis. We have previously identified major outer membrane proteins from P. gingivalis, which include representative virulence factors such as gingipains, a 75 kDa major protein, RagA, RagB, and putative porin. Fimbriae, another important virulence factor, exist on the cell surface. In this study, we identified major supernatant proteins. They were fimbrilin, the 75 kDa major protein, gingipains and their adhesin domains. Microscopic examination showed that supernatant proteins formed vesicle-like and fimbrial structures. To learn more about the character of this bacterium, we examined effects of growth temperature on localization and expression of these virulence factors. In general, localization of major virulence factors did not change at the various growth temperatures used. Most of the 75 kDa major protein, RagA, RagB, and putative porin were found in the envelope fraction, not in cell-free culture supernatant. Gingipains were found in both the envelope fraction and supernatant. More than 80% of fimbriae were associated with cells, less than 20% migrated to the supernatant. Most fimbriae existed in the whole cell lysate, although there was a small amount in the envelope fraction. When the growth temperature was increased, expression of fimbriae, gingipains, the 75 kDa major protein, RagA, and RagB decreased. However, temperature had almost no effect on expression of putative porin. The tendency for expression of major virulence factors to decrease at higher temperatures may enable P. gingivalis to survive under hostile conditions.

Porphyromonas gingivalis Outer Membrane Vesicles Mediate Coaggregation and Piggybacking of Treponema denticola and Lachnoanaerobaculum saburreum

Porphyromonas gingivalis sheds outer membrane vesicles that contain several virulence factors, including adhesins. In this study, we investigated the ability of P. gingivalis outer membrane vesicles to mediate the coaggregation and piggybacking of Treponema denticola and Lachnoanaerobaculum saburreum. Marked coaggregation between T. denticola and L. saburreum occurred in the presence of P. gingivalis outer membrane vesicles. Sucrose was an effective chemoattractant for the motile species T. denticola. The addition of outer membrane vesicles to a mixture of T. denticola and L. saburreum significantly increased the number of nonmotile bacteria that migrated into a sucrose-filled capillary tube immersed in the bacterial mixture. Under optimal conditions, the number of nonmotile L. saburreum in the capillary tube increased approximately 5-fold, whereas no increase occurred when boiled vesicles were used. This study showed that P. gingivalis outer membrane vesicles mediate coaggregation between T. denticola and L. saburreum and that nonmotile bacteria can be translocated by piggybacking on spirochetes.

Effects of installation depth on survival of an hydroxyapatite-coated Bicon implant for single-tooth restoration

PURPOSE

The present retrospective study evaluated various implant surface factors associated with Bicon implant survival for single-tooth restoration in the healthy individual.

PATIENTS AND METHODS

A retrospective cohort study design was used. A total of 613 Bicon (Bicon System, Boston, MA) implants (272 patients) were included. Because the use of hydroxyapatite (HA) coating has been controversial, the surface type was chosen according to the patient's preference. A total of 308 HA-coated implants and 305 titanium plasma-sprayed (TPS) implants were used. The macroanatomy of both implant types was identical. Patients who had systemic disease, poor quality bone, or removable prosthetics were excluded from the present study. A chart review was conducted to record age, gender, implant diameter, implant length, installation depth, installation location, and the use of bone grafting. Implant failure was recorded, and the data were analyzed using the chi(2) test and logistic regression analysis.

RESULTS

The installation depth was an important prognostic factor in the HA-coated implants. The failure rate for the HA-coated implants installed at margin level and 2 mm below level was 10.29% and 3.01%, respectively (chi(2) = 6.035, P = .014). The implant length was an important prognostic factor for the TPS-treated implants. The failure rate recorded for the TPS-treated implants installed with a length of less than 10 mm and 10 mm or longer was 15.46% and 2.40%, respectively (chi(2) = 18.414, P < .001).

CONCLUSION

Many factors can influence the failure rate of TPS and HA-coated Bicon implants. Among these, installation depth played an especially significant role in the success of HA-coated Bicon implants in the present study.

Further evidence that major outer membrane proteins homologous to OmpA in Porphyromonas gingivalis stabilize bacterial cells

INTRODUCTION

Porphyromonas gingivalis is one of the most important bacteria in the progression of chronic periodontal disease. We hypothesized that the major outer membrane proteins Pgm6/7, which are homologous to the OmpA protein in Escherichia coli, might contribute to the stabilization of the cell surface. In this study, the effects of Pgm6/7 on the cell surface were examined morphologically.

METHODS

Deletion mutants of Pgm6/7 (Delta694, Delta695 and Delta695-694) were constructed using the polymerase chain reaction-based overlap extension method. Wild-type ATCC 33277 and Pgm6/7 mutants were grown under anaerobic conditions. Whole cells and thin sections of fixed cells were stained and examined by transmission electron microscopy.

RESULTS

Compared with the wild-type, numerous vesicles released from cells were observed in each deletion mutant. The outer membrane appeared wavy and irregular. Increased numbers of vesicles were confirmed after their preparation from the culture supernatant. Total gingipain activity in vesicles was increased five- to 10-fold in the deletion mutants.

CONCLUSION

This report provides further evidence that Pgm6/7 proteins in P. gingivalis play an important role in the maintenance of bacterial outer membrane integrity.

Membrane vesicles: an overlooked component of the matrices of biofilms

The matrix helps define the architecture and infrastructure of biofilms and also contributes to their resilient nature. Although many studies continue to define the properties of both gram-positive and gram-negative bacterial biofilms, there is still much to learn, especially about how structural characteristics help bridge the gap between the chemistry and physical aspects of the matrix. Here, we show that membrane vesicles (MVs), structures derived from the outer membrane of gram-negative bacteria, are a common particulate feature of the matrix of Pseudomonas aeruginosa biofilms. Biofilms grown using different model systems and growth conditions were shown to contain MVs when thin sectioned for transmission electron microscopy, and mechanically disrupted biofilms revealed MVs in association with intercellular material. MVs were also isolated from biofilms by employing techniques for matrix isolation and a modified MV isolation protocol. Together these observations verified the presence and frequency of MVs and indicated that MVs were a definite component of the matrix. Characterization of planktonic and biofilm-derived MVs revealed quantitative and qualitative differences between the two and indicated functional roles, such as proteolytic activity and binding of antibiotics. The ubiquity of MVs was supported by observations of biofilms from a variety of natural environments outside the laboratory and established MVs as common biofilm constituents. MVs appear to be important and relatively unacknowledged particulate components of the matrix of gram-negative or mixed bacterial biofilms.

Outer Membrane Vesicles FromPorphyromonas gingivalisAffect the Growth and Function of Cultured Human Gingival Fibroblasts and Umbilical Vein Endothelial Cells

BACKGROUND

The purpose of this study was to examine the effects of outer membrane vesicles (OMV) obtained from Porphyromonas gingivalis (Pg) on the growth and function of human gingival fibroblasts (HGF) and human umbilical vein endothelial cells (HUVEC).

METHODS

OMV were obtained from a cell-free growth medium of Pg ATCC 33277 by 40% NH2SO4 precipitation and ultracentrifugation. Cell proliferation was measured by 3H-thymidine incorporation into growing HGF and HUVEC. Endothelial cell function was determined by their capacity to form a network of capillary tubes on an extracellular matrix (ECM).

RESULTS

Proliferating HGF and HUVEC demonstrated a significant dose-dependent inhibition of 3H-thymidine uptake when cultured with 0 to 40 microg/ml of OMV protein. HGF and HUVEC showed an IC50 of growth of about 9.0 microg/ml and 4.5 microg/ml of OMV protein, respectively. Capillary tube formation by HUVEC cultured on an ECM was suppressed by 70% to 80% with 5 microg/ml OMV protein after 18 hours of incubation. The presence of proteolytic enzymes in the OMV did not contribute to capillary tube disruption, since blocking enzyme activity with specific inhibitors did not reduce the suppression of capillary tube formation. After heating at 90 degrees C for 5 minutes, OMV significantly lost their capacity to suppress capillary tube formation.

CONCLUSIONS

OMV significantly inhibit the proliferation of cultured HGF and HUVEC in a dose-dependent manner. OMV suppressed the capillary tube formation by cultured HUVEC. The factor(s) appeared to be a protein and not endotoxin because its inhibitory activity was markedly reduced by heat inactivation. These studies suggest that OMV contribute to chronic periodontitis by suppressing cell proliferation and revascularization in periodontal tissues.

Specific antibodies induced by nasally administered 40-kDa outer membrane protein of Porphyromonas gingivalis inhibits coaggregation activity of P. gingivalis

In this study, we have assessed the efficacy of the 40-kDa outer membrane protein (40k-OMP) of Porphyromonas gingivalis as a nasal vaccine for the prevention of adult periodontitis. Mice nasally immunized with 40k-OMP and cholera toxin as mucosal adjuvant displayed significant levels of 40k-OMP-specific serum IgG1, IgG2b and IgA as well as mucosal IgA antibodies (Abs) in saliva and nasal secretions. Ab-forming cell (AFC) analysis confirmed the antibody titers by detecting high numbers of 40k-OMP-specific AFCs in spleen, salivary glands and nasal passages. Because 40k-OMP-specific IgG inhibited coaggregation of P. gingivalis vesicles and S. gordonii, it may be an important tool for the prevention of 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.

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.

Degradation of host protease inhibitors and activation of plasminogen by proteolytic enzymes from Porphyromonas gingivalis and Treponema denticola

Bacterial proteases may participate in the pathogenesis of periodontal diseases through their action on host proteins. In the present study, the ability of selected periodontopathogens, as well as two proteases isolated from Porphyromonas gingivalis and Treponema denticola, to degrade host protease inhibitors was evaluated. The activation of human plasminogen by the two bacterial proteases was also investigated. Proteolytic breakdown of host protease inhibitors (alpha-1-antitrypsin, antichymotrypsin, alpha 2-macroglobulin, antithrombin III, antiplasmin and cystatin C) was evaluated by SDS-PAGE. The 80 kDa trypsin-like protease of P. gingivalis completely digested the six protease inhibitors under investigation, whereas the 95 kDa chymotrypsin-like protease of T. denticola was slightly less active, more particularly on alpha 2-macroglobulin and cystatin C. When whole cells from a number of oral bacterial species were tested, the most significant degradation was obtained with P. gingivalis, T. denticola, Prevotella intermedia, Prevotella nigrescens and Capnocytophaga spp. Peptostreptococcus micros and Propionibacterium acnes had only some degradative activity on selected inhibitors, whereas three bacterial species, Actinobacillus actinomycetemcomitans, Bacteroides forsythus and Fusobacterium nucleatum, had no effect on the protease inhibitors. The 80 kDa protease of P. gingivalis demonstrated strong plasminogen activation, whereas no such activity was associated with the 95 kDa protease of T. denticola. This study indicates the high potential of some periodontal pathogens to destroy protease inhibitors and activate plasminogen. This may result in an uncontrolled degradation of periodontal tissues and a rapid progression of the disease.

Porphyromonas gingivalis outer membrane vesicles promote bacterial resistance to chlorhexidine

Porphyromonas gingivalis has been frequently associated with some types of periodontal diseases and possesses various mechanisms favoring the pathogenic process. It has been recently observed that vesicles elaborated by P. gingivalis are able to protect bacteria from the bactericidal activity of human serum. The aim of the present investigation was to evaluate the ability of vesicles from P. gingivalis in protecting oral bacteria against chlorhexidine. Data indicate that vesicles released by P. gingivalis may bind chlorhexidine, thus allowing protection for itself and for other oral bacterial species. It has also been demonstrated that lipopolysaccharides are the major component involved in the binding of chlorhexidine by vesicles. The mechanism of resistance reported in this study indicates that bacterial interactions in the oral cavity may influence the sensitivity of microbes.

Effect of Porphyromonas gingivalis ATCC 33277 vesicle on adherence of Streptococcus mutans OMZ 70 to the experimental pellicle

The vesicles of Porphyromonas gingivalis ATCC 33277 strongly aggregated Streptococcus cricetus, S. rattus, and S. mutans, but poorly aggregated S. sobrinus. The adherence of S. mutans OMZ 70 to hydroxyapatite (HA) coated with whole saliva was increased in parallel with the quantity of the vesicles. The significant increase of adherence of S. mutans OMZ 70 by the vesicles was also observed on the HA coated with parotid saliva, submandibular saliva, serum, and type I collagen. These findings suggest that the vesicles may act as a bridge between mutans streptococcus and the tooth surface.

Demonstration of adherence properties of Porphyromonas gingivalis outer membrane vesicles using a new microassay

Vesicles made by Porphyromonas gingivalis possess several biological activities, including the ability to adhere to oral surfaces and to bacteria. In this study, a new and simple method was developed to measure the adherence capability of outer membrane vesicles from P. gingivalis. Vesicles were conjugated to fluorescent microspheres (0.7 micron) and added to wells of a Teflon-coated microscope slide previously covered with a variety of soluble ligands. After incubation and washes, the number of fluorescent microspheres per microscopic field were counted. Vesicle-coated microspheres attached best to gelatin (> 200 per field), whereas other compounds (such as fibronectin, fibrinogen, collagen and laminin) provided moderate attachment, and no attachment was observed to bovine serum albumin. Adherence to any of the tested ligands was not observed when fluorescent microspheres were conjugated to bovine serum albumin or lipopolysaccharides from P. gingivalis. The adherence of vesicle-coated microspheres to ligands was not significantly affected when the pH of the reaction mixture was between 4 and 10. None of the tested carbohydrates lowered the attachment capability of vesicle-coated microspheres to substrates. When vesicle-coated microspheres were treated with trypsin and chymotrypsin or heated, this resulted in a significant loss of attachment, suggesting a possible involvement of proteinaceous molecules in the process. The present study confirms that vesicles of P. gingivalis are capable of attachment to various molecules and indicate their potential role in colonization.

Characteristics of adherence of Actinobacillus actinomycetemcomitans to epithelial cells

Actinobacillus actinomycetemcomitans smooth variants [SUNY 75(S), SUNY 465, 652] were investigated for their ability to adhere to KB epithelial cells. Both the type of medium (broth versus agar) and anaerobicity influenced adherence levels and cell surface characteristics. Optimal adherence was observed with all three strains after growth of the bacterial cells in broth under anaerobic conditions, a condition which was associated with extracellular microvesicles. Adherence of SUNY 75(S) also was correlated with extracellular amorphous material, whereas adherence of SUNY 465 was also associated with fimbriation which accompanied a smooth to rough phenotype shift. The relationship between adherence and extracellular vesicles, extracellular amorphous material, and fimbriation suggests that all of these components may function in A. actinomycetemcomitans adherence to epithelial cells. The phenotype shift observed in SUNY 465 cells is further evidence that A. actinomycetemcomitans SUNY 465 is predisposed to variant shifts which are associated with changes in adherence and invasion properties.

Correlation between cell-adherent activity and surface structure in Porphyromonas gingivalis

The cell-adherent ability of 6 strains of Porphyromonas gingivalis (381, ATCC 33277, SU63, KD1, W50 and W83) was compared by using radiolabeled bacterial cells and human gingival fibroblasts (Gin 1), human periodontal ligament fibroblasts (HPLF) and human epithelial cells (Ca9-22) that had been grown on collagen beads. The cell-adherent activity of these organisms varied among strains; P. gingivalis strains 381, ATCC 33277 and SU63 bound to the target cells at a range of 14% to 72%, but the other 3 strains (KD1, W50 and W83) were scarcely bound (0.6% to 3.5%). On the other hand, whole bacterial cells and culture supernatants of all strains showed distinct hemagglutinating activity. The 3 strains showing high cell-adherent activity were hydrophobic and the other strains showing less activity were relatively hydrophilic. Furthermore, a number of peritrichous fimbriae were found on the surface of P. gingivalis strains 381, ATCC 33277 and SU63, which showed high adherent activity, whereas, fimbriae on the other 3 strains showing low adherent ability were barely apparent. Therefore, it was assumed that the cell-adherent activity of P. gingivalis was related to the hydrophobicity of the cell surface, which was related to the number of fimbriae.

Role of Porphyromonas gingivalis 40-kDa outer membrane protein in the aggregation of P. gingivalis vesicles and Actinomyces viscosus

Porphyromonas gingivalis, an important pathogen in periodontitis, produces extracellular vesicles that aggregate with Actinomyces viscosus cells. A 40-kDa outer membrane protein (OMP)-coding gene from P. gingivalis was cloned and the protein was found to be localized in these vesicles. The recombinant 40-kDa OMP did not show aggregation activity. However, affinity-purified antibody against the recombinant protein significantly inhibited aggregation of P. gingivalis vesicles with A. viscosus cells. The antibody also inhibited cellular coaggregation of several strains of P. gingivalis with A. viscosus cells, but not with other periodontal pathogens. Moreover, aggregation of A. viscosus cells with P. gingivalis vesicles was inhibited in a dose-dependent manner by pre-treatment of the A. viscosus cells with the recombinant protein. These findings suggest that the 40-kDa OMP may be an important aggregation factor of P. gingivalis.

Inactivation of human serum bactericidal activity by a trypsinlike protease isolated from Porphyromonas gingivalis

A protease was isolated from an outer membrane vesicle preparation of Porphyromonas gingivalis ATCC 33277 and assessed for its ability to inactivate the bactericidal activity of normal human serum. The enzyme, which was activated by reducing agents, was found to be a trypsinlike protease with a molecular mass of approximately 80 kDa. Prior to being tested in the bactericidal assay, pooled human serum was preincubated with the partially purified enzyme. Under conditions in which the trypsinlike protease was activated, a strong reduction of the serum bactericidal activity against Capnocytophaga ochracea was noted. On the other hand, no reduction of the bactericidal action of serum was observed when the serum-protease mixture was preincubated in the presence of an inhibitor of the enzyme. As determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, the protease was shown to degrade immunoglobulins G and M as well as complement factor C3. This study confirms the previous hypothesis that the proteases of P. gingivalis can interfere with the protective action of human serum.

Evidence that Porphyromonas (Bacteroides) gingivalis fimbriae function in adhesion to Actinomyces viscosus

Porphyromonas (Bacteroides) gingivalis adheres to gram-positive bacteria, such as Actinomyces viscosus, when colonizing the tooth surface. However, little is known of the adhesins responsible for this interaction. A series of experiments were performed to determine whether P. gingivalis fimbriae function in its coadhesion with A. viscosus. Fimbriae typical of P. gingivalis were isolated from strain 2561 (ATCC 33277) by the method of Yoshimura et al. (F. Yoshimura, K. Takahashi, Y. Nodasaka, and T. Suzuki, J. Bacteriol. 160:949-957, 1984) in fractions enriched with a 40-kDa subunit, the fimbrillin monomer, P. gingivalis-A. viscosus coaggregation was inhibited by purified rabbit antifimbrial immunoglobulin G (IgG) at dilutions eightfold higher than those of preimmune IgG, providing indirect evidence implicating P. gingivalis fimbriae in coadhesion. Three types of direct binding assays further supported this observation. (i) Mixtures of isolated P. gingivalis fimbriae and A. viscosus WVU627 cells were incubated for 1 h, washed vigorously with phosphate-buffered saline (pH 7.2), and subjected to electrophoresis. Transblots onto nitrocellulose were probed with antifimbrial antiserum. Fimbrillin labeled positively on these blots. No reaction occurred with the control protein, porcine serum albumin, when blots were exposed to anti-porcine serum albumin, (ii) A. viscosus cells incubated with P. gingivalis fimbriae were agglutinated only after the addition of antifimbrial antibodies. (iii) Binding curves generated from an enzyme immunoassay demonstrated concentration-dependent binding of P. gingivalis fimbriae to A. viscosus cells. From these lines of evidence, P. gingivalis fimbriae appear to be capable of binding to A. viscosus and mediating the coadhesion of these species.

Protective effect of Porphyromonas gingivalis outer membrane vesicles against bactericidal activity of human serum

The present study was undertaken to evaluate the effect of Porphyromonas gingivalis outer membrane vesicles on the bactericidal activity of human serum. Human serum was pretreated with extracellular vesicles and then incubated with a cell suspension of Capnocytophaga ochracea. After 2 h at 37 degrees C, the percent viability of C. ochracea was determined by cultivation on blood agar plates. At a final concentration of 0.3 mg/ml, outer membrane vesicles completely inhibited the serum bactericidal activity against C. ochracea. Boiling the vesicles prevented this inhibition. However, partial inhibition of the serum lethal action was obtained when a higher concentration (1.5 mg/ml) of boiled vesicles was used, which indicates the involvement of both heat-labile and heat-stable components associated with vesicles. Combining vesicles at a suboptimal concentration (0.1 mg/ml) with a reducing agent brought back inhibition of the bactericidal activity, whereas combining vesicles at an optimal concentration (0.3 mg/ml) with a thiol-blocking reagent caused a restoration of the bactericidal activity. When a purified preparation of P. gingivalis lipopolysaccharides was used instead of vesicles, inhibition of the bactericidal activity was also observed. These results indicate that the lipopolysaccharides and the proteolytic enzyme(s) associated with P. gingivalis outer membrane vesicles are likely to represent the heat-stable and the heat-labile components, respectively. It is possible that outer membrane vesicles released by P. gingivalis protect other bacterial species from complement action, thus favoring the pathogenic process of periodontal disease.