Identification of Fusobacterium species by the electrophoretic migration of glutamate dehydrogenase and 2-oxoglutarate reductase in relation to their DNA base composition and peptidoglycan dibasic amino acids

Rapid identification of Fusobacterium spp. is hampered by their inability to ferment carbohydrates and the availability of relatively few useful phenotypic characters. In an attempt to identify new diagnostic markers for species, we reported recently the potential utility of glutamate dehydrogenase (GDH) electrophoretic mobilities for distinguishing eight species of Fusobacterium. We have extended these observations to include all recognised members of the genus except F. prausnitzii and F. perfoetens, and our results show that they cluster into three broad electrophoretic groups. Some species, such as F. periodonticum, F. simiae and F. necrophorum, possessed GDH with similar electrophoretic mobilities. However, within such clusters, the electrophoretic migration of 2-oxoglutarate reductase (OGR) distinguished between species. Neither GDH or OGR mobility alone clearly differentiated all species, but their combined use provided unambiguous discrimination of all species except F. varium and F. mortiferum. The DNA base compositions of all species except F. naviforme (ATCC 25832) and F. sulci, were within the range 26-34 mol% G + C, suggesting the genus may be homogeneous. However, the peptidoglycan composition divided the genus into two major groups that contained either lanthionine or diaminopimelic acid; F. mortiferum peptidoglycan contained both dibasic amino acids.

Amino acid utilization by Fusobacterium nucleatum grown in a chemically defined medium

The present investigation evaluated amino acid utilization by 120 strains of Fusobacterium nucleatum in a chemically defined medium and attempted to relate the patterns to 3 proposed subspecies of F. nucleatum. Strains were inoculated into a chemically defined medium, with and without 2 g/l glucose, consisting of 14 inorganic salts, 21 amino acids, 23 vitamins and cofactors, and 7 purines and pyrimidines. After 7 days of anaerobic incubation, the spent culture medium, as well as the uninoculated control medium, were analyzed for amino acid content by ion chromatography. Amino acid utilization was determined by the differences in concentrations of amino acids found in inoculated and uninoculated samples. If greater than 34% of the amino acid was removed from the medium, the amino acid was considered to be utilized. Of the 21 amino acids present in the chemically defined medium, 8 amino acids, lysine, glutamine, asparagine, histidine, threonine, serine, glutamate and cysteine were consistently utilized. Four amino acids, tyrosine, tryptophan, methionine and aspartate were utilized by some strains but not others. Nine amino acids, alanine, leucine, isoleucine, glycine, valine, phenylalanine, proline, ornithine, and arginine were not utilized by any of the strains. The utilization patterns did not relate to subspecies formed on the basis of SDS-PAGE and DNA hybridization.

The problem of the taxonomy of the fusiform bacillus of acute necrotizing ulcerative gingivitis (Vincent's gingivitis)

The characteristic microscopic appearance of the fusospirochaetal complex in smears from patients with acute necrotizing ulcerative gingivitis has long been regarded as virtually pathognomonic of the disease. Unfortunately there is considerable confusion surrounding the taxonomy of the fusiform organism in the fusospirochaetal complex. The conflicting views appear to be irreconcilable and a re-evaluation of the taxonomy of oral fusiforms is urgently required.

Proposal of three subspecies of Fusobacterium nucleatum Knorr 1922: Fusobacterium nucleatum subsp. nucleatum subsp. nov., comb. nov.; Fusobacterium nucleatum subsp. polymorphum subsp. nov., nom. rev., comb. nov.; and Fusobacterium nucleatum subsp. vincentii subsp. nov., nom. rev., comb. nov

Heterogeneity among isolates of Fusobacterium nucleatum has been recognized for many years. The phenotypic properties of 340 strains considered to be F. nucleatum were examined. While these strains were phenotypically similar and fit the description of F. nucleatum, they could be differentiated into three groups on the basis of electrophoretic patterns of whole-cell proteins and DNA homology. Strains in groups I and II showed greater than 80% DNA homology within groups and less than 75% similarity between groups. Strains of group III demonstrated greater than 85% DNA homology to each other and less than 65% similarity to strains in groups I and II. We propose that Fusobacterium nucleatum be divided into the following three subspecies: Fusobacterium nucleatum subsp. nucleatum, with type strain ATCC 25586; Fusobacterium nucleatum subsp. polymorphum, with type strain ATCC 10953; and Fusobacterium nucleatum subsp. vincentii, with type strain ATCC 49256.

Preliminary study of the anaerobic bacteria isolated from subgingival plaque from sheep

A preliminary study was made to determine the genera of cultivable anaerobic bacteria which could be isolated from subgingival plaque of sheep. Samples were taken from 10 sheep on farms with a known record of broken mouth periodontitis. For assessment of the sampling technique, samples were also taken from freshly exposed tooth roots in killed sheep. The bacteria isolated on several selective and non-selective media were identified to genus level by a combination of Gram reaction, colony morphology and gas chromatographic analysis of volatile and non-volatile fatty acid metabolic end products. At least 10 different genera were isolated and these findings are discussed in relation to the bacteriology of human periodontitis and recent studies of sheep broken mouth periodontitis.

Accuracy and reproducibility of the 4-hour ATB 32A method for anaerobe identification

The ATB 32A system (API System SA, La Balme les Grottes, Montalieu-Vercieu, France) was evaluated for use in the identification of 214 anaerobes. Organisms included 73 isolates of the Bacteroides fragilis group, 24 Bacteroides spp., 10 fusobacteria, 43 clostridia, 28 cocci, and 36 gram-positive, nonsporeforming rods. With the concomitant use of Gram stain, pigmentation, catalase testing, and aerobic growth, the ATB 32A system correctly identified 97% of the B. fragilis group isolates, 88% of Bacteroides spp., 50% of fusobacteria, 74% of clostridia, 100% of cocci, and 86% of the gram-positive, nonsporeforming rods. Overall, 188 strains (88%) were correctly identified, with 18 (8%) requiring extra tests, other than the four mentioned above, for correct identification. Eight strains were misidentified, including one Bacteroides sp., three fusobacteria, one Clostridium sp., and three gram-positive, nonsporeforming rods. Reproducibility was very good, with 12 of 14 strains (86%) tested in triplicate yielding identical correct results on each of three occasions and 2 strains (14%) yielding identical correct results on two occasions. There was a low-probability identification (including the correct species) on the third testing. The ATB 32A system represents a worthwhile advance in systems used for the identification of clinically significant anaerobic bacteria.

Recognition of Fusobacterium nucleatum subgroups Fn-1, Fn-2 and Fn-3 by ribosomal RNA gene restriction patterns

DNA from representative strains of Fusobacterium nucleatum subgroups Fn-1, Fn-2 and Fn-3 was digested with restriction enzymes EcoRI and TaqI and the electrophoretically separated fragments hybridized with a 32P-16S rRNA gene probe from E. coli. The rRNA gene restriction patterns from DNA digested with either enzyme allowed the clustering of strains into the three subgroups. However, TaqI digested DNA yielded a wider distribution of taxonomically useful bands (ca 0.65 +/- 14.3 kbp) and the pattern produced was characteristic of each subgroup. The present method is a simple and reliable means of identifying the three subgroups of F. nucleatum and provides a useful method for further studies of the heterogeneity of F. nucleatum.

A pyrolysis mass spectrometry study of fusobacteria

Strains of fusobacteria (143) were examined by pyrolysis mass spectrometry (Py-MS) with a Horizon Instruments PYMS 200X. Fusobacterium necrogenes, F. necrophorum, F. nucleatum, F. mortiferum, F. varium, F. gonidiaformans, F. naviforme, F. russii and Leptotrichia buccalis were discriminated. Strains of fusobacteria isolated from tropical ulcers, although similar to F. mortiferum in conventional tests, were discriminated from each of these species in Py-MS. Identification of 416 spectra to species level agreed with conventional bacteriological methods in 91.8% of cases, was equivocal in 3.4% and disagreed in 4.8%. Classification based on pyrolysis data resolved groups largely corresponding to the recognised species. However, F. nucleatum strains were divided between two distinct groups. The tropical ulcer strains were resolved as a distinct homogeneous group. Py-MS is a rapid, inexpensive and convenient procedure for characterisation of bacteria, with the capacity for a high throughput of samples, although the initial cost of the apparatus is high.

Utilization of amino acids and peptides by Fusobacterium nucleatum

Fusobacterium nucleatum strains ATCC 10953, Fevl, F1, F3, and F6 utilized amino acids, in particular glutamate, histidine, and aspartate were common to all strains. Strain differences were observed in the utilization of threonine, serine, lysine, tyrosine, and methionine, and only strain ATCC 10953 utilized all these amino acids. The glutamate and histidine pools were in all cases fully depleted before the other amino acids were attacked and at the same time all strains except 10953 started to utilize peptides at a noticeable rate. For strain Fevl, glutamyl- and aspartyl-containing peptides seemed to be of considerable nutritional importance, and this strain did not grow on a medium based on amino acids alone. On the other hand, strain 10953 did not utilize any peptides to a noticeable extent, and it could grow on an amino acid based medium.

5S ribosomal ribonucleic acid sequences in Bacteroides and Fusobacterium: evolutionary relationships within these genera and among eubacteria in general

The 5S ribosomal ribonucleic acid (rRNA) sequences were determined for Bacteroides fragilis, Bacteroides thetaiotaomicron, Bacteroides capillosus, Bacteroides veroralis, Porphyromonas gingivalis, Anaerorhabdus furcosus, Fusobacterium nucleatum, Fusobacterium mortiferum, and Fusobacterium varium. A dendrogram constructed by a clustering algorithm from these sequences, which were aligned with all other hitherto known eubacterial 5S rRNA sequences, showed differences as well as similarities with respect to results derived from 16S rRNA analyses. In the 5S rRNA dendrogram, Bacteroides clustered together with Cytophaga and Fusobacterium, as in 16S rRNA analyses. Intraphylum relationships deduced from 5S rRNAs suggested that Bacteroides is specifically related to Cytophaga rather than to Fusobacterium, as was suggested by 16S rRNA analyses. Previous taxonomic considerations concerning the genus Bacteroides, based on biochemical and physiological data, were confirmed by the 5S rRNA sequence analysis.

Classification and distribution of large intestinal bacteria in nonhibernating and hibernating leopard frogs (Rana pipiens)

The large intestinal flora of the leopard frog, Rana pipiens, was examined to determine whether differences existed between the nonhibernating and hibernating states of the animal and to determine the relative concentrations and proportions of potential frog pathogens. Hibernators had a logarithmic decrease of bacteria per milligram of intestine averaging one, and significantly greater proportions of facultative bacteria and psychrophiles relative to nonhibernators. The predominant anaerobic bacteria were gram-positive Clostridium species and gram-negative Bacteroides and Fusobacterium species. The predominant facultative bacteria were enterobacteria in nonhibernators but Pseudomonas species in hibernators. Many species of Pseudomonas are pathogenic for frogs, and thus the intestinal flora in hibernators may be a potential source of infectious disease.

Characteristics of glutamate dehydrogenase, a new diagnostic marker for the genus Fusobacterium

Enzymes representative of carbohydrate and nitrogen metabolism were screened for their presence and activity amongst species of the genus Fusobacterium. Glutamate dehydrogenase (GDH) was reliably detected in all 25 strains studied. The pH profile of this enzyme and the DNA base composition of selected strains were also determined. DNA base composition of selected strains ranged between 28-32.9 mol% G + C. GDH was active between pH 7.5-11.5 but two pH profiles of activity, with optima at 9.5 and 10.5, were discernible among species. Apart from Fusobacterium nucleatum, which had a heterogeneous enzyme pattern, the GDH electrophoretic mobility was constant within a species but in a few cases the enzyme bands overlapped. A combination of the pH profile, the GDH electrophoretic pattern and the DNA base composition provided clear separation of the test organisms into discrete groups; however, a larger number of strains must be examined before the full potential of these tests can be evaluated.

The identification of Bacteroides ureolyticus from patients with non-gonococcal urethritis by conventional biochemical tests and by DNA and protein analyses

Twenty-seven strains of gram-negative anaerobic bacteria isolated from patients with non-gonococcal urethritis (NGU-associated strains) were compared with reference strains of Bacteroides ureolyticus and representatives of other species of Bacteroides and Fusobacterium. Conventional biochemical tests, electrophoretic (PAGE) protein profiles and DNA base compositions of 29.5 +/- 1.2 mol% G + C indicated striking similarities between the NGU-associated strains and B. ureolyticus. Three of the reference strains previously assigned to that species were atypical in some respects as was one of the strains from urethritis and one strain, NCTC 10939, was incorrectly classified as B. ureolyticus. Casein hydrolysis by B. ureolyticus was the principal test difference between the two sets of strains. DNA-DNA hybridisation results of greater than or equal to 72% at optimum temperature conditions provided further evidence of the close relationship between B. ureolyticus and the NGU-associated strains and we conclude that these organisms should be identified as B. ureolyticus. There was insufficient evidence for recognising subspecies or biotypes within this revised concept of B. ureolyticus although several types (PAGE-type I, 17 strains; type II, 6 strains; type III, 3 strains) were detected which might provide the basis for future studies of hospital strains. The DNA base composition and hybridisation data indicated that B. ureolyticus was not related to other species of Bacteroides or Fusobacterium.

API ZYM and API An-Ident reactions of fastidious oral gram-negative species

API ZYM and API An-Ident enzymatic substrate tests were done on six oral species which are difficult to characterize with conventional biochemical tests. "Bacteroides forsythus, the "fusiform" Bacteroides species (A. C. R. Tanner, M. A. Listgarten, M. N. Strzempko, and J. L. Ebersole, manuscript in preparation), is difficult to cultivate in broth media, yet it gave 15 positive tests in these series. The tests were able to separate this new species from species of Capnocytophaga and Fusobacterium. "B. forsythus" reactions were similar but not identical to those of reference Bacteroides species. Positive reactions for alpha-glucosidase, beta-glucosidase, alpha-fucosidase, and alpha-glucuronidase suggest that "B. forsythus" may be saccharolytic. It was the only species tested which was trypsin positive. Wolinella species, Campylobacter concisus, B. gracilis, and Eikenella corrodens are asaccharolytic, and characterization relies heavily on sensitivities to inhibitory agents. These species reacted weakly in the API ZYM and API An-Ident enzymatic substrate tests, and the reactions were not useful for separating these species. The enzyme reactions differentiated Wolinella recta and C. concisus from Selenomonas sputigena, another oral motile but saccharolytic organism.

Lack of constitutive beta-glucosidase (esculinase) in the genus Fusobacterium

Esculin has been incorporated into both a medium and test with 20% bile for many years to differentiate Bacteroides from Fusobacterium organisms. After 24 to 48 h, all members of the Bacteroides fragilis group grow in 20% bile and hydrolyze esculin. Fusobacterium mortiferum can both grow in bile and hydrolyze esculin, thus limiting the use of the bile-esculin medium and test. The hypothesis that constitutive esculinase (beta-glucosidase) could differentiate Bacteroides from Fusobacterium organisms was investigated. Clinical isolates and American Type Culture Collection clones of the B. fragilis group and other species of Bacteroides and Fusobacterium were tested. All B. fragilis were positive within 30 min. In no case was a Fusobacterium organism positive for constitutive enzyme in a hydrolyzable substrate-based test. The percentage of positive results for other species of Bacteroides agreed with those published in the literature for the esculin test. The genus Fusobacterium can be separated from Bacteroides organisms based on a lack of constitutive beta-glucosidase in the former in a 30-min one-tube test.

Identification of fusobacteria in a routine diagnostic laboratory

A scheme for differentiating Fusobacterium spp. and Leptotrichia spp. from Bacteroides spp. was devised after examining 114 strains of fusobacteria and asaccharolytic bacteroides (17 reference strains and 97 clinical isolates). Sensitivity to a 300 micrograms/ml plate of phosphomycin and an acid reaction on a lysine plate were found to be reliable for differentiating Fusobacterium spp. and L. buccalis from Bacteroides. Using a short set of simple cultural and biochemical tests, isolates could be identified as F. necrophorum, F. necrogenes, F. nucleatum, F. varium or L. buccalis. These tests were: indole, lecithinase, phosphatase, DNase and gas production, aesculin and casein hydrolysis, greening of casein/methylene blue agar, nitrite reduction, bile tolerance and haemolysis on horse blood agar.

Comparative evaluation of three identification systems for anaerobes

The accuracy of two new 4-h identification systems for anaerobes, the AN-IDENT (Analytab Products, Plainview, N.Y.) and the RapID ANA (Innovative Diagnostic Systems, Inc., Atlanta, Ga.) was compared with that of the API 20A system (Analytab Products). A total of 132 clinical isolates were tested in each of the three systems. The overall accuracies at the genus and species level for the three systems were: API 20A, 68.9 and 56.8%, respectively; AN-IDENT, 90.2 and 73.5%; and RapID ANA, 93.9 and 81.8%. Improved identification of anaerobes with the AN-IDENT and the RapID ANA systems was observed for isolates of the genus Fusobacterium, Clostridium species other than Clostridium perfringens, non-spore-forming bacilli, and isolates of the genus Peptostreptococcus. Reproducibility studies demonstrated that the results of the individual test reactions in all three identification systems were reproducible when the interpretive guidelines of the manufacturer were followed precisely.

[Identification of Bacteroides and Fusobacterium using antibiotic- and bile-impregnated disks]

Fifty-nine strains of gram-negative non-sporulating anerobic bacteria were identified to the genus. Comparison of the data on the biochemical identification with the phenotypes by sensitivity to antibiotics and bile showed, that the bacteroids of the fragilis group had the same phenotype. Sensitivity was determined with anaerodisks impregnated with antibiotics and bile. The other species of bacteroids and fusobacteria had several phenotypes. However, these phenotypes being non-specific for the species were characteristic of the genus: none of the bacteroid species had the fusobacteria phenotype. The presented table of the bacteroid and fusobacteria phenotypes by sensitivity to antibiotics and bile may be useful in identification of these organism.

Comparison of the PRAS II, AN-Ident, and RapID-ANA systems for identification of anaerobic bacteria

Two rapid systems for the identification of anaerobes were compared to a conventional growth system aided by a computer. The rapid systems (AN-Ident and RapID-ANA) are non-growth-dependent micromethods that identify anaerobes in 4 h by the action of various constitutive enzymes on chromogenic substrates. The organisms tested were 98 anaerobes, most of which were clinical isolates. The AN-Ident system identified 76 of these to species level and 86 to genus level; the RapID-ANA system correctly identified 74 of the organisms to species level and identified 93 to genus level. The PRAS II system correctly identified 77 to species level and 96 to genus level. In most instances, adequate identification could be obtained with either of the two rapid systems, but the conventional PRAS II system remains the most accurate.

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.

Comparison of PRAS II, RapID ANA, and API 20A systems for identification of anaerobic bacteria

This study evaluated the PRAS II, RapID ANA, and API 20A systems for the identification of anaerobic bacteria. A total of 80 isolates (68 fresh clinical isolates and 12 stock cultures) were examined and included 25 Bacteriodes spp., 7 Fusobacterium spp., 12 Clostridium spp., 2 Veillonella spp., 16 gram-positive cocci, and 18 gram-positive nonsporeforming bacilli. All isolates were initially identified by the procedures outlined in Holdeman et al. (ed.), Anaerobe Laboratory Manual, Virginia Polytechnic Institute and State University, Blacksburg, Va., 1977; identifications from the PRAS II, RapID ANA, and API 20A systems were compared with these initial identifications. If no supplemental tests were required, the RapID ANA and API 20A systems had incubation times of 4 and 24 h, respectively; the PRAS II system generally required 2 to 5 days of incubation, depending on the growth rate of the isolate. PRAS II identified 74% correct to species level, 14% correct to genus only, and 6% incorrect; 6% could not be identified. PRAS II data were reevaluated according to a revised data base that was provided after completion of the study; PRAS II (revised) identified 82% correct to species, 12% correct to genus only, and 6% incorrect. RapID ANA identified 62% correct to the species level, 28% correct to genus only, and 10% incorrect. API 20A identified 71% correct to the species level, 10% correct to genus only, and 3% incorrect; 16% could not identified. The API 20A is a more established system for identification of anaerobic bacteria; PRAS II and RapID ANA appear to be promising new methods for the identification of anaerobic bacteria.