Attachment of Bacteroides melaninogenicus subsp. asaccharolyticus to oral surfaces and its possible role in colonization of the mouth and of periodontal pockets

Porphyromonas gingivalis genes involved in community development with Streptococcus gordonii

Porphyromonas gingivalis, one of the causative agents of adult periodontitis, develops biofilm microcolonies on substrata of Streptococcus gordonii but not on Streptococcus mutans. P. gingivalis genome microarrays were used to identify genes differentially regulated during accretion of P. gingivalis in heterotypic biofilms with S. gordonii. Thirty-three genes showed up- or downregulation by array analysis, and differential expression was confirmed by quantitative reverse transcription-PCR. The functions of the regulated genes were predominantly related to metabolism and energy production. In addition, many of the genes have no current known function. The roles of two upregulated genes, ftsH (PG0047) encoding an ATP-dependent zinc metallopeptidase and ptpA (PG1641) encoding a putative tyrosine phosphatase, were investigated further by mutational analysis. Strains with mutations in these genes developed more abundant biofilms with S. gordonii than the parental strain developed. ftsH and ptpA may thus participate in a regulatory network that constrains P. gingivalis accumulation in heterotypic biofilms. This study provided a global analysis of P. gingivalis transcriptional responses in an oral microbial community and also provided insight into the regulation of heterotypic biofilm development.

Streptococcus gordonii utilizes several distinct gene functions to recruit Porphyromonas gingivalis into a mixed community

Dental plaque biofilm formation proceeds through a developmental pathway initiated by the attachment of pioneer organisms, such as Streptococcus gordonii, to tooth surfaces. Through a variety of synergistic interactions, pioneer organisms facilitate the colonization of later arrivals including Porphyromonas gingivalis, a potential periodontal pathogen. We have investigated genes of S. gordonii required to support a heterotypic biofilm community with P. gingivalis. By screening a plasmid integration library of S. gordonii, genes were identified that are crucial for the accumulation of planktonic P. gingivalis cells into a multispecies biofilm. These genes were further investigated by specific mutation and complementation analyses. The biofilm-associated genes can be grouped into broad categories based on putative function as follows: (i) intercellular or intracellular signalling (cbe and spxB), (ii) cell wall integrity and maintenance of adhesive proteins (murE, msrA and atf), (iii) extracellular capsule biosynthesis (pgsA and atf), and (iv) physiology (gdhA, ccmA and ntpB). In addition, a gene for a hypothetical protein was identified. Biofilm visualization and quantification by confocal microscopy confirmed the role of these genes in the maturation of the multispecies community, including biofilm architectural development. The results suggest that S. gordonii governs the development of heterotypic oral biofilms through multiple genetic pathways.

Oral microbial communities in sickness and in health

The relationship between humans and their oral microflora begins shortly after birth and lasts a lifetime. Up until fairly recently, the associations between the host and oral bacteria were considered in terms of a multiplicity of single species interactions. However, it is becoming more apparent that the oral microbes comprise a complex community, and that oral health or disease depends on the interface between the host and the microbial community as a whole. Although it is important to continue studies of the pathogenic properties of specific microbes, these are relevant only in the context of the properties of the community within which they reside. Understanding the microbial communities that drive sickness or health is a key to combating human oral diseases.

Short fimbriae of Porphyromonas gingivalis and their role in coadhesion with Streptococcus gordonii

Porphyromonas gingivalis, one of the causative agents of adult periodontitis, attaches and forms biofilms on substrata of Streptococcus gordonii. Coadhesion and biofilm development between these organisms requires the interaction of the short fimbriae of P. gingivalis with the SspB streptococcal surface polypeptide. In this study we investigated the structure and binding activities of the short fimbriae of P. gingivalis. Electron microscopy showed that isolated short fimbriae have an average length of 103 nm and exhibit a helical structure with a pitch of ca. 27 nm. Mfa1, the major protein subunit of the short fimbriae, bound to SspB protein, and this reaction was inhibited by purified recombinant Mfa1 and monospecifc anti-Mfa1 serum in a dose-dependent manner. Complementation of a polar Mfa1 mutant with the mfa1 gene restored the coadhesion phenotype of P. gingivalis. Hence, the Mfa1 structural fimbrial subunit does not require accessory proteins for binding to SspB. Furthermore, the interaction of Mfa1 with SspB is necessary for optimal coadhesion between P. gingivalis and S. gordonii.

Construction of novel human monoclonal antibodies neutralizing Porphyromonas gingivalis hemagglutination activity using transgenic mice expressing human Ig loci

Porphyromonas gingivalis has been implicated as an important pathogen in the development of adult periodontitis, and its colonization of subgingival sites is critical in the pathogenic process. One potential virulence factor, hemagglutinin, may mediate bacteria attachment onto and penetration into host cells, as well as agglutinate and lyses erythrocytes to intake heme, an absolute requirement for growth. Toward the development of passive immunotherapy, the construction of a human type monoclonal antibody, which is capable of inhibiting the hemagglutinating ability, will be significant and important. The human mAbs, both exhibiting a high degree of specificity and affinity against the recombinant 130 kDa hemagglutinin domain protein have been prepared using XenoMouse technology. The constructed Xeno-mAbs, IgG2 subclass, significantly inhibited hemagglutination of P. gingivalis and its vesicles. The newly constructed Xeno-mAbs may prove to be useful for the development of passive immunization against periodontal diseases caused by P. gingivalis infection, pending the results of fertility study in disease mode.

Inhibition ofPorphyromonas gingivalisHemagglutinating Activity by Synthetic Peptides Derived from Phage Display Selection Using MAb Against the Recombinant Outer Membrane Protein

Porphyromonas gingivalis has been implicated as an pathogen in the development of periodontitis, and hemagglutinins have been identified as an important adhesion onto the gingival tissue cells, and to attach and lyse erythrocytes to uptake Fe ion as an essential nutriant. The 40-kDa outer membrane protein (OMP) has been moleculary cloned from P. gingivalis 381. Since the antibody against recombinant (r) 40-kDa OMP inhibited the hemagglutinating activity, and the polymeric form of r40-kDa OMP itself expressed hemagglutinating activity, the 40-kDa OMP is thought to be one of the hemagglutinins. Moreover, we established MAbs against r40-kDa OMP which were capable of inhibiting hemagglutinating activity of P. gingivalis vesicles. In the present study, a phage-displayed epitope mapping system was used to identify the functional domain expressing hemagglutinating activity by biopanning using the neutralizing mAb, Pg-ompA1. The minimal epitope requirements of the MAb and the predicted amino acid sequences were identified in the region of (96)IALDQTLGIP(105) in 40-kDa OMP. Synthetic peptide, (87)WPRVGQLFIALDQTLGIPTFSVCRME(116), mapped the relevant molecule within a short stretch and is corresponding to residues of 40-kDa OMP. Chemically synthesized peptide was used to determine its inhibitory activity against hemagglutinating activity. The synthetic peptide significantly abolished hemagglutinating activity in a dose-dependent manner. These findings suggest that the synthetic peptide is an effective antagonist of erythrocyte binding, and this peptide may be a potent inhibitor of hemagglutination of P. gingivalis cells. The use of synthetic peptide neutralizing hemagglutinating activity of P. gingivalis represents a possible new therapeutic approach to P. gingivalis infected periodontitis.

Characterization of binding of Streptococcus oralis glyceraldehyde-3-phosphate dehydrogenase to Porphyromonas gingivalis major fimbriae

Binding of Streptococcus oralis glyceraldehyde-3-phosphate dehydrogenase (GAPDH) to Porphyromonas gingivalis fimbriae was characterized via a biomolecular interaction analysis system. The interaction was specific, and the association constant value was 4.34 x 10(7) M(-1), suggesting that S. oralis GAPDH functions as a dominant receptor for P. gingivalis and contributes to P. gingivalis colonization.

Glyceraldehyde-3-phosphate dehydrogenase of Streptococcus oralis functions as a coadhesin for Porphyromonas gingivalis major fimbriae

Cohesive interactions between Porphyromonas gingivalis and plaque-forming bacteria, such as Streptococcus oralis, are considered to play an important role in the colonization of P. gingivalis in periodontal sites. Although P. gingivalis fimbriae have been reported to mediate coaggregation with S. oralis, the S. oralis molecule involved has not been identified. We identified the coadhesin of S. oralis ATCC 9811 and purified it by affinity column chromatography. We found that the molecular mass of the purified protein was approximately 40 kDa. Dot blot and Western blot assays showed binding of the 40-kDa protein to P. gingivalis fimbriae. Further, turbidimetric assays showed that the coadhesin inhibited coaggregation between P. gingivalis and S. oralis in a dose-dependent manner. Analyses of the amino-terminal sequences of the protein and its lysyl endopeptidase-cleaved fragments revealed that the coadhesin was identical to glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Next, we cloned the gene that encodes S. oralis GAPDH and found that the sequence had a high degree of homology with the sequences of GAPDHs of various bacteria, including Streptococcus gordonii and Fusobacterium nucleatum. To confirm the contribution of S. oralis GAPDH to the interaction with P. gingivalis, a recombinant GAPDH protein was generated in Escherichia coli; this protein bound to P. gingivalis fimbriae and had an inhibitory effect on coaggregation. These results suggest that S. oralis GAPDH functions as a coadhesin for P. gingivalis fimbriae. In addition, considering the high degree of homology of the GAPDHs of various bacteria, those of other plaque-forming bacteria also may contribute to the colonization of P. gingivalis.

Effect of various chlorhexidine regimens on salivary bacteria and de novo plaque formation

AIM

The aim of the present experiment was to study the effect of different chlorhexidine regimens on the number of bacteria in saliva, and on de novo plaque formation.

MATERIAL AND METHODS

Ten subjects with gingivitis, but no signs of destructive periodontitis, were recruited. Following a screening examination, the volunteers were given oral hygiene instruction, meticulous scaling and professional mechanical tooth cleaning (PTC). The PTC was repeated once every 3 days during a 2-week period to establish healthy gingival conditions. The study was designed as a double-blind cross-over clinical trial including three phases. Each experimental phase comprised one preparatory period of 7 days and one plaque accumulation period (no oral hygiene measures) of 4 days. During all preparatory periods, the volunteers (i) performed mechanical tooth cleaning using a toothbrush and dentifrice and (ii) were, in addition, given two sessions of PTC. The final PTC was delivered after bacterial sampling had been made on Day 0. Preparatory period A: the participants continued the self-performed plaque control regimen that employed only mechanical means. Preparatory period B: the participants were in addition instructed to rinse and gargle, twice daily, with a 0.2% chlorhexidine mouthrinse. Preparatory period C: in addition to the above, the participants were instructed to brush the dorsum of the tongue for 60 s, twice daily, with a 1.0% chlorhexidine gel. Following each plaque accumulation period, there was a 10-day washout interval. The presence and amount of dental plaque (QHI) was scored after 1, 2 and 4 days of no oral hygiene. Samples of saliva were obtained on Day 0 and after 1 and 2 days. The samples were placed on Brucella agar plates and incubated (anaerobically) for 5 days. The total number of colony-forming units was determined and used to estimate the density of bacteria in saliva.

RESULTS

In period A, the mean QHI increased from 1.0 (Day 1) to 1.4 (Day 2) and 2.1 (Day 4). The corresponding scores for periods B and C were 0.5, 0.8, 1.6 and 0.3, 0.8, 1.2, respectively. At all re-examination intervals more plaque formed during period A than during periods B and C. Further, during period C, less plaque formed than that during period B. Saliva samples from Day 0 in period A contained a larger number of TVC than the baseline samples in periods B and C. There was no significant difference in TVC among the groups on Day 2.

CONCLUSION

The daily use of chlorhexidine as an adjunct to mechanical tooth cleaning markedly reduced the number of microorganisms that could be detected in saliva. The number of salivary bacteria may have influenced the amount of plaque that formed during an early phase of no oral hygiene.

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

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

Adhesins encoded by the gingipain genes of Porphyromonas gingivalis are responsible for co-aggregation with Prevotella intermedia

Co-aggregation among bacterial cells caused by the adherence of one bacterial species to another is a potential colonization mechanism. Several putative aggregation factors for co-aggregation between Porphyromonas (Por.) gingivalis and Prevotella (Pre.) intermedia were partially purified from Por. gingivalis vesicles by gel filtration and affinity chromatography. Antisera against the aggregation factors were made. Analysis using these antisera revealed that 18 and 44 kDa proteins might be responsible for Por. gingivalis vesicle-mediated aggregation of Pre. intermedia. Using antiserum against the 18 kDa protein, the DNA region encoding it was cloned from Por. gingivalis genomic DNA. Sequence analysis revealed that the DNA region was located within the rgpA and kgp genes, encoding Arg-gingipain (Rgp) and Lys-gingipain (Kgp), respectively, and it encoded non-catalytic adhesin domain regions, namely a C-terminal portion of HGP15, the entire HGP17 sequence and an N-terminal portion of HGP27. A portion of the DNA sequence was also found in the haemagglutinin A (hagA) gene. A recombinant glutathione S-transferase (GST)-HGP17 fusion protein reacted to antiserum against the 18 kDa protein and Pre. intermedia cells could adhere to GST-HGP17-conjugated Sepharose 4B beads, indicating that the HGP17 domain protein is responsible for Por. gingivalis vesicle-mediated aggregation of Pre. intermedia.

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

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

Antimicrobial effects of mechanical debridement

Self-performed plaque removal using manual or powered toothbrushes and interdental cleaning devices is improved in subjects that have received oral hygiene instructions. Personal oral hygiene coupled with regular professional supragingival debridement may further improve the level of plaque control but still fails to achieve a completely plaque-free dentition. Both patient-performed and professional supragingival plaque removal has an effect on subgingival microbiota that is limited to the marginal 3 mm of the periodontal pocket. At sites with 4 mm or more of probing depth, only subgingival scaling leads to a significant reduction of the bacterial load. The subgingival microflora can be further reduced by pocket elimination surgery. Due to the sequence of bacterial recolonization that occurs following mechanical debridement, the level of periodontal pathogens such as B. forsythus, P. gingivalis and T. denticola may be reduced for several months. Mechanical debridement also influences the patient's immune system response, resulting in antibody titers and avidity against periodontal pathogens. As a basis for the restoration and maintenance of periodontal health, repeated subgingival debridement, as performed in supportive periodontal therapy, can reduce the number and proportions of periodontopathogenic bacteria in subgingival plaque. However, intensive subgingival scaling and root planing should be avoided in sites that probe less than 3 mm, as this is likely to traumatize the periodontium and cause attachment loss.

Influence of secondary colonizers and human plasma on the adherence of Porphyromonas gingivalis in vitro

The influence of secondary colonizers (Fusobacterium nucleatum and Actinomyces naeslundii) and the effect of human plasma on the adherence of Porphyromonas gingivalis were investigated. Hydroxyapatite (HAP) discs coated with Streptococcus sanguis were immersed in a 3H-labeled bacterial cell suspension of F. nucleatum or A. naeslundii and then in a 14C-labeled P. gingivalis cell suspension. Bacterial cells on the discs were pyrolysed to quantify the radioisotopes released. The cell numbers of secondary colonizers on the discs increased with immersion time and this, in turn, resulted in significantly elevated adherence of P. gingivalis. These two secondary colonizers had very similar positive effects on the adherence of P. gingivalis. Human plasma significantly inhibited the adherence of P. gingivalis and secondary colonizers to S. sanguis-coated HAP discs. Adherence of P. gingivalis and A. naeslundii was strongly inhibited by plasma, while that of F. nucleatum was affected the least. Treatment with plasma, after immersion of streptococcal-coated discs in individual cell suspension of secondary colonizers, also reduced subsequent adherence of P. gingivalis. The rate of decrease was much smaller in F. nucleatum. These results indicate that both F. nucleatum and A. naeslundii enhance the adherence of P. gingivalis, and that the former may play a more important role in the establishment of P. gingivalis in dental plaque where plasma-derived components are present.

Cytokine production induced by a 67-kDa fimbrial protein from Porphyromonas gingivalis

Fimbriae have been reported to play an important role in the adherence of Porphyromonas gingivalis to oral surfaces and possibly in triggering host responses. P. gingivalis ATCC 33277 has two distinctly different fimbriae expressed on the cell surface. The 67-kDa fimbriae differ in size and antigenicity from the earlier reported FimA, a major 41-kDa fimbrial component of P. gingivalis. Expression of the 67-kDa fimbriae on the cell surface of a fimA mutant was investigated by electron microscopy. The 67-kDa fimbrial protein was purified from the fimA mutant by sonication, precipitation, and chromatography on a DEAE Sepharose CL-6B column. The N-terminal amino acid sequence of the 67-kDa fimbrillin was distinct from that of the 41-kDa fimbrillin. Moreover, we have found that the 67-kDa fimbrial protein from P. gingivalis ATCC 33277 induced IL-1alpha, IL-beta, IL-6 and TNFalpha cytokine expression in mouse peritoneal macrophages. These results suggest that P. gingivalis 67-kDa fimbriae may play a part in the inflammatory response during the development of periodontal diseases.

Passive immunization against dental caries and periodontal disease: development of recombinant and human monoclonal antibodies

Indigenous micro-organisms in the oral cavity can cause two major diseases, dental caries and periodontal diseases. There is neither agreement nor consensus as to the actual mechanisms of pathogenesis of the specific virulence factors of these micro-organisms. The complexity of the bacterial community in dental plaque has made it difficult for the single bacterial agent of dental caries to be determined. However, there is considerable evidence that Streptococcus mutans is implicated as the primary causative organism of dental caries, and the cell-surface protein antigen (SA I/II) as well as glucosyltransferases (GTFs) produced by S. mutans appear to be major colonization factors. Various forms of periodontal diseases are closely associated with specific subgingival bacteria. Porphyromonas gingivalis has been implicated as an important etiological agent of adult periodontitis. Adherence of bacteria to host tissues is a prerequisite for colonization and one of the important steps in the disease process. Bacterial coaggregation factors and hemagglutinins likely play major roles in colonization in the subgingival area. Emerging evidence suggests that inhibition of these virulence factors may protect the host against caries and periodontal disease. Active and passive immunization approaches have been developed for immunotherapy of these diseases. Recent advances in mucosal immunology and the introduction of novel strategies for inducing mucosal immune responses now raise the possibility that effective and safe vaccines can be constructed. In this regard, some successful results have been reported in animal experimental models. Nevertheless, since the public at large might be skeptical about the seriousness of oral diseases, immunotherapy must be carried out with absolute safety. For this goal to be achieved, the development of safe antibodies for passive immunization is significant and important. In this review, salient advances in passive immunization against caries and periodontal diseases are summarized, and the biotechnological approaches for developing recombinant and human-type antibodies are introduced. Furthermore, our own attempts to construct single-chain variable fragments (ScFv) and human-type antibodies capable of neutralizing virulence factors are discussed.

Coaggregation of Porphyromonas gingivalis and Prevotella intermedia

Porphyromonas gingivalis cells coaggregated with Prevotella intermedia cells. The coaggregation was inhibited with L-arginine, L-lysine, Nalpha-p-tosyl-L-lysine chloromethyl ketone, trypsin inhibitor, and leupeptin. Heat- and proteinase K-treated P. gingivalis cells showed no coaggregation with P. intermedia cells, whereas heat and proteinase K treatments of P. intermedia cells did not affect the coaggregation. The vesicles from P. gingivalis culture supernatant aggregated with P. intermedia cells, and this aggregation was also inhibited by addition of L-arginine or L-lysine and by heat treatment of the vesicles. The rgpA rgpB, rgpA kgp, rgpA rgpB kgp, and rgpA kgp hagA mutants of P. gingivalis did not coaggregate with P. intermedia. On the other hand, the fimA mutant lacking the FimA fimbriae showed coaggregation with P. intermedia as well as the wild type parent. These results strongly imply that a heat-labile and proteinous factor on the cell surface of P gingivalis, most likely the gingipain-adhesin complex, is involved in coaggregation of P. gingivalis and P. intermedia.

Bacteroides forsythus hemagglutinin is inhibited by N-acetylneuraminyllactose

Bacteroides forsythus, which has been recognized as a pathogen associated with periodontitis, produces a hemagglutinin. The hemagglutinin was localized in the envelope of B. forsythus. The hemagglutinating activity was inhibited by lactose at concentrations as low as 1 mM, and by L-arginine and L-lysine at concentrations of 100 mM. N-Acetylneuraminyllactose (NeuAc-lactose) was at least 100 times more potent an inhibitor than lactose, as it completely inhibited the hemagglutination at concentrations below 10 microM. This is similar to the Helicobacter pylori hemagglutinin. The hemagglutinin was heat-labile, and resistant to treatment with proteases such as trypsin. A specific antibody raised against one of the S-layer proteins that are major species-specific proteins had no inhibitory effect on the hemmaglutination. These results suggest that the NeuAc-lactose-sensitive adhesin of B. forsythus may play an important role in colonization in the oral cavity.

Discrete protein determinant directs the species-specific adherence of Porphyromonas gingivalis to oral streptococci

For pathogens to survive in the human oral cavity, they must identify a suitable niche in the complex multispecies biofilm that exists on oral tissues. The periodontal pathogen Porphyromonas gingivalis adheres to Streptococcus gordonii by interacting with a specific region of the streptococcal SspB polypeptide, designated BAR. However, it does not adhere to Streptococcus mutans, which expresses SpaP, a highly conserved homolog of SspB. Comparison of the predicted secondary structure of BAR with the corresponding region of SpaP suggested that the substitution of Asn for Gly1182 and Val for Pro1185 in SspB may confer a unique local structure that is not conserved in SpaP. A synthetic peptide of 26 amino acids that encompassed residues 1167 to 1193 of SspB promoted avid adherence of P. gingivalis, whereas a peptide derived from the region corresponding to BAR in SpaP was inactive. Substitution of Gly1182 and Pro1185 for Asn1182 and Val1185 in SspB by site-specific mutation generated proteins that were predicted to assume an SpaP-like secondary structure, and the purified proteins did not promote P. gingivalis adherence. Furthermore, Enterococcus faecalis strains expressing the site-specific mutants did not support adherence of P. gingivalis cells. In contrast, P. gingivalis adhered efficiently to E. faecalis strains expressing intact SspB or SspB-SpaP chimeric proteins containing BAR. These results suggest that a region of SspB consisting of 26 amino acids is sufficient to mediate the adherence of P. gingivalis to S. gordonii and that the species specificity of adherence arises from its interaction with a discrete structural determinant of SspB that is not conserved in SpaP.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Identification of a Porphyromonas gingivalis receptor for the Streptococcus gordonii SspB protein

Colonization of the plaque biofilm by the oral pathogen Porphyromonas gingivalis is favored by the presence of antecedent organisms such as Streptococcus gordonii. Coadhesion between P. gingivalis and S. gordonii can be mediated by the SspB protein of S. gordonii; however, the P. gingivalis cognate receptor for this protein has not been identified. In this study, we identified a surface protein of P. gingivalis that interacts with the SspB protein. Coprecipitation between P. gingivalis outer membrane proteins and purified SspB protein demonstrated that a 100-kDa P. gingivalis protein bound to SspB. The 100-kDa protein also bound to an engineered strain of Enterococcus faecalis that expresses the SspB protein on the cell surface. Monospecific polyclonal antibodies to the 100-kDa protein inhibited the binding between P. gingivalis and S. gordonii in a dose-dependent manner up to 86%. Amino acid sequencing of the 100-kDa protein showed homology to a protein previously identified as the P. gingivalis minor fimbria. The minor fimbrial protein may exist as a complex with a hemagglutinin-like protein since the genes encoding these proteins are adjacent on the chromosome and are cotranscribed. Thus, the P. gingivalis receptor for S. gordonii SspB is a 100-kDa protein that structurally may be a minor fimbria-protein complex and functionally effectuates coadhesion.

Subgingival colonization by Porphyromonas gingivalis

Porphyromonas gingivalis, a gram-negative anaerobe, is a major causative agent in the initiation and progression of severe forms of periodontal disease. In order to cause periodontal disease, P. gingivalis must colonize the subgingival region, a process that involves several distinct steps and multiple gene products. The organism must first navigate within the oral fluids in order to reach the hard or soft tissues of the mouth. Retention and growth of bacteria on these surfaces is facilitated by a repertoire of adhesins including fimbriae, hemagglutinins and proteinases. Once established subgingivally, P. gingivalis cells participate in intercellular communication networks with other oral prokaryotic cells and with eukaryotic cells. The establishment of these multiple interactive interfaces can lead to biofilm formation, invasion of root dentin and internalization within gingival epithelial cells. The resulting bacterial and host cellular locations, products and fate contribute to the success of P. gingivalis in colonizing the periodontal region.

Dental plaque formation

Dental plaque is a complex biofilm that accumulates on the hard tissues (teeth) in the oral cavity. Although over 500 bacterial species comprise plaque, colonization follows a regimented pattern with adhesion of initial colonizers to the enamel salivary pellicle followed by secondary colonization through interbacterial adhesion. A variety of adhesins and molecular interactions underlie these adhesive interactions and contribute to plaque development and ultimately to diseases such as caries and periodontal disease.

Pleiotropic pigmentation mutants of Porphyromonas gingivalis

Porphyromonas gingivalis is a Gram-negative, black pigmented oral anaerobe associated with adult periodontitis. The adherence of the bacterium to junctional epithelial cells is the first step in infection and colonization. The molecular mechanisms and genetics of colonization are, as yet, not well understood, although it has been demonstrated that P. gingivalis fimbriae are involved in adhesion. In addition, cell surface cysteine proteinases may play a role either directly as adhesins or indirectly through their involvement in the biogenesis of fimbriae. A link has been established between cysteine proteinase-hemagglutinating activity and colongy pigmentation on blood agar. In this study a P. gingivalis ATCC 33277 transposon library was screened for white mutants. Pleiotropic mutants were identified with altered pigmentation, proteinase, hemagglutinin and haemolytic activities. Although the mutants fell into two classes based on the above phenotypes, by electron microscopy both classes showed increased fimbriation and decreased vesicle formation. Sequencing of genomic DNA flanking the transposon insertions revealed that one class of mutants carried disruptions in the gene encoding Lys-gingipain (kgp) and the other in a gene homologous to a glycosyl transferase. Potential roles for these genes in pigmentation, fimbriation, vesicle formation and attachment to epithelial cells are discussed.

The relationship between gingivitis and colonization by Porphyromonas gingivalis and Actinobacillus actinomycetemcomitans in children

BACKGROUND

Porphyromonas gingivalis and Actinobacillus actinomycetemcomitans are closely associated with the onset and severity of adult periodontal disease. However, little is known regarding the colonization by, and host antibody response to, these microorganisms in children.

METHODS

Plaque and sera were obtained from 40 healthy children, 2 to 18 years old. Gingival health was assessed by the periodontal disease index (PDI), papillary bleeding score (BS) and the modified total papillary margin attachment index (M-PMA). P. gingivalis and A. actinomycetemcomitans in plaque samples were detected by slot immunoblotting (SIB). Serum antibody levels against these microorganisms were evaluated using ELISA.

RESULTS

More than 60% of the children had detectable levels of P. gingivalis in their plaque. Those having detectable levels had more gingival inflammation than those having none; however, these differences were significant only in children over the age of 12 years (PDI, BS). In contrast, while 75% of the children had detectable A. actinomycetemcomitans, there were significant differences in gingival inflammation associated with colonization in children from 3 to 7 years of age (PDI) and over 12 years of age (M-PMA). Serum antibody levels to P. gingivalis were inversely correlated with gingival inflammation in all age groups, while A. actinomycetemcomitans titers were positively correlated with gingival inflammation only in the children over 12 years. No significant relationship between the presence of either A. actinomycetemcomitans or P. gingivalis and antibodies to them was found.

CONCLUSIONS

Our findings show that P. gingivalis and A. actinomycetemcomitans are readily detected as early as 3 years of age and that their presence is associated with the onset and severity of gingivitis.

Peptostreptococcus micros coaggregates with Fusobacterium nucleatum and non-encapsulated Porphyromonas gingivalis

Coaggregation is one of the potential colonization strategies of oral microorganisms, often involving fimbrial structures in the interactions. In this study, the coaggregation characteristics of the rough and smooth genotypes of the periodontal pathogen Peptostreptococcus micros were compared to investigate the role of the fibril-like structures of the rough genotype in coaggregation. Of the 11 oral species tested, only Fusobacterium nucleatum strains and non-encapsulated Porphyromonas gingivalis strains coaggregated with P. micros. No differences in coaggregation between the smooth type (Sm), the rough type (Rg) and the smooth variant of the Rg type (Rg(Sm)) of P. micros were observed. Heat-stable, periodate-sensitive structures on P. micros appeared to interact with heat- and protease-sensitive structures on F. nucleatum and P. gingivalis. These data indicate that these unimodal coaggregations are not mediated by the proteinaceous fibril-like structures of the Rg genotype, but by carbohydrates present on both genotypes of P. micros.

Genetic analyses of proteolysis, hemoglobin binding, and hemagglutination of Porphyromonas gingivalis. Construction of mutants with a combination of rgpA, rgpB, kgp, and hagA

Porphyromonas gingivalis produces arginine-specific cysteine proteinase (Arg-gingipain, RGP) and lysine-specific cysteine proteinase (Lys-gingipain, KGP) in the extracellular and cell-associated forms. Two separate genes (rgpA and rgpB) and a single gene (kgp) have been found to encode RGP and KGP, respectively. We constructed rgpA rgpB kgp triple mutants by homologous recombination with cloned rgp and kgp DNA interrupted by drug resistance gene markers. The triple mutants showed no RGP or KGP activity in either cell extracts or culture supernatants. The culture supernatants of the triple mutants grown in a rich medium had no proteolytic activity toward bovine serum albumin or gelatin derived from human type I collagen. Moreover, the mutants did not grow in a defined medium containing bovine serum albumin as the sole carbon/energy source. These results indicate that the proteolytic activity of P. gingivalis toward bovine serum albumin and gelatin derived from human type I collagen appears to be attributable to RGP and KGP. The hemagglutinin gene hagA of P. gingivalis possesses the adhesin domain regions responsible for hemagglutination and hemoglobin binding that are also located in the C-terminal regions of rgpA and kgp. A rgpA kgp hagA triple mutant constructed in this study exhibited no hemagglutination using sheep erythrocytes or hemoglobin binding activity, as determined by a solid-phase binding assay with horseradish peroxidase-conjugated human hemoglobin, indicating that the adhesin domains seem to be particularly important for P. gingivalis cells to agglutinate erythrocytes and bind hemoglobin, leading to heme acquisition.

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.

Oral ecology and person-to-person transmission of Actinobacillus actinomycetemcomitans and Porphyromonas gingivalis

The ecological characteristics of the oral cavity are dissimilar for A. actinomycetemcomitans and for P. gingivalis, as judged by differences in their colonization preferences and patterns, associations with periodontal disease parameters, relationships with the subgingival microbiota and the type of periodontitis and their clonal persistence in the oral cavity. These features also suggest that as a periodontal pathogen, A. actinomycetemcomitans is different from P. gingivalis. Probably in most infected individuals, low levels of A. actinomycetemcomitans can persist for years in equilibrium with the host and the resident oral microbiota. However, it is well established that A. actinomycetemcomitans can cause disease in some individuals or in some circumstances when the regulatory mechanisms are unable to maintain homeostasis in the ecosystem. Elevated A. actinomycetemcomitans proportions of the biota can be regarded as a sign of ecological imbalance, leading to increased risk of periodontal destruction. There is also evidence showing elevated pathogenic potential of certain A. actinomycetemcomitans clones. Although A. actinomycetemcomitans seems to be relatively rarely transmitted between cohabiting adults, transmission can occur to periodontally healthy children of A. actinomycetemcomitans-positive parents. Parents and children may share factors that promote successful oral colonization of A. actinomycetemcomitans, or the window of opportunity is in childhood. Therefore, to prevent parent-child transmission of A. actinomycetemcomitans, bacterium-positive parents of young children are optimal targets for enhanced information and treatment. In selected populations, screening for specific clones of A. actinomycetemcomitans has been employed in prevention of peridontitis. Future research aiming at finding the reasons which cause the changes in the oral homeostasis to allow the growth of A. actinomycetemcomitans may give insight into novel prevention strategies for A. actinomycetemcomitans-associated periodontitis. Compared with A. actinomycetemcomitans, P. gingivalis shows a different pattern of coexistence with the host. In periodontal health or in children, P. gingivalis is absent or only rarely detected. When present, P. gingivalis is commonly recovered in high numbers from dentitions exhibiting inflamed periodontitis and poor oral hygiene. Contrary to A. actinomycetemcomitans, the data on the vertical transmission of P. gingivalis are limited. The major infection route of P. gingivalis seems to be between adults, indicating that P. gingivalis commonly colonizes in an established oral microbiota. These characteristics suggest that the degree of tolerance between P. gingivalis and the host is inferior to that between A. actinomycetemcomitans and the host. It appears that the association of P. gingivalis with disease is a rule rather than an accidental incident. On these grounds, it seems that the host-P. gingivalis relationship approaches antibiosis. Since P. gingivalis infection is related to a typical periodontal eco-pathology, the susceptibility to person-to-person transmission of this pathogen may be controlled by periodontal treatment and emphasizing the significance of high standard oral hygiene.

Determination and characterization of the hemagglutinin-associated short motifs found in Porphyromonas gingivalis multiple gene products

Porphyromonas gingivalis is a Gram-negative anaerobic bacterial species implicated as an important pathogen in the development of adult periodontitis. In our studies of P. gingivalis and ways to protect against periodontal disease, we have prepared the monoclonal antibody mAb-Pg-vc and its recombinant antibody, which are capable of inhibiting the hemagglutinating activity of P. gingivalis (Shibata, Y., Kurihara, K., Takiguchi, H., and Abiko, Y. (1998) Infect. Immun. 66, 2207-2212). To clarify the antigenically related hemagglutinating domains, we attempted to determine the minimum motifs responsible for P. gingivalis hemagglutinin. Initially, the 9-kilobase EcoRI fragment encoding the 130-kDa protein was cloned from the P. gingivalis chromosome using mAb-Pg-vc. Western blot analysis of nested deletion clones, the competition experiments using synthetic peptides, and the binding assay of the phage-displayed peptides using the mAb-Pg-vc allowed us to identify the minimum motifs, PVQNLT. Furthermore, the presence of multi-gene family coding for this epitope was confirmed via Southern blot analysis and PCR using the primers complementary to the domain corresponding to this epitope. It is suggested that the hemagglutinin-associated motif may be PVQNLT and that the gene families specifying this motif found in P. gingivalis chromosome encode many hemagglutinin and/or hemagglutinin-related proteases.

Adherence of Peptostreptococcus micros morphotypes to epithelial cells in vitro

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

Life below the gum line: pathogenic mechanisms of Porphyromonas gingivalis

Porphyromonas gingivalis, a gram-negative anaerobe, is a major etiological agent in the initiation and progression of severe forms of periodontal disease. An opportunistic pathogen, P. gingivalis can also exist in commensal harmony with the host, with disease episodes ensuing from a shift in the ecological balance within the complex periodontal microenvironment. Colonization of the subgingival region is facilitated by the ability to adhere to available substrates such as adsorbed salivary molecules, matrix proteins, epithelial cells, and bacteria that are already established as a biofilm on tooth and epithelial surfaces. Binding to all of these substrates may be mediated by various regions of P. gingivalis fimbrillin, the structural subunit of the major fimbriae. P. gingivalis is an asaccharolytic organism, with a requirement for hemin (as a source of iron) and peptides for growth. At least three hemagglutinins and five proteinases are produced to satisfy these requirements. The hemagglutinin and proteinase genes contain extensive regions of highly conserved sequences, with posttranslational processing of proteinase gene products contributing to the formation of multimeric surface protein-adhesin complexes. Many of the virulence properties of P. gingivalis appear to be consequent to its adaptations to obtain hemin and peptides. Thus, hemagglutinins participate in adherence interactions with host cells, while proteinases contribute to inactivation of the effector molecules of the immune response and to tissue destruction. In addition to direct assault on the periodontal tissues, P. gingivalis can modulate eucaryotic cell signal transduction pathways, directing its uptake by gingival epithelial cells. Within this privileged site, P. gingivalis can replicate and impinge upon components of the innate host defense. Although a variety of surface molecules stimulate production of cytokines and other participants in the immune response, P. gingivalis may also undertake a stealth role whereby pivotal immune mediators are selectively inactivated. In keeping with its strict metabolic requirements, regulation of gene expression in P. gingivalis can be controlled at the transcriptional level. Finally, although periodontal disease is localized to the tissues surrounding the tooth, evidence is accumulating that infection with P. gingivalis may predispose to more serious systemic conditions such as cardiovascular disease and to delivery of preterm infants.

Preparation and characterization of an Actinomyces naeslundii aggregation factor that mediates coaggregation with Porphyromonas gingivalis

Intergeneric coaggregation is responsible for the complexity of the microbiota in human dental plaque and is believed to be important in the initial bacterial colonization of the human oral cavity. Actinomyces naeslundii, an early colonizer of the tooth surface, may enhance subsequent colonization by Porphyromonas gingivalis which is associated with adult periodontitis. The purpose of this study was to isolate and characterize the A. naeslundii aggregation factor (AnAF) that mediates coaggregation with P. gingivalis. AnAF was isolated from A. naeslundii sonic extract (SE) by gel filtration on a Sephacryl S-400HR, by hydrophobic interaction chromatography on a HiTrap Octyl Sepharose 4FF, and by ion exchange chromatography on a HiTrap Q. The specific activity increased 12-fold with a yield of 2.5%. SDS-PAGE analysis of AnAF revealed a protein band of high molecular weight in excess of 200 kDa. Carbohydrate was detected as the only material coinciding with the protein band, indicating that the AnAF was a glycoprotein. Immunoblotting analysis indicated that AnAF directly bound to P. gingivalis cells. AnAF was sensitive to sodium metaperiodate treatment but not to heat or protease treatments. These results suggest that the AnAF carbohydrate component mediated coaggregation with P. gingivalis cells. AnAF also inhibited coaggregation with other periodontal disease-associated bacteria such as Prevotella intermedia, Fusobacterium nucleatum, Capnocytophaga ochracea, but not streptococci.

Arg-gingipain acts as a major processing enzyme for various cell surface proteins in Porphyromonas gingivalis

Arg-gingipain (RGP) is an Arg-X-specific cysteine proteinase produced by the Gram-negative anaerobe Porphyromonas gingivalis and has been shown to be a potent virulence factor in progressive periodontal disease (Nakayama, K., Kadowaki, T., Okamoto, K., and Yamamoto, K. (1995) J. Biol. Chem. 270, 23619-23626). In this study, we provide evidence that RGP acts as a major processing enzyme for various cell surface and secretory proteins in P. gingivalis. Fimbrilin, a major component of fimbriae, remained in the precursor form in the RGP-null mutant. Prefimbrilin expressed in Escherichia coli was converted to the mature fimbrilin in vitro when incubated with purified RGP, but its conversion was suppressed by potent RGP inhibitors. The results were consistent with the electron microscopic observation indicating little or no fimbriation in the RGP-null mutant. The immunogenic 75-kDa cell surface protein was also shown to retain its proform in the RGP-null mutant. In addition, Lys-gingipain (KGP) was found to be abnormally processed in the RGP-null mutant. In contrast, both prefimbrilin and the 75-kDa protein precursor were processed to their respective mature forms in the KGP-null mutant, suggesting that KGP is not involved in the normal processing mechanisms of these proteins. These results suggest that RGP not only acts as a direct virulence factor but also makes a significant contribution as a major processing enzyme to the virulence of P. gingivalis.

Biofilm formation by Porphyromonas gingivalis and Streptococcus gordonii

Confocal scanning laser microscopy (CSLM) was used to visualize and quantify biofilm formation by the oral bacteria Streptococcus gordonii and Porphyromonas gingivalis. A saliva-coated glass coverslip under continuous bacterial challenge and conditions of low shear force was used to investigate attachment to the salivary pellicle and also the effect of cell-cell interactions on the extent of colonization and biofilm development. S. gordonii bound to the salivary pellicle and outcompeted P. gingivalis for attachment sites. Both P. gingivalis and S. gordonii failed to establish substantial biofilm formation independently. However, biofilm formation did occur subsequent to initial adherence of P. gingivalis to S. gordonii cells deposited on the salivary pellicle. The commensal species S. gordonii may, therefore, provide an attachment substrate for colonization and biofilm accretion by the potential pathogen, P. gingivalis.

The importance of fimbriae in the virulence and ecology of some oral bacteria

Cumulative evidence indicates that bacterial adherence to mucosal and tooth surfaces as well as bacterial coaggregation are essential steps for colonization of various oral bacterial species. Bacterial fimbriae have been shown to play an important role in the interaction between bacteria and host cells or among bacterial cells. The properties of fimbriae from selected species of oral bacteria are discussed in terms of virulence traits and ecological significance. Among others, Porphyromonas gingivalis fimbriae have been most extensively studied. The fimbrial structure is composed of 41-kDa fimbrillin proteins. DNA sequencing of the fimbrillin gene (fimA) from nine strains of P. gingivalis suggests intraspecies variation in the structure of fimA, while retaining common immunochemical specificities. P. gingivalis fimbriae exhibit a wide variety of biological activities including immunogenicity, binding to various host proteins, stimulation of cytokine production and promotion of bone resorption, Actinobacillus actinomycetemcomitans also possesses fimbriae; however, little is known concerning their chemical, genetical, and biological properties. Fimbriae of Prevotella intermedia are shown to induce hemagglutination reaction, while those of Prevotella loescheii are found to cause coaggregation with other bacteria, i.e., Actinomyces viscosus and sanguis streptococci. Fimbriae from gram-positive oral bacteria such as oral Actinomyces and sanguis streptococci are described. These fimbriae may participate in coaggregation, binding to saliva-coated hydroxyapatite or glycoprotein of the surface layer of oral epithelial cells. Taken together, fimbriae are key components in cell-to-surface and cell-to-cell adherence of oral bacteria and pathogenesis of some oral and systemic diseases.

Identification of a Streptococcus gordonii SspB domain that mediates adhesion to Porphyromonas gingivalis

Porphyromonas gingivalis, a primary pathogen in adult periodontitis, may establish itself in the oral cavity by adhering to early plaque bacteria such as Streptococcus gordonii. Our previous studies (R. J. Lamont et al., Microbiology 140:867-872, 1994) suggested that this interaction is mediated by the SspB polypeptide, a member of the antigen I/II family of streptococcal surface proteins. S. gordonii was recently shown to express a second Ssp polypeptide (SspA) that resembles SspB and the structurally homologous antigen I/II polypeptide (Pac) of Streptococcus mutans. To determine if all of these related antigen I/II proteins interacted with P. gingivalis, SspA, SspB, and Pac were tested for adhesion to P. gingivalis cells. Both of the S. gordonii Ssp proteins bound labeled target cells, whereas the S. mutans Pac polypeptide did not, suggesting that antigen I/II-mediated binding of P. gingivalis by streptococci may be species specific. To investigate the molecular basis for this functional difference, the P. gingivalis binding domain of SspB was mapped. The binding properties of a family of truncated SspB polypeptides lacking C-terminal sequences were determined. In addition, the lack of binding activity exhibited by the Pac protein was exploited to construct and analyze chimeric SspB-Pac polypeptides. Both approaches revealed that the region defined by residues 1167 to 1250 of SspB was essential for P. gingivalis binding. This region of SspA and SspB is entirely conserved, consistent with the binding properties determined for these proteins. However, the corresponding region of Pac differs in both the primary sequence and predicted secondary structure, suggesting that the overall structure of this domain may define its functional activity.

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

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

Inhibition of a Porphyromonas gingivalis colonizing factor between Actinomyces viscosus ATCC 19246 by monoclonal antibodies against recombinant 40-kDa outer-membrane protein

1. Porphyromonas gingivalis, an important pathogen in human periodontal disease, aggregates with Actinomyces viscosus ATCC 19246. 2. Monoclonal antibodies (mAbs) against purified recombinant 40-kDa outer-membrane protein (r40-kDa, OMP) of P. gingivalis 381 inhibited its coaggregation with A. viscosus ATCC 19246 in a dose-dependent manner. 3. Five mAb clones against r40-kDa OMP were selected. The isotype of the five was IgG1. 4. Pg-ompA2 inhibited the coaggregation of several strains of P. gingivalis with A. viscosus ATCC 19246 cells.

Role of the carboxyl-terminal region of Porphyromonas gingivalis fimbrillin in binding to salivary proteins

Porphyromonas gingivalis fimbriae are considered to play an important role in the adherence and colonization of the bacteria in the oral cavity. In this study, we generated and purified three carboxyl-terminal variants of recombinant fimbrillin (r-FimA 224-337, r-FimA 266-337, and r-FimA 287-337, corresponding to amino acid residues 224 to 337, 266 to 337, and 287 to 337, respectively, of the 43-kDa fimbrillin of P. gingivalis 2561). They were used as inhibitors of P. gingivalis cell binding to human salivary protein-coated hydroxyapatite (HAP) beads. All of the carboxyl-terminal region polypeptides inhibited binding in a dose-dependent manner; however, the inhibitory effect of r-FimA 287-337 was less than that of the other two polypeptides when HAP beads were coated with whole saliva or purified salivary proline-rich protein 1 (PRP1). Assays of binding of a synthetic peptide corresponding to amino acid residues 266 to 286 of P. gingivalis 2561 fimbrillin to salivary proteins showed that this peptide bound strongly to whole saliva or PRP1 but only weakly to statherin. These results suggest that the carboxyl-terminal region corresponding to amino acid residues 266 to 337 of P. gingivalis fimbrillin plays an important role in binding to salivary proteins and that the domain corresponding to amino acids 266 to 286 is likely a major binding site for PRP1s and the domain corresponding to amino acids 287 to 337 is likely a major binding site for statherin.

Multiple colonization defects in a cysteine protease mutant of Porphyromonas gingivalis

A cysteine protease mutant, G-102, of Porphyromonas gingivalis 381 defective in the rgp-1 gene has been recently constructed in this laboratory. In order to evaluate the role of the protease in the virulence properties of P. gingivalis, a number of putative periodontopathic properties of the mutant were evaluated. Relative to the parental strain, mutant G-102 was demonstrated to be defective in interacting with Gram-positive bacteria as well as cultured epithelial cells. In addition, the mutant was altered in attaching to the protein components of extracellular matrix as well as to type I collagen. Some of these alterations could result from the decreased autoaggregation displayed by mutant G-102 relative to strain 381. However, since the epithelial cell attachment assays were carried out at very low bacterial densities, it is unlikely that reduced autoaggregation of the mutant is responsible for its decreased ability to attach to these eucaryotic cells. Electron microscopic examination of the cells also revealed that mutant G-102 was altered in normal fimbrae expression. In addition, reduced expression of the 43 kDa fimbrial subunit in the mutant was detected with both Western and Northern blotting. These results indicated that the rgp-1 gene product can play either a direct or indirect role in the colonization properties of P. gingivalis.

Streptococcal adhesion and colonization

Streptococci express arrays of adhesins on their cell surfaces that facilitate adherence to substrates present in their natural environment within the mammalian host. A consequence of such promiscuous binding ability is that streptococcal cells may adhere simultaneously to a spectrum of substrates, including salivary glycoproteins, extracellular matrix and serum components, host cells, and other microbial cells. The multiplicity of streptococcal adherence interactions accounts, at least in part, for their success in colonizing the oral and epithelial surfaces of humans. Adhesion facilitates colonization and may be a precursor to tissue invasion and immune modulation, events that presage the development of disease. Many of the streptococcal adhesins and virulence-related factors are cell-wall-associated proteins containing repeated sequence blocks of amino acids. Linear sequences, both within the blocks and within non-repetitive regions of the proteins, have been implicated in substrate binding. Sequences and functions of these proteins among the streptococci have become assorted through gene duplication and horizontal transfer between bacterial populations. Several adhesins identified and characterized through in vitro binding assays have been analyzed for in vivo expression and function by means of animal models used for colonization and virulence. Information on the molecular structure of adhesins as related to their in vivo function will allow for the rational design of novel acellular vaccines, recombinant antibodies, and adhesion agonists for the future control or prevention of streptococcal colonization and streptococcal diseases.

Endotoxic properties of free lipid A from Porphyromonas gingivalis

The relationship between chemical structure and biological activity of the lipid A from Porphyromonas gingivalis, which we recently isolated and whose complete chemical structure was determined [Kumada et al. (1995). J Bacteriol 177, 2098-2106], was studied. The lipid A exhibited endotoxic activity in all the assay systems tested: Limulus gelation activity, lethal toxicity in galactosamine-sensitized mice, mitogenicity in mouse spleen cells and induction of nitric oxide (NO) and tumour necrosis factor alpha (TNF) release from both mouse peritoneal macrophages and the J774-1 mouse macrophage-like cell line. The activity was, however, about 100-fold less than that of Salmonella minnesota LPS used as a control. The moderate activity of the lipid A may be partially explained by its unique fatty acid composition and the lack of a phosphate group in position 4. In contrast, the lipid A as well as whole LPS of P. gingivalis unexpectedly exhibited an even stronger induction of TNF from the human monocytic THP-1 cell line than control LPS when measured by the minimum stimulatory dose. The difference in sensitivity of human and mouse cells to P. gingivalis lipid A suggests that the recognition mechanism, including that for the receptor for endotoxin, may be regulated in different ways in the two cells.

Adhesion of Porphyromonas gingivalis fimbriae to human gingival cell line Ca9-22

In this study, we examined the effects of selected environmental factors on the adhesion of Porphyromonas gingivalis fimbriae, an important structure involved in attachment of the bacteria to human gingival cells. The human gingival carcinoma cell line Ca9-22 was grown in microculture plates, and adherence was detected by use of 125I-labeled fimbriae. Adhesion was increased by changes in pH from 7.0-8.0, but was decreased by increase in the sodium chloride concentration above 0.15 M. Trypsin treatment of Ca9-22 cells also augmented adhesion of the fimbriae to the cells. These results indicate that fimbrial adhesion to gingival cells is controlled by various environmental factors, and the data on trypsin treatment suggest that elevated levels of protease in the gingival sulcus, such as can occur with poor oral hygiene and gingivitis, may expose adhesion molecules on the gingival cell surface, thereby promoting the attachment of P. gingivalis fimbriae.

Isolation and characterization of a minor fimbria from Porphyromonas gingivalis

We have discovered two distinctly different fimbriae expressed by the same Porphyromonas gingivalis strain. The construction of a fimA mutant of P. gingivalis ATCC 33277 has previously been reported by N. Hamada et al. (Infect. Immun. 62:1696-1704, 1994). Expression of fimbriae on the surface of the fimA mutant and the wild-type strain, ATCC 33277, were investigated by electron microscopy. The wild-type strain produced long fimbrial structures extending from the cell surface, whereas those structures were not observed on the fimA mutant. However, short fimbrial structures were seen on the surface of the fimA mutant. The short fimbrial protein was purified from the fimA mutant by selective protein precipitation and chromatography on DEAE Sepharose CL-6B. We have found that the second fimbrial structure of P. gingivalis ATCC 33277 is distinct from the 41-kDa (43-kDa) major fimbrial protein (FimA). We provisionally call this protein minor fimbriae. The molecular mass of the minor fimbriae is 67 kDa as estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis under reducing conditions after boiling at 100 degrees C. The component shows a ladder-like pattern at 80 degrees C under nonreducing conditions, suggesting a tendency to aggregate or polymerize. In immunoblotting analysis, anti-minor fimbria serum reacted with both the 100 degrees C- and the 80 degrees C-treated minor fimbriae. The anti-minor fimbria serum also reacts with the same-molecular-size fimbrial preparation from the wild-type strain. Immunogold electron microscopy showed that the anti-minor fimbria serum bound to the minor fimbria on the cell surface of the wild-type strain. This is the first report on the identification of the minor fimbria produced by P. gingivalis. These results suggest that the minor fimbriae appearing on the fimA mutant strain are produced together with numerous long major fimbriae on the wild-type strain. Moreover, the minor fimbriae are different in size and antigenicity from the earlier-reported FimA, a major 41-kDa fimbrial component of P. gingivalis.

Role of Porphyromonas gingivalis protease activity in colonization of oral surfaces

Cysteine proteases, including Arg-gingipain of Porphyromonas gingivalis, have been implicated as important virulence factors in periodontal diseases. These enzymes are also involved in the hemagglutinating activity of the organisms. In order to determine the role of proteases in the colonization of the gingival margin, we have compared the attachment properties of P. gingivalis 381 with those of its Arg-gingipain-defective mutant, G-102. Interactions with gram-positive bacteria, human oral epithelial cells, extracellular matrix proteins, and type I collagen were evaluated. In all cases, mutant G-102 was deficient in attachment relative to the parental strain. The mutant's defects could be explained, in part, by the weak autoaggregation displayed by the mutant, which appeared to result from altered fimbrial expression. Both Western blot (immunoblot) and Northern (RNA) blot analyses indicated reduced expression of the major 43-kDa fimbrillin subunit in the mutant. These results suggest that Arg-gingipain may play both direct and indirect roles in the colonization of the gingival margin. In addition, fimbriae may play a direct role in interacting with some host surfaces.

Binding sites of salivary statherin for Porphyromonas gingivalis recombinant fimbrillin

We investigated the binding sites of salivary statherin involved in the interaction with Porphyromonas gingivalis recombinant fimbrillin (r-Fim). Synthetic peptides representing statherin analogs were used to localize the binding domains of statherin. Peptide F4 (residues 29 to 43) significantly bound to r-Fim and inhibited r-Fim binding to statherin-coated hydroxyapatite beads. Successive peptides in which pairs of amino acid residues were deleted starting at the N terminus of peptide F4 were synthesized. Peptide N1 without Leu-29-Tyr-30 had significantly reduced direct binding and inhibition ability. The deletions of residues 31 to 40 had little effect on interaction with r-Fim. The tripeptide N6 representing Tyr-41-Thr-42-Phe-43 retained significant binding to r-Fim. Another set of peptides was synthesized by deleting individual amino acid residues from the C and N termini of peptide F4 to identify functional residues among the five putative functional residues 29, 30, and 41 to 43. Peptide C1 missing Phe-43 lost over 50% of its binding ability. Binding ability was gradually reduced with deletions from the peptides. Peptide C5 (amino acids 31 to 40) weakly affected direct binding and inhibition. Collectively, the results of this study suggests that Leu-29-Tyr-30 and Tyr-41-Thr-42-Phe-43 are important binding regions that mediate the binding of statherin to P. gingivalis fimbrillin.