Chemiluminescence of human leukocytes by black-pigmented Bacteroides strains from dental plaque and other sites

Evidence of recombination in Porphyromonas gingivalis and random distribution of putative virulence markers

The association of Porphyromonas gingivalis to periodontal disease is not clearly understood. Similar proportions of P. gingivalis may be cultivated from both inactive and actively degrading periodontal pockets. Differences in virulence among strains of P. gingivalis exist, but the molecular reason for this remains unknown. We examined the population structure of P. gingivalis to obtain a framework in which to study pathogenicity in relation to evolution. Phylogenetic trees derived from the sequencing of fragments of four housekeeping genes, ahp, thy, rmlB, and infB, in 57 strains were completely different with no correlation between clustering of strains in the four dendrograms. Combining the various alleles of the four gene fragments sequenced resulted in 41 different sequence types. The index of association, I(A), based on a single representative of each sequence type was 0.143 +/- 0.202, indicating a population at linkage equilibrium. Inclusion of all isolates for the calculation of I(A) resulted in a value of 0.206 +/- 0.171. This suggests an epidemic population structure supported by the finding of genetically identical strains in different parts of the world. We observed a random distribution of two virulence-associated mobile genetic elements, the ragB locus and the insertion sequence IS1598, among 132 strains tested. In conclusion, P. gingivalis has a nonclonal population structure characterized by frequent recombination. Our study suggests that particular genotypes, possibly with increased pathogenic potential, may spread successfully in the human population.

The capacity of Porphyromonas gingivalis to multiply under iron-limiting conditions correlates with its pathogenicity in an animal model

Isolates of Porphyromonas gingivalis have various abilities to induce infections in an animal model. The hypothesis of this study was that pathogenic strains of P. gingivalis could multiply under iron-limiting conditions, while non-pathogenic strains could not. Three pathogenic strains (W50, W83, and ATCC 49417) grew to a final optical density (660 nm) > 2 in horse serum, while the growth of the 3 non-pathogenic strains (ATCC 33277, LB13D-2, and HW24D-1) was negligible. When an excess of hemin or ferric chloride was added to the serum, significant growth of the non-pathogenic strains occurred. Under iron-limiting conditions, the pathogenic strains of P. gingivalis had a much lower requirement for human iron-loaded transferrin and hemin than the non-pathogenic strains. Proteolytic degradation of transferrin, which may be associated with the release of iron, was not markedly different for pathogenic and non-pathogenic strains. In addition, no relationship could be established between the level of 55Fe uptake from 55Fe-transferrin and the pathogenicity of strains. Our study provided evidence that the ability of P. gingivalis to multiply in vitro under iron-limiting conditions may be correlated with its ability to induce infections in an animal model. Isolates of P. gingivalis possessing a low requirement for iron are likely to have a higher potential for initiating periodontal infections.

Prevalence and distribution of six capsular serotypes of Porphyromonas gingivalis in periodontitis patients

Previous reports have described six serotypes based on K antigens in Porphyromonas gingivalis strains. The purpose of the present study was to investigate the prevalence and distribution of these serotypes in 185 patients with P. gingivalis-associated periodontitis. Polyclonal rabbit antisera, raised against each of the different type strains, were used in double-immunodiffusion and immunoelectrophoresis assays. In addition, a subset of 76 strains was investigated for the presence of capsular structures by means of the India ink and Bruce White staining techniques. These strains were also tested for auto-aggregation in phosphate-buffered saline (PBS). All six K serotypes were present in the study sample. In total, 84 (45.4%) patients were colonized with a K-typeable P. gingivalis strain with a predominance of types K5 (12%) and K6 (23.2%). A correlation was found between arbitrary age categories and the prevalence of currently known K serotypes, which were found in 60% of patients aged 12 to 30 years, in 49% of patients aged 31 to 50, and in 25% of patients aged 51 to 70 years. In the subset of 76 P. gingivalis strains, 32 (42.1%) were K-typeable. Fifty-three strains (69.7%) showed microscopic evidence of encapsulation, suggesting the existence of K serotypes other than K1 to K6. Twenty-one strains (27.6%) auto-aggregated in PBS and were not K-typeable, nor did they show any evidence of encapsulation. It was concluded that the majority of clinical P. gingivalis isolates is encapsulated and that encapsulation is associated with the presence of a K antigen. Auto-aggregation seems to be associated with the absence of a capsular structure and, consequently, the absence of a K antigen.

Release and activation of human neutrophil matrix metallo- and serine proteinases during phagocytosis of Fusobacterium nucleatum, Porphyromonas gingivalis and Treponema denticola

The phagocytic ingestion of reference strains and clinical isolates of Fusobacterium nucleatum, Porphyromonas gingivalis, and Treponema denticola by polymorphonuclear leukocytes (PMNs) and the concomitant release of PMN granule proteinases were studied by specific functional and immunological assays. PMNs were incubated with the microorganisms anaerobically at 37 degrees C for indicated time periods. The suspensions and pellets were used for phagocytic ingestion assay and electron microscopic study, respectively. The supernatants were used for the measurements of the amounts and activities of the released PMN enzymes including PMN gelatinase (MMP-9), collagenase (MMP-8), serine proteases (elastase and cathepsin G), and lactate dehydrogenase (LDH). Both fluorescence microscopy and transmission electron microscopy showed that F. nucleatum, P. gingivalis and T. denticola were ingested by the PMNs in comparable numbers. However, measurements of the enzymes released from the triggered PMNs revealed major differences among the three species. High amount of elastase was released from the PMNs triggered by F. nucleatum, but not by P. gingivalis or T. denticola. The treatment of PMNs with P. gingivalis whole cells resulted in the release of gelatinase partly in the 82 kD active form, suggesting proteolytic activation of the degranulated 92 kD proMMP-9. The 82 kD active form of gelatinase was not detected upon triggering the PMNs with F. nucleatum and T. denticola. The PMN-bacteria interaction did not result in release of LDH from triggered PMNs indicating the proteinase release was not due to the PMN cell death. The results show that the susceptibilities of the 3 potentially periodontopathogenic microorganisms, F. nucleatum, P. gingivalis and T. denticola to phagocytic ingestion are not directly related to the amounts and activities of PMN enzymes released during the bacteria-PMN interactions. As PMN degranulation is considered as one of the major pathogenic mechanisms in periodontitis, the observed differences among the microorganisms may be important virulence characteristics of these species.

Microbiologic factors in endodontology

The role of microorganisms in the cause of endodontic lesions has been intensively investigated. Bacterial components such as endotoxin and other cell wall components are implicated in the development of pulpal and periapical inflammation. Newer anaerobic microbiologic techniques have facilitated accurate and reproducible identification of endodontic pathogens, some of which have been reclassified. This article reviews and correlates newer microbiologic findings with clinical symptoms.

Elevated opsonic activity for Porphyromonas (Bacteroides) gingivalis in serum from patients with a history of destructive periodontal disease. A case: control study

We have measured the opsonic capacity of serum for the phagocytosis of Porphyromonas (Bacteroides) gingivalis by polymorphonuclear leucocytes (PMN) in 35 patients with a history of destructive periodontitis and 35 matched control subjects. The serum from cases, tested at concentrations of 8% and 0.8% opsonised P. gingivalis for phagocytosis by PMN to a level significantly greater than controls (p < 0.0001 and < 0.01 respectively). IgG antibody levels to P. gingivalis whole cells estimated by ELISA were also significantly higher in the cases (p < 0.0001). The IgG antibody levels correlated significantly with the opsonic capacity of the serum tested at 8% concentration in controls (r = 0.371, p = 0.03) but not in cases (r = 0.235, p = 0.17); in 0.8% serum, the opsonic capacity of the cases and controls were not significantly correlated. Elevated opsonisation by serum was a significant predictor that a subject was a case rather than a control, even after allowing for the effect of elevated IgG antibody in the cases. The data suggest that an elevated capacity of serum to opsonise P. gingivalis is a distinctive feature in patients with past destructive periodontal disease.

Characterization of recombinant and native forms of a cell surface antigen of Porphyromonas (Bacteroides) gingivalis

The cloning of genes encoding putative cell surface antigens of Porphyromonas gingivalis ATCC 33277 has been reported previously (B. C. McBride, A. Joe, and U. Singh, Arch. Oral Biol. 55:59S-68S, 1990). This study characterizes the recombinant protein rPgAg1, which is highly expressed in clone BA3, and the corresponding 51-kDa native antigen PgAg1. Cellular localization studies with monospecific antibodies to rPgAg1 in a Western immunoblot assay of a P. gingivalis membrane fraction and immunogold labeling of intact P. gingivalis cells confirmed the cell surface location of the native PgAg1 molecule. The pgag1 gene was found to be present in all four strains of P. gingivalis examined, and the gene product was expressed. Highly homologous DNA sequences and immunologically related proteins, however, were not detected in related species in the group formerly known as black-pigmented Bacteroides. This suggests that PgAg1 is specific to P. gingivalis and is highly conserved within this species. A protein data base search with the NH2-terminal amino acid sequence of rPgAg1 did not identify any significantly similar protein sequences. The high level of expression of rPgAg1 was not dependent on the insertional orientation of the cloned fragment. It therefore appears that a P. gingivalis promoter is present which is well recognized by the transcriptional apparatus of the Escherichia coli cloning host. The promoter element and structural gene for a specific cell surface antigen of P. gingivalis have been cloned.

Black-pigmented gram-negative anaerobes in endodontic infections

Necrotic dental root canal infections are polymicrobial infections dominated by anaerobic bacteria. The number of different species in one canal is usually low, approx. 4-7 species. The species isolated most frequently belong to the genera Prevotella, Porphyromonas, Fusobacterium, Peptostreptococcus, Eubacterium and Streptococcus. The frequency of isolation of black-pigmented Gram-negative anaerobes in endodontic infections varies from 25% to > 50%. Pr. intermedia is the most commonly found pigmented species, followed by Pr. denticola and two Porphyromonas species, P. gingivalis and P. endodontalis. Several studies have shown that P. gingivalis and P. endodontalis are closely related to the presence of acute symptoms in endodontic infections, whereas other black-pigmented Gram-negative anaerobes are not. However, several other species may also be involved in acute infections. Moreover, Porphyromonas species have occasionally been isolated from cases with no symptoms. Although Porphyromonas spp. are clearly related to symptoms at the beginning of therapy, they are not important for the prognosis of the treatment.

Differential morphological changes in human polymorphonuclear leucocytes induced by culture products of Porphyromonas (Bacteroides) Gingivalis W50 and its colonial variants with reduced virulence

The colonial variants of W50, derived after growth in a chemostat and previously designated W50/BP1, W50/BR1 and W50/BE1, produced black-, brown- and beige-pigmented colonies, respectively, and showed reductions in mouse virulence and proteolytic activity correlating with their reduced pigmentation. Incubation of glass-adherent polymorphonuclear leucocytes with culture supernatants from the virulent, highly proteolytic, black-pigmented strain produced significant changes in morphology when compared with changes among sterile bacterial growth medium treated, control polymorphonuclear leucocytes. Large, non-polar cells (greater than or equal to 18 microns dia) increased by 130% (p less than 0.01) while polarized and small non-polar cells (less than 18 microns dia) decreased by 48 and 30% (p less than 0.05), respectively. Changes in percentages of the different morphological forms of polymorphonuclear leucocyte after exposure to the culture supernatant from the less virulent W50/BR1 variant showed similar, though less marked trends, while the avirulent W50/BE1 variant failed to produce significant changes in any morphological category. The specific activities of trypsin-like enzyme in the culture supernatants of the different variants were greater in black-pigmented than brown-pigmented and least in the beige-pigmented variant, thus correlating with the morphological changes in polymorphonuclear leucocytes. Morphological changes similar to those seen with culture supernatants from black-pigmented strains were reproduced by exposure of polymorphonuclear leucocytes to commercially available trypsin type II and prior heat treatment of these culture supernatants abolished the shape changes in polymorphonuclear leucocytes. Thus a bacterial, trypsin-like enzyme may play a role in the morphological changes observed.

Hydrophobicities of human polymorphonuclear leukocytes and oral Bacteroides and Porphyromonas spp., Wolinella recta, and Eubacterium yurii with special reference to bacterial surface structures

The hydrophobicities of human polymorphonuclear leukocytes (PMNLs) and Bacteroides buccae, B. oris, B. oralis, B. veroralis, B. buccalis, B. heparinolyticus, B. intermedius, B. denticola, B. loescheii, B. melaninogenicus, Porphyromonas gingivalis, P. endodontalis, Wolinella recta, and Eubacterium yurii were studied by the hexadecane method. The majority of the strains were equally or less hydrophobic than the PMNLs. Only in the case of E. yurii and the only strain of B. buccalis were all strains more hydrophobic than the PMNLs. However, some strains of B. intermedius, B. oris, B. denticola, and P. gingivalis were also more hydrophobic than the PMNLs. With the exception of B. intermedius and species with a crystalline surface protein layer (S-layer), the strains of all other species with a thick capsule were more hydrophilic than the strains with little or no extracellular polymeric material. All strains of the S-layer species were either quite hydrophilic or hydrophobic depending on the species, totally irrespective of the presence of the capsule. The results suggest that the S-layers of oral anaerobic bacteria may be important determinants of cell surface hydrophobicity.

Effects of Porphyromonas gingivalis culture products on human polymorphonuclear leukocyte function

Porphyromonas gingivalis culture supernate was found to induce homotypic agglutination of human polymorphonuclear leukocytes (PMN). Pretreatment of PMN with P. gingivalis supernate inhibited both the rate and the degree of agglutination induced by the secretagogues PMA and FMLP. Lipopolysaccharide from P. gingivalis upregulated the CR3 (Mac-1, CD11b) receptors on PMN. Treatment of glass-adherent PMN with P. gingivalis supernate did not alter their phagocytic capacity for P. gingivalis cells but when PMN were pretreated in suspension the cells adhered less well to glass and phagocytosis of those PMN that did adhere was reduced. P. gingivalis supernate treatment of PMN induced lysozyme release but the amount released during phagocytosis when supernate was present did not change. Neither P. gingivalis supernate nor LPS were cytotoxic for PMN. The data suggest that P. gingivalis factors could interfere with PMN elimination of this organism at the site of infection by inappropriately stimulating PMN, depressing phagocytosis and causing enhanced CR3 expression. The consequent agglutination or enhanced adherence could also lead to decreased phagocytic capacity of the adherent or agglutinated cells.

Ingestion of Bacteroides buccae, Bacteroides oris, Porphyromonas gingivalis, and Fusobacterium nucleatum by human polymorphonuclear leukocytes in vitro

The phagocytic ingestion of clinical isolates and reference strains of Bacteroides buccae, Bacteroides oris, Porphyromonas gingivalis and Fusobacterium nucleatum by polymorphonuclear leukocytes (PMNs) was studied. Special attention was focused on the hydrophobicity of the strains. B. buccae strains, less or equally hydrophobic than PMNs, were poorly ingested without opsonization. Hydrophobic, but not hydrophilic, strains of B. oris and both hydrophilic and hydrophobic P. gingivalis and F. nucleatum strains were readily ingested without opsonization. Hydrophobicity thus contributes to the adherence of bacteria to PMNs in some, but not all, species tested. Normal human serum enhanced the ingestion of B. buccae, but failed to do so after heat-inactivation. Heat-inactivation of the immune serum to B. buccae strain ES57 did not reduce opsonic activity suggesting that specific antibodies enhanced the ingestion of B. buccae.

Effects of Bacteroides gingivalis culture products on human polymorphonuclear leucocyte morphology

This study aimed to determine whether leucocytes exposed to Bacteroides gingivalis culture supernatant exhibited consistent morphological changes and whether measurement of such changes could provide a simple screening assay for bacterial products with potential biological activity. Glass-adherent polymorphonuclear leucocytes were obtained from clotted blood preparations and from blood after purification by centrifugation through Ficoll-Hypaque. These were then incubated in Hanks' balanced salt solution, a sterile liquid medium (BM) and B. gingivalis (W83) culture supernatant. Polymorphonuclear leucocytes were classified by their shape into small non-polar (less than 18 microns diameter), large non-polar (greater than or equal to 18 microns diameter), bipolar and hyperpolar types. Treatment with B. gingivalis culture supernatant consistently increased large non-polar cells by 150% to over 300% (p less than 0.01), when compared with polymorphonuclear leucocytes incubated with the sterile liquid medium (control). This change was accompanied by smaller decreases in small non-polar, bipolar and hyperpolar cells, these being significant for bipolar cells in clot preparations (p less than 0.01) and small non-polar cells after Ficoll-Hypaque isolation (p less than 0.01). Neither the liquid medium nor the B. gingivalis culture supernatant was toxic to the cells as indicated by trypan blue exclusion tests. Lipopolysaccharide and short-chain fatty acids were not responsible for the changes in polymorphonuclear leucocyte shape. However, the activity of the culture supernatant was destroyed by heating at 80 degrees C for 30 min, indicating that proteolytic enzymes may have been involved.

The role of black-pigmented Bacteroides in human oral infections

Today, 10 black-pigmented Bacteroides (BPB) species are recognized. The majority of these species can be isolated from the oral cavity. BPB species are involved in anaerobic infections of oral and non-oral sites. In the oral cavity, BPB species are associated with gingivitis, periodontitis, endodontal infections and odontogenic abscesses. Cultural studies suggest a specific role of the various BPB species in the different types of infection. Bacteroides gingivalis is closely correlated with destructive periodontitis in adults as well as in juveniles. Bacteroides intermedius seems to be less specific since it is found in gingivitis, periodontitis, endodontal infections and odontogenic abscesses. The recently described Bacteroides endodontalis is closely associated with endodontal infections and odontogenic abscesses of endodontal origin. There are indications that these periodontopathic BPB species are only present in the oral cavity of subjects suffering from periodontal breakdown, being absent on the mucosal surfaces of subjects without periodontal breakdown. BPB species associated with healthy oral conditions are Bacteroides melaninogenicus, Bacteroides denticola and Bacteroides loescheii. There are indications that these BPB species are part of the normal indigenous oral microflora. Many studies in the past have documented the pathogenic potential and virulence of BPB species. This virulence can be explained by the large numbers of virulence factors demonstrated in this group of micro-organisms. Among others, the proteolytic activity seems to be one of the most important features. Several artificial substrates as well as numerous biological proteins are degraded. These include anti-inflammatory proteins such as alpha-2-macroglobulin, alpha-1-antitrypsin, C3 and C5 complement factors and immunoglobulins. B. gingivalis is by far the most proteolytic species, followed by B. endodontalis. Like other bacteria, the lipopolysaccharide of B. gingivalis has shown to be active in bone resorption in vitro and is capable in stimulating interleukin-1 production in human peripheral monocytes. Based on the well documented association with periodontal disease and the possession of relevant virulence factors, BPB species must be considered as important micro-organisms in the etiology of oral infections. B. gingivalis seems to be the most pathogenic and virulent species.

Biology of asaccharolytic black-pigmented Bacteroides species

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Differences in virulence within the species Bacteroides gingivalis

In order to gain insight into the relative importance of several virulence factors of Bacteroides gingivalis, 8 strains with a varying virulence were studied. The virulence of B. gingivalis was determined in a mouse model. Strains HG 66, HG 76 and HG 184 were very virulent causing phlegmonous abscesses with lesions and necrosis. The strains HG 405 and HG 462 caused phlegomonous abscesses with pus. Strains HG 91, HG 94 and HG 185 were less virulent and induced gravity abscesses. In vitro strains HG 66, HG 76 and HG 184 induced low amounts of chemiluminescence by polymorphonuclear leucocytes. All other strains including HG 405 and HG 462 caused a relatively high chemiluminescence. Most strains displayed a high sensitivity to the bactericidal activity of fresh serum except for the highly virulent strains HG 66, HG 76 and HG 184. No differences in extracellular proteolytic activity on Azocoll, production of volatile fatty acids and ammonia were found between the B. gingivalis strains studied. In conclusion, differences in virulence were shown within the species B. gingivalis; the relative importance of several virulence factors was investigated.

Effect of dental plaque on the oxidative metabolism of normal neutrophils

The purpose of this study was to investigate the interaction between dental plaque and the oxidative metabolism of blood (PB), crevicular (CR) and salivary (SAL) PMN. Data indicated that supragingival plaque induced an in vitro production of chemiluminescence by both PB and CR--PMN in a dose-dependent manner with a maximum activity after 30 min incubation. Comparison between PB, CR and SAL-PMNs indicated that 1) both CR and SAL-PMNs spontaneously produced large quantities of oxygen radicals, 2) CR and SAL-PMNs further produced oxygen radicals upon phorbol myristate acetate or opsonized-zymosan stimulation, and 3) SAL-PMN could not be further activated by supragingival plaque.

Selected characteristics of pathogenic and nonpathogenic strains of Bacteroides gingivalis

Strains of Bacteroides gingivalis were compared for the presence of properties associated with pathogenicity. Some strains were infectious in pure culture in an in vivo model (guinea pig), and all but one of these were more collagenolytic than those which failed to cause lesions in guinea pigs. However, other factors seem to be necessary for the induction of an infection in this animal model.