Deoxyribonucleic Acid Homology Groups Research Articles

Fatty Acids, Antibiotic Resistance, and Deoxyribonucleic Acid Homology Groups of Bradyrhizobium japonicum

The fatty acid compositions and multiple antibiotic resistance patterns of 32 strains of Bradyrhizobium japonicum correlated with two major deoxyribonucleic acid homology groups. In group I, the fatty acid composition was 1.3% 16:1 cis9 acid, 3.6% 16:1C acid, 8.8% 16:0 acid, 1.2% 19:0 cyclopropane acid, and 81.2% 18:1 acid. Group II contained 0.5% 16:1C acid, 11.1% 16:0 acid, 0.8% 17:0 cyclopropane acid, 24.7% 19:0 cyclopropane acid, and 62.3% 18:1 acid. Group I strains were susceptible to rifampin (500 μg/ml), tetracycline (100 μg/ml), streptomycin (100 μ/ml), chloramphenicol (500 μg/ml), erythromycin (250 μg/ml), carbenicillin (500 μg/ml), and nalidixic acid (50 μg/ml), whereas group II strains were resistant to these antibiotics. Both groups were resistant to trimethoprim (50 μg/ml) and vancomycin (100 μg/ml).

Deoxyribonucleic Acid Base Sequence Relatedness among Members of the Yeast Genus Kluyveromyces

Deoxyribonucleic acid (DNA) base composition and DNA base sequence relatedness comparisons were used for species delineation in the genus Kluyveromyces. Base composition values separated the members of the genus into three groups. The groups were further subdivided by comparing base sequences by using DNA/DNA renaturation experiments. Two DNA homology groups were identified. The first group included Kluyveromyces marxianus, Kluyveromyces fragilis, Kluyveromyces bulgaricus, Kluyveromyces cicerisporus, Kluyveromyces wikenii, and three anamorphs (Candida kefyr, Candida pseudotropicalis, and Torula cremoris); the members of this group exhibited ≥90% DNA base sequence complementarity. The second group consisted of Kluyveromyces lactis, Kluyveromyces vanudenii, Kluyveromyces drosophilarum, and Kluyveromyces phaseolosporus; various pairs of these yeasts shared 64 to 98% of their DNA sequences. The two groups were only distantly related to each other (≤15% DNA base sequence complementarity). The other Kluyveromyces species appear to be unique, not being closely related to either of the two homology groups or to one another. Relationships deduced from comparisons of DNAs agreed well with those deduced by other workers from immunological comparisons of exo-β-glucanases and from isoenzyme analysis but were only in partial agreement with a taxonomic arrangement made on the basis of mating studies. We propose recognition of the following species: Kluyveromyces aestuarii, Kluyveromyces africanus, Kluyveromyces blattae, Kluyveromyces delphensis, Kluyveromyces dobzhanskii, K. lactis (syn. K. drosophilarum, K. phaseolosporus, and K. vanudenii), Kluyveromyces lodderi, K. marxianus (syn. K. bulgaricus, K. cicerisporus, K. fragilis, and K. wikenii), Kluyveromyces phaffii, Kluyveromyces polysporus, Kluyveromyces thermotolerans, Kluyveromyces waltii, and Kluyveromyces wickerhamii.

DNA Homologies between Rhizobium fredii, Rhizobia That Nodulate Galega sp., and Other Rhizobium and Bradyrhizobium Species

The relationships between Rhizobium fredii and the rhizobia that nodulate Galega officinalis and Galega orientalis (goat’s rue) and recognized species of Rhizobium and Bradyrhizobium were investigated by using deoxyribonucleic acid (DNA)-DNA hybridization, legume nodulation tests, and phage typing. The R. fredii strains formed a distinct DNA homology group which could be divided into two subgroups. The mean levels of relative homology at 65°C of 11 strains of R. fredii with R. fredii reference strains USDA 208 and USDA 191 were 86 and 80%, respectively. These values were significantly higher (Student’s t test, P < 0.001) than the mean levels of relative homology with DNAs from other groups of rhizobia. The Galega-nodulating rhizobia also formed a distinct DNA homology group. The mean levels of relative homology at 65°C of DNAs from 11 strains with DNAs from reference strains gall and galNW3, which effectively nodulate G. officinalis, were 79 and 85%, respectively. These values were also significantly higher (Student’s t test, P < 0.001) than the values obtained with DNAs from other groups of rhizobia. These results correlated with cross-inoculation and phage-typing results and indicated that the two groups are genetically distinct. Genomic DNA was used as a probe in a modified colony hybridization autoradiographic procedure for the identification of DNAs from Rhizobium leguminosarum, R. fredii, and Rhizobium sp. (Galega) in colonies and from nodules.

Differentiation between T-Catalases Derived from Mycobacterium avium and Mycobacterium intracellular by a Solid-Phase Immunosorbent Assay

Antibody to the T-catalase derived from a culture of Mycobacterium avium serovar 8 was purified by immunoaffinity absorption and elution and tested in a solid-phase immunosorbent assay against T-catalases from 31 strains in the M. avium complex. The immunologic distances from the homologous antigen exhibited a bimodal distribution. Strains of serovars 1 through 6 and 8, which correspond to the M. avium deoxyribonucleic acid (DNA) homology group of Baess, yielded immunologic distance scores against the reference serovar 8 preparation ranging from 2 to 16 U. Strains of serovars 7, 12, 14, 16, 18, and 19, which correspond to the Mycobacterium intracellulare DNA homology group, yielded immunologic distance scores ranging from 20 to 30 U. Among serovars for which DNA homology data were not available, strains of serovar 10 fell into the M. avium catalase serogroup, and serovars 13, 15, 17, 20, 23, and 25 fell into the M. intracellulare group. The status of serovar 9 was ambiguous. When the reference antibody was cross-absorbed with T-catalase from a serovar 14 strain, many of the antibodies to common epitopes were removed; the remaining antibodies reacted strongly with catalases from all strains belonging to serovars of the M. avium DNA homology group, but only minimally with catalases from strains of serovars in the M. intracellulare DNA homology group. Our results provide support for continued recognition of M. avium and M. intracellulare as separate species and for reassignment of some serovars from M. intracellulare to M. avium.

Physiological Characteristics and Deoxyribonucleic Acid Relatedness of Human Isolates of Streptococcus bovis and Streptococcus bovis (var.)

The current classification of Streptococcus bovis is problematic. Many bovine strains, including the type strain, are not typical of S. bovis strains derived from humans, especially in physiologic characteristics. Further, a number of strains physiologically resembling some S. intermedius (MG) strains carry the group D antigen and have been classified as S. bovis (var.) strains. In this work, we compared the physiologic characteristics and deoxyribonucleic acid relatedness of human strains of S. bovis and S. bovis (var.), the bovine type strain, and selected bile-tolerant, esculin-hydrolyzing strains of viridans streptococci. Our results indicate a lack of relationship between strains derived from humans and the bovine S. bovis type strain. Although, like the classic S. bovis strains of human origin, the bovine type strain was able to hydrolyze starch, it differed from human S. bovis strains in that it failed to form acid from mannitol and melibiose. The S. bovis (var.) strains did not hydrolyze starch or form acid from mannitol. They were distinguished from the bile-tolerant, esculin-hydrolyzing S. intermedius (MG) strains by their inability to decarboxylate arginine, their ability to form acid from melibiose, and their production of the Lancefield group D antigen. All S. bovis strains of human origin, including the S. bovis (var.) strains, formed a single deoxyribonucleic acid homology group distinct from the bovine type strain. Further, none of the S. bovis strains were homologous to the S. intermedius (MG) or S. salivarius strains studied. Our findings suggest that S. bovis (var.) forms a subspecies of strains of human origin and that S. bovis strains derived from humans should be removed from the S. bovis taxon.

Pasteurella avium (Hinz and Kunjara 1977) comb. nov. and Pasteurella volantium sp. nov.

A deoxyribonucleic acid-deoxyribonucleic acid hybridization study (spectrophotometric method) showed that the species Haemophilus avium Hinz and Kunjara 1977 is composed of three deoxyribonucleic acid homology groups; these three groups are genetically closer to Pasteurella multocida, the type species of the genus Pasteurella, than to Haemophilus influenzae, the type species of the genus Haemophilus. We propose to transfer the species Haemophilus avium to the genus Pasteurella as Pasteurella avium comb. nov. (type strain, ATCC 29546) and to change the circumscription of this taxon to include only strains that are unable to ferment l-arabinose, maltose, and mannitol and unable to hydrolyze o-nitrophenyl-β-d-galactopyranoside. The name Pasteurella volantium sp. nov. (type strain, NCTC 3438) is proposed for strains (formerly identified as H. avium) that are unable to ferment L-arabinose and are able to ferment maltose and mannitol and to hydrolyze o-nitrophenyl-β-d-galactopyranoside. A third unnamed species consists of former H. avium strains that are able to ferment l-arabinose.

Deoxyribonucleic Acid Homologies Among Organisms in the Genus Gluconobacter

The taxonomy of the genus Gluconobacter has undergone many changes during the past 40 years. Based on phenotypic properties, this genus has changed from numerous species to one species containing five subspecies and then to a single species, Gluconobacter oxydans, with no subspecies. The present study was designed to test the validity of this latter view. Nucleotide sequence similarites were determined for 54 strains of Gluconobacter by using an S1 nuclease procedure. Three distinct deoxyribonucleic acid homology groups were obtained. The average level of relatedness among these groups was 16%. Homology group 1 contained 32 strains and included the type strain of G. oxydans and the type strains of all previously recognized subspecies. Homology group II contained 12 strains that had an intragroup homology level of 44 to 87% (average, 65%) with reference strain IFO 3264. Homology group III contained six strains with an average intragroup homology level of 86% with reference strain IFO 3276a. Reference strains IFO 3264 and IFO 3276 were previously recognized as G. oxydans. The remaining four strains of Gluconobacter had from 0 to 23% homology with reference strains used to delineate the three homology groups. Although these data show that the genus Gluconobacter is composed of at least three species, they also support elimination of the previously designated subspecies. Three isolates implicated in pink disease of pineapples were shown either not to be gluconobacters or to be mixed with gluconobacters. The occurrence of colony variants within many of the Gluconobacter strains is described, and the significance of this observation is discussed.

Deoxyribonucleic Acid Homology Between Fast-Growing Soybean-Nodulating Bacteria and Other Rhizobia

Deoxyribonucleic acid homologies were determined between five fast-growing soybean-nodulating strains from the People's Republic of China and other rhizobia. Type strains Rhizobium trifolii ATCC 14480, Rhizobium meliloti ATCC 9930, Rhizobium phaseoli ATCC 14482, Rhizobium leguminosarum ATCC 10004, and Bradyrhizobium japonicum ATCC 10324 were used to represent recognized species. Bradyrhizobium sp. (Lupinus) strain ATCC 10319, the type strain of the former species Rhizobium lupini, and Bradyrhizobium sp. strain 3G4b5 were also included. The fast-growing soybean-nodulating strains had low levels of deoxyribonucleic acid homology with the type strains studied (5 to 43%). The fast-growing soybean-nodulating strains studied constitute at least two distinct deoxyribonucleic acid homology groups.

Lipid composition in the classification of the butyric acid-producing clostridia.

An examination of 20 strains of butyric acid-producing Clostridium species for phospholipid class compositions, plasmalogen content, and acyl and alk-l-enyl chains showed that the deoxyribonucleic acid homology groups I (Clostridium butyricum) and II (Clostridium beijerinckii) could be distinguished by their lipid compositions. The phospholipids of C. butyricum strains had ethanolamine as the major nitrogenous lipid polar head-group moiety, more octadecenoate plus C19-cyclopropane than hexadecenoate plus C17-cyclopropane acyl chains, and the predominant alk-l-enyl chain was C18-monounsaturated. Clostridium beijerinckii strains had N-methylethanolamine plus ethanolamine in phospholipid head-groups, more hexadecenoate plus C17-cyclopropane than octadecenoate plus C19-cyclopropane acyl chains, and the major alk-l-enyl chain was C16-saturated. Three species falling outside the two homology groups Clostridium fallax, Clostridium pseudofallax and Clostridium acetobutylicum had ethanolamine as the major phospholipid base, but these species could be distinguished from C. butyricum by their acyl and alk-l-enyl chain compositions. The lipid composition of Clostridium pasteurianum is even more distinct.

Bacteroides intermedius comb. nov. and Descriptions of Bacteroides corporis sp. nov. and Bacteroides levii sp. nov.

Deoxyribonucleic acid homology studies of 66 strains formerly classified as Bacteroides melaninogenicus subsp. intermedius showed two distinct groups with negligible intergroup homology. The larger group, with homology to the type strain of B. melaninogenicus subsp. intermedius, is designated Bacteroides intermedius, and the description of the taxon is emended. The other deoxyribonucleic acid homology group, which includes strains that differ from B. intermedius in not fermenting sucrose or producing indole, is designated Bacteroides corporis sp. nov.; ATCC 33547T (= VPI 9342) is the type strain. Strains of B. intermedius and B. corporis do not ferment lactose, as strains of B. melaninogenicus, Bacteroides loescheii, and Bacteroides denticola do. Strain ATCC 29147T is designated the type strain of Bacteroides levii sp. nov. This organism is a pigmenting bacteroides whose strains have been isolated from cattle and include the LEV strain (previously called B. melaninogenicus or “B. melaninogenicus subsp. levii”). Phenotypic characteristics useful in differentiating among nine species that formerly have been included in or identified as B. melaninogenicus are listed.

NOTES: Leuconostoc mesenteroides subsp. cremoris (Knudsen and Sorensen) comb. nov. and Leuconostoc mesenteroides subsp. dextranicum (Beijerinck) comb. nov.

Leuconostoc mesenteroides (Tsenkovskii) van Tieghem 1878, Leuconostoc dextranicum (Beijerinck) Hucker and Pederson 1930, and Leuconostoc cremoris (Knudsen and Sørensen) Garvie 1960 belong to a single deoxyribonucleic acid homology group. These three organisms have similar lactate dehydrogenases and glucose-6-phosphate dehydrogenases. Because of these common properties, these organisms are here regarded as subspecies within a single species, Leuconostoc mesenteroides. The names of the subspecies are Leuconostoc mesenteroides subsp. mesenteroides, Leuconostoc mesenteroides subsp. dextranicum (Beijerinck) comb. nov., and Leuconostoc mesenteroides subsp. cremoris (Knudsen and Sørensen) comb. nov. The type strains of these subspecies are ATCC 8293, NCDO 529, and NCDO 543, respectively.

Phenotypic differentiation of some of the Veillonella species with the API ZYM system.

The genus Veillonella comprises at least eight deoxyribonucleic acid homology groups distinct at the species level. Conventional phenotypic tests are unable to differentiate these species. Use of the API ZYM system allows differentiation of four of the eight homology groups.

Taxonomy of the Genus Veillonella Prevot

Results of deoxyribonucleic acid homology studies of 116 strains of Veillonella Prevot, representing the two species and seven subspecies currently recognized in this genus, showed seven deoxyribonucleic acid homology groups distinct at the species level. Because the type strains of V. parvula subsp. parvula and V. alcalescens subsp. alcalescens had high homology, we regard V. alcalescens Prevot 1933 as a later subjective synonym of V. parvula (Veillon and Zuber, 1896) Prevot 1933. The species V. parvula, V. dispar (Rogosa) comb. nov., V. atypica (Rogosa) comb. nov., V. rodentium (Rogosa) comb. nov., V. ratti (Rogosa) comb. nov., V. criceti (Rogosa) comb. nov., and V. caviae sp. nov. (type strain, ATCC 33540) are recognized. Because most strains of V. criceti produced acid in peptone-yeast extract-fructose media, the genus description is emended to include strains that ferment fructose.

Vibrio ordalii sp. nov.: A causative agent of vibriosis in fish

Vibrio ordalii sp. nov. is the name proposed for the bacterium previously designated asV. anguillarum biotype 2. The change in the classification of this fish pathogen is based on differences between the classicalV. anguillarum andV. ordalii in cultural and biochemical characteristics, and in deoxyribonucleic acid (DNA) sequence relatedness. Phenotypically,V. ordalii was distinguishable fromV. anguillarum based on: negative Voges-Proskauer reaction; negative reaction with arginine in Moeller's medium; negative Simmons' and Christensen's citrate test; negative ONPG test; failure to hydrolyze starch; failure to show lipase activity; inability to grow at 37°C; and failure to ferment cellobiose, glycerol, sorbitol, and trehalose. Genotypically, strain ofV. ordalii formed a highly conserved DNA homology group which showed 83 to 100% within-group homology and only 58 to 69% relatedness toV. anguillarum. In contrast, theV. anguillarum strains tested showed greater than 70% withingroup homology and 53 to 67% relatedness toV. ordalii. NeitherV. ordalii norV. anguillarum were related toV. parahaemolyticus orV. alginolyticus. The proposed type strain (holotype) ofV. ordalii is ATCC 33509 (=DF3K=Dom F3 kid).

Confirmation of Bacteroides gingivalis as a Species Distinct from Bacteroides asaccharolyticus

We divided the asaccharolytic, black-pigmented Bacteroides strains into two groups on the basis of deoxyribonucleic acid (DNA) base ratios, DNA hybridization (S1 nuclease method) results, and direct hemagglutination. One homologous group of strains, which included the type strain of Bacteroides asaccharolyticus and had guanine-plus-cytosine contents of 52 to 54 mol%, contained only nonoral isolates. Another DNA homology group contained all of the strains from periodontal pockets and some nonoral isolates. These strains appeared to belong to the recently described new species Bacteroides gingivalis Coykendall et al. B. gingivalis strains had guanine-plus-cytosine contents of 48 to 50 mol%, showed high DNA homology values, and shared hemagglutinating activity. No DNA homology was observed between the two groups. Using a different method of analysis for DNA homology (S1 nuclease method), we confirmed the conclusion of Coykendall et al., who separated these two groups into different species, B. asaccharolyticus and B. gingivalis. Two strains from infected root canals could not be placed in either of these two species. On the basis of the DNA homology results, all asaccharolytic strains were distinguished clearly from the saccharolytic, black-pigmented Bacteroides strains, which at present are classified in the species Bacteroides melaninogenicus.

Deoxyribonucleic Acid Reassociation in the Classification of the Genus Rhodococcus Zopf 1891 (Approved Lists, 1980)

We determined the degree of binding between deoxyribonucleic acid (DNA) preparations from representative rhodococci and thymine-labeled DNAs (derived from labeled uracil) from the following six reference strains: Rhodococcus coprophilus (Approved Lists, 1980) strain N744, R. corallinys (Bergey et al. 1923) Goodfellow and Alderson 1979 (Approved Lists, 1980) strain N657, R. equi (Approved Lists, 1980) strain C7, R. rhodochrous (Approved Lists, 1980) strain N54, R. ruber (Approved Lists, 1980) strain N361, and R. rubropertinctus (Hefferan 1904) Goodfellow and Alderson 1979 (Approved Lists, 1980) strain N4. Although the congruence between the DNA reassociation and earlier numerical phenetic data was good, there was evidence that some strains had been misclassified in the numerical phenetic study. In particular, strains labeled R. corallinus (including the type strain of R. corallinus) and R. rubropertinctus belonged to a single DNA homology group. The former name is thus a later, subjective synonym of the latter. The guanine plus cytosine contents of the DNAs of the rhodococci fell within the range of 65 to 73 mo1%.

Characterization of a pyridine nucleotide-nonspecific glutamate dehydrogenase from Bacteroides thetaiotaomicron.

An oxidized nicotinamide adenine dinucleotide phosphate/oxidized nicotinamide adenine dinucleotide (NADP+/NAD+) nonspecific L-glutamate dehydrogenase from Bacteroides thetaiotaomicron was purified 40-fold (NADP+ or NAD+ activity) over crude cell extract by heat treatment, (NH4)2SO2 fractionation, diethylaminoethyl-cellulose, Bio-Gel A 1.5m, and hydroxylapatite chromatography. Both NADP+- and NAD+-dependent activities coeluted from all chromatographic treatments. Moreover, a constant ratio of NADP+/NAD+ specific activities was demonstrated at each purification step. Both activities also comigrated in 6% nondenaturing polyacrylamide gels. Affinity chromatography of the 40-fold-purified enzyme using Procion RED HE-3B gave a preparation containing both NADP+- and NAD+-linked activities which showed a single protein band of 48,5000 molecular weight after sodium dodecyl sulfate-polyacrylamide gradient gel electrophoresis. The dual pyridine nucleotide nature of the enzyme was most readily apparent in the oxidative direction. Reductively, the enzyme was 30-fold more active with reduced NADP than with reduced NAD. Nonlinear concave 1/V versus 1/S plots were observed for reduced NADP and NH4Cl. Salts (0.1 M) stimulated the NADP+-linked reaction, inhibited the NAD+-linked reaction, and had little effect on the reduced NADP-dependent reaction. The stimulatory effect of salts (NADP+) was nonspecific, regardless of the anion or cation, whereas the degree of NAD+-linked inhibition decreased in the order to I- greater than Br- greater than Cl- greater than F-. Both NADP+ and NAD+ glutamate dehydrogenase activities were also detected in cell extracts from representative strains of other bacteroides deoxyribonucleic acid homology groups.

Taxonomy of the Lactobacillus acidophilus Group

A total of 89 strains designated Lactobacillus acidophilus were examined for physiological properties, type of lactic acid produced, cell wall sugar pattern, guanine plus cytosine content of deoxyribonucleic acid (DNA), and DNA homology values compared with selected reference strains. Immunological reactions among a group of the strains were determined by gel diffusion tests, using antiserum to purified lactic acid dehydrogenase (LDH) from a single strain (Sharpe strain A18). Antiserum to glyceraldehyde-3-phosphate dehydrogenase from strain ATCG 4356 was used in microcomplement fixation tests to determine relationships among some strains. DNA preparations from 78 of the 89 strains of L. acidophilus were distributed among six distinct homology groups, designated Al, A2, A3, A4, Bl, and B2. The A group strains had 20 to 30% intergroup homology but very low homology to groups Bl and B2. Likewise, the strains in the two B groups had 20 to 30% intergroup homology but very low homology to the A group strains. Nine strains did not fall into any of the six homology groups. The guanine plus cytosine contents of the DNAs in strains comprising the six homology groups varied from 32 to 38 mol%. In the nine strains not falling into any of the homology groups, the guanine plus cytosine contents were 39 to 47 mol%. Homology group Al, which includes the neotype strain of L. acidophilus (ATCC 4356), is very homogeneous, with most strains showing 95% or more homology to the reference strain. This group corresponds to LDH serogroup III. Strains in the other homology groups showed 60 to 90% homology to then-reference strains. Strains of LDH serogroup II were found in homology groups A2, A3, and A4, and those in LDH serogroup I were in homology groups Bl and B2. In general, the glyceraldehyde-3-phosphate dehydrogenase serology results correlated well with the LDH results. Other phenotypic test results were similar for all of the DNA homology groups. It is recommended that homology group Al be designated L. acidophilus and that strain ATCC 4356 remain the neotype strain.

Bifidobacterium cuniculi, Bifidobacterium choerinum, Bifidobacterium boum, and Bifidobacterium pseudocatenulatum: Four New Species and Their Deoxyribonucleic Acid Homology Relationships

Among the several thousand bifidobacteria of our collection, 244 strains from the feces of rabbits and suckling pigs, the rumen of cattle, the feces of breast-and bottle-fed infants, the feces of calves, and from sewage are recognized by means of deoxyribonucleic acid (DNA)-DNA hybridization (competition filter method) as belonging to four new, distinct DNA homology groups. Twenty reference DNA preparations from the type strains of the currently known species or from reference strains of the homology groups of Bifidobacterium were used for comparison. The phenotypic traits which distinguish these four groups from previously described species of the genus Bifidobacterium include gross morphology, fermentation characteristics, guanine plus cytosine content of the DNA, the interpeptide bridge of the cell-wall peptidoglycan, and the transaldolase and 6-phosphogluconate dehydrogenase isozyme pattern (by starch gel electrophoresis). The four groups are named and described as new species of the genus Bifidobacterium: B. cuniculi, B. choerinum, B. boum, and B. pseudocatenulatum. The type strains of these species are RA93 (=ATCC 27916), SU806 (=ATCC 27686), RU917 (=ATCC 27917), and B1279 (=ATCC 27919), respectively.

Use of an immunoperoxidase method for identification of Bacteroides fragilis

An indirect immunoperoxidase (IP) slide test was evaluated for the laboratory identification of Bacteroides fragilis. Antigen-antibody complexes were detected with goat anti-rabbit immunoglobulin G-peroxidase conjugate with 3-amino-9-ethyl-carbazole as the peroxidase substrate. Ninety-one percent of 44 B. fragilis strains tested were IP positive (3+ to 4+ reactions) with greater than or equal to 1:160 dilutions of rabbit antiserum produced against whole cells of B. fragilis ATCC 23745. The antiserum was species specific. No cross-reactions were observed with 35 Bacteroides strains of other species or with a variety of facultative or aerobic gram-negative bacilli. Four B. fragilis strains were IP negative. One of these (VPI 2393) was the deoxyribonucleic acid (DNA) homology group II reference strain. The other three were clinical isolates. IP-negative and representative IP-positive strains were tested for DNA homology with the type strains for DNA homology groups I and II (VPI 2553 and VPI 2393). Two of the three clinical isolates were classified as DNA homology group II, and the remaining strain was classified as a group I. Capsular material known to be unique to B. fragilis was common to both DNA homology groups as indicated by reactions with purified anticapsular antiserum. The IP technique provides a suitable alternative to fluorescent microscopy for the rapid immunological identification of B. fragilis.