Relationships among the oral fusobacteria assessed by DNA-DNA hybridization

Pangenomic Study of Fusobacterium nucleatum Reveals the Distribution of Pathogenic Genes and Functional Clusters at the Subspecies and Strain Levels

Fusobacterium nucleatum is a prevalent periodontal pathogen and is associated with many systemic diseases. Our knowledge of the genomic characteristics and pathogenic effectors of different F. nucleatum strains is limited. In this study, we completed the whole genome assembly of the 4 F. nucleatum strains and carried out a comprehensive pangenomic study of 30 strains with their complete genome sequences. Phylogenetic analysis revealed that the F. nucleatum strains are mainly divided into 4 subspecies, while 1 of the sequenced strains was classified into a new subspecies. Gene composition analysis revealed that a total of 517 "core/soft-core genes" with housekeeping functions widely distributed in almost all the strains. Each subspecies had a unique gene cluster shared by strains within the subspecies. Analysis of the virulence factors revealed that many virulence factors were widely distributed across all the strains, with some present in multiple copies. Some virulence genes showed no consistent occurrence rule at the subspecies level and were specifically distributed in certain strains. The genomic islands mainly revealed strain-specific characteristics instead of subspecies level consistency, while CRISPR types and secondary metabolite biosynthetic gene clusters were identically distributed in F. nucleatum strains from the same subspecies. The variation in amino acid sites in the adhesion protein FadA did not affect the monomer and dimer 3D structures, but it may affect the binding surface and the stability of binding to host receptors. This study provides a basis for the pathogenic study of F. nucleatum at the subspecies and strain levels. IMPORTANCE We used F. nucleatum as an example to analyze the genomic characteristics of oral pathogens at the species, subspecies, and strain levels and elucidate the similarities and differences in functional genes and virulence factors among different subspecies/strains of the same oral pathogen. We believe that the unique biological characteristics of each subspecies/strain can be attributed to the differences in functional gene clusters or the presence/absence of certain virulence genes. This study showed that F. nucleatum strains from the same subspecies had similar functional gene compositions, CRISPR types, and secondary metabolite biosynthetic gene clusters, while pathogenic genes, such as virulence genes, antibiotic resistance genes, and GIs, had more strain level specificity. The findings of this study suggest that, for microbial pathogenicity studies, we should carefully consider the subspecies/strains being used, as different strains may vary greatly.

Genome-Based Reclassification of Fusobacterium nucleatum Subspecies at the Species Level

Fusobacterium nucleatum is classified as four subspecies, subsp. nucleatum, polymorphum, vincentii, and animalis, based on DNA-DNA hybridization (DDH) patterns, phenotypic characteristics, and/or multilocus sequence analysis (MLSA). The gold standards for classification of bacterial species are DDH and 16S ribosomal RNA gene (16S rDNA) sequence homology. The thresholds of DDH and 16S rDNA similarity for delineation of bacterial species have been suggested to be >70 and 98.65%, respectively. Average nucleotide identity (ANI) and genome-to-genome distance (GGD) analysis based on genome sequences were recently introduced as a replacement for DDH to delineate bacterial species with ANI (95-96%) and GGD (70%) threshold values. In a previous study, F. hwasookii was classified as a new species based on MLSA and DDH results. 16S rDNA similarity between F. hwasookii type strain and F. nucleatum subspecies type strains was higher than that between F. nucleatum subspecies type strains. Therefore, it is possible that the four F. nucleatum subspecies can be classified as Fusobacterium species. In this study, we performed ANI and GGD analyses using the genome sequences of 36 F. nucleatum, five F. hwasookii, and one Fusobacterium periodonticum strain to determine whether the four F. nucleatum subspecies could be classified as species using OrthoANI and ANI web-based softwares provided by ChunLab and Kostas lab, respectively, and GGD calculator offered by German Collection of Microorganisms and Cell Cultures. ANI values calculated from OrthoANI and ANI calculators between the type strains of F. nucleatum subspecies ranged from 89.80 to 92.97 and from 90.40 to 91.90%, respectively. GGD values between the type strains of F. nucleatum subspecies ranged from 42.3 to 46.0%. ANI and GGD values among strains belonging to the same F. nucleatum subspecies, subsp. nucleatum, subsp. polymorphum, subsp. vincentii, and subsp. animalis were >96 and >68.2%, respectively. These results strongly suggest that F. nucleatum subsp. nucleatum, subsp. polymorphum, subsp. vincentii, and subsp. animalis should be classified as F. nucleatum, F. polymorphum, F. vincentii, and F. animalis, respectively.

Streptococcus mutans SpaP binds to RadD of Fusobacterium nucleatum ssp. polymorphum

Adhesin-mediated bacterial interspecies interactions are important elements in oral biofilm formation. They often occur on a species-specific level, which could determine health or disease association of a biofilm community. Among the key players involved in these processes are the ubiquitous fusobacteria that have been recognized for their ability to interact with numerous different binding partners. Fusobacterial interactions with Streptococcus mutans, an important oral cariogenic pathogen, have previously been described but most studies focused on binding to non-mutans streptococci and specific cognate adhesin pairs remain to be identified. Here, we demonstrated differential binding of oral fusobacteria to S. mutans. Screening of existing mutant derivatives indicated SpaP as the major S. mutans adhesin specific for binding to Fusobacterium nucleatum ssp. polymorphum but none of the other oral fusobacteria tested. We inactivated RadD, a known adhesin of F. nucleatum ssp. nucleatum for interaction with a number of gram-positive species, in F. nucleatum ssp. polymorphum and used a Lactococcus lactis heterologous SpaP expression system to demonstrate SpaP interaction with RadD of F. nucleatum ssp. polymorphum. This is a novel function for SpaP, which has mainly been characterized as an adhesin for binding to host proteins including salivary glycoproteins. In conclusion, we describe an additional role for SpaP as adhesin in interspecies adherence with RadD-SpaP as the interacting adhesin pair for binding between S. mutans and F. nucleatum ssp. polymorphum. Furthermore, S. mutans attachment to oral fusobacteria appears to involve species- and subspecies-dependent adhesin interactions.

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.

Arbitrarily primed-polymerase chain reaction for identification and epidemiologic subtyping of oral isolates of Fusobacterium nucleatum

BACKGROUND

Fusobacterium nucleatum is the most frequently isolated bacterium in periodontal disease and plays an important role in serious infections in other parts of the body. Arbitrarily primed-polymerase chain reaction (AP-PCR) was used to construct primers for specific identification and subtyping of F. nucleatum. Subtypes may differ in virulence and, hence, are important as periodontal pathogens. Subtypes also may differ in antibiotic susceptibility; therefore, knowing the subtypes may influence choice of treatment.

METHODS

We analyzed 70 DNA samples of F. nucleatum isolated from patients with periodontal disease (PD) (N = 32) or AIDS-related PD (N = 8) and from healthy carriers (N = 30). From 90 AP-PCR primers screened, five amplification products were selected, cloned in pCR II vector, and sequenced. These sequences were used to design new pairs of specific primers. Sequences were compared to GenBank entries with BLAST and showed no significant matches.

RESULTS

Three primer pairs produced bands of approximately 1 Kb (primer 5059S) or 0.5 Kb (primers FN5047 or M1211) with all F. nucleatum DNAs tested. PCR amplification using primer pair M8171 produced a 1 Kb band with isolates from 7 (22%) PD and 5 (63%) PD-AIDS patients and 9 (30%) healthy controls. Using the same primer pair, 2 other bands of approximately 0.5 Kb and 0.4 Kb were observed with DNA from isolates from 2 (6%) PD and all PD-AIDS patients, but were not observed with DNA samples from healthy controls (P<0.0001). All the primer pairs produced no or different amplicon profiles with DNA samples from bacterial species other than F. nucleatum.

CONCLUSIONS

Our results suggest that PCR primer pairs 5059S, FN5047 or M1211 can be used to specifically identify F. nucleatum isolates and distinguish them from other bacteria. The primer pair M8171 could also be used to differentiate F. nucleatum isolated from periodontal patients or healthy individuals. These specific primers can be used in PCR analysis for specific identification of F. nucleatum and to distinguish it from other bacteria associated with human periodontitis. These approaches appear promising in facilitating laboratory identification, molecular subtyping, and taxonomy of putative periodontopathogens.

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.

Intergeneric coaggregation of oral Treponema spp. with Fusobacterium spp. and intrageneric coaggregation among Fusobacterium spp

A total of 22 strains of Treponema spp. including members of all four named human oral species were tested for coaggregation with 7 strains of oral fusobacteria, 2 strains of nonoral fusobacteria, and 45 strains of other oral bacteria, which included actinobacilli, actinomyces, capnocytophagae, eubacteria, porphyromonads, prevotellae, selenomonads, streptococci, and veillonellae. None of the treponemes coaggregated with any of the latter 45 oral strains or with the two nonoral fusobacteria. All treponemes, eight Treponema denticola strains, eight T. socranskii strains, four oral pectinolytic treponemes, one T. pectinovorum strain, and one T. vincentii strain coaggregated with at least one strain of the fusobacteria tested as partners. The partners consisted of one strain of Fusobacterium periodonticum, five F. nucleatum strains including all four subspecies of F. nucleatum, and a strain of F. simiae obtained from the dental plaque of a monkey. In the more than 100 coaggregations observed, the fusobacterial partner was heat inactivated (85 degrees C for 30 min), while the treponemes were unaffected by the heat treatment. Furthermore, the fusobacteria were usually inactivated by proteinase K treatment, and the treponemes were not affected. Only the T. denticola coaggregations were inhibited by lactose and D-galactosamine. None were inhibited by any of 23 other different sugars or L-arginine. Intragenic coaggregations were seen among the subspecies of F. nucleatum and with F. periodonticum, and none were inhibited by any of the sugars tested or by L-arginine. No intrageneric coaggregations were observed among the treponemes. These data indicate that the human oral treponemes show a specificity for oral fusobacteria as coaggregation partners. Such cell-to cell contact may facilitate efficient metabolic communication and enhance the proliferation of each cell in the progressively more severe stages of periodontal disease.

Molecular characterization of a 40-kDa outer membrane protein, FomA, of Fusobacterium periodonticum and comparison with Fusobacterium nucleatum

The 40 kDa-outer membrane protein FomA of Fusobacterium periodonticum ATCC 33693 was found to exhibit heat modifiable properties, typical for a porin, and N-terminal sequencing indicated a close relationship to the porin FomA of Fusobacterium nucleatum. A polymerase chain reaction approach was therefore applied for sequencing the fomA gene of F. periodonticum, and nucleotide and deduced amino acid sequences were aligned and compared with the corresponding sequences of different strains of F. nucleatum. In all strains we found a common protein upstream of the fomA gene. The noncoding area upstream of the putative -35 region of the F. periodonticum fomA gene exhibited little sequence similarity with the F. nucleatum gene. The transcriptional unit of FomA, on the other hand, was very similar, with the similarities concentrated in domains that were interspersed with hypervariable regions. A topology model was made and compared with those made for F. nucleatum. This indicated that the great similarities reside in the membrane-spanning segments of the protein, while most cell surface exposed loops were hypervariable. The results strongly support the proposed model for FomA and also indicate that these taxa are related but on a lower level than the subspecies level. The codon usage of F. periodonticum is comparable to that of F. nucleatum, and the triplet AGA is the only codon used for arginine.

Sizing the Fusobacterium nucleatum genome by pulsed-field gel electrophoresis

The genome sizes of Fusobacterium nucleatum strains F1, F3, F6, ATCC 10953, ATCC 25586 and Fev1 were determined by pulsed-field gel electrophoresis (PFGE). The restriction enzymes SmaI, SacII,SalI and XhoI were found to generate a reasonable number of DNA fragments which could be separated by PFGE in agarose gels. The apparent chromosomal lengths of the F. nucleatum strains were determined to be approximately 2.4 million base pairs. This was within the size-range found by experiments exploiting renaturation kinetics.

Polymerase chain reaction-amplified nonradioactive probes for identification of Fusobacterium nucleatum

A polymerase chain reaction probe with 100% sequence identity to 120 deoxyribonucleotides of Fusobacterium nucleatum Fev1, coding for a part of the 40-kDa major outer membrane protein, was labeled with the steroid hapten digoxigenin. The probe was compared with various degenerate oligonucleotide probes and found to tolerate much more stringent washing conditions. It was therefore superior in distinguishing, by means of Southern blots and slot blots, F. nucleatum from other oral gram-negative bacteria in the periodontal pocket and from other fusobacterial species and in distinguishing among different strains of F. nucleatum. F. periodonticum was found to be more similar to F. nucleatum than the other fusobacterial species tested.

Cellular fatty acids in Fusobacterium species as a tool for identification

Identification of fusobacteria from clinical specimens currently requires analysis of metabolic end products by gas-liquid chromatography in addition to certain biochemical and enzymatic tests because of the relative biochemical inactivity of these bacteria. Even the finding of pointed, thin gram-negative cells on Gram-stained slides can no longer be relied on for identification of Fusobacterium nucleatum, since at least four other species of fusobacteria have been seen to exhibit similar morphology. We examined 46 clinical isolates and six American Type Culture Collection type strains of fusobacteria by conventional methods and by the Microbial ID Systems MIDI software package for analyzing cellular fatty acid patterns measured by capillary column gas-liquid chromatography. Distinctive patterns of major fatty acids could be used to reliably identify most clinical isolates to the species level. The MIDI system identified 89% of the isolates correctly and provides an alternative to conventional methods.

Characterization of shared antigens of Fusobacterium nucleatum and Fusobacterium necrophorum

Fusobacterium nucleatum and Fusobacterium necrophorum are gram-negative, non-spore-forming anaerobic rods, frequently isolated from the normal flora and diseased lesions of the human oral cavity, gastrointestinal and genitourinary tracts. F. necrophorum is also known to be an animal pathogen. Studies were undertaken with rabbit anti-F. nucleatum sera and with human adult periodontitis (AP) sera that demonstrated the sharing of antigens between the two species. Immunodiffusion and immunoelectrophoresis studies of Fusobacterium species with rabbit anti-F. nucleatum sera demonstrated the presence of shared antigen(s) between F. nucleatum and F. necrophorum. Adsorption studies of AP sera in an enzyme-linked immunosorbent assay demonstrated the presence of antibodies reacting with the shared antigens of the two species. Immunoblot (IB) analysis of a soluble protein preparation of the two species of Fusobacterium, when allowed to react with rabbit anti-F. nucleatum 10197 serum, demonstrated 53 kDa and 30 kDa bands present in members of the two species. Further, IB analysis of protein preparations of the two species with AP sera indicated the presence of antibodies reacting with the shared 53 kDa band and in some cases the 30 kDa band. During serological testing with antisera or host immune studies with human sera to these species, the presence of shared antigens must be considered.

DNA base composition, aerotolerance and enzyme patterns of Leptotrichia buccalis

The guanine plus cytosine content of the DNA of Leptotrichia buccalis varied from 28.4 to 29.5 mol% (three strains). Eleven strains examined grew well under anaerobic and microaerobic conditions, but slowly in air in the presence of CO2. When examined for preformed enzymes in the APIZYM Complete Research Kit, positive reactions were obtained for several glucosidases and carboxylic ester hydrolases, and for a few peptidases.

Production of volatile sulfur compounds by various Fusobacterium species

In 12 species of Fusobacterium the following characteristics were studied; the desulfhydration of L-cysteine and L-methionine by resting cell suspensions, the formation of alpha-keto-acids from L-cysteine, D-cysteine and L-methionine by cell extracts, and the formation of hydrogen sulfide from L-cysteine, D-cysteine and L-cysteine by cell extracts separated by polyacrylamide gel electrophoresis. Multiple forms of L-cysteine desulfhydrase activity were found in most of the species. In some of them also D-cysteine desulfhydrase activity was demonstrated. Seven of the species had high L-methionine gamma-lyase activity. L-cysteine activity was present in 5 of the species.

DNA homologies shared among E. corrodens isolates and other corroding bacilli from the oral cavity

In a previous microbiological study of Eikenella corrodens, we noted the presence of E. corrodens strains with variability in colony morphology, as well as other corroding bacilli phenotypically similar to E. corrodens but which were unidentifiable on the basis of biochemical reactions. This raised questions as to whether E. corrodens constitutes a genetically heterogeneous group of organisms, and whether the unidentified corroding bacilli represent atypical E. corrodens or genetically unrelated organisms. In the present study, the genetic relationship among 14 E. corrodens isolates and 6 unidentified corroding bacilli was examined. DNA base compositions were determined from the melting temperatures of DNA samples. DNA homologies among E. corrodens and corroding bacilli were determined by DNA hybridization in solution using S1 nuclease. The % G + C content of E. corrodens strains varied from 56 to 58%, and from 56 to 60% for unidentified corroding bacilli. The DNA homologies among 12 E. corrodens isolates and 2 reference strains varied from 57 to 97%. Although these E. corrodens isolates exhibited variabilities in colony morphology and biochemical profile, no subspecies was identified. The unidentified corroding bacilli shared less than 33% homology with either of the E. corrodens reference strains. These corroding bacilli were further divided into 3 species on the basis of DNA hybridization studies using radiolabeled DNA from 2 representative corroding bacilli. One of the unidentified corroding bacilli appears to be a component of the normal flora in the human oral cavity. Our results indicate that E. corrodens is a genetically homogeneous species containing no recognizable subspecies.(ABSTRACT TRUNCATED AT 250 WORDS)

Coaggregation of Fusobacterium nucleatum, Selenomonas flueggei, Selenomonas infelix, Selenomonas noxia, and Selenomonas sputigena with strains from 11 genera of oral bacteria

Twenty-eight strains of Fusobacterium nucleatum and 41 Selenomonas strains, including S. sputigena (24 strains), S. flueggei (10 strains), S. infelix (5 strains), and S. noxia (2 strains), were tested for their ability to coaggregate with each other and with 49 other strains of oral bacteria representing Actinobacillus, Actinomyces, Bacteroides, Capnocytophaga, Gemella, Peptostreptococcus, Porphyromonas, Propionibacterium, Rothia, Streptococcus, and Veillonella species. Selenomonads coaggregated with fusobacteria and with Actinomyces naeslundii PK984 but not with any of the other bacteria, including other selenomonads. In contrast, fusobacteria coaggregated with members of all genera, although not with all strains of each species tested. Each fusobacterium strain appeared to have its own set of partners and coaggregation properties, unlike their partners, whose coaggregation properties in earlier surveys delineated distinct coaggregation groups. Coaggregations of fusobacteria with the 63 gram-negative strains were usually inhibited by EDTA, whereas those with the 27 gram-positive strains were usually not inhibited. Likewise, lactose-inhibitable coaggregations were common among some strains of fusobacteria and some strains from each of the genera containing gram-negative partners but were rarely observed with gram-positive partners. Heating the fusobacteria at 85 degrees C for 30 min completely prevented coaggregation with most partners, suggesting the involvement of a protein on the fusobacteria. Heat treatment of many of the gram-negative partners not only enhanced their coaggregation with the fusobacteria but also changed lactose-sensitive coaggregations to lactose-insensitive coaggregations. Although fusobacteria coaggregated with a broader variety of oral partner strains than any other group of oral bacteria tested to date, each fusobacterium exhibited coaggregation with only a certain set of partner strains, and none of the fusobacteria adhered to other strains of fusobacteria, indicating that recognition of partner cell surfaces is selective. The strains of F. nucleatum are heterogeneous and cannot be clustered into distinct coaggregation groups. Collectively, these results indicate that coaggregation between fusobacteria and many gram-negative partners is significantly different from their coaggregation with gram-positive partners. The contrasting variety of partners for fusobacteria and selenomonads supports the concept of coaggregation partner specificity that has been observed with every genus of oral bacteria so far examined.

"Reverse" DNA hybridization method for the rapid identification of subgingival microorganisms

A "reverse" hybridization method is described, in which whole chromosomal DNA was extracted from 10-20 colonies of "unknown" strains in pure culture and labelled with digoxigenin by a random primer technique. DNA probes were prepared from a total of 23 strains and hybridized with targets containing 100 ng purified, denatured DNA from 38 reference strains fixed to nitrocellulose. 21/23 digoxigenin-labelled DNA probes successfully detected all members of the homologous species present on filters. Probes to Fusobacterium nucleatum strains 364 and MG detected 3/4 and 1/4 members of this species, respectively; 13/23 probes were 100% specific, but cross reactions between 10 probes and DNA targets from closely related, heterologous species occurred in 15/834 possible instances. False-positive reactions that occurred between closely related species were, however, easily distinguished and did not prevent the accurate identification of probe strains. Digoxigenin-labelled probes were capable of detecting 100 pg of homologous DNA. The reverse hybridization procedure allows identification or grouping of a large number of isolates within 3 days and provides a more economical means of characterizing subgingival isolates than predominant cultivable techniques and conventional phenotypic testing. This method could be adapted for the direct identification of microorganisms in subgingival plaque samples.

The predominant cultivable microbiota of active and inactive lesions of destructive periodontal diseases

Subgingival plaque samples were taken from active and inactive lesions in 33 subjects exhibiting active destructive periodontal diseases. Active diseased sites were those which showed a significant loss of attachment within a 2-month interval as computed by the "tolerance method". The predominant cultivable species from 100 active sites were compared with those found in 150 inactive sites of comparable pocket depth and attachment level loss. Among the 33 subjects, W. recta, B. intermedius, F. nucleatum, B. gingivalis and B. forsythus were elevated more often in active sites; whereas, S. mitis, C. ochracea, S. sanguis II, V. parvula and an unnamed Actinomyces sp. were elevated in inactive sites. The likelihood of a site being active was increased if B. forsythus, B. gingivalis, P. micros, A. actinomycetemcomitans, W. recta, or B. intermedius were detected in that site, and decreased if S. sanguis II, the Actinomyces sp., or C. ochracea were detected.

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.

Relationships among isolates of oral haemophili as determined by DNA-DNA hybridization

In order to assess the relationships among strains of the genera Actinobacillus and Haemophilus, DNAs from 50 strains of these genera were isolated and purified. The guanine plus cytosine (G + C) content of DNAs from strains of Haemophilus segnis and Haemophilus parainfluenzae were determined by thermal denaturation. DNA-DNA homologies were measured using labelled probes from one strain representing Haemophilus segnis (strain ATCC 10977), and two strains representing Haemophilus parainfluenzae (strains ATCC 9796 and ATCC 7901). Strains isolated as H. segnis had a G + C content of 39.0 to 42.9% and were 49-92% homologous with the ATCC 10977 DNA probe. All of the strains freshly isolated as H. parainfluenzae were 70-81% homologous with the ATCC 9796 DNA probe and had a G + C content of 34.9 to 38.3%. Strain ATCC 7901 was 11% homologous with the ATCC 9796 DNA probe, had a G + C content of 42.4%, and was 65-78% homologous to DNA from strains identified as Haemophilus aphrophilus and Haemophilus paraphrophilus. From these results we conclude that strain ATCC 7901 is a mislabelled strain of H. paraphrophilus. The results of multiple DNA-DNA hybridizations indicated that separate species designations were appropriate for H. segnis, H. parainfluenzae, Actinobacillus actinomycetemcomitans ("Haemophilus actinomycetemcomitans"), and H. aphrophilus. H. aphrophilus and H. paraphrophilus were closely related organisms and did not fulfill the generally accepted criteria for designation as separate species.

Biologic activity of type I and type II Fusobacterium nucleatum isolates from clinically characterized sites

Fusobacterium nucleatum is a microorganism commonly cultured from periodontal disease sites. F. nucleatum isolates (120) were obtained from subgingival plaque samples taken from 27 clinically characterized sites using a selective culture medium. All isolates were verified by morphology, Gram-stain reactions, oxygen tolerance and biochemical reactions. A total of eight clinical isolates and two typed strains were used for further evaluation. In this study, there was no relationship found between GI and probing depth or between probing depth and frequency of isolation of Type I or Type II F. nucleatum colonies. There was a significant increase in isolation of Type II colonies with a GI of 2 (P less than 0.0001). All isolates tested shared lines of identity by double diffusion in agar and displayed similar ability to hemagglutinate sheep erythrocytes and a reduction in this hemagglutination activity by previous exposure to 50 mM D-galactose. All isolates tested showed similar protein patterns as determined by polyacrylamide gel electrophoresis. By the methods used, no differences were detected between Type I and Type II F. nucleatum; however, there was a statistically significant increase in Type II isolates with increasing levels of gingivitis.