The predominant cultivable microflora of advanced periodontitis

Reexamining the role of Fusobacterium nucleatum subspecies in clinical and experimental studies

The Gram-negative anaerobic species Fusobacterium nucleatum was originally described as a commensal organism from the human oral microbiome. However, it is now widely recognized as a key inflammophilic pathobiont associated with a wide variety of oral and extraoral diseases. Historically, F. nucleatum has been classified into four subspecies that have been generally considered as functionally interchangeable in their pathogenic potential. Recent studies have challenged this notion, as clinical data reveal a highly biased distribution of F. nucleatum subspecies within disease sites of both inflammatory oral diseases and various malignancies. This review details the historical basis for the F. nucleatum subspecies designations and summarizes our current understanding of the similarities and distinctions between these organisms to provide important context for future clinical and laboratory studies of F. nucleatum.

Europe's contribution to the evaluation of the use of systemic antimicrobials in the treatment of periodontitis

This narrative review celebrates Europe's contribution to the current knowledge on systemically administered antimicrobials in periodontal treatment. Periodontitis is the most frequent chronic noncommunicable human disease. It is caused by dysbiotic bacterial biofilms and is commonly treated with subgingival instrumentation. However, some sites/patients do not respond adequately, and its limitations and shortcomings have been recognized. This has led to the development of alternative or adjunctive therapies. One is the use of antimicrobials to target bacteria in subgingival biofilms in the periodontal pocket, which can be targeted directly through the pocket entrance with a locally delivered antibiotic or systemically by oral, intravenous, or intramuscular methods. Since the early 20th century, several studies on systemic antibiotics have been undertaken and published, especially between 1990 and 2010. Europe's latest contribution to this topic is the first European Federation of Periodontology, S3-level Clinical Practice Guideline, which incorporates recommendations related to the use of adjuncts to treat stage I-III periodontitis. Understanding the etiopathogenesis of periodontal diseases, specifically periodontitis, has influenced the use of systemic periodontal antibiotic therapy. Randomized clinical trials and systematic reviews with meta-analyses have demonstrated the clinical advantages of adjunctive systemic antimicrobials. However, current recommendations are restrictive due to concerns about antibiotic misuse and the increase in microbial antibiotic resistance. European researchers have contributed to the use of systemic antimicrobials in the treatment of periodontitis through clinical trials and by providing rational guidelines. Nowadays, European researchers are exploring alternatives and directing clinical practice by providing evidence-based guidelines to limit the use of systemic antimicrobials.

Enhanced Fusobacterium nucleatum Genetics Using Host DNA Methyltransferases To Bypass Restriction-Modification Systems

Bacterial restriction-modification (R-M) systems are a first-line immune defense against foreign DNA from viruses and other bacteria. While R-M systems are critical in maintaining genome integrity, R-M nucleases unfortunately present significant barriers to targeted genetic modification. Bacteria of the genus Fusobacterium are oral, Gram-negative, anaerobic, opportunistic pathogens that are implicated in the progression and severity of multiple cancers and tissue infections, yet our understanding of their direct roles in disease have been severely hindered by their genetic recalcitrance. Here, we demonstrate a path to overcome these barriers in Fusobacterium by using native DNA methylation as a host mimicry strategy to bypass R-M system cleavage of transformed plasmid DNA. We report the identification, characterization, and successful use of Fusobacterium nucleatum type II and III DNA methyltransferase (MTase) enzymes to produce a multifold increase in gene knockout efficiency in the strain Fusobacterium nucleatum subsp. nucleatum 23726, as well as the first system for efficient gene knockouts and complementations in F. nucleatum subsp. nucleatum 25586. We show plasmid protection can be accomplished in vitro with purified enzymes, as well as in vivo in an Escherichia coli host that constitutively expresses F. nucleatum subsp. nucleatum MTase enzymes. In summary, this proof-of-concept study characterizes specific MTases that are critical for bypassing R-M systems and has enhanced our understanding of enzyme combinations that could be used to genetically modify clinical isolates of Fusobacterium that have thus far been inaccessible to molecular characterization. IMPORTANCE Fusobacterium nucleatum is an oral opportunistic pathogen associated with diseases that include cancer and preterm birth. Our understanding of how this bacterium modulates human disease has been hindered by a lack of genetic systems. Here, we show that F. nucleatum DNA methyltransferase-modified plasmid DNA overcomes the transformation barrier and has allowed the development of a genetic system in a previously inaccessible strain. We present a strategy that could potentially be expanded to enable the genetic modification of highly recalcitrant strains, thereby fostering investigational studies to uncover novel host-pathogen interactions in Fusobacterium.

Comparative Metatranscriptomics of Periodontitis Supports a Common Polymicrobial Shift in Metabolic Function and Identifies Novel Putative Disease-Associated ncRNAs

Periodontitis is an inflammatory disease that deteriorates bone supporting teeth afflicting ∼743 million people worldwide. Bacterial communities associated with disease have been classified into red, orange, purple, blue, green, and yellow complexes based on their roles in the periodontal pocket. Previous metagenomic and metatranscriptomics analyses suggest a common shift in metabolic signatures in disease vs. healthy communities with up-regulated processes including pyruvate fermentation, histidine degradation, amino acid metabolism, TonB-dependent receptors. In this work, we examine existing metatranscriptome datasets to identify the commonly differentially expressed transcripts and potential underlying RNA regulatory mechanisms behind the metabolic shifts. Raw RNA-seq reads from three studies (including 49 healthy and 48 periodontitis samples) were assembled into transcripts de novo. Analyses revealed 859 differentially expressed (DE) transcripts, 675 more- and 174 less-expressed. Only ∼20% of the DE transcripts originate from the pathogenic red/orange complexes, and ∼50% originate from organisms unaffiliated with a complex. Comparison of expression profiles revealed variations among disease samples; while specific metabolic processes are commonly up-regulated, the underlying organisms are diverse both within and across disease associated communities. Surveying DE transcripts for known ncRNAs from the Rfam database identified a large number of tRNAs and tmRNAs as well as riboswitches (FMN, glycine, lysine, and SAM) in more prevalent transcripts and the cobalamin riboswitch in both more and less prevalent transcripts. In silico discovery identified many putative ncRNAs in DE transcripts. We report 15 such putative ncRNAs having promising covariation in the predicted secondary structure and interesting genomic context. Seven of these are antisense of ribosomal proteins that are novel and may involve maintaining ribosomal protein stoichiometry during the disease associated metabolic shift. Our findings describe the role of organisms previously unaffiliated with disease and identify the commonality in progression of disease across three metatranscriptomic studies. We find that although the communities are diverse between individuals, the switch in metabolic signatures characteristic of disease is typically achieved through the contributions of several community members. Furthermore, we identify many ncRNAs (both known and putative) which may facilitate the metabolic shifts associated with periodontitis.

Oral Biofilms from Symbiotic to Pathogenic Interactions and Associated Disease -Connection of Periodontitis and Rheumatic Arthritis by Peptidylarginine Deiminase

A wide range of bacterial species are harbored in the oral cavity, with the resulting complex network of interactions between the microbiome and host contributing to physiological as well as pathological conditions at both local and systemic levels. Bacterial communities inhabit the oral cavity as primary niches in a symbiotic manner and form dental biofilm in a stepwise process. However, excessive formation of biofilm in combination with a corresponding deregulated immune response leads to intra-oral diseases, such as dental caries, gingivitis, and periodontitis. Moreover, oral commensal bacteria, which are classified as so-called “pathobionts” according to a now widely accepted terminology, were recently shown to be present in extra-oral lesions with distinct bacterial species found to be involved in the onset of various pathophysiological conditions, including cancer, atherosclerosis, chronic infective endocarditis, and rheumatoid arthritis. The present review focuses on oral pathobionts as commensal and healthy members of oral biofilms that can turn into initiators of disease. We will shed light on the processes involved in dental biofilm formation and also provide an overview of the interactions of P. gingivalis, as one of the most prominent oral pathobionts, with host cells, including epithelial cells, phagocytes, and dental stem cells present in dental tissues. Notably, a previously unknown interaction of P. gingivalis bacteria with human stem cells that has impact on human immune response is discussed. In addition to this very specific interaction, the present review summarizes current knowledge regarding the immunomodulatory effect of P. gingivalis and other oral pathobionts, members of the oral microbiome, that pave the way for systemic and chronic diseases, thereby showing a link between periodontitis and rheumatoid arthritis.

Microbiological effects and recolonization patterns after adjunctive subgingival debridement with Er:YAG laser

OBJECTIVES

The objective of this study was to assess the microbiological effects and recolonization patterns after non-surgical periodontal treatment protocol based on the adjunctive use of erbium-doped yttrium aluminium garnet (Er:YAG) laser.

MATERIAL AND METHODS

Patients diagnosed with chronic periodontitis were randomly assigned to two different treatment protocols: test, full-mouth subgingival ultrasonic instrumentation followed by Er-YAG laser application 1 week later to sites with initial probing pocket depth ≥4.5 mm; and control, full-mouth ultrasonic subgingival instrumentation within 1 week. Clinical (at sampled sites) and microbiological (culture-based) parameters were recorded at baseline and 3 and 12 months. Microbiological variables included total counts, frequency of detection, proportions and counts of target species.

RESULTS

Results from 19 test and 21 control patients were compared. Minor changes were observed for total colony-forming units, with no differences between groups. For the frequency of detection, a limited and similar impact in both groups was observed for the most prevalent (over 80 %) periodontal pathogens (Porphyromonas gingivalis, Prevotella intermedia, Fusobacterium nucleatum). For proportions, reductions in P. gingivalis occurred at 3 months, both in the test and control groups (from 16.3 to 10 % and 16 to 14.8 %, respectively), although these differences were not statistically significant. At 12 months, the test group showed a statistically significant greater reduction in probing depth for the sampled sites.

CONCLUSIONS

The adjunctive use of Er:YAG laser when compared with conventional ultrasonic debridement did not provide a microbiological added benefit.

CLINICAL RELEVANCE

Even though some clinical benefits with the adjunctive laser application were identified when comparing both treatment protocols, there were no differences in microbiological outcomes or in the bacterial recolonization patterns.

Anaerobic culture to detect periodontal and caries pathogens

BACKGROUND

Anaerobic culture has been critical in our understanding of the oral microbiotas.

HIGHLIGHT

Studies in advanced periodontitis in the 1970's revealed microbial complexes that associated with different clinical presentations. Taxonomy studies identified species newly-observed in periodontitis as Aggregatibacter (Actinobacillus) actinomycetemcomitans, Campylobacter (Wolinella) rectus and other Campylobacter species, and Tannerella (Bacteroides) forsythia. Anaerobic culture of initial periodontitis showed overlap in the microbiota with gingivitis, and added Selenomonas noxia and Filifactor alocis as putative periodontal pathogens. Porphyromonas gingivalis and T. forsythia were found to be associated with initial periodontitis in adults. The dominant microbiota of dental caries differs from that of periodontitis. The major cariogenic species are acidogenic and acid tolerant species particularly Streptococcus mutans, and Lactobacillus and Bifidobacterium species. Anaerobic culture of severe early childhood caries revealed a widely diverse microbiota, comparable to that observed using cloning and sequencing. The PCR-based cloning approach, however, underestimated Actinobacteria compared with culture. Only a subset of the caries-associated microbiota was acid tolerant, with different segments of the microbiota cultured on blood agar compared to a low pH acid agar. While the major caries-associated species was S. mutans, a new species, Scardovia wiggsiae, was significantly associated with early childhood caries. Higher counts of S. wiggsiae were also observed in initial white spot carious lesions in adolescents.

CONCLUSION

In periodontitis and dental caries, anaerobic culture studies of advanced disease provided a comprehensive analysis of the microbiota of these infections. Anaerobic culture highlighted the limitation of PCR with standard primers that underestimate detection of Actinobacteria.

Clinical and Microbiological Effects of Photodynamic Therapy Associated with Non-surgical Treatment in Aggressive Periodontitis

Background and aims. The aim of this study was to compare the effectiveness of adjunctive photodynamic therapy (PDT) in the treatment of aggressive periodontitis.

Materials and methods. A total of 24 patients with clinical diagnosis of aggressive periodontitis received scaling and root planing (SRP) for periodontal treatment. In a split-mouth design study, the teeth of one quadrant of each arch with ≥4 mm of probing depth were selected randomly for additional treatment with PDT (test group). PDT was performed with a diode laser beam with a wavelength of 670-690 nm and a power of 75 Mw. The control group consisted of selected teeth of the contralateral quadrant (SRP only). Before any treatment, subgingival plaque samples were collected by an endodontic paper cone for microbiological analysis by real-time polymerase chain reaction (PCR) for detection of Aggregatibacter actinomycetecommitans. Clinical parameters including clinical attachment loss (CAL) as primary outcome, plaque index (PI), bleeding on probing (BOP), probing depth (PD) and gingival recession (REC) were measured at baseline and after 90 days. Inter-group and intra-group statistical analyses were performed.

Results. Treatment groups showed an improvement in all the clinical parameters and a significant reduction in the counts of A. actinomycetecommitans at 90 days compared to baseline (P < 0.05). None of the periodontal parameters exhibited significant differences between the two groups (P > 0.05).

Conclusion. Within the limitations of this study, the results did not show additional benefits from PDT as an adjunctive treatment for patients with aggressive periodontitis.

Evaluation of a new oral health scale of infectious potential based on the salivary microbiota

OBJECTIVES

The objective of this study is to analyse the correlation of our own design of oral health scale (grades 0 and 1-better oral health vs. grades 2 and 3-poorer oral health) with the salivary microbiota.

PATIENTS AND METHODS

The oral health scale we elaborated was evaluated in 100 adults (25 patients from each global oral health grade). Saliva samples collected from these patients were analysed using microbiological culture techniques, determining the presence/absence and the concentrations of some odontopathogens and periodontopathogens.

RESULTS

In comparison with the global oral health grades 0-1, the grades 2-3 presented significantly higher values for the presence of odontopathogens (78 vs. 38 %; Streptococcus mutans, Lactobacillus spp. and Actinomyces spp.) and periodontopathogens (100 vs. 90 %; Aggregatibacter actinomycetemcomitans, Campylobacter spp., Fusobacterium spp. and Prevotella gingivalis). In comparison with the grades 0-1, the grades 2-3 presented significantly higher values for the concentrations (CFU/mL log10) of facultative anaerobes, strict anaerobes, odontopathogens (S. mutans, Lactobacillus spp. and Actinomyces spp.) and periodontopathogens (A. actinomycetemcomitans, Capnocytophaga spp., Campylobacter spp. and Fusobacterium spp.).

CONCLUSION

Our new global oral health scale shows a positive correlation with the detection and quantification of certain odontopathogens and periodontopathogens present in the saliva, confirming their possible infectious potential.

CLINICAL RELEVANCE

Our own design of oral health scale could be particularly useful for the epidemiological study of different populations, the evaluation of the influence of oral health on the development of certain systemic diseases as well as the analysis of inter- and intra-individual variability of the oral microbiota in relation to the different grades of the oral health scale.

Kinetics of drug release from a biodegradable local drug delivery system and its effect on Porphyromonas gingivalis isolates: An in vitro study

BACKGROUND

Conventional anti-microbial therapy largely consisted of systemic administration of various drugs effective against periodontal pathogens, but fraught with several problems. Based on the concept of local drug delivery a bioresorbable device made of pure fibrillar collagen has been developed. The aim of this study was to study the release of Tetracycline from this collagen fiber (Type I collagen) impregnated with Tetracycline and its antibacterial activity against Porphyromonas gingivalis.

MATERIALS AND METHODS

Porphyromonas gingivalis was isolated from plaque samples of chronic periodontitis patients by using a CO2 incubator. DNA isolation was done followed by polymerase chain reaction (PCR) amplification to confirm the presence of bacteria. The release pattern of Tetracycline was assessed for a period of 10 days in water (group I) and Serum inoculated with Porphyromonas gingivalis (group II).

RESULTS

A significant presence of Tetracycline on all days in Group I and group II and the zone of inhibition was also present in both groups with a steady decline from day 1 to day 10.

CONCLUSION

Since the results were well within the therapeutic concentration of drug required to inhibit the growth of gram -ve bacteria (Porphyromonas gingivalis), this bioresorbable Tetracycline fiber has the potential for clinical application.

Role of complement in host-microbe homeostasis of the periodontium

Complement plays a key role in immunity and inflammation through direct effects on immune cells or via crosstalk and regulation of other host signaling pathways. Deregulation of these finely balanced complement activities can link infection to inflammatory tissue damage. Periodontitis is a polymicrobial community-induced chronic inflammatory disease that can destroy the tooth-supporting tissues. In this review, we summarize and discuss evidence that complement is involved in the dysbiotic transformation of the periodontal microbiota and in the inflammatory process that leads to the destruction of periodontal bone. Recent insights into the mechanisms of complement involvement in periodontitis have additionally provided likely targets for therapeutic intervention against this oral disease.

Beyond the red complex and into more complexity: the polymicrobial synergy and dysbiosis (PSD) model of periodontal disease etiology

Recent advancements in the periodontal research field are consistent with a new model of pathogenesis according to which periodontitis is initiated by a synergistic and dysbiotic microbial community rather than by select 'periopathogens', such as the 'red complex'. In this polymicrobial synergy, different members or specific gene combinations within the community fulfill distinct roles that converge to shape and stabilize a disease-provoking microbiota. One of the core requirements for a potentially pathogenic community to arise involves the capacity of certain species, termed 'keystone pathogens', to modulate the host response in ways that impair immune surveillance and tip the balance from homeostasis to dysbiosis. Keystone pathogens also elevate the virulence of the entire microbial community through interactive communication with accessory pathogens. Other important core functions for pathogenicity require the expression of diverse molecules (e.g. appropriate adhesins, cognate receptors, proteolytic enzymes and proinflammatory surface structures/ligands), which in combination act as community virulence factors to nutritionally sustain a heterotypic, compatible and proinflammatory microbial community that elicits a non-resolving and tissue-destructive host response. On the basis of the fundamental concepts underlying this model of periodontal pathogenesis, that is, polymicrobial synergy and dysbiosis, we term it the PSD model.

Development of Porphyromonas gingivalis-specific quantitative real-time PCR primers based on the nucleotide sequence of rpoB

Species-specific quantitative real-time PCR (qPCR) primers were developed for the detection of Porphyromonas gingivalis. These primers, Pg-F/Pg-R, were designed based on the nucleotide sequences of RNA polymerase β-subunit gene (rpoB). Species-specific amplicons were obtained from the tested P. gingivalis strains but not in any of the other strains (46 strains of 46 species). The qPCR primers could detect as little as 4 fg of P. gingivalis chromosomal DNA. These findings suggest that these qPCR primers are suitable for applications in epidemiological studies.

Purification, characterization, and sequence analysis of a potential virulence factor from Porphyromonas gingivalis, peptidylarginine deiminase

The initiation and progression of adult-onset periodontitis has been associated with infection of the gingival sulcus by Porphyromonas gingivalis. This organism utilizes a multitude of virulence factors to evade host defenses as it establishes itself as one of the predominant pathogens in periodontal pockets. A feature common to many other oral pathogens is the production of ammonia due to its protective effect during acidic cleansing cycles in the mouth. Additionally, ammonia production by P. gingivalis has been proposed as a virulence factor due to its negative effects on neutrophil function. In this study, we describe the first purification of a peptidylarginine deiminase (PAD) from a prokaryote. PAD exhibits biochemical characteristics and properties that suggest that it may be a virulence agent. PAD deiminates the guanidino group of carboxyl-terminal arginine residues on a variety of peptides, including the vasoregulatory peptide-hormone bradykinin, to yield ammonia and a citrulline residue. The soluble protein has an apparent mass of 46 kDa, while the DNA sequence predicts a full-length protein of 61.7 kDa. PAD is optimally active at 55 degrees C, stable at low pH, and shows the greatest activity above pH 9.0. Interestingly, in the presence of stabilizing factors, PAD is resistant to limited proteolysis and retains significant activity after short-term boiling. We propose that PAD, acting in concert with arginine-specific proteinases from P. gingivalis, promotes the growth of the pathogen in the periodontal pocket, initially by enhancing its survivability and then by assisting the organism in its circumvention of host humoral defenses.

Interleukin-6 (IL-6) and IL-8 are induced in human oral epithelial cells in response to exposure to periodontopathic Eikenella corrodens

Periodontitis is the inflammatory response in periodontal tissues elicited by bacterial colonization in periodontal pockets. In this response, pocket epithelial cells are the first cells to come into contact with bacteria. To elucidate this mechanism, we determined the adherence of the periodontopathic bacterium Eikenella corrodens 1073, which has a GalNAc-sensitive lectin-like adhesin (EcLS), to a human oral epithelial carcinoma cell line (KB) and the induction of proinflammatory cytokine production in the cells following exposure to this bacterium in vitro. In the adherence assay, EcLS played a role as the adhesin of this bacterium in adherence to KB cells. In a reverse transcriptase PCR, significant interleukin-8 (IL-8) and IL-6 mRNA levels were induced in response to exposure to this bacterium. In an enzyme-linked immunosorbent assay after an 8-h bacterial exposure, the IL-8 and IL-6 protein levels were 13.5- and 8.3-fold higher than those in the nonexposed controls, respectively. These protein responses were time dependent. Interestingly, when E. corrodens was separated from KB cells by cell culture inserts, a slight stimulation of the IL-6 and IL-8 mRNA and secreted protein levels was seen. These results imply that the direct contact of E. corrodens 1073 with oral epithelial cells is not necessarily required for the stimulation of IL-6 and IL-8 secretion. We suggest that E. corrodens induces the epithelial cells to secrete proinflammatory cytokines which serve as an early signaling system to host immune and inflammatory cells in underlying connective tissues.

Identification and analysis of fipA, a Fusobacterium nucleatum immunosuppressive factor gene

We have previously demonstrated that sonic extracts of Fusobacterium nucleatum FDC 364 were capable of inhibiting human T-cell responses to mitogens and antigens. The purified F. nucleatum immunosuppressive protein (FIP) is composed of two subunits of 44 and 48 kDa. Furthermore, FIP inhibits T-cell activation by arresting cells in the middle of the G(1) phase of the cell cycle; the data available to date suggest that FIP impairs the expression of the proliferating-cell nuclear antigen. To initiate delineation of FIP structure-function relationships, molecular cloning of the FIP gene was carried out. A DNA library of F. nucleatum FDC 364 was constructed by partial digestion of genomic DNA with Sau3A and screened for the production of FIP with polyclonal antibody. Twelve immunoreactive clones were identified. One of these clones contained a 3.1-kbp insert and was chosen for further study. Cell lysates were found to contain an immunoreactive band that comigrated with the 44-kDa subcomponent of the native FIP. Sequencing of the 3.1-kpb insert revealed the presence of three open reading frames (ORFs). One ORF extends from nucleotides 415 to 1620, encodes 402 amino acids, and is preceded by a ribosome-binding site. Deletion analysis and antibody elution analysis showed that this ORF encodes the 44-kDa subunit (FipA) of native FIP. A second ORF is situated upstream of fipA. However, Northern (RNA) analysis suggested that fipA is not transcribed as part of an operon but transcribed from its own promotor. Finally, the partially purified recombinant FipA protein was capable of impairing T-cell activation in a manner consistent with the native protein. These results indicate that the two components that form the native protein are most probably distinct gene products and suggest that the 44-kDa FipA polypeptide is sufficient to mediate the immunosuppressive activities of the native protein complex.

Fusobacterium nucleatum inhibits human T-cell activation by arresting cells in the mid-G1 phase of the cell cycle

Fusobacterium nucleatum has been implicated in the pathogenesis of several diseases, including urinary tract infections, bacteremia, pericarditis, otitis media, and disorders of the oral cavity such as pulpal infections, alveolar bone abscesses, and periodontal disease. We have previously demonstrated that sonic extracts of F. nucleatum FDC 364 were capable of inhibiting human T-cell responses to mitogens and antigens. In this study, we have further characterized this immunosuppressive protein (FIP) and initiated experiments to determine its mode of action. The purified FIP has an apparent molecular mass of 90 to 100 kDa; sodium dodecyl sulfate-polyacrylamide gel electrophoresis indicates that the FIP is actually composed of two subunits with molecular masses of 48 and 44 kDa. Purified FIP retained its biological activity and was capable of inhibiting mitogen-induced proliferation of human T cells. Inhibition was dose dependent, and the FIP exhibited a specific activity approximately 250-fold greater than that of the crude extract. Cell cycle analysis indicates that FIP-treated cells were prevented from exiting the G0/G1 phase of the cell cycle. However, FIP did not alter the expression of activation markers (CD69, CD25, and CD71) or interleukin-2 secretion. The latter observations suggest that the T cells did indeed become activated and had entered the G1 phase of the cell cycle. Analysis of the expression of cyclins indicates that the phase of the cell cycle that is FIP sensitive resides somewhere beyond the restriction point of cyclin D2 (early to mid-G1) but prior to that of cyclins D3 and E (mid- to late G1). Finally, analysis of the expression of the proliferating cell nuclear antigen indicates that this is the earliest detectable defect in T cells exposed to FIP. We propose that if a block in the G1 phase of the cell cycle occurs in vivo in lymphocytes, it may result in a state of local and/or systemic immunosuppression. These suppressive effects could alter the nature and consequences of host-parasite interactions, thereby enhancing the pathogenicity of F. nucleatum itself or that of some other opportunistic organisms.

Pathogenesis of periodontitis: a major arginine-specific cysteine proteinase from Porphyromonas gingivalis induces vascular permeability enhancement through activation of the kallikrein/kinin pathway

To elucidate the mechanism of production of an inflammatory exudate, gingival crevicular fluid (GCF), from periodontal pockets in periodontitis, we examined the vascular permeability enhancement (VPE) activity induced by an arginine-specific cysteine proteinase, Arg-gingipain-1 (RGP-1), produced by a major periopathogenic bacterium, Porphyromonas gingivalis. Intradermal injections into guinea pigs of RGP-1 (> 10(-8) M), or human plasma incubated with RGP-1 (> 10(-9) M), induced VPE in a dose- and activity-dependent manner but with different time courses for the two routes of production. VPE activity induced by RGP-1 was augmented by kininase inhibitors, inhibited by a kallikrein inhibitor and unaffected by an antihistamine drug. The VPE activity in human plasma incubated with RGP-1 also correlated closely with generation of bradykinin (BK). RGP-1 induced 30-40% less VPE activity in Hageman factor-deficient plasma and no VPE in plasma deficient in either prekallikrein (PK) or high molecular weight kininogen (HMWK). After incubation with RGP-1, plasma deficient in PK or HMWK, reconstituted with each missing protein, caused VPE, as did a mixture of purified PK and HMWK, but RGP-1 induced no VPE from HMWK. The VPE of extracts of clinically isolated P. gingivalis were reduced to about 10% by anti-RGP-1-IgG, leupeptin, or tosyl-L-lysine chloromethyl ketone, which paralleled effects observed with RGP-1. These results indicate that RGP-1 is the major VPE factor of P. gingivalis, inducing this activity through PK activation and subsequent BK release, resulting in GCF production at sites of periodontitis caused by infection with this organism.

Proteins with molecular masses of 50 and 80 kilodaltons encoded by genes downstream from the fimbrilin gene (fimA) are components associated with fimbriae in the oral anaerobe Porphyromonas gingivalis

Flanking DNA regions of the fimbrilin gene (designated fimA), which encodes the major subunit protein of Porphyromonas (Bacteroides) gingivalis fimbriae, were cloned in several manners from the P. gingivalis chromosome into Escherichia coli by screening with probes derived from a 2.5-kb SacI DNA fragment previously cloned. A total of 10.4 kb of DNA fragments from the P. gingivalis genome was cloned in the pUC plasmid. Expression of the fimA gene and possible flanking genes in the fragments cloned was examined in a pUC plasmid vector system and in a bacteriophage T7 RNA polymerase-promoter expression vector system. The results show that in the pUC plasmid system, a 45-kDa protein, a product of fimA, was only poorly expressed as a precursor of the fimbrilin protein (FimA) and could be detected from cell extracts in Western blotting (immunoblotting) analysis as a sharp band but not in colony immunoblotting analysis. On the other hand, in the T7 RNA polymerase-promoter system, the product of fimA and products of the possible flanking genes responsible for fimbriation were overproduced as thick bands of the 45-kDa protein and as 63-, 50-, and 80-kDa proteins, respectively, in stained electrophoresis gels. All of the recombinant proteins were insoluble and seemed to be expressed as precursors with leader peptides. The 63-kDa, 45-k*Da (a truncated protein of the 50-kDa protein), and 80-kDa proteins were purified after solubilization with sodium dodecyl sulfate. N-terminal amino acid sequences of the 45-k*Da and 80-kDa proteins were analyzed up to the first 35 residues with a gas-phase sequencer. Monospecific antibodies directed to the recombinant proteins, i.e., the 63-kDa, 45-k*Da, and 80-kDa proteins, were raised in rabbits. By using the antibodies, localization of their matured proteins in P. gingivalis was investigated by Western blotting analysis. Immunoblotting analysis suggests that at least the 50- and 80-kDa proteins, encoded by genes downstream from the fimA gene, are minor components associated with fimbriae.

Sequence analysis and characterization of the Porphyromonas gingivalis prtC gene, which expresses a novel collagenase activity

In order to examine the potential role of bacterial collagenases in periodontal tissue destruction, we recently isolated a gene, prtC, from Porphyromonas gingivalis ATCC 53977, which expressed collagenase activity (N. Takahashi, T. Kato, and H. K. Kuramitsu, FEMS Microbiol. Lett. 84:135-138, 1991). The nucleotide sequence of the gene has been determined, and the deduced amino acid sequence corresponds to a basic protein of 37.8 kDa. In addition, Southern blot analysis indicated that the prtC gene is conserved among the three major serotypes of P. gingivalis. The enzyme has been purified to near homogeneity from Escherichia coli clone NTS1 following Mono Q anion exchange and sequential gel filtration chromatography. The molecular mass of the purified enzyme was estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis to be ca. 35 kDa, and the active enzyme behaved as a dimer following gel filtration chromatography. The collagenase degraded soluble and reconstituted fibrillar type I collagen, heat-denatured type I collagen, and azocoll but not gelatin or the synthetic collagenase substrate 4-phenylazobenzyloxycarbonyl-Pro-Leu-Gly-Pro-D-Arg. Enzyme activity was enhanced by Ca2+ and inhibited by EDTA, sulfhydryl-blocking agents, and the salivary peptide histatin. Preliminary evidence for the existence of a second collagenase expressed by strain 53977 was also obtained.

Sugar metabolism by fusobacteria: regulation of transport, phosphorylation, and polymer formation by Fusobacterium mortiferum ATCC 25557

Strains of eight Fusobacterium species differed in the ability to use sugars as energy sources for growth. For Fusobacterium russii ATCC 25533, F. gonidiaformans ATCC 25563, and F. nucleatum ATCC 10953 (except for fructose), growth was marginal to poor on all of the sugars tested. Other species displayed reasonable growth on glucose, fructose, mannose, and galactose, and two strains of F. mortiferum (ATCC 25557 and ATCC 9817) grew well on six of the sugars tested, including sucrose and maltose. Glucose transport by resting cells of most of the species was dependent upon (or markedly stimulated by) the presence of a fermentable amino acid. By contrast, F. mortiferum cells rapidly accumulated glucose and other sugars in the absence of amino acids. Although these cells were constitutive for glucose uptake, accumulation of other sugars was specifically induced by growth of F. mortiferum on the appropriate sugar. Spectrophotometric analyses and in situ staining of anionic polyacrylamide gels showed that glucose and fructose (mannose) are phosphorylated by separate ATP-dependent kinases. Fructokinase was stable in air at 4 degrees C, but under these conditions, greater than 70% of the glucokinase activity was lost. After overnight dialysis of the extract, no glucokinase activity was detectable; however, 65% of the initial enzyme activity was retained by inclusion of 1 mM dithiothreitol in the dialysis buffer. Thin-section electron microscopy showed that cells of F. mortiferum produced various amounts of intracellular glycogen during growth on the following sugars (in decreasing order of formation): galactose greater than sucrose greater than glucose greater than mannose greater than fructose. Mechanisms for sugar transport regulation, phosphorylation, and polymer synthesis by F. mortiferum cells are proposed.

Isolation, expression, and nucleotide sequence of the sod gene from Porphyromonas gingivalis

The sod gene coding for the Mn/Fe-dependent superoxide dismutase (SOD) enzyme has been isolated on a 5.9-kb DNA fragment from Porphyromonas gingivalis ATCC 53977. SOD activity can be expressed from the P. gingivalis fragment and from a subcloned fragment in Escherichia coli. However, the enzyme does not appear to be expressed from its own promoter in E. coli cells. The nucleotide sequence of the gene has been determined, and the deduced amino acid sequence of the enzyme is nearly identical to that of the enzyme purified from P. gingivalis 381 and shares extensive sequence similarity with comparable enzymes from E. coli.

Regulation of fructose metabolism and polymer synthesis by Fusobacterium nucleatum ATCC 10953

Energy for the anaerobic growth of Fusobacterium nucleatum ATCC 10953 can be derived from the fermentation of sugar (fructose) or amino acid (glutamate). During growth on fructose, the cells formed large intracellular granules which after extraction yielded glucose by either acid or enzymatic hydrolysis. The endogenous polymer was subsequently metabolized, and after overnight incubation of the cells in buffer, the glucan granules were no longer detectable by electron microscopy. Anaerobically, washed cells grown previously on fructose fermented this sugar to a mixture of lactic, acetic, and butyric acids, and little intracellular glucan was formed. Aerobically, the cells slowly metabolized fructose to acetate. Provision of glutamic acid as an additional energy (ATP) source elicited rapid synthesis of polymer by glycolyzing cells. Intracellular granules were not present in glutamate-grown cells, and under anaerobic conditions, the resting cells failed to metabolize [14C] fructose. However, the addition of glutamic acid to the suspension resulted in the rapid accumulation of sugar by the cells. Approximately 15% of the 14C-labeled material was extractable with boiling water, and by 31P nuclear magnetic resonance spectroscopy, this phosphorylated derivative was identified as [14C]fructose-1-phosphate. The nonextractable material represented [14C]glucan polymer. Fructose-1-phosphate kinase activity in fructose-grown cells was fivefold greater than that in glutamate-grown cells. We suggest that the activity of fructose-1-phosphate kinase and the availability of ATP regulate the flow of fructose into either the glycolytic or polymer-synthesizing pathway in F. nucleatum.

Newly delineated periodontal pathogens with special reference to selenomonas species

Many new species have been isolated from subgingival periodontal pockets, for example Wolinella recta and Bacteroides forsythus, reflecting better basic microbiological techniques. Other species were created from existing species as a result of better characterization methods, i.e. Bacteroides buccae and Bacteroides oris. We can recognize different types of periodontal disease and can find differences relating to the progressive compared to inactive lesions. Data illustrated in this presentation suggest that potential pathogens within new species include B. forsythus, W. recta and quite probably Selenomonas noxia. Methods that are rapid and sensitive for these new species include the use of protein profiles determined using SDS-PAGE, and DNA probes.

Activities of Nigerian chewing stick extracts against Bacteroides gingivalis and Bacteroides melaninogenicus

The in vitro activities of extracts of Nigerian chewing sticks against Bacteroides gingivalis and B. melaninogenicus are presented. The greatest inhibitory action was produced by Serindeia werneckei, whereas Fagara zanthoxyloides produced no appreciable inhibitory effect. A generally good correlation was found between the killing curves and MICs. Only extracts of Anogeissus leiocarpus showed acute toxicity in mice.

Partial purification of a bacterial lectinlike substance from Eikenella corrodens

A bacterial lectinlike substance, which is considered to participate in the adherence of Eikenella corrodens to various host cells, was purified from E. corrodens cells. The substance was extracted in 1% Triton X-100 with sonication from the cell envelope of E. corrodens 1073 and partially purified by galactosamine affinity chromatography and gel filtration chromatography based on its hemagglutination (HA) activity. The lectinlike substance was purified about 256-fold as evaluated by its specific HA activity. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the partially purified lectinlike substance (PPL) produced a single protein band of large molecular weight when it was applied to the gel without the addition of beta-mercaptoethanol and heating. Chemical analysis showed that PPL contained 14.4 micrograms of hexose per 100 micrograms of protein and that it did not contain muramic acid, glucosamine, or 2,6-diaminopimelic acid, which are characteristic of peptidoglycans. The HA activity of PPL was inhibited by EDTA but restored by adding Ca2+. The HA activity was remarkably inhibited by sugars containing N-acetyl-D-galactosamine and D-galactose. These results indicate that the lectinlike substance on the E. corrodens cells is an essential factor for the adherence to host cells.

Production of monoclonal antibodies that recognize specific and cross-reactive antigens of Fusobacterium nucleatum

Monoclonal antibodies (MAbs) against the cell surface antigens of Fusobacterium nucleatum 263 were obtained by fusion of murine myeloma cells (P3-NSI/1-Ag4-1) with the splenocytes of BALB/c mice immunized with whole cells of F. nucleatum 263. Screening was performed using an enzyme-linked immunosorbent assay (ELISA) against the immunizing strain, F. nucleatum 263. Further selection was done using a bacterial panel consisting of Bacteroides, Actinomyces, Streptococcus, Fusobacterium, and Escherichia species. Twelve MAbs were selected on the basis of this screening procedure, seven of which reacted specifically with F. nucleatum 263. Two reacted with F. nucleatum 263 and ATCC 25586, and three reacted with F. nucleatum 263, ATCC 25586, and UQD-003 (a clinical isolate) and also cross-reacted with Fusobacterium russii ATCC 25533. The selected MAbs were then further characterized by absorption experiments with suspensions of intact whole bacterial cells, and the residual binding activity of the supernatants was determined in an ELISA. To determine whether the MAbs reacted with the same or different epitopes, pairs of MAbs were reacted together and independently in a checkerboard manner in an ELISA. The additive or nonadditive nature of the reactivity was determined. A competitive inhibition assay was performed using one labeled and selected unlabeled MAbs. The results of these experiments suggested some epitope sharing among the selected MAbs that reacted with a specific antigen on F. nucleatum and also shared cross-reactive antigens with the three strains of F. nucleatum and F. russii.

Purification and properties of hemagglutinin from culture supernatant of Bacteroides gingivalis

The hemagglutinating factor (hemagglutinin) of Bacteroides gingivalis was prepared from the supernatant of a 5-day diffusate broth culture by ammonium sulfate precipitation and column chromatography with a hydrophobic column of Phenyl-Sepharose CL-4B, DEAE-Sephadex A-50, and Sephadex G-100 gel filtration. The hemagglutinating activity of the preparation was 53.3 times higher than that of ammonium sulfate precipitate. In electron microphotographs, hemagglutinin appears to have a vesicle or tubelike structure. The hemagglutinating activity of intact cells was completely destroyed by heating at 100 degrees C for 10 min, but the activity of extracted hemagglutinin was heat stable. The activity of hemagglutinin was inhibited by L-arginine and L-lysine and partially inhibited by phospholipase D, but it was not affected by proteolytic enzymes, neuraminidase, hyaluronidase, lipase, phospholipase A and C, or sugars. The B. gingivalis hemagglutinin appeared to be comprised mainly of a 40,000-molecular-weight material. The Fab fragment of immunoglobulin G prepared from rabbit antiserum to whole cells of B. gingivalis and monoclonal antibody against the hemagglutinin bound to the cell surface and inhibited the hemagglutinating activity of both the cells and the purified hemagglutinin.

Nutritional relationships between oral bacteria

Nutritional relationships were revealed during the coculturing of Bacteroides gingivalis with Wolinella recta and Bacteroides melaninogenicus with W. recta. W. recta produced a substance that stimulated the growth of B. gingivalis and B. melaninogenicus. Characterization by thin-layer chromatography and absorption spectrometry identified the compound as protoheme. Production of large amounts of formate by B. melaninogenicus stimulated the growth of W. recta. These nutritional relationships could represent examples of mechanisms favoring bacterial succession in periodontal sites.

Sensitization with Fusobacterium nucleatum targets antibody-dependent cellular cytotoxicity to mammalian cells

Incubation of mammalian tumor cells with either soluble of insoluble fractions (10 to 100 micrograms/ml) of Fusobacterium nucleatum sensitizes them to the destructive activity of antibody-dependent cellular cytotoxicity (ADCC) effector cells in the presence of anti-F. nucleatum antisera. All three types of ADCC effector cells are capable of destroying F. nucleatum-sensitized target cells with varying degrees of effectiveness (lymphocytes much greater than monocytes greater than neutrophils). Hyperimmune rabbit anti-F. nucleatum antisera were active at a dilution as high as 1/100,000. Our studies indicated that F. nucleatum must be bound to the target cells since if either the effector cells are treated with F. nucleatum or F. nucleatum is directly to an ADCC reaction, there is no significant effect on cytotoxicity. The kinetics of F. nucleatum-targeted ADCC are identical to those of classical ADCC, suggesting a similar mechanism. The specificity of F. nucleatum-targeted ADCC was demonstrated by cold target inhibition studies and by showing that other antibacterial antisera were incapable of mediating the activity.

Penicillin resistance in the subgingival microbiota associated with adult periodontitis

In this investigation, the penicillin-resistant and beta-lactamase-producing subgingival microbiota associated with adult periodontitis was identified, and the impact of a recent exposure to penicillin on the recovery of resistant organisms from this microbiota was assessed. Subjects with adult periodontitis were examined clinically and microbiologically. Twenty-one subjects had a documented history of penicillin therapy within the previous 6 months whereas an additional 21 subjects had no history of antibiotic use within 1 year. Subgingival plaque samples were cultured anaerobically on nonselective and penicillin-containing elective media. MICs and beta-lactamase production were determined for the isolates from the elective medium. The penicillin-resistant microbiota consisted primarily of gram-negative organisms, including Bacteroides, Veillonella, Haemophilus, Eikenella, and Capnocytophaga species. The prevalence (P less than 0.05) and proportions (P less than 0.005) of both penicillin-resistant pigmented Bacteroides and Veillonella species were significantly greater in subjects with recent penicillin exposure. Of the penicillin-resistant genera identified, beta-lactamase production was detected in species of pigmented Bacteroides, Capnocytophaga, and Streptococcus. The prevalence of beta-lactamase-producing Bacteroides species was significantly greater in subjects with recent penicillin exposure (P less than 0.05). Of the antibiotics examined, no single agent was uniformly effective against all of the penicillin-resistant strains, but metronidazole and clindamycin were active against all of the penicillin-resistant pigmented Bacteroides strains.

Fimbriae from the oral anaerobe Bacteroides gingivalis: physical, chemical, and immunological properties

Circular dichroism spectra indicated the predominance of beta-sheet structure in Bacteroides gingivalis fimbriae regardless of the presence of sodium dodecyl sulfate. By using a computer program, the alpha-helix, beta-sheet, and beta-turn contents and the remainder were estimated to be 0, 55, 18, and 27%, respectively, judging from the circular dichroism spectra of the fimbriae. Heating for 5 min at 100 degrees C in sodium dodecyl sulfate was necessary to denature the fimbriae into their constituent protein (fimbrilin) monomers with a reduced content of beta-sheet structure. The amino-terminal amino acid sequence of the fimbrilin was different from partial or complete amino acid sequences of fimbrilins so far determined from Bacteroides nodosus, which falls into the same nonfermentative species of the genus Bacteroides as B. gingivalis, and from various other bacteria. Fimbrilin monomers had an isoelectric point of 6.0. Examination of antibodies against fimbriae and sodium dodecyl sulfate-denatured fimbrilin by enzyme-linked immunosorbent assay reinforced a previous notion (F. Yoshimura, K. Takahashi, Y. Nodasaka, and T. Suzuki, J. Bacteriol. 160:949-957, 1984) that different sets of antigenic determinants seemed to be exposed on their surfaces.

Coaggregation of oral Bacteroides species with other bacteria: central role in coaggregation bridges and competitions

Seventy-three freshly isolated oral strains representing 10 Bacteroides spp. were tested for their ability to coaggregate with other oral gram-negative and gram-positive bacteria. None coaggregated with any of the gram-negative strains tested, which included Capnocytophaga gingivalis, C. ochracea, C. sputigena, and Actinobacillus actinomycetemcomitans. Strains of Bacteroides buccae, B. melaninogenicus, B. oralis, and B. gingivalis failed to coaggregate with any of the gram-positive strains tested. However, six Bacteroides spp. coaggregated with one or more species of gram-positive bacteria. Most isolates of B. buccalis, B. denticola, B. intermedius, B. loescheii, B. oris, and B. veroralis coaggregated with strains of Actinomyces israelii, A. viscosus, A. naeslundii, A. odontolyticus, Rothia dentocariosa, or Streptococcus sanguis. The strongest coaggregations involved B. denticola, B. loescheii, or B. oris; 22 of 25 strains coaggregated with A. israelii. Only B. loescheii interacted with certain strains of S. sanguis; these coaggregations were lactose inhibitable and were like coaggregations between A. viscosus and the same strains of S. sanguis. In fact, B. loescheii and A. viscosus were competitors for binding to S. sanguis. Many bacteroides also acted as coaggregation bridges by mediating coaggregations between two noncoaggregating cell types (e.g., S. sanguis and A. israelii). Evidence for binding-site competition and coaggregation bridging involving noncoaggregating cell types from three different genera provides support for the hypothesis that these intergeneric cell-to-cell interactions have an active role in bacterial colonization of the oral cavity.

Microbial ecology of plaque in rats with naturally occurring gingivitis

The microbial ecology of adherent plaque was investigated in relation to the pathological findings of gingivitis in plaque-susceptible rats. Plaque developed in the gingiva of the lower incisor in plaque-susceptible rats, but not in plaque-resistant rats, after they were fed a commercial powder diet. With increase in plaque volume, the total counts of bacteria increased 10(9) to 10(11)/g. In the first 3 months, Bacteroides species increased and became the predominant population. Streptococcus species also increased at the same time. After 9 months, Fusobacterium species and oral Treponema species were recognized in increasing numbers. The anaerobic bacteria increased in proportion with the progression of plaque development. Bacteroides intermedius, Fusobacterium nucleatum, Streptococcus salivarius, and other species were isolated. Acute gingivitis was observed within 3 months, and subacute-chronic gingivitis was observed between 2 and 12 months. These findings suggest that proportional changes in the gingival plaque flora may uniquely contribute to the development of gingival inflammation in this experimental model.

Biochemical and immunobiological properties of lipopolysaccharide (LPS) from Bacteroides gingivalis and comparison with LPS from Escherichia coli

Lipopolysaccharides (LPSs) were isolated from Bacteroides gingivalis and Escherichia coli by the phenol-water and butanol-water procedures. The phenol-water-extracted LPS from B. gingivalis 381 was composed of 46% carbohydrate, 23% hexosamine, 18% fatty acid, and 5% protein. The major component sugars of this preparation were glucose, glucosamine, rhamnose, galactose, galactosamine, and mannose, and their molecular ratio was 1:0.9:0.7:0.6:0.6:0.4, respectively. Neither heptose nor 2-keto-3-deoxyoctonate was detected. The butanol-water-extracted LPS from this strain was composed of 76% glucose, 7% fatty acid, and 13% protein, and it was associated with a number of polypeptides (13 to 56 kilodaltons). The main fatty acid of both LPS preparations was palmitic acid. It was found that biological activities of LPS from B. gingivalis were comparable to those of LPS from E. coli in terms of activation of the clotting enzyme of Limulus amebocyte lysate, mitogenicity, polyclonal B cell activation, and stimulation of interleukin 1 production in BALB/c mice. Furthermore, LPS-nonresponsive C3H/HeJ spleen cells were found to yield good mitogenic responses to both phenol-water-extracted LPS and butanol-water-extracted LPS from B. gingivalis or butanol-water-extracted LPS from E. coli. On the other hand, spleen cells from LPS-responsive C3H/HeN mice responded well to all these LPS preparations.

Purification and characterization of a novel type of fimbriae from the oral anaerobe Bacteroides gingivalis

Fimbriae and their constituent protein (fimbrilin) were purified to homogeneity from the bacterial wash fluid and cell lysate fraction, respectively, of Bacteroides gingivalis 381. Fimbriae, observed by negative staining, were curly, single-stranded filaments with a diameter of ca. 5 nm. The apparent molecular weight of the fimbrilin was 43,000. Fimbriae were resistant to sodium dodecyl sulfate denaturation at 70 degrees C. Heating at 100 degrees C in sodium dodecyl sulfate was needed to completely dissociate them to monomers of fimbrilin. Different sets of antigenic determinants seemed to be exposed on the surfaces of fimbriae and sodium dodecyl sulfate-denatured fimbrilin. Purified fimbriae did not show either hemagglutinating activity or hemagglutination inhibitory activity, although it has been inferred on the basis of circumstantial evidence that fimbriae are correlated to hemagglutinating activity of the organism. Hemagglutinin activity, however, was detected in culture supernatant, and this observation suggests that fimbriae of a different type or a lectin-like protein may be acting as hemagglutinin in B. gingivalis.

Pathogenic synergy: mixed infections in the oral cavity

In almost all infections in the oral cavity, mixed populations of bacteria are present. However, recent evidence points to a certain specificity in these infections: Streptococcus mutans is related to caries and black-pigmented Bacteroides species are suspected pathogens in periodontal disease. Periodontal diseases, endodontic infections and submucous abscesses in the oral cavity are probably mixed infections in which anaerobic bacteria together with facultatives or other anaerobes are present. In experimental mixed anaerobic infections black-pigmented Bacteroides strains have been shown to play a key role. Little is known about the pathogenic synergy between the bacteria involved in mixed infections. Important mechanisms could be nutritional interrelationships and interactions with the host defense. Within the group of black-pigmented Bacteroides B. gingivalis seems to be the most virulent species. These bacteria possess a great number of virulence factors, which might be important in the pathogenesis of oral infections.

Polyclonal activation of human peripheral blood B lymphocytes by Fusobacterium nucleatum

The present study examined in vitro polyclonal human B-lymphocyte (B-cell) activation (PBA) by Fusobacterium nucleatum. Pokeweed mitogen, a well-studied PBA activator, was included in some experiments for comparison. PBA was determined by the total immunoglobulin A, G, and M concentrations in the culture supernatants as measured by micro-enzyme-linked immunosorbent assay. F. nucleatum, at concentrations between 1 and 10 micrograms/ml, stimulated optimal PBA in monocyte-depleted cultures, whereas the pokeweed mitogen response was optimal in unfractionated, monocyte-containing cultures. Immunoglobulin synthesis occurred primarily between days 6 and 8 after stimulation with F. nucleatum. T lymphocytes enhanced the PBA response to F. nucleatum, particularly at a T- to B-cell ratio of 1:1. Immunoglobulin production was greater in round-bottomed wells than in flat-bottomed wells at lymphocyte concentrations of 200,000 cells per well. The PBA response, however, increased dramatically in flat-bottomed wells containing higher lymphocyte concentrations, suggesting that PBA is enhanced by cell-to-cell contact. A delay in stimulation of the lymphocytes with F. nucleatum resulted in diminished immunoglobulin production. The results provide information on the regulation of in vitro PBA induced by F. nucleatum. The data also suggest that there may be differences in the mechanisms by which F. nucleatum and pokeweed mitogen stimulate PBA.

Bacteriology of severe periodontitis in young adult humans

A total of 78 bacteriological samples were taken from the supragingival tooth surface after superficial cleaning with toothpicks or from the periodontal sulci of 42 affected sites in 21 adolescents or young adults with severe generalized periodontitis. Of 190 bacterial species, subspecies, or serotypes detected among 2,723 isolates, 11 species exceeded 1% of the subgingival flora and were most closely associated with the diseased sulci. Eleven others were also sufficiently frequent to be suspect agents of tissue destruction. Many of these species are known pathogens of other body sites. In addition, 10 species of Treponema were isolated. One of these and the "large treponeme" were also more closely associated with severe periodontitis than they were with healthy sites or gingivitis. There were highly significant differences between the composition of the flora of the affected sulci and the flora of (i) the adjacent supragingival tooth surface, (ii) the gingival crevice of periodontally healthy people, and (iii) sites with a gingival index score of 0 or 2 in experimental gingivitis studies. The floras of different individuals were also significantly different. There was no statistically detectable effect of sampling per se upon the composition of the flora of subsequent samples from the same sites. The composition of the supragingival flora of the patients with severe generalized periodontitis that had serum antibody to Actinobacillus actinomycetemcomitans was significantly different from the supragingival flora of patients without this serum antibody. However, there was no statistically significant difference in the composition of their subgingival floras.

Influence of sublethal antibiotic concentrations on bacterial adherence to saliva-treated hydroxyapatite

The influence of growth in the presence of sublethal concentrations of nine antibiotics on the ability of certain potentially odontopathic bacteria to attach to saliva-treated hydroxyapatite surfaces which mimic teeth was studied. Cells of Actinomyces viscosus LY7 and S2, Bacteroides gingivalis 381, Capnocytophaga ochraceus 6, and Actinobacillus actinomycetemcomitans N27 attached in lower numbers to saliva-treated hydroxyapatite when grown in the presence of 50% of the minimum inhibitory concentration of tetracycline. Electron microscopic observations of negatively stained preparations indicated that tetracycline-grown A. viscosus LY7 cells had fewer fimbriae than did untreated cells, which may account for the impaired ability of the treated cells to attach. However, cells of Actinomyces naeslundii L13 and S4 attached in higher numbers when grown in the presence of tetracycline, clindamycin, erythromycin, chloramphenicol, or neomycin. Streptococcus mutans strains H12 and JBP also exhibited increased adherence to saliva-treated hydroxyapatite when grown in the presence of 50 or 25% of the minimum inhibitory concentration of penicillin. Thus, growth in the presence of sublethal antibiotic concentrations could increase as well as decrease the adherence of bacteria to saliva-treated hydroxyapatite. Antibiotic-grown cells of the Actinomyces strains showed enhanced hemagglutination activity, but this did not correlate with their ability to attach to saliva-treated hydroxyapatite. Sublethal concentrations of antibiotics in the growth media also affected the coaggregation reactions of several organisms; the effects were specific for one member of the coaggregation pair.

Polyclonal B-cell activation induced by extracts of Gram-negative bacteria isolated from periodontally diseased sites

The objective of this research was to determine whether gram-negative bacteria frequently isolated from periodontally diseased sites contained polyclonal B-cell activators. Polyclonal B-cell activation, which results in nonspecific activation of multiple B-cell clones was analyzed by a hemolysis-in-gel assay designed to detect a broad range of antibody specificities. Extracts from numerous bacterial strains, including Bacteroides gingivalis, Bacteroides melaninogenicus subsp. melaninogenicus, B. melaninogenicus subsp. intermedius, Fusobacterium nucleatum, Selenomonas sputigena, Capnocytophaga ochracea, and Actinobacillus actinomycetemcomitans, were tested. Extracts of the above organisms were found to stimulate polyclonal antibody responses in cultures of normal human peripheral blood lymphocytes, although the magnitude of stimulation varied among the extracts. Optimal antibody-forming cell responses were found at stimulator doses between 5 and 1,000 micrograms/ml. We conclude that the resident gram-negative subgingival flora associated with periodontal lesions possesses potent polyclonal B-cell activators. These activators may contribute to disease pathogenesis by inducing B lymphocytes to produce antibody, osteolytic factors, or both and possibly other mediators of inflammation.

Gingival crevicular fluid levels of clindamycin compared with its minimal inhibitory concentrations for periodontal bacteria

Clindamycin concentrations in gingival crevicular fluid and in blood were determined over a 7-h period and were related to the minimal inhibitory concentrations of this agent for 340 bacterial strains isolated from diseased periodontal sites. The clindamycin levels after administration of single 300-mg oral doses were measured in gingival crevicular fluids by using an agar diffusion bioassay. Minimal inhibitory concentrations were determined by agar dilution techniques for 30 species of periodontal bacteria. With the exception of Eikenella corrodens and Actinobacillus actinomycetemcomitans, most of the bacteria were inhibited by a concentration of 1.0 microgram of clindamycin per ml or less. The peak concentrations in crevicular fluid (2.0 +/- 0.3 microgram/ml) and in blood (1.9 +/- 0.3 micrograms/ml) were approximately the same. However, crevicular fluid levels of 1.0 micrograms/ml and above were present for up to 6 h, whereas blood concentrations dropped below 1.0 micrograms/ml within 2 h after administration. Based on its minimal inhibitory concentrations, clindamycin at crevicular fluid levels of 1.0 micrograms/ml or above should inhibit most bacteria associated with diseased periodontal sites.

Butyrate and propionate: important components of toxic dental plaque extracts

Extracts of in vitro-cultured human dental plaque contain factors toxic to mammalian cells. Previous studies demonstrated that those toxic factors most readily released from cultured plaque had very low molecular weights and were heat stable. Studies reported here demonstrate that metabolic end products including short-chain fatty acids were present in fractions containing the low-molecular-weight, heat-stable factors. The salts of two of these acids, butyrate and propionate, inhibited proliferation of both mouse L929 cells and human gingival fibroblasts. Furthermore, when tested at concentrations present in plaque extracts, the inhibitory effects of butyrate and propionate accounted for essentially all the inhibitory potential of the extracts. These findings, taken together with those of other groups, suggest that butyrate and propionate, end products of dental plaque metabolism, may have an etiological role in periodontal disease.

Serum antibodies to oral Bacteroides asaccharolyticus (Bacteroides gingivalis): relationship to age and periondontal disease

An enzyme-linked immunosorbent assay microplate method was used for measuring levels of antibody specific for the oral serotype of Bacteroides asaccharolyticus (Bacteroides gingivalis) in serum samples obtained from umbilical cords, infants, children, periodontally normal adults, and edentulous adults. Serum from patients with various periodontal diseases, including adult periodontitis, localized juvenile periodontitis, generalized juvenile periodontitis, post-localized juvenile periodontitis, and acute necrotizing ulcerative gingivitis, were also studied. A positive correlation between increase in age and increase in both prevalence and level of specific antibody in the G, A, and M classes of immunoglobulins was observed. This indicates that antibodies reactive with oral B. asaccharolyticus found in up to 84% of normal adults are natural antibodies, presumably with a protective role. Among the patient groups, those with adult periodontitis were found to have levels of immunoglobulin G antibodies to oral B. asaccharolyticus that were five times higher than the antibody levels found in control subjects. The levels of IgG antibodies to this organism in the other patient groups were comparable to the levels found in the control group. However, 50% of the individuals in the generalized juvenile periodontitis group had high levels of immunoglobulin G antibodies to B. asaccharolyticus, suggesting heterogeneity with respect to immune response in these patients. These results indicate that antibodies to oral B. asaccharolyticus (B. gingivalis) occur at low levels in most normal children and adults and that the rise in titer of the specific antibodies of each major class of immunoglobulins parallels the ontogenic change in serum levels of that isotype. In contrast, there is a marked increase in titer of immunoglobulin G antibodies to oral B. asaccharolyticus in the group of patients with adult periodontitis and in patients with the generalized form of juvenile periodontitis.

Transmission-scanning electron microscopic observations of selected Eikenella corrodens strains

The morphology of Eikenella corrodens 333/54-55 (ATCC 23834) and two human periodontal lesion isolates, strains 470 and 373, was examined by transmission and scanning electron microscopy. All strains exhibited a cell envelope characteristic of gram-negative bacteria. Staining with ruthenium red and alcian blue revealed a loosely organized fibrous slime layer associated with the outer surface of the outer membrane. Slime "stabilization" was achieved by incubation of cells with antisera prepared against whole cells of the Eikenella strains. The stabilized slime appeared as a thick, electron-opaque layer juxtaposed to the outer membrane. Negative staining and heavy metal shadow-casting revealed an interwoven network of fibrils approximately 4 nm in diameter. These fibrils appeared to represent subunits of a larger fibril. Scanning electron microscopy after antibody slime stabilization confirmed the presence and location of the slime layer.

Characteristics of Bacteroides asaccharolyticus from dental plaques of beagle dogs

Gram-negative, non-saccharolytic, brown- or black-pigment-forming, nonmotile anaerboic coccobacilli, capable of decomposing hydrogen peroxide and identified as Bacteroides asaccharolyticus (B. melaninogenicus subsp. asaccharolyticus), were isolated from the supra- and subgingival plaques of beagle dogs with gingivitis or periodontitis. The organisms remained viable for many hours in an aerobic atmosphere as evidenced by their ability to grow subsequently in an anaerobic environment. They also grew well on agar media that were not reduced before use. Although blood was required for pigmentation of colonies, organisms grew on media that lacked hemin, menadione, blood, or reducing compounds. Increased oxygen tolerance, catalase activity, and different nutritional requirements differentiate these organisms from strains of B. asaccharolyticus isolated from humans.