Heterogeneity of virulence among strains of Bacteroides gingivalis

Experimental Porphyromonas gingivalis infection in nonimmune athymic BALB/c mice

The purpose of this report was to study the role of T lymphocytes following injection of Porphyromonas gingivalis in a mouse abscess model. Three invasive P. gingivalis isolates (ATCC 53977, W83, and AJW4) were injected into athymic BALB/c mice and their heterozygous (nu/+) littermates. The athymic BALB/c (nu/nu) mice were able to localize the invasive P. gingivalis isolates at the injection site. By comparison, the heterozygous BALB/c (nu/+) littermates developed hemorrhagic secondary lesions within 24 h after subcutaneous injection of the same invasive P. gingivalis isolates. These results suggest that naive T lymphocytes may contribute to the pathology associated with P. gingivalis infection.

Depolarization of polymorphonuclear leukocytes by Porphyromonas (Bacteroides) gingivalis 381 in the absence of respiratory burst activation

Bacteroides spp. may contribute to the chronicity of mixed infections by affecting the normal functions of polymorphonuclear leukocytes (PMN). This study evaluated the physiologic and biochemical responses of human peripheral blood PMN to a variety of strains of the oral periodontal pathogen Porphyromonas (Bacteroides) gingivalis. Strain 381 and ATCC type strain 33277 caused rapid and lasting depolarization of the electrochemical potential that exists across the PMN membrane by a mechanism that was independent of activation of the pertussis toxin-sensitive G protein or protein kinase C. Membrane depolarization did not initiate increases in intracellular calcium or respiratory burst activation, and activity was not inhibited by surface proteolysis or sugars. However, membrane depolarization was associated with inhibition of PMN responses to the chemotactic peptide N-formylmethionyl leucyl phenylalanine. Membrane-depolarizing activity was isolated with the outer membrane of strain 381 by surface extraction of the bacteria by using Zwittergent 3,14, followed by Sephacryl S-200 gel filtration chromatography. The partially purified outer membrane components were heat stable, were not inhibited by tosyl-lysine chloromethyl ketone, and inhibited N-formylmethionyl leucyl phenylalanine-stimulated superoxide production. The results suggest that outer membrane components of P. gingivalis 381 and 33277 have porinlike activity that can depolarize PMN membranes and immobilize PMN responses to chemotactic peptides. This may prove to be an important virulence characteristic of these strains.

Virulence of Wolinella recta in a murine abscess model

The virulence of Wolinella recta isolates was studied in an experimental animal model by using monoinfection of BALB/c mice. Infection with clinical isolates of W. recta 576 and W. recta 234 induced dry, flat, depressed gangrenous necrotic skin lesions, whereas W. recta ATCC 33238 failed to induce a similar lesion. Histological examination of the skin lesion 72 h postinfection revealed coagulation necrosis of the epidermis, subcutis and cutaneous truncus muscle, with marked exudation of serum proteins and neutrophils. Virulence-modulating agents such as dexamethasone, galactosamine, hydrazine sulfate, and dextran microcarrier beads were used in conjunction with W. recta infection. Dexamethasone, hydrazine sulfate, and dextran beads enhanced the infectivity and pathogenicity of W. recta for lesion formation and tissue destruction compared with what was found in untreated control mice. Galactosamine sensitization enhanced the virulence potential of W. recta to such an extent that a lethal outcome was observed. Laboratory passage of clinical isolates demonstrated a decreased virulence in high-passage strains, which correlated with the minimal virulence observed in the extensively passaged W. recta ATCC 33238. Serum immunoglobulin G (IgG) and IgM responses were detected in the serum of infected animals, and cross-reacting antibody indicated variation in the antigenic makeup of various W. recta strains. Enhanced IgG antibody responses were observed following the secondary challenge. Mice with acquired antibody response to initial infection remained susceptible to lesion formation with subsequent challenge, but the size of the lesion was significantly reduced, indicating partial protection. Serum IgG and IgM antibody levels were significantly increased by active immunization when compared with levels in mice which had recovered from infection. The immunization significantly decreased the lesion size; however, even these high levels of antibody failed to abrogate the lesion induction.

Complement factor D-like activity of Porphyromonas gingivalis W83

Porphyromonas gingivalis is a proteolytic gram-negative anaerobic bacterium that is frequently isolated from lesions of human periodontal disease. Previous studies have shown that P. gingivalis strain W83 inactivates C3 in pooled normal human serum (NHS) by a mechanism that is inhibitable by EDTA, yet it degrades purified complement proteins by a mechanism that is not EDTA-inhibitable. Furthermore, during complement activation, only a small number of C3 molecules accumulate on the surface of this organism unless the bacteria are treated with the protease inhibitor TLCK prior to complement activation. The hypothesis was tested that P. gingivalis W83 contains protease activity mimicking that of complement factor D, thus enabling it to activate C3 in serum without significant C3 accumulation on the cell surface. It was first noted that incubation of P. gingivalis W83 in absorbed human serum that was depleted of factor D resulted in C3 consumption that was reversed in the presence of the protease inhibitor TLCK. To directly demonstrate that factor B-dependent C3 consumption occurs in the absence of factor D, P. gingivalis W83 was incubated with purified C3 or a mixture of C3 and B. Although some proteolysis of C3 was noted, increased C3 consumption was noted in mixtures containing both C3 and B. This increment in C3 consumption was inhibited by both EDTA and TLCK. Furthermore, the addition of purified factor H to this mixture inhibited the increment in C3 consumption, indicating that a C3 convertase was probably formed.(ABSTRACT TRUNCATED AT 250 WORDS)

Periodontal bone level and gingival proteinase activity in gnotobiotic rats immunized with Bacteroides gingivalis

Bacteroides gingivalis is associated with various forms of periodontal disease. To assess the role of the immune response in modulating B. gingivalis-associated periodontal disease, the effect of immunization of B. gingivalis-induced periodontal bone loss was evaluated in gnotobiotic rats. Male Sprague-Dawley rats immunized with various doses of whole cells or sham-immunized with incomplete Freund's adjuvant were monoinfected with B. gingivalis in carboxymethylcellulose by gavage. Two additional groups served as either sham-immunized or untreated germ-free controls. Forty-two days after infection, all rats were killed, periodontal bone level was assessed morphometrically and radiographically, and gingival proteinase (mammalian collagenase and acid cathepsin) activity was assessed biochemically. B. gingivalis was present in oral samples from all monoinfected rats, and no contaminating bacteria were detected in any oral or fecal sample. Animals immunized with B. gingivalis cells had elevated serum and saliva antibodies to whole cells and partially purified fimbriae from B. gingivalis. Infected sham-immunized rats had significantly more periodontal bone loss than noninfected controls, whereas the periodontal bone level in infected rats immunized with 10(10) B. gingivalis cells was similar to that of the noninfected controls. The activities of gingival collagenase and cathepsin B and L were high in sham-immunized infected rats and low in all other animal groups. In conclusion, it is possible to reduce B. gingivalis-induced periodontal tissue loss in gnotobiotic rats by immunization.

A novel mouse model to study the virulence of and host response to Porphyromonas (Bacteroides) gingivalis

We describe here the development of a mouse subcutaneous chamber model that allows for the examination of host-parasite interactions as well as the determination of gross pathology with Porphyromonas (Bacteroides) gingivalis challenge. When inoculated into stainless-steel chambers implanted subcutaneously in female BALB/c mice, P. gingivalis W83, W50, and A7436 (10(8) to 10(10) CFU) caused cachexia, ruffling, general erythema and phlegmonous, ulcerated, necrotic lesions, and death. P. gingivalis W50/BEI, HG405, and 33277 (10(10) CFU) produced localized abscesses in the mouse chamber model with rejection of chambers at the injection site. Analysis of chamber fluid from 33277-, HG405-, and W50/BEI-infected mice by cytocentrifugation revealed inflammatory cell debris, polymorphonuclear leukocytes, and high numbers of dead bacteria. In contrast, fluid from A7436-, W50-, and W83-infected mice revealed infiltration predominantly of polymorphonuclear leukocytes and live bacteria. Bacteria were found primarily associated with polymorphonuclear leukocytes in the fluid from W50-, HG405-, and W83-infected mice but not from A7436-infected mice. Viable isolates were recoverable from the chamber fluid through day 3 for W50/BEI, day 5 for 33277, day 6 for HG405, day 7 for W50, day 14 for W83, and day 26 for A7436. All strains induced a systemic immunoglobulin G response in serum and chamber fluid samples. The use of this model will allow us to examine the virulence of P. gingivalis as defined by the interaction of host response to localized infection with P. gingivalis.

Phagocytosis and virulence of different strains of Porphyromonas gingivalis

In this study 17 strains of Porphyromonas gingivalis, both reference and clinical isolates, were investigated for their in vitro interaction with human polymorphonuclear leukocytes, hydrophobicity, density, and virulence in a mouse model. The results of the phagocytosis, hydrophobicity, and density experiments showed that P. gingivalis strains could be divided into two distinct groups. One group of strains were readily attached and phagocytosed when exposed to the leukocytes. These bacteria were hydrophobic and had a higher buoyant density than the other group, which were poorly phagocytosed, had a low buoyant density, and were hydrophilic. This latter group also exhibited an extracellular meshwork resembling a glycocalyx when examined by electron microscopy. There were also significant differences between strains in the mouse pathogenicity model. Two strains caused an invasive, spreading infection compared with the other 15 strains which produced small, localized abscesses. There was no clear correlation between the results of the phagocytosis assay and the virulence of the bacteria when injected subcutaneously in mice. Resistance to phagocytosis may be important for survival of these bacteria, but it does not in itself imply the ability to cause damage to the host.

Microbiological and immunological aspects of experimental periodontal disease in rats: a review article

Animal models in which microbiological and immunological aspects of periodontal disease can be studied prospectively seem well warranted. The rat bears much resemblance to man with respect to periodontal anatomy, development and composition of dental plaque, histopathology of periodontal lesions, and basic immunobiology. Furthermore, reproducible methods are available for assessment of periodontal disease in rats, and detectable periodontal destruction can be induced in a few weeks in these animals without traumatizing periodontal tissues with ligatures. Experimental periodontitis studies in germ-free rats have confirmed the pathogenicity of several suspected periodontal pathogens (Actinobacillus actinomycetemcomitans, Porphyromonas gingivalis, Capnocytophaga sputigena, Eikenella corrodens, and Fusobacterium nucleatum). The studies also suggest that the number of periodontal pathogens may be higher than generally believed, since species like Streptococcus sobrinus and Actinomyces viscosus are associated with periodontal bone loss in rats. Studies in rats with congenital or induced immune defects indicate that generalized or selective immunosuppression at the time of infection with periodontal pathogens may aggravate periodontal disease. Studies in immunized rats indicate that periodontal disease can be prevented by immunization against periodontal pathogens. However, it is also possible by immunization to induce periodontal destruction; i.e., the immune system has a destructive potential which should not be overlooked. In the future, the rat model may prove valuable for initial screening of antigen preparations and immunization regimens in the search for a periodontitis vaccine.

Effect of iron limitation on Bacteroides gingivalis

This study was undertaken to describe the effects of iron limitation on Bacteroides gingivalis. Four strains of B. gingivalis were grown in brain heart infusion broth, substituting protoporphyrin IX for hemin. Culture with protoporphyrin IX resulted in a loss of a 28 kDa membrane protein, but no decrease in growth. Iron-restricted cultural conditions for the growth of B. gingivalis were achieved using alpha/alpha'-dipyridyl, a ferrous iron chelator, at concentrations from 12.5 microM to 300 microM. Total suppression of bacterial growth for strain A7A1-28 and strain 381 was achieved at 200 microM alpha/alpha'-dipyridyl. At 300 microM alpha/alpha'-dipyridyl, strain W50 and Bowden 18/10 showed 100% and 80% suppression of growth, respectively. The ferric iron chelator Desferal did not show suppression of growth in concentrations up to 500 microM. The dipyridyl inhibition of cell growth for strain A7A1-28 could be reversed by adding excess ferrous ammonium sulphate but not by ferric nitrate. Iron regulation of proteolytic enzymes could not be demonstrated. Two new membrane proteins 42 kDa and 24 kDa are expressed with iron limitation, and the 45 kDa membrane protein was decreased with iron limitation.

Protective immunization against experimental Bacteroides (Porphyromonas) gingivalis infection

The effects of immunization in modulating the pathogenesis of Bacteroides (Porphyromonas) gingivalis infection in a murine model system were examined. BALB/c mice were immunized by intraperitoneal injection with B. gingivalis ATCC 53977 (one injection per week for 3 weeks), or with a lithium diiodosalicylate (LIS) extract (one injection per week for 3 weeks), or with lipopolysaccharide (LPS; one intravenous or intraperitoneal injection) from this same strain. Two weeks after the final immunization, the mice were challenged by subcutaneous injection of B. gingivalis ATCC 53977. Mice immunized with bacteria had no secondary lesions and no septicemia, whereas mice immunized with LIS extract had few secondary lesions and no septicemia. Mice immunized with LPS and nonimmunized mice demonstrated secondary abdominal lesions and septicemia after challenge. Bacterial cells and LIS extract, but not LPS, induced serum antibody and antigen reactive lymphocytes, as measured by enzyme-linked immunosorbent assay, immunoblot, Western immunoblot transfer, and in vitro lymphoproliferative responses. The present study suggests that immunization with a LIS extract or whole cells may induce a protective response against experimental B. gingivalis infection.

Cloning of Bacteroides gingivalis surface antigens involved in adherence

Despite the acknowledge importance of Bacteroides gingivalis as a periodontal pathogen, relatively little is known about the molecular basis for its pathogenicity. Recombinant DNA technology has created the opportunity to identify and characterize the virulence determinants. A Bact. gingivalis library was prepared in Escherichia coli JM83 with the vector pUC18. The library was screened for surface antigens by colony immunoblot and 337 putative surface antigen recombinants were identified. Two of these clones were found to have haemagglutinating activity. Antiserum raised against one of these clones reacted with a 43 kDa Bact. gingivalis protein that has haemagglutinating activity.