Virulence characteristics of oral treponemes in a murine model

New putative periodontopathogens and periodontal health-associated species: A systematic review and meta-analysis

To investigate the existence of any association between new putative periodontal pathogens and periodontitis. Two independent reviewers conducted electronic literature searches in the MEDLINE (PubMed), EMBASE, DOSS and Google Scholar databases as well as a manual search to identify eligible clinical studies prior to November 2022. Studies comparing the prevalence of microorganisms other than the already-known periodontal pathogens in subgingival plaque and/or saliva samples between subjects with periodontitis and subject with periodontal health were included. Meta-analyses were performed on data provided by the included studies. Fifty studies including a total of 2739 periodontitis subjects and 1747 subjects with periodontal health were included. The Archaea domain and 25 bacterial species (Anaeroglobus geminatus, Bacteroidales [G-2] bacterium HMT 274, Desulfobulbus sp. HMT 041, Dialister invisus, Dialister pneumosintes, Eubacterium brachy, Enterococcus faecalis, Eubacterium nodatum, Eubacterium saphenum, Filifactor alocis, Fretibacterium sp. HMT 360, Fretibacterium sp. HMT 362, Mogibacterium timidum, Peptoniphilaceae sp. HMT 113, Peptostreptococcus stomatis, Porphyromonas endodontalis, Slackia exigua, Streptococcus gordonii, Selenomonas sputigena, Treponema amylovorum, Treponema lecithinolyticum, Treponema maltophilum, Treponema medium, Treponema parvum and Treponema socranskii) were found to be statistically significantly associated with periodontitis. Network studies should be conducted to investigate the role of these newly identified periodontitis-associated microorganisms through interspecies interaction and host-microbe crosstalk analyses.

Host and bacterial factors linking periodontitis and rheumatoid arthritis

Observations from numerous clinical, epidemiological and serological studies link periodontitis with severity and progression of rheumatoid arthritis. The strong association is observed despite totally different aetiology of these two diseases, periodontitis being driven by dysbiotic microbial flora on the tooth surface below the gum line, while rheumatoid arthritis being the autoimmune disease powered by anti-citrullinated protein antibodies (ACPAs). Here we discuss genetic and environmental risk factors underlying development of both diseases with special emphasis on bacteria implicated in pathogenicity of periodontitis. Individual periodontal pathogens and their virulence factors are argued as potentially contributing to putative causative link between periodontal infection and initiation of a chain of events leading to breakdown of immunotolerance and development of ACPAs. In this respect peptidylarginine deiminase, an enzyme unique among prokaryotes for Porphyromonas gingivalis, is elaborated as a potential mechanistic link between this major periodontal pathogen and initiation of rheumatoid arthritis development.

Potential Treponema denticola-based periodontal vaccine to resolve a global public health challenge: a narrative literature review

INTRODUCTION

Periodontitis is a diseased condition of the gum which imposes considerable costs on healthcare systems. It progresses further beyond the inflammation of supportive tissues of the teeth, and the collateral damages are closely associated with Alzheimer's disease, cardiovascular disease, and diabetes mellitus.

AREAS COVERED

A comprehensive literature review was performed to summarize published studies in English during the period of 1990-2021 to discuss the rationales for developing periodontal vaccine, cost-effectiveness analyses on the prevention of periodontitis, Treponema denticola-based vaccine candidates, as well as immunological mechanisms in animal models.

EXPERT OPINION

Preventive strategies against periodontitis may halt the onset of gum inflammation itself and the consequent chronic diseases. Considering the multi-microbial condition of periodontitis, an ideal periodontal vaccine should target multiple pathological pathways. Preventive approaches compared to surgical treatments evidently have significant impact on the healthcare budget and long-term health of the individuals in different communities. Despite many advances in periodontal vaccine research, there are still significant hurdles to overcome in developing a vaccine. Investment in research and development activities on key periodontal pathogens including Treponema denticola and Porphyromonas gingivalis in the foreseeable future is a worthy and cost-effective approach for the policymakers to prevent deleterious impacts of periodontitis.

Treponema spp. Isolated from Bovine Digital Dermatitis Display Different Pathogenicity in a Murine Abscess Model

Digital dermatitis (DD) causes lameness in cattle with substantial negative impact on sustainability and animal welfare. Although several species of Treponema bacteria have been isolated from various DD stages, their individual or synergistic roles in the initiation or development of lesions remain largely unknown. The objective of this study was to compare effects of the three most common Treponema species isolated from DD lesions in cattle (T. phagedenis, T. medium and T. pedis), both as individual and as mixed inoculations, in a murine abscess model. A total of 109 or 5 × 108Treponema spp. were inoculated subcutaneously, and produced abscess was studied after 7 days post infection. There were no synergistic effects when two or three species were inoculated together; however, T. medium produced the largest abscesses, whereas those produced by T. phagedenis were the smallest and least severe. Treponema species were cultured from skin lesions at 7 days post infection and, additionally, from the kidneys of some mice (2/5), confirming systemic infection may occur. Taken together, these findings suggest that T. medium and T. pedis may have more important roles in DD lesion initiation and development than T. phagedenis.

Effect of azithromycin on a red complex polymicrobial biofilm

Azithromycin has recently gained popularity for the treatment of periodontal disease, despite sparse literature supporting efficiency in treating periodontal bacterial biofilms. The aim of this study was to evaluate the effect of azithromycin on biofilms comprised of Porphyromonas gingivalis, Treponema denticola, and Tannerella forsythia in comparison to an amoxicillin and metronidazole combination. P. gingivalis W50, T. denticola ATCC35405, and T. forsythia ATCC43037 grown under anaerobic conditions at 37°C were aliquoted into 96-well flat-bottom plates in different combinations with addition of azithromycin or amoxicillin + metronidazole at various concentrations. For the biofilm assay, the plates were incubated at 37°C anaerobically for 48 h, after which the biofilms were stained with crystal violet and measured for absorbance at AU₆₂₀. In this model, polymicrobial biofilms of P. gingivalis + T. denticola, P. gingivalis + T. forsythia, and T. denticola + T. forsythia were cultured. Combination of all three bacteria enhanced biofilm biomass. Azithromycin demonstrated a minimal biofilm inhibitory concentration (MBIC) of 10.6 mg/L, while the amoxicillin + metronidazole combination was more effective in inhibiting biofilm formation with a MBIC of 1.63 mg/L. Polymicrobial biofilm formation was demonstrated by combination of all three red complex bacteria. Azithromycin was ineffective in preventing biofilm formation within a clinically achievable concentration, whereas the combination of amoxicillin and metronidazole was more effective for this purpose.

The Treponema denticola FhbB Protein Is a Dominant Early Antigen That Elicits FhbB Variant-Specific Antibodies That Block Factor H Binding and Cleavage by Dentilisin

The Treponema denticola FhbB protein contributes to immune evasion by binding factor H (FH). Cleavage of FH by the T. denticola protease, dentilisin, may contribute to the local immune dysregulation that is characteristic of periodontal disease (PD). Although three FhbB phyletic types have been defined (FhbB1, FhbB2, and FhbB3), the in vivo expression patterns and antigenic heterogeneity of FhbB have not been assessed. Here, we demonstrate that FhbB is a dominant early antigen that elicits FhbB type-specific antibody (Ab) responses. Using the murine skin abscess model, we demonstrate that the presence or absence of FhbB or dentilisin significantly influences Ab responses to infection and skin abscess formation. Competitive binding analyses revealed that α-FhbB Ab can compete with FH for binding to T. denticola and block dentilisin-mediated FH cleavage. Lastly, we demonstrate that dentilisin cleavage sites reside within critical functional domains of FH, including the complement regulatory domain formed by CCPs 1 to 4. Analysis of the FH cleavage products revealed that they lack cofactor activity. The data presented here provide insight into the in vivo significance of dentilisin, FhbB and its antigenic diversity, and the potential impact of FH cleavage on the regulation of complement activation.

pyrF as a Counterselectable Marker for Unmarked Genetic Manipulations in Treponema denticola

The pathophysiology of Treponema denticola, an oral pathogen associated with both periodontal and endodontic infections, is poorly understood due to its fastidious growth and recalcitrance to genetic manipulations. Counterselectable markers are instrumental in constructing clean and unmarked mutations in bacteria. Here, we demonstrate that pyrF, a gene encoding orotidine-5'-monophosphate decarboxylase, can be used as a counterselectable marker in T. denticola to construct marker-free mutants. T. denticola is susceptible to 5-fluoroorotic acid (5-FOA). To establish a pyrF-based counterselectable knockout system in T. denticola, the pyrF gene was deleted. The deletion conferred resistance to 5-FOA in T. denticola. Next, a single-crossover mutant was constructed by reintroducing pyrF along with a gentamicin resistance gene (aacC1) back into the chromosome of the pyrF mutant at the locus of choice. In this study, we chose flgE, a flagellar hook gene that is located within a large polycistronic motility gene operon, as our target gene. The obtained single-crossover mutant (named FlgE(in)) regained the susceptibility to 5-FOA. Finally, FlgE(in) was plated on solid agar containing 5-FOA. Numerous colonies of the 5-FOA-resistant mutant (named FlgE(out)) were obtained and characterized by PCR and Southern blotting analyses. The results showed that the flgE gene was deleted and FlgE(out) was free of selection markers (i.e., pyrF and aacC1). Compared to previously constructed flgE mutants that contain an antibiotic selection marker, the deletion of flgE in FlgE(out) has no polar effect on its downstream gene expression. The system developed here will provide us with a new tool for investigating the genetics and pathogenicity of T. denticola.

Kanamycin Resistance Cassette for Genetic Manipulation of Treponema denticola

Treponema denticola has been recognized as an important oral pathogen of the "red complex" bacterial consortium that is associated with the pathogenesis of endodontal and periodontal diseases. However, little is known about the virulence of T. denticola due to its recalcitrant genetic system. The difficulty in genetically manipulating oral spirochetes is partially due to the lack of antibiotic resistance cassettes that are useful for gene complementation following allelic replacement mutagenesis. In this study, a kanamycin resistance cassette was identified and developed for the genetic manipulation of T. denticola ATCC 35405. Compared to the widely used ermF-ermAM cassette, the kanamycin cassette used in the transformation experiments gave rise to additional antibiotic-resistant T. denticola colonies. The kanamycin cassette is effective for allelic replacement mutagenesis as demonstrated by inactivation of two open reading frames of T. denticola, TDE1430 and TDE0911. In addition, the cassette is also functional in trans-chromosomal complementation. This was determined by functional rescue of a periplasmic flagellum (PF)-deficient mutant that had the flgE gene coding for PF hook protein inactivated. The integration of the full-length flgE gene into the genome of the flgE mutant rescued all of the defects associated with the flgE mutant that included the lack of PF filament and spirochetal motility. Taken together, we demonstrate that the kanamycin resistance gene is a suitable cassette for the genetic manipulation of T. denticola that will facilitate the characterization of virulence factors attributed to this important oral pathogen.

Evidence that TP_0144 of Treponema pallidum is a thiamine-binding protein

Thiamine pyrophosphate (TPP), the biologically active form of thiamine (also known as vitamin B1), is an essential cofactor for several important enzymes involved in carbohydrate metabolism, and therefore, it is required for all living organisms. We recently found that a thiamine-binding protein (TDE_0143) is essential for the survival of Treponema denticola, an important bacterial pathogen that is associated with human periodontitis. In this report, we provide experimental evidence showing that TP_0144, a homolog of TDE_0143 from the syphilis spirochete Treponema pallidum, is a thiamine-binding protein that has biochemical features and functions that are similar to those of TDE_0143. First, structural modeling analysis reveal that both TDE_0143 and TP_0144 contain a conserved TPP-binding site and share similar structures to the thiamine-binding protein of Escherichia coli. Second, biochemical analysis shows that these two proteins bind to TPP with similar dissociation constant (Kd) values (TDE_0143, Kd of 36.50 nM; TP_0144, Kd of 32.62 nM). Finally, heterologous expression of TP_0144 in a ΔTDE_0143 strain, a previously constructed TDE_0143 mutant of T. denticola, fully restores its growth and TPP uptake when exogenous thiamine is limited. Collectively, these results indicate that TP_0144 is a thiamine-binding protein that is indispensable for T. pallidum to acquire exogenous thiamine, a key nutrient for bacterial survival. In addition, the studies shown in this report further underscore the feasibility of using T. denticola as a platform to study the biology and pathogenicity of T. pallidum and probably other uncultivable treponemal species as well.

Characterization of Treponema denticola mutants defective in the major antigenic proteins, Msp and TmpC

Treponema denticola, a gram-negative and anaerobic spirochete, is associated with advancing severity of chronic periodontitis. In this study, we confirmed that two major antigenic proteinswere Msp and TmpC, and examined their physiological and pathological roles using gene-deletion mutants. Msp formed a large complex that localized to the outer membrane, while TmpC existed as a monomer and largely localized to the inner membrane. However, TmpC was also detected in the outer membrane fraction, but its cell-surface exposure was not detected. Msp defects increased cell-surface hydrophobicity and secretion of TNF-α from macrophage-like cells, whereas TmpC defects decreased autoagglutination and chymotrypsin-like protease activities. Both mutants adhered to gingival epithelial cells similarly to the wild-type and showed slightly decreased motility. In addition, in Msp-defective mutants, the TDE1072 protein, which is a major membrane protein, was abolished; therefore, phenotypic changes in the mutant can be, at least in part, attributed to the loss of the TDE1072 protein. Thus, the major antigenic proteins, Msp and TmpC, have significant and diverse impacts on the characteristics of T. denticola, especially cell surface properties.

Porphyromonas gingivalis and Treponema denticola exhibit metabolic symbioses

Porphyromonas gingivalis and Treponema denticola are strongly associated with chronic periodontitis. These bacteria have been co-localized in subgingival plaque and demonstrated to exhibit symbiosis in growth in vitro and synergistic virulence upon co-infection in animal models of disease. Here we show that during continuous co-culture a P. gingivalis:T. denticola cell ratio of 6∶1 was maintained with a respective increase of 54% and 30% in cell numbers when compared with mono-culture. Co-culture caused significant changes in global gene expression in both species with altered expression of 184 T. denticola and 134 P. gingivalis genes. P. gingivalis genes encoding a predicted thiamine biosynthesis pathway were up-regulated whilst genes involved in fatty acid biosynthesis were down-regulated. T. denticola genes encoding virulence factors including dentilisin and glycine catabolic pathways were significantly up-regulated during co-culture. Metabolic labeling using ¹³C-glycine showed that T. denticola rapidly metabolized this amino acid resulting in the production of acetate and lactate. P. gingivalis may be an important source of free glycine for T. denticola as mono-cultures of P. gingivalis and T. denticola were found to produce and consume free glycine, respectively; free glycine production by P. gingivalis was stimulated by T. denticola conditioned medium and glycine supplementation of T. denticola medium increased final cell density 1.7-fold. Collectively these data show P. gingivalis and T. denticola respond metabolically to the presence of each other with T. denticola displaying responses that help explain enhanced virulence of co-infections.

Unlike the traditional view that most diseases are caused by infection with a single bacterial species, some chronic diseases including periodontitis result from the perturbation of the natural microbiota and the proliferation of a number of opportunistic pathogens. Both Porphyromonas gingivalis and Treponema denticola have been associated with the progression and severity of chronic periodontitis and have been shown to display synergistic virulence in animal models. However, the underlying mechanisms to these observations are unclear. Here we demonstrate that these two bacteria grow synergistically in continuous co-culture and modify their gene expression. The expression of T. denticola genes encoding known virulence factors and enzymes involved in the uptake and metabolism of the amino acid glycine was up-regulated in co-culture. T. denticola stimulated the proteolytic P. gingivalis to produce free glycine, which T. denticola used as a major carbon source. Our study shows P. gingivalis and T. denticola co-operate metabolically and this helps to explain their synergistic virulence in animal models and their intimate association in vivo.

Microbiology and treatment of acute apical abscesses

Acute apical abscess is the most common form of dental abscess and is caused by infection of the root canal of the tooth. It is usually localized intraorally, but in some cases the apical abscess may spread and result in severe complications or even mortality. The reasons why dental root canal infections can become symptomatic and evolve to severe spreading and sometimes life-threatening abscesses remain elusive. Studies using culture and advanced molecular microbiology methods for microbial identification in apical abscesses have demonstrated a multispecies community conspicuously dominated by anaerobic bacteria. Species/phylotypes commonly found in these infections belong to the genera Fusobacterium, Parvimonas, Prevotella, Porphyromonas, Dialister, Streptococcus, and Treponema. Advances in DNA sequencing technologies and computational biology have substantially enhanced the knowledge of the microbiota associated with acute apical abscesses and shed some light on the etiopathogeny of this disease. Species richness and abundance and the resulting network of interactions among community members may affect the collective pathogenicity and contribute to the development of acute infections. Disease modifiers, including transient or permanent host-related factors, may also influence the development and severity of acute abscesses. This review focuses on the current evidence about the etiology and treatment of acute apical abscesses and how the process is influenced by host-related factors and proposes future directions in research, diagnosis, and therapeutic approaches to deal with this disease.

A surface-exposed neuraminidase affects complement resistance and virulence of the oral spirochaete Treponema denticola

Neuraminidases (sialidases) catalyse the removal of terminal sialic acid from glycoconjugates. Bacterial pathogens often utilize neuraminidases to scavenge host sialic acid, which can be utilized either as a nutrient or as a decorating molecule to disguise themselves from host immune attacks. Herein, a putative neuraminidase (TDE0471) was identified in Treponema denticola, an oral spirochaete associated with human periodontitis. TDE0471 is a cell surface-exposed exo-neuraminidase that removes sialic acid from human serum proteins; it is required for T.denticola to grow in a medium that mimics gingival crevice fluid, suggesting that the spirochaete may use sialic acid as a nutrient in vivo. TDE0471 protects T.denticola from serum killing by preventing the deposition of membrane attack complexes on the bacterial cell surface. Animal studies revealed that a TDE0471-deficient mutant is less virulent than its parental wild-type strain in BALB/C mice. However, it causes a level of tissue damage similar to the wild type in complement-deficient B6.129S4-C3(tm1) (Crr) /J mice albeit the damage caused by both bacterial strains is more severe in these transgenic mice. Based on these results, we propose that T.denticola has evolved a strategy to scavenge host sialic acid using its neuraminidase, which allows the spirochaete to acquire nutrients and evade complement killing.

Inactivation of cyclic Di-GMP binding protein TDE0214 affects the motility, biofilm formation, and virulence of Treponema denticola

As a ubiquitous second messenger, cyclic dimeric GMP (c-di-GMP) has been studied in numerous bacteria. The oral spirochete Treponema denticola, a periodontal pathogen associated with human periodontitis, has a complex c-di-GMP signaling network. However, its function remains unexplored. In this report, a PilZ-like c-di-GMP binding protein (TDE0214) was studied to investigate the role of c-di-GMP in the spirochete. TDE0214 harbors a PilZ domain with two signature motifs: RXXXR and DXSXXG. Biochemical studies showed that TDE0214 binds c-di-GMP in a specific manner, with a dissociation constant (Kd) value of 1.73 μM, which is in the low range compared to those of other reported c-di-GMP binding proteins. To reveal the role of c-di-GMP in T. denticola, a TDE0214 deletion mutant (TdΔ214) was constructed and analyzed in detail. First, swim plate and single-cell tracking analyses showed that TdΔ214 had abnormal swimming behaviors: the mutant was less motile and reversed more frequently than the wild type. Second, we found that biofilm formation of TdΔ214 was substantially repressed (∼6.0-fold reduction). Finally, in vivo studies using a mouse skin abscess model revealed that the invasiveness and ability to induce skin abscesses and host humoral immune responses were significantly attenuated in TdΔ214, indicative of the impact that TDE0214 has on the virulence of T. denticola. Collectively, the results reported here indicate that TDE0214 plays important roles in motility, biofilm formation, and virulence of the spirochete. This report also paves a way to further unveil the roles of the c-di-GMP signaling network in the biology and pathogenicity of T. denticola.

Dentipain, a Streptococcus pyogenes IdeS protease homolog, is a novel virulence factor of Treponema denticola

Treponema denticola is a major pathogen of chronic periodontitis. Analysis of the T. denticola genome revealed a gene orthologous with a cysteine protease-encoding gene from Streptococcus pyogenes (IdeS). IdeS interferes with IgG-dependent opsonophagocytosis by specific cleavage of IgG molecules. Analysis of this gene (termed ideT) revealed it to encode a two-domain protein whose N-terminus is composed of tandem immunoglobulin-like domains followed by a C-terminal IdeS-like protease domain. In this study we show that during secretion the IdeT protein is processed into an N-terminal fragment which remains associated with the cell, and a C-terminal part released into the medium. Although the secreted domain of IdeT, termed dentipain, shows only 25% identity to the IdeS protease, the putative catalytic cysteine and histidine residues are strongly conserved. Recombinant dentipain cleaves the insulin β-chain, an activity which is inhibited by E-64, a diagnostic inhibitor of cysteine proteases. Apart from insulin no cleavage of other protein substrates was detected, suggesting that dentipain has oligopeptidase activity. A mutant strain was constructed expressing a modified IdeT variant, the dentipain domain of which was deleted. This strain was found to be significantly reduced in its abscess-forming activity compared with the parental strain in a murine abscess model, suggesting that dentipain contributes to the virulence of T. denticola.

Synergistic virulence of Porphyromonas gingivalis and Treponema denticola in a murine periodontitis model

Chronic periodontitis is characterized by the destruction of the tissues supporting the teeth and has been associated with the presence of a subgingival polymicrobial biofilm containing Porphyromonas gingivalis and Treponema denticola. We have investigated the potential synergistic virulence of P. gingivalis and T. denticola using a murine experimental model of periodontitis. An inoculation regime of four intra-oral doses of 1 × 10(10) P. gingivalis cells induced significant periodontal bone loss compared with loss in sham-inoculated mice, whereas doses of 1 × 10(9) cells or lower did not induce bone loss. Inoculation with T. denticola with up to eight doses of 1 × 10(10) cells failed to induce bone loss in this model. However, four doses of a co-inoculum of a 1 : 1 ratio of P. gingivalis and T. denticola at 5 × 10(8) or 1 × 10(9) total bacterial cells induced the same level of bone loss as four doses of 1 × 10(10) P. gingivalis cells. Co-inoculation induced strong P. gingivalis-specific T-cell proliferative and interferon-γ-dominant cytokine responses, and induced a strong T. denticola-specific interferon-γ dominant cytokine response. Only at the higher co-inoculum dose of 1 × 10(10) total cells was a T. denticola-specific T-cell proliferative response observed. These data show that P. gingivalis and T. denticola act synergistically to stimulate the host immune response and to induce alveolar bone loss in a murine experimental periodontitis model.

Molecular characterization of Treponema denticola infection-induced bone and soft tissue transcriptional profiles

Treponema denticola is associated with subgingival biofilms in adult periodontitis and with acute necrotizing ulcerative gingivitis. However, the molecular mechanisms by which T. denticola impacts periodontal inflammation and alveolar bone resorption remain unclear. Here, we examined changes in the host transcriptional profiles during a T. denticola infection using a murine calvarial model of inflammation and bone resorption. T. denticola was injected into the subcutaneous soft tissue over the calvaria of BALB/c mice for 3 days, after which the soft tissues and the calvarial bones were excised. RNA was isolated and analysed for transcript profiling using Murine GeneChip arrays. Following T. denticola infection, 2905 and 1234 genes in the infected calvarial bones and soft tissues, respectively, were differentially expressed (P <or= 0.05). Biological pathways significantly impacted by T. denticola infection in calvarial bone and calvarial tissue included leukocyte transendothelial migration, cell adhesion (immune system) molecules, cell cycle, extracellular matrix-receptor interaction, focal adhesion, B-cell receptor signaling and transforming growth factor-beta signaling pathways resulting in proinflammatory, chemotactic effects, and T-cell stimulation. In conclusion, localized T. denticola infection differentially induces transcription of a broad array of host genes, the profiles of which differed between inflamed calvarial bone and soft tissues.

Virulence factors of the oral spirochete Treponema denticola

There is compelling evidence that treponemes are involved in the etiology of several chronic diseases, including chronic periodontitis as well as other forms of periodontal disease. There are interesting parallels with other chronic diseases caused by treponemes that may indicate similar virulence characteristics. Chronic periodontitis is a polymicrobial disease, and recent animal studies indicate that co-infection of Treponema denticola with other periodontal pathogens can enhance alveolar bone resorption. The bacterium has a suite of molecular determinants that could enable it to cause tissue damage and subvert the host immune response. In addition to this, it has several non-classic virulence determinants that enable it to interact with other pathogenic bacteria and the host in ways that are likely to promote disease progression. Recent advances, especially in molecular-based methodologies, have greatly improved our knowledge of this bacterium and its role in disease.

An efficient method for enumerating oral spirochetes using flow cytometry

Spirochetes, such as Treponema denticola, are thin walled, helical, motile bacteria. They are notoriously difficult to enumerate due to their thinness and the difficulties associated with culturing them. Here we have developed a modified oral bacterial growth medium (OBGM) that significantly improves the cultivation of T. denticola compared with a previously published growth medium. Three methods for the enumeration of T. denticola, semi-solid growth medium colony-forming unit (CFU) counts, DNA analysis and flow cytometry, are described and compared. Enumeration of T. denticola using the semi-solid agar method resulted in a positive linear relationship with absorbance of the culture (R(2)=0.9423). However, the semi-solid agar method was found to consistently underestimate (by 50 fold) the T. denticola cell density compared to previously published data. DNA analysis of T. denticola cultures reliably and consistently resulted in a positive linear relationship with absorbance (R(2)=0.9360), giving a calculated cell density of 6.9 x 10(8)cells/mL at an absorbance of 0.2 at 650 nm. Flow cytometry was also found to result in a positive linear relationship with absorbance (R(2)=0.9874), giving a calculated cell density of 6.6 x 10(8)cells/mL at an absorbance of 0.2 at 650 nm. In comparing all of these enumeration methods, the flow cytometry method was found to have distinct advantages, as it is accurate, rapid, and could distinguish between live and dead bacteria. Thus flow cytometry is a recommended means for the rapid and reliable enumeration of viable spirochetes from culture.

Major proteins and antigens of Treponema denticola

Treponema denticola is a Gram-negative, motile, asaccharolytic, anaerobic spirochaete which along with Porphyromonas gingivalis and Tannerella forsythia has been shown to form a bacterial consortium called the Red Complex that is strongly associated with the clinical progression of chronic periodontitis. T. denticola was grown in continuous culture in a complex medium with a mean generation time of 15.75 h. Samples from two different membrane-enriched preparations and a cytoplasm-enriched preparation were separated by two-dimensional gel electrophoresis and the proteins identified by MALDI-TOF/TOF mass spectrometry. In total, 219 non-redundant proteins were identified including numerous virulence factors, lipoproteins, ABC transporter proteins and enzymes involved in the metabolism of nine different amino acids of which glycine seems to be of particular importance. Novel findings include the identification of several abundant peptide uptake systems, and the identification of three flagellar filament outer layer proteins. Two-dimensional Western blot analysis using sera from mice immunized with formalin-killed T. denticola cells suggested that Msp, PrcA, OppA, OppA10, MglB, TmpC and several flagellar filament proteins are antigenic.

Detection of treponema denticola in symptomatic apical periodontitis and in symptomatic apical abscesses by real-time PCR

OBJECTIVES

The aim of this study was to investigate the presence of Treponema denticola in symptomatic apical periodontitis and in symptomatic apical abscesses by real-time polymerase chain reaction (PCR) method.

METHODS

Microbial samples were collected from 60 single-rooted teeth having carious lesions and necrotic pulps. For each tooth, clinical data including patient symptoms were recorded. Teeth were categorized by diagnosis as having symptomatic apical periodontitis or symptomatic apical abscess. Aseptic microbial samples were collected using paper points from 30 infected root canals and from aspirates of 30 abscesses. DNA was extracted from the samples by using a QIAamp(R) DNA mini-kit and analyzed with real-time PCR.

RESULTS

T. denticola was detected in 24 of 30 cases diagnosed as symptomatic apical abscesses (80%), and 19 of 30 cases diagnosed as symptomatic apical periodontitis (63.3%). In general T. denticola was found in 43 of 60 cases (71.6%).

CONCLUSIONS

Our findings suggest that T. denticola can participate in the pathogenesis of symptomatic apical abscesses.

Lesion formation and antibody response induced by papillomatous digital dermatitis-associated spirochetes in a murine abscess model

Papillomatous digital dermatitis (PDD), also known as hairy heel wart, is a growing cause of lameness of cows in the U.S. dairy industry. Farms with PDD-afflicted cows experience economic loss due to treatment costs, decreased milk production, lower reproductive efficiency, and premature culling. While the exact cause of PDD is unknown, lesion development is associated with the presence of anaerobic spirochetes. This study was undertaken to investigate the virulence and antigenic relatedness of four previously isolated Treponema phagedenis-like spirochetes (1A, 3A, 4A, and 5B) by using a mouse abscess model with subcutaneous inoculation of 10(9), 10(10), and 10(11) spirochetes. Each of the PDD isolates induced abscess formation, with strain 3A causing cutaneous ulceration. Lesion development and antibody responses were dose dependent and differed significantly from those seen with the nonpathogenic human T. phagedenis strain. Strains 3A, 4A, and 5B showed two-way cross-reactivity with each other and a one-way cross-reaction with T. phagedenis. Strain 5B showed one-way cross-reactivity with 1A. None of the isolates showed cross-reactivity with T. denticola. In addition, distinct differences in immunoglobulin G subclass elicitation occurred between the PDD strains and T. phagedenis. From these data, we conclude that spirochetes isolated from PDD lesions have differential virulence and antigenic traits in vivo. Continuing investigation of these properties is important for the elucidation of virulence mechanisms and antigenic targets for vaccine development.

The chymotrypsin-like protease complex of Treponema denticola ATCC 35405 mediates fibrinogen adherence and degradation

Treponema denticola is an anaerobic spirochete strongly associated with human periodontal disease. T. denticola bacteria interact with a range of host tissue proteins, including fibronectin, laminin, and fibrinogen. The latter localizes in the extracellular matrix where tissue damage has occurred, and interactions with fibrinogen may play a key role in T. denticola colonization of the damaged sites. T. denticola ATCC 35405 showed saturable binding of fluid-phase fibrinogen to the cell surface and saturable adherence to immobilized fibrinogen. Levels of fibrinogen binding were enhanced in the presence of the serine protease inhibitor phenylmethylsulfonyl fluoride. The Aalpha and Bbeta chains of fibrinogen, but not the gamma chains, were specifically recognized by T. denticola. Following fibrinogen affinity chromatography analysis of cell surface extracts, a major fibrinogen-binding component (polypeptide molecular mass, approximately 100 kDa), which also degraded fibrinogen, was purified. Upon heating at 100 degrees C, the polypeptide was dissociated into three components (apparent molecular masses, 80, 48, and 45 kDa) that did not individually bind or degrade fibrinogen. The native 100-kDa polypeptide complex was identified as chymotrypsin-like protease (CTLP), or dentilisin. In an isogenic CTLP(-) mutant strain, CKE, chymotrypsin-like activity was reduced >90% compared to that in the wild type and fibrinogen binding and hydrolysis were ablated. Isogenic mutant strain MHE, deficient in the production of Msp (major surface protein), showed levels of CTLP reduced 40% relative to those in the wild type and exhibited correspondingly reduced levels of fibrinogen binding and proteolysis. Thrombin clotting times in the presence of wild-type T. denticola cells, but not strain CKE (CTLP(-)) cells, were extended. These results suggest that interactions of T. denticola with fibrinogen, which may promote colonization and modulate hemostasis, are mediated principally by CTLP.

Rat model of polymicrobial infection, immunity, and alveolar bone resorption in periodontal disease

One of the predominant polymicrobial infections of humans is expressed clinically as periodontal disease. Porphyromonas gingivalis, Treponema denticola, and Tannerella forsythia have been strongly implicated as members of a pathogenic consortium in the etiology of adult periodontitis. In this study we hypothesized that P. gingivalis, T. denticola, and T. forsythia are synergistic in terms of virulence potential and induce chronic periodontal inflammation that leads to alveolar bone resorption in a polymicrobial infection in rats. Groups of rats were infected with either P. gingivalis, T. denticola, or T. forsythia in monomicrobial infections or with all three species in polymicrobial oral infections with or without Fusobacterium nucleatum. PCR analyses of oral microbial samples demonstrated that rats infected with one bacterium were orally colonized by each of the bacteria during the study interval, and increased serum immunoglobulin G (IgG) antibody levels substantiated the interaction of the host with the infecting bacteria. PCR analyses of the rats with polymicrobial infections demonstrated that most rats were infected with P. gingivalis, T. denticola, and T. forsythia as a consortium. Furthermore, all rats exhibited a significant increase in the level of IgG antibody to the polymicrobial consortium. Radiographic measurement of alveolar bone resorption showed that rats infected with the polymicrobial consortium with or without F. nucleatum exhibited significantly increased alveolar bone resorption compared to the resorption in uninfected control rats, as well as the resorption in rats infected with one of the microbes. These results documented that P. gingivalis, T. denticola, and T. forsythia not only exist as a consortium that is associated with chronic periodontitis but also exhibit synergistic virulence resulting in the immunoinflammatory bone resorption characteristic of periodontitis.

The Treponema denticola surface protease dentilisin degrades interleukin-1 beta (IL-1 beta), IL-6, and tumor necrosis factor alpha

Dentilisin is a major surface protease and virulence factor of the bacterium Treponema denticola. In this study, we found that T. denticola reduced inflammatory cytokines, including interleukin-1beta (IL-1beta), IL-6, and tumor necrosis factor alpha, in peripheral blood mononuclear cells through degradation by dentilisin.

Treponema species associated with abscesses of endodontic origin

Spirochetes have been frequently observed in abscesses of endodontic origin, but they have rarely been identified. This study sought to investigate the prevalence of eight oral treponemes in acute periradicular abscesses using a species-specific nested polymerase chain reaction assay. Purulent exudate was collected by aspiration from 19 cases diagnosed as acute periradicular abscesses and DNA extracted from the samples was initially amplified using universal 16S rDNA primers. A second round of amplification used the first polymerase chain reaction products to detect a specific fragment of the 16S rDNA of each Treponema species. The species-specific nPCR assay used in this study allowed the detection of Treponema denticola in 79%(15 of 19), Treponema socranskii in 26%(5 of 19), Treponema pectinovorum in 21% (4 of 19), Treponema amylovorum in 16% (3 of 19), and Treponema medium in 5% (1 of 19) of the cases. Spirochetal DNA was found in 89% of the cases (17 of 19). The number of Treponema species per case ranged from 1 to 3 (mean, 1.5). Treponema vincentii, Treponema lecithinolyticum and Treponema maltophilum were not detected in any pus sample. The present data lend support to the assertion that Treponema species, particularly T. denticola and T. socranskii, may be involved in the pathogenesis of acute periradicular abscesses.

Identification of spirochetes (treponemes) in endodontic infections

The purpose of this study was to determine the prevalence of spirochetes in asymptomatic infected root canals and in endodontic abscesses/cellulitis. Aseptic clinical samples were collected using paper points from 54 infected root canals and from aspirates of 84 abscesses/cellulitis. Oligonucleotide primers were produced for PCR identification of Treponema vincentii, T. pectinovorum, T. medium, T. amylovorum, T. denticola, T. maltophilum, and T. socranskii. PCR detected spirochetes in 51 of 84 (60.7%) samples from abscesses/cellulitis and in 20 of 54 (37.0%) samples from asymptomatic infected root canals. T. socranskii was the most frequently detected (44.9%), followed by T. maltophilum (29.7%), T. denticola (28.9%), T. pectinovorum (13.7%), and T. vincentii (5.1%). The number of treponema species detected ranged from 1 to 5 species per sample. The mean numbers of species detected were 2.3 in abscesses/cellulitis and 2.6 in infected root canals. Significant association among species was found between T. maltophilum and T. socranskii, as well as between T. maltophilum and T. denticola by determining the odds ratio (> 2.0).

Treponemal phospholipids inhibit innate immune responses induced by pathogen-associated molecular patterns

Host innate immune responses to microbial components, known as pathogen-associated molecular patterns (PAMPs), are regulated and modified by cellular receptors and serum proteins, including Toll-like receptors (TLRs), CD14, and LPS-binding protein (LBP). We demonstrated that a treponemal membrane lipid inhibited PAMPs-induced immune responses. The chemical structure of the lipid was elucidated as a phosphatidylglycerol (PG) derivative, which is scarce in most mammalian tissues, but relatively abundant in treponemal membrane lipids. Natural and synthetic PG counterparts as well as related natural anionic phospholipids, phosphatidylinositol, phosphatidylserine, and cardiolipin, also demonstrated an inhibitory effect. Further, we noted that PG inhibited PAMPs-induced immune responses by blocking the binding of PAMPs with LBP and CD14. In addition, PG decreased proinflammatory cytokine production in serum of LPS-injected mice and depressed abscess formation in mice infected with treponemes. These results suggest that treponemal phospholipid interfere the function of LBP/CD14 and act as a modulator of innate immune responses.

Treponema socranskii in primary endodontic infections as detected by nested PCR

Spirochetes have been frequently observed in root canal infections, but they were rarely identified. The purpose of this study was to investigate the prevalence of Treponema socranskii in primary endodontic infections using a species-specific nested polymerase chain reaction assay. Samples were collected from 60 teeth having carious lesions, necrotic pulps, and different forms of periradicular diseases. DNA extracted from the samples was initially amplified using universal 16S rDNA primers. A second round of amplification used the first polymerase chain reaction products to detect a specific fragment of T. socranskii 16S rDNA. T. socranskii was detected in 11 of 28 asymptomatic cases (39.3%), five of 12 root canals associated with acute apical periodontitis (41.7%), and five of 20 cases diagnosed as acute periradicular abscesses (25%). There was no relationship between the presence of T. socranskii and the occurrence of symptoms. In general, this spirochete was detected in 21 of 60 samples of endodontic infections (35%). Findings suggest that T. socranskii can be involved in the pathogenesis of different forms of periradicular lesions.

Oral treponemes and their outer membrane extracts activate human gingival epithelial cells through toll-like receptor 2

Oral treponemes are considered to be important in the development and progression of periodontal diseases. We investigated the mechanisms of recognition and activation of human gingival epithelial cells (HGEC) with the oral treponemes Treponema denticola, Treponema vincentii, and Treponema medium and their outer membrane extracts (OMEs). T. vincentii and T. medium but not T. denticola produced interleukin 8 (IL-8) in an HGEC culture. Further, all three treponemes induced IL-8 mRNA expression and NF-kappaB activation in HGEC. Among them, T. denticola especially exhibited trypsin- and chymotrypsin-like protease activities, and the addition of chymostatin, a chymotrypsin protease inhibitor, resulted in detectable IL-8 production by HGEC cultured with T. denticola. Additionally, IL-8 mRNA expression in HGEC cultured with the three treponemes and their OMEs was definitely inhibited by the mouse anti-human Toll-like receptor 2 (TLR2) monoclonal antibody TL2.1. These findings suggest that oral treponemes and their OMEs activate HGEC through TLR2.

EFFECTS OF A MIXED INFECTION WITH Porphyromonas gingivalis AND Treponema denticola ON ABSCESS FORMATION AND IMMUNE RESPONSES IN MICE

Porphyromonas gingivalis and Treponema denticola have been found together in lesions of human periodontitis. We examined the ability of a mixed infection by both bacteria to synergistically form abscesses and disturb immune responses in mice. Absorbance of an invasive P. gingivalis 16-1 strain grown in tryptic soy broth and T. denticola ATCC 33520 strain grown in TYGVS medium were adjusted. BALB/c mice were injected with 200 microliters of the cell suspension at a site on the lateral dorsal area. The sizes of the subsequent subcutaneous abscesses were measured with a caliper gauge, and the area was expressed in square mm. Mixed infections by P. gingivalis and T.denticola produced larger abscesses than those formed after mono-infections by either P. gingivalis or T.denticola. The abscesses caused by mixed infection reached their maxima on the 6th day and maintained that size for the subsequent 5 days. The delayed type hypersensitivities against extracted antigens of P.gingivalis in mixed infection mice were significantly lower than those in the mono-infected mice. However, the IgG response to sonicated antigen of P.gingivalis did not differ between the two groups. The sizes of the abscesses caused by mixed infections in mice immunized with whole cells of P.gingivalis 16-1 were compared to those caused in sham-immunized mice. The average size of the abscess caused by mixed infection in immunized mice did not differ from that in sham-immunized mice, but many of the abscesses in immunized mice ruptured on the 4th or 5th day, followed by recovery in two weeks. These results suggest that mixed infection with P.gingivalis and T.denticola attenuates protective immune responses.

Oral treponemes in primary root canal infections as detected by nested PCR

AIM

To investigate the prevalences of four Treponema species in primary root canal infections using a nested PCR assay.

METHODOLOGY

Samples were obtained from 32 infected root canals. Twenty-two cases showed chronic asymptomatic periradicular lesions and 10 symptomatic cases were diagnosed as acute apical periodontitis. DNA extracted from the samples was initially amplified using universal 16S rDNA primers. A second round of amplification used the first PCR products to detect a specific fragment of the 16S rDNA of each Treponema denticola, T. socranskii, T. vincentii and T. pectinovorum.

RESULTS

Bacteria were present in all cases sampled. T. denticola was detected in 77.3% of the asymptomatic cases, T. socranskii in 40.9%, T. vincentii in 18.2% and T. pectinovorum in 13.6%. In the cases diagnosed as acute apical periodontitis, T. denticola was detected in 80%, whilst T. socranskii and T. vincentii were detected in 40% and 10% of cases, respectively. No symptomatic case yielded T. pectinovorum. In general, nested PCR detected T. denticola in 78.1% of the cases, T. socranskii in 40.6%, T. vincentii in 15.6% and T. pectinovorum in 9.4%. At least one of the four Treponema species was found in 84.4% of the cases examined.

CONCLUSIONS

The species T. denticola was detected in a large number of the cases examined: the prevalence of T. socranskii was also relatively high. The species T. vincentii and T. pectinovorum were also found, but in a smaller number of cases. Based on these data, the recognized pathogenicity of these microorganisms and their involvement with other oral diseases, they should be included in the restricted set of putative endodontic pathogens.

Role of Treponema denticola in periodontal diseases

Among periodontal anaerobic pathogens, the oral spirochetes, and especially Treponema denticola, have been associated with periodontal diseases such as early-onset periodontitis, necrotizing ulcerative gingivitis, and acute pericoronitis. Basic research as well as clinical evidence suggest that the prevalence of T denticola, together with other proteolytic gram-negative bacteria in high numbers in periodontal pockets, may play an important role in the progression of periodontal disease. The accumulation of these bacteria and their products in the pocket may render the surface lining periodontal cells highly susceptible to lysis and damage. T. denticola has been shown to adhere to fibroblasts and epithelial cells, as well as to extracellular matrix components present in periodontal tissues, and to produce several deleterious factors that may contribute to the virulence of the bacteria. These bacterial components include outer-sheath-associated peptidases, chymotrypsin-like and trypsin-like proteinases, hemolytic and hemagglutinating activities, adhesins that bind to matrix proteins and cells, and an outer-sheath protein with pore-forming properties. The effects of T. denticola whole cells and their products on a variety of host mucosal and immunological cells has been studied extensively (Fig. 1). The clinical data regarding the presence of T. denticola in periodontal health and disease, together with the basic research results involving the role of T. denticola factors and products in relation to periodontal diseases, are reviewed and discussed in this article.

Biological characterization of lipopolysaccharide from Treponema pectinovorum

This study investigated the endotoxic and biological properties of purified lipopolysaccharide (LPS) isolated from an oral spirochete, Treponema pectinovorum. Endotoxicity, measured by Limulus amoebocyte lysate kinetic assay, showed that the LPS contained 1.28 endotoxin units per microg of purified LPS, which was approximately 4,000 times less than Escherichia coli O55:B5 LPS. To determine in vivo endotoxicity, LPS responder mice were administered LPS following galactosamine (GalN) sensitization. The LPS induced neither endotoxic symptoms nor lethality for 96 h, suggesting negligible or very low endotoxicity. In contrast, infection with live T. pectinovorum induced 100% lethality within 12 h in GalN-sensitized LPS responder mice, indicating an endotoxin-like property of this treponeme. Heat-killed microorganisms exhibited no lethality in GalN-sensitized mice, suggesting that the endotoxicity was associated with heat-labile components. To determine cytokine and chemokine induction by LPS, human gingival fibroblasts were stimulated and secretion of interleukin 1beta (IL-1beta), granulocyte-macrophage colony-stimulating factor, gamma interferon, IL-6, IL-8, and monocyte chemoattractant protein 1 (MCP-1) was assessed. The purified LPS induced significant amounts of only IL-6, IL-8, and MCP-1, although they were substantially lower than levels after challenge with live T. pectinovorum. After injection of LPS or live or heat-killed T. pectinovorum, serum was collected from mice and analyzed for proinflammatory cytokines IL-1beta, tumor necrosis factor alpha (TNF-alpha), and IL-6. LPS induced only IL-6 consistently. Both live and heat-killed T. pectinovorum induced serum IL-6, which was higher than the level detected following LPS administration. Importantly, live bacteria elicited systemic TNF-alpha and IL-1beta levels similar to those induced by a lethal dose of live E. coli O111. The results indicated that T. pectinovorum LPS has very low or no endotoxicity, although it can elicit low levels of cytokines from host cells. In contrast to the LPS, live T. pectinovorum demonstrated in vivo toxicity, which was associated with serum IL-1beta, TNF-alpha, and IL-6, suggesting an endotoxin-like property of a heat-labile molecule(s) of the spirochete.

Cytokine responses to treponema pectinovorum and treponema denticola in human gingival fibroblasts

Human gingival fibroblasts were challenged with Treponema pectinovorum and Treponema denticola to test three specific hypotheses: (i) these treponemes induce different cytokine profiles from the fibroblasts, (ii) differences in cytokine profiles are observed after challenge with live versus killed treponemes, and (iii) differences in cytokine profiles are noted from different gingival fibroblast cell lines when challenged with these treponemes. Three normal gingival fibroblast cell cultures were challenged with T. pectinovorum and T. denticola strains, and the supernatants were analyzed for cytokine production (i.e., interleukin-1alpha [IL-1alpha], IL-1beta, IL-6, IL-8, IL-10, gamma interferon, macrophage chemotactic protein 1 [MCP-1], platelet-derived growth factor, tumor necrosis factor alpha, and granulocyte-macrophage colony-stimulating factor). Unstimulated fibroblast cell lines produced IL-6, IL-8, and MCP-1. T. pectinovorum routinely elicited the greatest production of these cytokines from the fibroblast cell lines, increasing 10- to 50-fold over basal production. While T. denticola also induced IL-6 and IL-8 production, these levels were generally lower than those elicited by challenge with T. pectinovorum. MCP-1 levels were significantly lower after T. denticola challenge, and the kinetics suggested that this microorganism actually inhibited basal production by the fibroblasts. No basal or stimulated production of the other cytokines was observed. Significant differences were noted in the responsiveness of the various cell lines with respect to the two species of treponemes and the individual cytokines produced. Finally, dead T. pectinovorum generally induced a twofold-greater level of IL-6 and IL-8 than the live bacteria. These results supported the idea that different species of oral treponemes can elicit proinflammatory cytokine production by gingival cells and that this stimulation did not require live microorganisms. Importantly, a unique difference was noted in the ability of T. pectinovorum to induce a robust MCP-1 production, while T. denticola appeared to inhibit this activity of the fibroblasts. While the general cytokine profiles of the fibroblast cell cultures were similar, significant differences were noted in the quantity of individual cytokines produced, which could relate to individual patient variation in local inflammatory responses in the periodontium.

Papillomatous pastern dermatitis with spirochetes and Pelodera strongyloides in a Tennessee Walking Horse

Papillomatous digital dermatitis is a common disease in cattle. The pastern dermatitis observed in a horse shared many of the gross characteristics of papillomatous digital dermatitis in cattle. Lesions included a mixture of proliferative and erosive changes, with a verrucose appearance in some areas. Microscopic similarities included pseudoepitheliomatous and papillomatous epidermal hyperplasia with hyperkeratosis, spongiosis of the epidermis, and intraepidermal spirochetes. The horse was also concurrently infected with Pelodera strongyloides. Papillomatous digital dermatitis in cattle is associated with poor husbandry practices. The environment of the affected horse was heavily contaminated with urine, manure, and other organic debris. Verrucous pododermatitis of horses may be the same as or similar to bovine papillomatous digital dermatitis, and these conditions have similar etiologies.

Taxonomy and virulence of oral spirochetes

All oral spirochetes are classified in the genus Treponema. This genus is in the family Spirochaetaceae as in Bergey's manual of systematic bacteriology. Other generic members of the family include Spirochaeta, Cristispira and Borrelia. This conventional classification is in accord with phylogenetic analysis of the spirochetes based on 16S rRNA cataloguing. The oral spirochetes fall naturally within the grouping of Treponema. Only four species of Treponema have been cultivated and maintained reliably: Treponema denticola, Treponema pectinovorum, Treponema socranskii and Treponema vincentii. These species have valid names according to the rules of nomenclature except for Treponema vincentii, which only has had effective publication. The virulence factors of the oral spirochetes updated in this mini-review have been discussed within the following broad confines: adherence, cytotoxic effects, iron sequestration and locomotion. T. denticola has been shown to attach to human gingival fibroblasts, basement membrane proteins, as well as other substrates by specific attachment mechanisms. The binding of the spirochete to human gingival fibroblasts resulted in cytotoxicity and cell death due to enzymes and other proteins. Binding of the spirochete to erythrocytes was accompanied by agglutination and lysis. Hemolysis releases hemin, which is sequestered by an outer membrane sheath receptor protein of the spirochete. The ability to locomote through viscous environments enables spirochetes to migrate within gingival crevicular fluid and to penetrate sulcular epithelial linings and gingival connective tissue. The virulence factors of the oral spirochetes proven in vitro underscore the important role they play in the periodontal disease process. This role has been evaluated in vivo by use of a murine model.

Molecular pathogenesis of the cell surface proteins and lipids from Treponema denticola

Treponema denticola, frequently isolated from the human oral cavity, is thought to be a major pathogen of human periodontal disease. Recent developments in molecular analysis have clarified the surface structure of this microorganism and the characteristics of its pathogenic factors. Structural analysis of the outer sheath showed T. denticola to have a new type of outer membrane lipid. Limited exposure of the major outer sheath protein is suggested by electron-microscopic analysis. A protease-deficient mutant has revealed the roles of the protease in the organization of the outer sheath material and in T. denticola pathogenicity. The surface features that contribute to the pathogenicity of T. denticola in periodontal disease are gradually being elucidated, and are reviewed.

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.

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.

Characterization of a novel methyl-accepting chemotaxis gene, dmcB, from the oral spirochete Treponema denticola

Immediately downstream from the previously isolated Treponema denticola ATCC 35405 prtB gene coding for a chymotrypsinlike protease activity, an open reading frame, ORF3, was identified which shared significant homology with the highly conserved domains (HCDs) of bacterial methyl-accepting chemotaxis proteins (MCPs). Nucleotide sequencing of this ORF revealed that the gene would code for a protein with a size of approximately 41 kDa. In addition, this sequence contained a domain which was virtually identical to the HCD of a recently characterized MCP, DmcA, of strain 35405. Therefore, this ORF was named dmcB. Northern blot analysis suggested that dmcB was part of an operon structure containing prtB. Insertional inactivation of dmcB utilizing an ermF-ermAM cassette resulted in a mutant with decreased chemoattraction toward nutrient supplements. In addition, the mutant displayed an altered pattern of methylated proteins under conditions of chemotaxis. Inactivation of the dmcB gene also attenuated the methylation of the DmcA protein. These results suggest that the dmcB gene codes for an MCP in T. denticola which may interact with other MCPs in these organisms.

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.