Resistance of a Tn4351-generated polysaccharide mutant of Porphyromonas gingivalis to polymorphonuclear leukocyte killing

Virulence Factors of the Periodontal Pathogens: Tools to Evade the Host Immune Response and Promote Carcinogenesis

Periodontitis is the most common chronic, inflammatory oral disease that affects more than half of the population in the United States. The disease leads to destruction of the tooth-supporting tissue called periodontium, which ultimately results in tooth loss if uncured. The interaction between the periodontal microbiota and the host immune cells result in the induction of a non-protective host immune response that triggers host tissue destruction. Certain pathogens have been implicated periodontal disease formation that is triggered by a plethora of virulence factors. There is a collective evidence on the impact of periodontal disease progression on systemic health. Of particular interest, the role of the virulence factors of the periodontal pathogens in facilitating the evasion of the host immune cells and promotion of carcinogenesis has been the focus of many researchers. The aim of this review is to examine the influence of the periodontal pathogens Aggregatibacter actinomycetemcomitans (A. actinomycetemcomitans), Porphyromonas gingivalis (P. gingivalis), and Fusobacterium nucleatum (F. nucleatum) in the modulation of the intracellular signaling pathways of the host cells in order to evade the host immune response and interfere with normal host cell death and the role of their virulence factors in this regard.

Glycobiology of the oral pathogen Porphyromonas gingivalis and related species

Until recently, glycoproteins had only been described in eukaryotes. However, advances in detection methods and genome analyses have allowed the discovery of N-linked or O-linked glycoproteins, similar to those found in eukaryotes, in some bacterial species. These prokaryotic glycoproteins play roles in adhesion, solubility, formation of protein complexes, protection from protein degradation, and changes in antigenicity. Periodontal pathogen Porphyromonas gingivalis secretes virulence proteins via the type IX secretion system, some of which localize on the cell surface by binding to lipopolysaccharide (LPS). These virulence proteins have a conserved C-terminal domain (CTD) region, which is used as a secretion signal. However, it is still uncertain how the secreted proteins on the cell surface bind to LPS. In this review, we discuss the synthesis of P. gingivalis O polysaccharide, which plays a role in anchoring the CTD protein on the cell surface, and recent discoveries of glycoproteins in P. gingivalis as well as other species in the phylum Bacteroidetes.

Porphyromonas gingivalis and related bacteria: from colonial pigmentation to the type IX secretion system and gliding motility

Porphyromonas gingivalis is a gram-negative, non-motile, anaerobic bacterium implicated as a major pathogen in periodontal disease. P. gingivalis grows as black-pigmented colonies on blood agar, and many bacteriologists have shown interest in this property. Studies of colonial pigmentation have revealed a number of important findings, including an association with the highly active extracellular and surface proteinases called gingipains that are found in P. gingivalis. The Por secretion system, a novel type IX secretion system (T9SS), has been implicated in gingipain secretion in studies using non-pigmented mutants. In addition, many potent virulence proteins, including the metallocarboxypeptidase CPG70, 35 kDa hemin-binding protein HBP35, peptidylarginine deiminase PAD and Lys-specific serine endopeptidase PepK, are secreted through the T9SS. These findings have not been limited to P. gingivalis but have been extended to other bacteria belonging to the phylum Bacteroidetes. Many Bacteroidetes species possess the T9SS, which is associated with gliding motility for some of these bacteria.

Impact of resolvin E1 on murine neutrophil phagocytosis in type 2 diabetes

Diabetic complications involve inflammation-mediated microvascular and macrovascular damage, disruption of lipid metabolism, glycosylation of proteins, and abnormalities of neutrophil-mediated events. Resolution of inflamed tissues to health and homeostasis is an active process mediated by endogenous lipid agonists, including lipoxins and resolvins. This proresolution system appears to be compromised in type 2 diabetes (T2D). The goal of this study was to investigate unresolved inflammation in T2D. Wild-type (WT) and genetically engineered mice, including T2D mice (db/db), transgenic mice overexpressing the human resolvin E1 (RvE1) receptor (ERV1), and a newly bred strain of db/ERV1 mice, were used to determine the impact of RvE1 on the phagocytosis of Porphyromonas gingivalis in T2D. Neutrophils were isolated and incubated with fluorescein isothiocyanate-labeled P. gingivalis, and phagocytosis was measured in a fluorochrome-based assay by flow cytometry. Mitogen-activated protein kinase (MAPK) (p42 and p44) and Akt (Thr308 and Ser473) phosphorylation was analyzed by Western blotting. The mouse dorsal air pouch model was used to evaluate the in vivo impact of RvE1. Results revealed that RvE1 increased the neutrophil phagocytosis of P. gingivalis in WT animals but had no impact in db/db animals. In ERV1-transgenic and ERV1-transgenic diabetic mice, phagocytosis was significantly increased. RvE1 decreased Akt and MAPK phosphorylation in the transgenic animals. In vivo dorsal air pouch studies revealed that RvE1 decreases neutrophil influx into the pouch and increases neutrophil phagocytosis of P. gingivalis in the transgenic animals; cutaneous fat deposition was reduced, as was macrophage infiltration. The results suggest that RvE1 rescues impaired neutrophil phagocytosis in obese T2D mice overexpressing ERV1.

Blocking proinflammatory cytokine release modulates peripheral blood mononuclear cell response to Porphyromonas gingivalis

BACKGROUND

Chronic periodontitis (CP) is an inflammatory disease in which cytokines play a major role in the progression of disease. Anti-inflammatory cytokines (interleukin 4 [IL-4] and IL-10) were reported to be absent or reduced in diseased periodontal tissues, suggesting an imbalance between the proinflammatory and anti-inflammatory mediators. This study tests the hypothesis that there is cellular crosstalk mediated by proinflammatory and anti-inflammatory cytokines and that blocking proinflammatory cytokine (tumor necrosis factor-α [TNF-α] and IL-1) production will enhance anti-inflammatory cytokine (IL-4 and IL-10) production from peripheral blood mononuclear cells (PBMCs) in response to Porphyromonas gingivalis.

METHODS

PBMCs were isolated from individuals diagnosed with CP or healthy individuals and cultured for 24 hours. Concanavalin A (ConA) was used as an activator of lymphocyte function. Live and heat-killed P. gingivalis or lipopolysaccharide from P. gingivalis were used as the bacterial stimulants. TNF-α and IL-1 production was neutralized by specific antibodies against TNF-α and IL-1α or IL-β. Culture supernatants were evaluated by enzyme-linked immunosorbent assay for TNF-α, IL-1β, IL-4, and IL-10 production.

RESULTS

Live P. gingivalis did not result in any significant IL-10 or IL-4 release, whereas heat-killed P. gingivalis led to a significant increase in IL-10 levels compared with unstimulated or live P. gingivalis-stimulated cells from both healthy individuals or those with CP. Overall, PBMCs from patients with CP produced significantly lower IL-10 in response to ConA and P. gingivalis, suggesting chronic suppression of the anti-inflammatory cytokine production. Blocking the proinflammatory cytokine response did not result in any substantial change in IL-10 or IL-4 response to live P. gingivalis. Blocking the proinflammatory cytokine response restored IL-10 production by cells from CP in response to P. gingivalis lipopolysaccharide.

CONCLUSIONS

These findings suggest that PBMCs from patients with CP have suppressed anti-inflammatory cytokine production that can, in part, be restored by neutralizing proinflammatory cytokines. Monocytes are an important source of IL-10 production, and monocyte-derived IL-10 might play a regulatory role in the pathogenesis of CP.

Genetic tools for studying Capnocytophaga canimorsus

Capnocytophaga canimorsus, a commensal bacterium from canine oral flora, has been isolated throughout the world from severe human infections caused by dog bites. Due to the low level of evolutionary relationship to Proteobacteria, genetic methods suitable for the genus Capnocytophaga needed to be established. Here, we show that Tn4351, derived from Bacteroides fragilis, could be introduced by conjugation into C. canimorsus and conferred resistance to erythromycin. By mapping and sequencing a naturally occurring plasmid isolated from a clinical isolate of C. canimorsus, we identified a repA gene that allowed us to construct Escherichia coli-Capnocytophaga shuttle vectors. Most commonly used antibiotic markers were not functional in C. canimorsus, but cefoxitin (cfxA), tetracycline (tetQ), and erythromycin (ermF) resistances could be used as markers for plasmid maintenance in C. canimorsus and even in some other Capnocytophaga spp. Shuttle vectors were introduced into C. canimorsus either by conjugation using the origin of transfer (oriT) of RP4 or by electrotransformation. Taking advantage of the promoter of ermF, an expression vector was constructed. Finally, a method that allows site-directed mutagenesis is described. All these genetic tools pave the way, not only for molecular studies of the pathogenesis of C. canimorsus, but also for studies of other oral Capnocytophaga species.

Enhanced biofilm formation and loss of capsule synthesis: deletion of a putative glycosyltransferase in Porphyromonas gingivalis

Periodontitis is a biofilm-mediated disease. Porphyromonas gingivalis is an obligate anaerobe consistently associated with severe manifestations of this disease. As an opportunistic pathogen, the ability to proliferate within and disseminate from subgingival biofilm (plaque) is central to its virulence. Here, we report the isolation of a P. gingivalis transposon insertion mutant altered in biofilm development and the reconstruction and characterization of this mutation in three different wild-type strains. The mutation responsible for the altered biofilm phenotype was in a gene with high sequence similarity ( approximately 61%) to a glycosyltransferase gene. The gene is located in a region of the chromosome that includes up to 16 genes predicted to be involved in the synthesis and transport of capsular polysaccharide. The phenotype of the reconstructed mutation in all three wild-type backgrounds is that of enhanced biofilm formation. In addition, in strain W83, a strain that is encapsulated, the glycosyltransferase mutation resulted in a loss of capsule. Further experiments showed that the W83 mutant strain was more hydrophobic and exhibited increased auto-aggregation. Our results indicate that we have identified a gene involved in capsular-polysaccharide synthesis in P. gingivalis and that the production of capsule prevented attachment and the initiation of in vitro biofilm formation on polystyrene microtiter plates.

Contribution of biofilm regulatory protein A of Streptococcus mutans, to systemic virulence

Streptococcus mutans is occasionally isolated from the blood of patients with bacteremia and infective endocarditis (IE), and the possibility that it could be pathogenic for those diseases has been discussed. The initial important step for the involvement of bacterial pathogens in the virulence of IE is thought to be survival in blood for an extended period. Recently, the brpA gene encoding biofilm regulatory protein A (BrpA) of S. mutans was cloned and sequenced, after which it was shown that inactivation of brpA in an isogenic mutant strain resulted in longer chain formation than in the parental strain. In the present study, a BrpA-defective isogenic mutant strain (MT8148BRD) was constructed from strain MT8148. In an analysis of its susceptibility to phagocytosis by human polymorphonuclear leukocytes (PMNs), the phagocytosis rate of MT8148BRD was shown to be significantly lower than that of MT8148 (P < 0.01). Next, strains with various chain lengths were produced by culturing MT8148 in media with various initial pH levels, which revealed that there was a statistically negative correlation between phagocytosis susceptibility and chain length (P < 0.01). Further, MT8148BRD was found to possess higher platelet aggregation properties than MT8148 (P < 0.05). In addition, injection of MT8148BRD into the jugular vein of specific pathogen-free Sprague-Dawley rats resulted in a longer duration of bacteremia, which prolonged systemic inflammation for a longer period than in those infected with MT8148. These results indicate that S. mutans BrpA is associated with virulence in blood, due to its correlation to phagocytosis susceptibility and platelet aggregation properties.

Identification of a new membrane-associated protein that influences transport/maturation of gingipains and adhesins of Porphyromonas gingivalis

The dual membrane envelopes of Gram-negative bacteria provide two barriers of unlike nature that regulate the transport of molecules into and out of organisms. Organisms have developed several systems for transport across the inner and outer membranes. The Gram-negative periodontopathogenic bacterium Porphyromonas gingivalis produces proteinase and adhesin complexes, gingipains/adhesins, on the cell surface and in the extracellular milieu as one of the major virulence factors. Gingipains and/or adhesins are encoded by kgp, rgpA, rgpB, and hagA on the chromosome. In this study, we isolated a P. gingivalis mutant (porT), which showed very weak activities of gingipains in the cell lysates and culture supernatants. Subcellular fractionation and immunoblot analysis demonstrated that precursor forms of gingipains and adhesins were accumulated in the periplasmic space of the porT mutant cells. Peptide mass fingerprinting and N-terminal amino acid sequencing of the precursor proteins and the kgp'-'rgpB chimera gene product in the porT mutant indicated that these proteins lacked the signal peptide regions, consistent with their accumulation in the periplasm. The PorT protein seemed to be membrane-associated and exposed to the periplasmic space, as revealed by subcellular fractionation and immunoblot analysis using anti-PorT antiserum. These results suggest that the membrane-associated protein PorT is essential for transport of the kgp, rgpA, rgpB, and hagA gene products across the outer membrane from the periplasm to the cell surface, where they are processed and matured.

Mice lacking inducible nitric oxide synthase demonstrate impaired killing of Porphyromonas gingivalis

Porphyromonas gingivalis is a primary etiological agent of generalized severe periodontitis, and emerging data suggest the importance of reactive oxygen and nitrogen species in periodontal tissue damage, as well as in microbial killing. Since nitric oxide (NO) released from inducible NO synthase (iNOS) has been shown to possess immunomodulatory, cytotoxic, and antibacterial effects in experimental models, we challenged iNOS-deficient (iNOS(-/-)) mice with P. gingivalis by using a subcutaneous chamber model to study the specific contribution of NO to host defense during P. gingivalis infection. iNOS(-/-) mice inoculated with P. gingivalis developed skin lesions and chamber rejection with higher frequency and to a greater degree than similarly challenged C57BL/6 wild-type (WT) mice. Chamber fluid from iNOS(-/-) mice possessed significantly more P. gingivalis than that of WT mice. The immunoglobulin G responses to P. gingivalis in serum was similar in WT and iNOS(-/-) mice, and the inductions of tumor necrosis factor alpha, interleukin-1 beta and interleukin-6, and prostaglandin E(2) were comparable between the two mouse strains. Although no differences in total leukocyte counts in chamber fluids were observed between iNOS(-/-) and WT mice, the percentage of dead polymorphonuclear leukocytes (PMNs) was significantly greater in iNOS(-/-) mouse chamber fluids than that of WT samples. Interestingly, casein-elicited PMNs from iNOS(-/-) mice released more superoxide than did WT PMNs when stimulated with P. gingivalis. These results indicate that modulation of superoxide levels is a mechanism by which NO influences PMN function and that NO is an important element of the host defense against P. gingivalis.

Construction and characterization of a nonpigmented mutant of Porphyromonas gingivalis: cell surface polysaccharide as an anchorage for gingipains

A nonpigmented mutant of Porphyromonas gingivalis was constructed by using transposon mutagenesis. The mutant possessed the transposon DNA at the novel gene porR. Gene targeted mutagenesis revealed that porR was responsible for pigmentation. The porR gene shared similarities with genes of the degT family, the products of which are now considered to be transaminases involved in biosynthesis of sugar portions of cell-surface polysaccharides and aminoglycosides. The porR mutant showed a pleiotropic phenotype: delayed maturation of fimbrillin, preferential presence of Rgp and Kgp proteinases in culture supernatants, and no haemagglutination. The porR mutant had altered phenol extractable polysaccharide compared to the porR(+) sibling strain. A mAb, 1B5, that reacts with sugar portions of P. gingivalis cell surface polysaccharide and membrane-type Rgp proteinase showed no reaction with the cell lysates of the porR mutant. These results indicate that porR is involved in biosynthesis of cell surface polysaccharide that may function as an anchorage for Rgp, Kgp, haemagglutinins and the haemoglobin receptor protein.

Prior exposure of mice to Fusobacterium nucleatum modulates host response to Porphyromonas gingivalis

Multiple periodontal pathogens sequentially colonize the subgingival niche during the conversion from gingivitis to destructive periodontal disease. An animal model of sequential immunization with key periodontal pathogens has been developed to determine whether T- and B-lymphocyte effector functions are skewed and fail to protect the host from pathogenic challenge. The present study was performed to evaluate the immunomodulatory effect of exposure to Fusobacterium nucleatum prior to Porphyromonas gingivalis. Group 1 (control) mice were immunized with phosphate-buffered saline, group 2 were immunized with F. nucleatum prior to P. gingivalis and group 3 were immunized with P. gingivalis alone. All the T-cell clones derived from group 2 demonstrated type 2 helper T-cell clone (Th2 subsets), whereas those from group 3 mice demonstrated Th1 subsets. Exposure of mice to F. nucleatum prior to P. gingivalis interfered with the opsonophagocytosis function of sera against P. gingivalis. In adoptive T-cell transfer experiments, in vivo protective capacity of type 2 helper T-cell clones (Th2) from group 2 was significantly lower than type 1 helper T-cell clones (Th1) from group 3 against the lethal dose infection of P. gingivalis. Western blot analysis indicated a different pattern of recognition of P. gingivalis fimbrial proteins between sera from group 2 and group 3. In conclusion, these studies suggest that exposure of a host to F. nucleatum prior to the periodontal pathogen P. gingivalis modulates the host immune responses to P. gingivalis at the humoral, cellular and molecular levels.

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.

Role of serotype-specific polysaccharide in the resistance of Streptococcus mutans to phagocytosis by human polymorphonuclear leukocytes

To clarify the role of cell surface components of Streptococcus mutans in resistance to phagocytosis by human polymorphonuclear leukocytes (PMNs), several isogenic mutants of S. mutans defective in cell surface components were studied with a luminol-enhanced chemiluminescence (CL) assay, a killing assay, and a transmission electron microscope. The CL responses of human PMNs to mutant Xc11 defective in a major cell surface antigen, PAc, and mutant Xc16 defective in two surface glucosyltransferases (GTF-I and GTF-SI) were the same as the response to the wild-type strain, Xc. In contrast, mutant Xc24R, which was defective in serotype c-specific polysaccharide, induced a markedly higher CL response than the other strains. The killing assay showed that human PMNs killed more Xc24R than the parent strain and the other mutants. The transmission electron microscopic observation indicated that Xc24R cells were more internalized by human PMNs than the parental strain Xc. These results may be reflected by the fact that strain Xc24R was more phagocytosed than strain Xc. The CL response of human PMNs to a mutant defective in polysaccharide serotype e or f was similar to the response to Xc24R. Furthermore, mutants defective in serotype-specific polysaccharide were markedly more hydrophobic than the wild-type strains and the other mutants, suggesting that the hydrophilic nature of polysaccharides may protect the bacterium from phagocytosis. We conclude that the serotype-specific polysaccharide, but not the cell surface proteins on the cell surface of S. mutans, may play an important role in the resistance to phagocytosis.

Identification and cloning of genes from Porphyromonas gingivalis after mutagenesis with a modified Tn4400 transposon from Bacteroides fragilis

Porphyromonas gingivalis is a gram-negative, black-pigmented, oral anaerobe strongly associated with adult periodontitis. Previous transposon mutagenesis studies with this organism were based on the Bacteroides transposon Tn4351. Characterization of Tn4351-disrupted genes by cloning has not been an efficient way to analyze large numbers of mutants and is further complicated by the high rate of cointegration of the suicide delivery vector containing Tn4351. In this study, we mutagenized P. gingivalis with a modified version of the Bacteroides fragilis transposon Tn4400. Plasmid pYT646B carrying the transposon was mobilized from Escherichia coli to P. gingivalis ATCC 33277 by conjugation. Both normal and inverse transposition frequencies were similar (3 x 10(-8)). However, the inverse transposon (Tn4400') contains a pBR322 replicon and a beta-lactamase gene; thus, the cloning of disrupted genomic DNAs from inverse transposition mutants was easily accomplished after ligation of genomic fragments and transformation into E. coli. Thousands of transconjugants could be obtained in a single mating experiment, and inverse transposition was random as demonstrated by Southern hybridization. By this procedure the disrupted genes from P. gingivalis pleiotropic mutants were quickly cloned, sequenced, and identified.

Identification by subtractive hybridization of a novel insertion sequence specific for virulent strains of Porphyromonas gingivalis

Subtractive hybridization was employed to isolate specific genes from virulent Porphyromonas gingivalis strains that are possibly related to abscess formation. The genomic DNA from the virulent strain P. gingivalis W83 was subtracted with DNA from the avirulent strain ATCC 33277. Three clones unique to strain W83 were isolated and sequenced. The cloned DNA fragments were 885, 369, and 132 bp and had slight homology with only Bacillus stearothermophilus IS5377, which is a putative transposase. The regions flanking the cloned DNA fragments were isolated and sequenced, and the gene structure around the clones was revealed. These three clones were located side-by-side in a gene reported as an outer membrane protein. The three clones interrupt the open reading frame of the outer membrane protein gene. This inserted DNA, consisting of three isolated clones, was designated IS1598, which was 1,396 bp (i.e., a 1,158-bp open reading frame) in length and was flanked by 16-bp terminal inverted repeats and a 9-bp duplicated target sequence. IS1598 was detected in P. gingivalis W83, W50, and FDC 381 by Southern hybridization. All three P. gingivalis strains have been shown to possess abscess-forming ability in animal models. However, IS1598 was not detected in avirulent strains of P. gingivalis, including ATCC 33277. The IS1598 may interrupt the synthesis of the outer membrane protein, resulting in changes in the structure of the bacterial outer membrane. The IS1598 isolated in this study is a novel insertion element which might be a specific marker for virulent P. gingivalis strains.

Flow cytometry to monitor phagocytosis and oxidative burst of anaerobic periodontopathogenic bacteria by human polymorphonuclear leukocytes

The reduced susceptibility to phagocytosis found among some periodontopathogenic anaerobes may account for the differences between invasive and non-invasive strains. We applied flow cytometry as a powerful tool to analyze and quantify phagocytosis using standardized cultures of oral anaerobes (Porphyromonas gingivalis, Prevotella intermedia, P. nigrescens, Capnocytophaga gingivalis, C. ochracea, C. sputigena, Fusobacterium nucleatum and Peptostreptococcus micros) and heparinized whole blood. Bacteria were labeled by a fluorescein-methylester and their esterase activity, resulting in green fluorescence. Ingested bacteria could be detected easily and quantified by a shift towards green fluorescence in the PMNL population involved and a concomitant decrease in the bacterial population. Furthermore, the oxidative burst of PMNLs was detected in parallel assays using the dye DHR123 which becomes fluorescent upon oxidation during the oxidative burst process. We found a great diversity in phagocytosis susceptibility determined by estimating the portion of phagocytosing PMNLs, ranging from 10.6% (strain W83) to > 99.4% (e.g. ATCC 33277T) in P. gingivalis and from 15.9% (strain MH5) to > 95% (ATCC 33563T) in P. nigrescens. In contrast, almost all P. intermedia strains as well as the representatives of the other anaerobic, putative periodontopathic species tested showed no or only moderate resistance in the phagocytosis assay. Comparison of clinical data of patients and the extent of phagocytosis resistance of the corresponding P. gingivalis strains suggests that this virulence factor may contribute to the clinical outcome.

Isolation and characterization of transposon-induced mutants of Porphyromonas gingivalis deficient in fimbriation

Fimbriae are considered to be an important virulence factor of Porphyromonas gingivalis. In order to identify genes essential for fimbriation, other than fimA which encodes the major subunit protein of fimbriae, transposon mutagenesis and immunological screening techniques were used to isolate fimbria-deficient mutants. R751::*Omega4, a suicide vector that carries Tn4351, was transferred from Escherichia coli to P. gingivalis by conjugation. Twenty-two independent fimbria-deficient mutants were identified among the resulting transformants. Southern hybridization analysis with pBlue 4351, a transposon-specific probe, and R751 indicated that 45% of the mutants resulted from single transposon insertions and that the remaining 55% of the mutants resulted from cointegration of R751 sequences. Southern hybridization analysis with pUCBg12.1, a probe for the fimA region, indicated that nine of the mutants contained insertions within the 2.5 kb SacI DNA fragment of P. gingivalis that contains fimA, ORF1 (which encodes a 15 kDa protein), and the C-terminal portion of ORF5 (which encodes a 63 kDa protein). Polymerase chain reaction (PCR) analysis and further Southern hybridization analysis indicated that the insertion site(s) for all nine of these mutants was within the fimA gene. Southern hybridization analysis also indicated that the remaining thirteen mutants contained insertions somewhere outside the 10 kb fimA region. Analysis by pulsed field gel electrophoresis (PFGE) revealed that insertions for most of the thirteen mutants mapped to a 300 kb NotI fragment and are located at least approximately 200 kb away from fimA. These results identify genetic loci other than fimA, that are required for fimbriation of P. gingivalis. Future cloning and characterization of these genetic loci should be straightforward since they are now marked by antibiotic resistance genes carried by the transposon.

Identification of a second endogenous Porphyromonas gingivalis insertion element

In this study a second endogenous Porphyromonas gingivalis insertion element (IS element) that is capable of transposition within P. gingivalis was identified. Nucleotide sequence analysis of the Tn4351 insertion site in a P. gingivalis Tn4351-generated transconjugant showed that a complete copy of the previously unidentified IS element, designated PGIS2, had inserted into IS4351R in Tn4351. PGIS2 is 1,207 bp in length with 19-bp imperfect terminal inverted repeats, and insertion resulted in a duplicated 10-bp target sequence. Results of Southern hybridization of chromosomal DNA isolated from several P. gingivalis strains with a PGIS2-specific probe demonstrated that the number of copies of PGIS2 per genome varies among different P. gingivalis strains. Computer analysis of the putative polypeptide encoded by PGIS2 revealed strong homologies to the products encoded by IS1358 from Vibrio cholerae, ISAS1 from Aeromonas salmonicida, and H-rpt in Escherichia coli K-12.

Role of the capsular polysaccharide-like serotype-specific antigen in resistance of Actinobacillus actinomycetemcomitans to phagocytosis by human polymorphonuclear leukocytes

Serotype b-specific polysaccharide antigen (SPA) of Actinobacillus actinomycetemcomitans Y4 consists of D-fucose and L-rhamnose. To clarify the role of SPA in phagocytosis of the organism by human polymorphonuclear leukocytes (PMNs), monoclonal antibodies (MAbs) against SPA and SPA-defective mutants, which were constructed by inserting the transposon Tn916 into strain Y4, were used in a chemiluminescence (CL) assay and a phagocytic killing assay. The CL responses of human PMNs to strain Y4 were very low, and the organism was not killed by PMNs. In contrast, SPA-defective mutants induced strong CL responses. The addition of immunoglobulin G MAbs against Y4 SPA enhanced significantly both the CL responses to strain Y4 and the killing of the organism in the presence of complement. The CL responses to SPA-defective mutants were little affected by the addition of these MAbs. We conclude that SPA of A. actinomycetemcomitans plays an important role in the resistance to host defenses by PMNs.

Characterization of a Tn4351-generated hemin uptake mutant of Porphyromonas gingivalis: evidence for the coordinate regulation of virulence factors by hemin

The ability of Porphyromonas gingivalis to acquire iron in the iron-limited environment of the host is crucial to the colonization of this organism. We report here on the isolation and characterization of a transpositional insertion mutant of P. gingivalis A7436 (designated MSM-3) which is defective in the utilization and transport of hemin. P. gingivalis MSM-3 was selected on the basis of its nonpigmented phenotype on anaerobic blood agar following mutagenesis with the Bacteroides fragilis transposon Tn4351. P. gingivalis MSM-3 grew poorly when supplied with hemin as a sole source of iron; however, growth was observed with hemoglobin or inorganic iron. P. gingivalis MSM-3 grown in either hemin-replete or hemin-depleted conditions bound and transported less [14C]hemin or [59Fe]hemin than did the parent strain. At 4 h, P. gingivalis MSM-3 grown in hemin-replete conditions transported only 10,000 pmol of hemin per mg of protein, or 14% of the amount transported by P. gingivalis A7436. Unlike P. gingivalis A7436, hemin binding and transport by P. gingivalis MSM-3 were not tightly regulated by hemin or iron. Examination of P. gingivalis MSM-3 cultures by electron microscopy revealed an overproduction of membrane vesicles, and determination of the dry weight of purified vesicles indicated that P. gingivalis MSM-3 produced twice as much membrane vesicles as did strain A7436. Extracellular vesicles isolated from P. gingivalis MSM-3 also were found to express increased hemolytic and trypsin-like protease activities compared with the parent strain. When inoculated into subcutaneous chambers implanted in mice, P. gingivalis MSM-3 was highly infectious and more invasive than the parent strain, as indicated by secondary lesion formation and death. Taken together, these results indicate that the decreased transport of hemin by P. gingivalis MSM-3 results in the increased expression of several virulence factors which may be coordinately regulated by hemin.