Coaggregation studies of the Eubacterium species

The microbial co-infection interaction network in apical periodontitis with sinus tracts

OBJECTIVES

This study aims to characterize the bacterial co-occurrence features and potential interactions associated with the presence of sinus tracts in apical periodontitis in a Chinese population by using 16S rRNA next-generation sequencing (NGS).

METHODS

Thirty-one samples from twenty-six patients were collected from root canals. Following the extraction of the bacterial DNA, the V3-V4 hypervariable regions of the 16S rRNA gene were sequenced. Compositional diversity, prominent taxa and co-occurrence network analysis were compared according to the presence or absence of sinus tracts.

RESULTS

The overall microbiota in two groups exhibited distinguished patterns. Actinomyces dominated in samples with sinus tracts while Prevotella was the most abundant in samples without sinus tracts. The major pathogens in sinus tracts exhibited a complex co-occurrence network, in which Pseudomonas formed a distinctive cluster with enriched abundance, and the extensive correlations centered on Desulfovibrio and Pseudoramibacter may suggest novel dependencies. In the network without sinus tracts, the Bacteroidetes and Firmicutes taxa presented close internal associations.

CONCLUSIONS

The sequencing results confirmed the complexity of the microbiota in AP. The presence of sinus tracts was associated with distinctive infective patterns and complicated microbial co-infection interaction networks. Further investigations should be adopted to elucidate the relationship between the novel interactions and disease progression.

CLINICAL SIGNIFICANCE

Exploring the microbial interactions leads to a better understanding of etiology of apical periodontitis. Utilizing next generation sequencing techniques, our research uncovered the bacterial community structure and observed co-infection networks associated with sinus tracts, providing potential insights for prognosis prediction and targeted therapeutics of persistent inflammation.

Brain abscess caused by Porphyromonas gingivalis and Eubacterium nodatum mimicking acute stroke

We described a case of a 65-year-old man with a brain abscess caused by Porphyromonas gingivalis and Eubacterium nodatum. The patient presented right central facial nerve palsy, mutism and right hemiparesis at the examination. The patient underwent a left frontal craniotomy with evacuation of the brain abscess. Specimens were collected for microbiological analysis and intravenous treatment was started with levetiracetam, dexamethasone, meropenem (1 g/8 h) and linezolid (600 mg/12 h). After identification of anaerobic bacteria the antibiotic treatment was changed to piperacillin/tazobactam (4 g/0,5 g/8 h), fulfilling 8 weeks of antibiotic with good clinical and radiological evolution.

Genetic and molecular determinants of polymicrobial interactions in Fusobacterium nucleatum

A gram-negative colonizer of the oral cavity, Fusobacterium nucleatum not only interacts with many pathogens in the oral microbiome but also has the ability to spread to extraoral sites including placenta and amniotic fluid, promoting preterm birth. To date, however, the molecular mechanism of interspecies interactions-termed coaggregation-by F. nucleatum and how coaggregation affects bacterial virulence remain poorly defined. Here, we employed genome-wide transposon mutagenesis to uncover fusobacterial coaggregation factors, revealing the intertwined function of a two-component signal transduction system (TCS), named CarRS, and a lysine metabolic pathway in regulating the critical coaggregation factor RadD. Transcriptome analysis shows that CarR modulates a large regulon including radD and lysine metabolic genes, such as kamA and kamD, the expression of which are highly up-regulated in the ΔcarR mutant. Significantly, the native culture medium of ΔkamA or ΔkamD mutants builds up abundant amounts of free lysine, which blocks fusobacterial coaggregation with streptococci. Our demonstration that lysine-conjugated beads trap RadD from the membrane lysates suggests that lysine utilizes RadD as its receptor to act as a metabolic inhibitor of coaggregation. Lastly, using a mouse model of preterm birth, we show that fusobacterial virulence is significantly attenuated with the ΔkamA and ΔcarR mutants, in contrast to the enhanced virulence phenotype observed upon diminishing RadD (ΔradD or ΔcarS mutant). Evidently, F. nucleatum employs the TCS CarRS and environmental lysine to modulate RadD-mediated interspecies interaction, virulence, and nutrient acquisition to thrive in the adverse environment of oral biofilms and extraoral sites.

Inter-bacterial correlations in subgingival biofilms: a large-scale survey

AIM

Although the complexity of the oral ecology and the ecological differences between health and disease are well accepted, a clear view on the dynamics in relation to disease is lacking. In this study, the prevalence and abundance of 20 key oral bacteria was assessed in health and disease and more importantly a closer look was given to the inter-bacterial relationships.

MATERIALS AND METHODS

A blinded microbiological database was analysed in this cross-sectional, retrospective study. The database was constructed based on microbiological analyses of samples from 6308 patients, with gradations of periodontitis (healthy to periodontitis). Data concerning the abundance of 20 oral bacteria and probing pocket depth were provided.

RESULTS

Porphyromonas gingivalis, Tannerella forsythia, Treponema denticola, Eubacterium nodatum, Porphyromonas micra and Porphyromonas intermedia showed a clear increase in abundance and prevalence with increasing pocket depth. Correlation matrices illustrated that almost all microorganisms were in one way correlated to other species and most of these correlations were significant. Several beneficial bacteria showed strong correlations with other beneficial bacteria.

CONCLUSION

Knowledge on bacterial correlations can pave the way for new treatment options focusing on restoring the shifted balance.

Autoaggregation response of Fusobacterium nucleatum

Fusobacterium nucleatum is a gram-negative oral bacterial species associated with periodontal disease progression. This species is perhaps best known for its ability to adhere to a vast array of other bacteria and eukaryotic cells. Numerous studies of F. nucleatum have examined various coaggregation partners and inhibitors, but it is largely unknown whether these interactions induce a particular genetic response. We tested coaggregation between F. nucleatum ATCC strain 25586 and various species of Streptococcus in the presence of a semidefined growth medium containing saliva. We found that this condition could support efficient coaggregation but, surprisingly, also stimulated a similar degree of autoaggregation. We further characterized the autoaggregation response, since few reports have examined this in F. nucleatum. After screening several common coaggregation inhibitors, we identified l-lysine as a competitive inhibitor of autoaggregation. We performed a microarray analysis of the planktonic versus autoaggregated cells and found nearly 100 genes that were affected after only about 60 min of aggregation. We tested a subset of these genes via real-time reverse transcription-PCR and confirmed the validity of the microarray results. Some of these genes were also found to be inducible in cell pellets created by centrifugation. Based upon these data, it appears that autoaggregation activates a genetic program that may be utilized for growth in a high cell density environment, such as the oral biofilm.

Laboratory maintenance of fusobacteria

This unit describes routine laboratory handling of fusobacteria. Different media that can be used to grow or enrich Fusobacterium nucleatum and other species of this genus are described. The growth and stock conditions as well as the susceptibility of F. nucleatum to oxygen in a pure culture are also discussed.

Identification and characterization of a novel adhesin unique to oral fusobacteria

Fusobacterium nucleatum is a gram-negative anaerobe that is prevalent in periodontal disease and infections of different parts of the body. The organism has remarkable adherence properties, binding to partners ranging from eukaryotic and prokaryotic cells to extracellular macromolecules. Understanding its adherence is important for understanding the pathogenesis of F. nucleatum. In this study, a novel adhesin, FadA (Fusobacterium adhesin A), was demonstrated to bind to the surface proteins of the oral mucosal KB cells. FadA is composed of 129 amino acid (aa) residues, including an 18-aa signal peptide, with calculated molecular masses of 13.6 kDa for the intact form and 12.6 kDa for the secreted form. It is highly conserved among F. nucleatum, Fusobacterium periodonticum, and Fusobacterium simiae, the three most closely related oral species, but is absent in the nonoral species, including Fusobacterium gonidiaformans, Fusobacterium mortiferum, Fusobacterium naviforme, Fusobacterium russii, and Fusobacterium ulcerans. In addition to FadA, F. nucleatum ATCC 25586 and ATCC 49256 also encode two paralogues, FN1529 and FNV2159, each sharing 31% identity with FadA. A double-crossover fadA deletion mutant, F. nucleatum 12230-US1, was constructed by utilizing a novel sonoporation procedure. The mutant had a slightly slower growth rate, yet its binding to KB and Chinese hamster ovarian cells was reduced by 70 to 80% compared to that of the wild type, indicating that FadA plays an important role in fusobacterial colonization in the host. Furthermore, due to its uniqueness to oral Fusobacterium species, fadA may be used as a marker to detect orally related fusobacteria. F. nucleatum isolated from other parts of the body may originate from the oral cavity.

Pseudoramibacter alactolyticus in primary endodontic infections

A nested polymerase chain reaction (PCR)-based method was used to directly survey samples taken from primary endodontic infections for the occurrence of Pseudoramibacter alactolyticus. Identification by nested PCR was performed in root-canal samples from teeth associated with asymptomatic periradicular lesions or acute apical periodontitis, and in pus samples from acute periradicular abscesses. DNA was extracted from the samples and initially amplified using universal 16S rDNA primers. A second round of amplification used the first PCR products to detect a specific fragment of P. alactolyticus 16S rDNA. P. alactolyticus was detected in 76% of root-canal samples from teeth showing asymptomatic periradicular lesions, in 60% of samples taken from root canals associated with acute apical periodontitis, and in 32% of pus samples aspirated from acute periradicular abscesses. No significant association of this species with clinical symptoms was observed (p > 0.01). In general, P. alactolyticus occurred in 56% of samples taken from infections of endodontic origin. The high prevalence of P. alactolyticus in infections of endodontic origin as detected by nested PCR in this study, and its apparent pathogenicity, particularly in mixed infections, indicate that this bacterial species is a candidate endodontic pathogen that can participate in the etiology of different forms of periradicular diseases.

Antagonistic interactions among Fusobacterium nucleatum and Prevotella intermedia with oral lactobacilli

Microbiota residing in oral ecosystems show great complexity because of the mutual interdependence of certain microorganisms that might influence their presence or absence at a given site. The aim of this work was to evaluate possible antagonistic interactions among Fusobacterium nucleatum and Prevotella intermedia, isolated from periodontal pockets, and Lactobacillus casei, L. salivarius, L. rhamnosus and L. plantarum isolated from saliva. Different tests were carried out using each strain as an effector as well as a sensitive strain, alternatively: (1) agar diffusion with paper disks embedded with supernatants and pellets in different culture media; (b) the well diffusion assay; (c) the double layer method; and (d) OD(560) measurements of the kinetic growth of Lactobacillus strains in LAPTg broth with different volumes of F. nucleatum supernatant. P. intermedia supernatant did not have an inhibitory effect on Lactobacillus growth, except for L. casei, when the double plaque method was used. F. nucleatum supernatant inhibited growth of all Lactobacillus strains when the well diffusion method was used. F. nucleatum inhibited L. casei growth whatever the method used. The substance responsible for inhibition was a thermoresistant extracellular protein which was hydrolyzed by trypsin-like proteases. None of the species of lactobacilli studied inhibited the growth of P. intermedia or F. nucleatum.

Influence of secondary colonizers and human plasma on the adherence of Porphyromonas gingivalis in vitro

The influence of secondary colonizers (Fusobacterium nucleatum and Actinomyces naeslundii) and the effect of human plasma on the adherence of Porphyromonas gingivalis were investigated. Hydroxyapatite (HAP) discs coated with Streptococcus sanguis were immersed in a 3H-labeled bacterial cell suspension of F. nucleatum or A. naeslundii and then in a 14C-labeled P. gingivalis cell suspension. Bacterial cells on the discs were pyrolysed to quantify the radioisotopes released. The cell numbers of secondary colonizers on the discs increased with immersion time and this, in turn, resulted in significantly elevated adherence of P. gingivalis. These two secondary colonizers had very similar positive effects on the adherence of P. gingivalis. Human plasma significantly inhibited the adherence of P. gingivalis and secondary colonizers to S. sanguis-coated HAP discs. Adherence of P. gingivalis and A. naeslundii was strongly inhibited by plasma, while that of F. nucleatum was affected the least. Treatment with plasma, after immersion of streptococcal-coated discs in individual cell suspension of secondary colonizers, also reduced subsequent adherence of P. gingivalis. The rate of decrease was much smaller in F. nucleatum. These results indicate that both F. nucleatum and A. naeslundii enhance the adherence of P. gingivalis, and that the former may play a more important role in the establishment of P. gingivalis in dental plaque where plasma-derived components are present.

Recovery of Candida dubliniensis and other yeasts from human immunodeficiency virus-associated periodontal lesions

Oral and subgingival samples from periodontal lesions were collected from 54 human immunodeficiency virus (HIV)-positive and 20 HIV-negative patients and cultured for yeast species. Of the 54 samples cultured from HIV-positive patients, 44 (82%) were positive for yeast species, of which 29 (66%) were subgingival. A total of 19 (48%) patients were positive for Candida dubliniensis, of which 15 (79%) were colonized in subgingival sites. Seven isolates of Candida glabrata, two isolates of Candida parapsilosis, and one isolate of Saccharomyces cerevisiae were recovered. This study reports for the first time the recovery of C. dubliniensis from subgingival intraoral sites and confirms the presence of Candida species in sites of periodontal disease associated with HIV.

Evaluation of co-aggregation among Streptococcus mitis, Fusobacterium nucleatum and Porphyromonas gingivalis

AIMS

To develop a semi-quantitative method for evaluating co-aggregation reactions among three bacterial species, and to examine the influence of Fusobacterium nucleatum on the adherence of Porphyromonas gingivalis.

METHODS AND RESULTS

The method involves coating hydroxyapatite (HAP) discs with streptococcal cells and treatment with radio-labelled bacterial cell suspensions. The sensitivity of the method was estimated by comparison with a turbidometric co-aggregation assay. Results from the two methods were in close agreement. Streptococcus mitis-coated HAP discs were immersed in a 3H-labelled Fus. nucleatum cell suspension and then a 14C-labelled P. gingivalis cell suspension. The discs were then pyrolysed to recover and quantify the released 3H and 14C radioactivity. The number of Fus. nucleatum cells on the discs increased with immersion time and this, in turn, resulted in elevated adherence of P. gingivalis.

CONCLUSION

The data indicate that the method closely reflects co-aggregation characters, and that Fus. nucleatum has a positive effect on the adherence of P. gingivalis.

SIGNIFICANCE AND IMPACT OF THE STUDY

The present method, which is designed to mimic the oral environment, should prove useful in the semi-quantitative evaluation of co-aggregation reactions.

New assay for measuring cell surface hydrophobicities of Candida dubliniensis and Candida albicans

Hydrophobic interactions, based on cell surface hydrophobicity (CSH), are among the many and varied mechanisms of adherence deployed by the pathogenic yeast Candida albicans. Recently it was shown that, unlike C. albicans, C. dubliniensis is a species that exhibits an outer fibrillar layer consistent with constant CSH. Previously, C. dubliniensis grown at 25 or 37 degrees C was shown to coaggregate with the oral anaerobic bacterium Fusobacterium nucleatum. C. albicans, however, demonstrated similar coaggregation only when hydrophobic or grown at 25 degrees C. This observation implied that coaggregation of Candida cells with F. nucleatum is associated with a hydrophobic yeast cell surface. To test this hypothesis, 42 C. albicans and 40 C. dubliniensis clinical isolates, including a C. albicans hydrophobic variant, were grown at 25 and 37 degrees C and tested with the established hydrophobicity microsphere assay, which determines CSH levels based on the number of microspheres attached to the yeast cells. The coaggregation assay was performed in parallel experiments. All C. dubliniensis isolates grown at either temperature, hydrophobic 25 degrees C-grown C. albicans isolates, and the C. albicans hydrophobic variant, unlike the 37 degrees C-hydrophilic C. albicans isolates, exhibited hydrophobic CSH levels with the microsphere assay and simultaneously showed maximum, 4+, coaggregation with F. nucleatum. The parallel results obtained for C. dubliniensis using both assays support the use of the CoAg assay both as a rapid assay to determine CSH and to differentiate between C. dubliniensis and C. albicans.

Isolation of fusobacteria from the oral cavities of malnourished Nigerian children living in agricultural and herding villages

A previous study demonstrated the presence and possible involvement of Fusobacterium necrophorum in the pathogenesis of noma lesions of children living in agricultural and herding villages in northwestern Nigeria. In order to determine if F. necrophorum was part of the oral flora of malnourished children with no noma lesions, a study of the fusobacteria present in the oral cavities of 30 children, 2-6 years of age in Sokoto State, was undertaken. Swabs taken of the oral cavity were cultured on selective fusobacteria medium using conventional anaerobic microbiological techniques. F. nucleatum was recovered from each child and F. necrophorum was isolated from the oral cavity of only one child. The presence of F. nucleatum and the lack of F. necrophorum, except in one case, suggests that the latter is not normal flora in the children at risk for noma. F. necrophorum, a putative trigger organism for noma may gain a foothold only when certain staging conditions (i.e., lowered host resistance and/or oral lesion) are present.

Peptostreptococcus micros coaggregates with Fusobacterium nucleatum and non-encapsulated Porphyromonas gingivalis

Coaggregation is one of the potential colonization strategies of oral microorganisms, often involving fimbrial structures in the interactions. In this study, the coaggregation characteristics of the rough and smooth genotypes of the periodontal pathogen Peptostreptococcus micros were compared to investigate the role of the fibril-like structures of the rough genotype in coaggregation. Of the 11 oral species tested, only Fusobacterium nucleatum strains and non-encapsulated Porphyromonas gingivalis strains coaggregated with P. micros. No differences in coaggregation between the smooth type (Sm), the rough type (Rg) and the smooth variant of the Rg type (Rg(Sm)) of P. micros were observed. Heat-stable, periodate-sensitive structures on P. micros appeared to interact with heat- and protease-sensitive structures on F. nucleatum and P. gingivalis. These data indicate that these unimodal coaggregations are not mediated by the proteinaceous fibril-like structures of the Rg genotype, but by carbohydrates present on both genotypes of P. micros.

Fimbria-mediated coaggregation between human oral anaerobes Treponema medium and Porphyromonas gingivalis

Bacterial binding phenomena among different bacterial genera or species play an important role in bacterial colonization in a mixed microbiota such as in the human oral cavity. The coaggregation reaction between two gram-negative anaerobes, Treponema medium and Porphyromonas gingivalis, was characterized using fimbria-deficient mutants of P. gingivalis and specific antisera against purified fimbriae and bacterial whole cells. T. medium ATCC 700273 strongly coaggregated with fimbriate P. gingivalis strains ATCC 33277 and 381, but not with afimbriate strains including transposon-induced fimbria-deficient mutants and KDP98 as a fimA-disrupted mutant of P. gingivalis ATCC 33277. In the P. gingivalis-T. medium coaggregation assay, the presence of rabbit antiserum against the purified fimbriae or the whole cells of P. gingivalis ATCC 33277 produced different "aggregates" consisting predominantly of P. gingivalis cells with few spirochetes, but both preimmune serum and the antiserum against the afimbriate KDP98 cells did not inhibit the coaggregation reaction. Heated P. gingivalis cells lost their ability to bind both heated and unheated T. medium cells. This T. medium-P. gingivalis coaggregation reaction was inhibited by a cysteine proteinase inhibitor, leupeptin, and also by arginine and lysine, but not by EDTA or sugars including lactose. A binding assay on nitrocellulose membranes and immunoelectron microscopy demonstrated that a heat-stable 37 kDa surface protein on the T. medium cell attached to the P. gingivalis fimbriae.

Coaggregation of Candida dubliniensis with Fusobacterium nucleatum

The binding of microorganisms to each other and oral surfaces contributes to the progression of microbial infections in the oral cavity. Candida dubliniensis, a newly characterized species, has been identified in human immunodeficiency virus-seropositive patients and other immunocompromised individuals. C. dubliniensis phenotypically resembles Candida albicans in many respects yet can be identified and differentiated as a unique Candida species by phenotypic and genetic profiles. The purpose of this study was to determine oral coaggregation (CoAg) partners of C. dubliniensis and to compare these findings with CoAg of C. albicans under the same environmental conditions. Fifteen isolates of C. dubliniensis and 40 isolates of C. albicans were tested for their ability to coaggregate with strains of Fusobacterium nucleatum, Peptostreptococcus micros, Peptostreptococcus magnus, Peptostreptococcus anaerobius, Porphyromonas gingivalis, and Prevotella intermedia. When C. dubliniensis and C. albicans strains were grown at 37 degrees C on Sabouraud dextrose agar, only C. dubliniensis strains coaggregated with F. nucleatum ATCC 49256 and no C. albicans strains showed CoAg. However, when the C. dubliniensis and C. albicans strains were grown at 25 or 45 degrees C, both C. dubliniensis and C. albicans strains demonstrated CoAg with F. nucleatum. Heating the C. albicans strains (grown at 37 degrees C) at 85 degrees C for 30 min or treating them with dithiothreitol allowed the C. albicans strains grown at 37 degrees C to coaggregate with F. nucleatum. CoAg at all growth temperatures was inhibited by mannose and alpha-methyl mannoside but not by EDTA or arginine. The CoAg reaction between F. nucleatum and the Candida species involved a heat-labile component on F. nucleatum and a mannan-containing heat-stable receptor on the Candida species. The CoAg reactions between F. nucleatum and the Candida species may be important in the colonization of the yeast in the oral cavity, and the CoAg of C. dubliniensis by F. nucleatum when grown at 37 degrees C provides a rapid, specific, and inexpensive means to differentiate C. dubliniensis from C. albicans isolates in the clinical laboratory.

Microbial complexes in subgingival plaque

It has been recognized for some time that bacterial species exist in complexes in subgingival plaque. The purpose of the present investigation was to attempt to define such communities using data from large numbers of plaque samples and different clustering and ordination techniques. Subgingival plaque samples were taken from the mesial aspect of each tooth in 185 subjects (mean age 51 +/- 16 years) with (n = 160) or without (n = 25) periodontitis. The presence and levels of 40 subgingival taxa were determined in 13,261 plaque samples using whole genomic DNA probes and checkerboard DNA-DNA hybridization. Clinical assessments were made at 6 sites per tooth at each visit. Similarities between pairs of species were computed using phi coefficients and species clustered using an averaged unweighted linkage sort. Community ordination was performed using principal components analysis and correspondence analysis. 5 major complexes were consistently observed using any of the analytical methods. One complex consisted of the tightly related group: Bacteroides forsythus, Porphyromonas gingivalis and Treponema denticola. The 2nd complex consisted of a tightly related core group including members of the Fusobacterium nucleatum/periodonticum subspecies, Prevotella intermedia, Prevotella nigrescens and Peptostreptococcus micros. Species associated with this group included: Eubacterium nodatum, Campylobacter rectus, Campylobacter showae, Streptococcus constellatus and Campylobacter gracilis. The 3rd complex consisted of Streptococcus sanguis, S. oralis, S. mitis, S. gordonii and S. intermedius. The 4th complex was comprised of 3 Capnocytophaga species, Campylobacter concisus, Eikenella corrodens and Actinobacillus actinomycetemcomitans serotype a. The 5th complex consisted of Veillonella parvula and Actinomyces odontolyticus. A. actinomycetemcomitans serotype b, Selenomonas noxia and Actinomyces naeslundii genospecies 2 (A. viscosus) were outliers with little relation to each other and the 5 major complexes. The 1st complex related strikingly to clinical measures of periodontal disease particularly pocket depth and bleeding on probing.

Mechanisms of adhesion by oral bacteria

Adherence to a surface is a key element for colonization of the human oral cavity by the more than 500 bacterial taxa recorded from oral samples. Three surfaces are available: teeth, epithelial mucosa, and the nascent surface created as each new bacterial cell binds to existing dental plaque. Oral bacteria exhibit specificity for their respective colonization sites. Such specificity is directed by adhesin-receptor cognate pairs on genetically distinct cells. Colonization is successful when adherent cells grow and metabolically participate in the oral bacterial community. The potential roles of adherence-relevant molecules are discussed in the context of the dynamic nature of the oral econiche.

The effect of cyclosporin-A on the oral microflora at gingival sulcus of the ferret

The effect of cyclosporin-A (CyA) on the dentogingival flora of ferrets with healthy and experimentally induced periodontal breakdown was studied. Five animals were given 10 mg/kg/d CyA. At the start of the experiments (day 0), ligatures were placed around 4 teeth in the right upper and lower jaws; corresponding contralateral teeth on the left side served as control. On days 0 and 28 (end of the experiment), microbiological samples were collected from the gingival sulcus of the experimental and the control teeth and from closely located gingival mucosa membrane. The samples were subjected to viable counts and to darkfield microscopic analyses. On day 0, facultative anaerobic rods, mainly Pasteurella spp, Alcaligenes spp, Corynebacterium spp. and Rothia spp dominated in the viable counts. No anaerobic bacteria were detected in the viable counts. On day 28 spirochetes increased in the experimental gingival sulcus samples and anaerobic bacteria appeared in most of the samples and constituted 40-60% of the total cultivable flora; Fusobacterium necrophorum and Eubacterium spp. predominated in the samples from the experimental sites. The results of the present study were compared with those of our previous investigation of ferrets not medicated with cyclosporin but also subject to experimental ligature periodontitis. Eubacterium spp. were absent in the animals not treated with cyclosporin, while this species was frequently present in the immunosuppressed ferrets. The results indicate that the presence of the large numbers of gram negative rods and of anaerobic bacteria may have enhanced the inflammatory process and further provoked the gingival overgrowth observed.

Taxonomy, biology, and periodontal aspects of Fusobacterium nucleatum

The pathogenic potential of Fusobacterium nucleatum and its significance in the development of periodontal diseases, as well as in infections in other organs, have gained new interest for several reasons. First, this bacterium has the potential to be pathogenic because of its number and frequency in periodontal lesions, its production of tissue irritants, its synergism with other bacteria in mixed infections, and its ability to form aggregates with other suspected pathogens in periodontal disease and thus act as a bridge between early and late colonizers on the tooth surface. Second, of the microbial species that are statistically associated with periodontal disease, F. nucleatum is the most common in clinical infections of other body sites. Third, during the past few years, new techniques have made it possible to obtain more information about F. nucleatum on the genetic level, thereby also gaining better knowledge of the structure and functions of the outer membrane proteins (OMPs). OMPs are of great interest with respect to coaggregation, cell nutrition, and antibiotic susceptibility. This review covers what is known to date about F. nucleatum in general, such as taxonomy and biology, with special emphasis on its pathogenic potential. Its possible relationship to other periodontal bacteria in the development of periodontal diseases and the possible roles played by OMPs are considered.

Taxonomy, biology, and periodontal aspects of Fusobacterium nucleatum

The pathogenic potential of Fusobacterium nucleatum and its significance in the development of periodontal diseases, as well as in infections in other organs, have gained new interest for several reasons. First, this bacterium has the potential to be pathogenic because of its number and frequency in periodontal lesions, its production of tissue irritants, its synergism with other bacteria in mixed infections, and its ability to form aggregates with other suspected pathogens in periodontal disease and thus act as a bridge between early and late colonizers on the tooth surface. Second, of the microbial species that are statistically associated with periodontal disease, F. nucleatum is the most common in clinical infections of other body sites. Third, during the past few years, new techniques have made it possible to obtain more information about F. nucleatum on the genetic level, thereby also gaining better knowledge of the structure and functions of the outer membrane proteins (OMPs). OMPs are of great interest with respect to coaggregation, cell nutrition, and antibiotic susceptibility. This review covers what is known to date about F. nucleatum in general, such as taxonomy and biology, with special emphasis on its pathogenic potential. Its possible relationship to other periodontal bacteria in the development of periodontal diseases and the possible roles played by OMPs are considered.

Dental plaque as a biofilm

Dental plaque is the diverse microbial community found on the tooth surface embedded in a matrix of polymers of bacterial and salivary origin. Once a tooth surface is cleaned, a conditioning film of proteins and glycoproteins is adsorbed rapidly to the tooth surface. Plaque formation involves the interaction between early bacterial colonisers and this film (the acquired enamel pellicle). To facilitate colonisation of the tooth surface, some receptors on salivary molecules are only exposed to bacteria once the molecule is adsorbed to a surface. Subsequently, secondary colonisers adhere to the already attached early colonisers (co-aggregation) through specific molecular interactions. These can involve protein-protein or carbohydrate-protein (lectin) interactions, and this process contributes to determining the pattern of bacterial succession. As the biofilm develops, gradients in biologically significant factors develop, and these permit the co-existence of species that would be incompatible with each other in a homogenous environment. Dental plaque develops naturally, but it is also associated with two of the most prevalent diseases affecting industrialised societies (caries and periodontal diseases). Future strategies to control dental plaque will be targeted to interfering with the formation, structure and pattern of development of this biofilm.