Virulence of Wolinella recta in a murine abscess model

Identification and functional analysis of the S-layer protein SplA of Paenibacillus larvae, the causative agent of American Foulbrood of honey bees

The Gram-positive, spore-forming bacterium Paenibacillus larvae is the etiological agent of American Foulbrood (AFB), a globally occurring, deathly epizootic of honey bee brood. AFB outbreaks are predominantly caused by two genotypes of P. larvae, ERIC I and ERIC II, with P. larvae ERIC II being the more virulent genotype on larval level. Recently, comparative proteome analyses have revealed that P. larvae ERIC II but not ERIC I might harbour a functional S-layer protein, named SplA. We here determine the genomic sequence of splA in both genotypes and demonstrate by in vitro self-assembly studies of recombinant and purified SplA protein in combination with electron-microscopy that SplA is a true S-layer protein self-assembling into a square 2D lattice. The existence of a functional S-layer protein is novel for this bacterial species. For elucidating the biological function of P. larvae SplA, a genetic system for disruption of gene expression in this important honey bee pathogen was developed. Subsequent analyses of in vivo biological functions of SplA were based on comparing a wild-type strain of P. larvae ERIC II with the newly constructed splA-knockout mutant of this strain. Differences in cell and colony morphology suggest that SplA is a shape-determining factor. Marked differences between P. larvae ERIC II wild-type and mutant cells with regard to (i) adhesion to primary pupal midgut cells and (ii) larval mortality as measured in exposure bioassays corroborate the assumption that the S-layer of P. larvae ERIC II is an important virulence factor. Since SplA is the first functionally proven virulence factor for this species, our data extend the knowledge of the molecular differences between these two genotypes of P. larvae and contribute to explaining the observed differences in virulence. These results present an immense advancement in our understanding of P. larvae pathogenesis.

Paenibacillus larvae is the most devastating bacterial pathogen of honey bees. However, the molecular interactions between infected larvae and P. larvae are poorly understood and little more than speculation exist concerning virulence factors. Recently, a putative S-layer protein has been identified in P. larvae. We here demonstrate that only representatives of P. larvae genotype ERIC II harbor a functional splA-gene and that SplA is a true S-layer protein with self-assembly capability. The presence of a functional S-layer protein is novel for P. larvae. When elucidating the biological function of SplA we broke new ground by establishing primary cell culture for pupal gut cells and by developing a genetic system for disruption of gene expression in this important honey bee pathogen. By using these novel methods we were able to prove that SplA serves as a shape-determining factor, mediates adhesion to host cells, and is a key virulence factor of P. larvae ERIC II. These results present an immense advancement in our understanding of P. larvae pathogenesis. Furthermore, we propose P. larvae as a model system for the analysis of the in vivo functions of S-layer proteins because P. larvae SlpA knockout-mutants retain viability and are thus suitable for functional studies.

Identification and characterization of the genes encoding a unique surface (S-) layer of Tannerella forsythia

A newly emerged periodontopathic pathogen Tannerella forsythia (formerly Bacteroides forsythus), a Gram-negative, filament-shaped, strict anaerobic, non-pigmented oral bacterium, possesses a surface (S-) layer. In our previous studies, the S-layer has been isolated, and shown to mediate hemagglutination, adhesion/invasion of epithelial cell, and murine subcutaneous abscess formation. In the present study, biochemical and molecular genetic characterization of the S-layer are reported. Amino acid sequencing and mass spectrometry indicated that the S-layer is composed of two different proteins, termed 200 and 210 kDa proteins. It was also shown that these proteins are glycosylated. The genes encoding the core proteins of these glycoproteins, designated as tfsA and tfsB, have been identified in silico, cloned, and their sequences have been determined. The tfsA (3.5 kb) and tfsB (4.1 kb) genes are located in tandem, and encode for 135 and 152 kDa proteins, respectively. An apparent discrepancy in molecular weights, 135 vs. 200 kDa and 152 vs. 210 kDa, is accounted for carbohydrate residues attached to the core proteins. Amino acid sequence comparison exhibited a 24% similarity between the 200 and 210 kDa proteins. Further sequence analyses showed that TfsA and TfsB possess putative signal peptide sequences with cleavage sites at alanine residues, and transmembrane domains on the C-terminal region. Northern blot and RT-PCR analyses confirmed an operon structure of tfsAB, suggesting co-regulation of these genes in producing the S-layer. Putative promoter sequences and transcription termination sequences for this operon have also been identified. Comparison with database indicates that the S-layer of T. forsythia has a unique structure exhibiting no homology to other known S-layers of prokaryotic organisms. The present study shows that the T. forsythia S-layer is very unique, since it appears to be composed of two large glycoproteins, and it does not reveal any homology to other known S-layer proteins or glycoproteins of prokaryotic organisms.

Campylobacter gracilis and Campylobacter rectus in primary endodontic infections

AIM

A species-specific nested polymerase chain reaction (PCR) assay was used to investigate the occurrence of Campylobacter gracilis and C. rectus in primary root canal infections.

METHODOLOGY

Samples were collected from 57 single-rooted teeth with carious lesions, necrotic pulps and radiographic evidence of periradicular disease. Twenty-eight cases were diagnosed as chronic asymptomatic periradicular lesions, 12 cases as acute apical periodontitis, and 17 cases as acute periradicular abscess. DNA was extracted from the samples and initially amplified using universal 16S rDNA primers. A second round of amplification using the first PCR products was performed to specifically detect C. gracilis or C. rectus in the samples.

RESULTS

Campylobacter gracilis and C. rectus were, respectively, detected in 21.4 (6 of 28) and 30% (6 of 20) of the root canals associated with chronic asymptomatic periradicular lesions. Campylobacter gracilis was found in 16.7% (2 of 12) of the cases diagnosed as acute apical periodontitis, whilst C. rectus was found in 33.3% (two of six cases). In the abscessed cases, C. gracilis and C. rectus were detected in 23.5 (4 of 17) and 11.8% (2 of 17) of the cases, respectively. No association of these species with clinical symptoms was observed (P > 0.01) In general, species-specific nPCR allowed the detection of C. gracilis in 21.1% (12 of 57) and C. rectus in 23.3% (10 of 43)of the samples taken from primary endodontic infections.

CONCLUSIONS

Findings confirmed the assertion that both C. gracilis and C. rectus participate in infections of endodontic origin and suggest a pathogenetic role with regard to periradicular diseases.

B-Cell deficiency predisposes mice to disseminating anaerobic infections: protection by passive antibody transfer

We have previously demonstrated that a high proportion of RAG-2 SCID knockout mice, which lack T and B cells, develop orofacial abscesses and disseminated infections following pulpal infection, whereas immunocompetent control mice do not. In the present study, we sought to identify the components of the adaptive immune response which contribute to protection against disseminating anaerobic infections and sepsis. For this purpose, various genetically engineered immunodeficient mice were employed, including RAG-2 SCID, Igh-6 (B-cell deficient), Tcrb Tcrd (T-cell deficient) and Hc(0) (C5 deficient). For abscess induction, the mandibular first molars were subjected to pulp exposure on day 0. Teeth were infected with a mixture of four anaerobic pathogens, including Prevotella intermedia, Streptococcus intermedius, Fusobacterium nucleatum, and Peptostreptococcus micros, and teeth were sealed to prevent communication with the oral cavity. The findings demonstrate that both RAG-2 SCID and B-cell-deficient mice, but not T-cell- or C5-deficient mice, have increased susceptibility to the development of disseminating anaerobic infections. Abscess-susceptible RAG-2 SCID and B-cell-deficient mice also showed a significant loss of body weight, splenomegaly, and absent antibacterial antibody production. Furthermore, dissemination was significantly reduced, from 74 to 25%, in susceptible RAG-2 mice by passively transferred antibody, predominantly immunoglobulin G2b (IgG2b) and IgM, against the infecting bacterial innoculum. Fractionated IgG-enriched preparations were more efficient in transferring protection than IgM preparations. We conclude that an antibody-mediated mechanism(s), most likely bacterial opsonization, is of importance in localizing anaerobic root canal infections and in preventing their systemic spread.

Use of defined mutants to assess the role of the Campylobacter rectus S-layer in bacterium-epithelial cell interactions

Campylobacter rectus is a periodontal pathogen with a 150-kDa protein on its cell surface. This protein forms a paracrystalline lattice, called the S-layer, surrounding the outer membrane of this gram-negative bacterium. To initiate a genetic analysis of the possible role of the S-layer in the initial interaction of C. rectus with host epithelial cells, C. rectus strains lacking the S-layer protein gene (crsA) were constructed by allelic exchange mutagenesis. Surprisingly, the lack of the S-layer had only a minor effect on the interaction of C. rectus with HEp-2 epithelial cells; CrsA(+) cells were 30 to 50% more adherent than were CrsA(-) bacteria. Since the host cell expression of cytokines appears to play an important role in the pathogenesis of periodontal diseases, the effect of the S-layer on the epithelial cell cytokine response was also examined by quantitative reverse transcriptase PCR and enzyme-linked immunosorbent assay. Although there were no changes in the mRNA levels for the anti-inflammatory cytokines interleukin-1 receptor agonist (IL-1ra), IL-13, and transforming growth factor beta, the expression and secretion of the proinflammatory cytokines IL-6, IL-8, and tumor necrosis factor alpha (TNF-alpha) were significantly induced by both wild-type C. rectus and CrsA(-) bacteria. Interestingly, the kinetics of cytokine induction differed for the CrsA(+) and CrsA(-) bacteria. At early time points, the HEp-2 cells challenged with CrsA(-) bacteria produced higher levels of IL-6, IL-8, and TNF-alpha mRNA and protein than did cells challenged with CrsA(+) bacteria. We conclude that C. rectus may help initiate periodontitis by increasing the expression of proinflammatory cytokines and that the S-layer may temper this response to facilitate the survival of C. rectus at the site of infection.

Lack of humoral immune protection against Treponema denticola virulence in a murine model

This study investigated the characteristics of humoral immune responses to Treponema denticola following primary infection, reinfection, and active immunization, as well as immune protection in mice. Primary infection with T. denticola induced a significant (400-fold) serum immunoglobulin G (IgG) response compared to that in control uninfected mice. The IgG response to reinfection was 20, 000-fold higher than that for control mice and 10-fold higher than that for primary infection. Mice actively immunized with formalin-killed treponemes developed serum antibody levels seven- to eightfold greater than those in animals after primary infection. Nevertheless, mice with this acquired antibody following primary infection or active immunization demonstrated no significant alterations of lesion induction or decreased size of the abscesses following a challenge infection. Mice with primary infection developed increased levels of IgG3, IgG2b, and IgG2a antibodies, with IgG1 being lower than the other subclasses. Reinfected mice developed enhanced IgG2b, IgG2a, and IgG3 and less IgG1. In contrast, immunized mice developed higher IgG1 and lower IgG3 antibody responses to infection. These IgG subclass distributions indicate a stimulation of both Th1 and Th2 activities in development of the humoral immune response to infection and immunization. Our findings also demonstrated a broad antigen reactivity of the serum antibody, which was significantly increased with reinfection and active immunization. Furthermore, serum antibody was effective in vitro in immobilizing and clumping the bacteria but did not inhibit growth or passively prevent the treponemal infection. These observations suggest that humoral immune responses, as manifested by antibody levels, isotype, and antigenic specificity, were not capable of resolving a T. denticola infection.

Paradoxical role of PGE2 and cAMP in Actinobacillus actinomycetemcomitants strain Y4-induced lymphocyte proliferation

An immune mechanism has been suggested in the pathogenesis of periodontal disease. Actinobacillus actinomycetemcomitants (Aa) has been implicated as one of the etiological agents that induces the major immune response together with a dense infiltrate of inflammatory cells. But the exact role of these immune cells in periodontal disease has not yet been clarified. In this study the T lymphocyte (TL) proliferative response was evaluated after having being exposed to free cell supernatant (SN) from Aa. Aa SN increased TL proliferation. This mitogenic effect of Aa SN was attenuated by pretreating TL with indomethacin (INDO) or acetylsalicylic acid (ASA) but not by polymyxin B. The inhibitory effect of INDO on cell proliferation was reversed by the addition of prostaglandin E2 (PGE2) to the culture assay. Moreover, when immune cells were exposed to Aa SN they were able to generate PGE2 at the same time as intracellular levels of cAMP decreased. Both, PGE2 release and decrease accumulation of cAMP in TL were blunted by treated lymphocytes with INDO. In this paper we demonstrate that cell free SN from Aa induces a mitogenic effect on murine lymphocytes. The mechanism involves the host's immunecompetent cells and the release of PGE2 and appears not to be induced by capsular-like polysaccharide antigen. Results show a paradoxical mitogenic effect of Aa SN accompanied by increased generation of PGE2 and decreased production of cAMP by lymphocytes.

Environmental modulation of oral treponeme virulence in a murine model

This investigation examined the effects of environmental alteration on the virulence of the oral treponemes Treponema denticola and Treponema pectinovorum. The environmental effects were assessed by using a model of localized inflammatory abscesses in mice. In vitro growth of T. denticola and T. pectinovorum as a function of modification of the cysteine concentration significantly enhanced abscess formation and size. In contrast, growth of T. denticola or T. pectinovorum under iron-limiting conditions (e.g., dipyridyl chelation) had no effect on abscess induction in comparison to that when the strains were grown under normal iron conditions. In vivo modulation of the microenvironment at the focus of infection with Cytodex beads demonstrated that increasing the local inflammation had no effect on lesion induction or size. In vivo studies involved the determination of the effects of increased systemic iron availability (e.g., iron dextran or phenylhydrazine) on the induction, kinetics, and size of lesions. T. denticola induced significantly larger lesions in mice with iron pretreatment and demonstrated systemic manifestations of the infectious challenge and an accompanying spreading lesion with phenylhydrazine pretreatment (e.g., increases in circulating free hemoglobin). In contrast, T. pectinovorum virulence was minimally affected by this in vivo treatment to increase iron availability. T. denticola virulence, as evaluated by lesion size, was increased additively by in vivo iron availability, and cysteine modified growth of the microorganism. Additionally, galactosamine sensitized mice to a lethal outcome following infection with both T. denticola and T. pectinovorum, suggesting an endotoxin-like activity in these treponemes. These findings demonstrated the ability to modify the virulence capacity of T. denticola and T. pectinovorum by environmental conditions which can be evaluated by using in vivo murine models.

Cloning and characterization of two bistructural S-layer-RTX proteins from Campylobacter rectus

Campylobacter rectus is an important periodontal pathogen in humans. A surface-layer (S-layer) protein and a cytotoxic activity have been characterized and are thought to be its major virulence factors. The cytotoxic activity was suggested to be due to a pore-forming protein toxin belonging to the RTX (repeats in the structural toxins) family. In the present work, two closely related genes, csxA and csxB (for C. rectus S-layer and RTX protein) were cloned from C. rectus and characterized. The Csx proteins appear to be bifunctional and possess two structurally different domains. The N-terminal part shows similarity with S-layer protein, especially SapA and SapB of C. fetus and Crs of C. rectus. The C-terminal part comprising most of CsxA and CsxB is a domain with 48 and 59 glycine-rich canonical nonapeptide repeats, respectively, arranged in three blocks. Purified recombinant Csx peptides bind Ca2+. These are characteristic traits of RTX toxin proteins. The S-layer and RTX domains of Csx are separated by a proline-rich stretch of 48 amino acids. All C. rectus isolates studied contained copies of either the csxA or csxB gene or both; csx genes were absent from all other Campylobacter and Helicobacter species examined. Serum of a patient with acute gingivitis showed a strong reaction to recombinant Csx protein on immunoblots.

Virulence of a polymicrobic complex, Treponema denticola and Porphyromonas gingivalis, in a murine model

The effect of a polymicrobic infection employing Treponema denticola and Porphyromonas gingivalis in the murine lesion model was used to determine the synergistic virulence of these two periodontopathic bacteria. At high doses of P. gingivalis W50, addition of T. denticola in the infection mixture had no effect on the formation and size of the spreading lesion caused by this microorganism. However, at low P. gingivalis challenge doses, T. denticola significantly enhanced the virulence of P. gingivalis compared with monoinfection of this microorganism. A potential role of the trypsin-like protease enzyme activity of P. gingivalis in this synergistic virulence was tested using P. gingivalis mutants deficient (i.e., BEI) or devoid (i.e., NG4B19) of this protease activity. These findings demonstrated that T. denticola-P. gingivalis complexes exhibit enhanced virulence in this model and that even using a polymicrobic challenge infection, the trypsin-like protease activity was important to P. gingivalis virulence expression.

The S-layer protein from Campylobacter rectus: sequence determination and function of the recombinant protein

The gene encoding the crystalline surface layer (S-layer) protein from Campylobacter rectus, designated slp, was sequenced and the recombinant gene product was expressed in Escherichia coli. The gene consisted of 4086 nucleotides encoding a protein with 1361 amino acids. The N-terminal amino acid sequence revealed that Slp did not contain a signal sequence, but that the initial methionine residue was processed. The deduced amino acid sequence displayed some common characteristic features of S-layer proteins previously reported. A homology search showed a high similarity to the Campylobacter fetus S-layer proteins, especially in their N-terminus. The C-terminal third of Slp exhibited homology with the RTX toxins from Gram-negative bacteria via the region including the glycine-rich repeats. The Slp protein had the same N-terminal sequence as a 104-kDa cytotoxin isolated from the culture supernatants of C. rectus. However, neither native nor recombinant Slp showed cytotoxicity against HL-60 cells or human peripheral white blood cells. These data support the idea that the N-terminus acts as an anchor to the cell surface components and that the C-terminus is involved in the assembly and/or transport of the protein.

Bone resorption caused by three periodontal pathogens in vivo in mice is mediated in part by prostaglandin

Gingival inflammation, bacterial infection, alveolar bone destruction, and subsequent tooth loss are characteristic features of periodontal disease, but the precise mechanisms of bone loss are poorly understood. Most animal models of the disease require injury to gingival tissues or teeth, and the effects of microorganisms are thus complicated by host responses to tissue destruction. To determine whether three putative periodontal pathogens, Porphyromonas gingivalis, Campylobacter rectus, and Fusobacterium nucleatum, could cause localized bone resorption in vivo in the absence of tissue injury, we injected live or heat-killed preparations of these microorganisms into the subcutaneous tissues overlying the calvaria of normal mice once daily for 6 days and then examined the bones histologically. We found that all three microorganisms (both live and heat killed) stimulated bone resorption and that the strain of F. nucleatum used appeared to be the strongest inducer of osteoclast activity. Treatment of the mice concomitantly with indomethacin reduced but did not completely inhibit bone resorption by these microorganisms, suggesting that their effects were mediated, in part, by arachidonic acid metabolites (e.g., prostaglandins). Our findings indicate that these potential pathogens can stimulate bone resorption locally when placed beside a bone surface in vivo in the absence of prior tissue injury and support a role for them in the pathogenesis of bone loss around teeth in periodontitis.

A new member of the S-layer protein family: characterization of the crs gene from Campylobacter rectus

Strains of the periodontal pathogen Campylobacter rectus express a 150- to 166-kDa protein on their cell surface. This protein forms a paracrystalline lattice, called the surface layer (S-layer), on the outer membrane of this gram-negative bacterium. To initiate a genetic analysis of the function of the S-layer in the pathogenesis of C. rectus, we have cloned and characterized its gene. The S-layer gene (crs) from C. rectus 314 encodes a cell surface protein which does not have a cleaved signal peptide at its amino terminus. Although the amino acid sequence deduced from the crs gene has 50% identity with the amino-terminal 30 amino acids of the four S-layer proteins from Campylobacter fetus, the similarity decreases to less than 16% over the rest of the protein. Thus, the crs gene from C. rectus encodes a novel S-layer protein whose precise role in pathogenesis may differ from that of S-layer proteins from other organisms. Southern and Northern blot analyses with probes from different segments of the crs gene indicate that the S-layer gene is a single-copy, monocistronic gene in C. rectus. RNA end mapping and sequence analyses were used to define the crs promoter; there is an exact match to the Escherichia coli -10 promoter consensus sequence but only a weak match to the -35 consensus element. Southern blots of DNA from another strain of C. rectus, ATCC 33238, demonstrated that the crs gene is also present in that strain but that there are numerous restriction fragment length polymorphisms in the second half of the gene. This finding suggests that the carboxy halves of the S-layer proteins from strains 314 and 33238 differ. It remains to be determined whether the diversities in sequence are reflected in functional or antigenic differences important for the pathogenesis of different C. rectus isolates.

Virulence characteristics of oral treponemes in a murine model

This study was designed to investigate the virulence characteristics of Treponema denticola, T. socranskii, T. pectinovorum, and T. vincentii following challenge infection of mice. These microorganisms induced well-demarcated, dose-dependent, raised subcutaneous (s.c.) abscesses which were similar in time of onset, lesion progression, and duration of healing. Only viable cells were capable of inducing these characteristic s.c. abscesses. Histological examination of the skin lesion 3 and 5 days postinfection revealed abscess formation in the s.c. tissues, and abundant spiral organisms were demonstrated to be present in the abscess. Host resistance modulation by dexamethasone (neutrophil alteration) and cyclophosphamide (neutrophil depletion) pretreatment had a minimal effect on the virulence expression by any of these treponemes. The T. denticola isolates demonstrated significant trypsin-like protease (TLPase) activity, while both T. socranskii and T. vincentii were devoid of this activity. Interestingly, T. pectinovorum strains were heterogeneous with respect to TLPase as high producers, low producers, and nonproducers. However, no differences in lesion formation were noted regardless of whether the species expressed this proteolytic activity or whether treatment with N alpha-p-tosyl-L-lysine chloromethyl ketone (TLCK) and dithiothreitol was performed. These results showed that (i) a murine model may be used to evaluate virulence expression by oral treponemes; (ii) while TLPase activity varies among the oral treponemes, this protease does not appear to participate in abscess induction in the mouse model; and (iii) T. pectinovorum strains show variation in TLPase activity.

Porphyromonas gingivalis virulence in a murine lesion model: effects of immune alterations

This study utilized various mouse strains with documented alterations in immune system components to assess their contribution to modify the virulence of Porphyromonas gingivalis. P. gingivalis W50 was cultivated on blood agar plates, harvested and used to challenge mice by subcutaneous injection on the dorsolateral surface of the back. Soft tissue lesion development was estimated by measuring the area of the spreading lesion formed by this microorganism over a period of 15 days. Challenge of various normal inbred and outbred mouse strains including: BALB/cN, BALB/cJ, BALB/c nu/+, ICR, B10.A(4R), B10.MBR, A/J, C57BL/6J, CBA/CaH, C.B-17/Icv Tacf DF and C3H/HeN with 2 x 10(10) bacteria showed similar lesion size among these strains (approximately 400 mm2). Genetically deficient mouse strains [C.B-17/Icr Tac (SCID); DBA/2 (C5 deficient); BALB/c nu/nu (T cell deficient); CBA/CaHN-XID/J (B cell deficient) and C3H/HeJ (LPS hyporesponsive)] demonstrated a lesion size which was similar to normal animals. C57BL/6J-BgJ (NK cell deficient) mice exhibited a significantly more severe lesion than the other strains tested. Following healing of the lesions, we initiated a secondary infection of the surviving animals to estimate the acquisition of protective immunity following recovery from the primary infection. Normal mice demonstrated a delayed onset and decrease in lesion size of 15 to 30% compared with the primary infection. In contrast, each of the immunodeficient strains appeared unable to develop immune protection to the secondary challenge. The findings suggest that protection against primary infections with P. gingivalis are mediated by innate immune mechanisms (PMN. NK cells). Additionally, it appears that T-cell-dependent humoral responses are critical to developing immunity to subsequent P. gingivalis infection.

Host modulation of tissue destruction caused by periodontopathogens: effects on a mixed microbial infection composed of Porphyromonas gingivalis and Fusobacterium nucleatum

These studies determined the ability of selected periodontopathogens to synergistically initiate soft tissue destruction in a murine abscess model. The development of immunity following recovery from infection or by active immunization was also examined. Mice were infected with P. gingivalis W50, F. nucleatum T18, or a combination of the two microorganisms. F. nucleatum caused only a localized lesion in contrast to P. gingivalis which caused a spreading suppurative inflammatory lesion of the skin and subcutaneous tissues, which, depending upon the dose, could result in death. Infection of mice with a combination of P. gingivalis and F. nucleatum elicited a significantly greater lesion size (P<0.001) and lethality compared with P. gingivalis alone. Mice infected with a subclinical dose (no visible lesion) of P. gingivalis failed to develop protective immunity to a secondary P. gingivalis challenge. Mice that had recovered from P. gingivalis lesions demonstrated partial protection against subsequent P. gingivalis challenge; however, the immunity was less protective against the mixed F. nucleatum + P. gingivalis infection. Active immunization with P. gingivalis protected against both the P. gingivalis and F. nucleatum + P. gingivalis challenges and this protection was correlated with the levels of specific serum immunoglobulin G (IgG) antibody. The results indicated that the murine model is ideally suited to examine bacterially-mediated mixed infections that result in soft tissue destruction. This destruction can be minimized, but not abrogated, with development of immunity. Challenge with sufficient numbers of the pathogens can overwhelm the acquired immunity.

Purification and characterization of Campylobacter rectus surface layer proteins

Campylobacter rectus is a putative periodontopathogen which expresses a proteinaceous surface layer (S-layer) external to the outer membrane. S-layers are considered to play a protective role for the microorganism in hostile environments. The S-layer proteins from six different C. rectus strains (five human isolates and a nonhuman primate [NHP] isolate) were isolated, purified, and characterized. The S-layer proteins of these strains varied in molecular mass (ca. 150 to 166 kDa) as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. They all reacted with monospecific rabbit antiserum to the purified S-layer of C. rectus 314, but a quantitative enzyme-linked immunosorbent assay demonstrated a strong antigenic relationship among the five human strains, while the NHP strain, 6250, showed weaker reactivity. Amino acid composition analysis showed that the S-layers of four C. rectus strains contained large proportions of acidic amino acids (13 to 27%) and that >34% of the amino acid residues were hydrophobic. Amino acid sequence analysis of six S-layer proteins revealed that the first 15 amino-terminal amino acids were identical and showed seven residues of identity with the amino-terminal sequence of the Campylobacter fetus S-layer protein SapA1. CNBr peptide profiles of the S-layer proteins from C. rectus 314, ATCC 33238, and 6250 confirmed that the S-layer proteins from the human strains were similar to each other and somewhat different from that of the NHP isolate (strain 6250). However, the S-layer proteins from the two human isolates do show some structural heterogeneity. For example, there was a 17-kDa fragment unique to the C. rectus 314 S-layer. The amino-terminal sequence of this peptide had homology with the C. rectus 51-kDa porin and was composed of nearly 50% hydrophobic residues. Thus, the S-layer protein from C. rectus has structural heterogeneity among different human strains and immunoheterogeneity with the NHP strain.

Production of inflammatory mediators and cytokines by human gingival fibroblasts following bacterial challenge

Bacteria can indirectly affect the course of periodontal diseases by activating host cells to produce and release inflammatory mediators and cytokines. These mediators and cytokines manifest potent proinflammatory and catabolic activity and may play key roles in local amplification of the immune response as well as in periodontal tissue breakdown. This study tested the effect of Actinobacillus actinomycetemcomitans (Aa) and Campylobacter rectus (Cr) challenge on PGE2, IL-1 beta, IL-6 and IL-8 production by human gingival fibroblasts (HGF). Contact-inhibited HGF were prepared and formalin-killed bacterial cells (Aa JP2, ATCC 29523 & 33384 and Cr ATCC 33238) at 10(6)-10(9) were added to the HGF. Culture supernatants were collected at varying time intervals and analyzed for cytokine and mediator content. All concentrations of Aa JP2 and Cr ATCC 33238 suppressed IL-1 beta production up to approximately 50% during the initial 3-12-h period. No bacterial concentration tested was able to increase IL-1 beta production above the maximum basal levels. Both bacterial species stimulated production of IL-6 and IL-8. Aa JP2 did not affect PGE2 levels significantly, whereas Cr ATCC 33238 was stimulatory only at the highest concentration tested (10(9)). There were no significant differences among the three Aa strains with respect to IL-1 beta production. However, Aa ATCC 29523 and ATCC 33384 were less capable of stimulating IL-6 secretion and more efficient in stimulating IL-8 production than Aa JP2. In general, Cr was the most potent enhancer of cytokine and mediator production by HGF. In conclusion, Aa and Cr are capable of amplifying the local immune response and promoting periodontal tissue inflammation by stimulating HGF to secrete mainly IL-6 and IL-8.

Cell envelope and cell wall immunization of Macaca fascicularis: effect on the progression of ligature-induced periodontitis

The nonhuman primate, Macaca fascicularis, was used to study the role of immunization with selected members of the periodontopathic microbiota in the longitudinal progression of ligature-induced periodontitis. Animals were immunized with cell envelope antigens prepared from Porphyromonas gingivalis and Prevotella intermedia, and a mixture prepared from Fusobacterium nucleatum, Campylobacter rectus, and Actinomyces viscosus. Serum immunoglobulin G (IgG), IgM and IgA isotype antibodies increased significantly in all immunization groups and were specific for each of the immunogens. P. gingivalis and P. intermedia immunization resulted in a stabilization of the proportions of these species throughout most of the experiment. The high P. gingivalis antibody titer resulted in low P. gingivalis numbers being recovered. P. gingivalis immunization, while lowering recoverable viable P. gingivalis, resulted in significantly increased levels of Prevotella loescheii, Prevotella buccae, Bacteroides macacae and Prevotella melaninogenica compared with preligation and preimmunization levels. Actinobacillus actinomycetemcomitans, Capnocytophaga spp. and Eikenella spp. remained at preligation levels postimmunization. Campylobacter spp. increased significantly during the course of the experiment in all groups, whereas the levels of Fusobacterium spp. decreased. Plaque indices and bleeding on probing showed significant increases in all groups following ligation, with the placebo group showing the greatest increase. Pocket depth measurements revealed that , whereas the placebo animals showed an approximate 5% increase, the P. gingivalis- and P. intermedia-immunized groups showed nearly a 20% increase in pocket depth. Attachment level measurements showed significantly greater attachment loss in the P. gingivalis- and P. intermedia-immunized groups, and the F. nucleatum + C. rectus + A. viscosus immunization appeared to prevent significant changes in pocket depth/attachment level loss. Radiographic measurement of bone loss by computer-assisted densitometric image analysis revealed that the placebo group lost bone throughout the experiment. P. gingivalis- and P. intermedia-immunized groups showed an exacerbated loss of bone density and the group immunized with F. nucleatum + C. rectus + A. viscosus exhibited significantly lower amounts of bone loss when analyzed by computer-assisted densitometric image analysis, compared with the other immunized groups. Although immunization with P. gingivalis and P. intermedia cell envelope antigens had an effect on their emergence in the complex microbiota of the developing periodontal pocket, this immunization also resulted in greater bone loss than immunization with F. nucleatum + C. rectus + A. viscosus, suggesting that, whereas selective members of the putative periodontopathic microbiota may play a direct role in periodontal tissue destruction, the complexity of the subgingival microbiota dictates that considerable scrutiny is required to select useful immunogens that can elicit functional protection from periodontal tissue destruction induced by oral microorganisms that already colonize or infect the host.

Comparative virulence of periodontopathogens in a mouse abscess model

OBJECTIVE(S)

This report compares the virulence of selected strains of P. gingivalis, A. actinomycetemcomitans, C. rectus, F. nucleatum and T. denticola in a murine model as a measure of pathogenic potential of these oral microorganisms. The characteristics of the tissue destruction associated with these monoinfections were then related to a potential model for bacterial synergism in progressing periodontitis.

DESIGN AND METHODS

All bacterial strains were grown to mid-logarithmic to early stationary growth phase, harvested and used at various doses to challenge BALB/c normal and BALB/c dexamethasone (DEX) treated mice to mimic a neutrophil dysfunction. The characteristics of tissue destruction, and overt tissue destructive capacity of these species were examined as a function of challenge dose and time.

OUTCOME MEASURES

The mice were examined for an interval of approximately 15 days post-challenge and the presence/absence of lesions, localized or generalized nature of the lesion (including size in mm2), and lethality of the infection were assessed.

RESULTS

Comparison of the virulence of the various P. gingivalis strains related to lethality and lesion size associated with destruction of the connective tissue, indicated a virulence capacity of P. gingivalis strains 53977>W50 = T22>3079>33277>381. C. rectus elicited localized necrotic lesions which were limited to the epithelial layers of the skin. The size of the lesions also indicated a graded difference in virulence, such that C. rectus strains 234>576>>33238. A. actinomycetemcomitans caused the formation of classic localized abscesses with a PMN infiltrate and inflammatory exudates. Although each of the A. actinomycetemcomitans strains exhibited a similar virulence pattern in this murine model, A. actinomycetemcomitans serotype b representative strains were potentially more pathogenic with a virulence capacity of 3113D-N = 3975A>JP2 > or = Y4>29523>33384. Both C. rectus and A. actinomycetemcomitans strains showed clear evidence that recent clinical isolates were more virulent than laboratory strains. Challenge with F. nucleatum resulted in tissue destructive responses which were different from those observed with the other strains used in this study. A rapid onset of dose-dependent lesion development, related to the formation of either closed abscesses or open lesions, was observed with F. nucleatum. Tissue involvement was also greater at lower F. nucleatum doses when compared to the other bacteria. F. nucleatum challenge of DEX-treated mice resulted in a shift to open lesions. T. denticola appeared to be more tissue invasive than the other species examined in this study. Challenge of mice with T. denticola resulted in involvement of multiple tissues, including epithelial and connective tissues, as well as appearing to invade muscle layers and deeper tissues. In addition to invading deeper tissues, the resulting lesions took considerably longer to resolve. In the DEX-treated mice (neutrophil depleted), P. gingivalis, C. rectus, and A. actinomycetemcomitans were significantly more virulent. In contrast, while DEX treatment altered the characteristics of lesions caused by F. nucleatum, the extent of lesions produced by F. nucleatum and T. denticola was not substantially enhanced.

CONCLUSIONS

The results obtained from this study suggest that different microorganisms have the ability to provide individual pathologies which may act in an additive/synergistic fashion contributing to the tissue destruction noted in periodontitis.

Specific antibodies and their potential role in periodontal diseases

Periodontal diseases are thought to result from inflammatory responses to bacterial challenges in the gingival crevicular area. Antibodies are a major host-protective mechanism in many bacterial infections. Consequently, the antibody responses to suspected periodontal pathogenic bacteria have been extensively measured as to their relationship to diseases and specificity for suspected pathogens associated with progressing disease sites. Recently, studies on the bacterial immunogen characterization, antibody-subclass identification, and antibody biological capabilities have been reported. Although increased antibody levels to certain suspected periodontal pathogens were associated with periodontal diseases in humans, little evidence exists as to the role of these antibodies in the infectious process. In vivo experiments in animals indicated that specific antibodies against certain suspected periodontal pathogens were associated with suppression of bacterial colonization, limiting the spread of infection, and a decrease in alveolar bone loss. However, in vitro as well as in vivo experiments suggested that phagocytic cells are required for efficient bactericidal activity of antibodies and that the presence of other sensitized immune cells may either have inhibited or enhanced the infectivity of certain periodontal pathogens. Possible explanations for the observed inconsistencies are presented and the potential for utilization of specific anti-periodontal pathogen responses in the understanding and prevention of diseases is discussed.

Campylobacter rectus in human periodontitis

Campylobacter rectus (formerly Wolinella recta) in periodontitis lesions was studied relative to age and sex distribution, relationship to disease-active periodontitis, response to periodontal debridement and in vitro antimicrobial susceptibility. Subgingival C. rectus was collected with paper points, transported in VMGA III and plated onto nonselective enriched brucella blood agar and Hammond's selective medium for C. rectus, both incubated anaerobically. C. rectus was recovered from 80% of 1654 periodontitis patients. Although the organism showed similar age and sex occurrence, its proportional recovery in culture-positive adults was inversely related to increasing age (r = 0.999, P < 0.001). The organism was positively associated (summary odds ratio = 2.95) with disease activity in a 24-month longitudinal study of 93 adult periodontitis patients on maintenance therapy. C. rectus decreased from 8.2% to 0.7% following local periodontal debridement of 20 culture-positive adult periodontitis patients. The organism exhibited high in vitro susceptibility to therapeutic levels of tetracycline hydrochloride, metronidazole, penicillin G and ciprofloxacin. These findings further delineate the epidemiology and potential pathogenic role of C. rectus in human periodontitis.

Antigenic properties of Campylobacter rectus (Wolinella recta) major S-layer proteins

The antigenic properties of the surface layer (S-layer) proteins of various Campylobacter rectus strains including 24 clinical isolates and the type strain ATCC 33238 were examined. S-layer proteins were extracted from whole cells by acid treatment according to the method of McCoy et al. (Infect. Immun. 11, 517-525, 1975). The acid extracts from 23 of the isolates and ATCC 33238 contained two major proteins with molecular masses of 130 kDa and 150 kDa, both of which were identified as subunits of the S-layer after comparison with the protein profiles of acid-treated (S-layer-deficient) cells. An S-layer protein from one isolate (CI-808) demonstrated a different molecular mass (160 kDa). Both the 150-kDa proteins of ATCC 33238 and isolate CI-306 and the 160-kDa protein of CI-808 were purified by ion-exchange chromatography in the presence of urea. In Ouchterlony immunodiffusion experiments with these purified proteins and rabbit antiserum raised to each purified protein, both common and strain-specific antigenic determinants were identified in the C. rectus S-layer proteins.

Factors in virulence expression and their role in periodontal disease pathogenesis

The classic progression of the development of periodontitis with its associated formation of an inflammatory lesion is characterized by a highly reproducible microbiological progression of a Gram-positive microbiota to a highly pathogenic Gram-negative one. While this Gram-negative microbiota is estimated to consist of at least 300 different microbial species, it appears to consist of a very limited number of microbial species that are involved in the destruction of periodontal diseases. Among these "putative periodontopathic species" are members of the genera Porphyromonas, Bacteroides, Fusobacterium, Wolinella, Actinobacillus, Capnocytophaga, and Eikenella. While members of the genera Actinomyces and Streptococcus may not be directly involved in the microbial progression, these species do appear to be essential to the construction of the network of microbial species that comprise both the subgingival plaque matrix. The temporal fluctuation (emergence/disappearance) of members of this microbiota from the developing lesion appears to depend upon the physical interaction of the periodontal pocket inhabitants, as well as the utilization of the metabolic end-products of the respective species intimately involved in the disease progression. A concerted action of the end-products of prokaryotic metabolism and the destruction of host tissues through the action of a large number of excreted proteolytic enzymes from several of these periodontopathogens contribute directly to the periodontal disease process.(ABSTRACT TRUNCATED AT 250 WORDS)