16S-23S rRNA Gene Spacer Region Research Articles

A molecular biological study on identification of common septicemia bacteria using 16s–23s rRNA gene spacer regions

In the search for a rapid and reliable method for identification of bacteria in blood and cerebrospinal fluid, we developed a unified set of primers and used them under polymerase chain reaction (PCR) to amplify the spacer regions between the 16s and 23s genes in the prokaryotic rRNA genetic loci. Spacer regions within these loci showed a significant level of length and sequence polymorphism across most of the species lines. A generic pair of priming sequences was selected from highly conserved sequences in the 16s and 23s genes occurring adjacent to these polymorphic regions. This single set of primers and reaction conditions were used for the amplification of the 16s–23s spacer regions for 61 strains of standard bacteria and corresponding clinical isolates belonging to 20 genera and 27 species, including Listeria, Staphylococcus and Salmonella species, et al. When the spacer amplification products were resolved by electrophoresis, the resulting patterns could be used to distinguish most of the bacteria species within the test group, and the amplification products of the clinical isolates clustered at the standard species level. Some species presenting similar pattern were further analyzed by HinfI or AluI digestion or DNA clone and sequences analysis in order to establish the specific 16s–23s rRNA gene spacer regions map. Analysis of 42 blood specimens from septicemic neonates and 6 CSF specimens from suspected purulent meningitis patients by bacterial culture and PCR-RFLP (Restriction Fregament Length Polymorphism) showed that 15 specimens of blood culture were positive (35.7%) in the 42 septicemic neonates; 27 specimens were positive(64.2%) by PCR, and that the positive rate by PCR was significantly higher than that by blood culture(P < 0.01). Among the 6 CSF specimens, one specimen found positive by blood culture was also positive by PCR, two found negative by blood culture showed positive by PCR; all three were S. epidermidis according to the DNA map. One C. neoformans found positive by blood culture showed negative by PCR. The remaining two specimens were both negative by PCR and blood culture. These results indicated that the method of detecting bacterial 16s–23s rRNA spacer regions using PCR and RFLP techniques was rapid, sensitive and specific in the detection of bacterial infections; and so, has very important application in the clinical diagnosis of sepsis in neonates.

Species identification of Acinetobacter calcoaceticus-Acinetobacter baumannii complex by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Objective To evaluate the ability of matrix-assisted laser desorption/ionization timeof-flight mass spectrometry (MALDI-TOF MS) in identifying species of Acinetobacter calcoaceticus-Acinetobacter baumannii complex,and investigate the species distribution of Acinetobacter calcoaceticus-Acinetobacter baumannii complex isolated in our hospital. Methods A total of 502 nonduplicate clinical isolates of Acinetobacter calcoaceticus-Acinetobacter baumannii complex were retrospectively collected from the second affiliated hospital of Zhejiang University between January 2012 and July 2012.All strains were re-identified by MALDI-TOF MS and were also verified by sequence analysis of 16S-23S rRNA gene spacer region. Results Among all the 502 strains of Acinetobacter calcoaceticus-Acinetobacter baumannii complex,identificaion results provided by MALDI-TOF MS were A.baumannii (431,85.9%),A.pittii (68,13.5%),A.calcoaceticus (3,0.6%).Sequence analysis of 16S-23S rRNA gene spacer region was used to identify all the 502 strains:403 (80.3%) were identified as A.baumannii,68 (13.5%) as A.pittii,28 (5.6%) as A.nosocomialis and 3 (0.6%) as A.calcoaceticus.MALDI-TOF MS correctly identified all the strains but erroneously identified all 28 strains of A.nosocomialis as A.baumannii,compared with sequence analysis of 16S-23S rRNA gene spacer region. Conclusions MALDI-TOF MS can be used as a fast,simple,reliable and excellently reproducible method to identify members of Acinetobacter calcoaceticus-Acinetobacter baumannii complex at low costs.MALDI-TOF MS is expected to be an ideal technique for routine clinical microbiology testing in the future.(Chin J Lab Med,2013,36:1115-1119) Key words: Acinetobacter calcoaceticus; Acinetobacter baumannii; Spectrometry; mass; matrix-assisted laser desorption-ionization

English

&nbsp; Probiotic bacteria are used for the protection and improvement of human intestinal microflora with added health effects. In search of new probiotics, 61 lactobacilli isolates were screened for survival in acidic conditions and simulated gastrointestinal juices, tolerance to ox-gall and antimicrobial activity. Selected strains (NWS09, NWS11, NWS14, NWS19 and NWS29) were identified by sequencing their 16S rRNA gene and 16S-23S rRNA gene spacer region, and further characterized by the absence of transferable antibiotic resistance, adhesion to Caco-2 cells and survival in gastrointestinal tract of BALB/c gnotobiotic. NWS09 had transferable resistance to erythromycin conferred byerm(B) gene, while NWS14 was resistant to tetracycline. NWS29, identified asLactobacillus fermentum&nbsp;showed remarkable tolerance to simulated gastrointestinal juices and bile and&nbsp;highest antimicrobial activity against 5 food borne pathogens by producing heat (100&deg;C) and pH resistant bacteriocins.&nbsp;L. fermentum&nbsp;NWS29 was also found to be highly adhesive to human caco-2 cells&nbsp;in vitro&nbsp;as compared to NWS11 and NWS19 and was isolated in highest numbers from BALB/c gnotobiotic after 24, 48 and 72 h of orogastric inoculation.&nbsp;L. fermentum&nbsp;NWS29 was identified as a probiotic strain that can be incorporated in functional foods for human use. &nbsp; Key words:&nbsp;Probiotic,&nbsp;Lactobacillus, acid and bile resistance, antimicrobial activity, Caco-2 cells.

Development and Evaluation of Oligonucleotide Chip Based on the 16S-23S rRNA Gene Spacer Region for Detection of Pathogenic Microorganisms Associated with Sepsis

Oligonucleotide chips targeting the bacterial internal transcribed spacer region (ITS) of the 16S-23S rRNA gene, which contains genus- and species-specific regions, were developed and evaluated. Forty-three sequences were designed consisting of 1 universal, 3 Gram stain-specific, 9 genus-specific, and 30 species-specific probes. The specificity of the probes was confirmed using bacterial type strains including 54 of 52 species belonging to 18 genera. The performance of the probes was evaluated using 825 consecutive samples that were positive by blood culture in broth medium. Among the 825 clinical specimens, 708 (85.8%) were identified correctly by the oligonucleotide chip. Most (536 isolates, or 75.7%) were identified as staphylococci, Escherichia coli, or Klebsiella pneumoniae. Thirty-seven isolates (4.5%) did not bind to the corresponding specific probes. Most of these also were staphylococci, E. coli, or K. pneumoniae and accounted for 6.3% of total number of the species. Sixty-two specimens (7.5%) did not bind the genus- or species-specific probes because of lack of corresponding specific probes. Among them, Acinetobacter baumannii was the single most frequent isolate (26/62). The oligonucleotide chip was highly specific and sensitive in detecting the causative agents of bacteremia directly from positive blood cultures.

Identification of Pathogenic Nocardia Species by Reverse Line Blot Hybridization Targeting the 16S rRNA and 16S-23S rRNA Gene Spacer Regions

Although 16S rRNA gene sequence analysis is employed most often for the definitive identification of Nocardia species, alternate molecular methods and polymorphisms in other gene targets have also enabled species determinations. We evaluated a combined Nocardia PCR-based reverse line blot (RLB) hybridization assay based on 16S and 16S-23S rRNA gene spacer region polymorphisms to identify 12 American Type Culture Collection and 123 clinical Nocardia isolates representing 14 species; results were compared with results from 16S rRNA gene sequencing. Thirteen 16S rRNA gene-based (two group-specific and 11 species-specific) and five 16S-23S spacer-targeted (two taxon-specific and three species-specific) probes were utilized. 16S rRNA gene-based probes correctly identified 124 of 135 isolates (sensitivity, 92%) but were unable to identify Nocardia paucivorans strains (n = 10 strains) and a Nocardia asteroides isolate with a novel 16S rRNA gene sequence. Nocardia farcinica and Nocardia cyriacigeorgica strains were identified by the sequential use of an N. farcinica-"negative" probe and a combined N. farcinica/N. cyriacigeorgica probe. The assay specificity was high (99%) except for weak cross-reactivity between the Nocardia brasiliensis probe with the Nocardia thailandica DNA product; however, cross-hybridization with closely related nontarget species may occur. The incorporation of 16S-23S rRNA gene spacer-based probes enabled the identification of all N. paucivorans strains. The overall sensitivity using both probe sets was >99%. Both N. farcinica-specific 16S-23S rRNA gene spacer-directed probes were required to identify all N. farcinica stains by using this probe set. The study demonstrates the utility of a combined PCR/RLB assay for the identification of clinically relevant Nocardia species and its potential for studying subtypes of N. farcinica. Where species assignment is ambiguous or not possible, 16S rRNA gene sequencing is recommended.

Identification of Acinetobacter Genomic Species 13TU by Sequence Analysis of the 16S-23S rRNA Gene Spacer Region

The genus Acinetobacter currently contains up to 32 described named and unnamed (genomic) species (3). Acinetobacter baumannii, genomic species 3, and 13TU, three of the most clinically relevant species, are genetically and phenotypically very similar to an environmental species, Acinetobacter calcoaceticus, and are therefore grouped together into the so-called A. calcoaceticus-A. baumannii (Acb) complex (3). Because phenotypic identification of Acinetobacter isolates to the species level has proven to be insufficient, several genotypic methods have been developed for genomic species identification (1, 3, 4). In the last 3 years, our laboratory has routinely used the 16S-23S rRNA gene intergenic spacer (ITS) sequence-based method described by Chang et al. (1) to delineate isolates belonging to the Acb complex to the genomic species level. We found the procedure accurate and easy to perform. However, we have recently encountered a discrepancy during the characterization of Acinetobacter strain 74510 isolated originally from a clinical source at the Prince of Wales Hospital, Hong Kong, in 1995 (2). Strain 74510 was previously identified as genomic species 13TU by restriction analysis of amplified ribosomal DNA (2, 4). However, examination of the single PCR amplicon of the ITS region of strain 74510 (GenBank accession no. {type:entrez-nucleotide,attrs:{text:FJ360743,term_id:210063372,term_text:FJ360743}}FJ360743) revealed an ITS sequence length of 607 bp, as opposed to the 615 bp reported by Chang et al. for the genomic species 13TU reference strain BCRC 15417 (1). On the other hand, DNA sequence analysis of this 607-bp ITS of strain 74510 showed an identity of 0.9561 to that of strain BCRC 15417 (Table ​(Table1).1). Upon further analysis of nucleotide sequences in GenBank, the strain 74510 ITS sequence was also found to share increasing identity (0.9950 to 0.9967) with three other genomic species 13TU strains, namely, v104-2, 00574, and DR25612/96 (Table ​(Table1).1). Interestingly, the ITS length (607 bp) of these three genomic species 13TU strains was also 607 bp, identical to that of strain 74510 (Table ​(Table1).1). In addition, the ITS sequences of these genomic species 13TU strains 74510, v104-2, 00574, and DR25612/96 appeared to be more closely related to the A. baumannii (genomic species 2) strain BCRC 10591T than to the 13TU reference strain BCRC 15417 (0.9538 to 0.9588 versus 0.9171 identity) (Table ​(Table1),1), which reinforces the notion that genetic similarity among A. baumannii and genomic species 13TU is high (3) and perhaps suggests that BCRC 15417 may not be as representative for genomic species 13TU. TABLE 1. ITS sequence similarity between A. baumannii and genomic species 13TUa Acinetobacter genomic species 13TU is the second most clinically relevant species in the Acb complex (3, 5, 6). Therefore, we believe that it is important to extend the number of Acinetobacter genomic species 13TU ITS sequences in the ITS sequence database for more-accurate genomic species identification. Also, we would suggest that the reference ITS sequence length for genomic species 13TU be 607 bp long and that strain 74510 could be considered as the “type” strain for genomic species 13TU.

Isolation and identification of a strain ofLeptospirillum ferriphilum from an extreme acid mine drainage site

Based on a new selective isolation strategy that mimicked physiological characteristics of leptospirilla, such as pH, temperature and its less sensitivity to the high ferric-ferrous iron ratio, a bacterial strain, called strain YSK, was isolated from an extreme acid mine drainage (AMD) site. Cells were Gram-negative, small curved rods measuring 0.27–0.52 by 0.81–3.17 μm. The cell shape suggested that strain YSK was likely a strain ofLeptospirillum ferrooxidans. However, based on the 16S rDNA sequence analysis, strain YSK possessed 100% sequence similarity with that of the typicalLeptospirillum ferriphilum strain Fairview; furthermore, the G+C content, the size of the 16S–23S rRNA gene spacer regions and the ability to grow at 45°C further indicated that strain YSK belonged to the speciesLeptospirillum ferriphilum.

Salinispora arenicola gen. nov., sp. nov. and Salinispora tropica sp. nov., obligate marine actinomycetes belonging to the family Micromonosporaceae

A taxonomic study was carried out to clarify the taxonomy of representatives of a group of marine actinomycetes previously designated MAR 1 and considered to belong to the family Micromonosporaceae. The organisms had phenotypic properties consistent with their assignment to this taxon. The strains formed a distinct taxon in the 16S rRNA Micromonosporaceae gene tree and shared a range of phenotypic properties that distinguished them from members of all of the genera with validly published names classified in this family. The name proposed for this novel taxon is Salinispora gen. nov. The genus contains two species recognized using a range of genotypic and phenotypic criteria, including comparative 16S-23S rRNA gene spacer region and DNA-DNA relatedness data. The names proposed for these taxa are Salinispora arenicola sp. nov., the type species, and Salinispora tropica sp. nov.; the type strains of these novel species have been deposited in service culture collections as strain CNH-643(T) (=ATCC BAA-917(T)=DSM 44819(T)) and strain CNB-440(T) (=ATCC BAA-916(T)=DSM 44818(T)), respectively.

Study on the bacterial identification using 16S-23S rRNA gene spacer regions

OBJECTIVE: To examine the use of PCR utilizing 16S-23S rRNA gene spacer regions in the identification of bacteria. METHODS Primers used in PCR were designed by using the target sequences from the genes encoding 16S-23S rRNA spacer regions. PCR was used for the detection of different standard and clinical bacterial strains. RESULTS Characteristic DNA maps were present after using the PCR to identify 27 standard strains from 27 species. The maps could be directly used for classification of the tested bacterial strains or further differentiated by RFLP. The sensitivity of the PCR may be as high as 2.5 CFU/ml. No non-specific amplification products were observed when using DNA from human PBMC funguses or viruses as templates. Thirty-two strains of bacteria isolated from clinical strains showed DNA maps similar to the DNA maps amplified from standard strains. CONCLUSION The PCR detection of bacteria using 16S-23S rRNA gene spacer regions is sensitive, rapid, specific and accurate for identification of bacteria and provides a new rapid method for determining the clinical diagnosis and the etiology of sepsis.

A molecular biological study on identification of common septicemia bacteria using 16s–23s rRNA gene spacer regions

A molecular biological study on identification of common septicemia bacteria using 16s–23s rRNA gene spacer regions

Molecular relationship between two groups of the genus Leptospirillum and the finding that Leptospirillum ferriphilum sp. nov. dominates South African commercial biooxidation tanks that operate at 40 degrees C.

Iron-oxidizing bacteria belonging to the genus Leptospirillum are of great importance in continuous-flow commercial biooxidation reactors, used for extracting metals from minerals, that operate at 40 degrees C or less. They also form part of the microbial community responsible for the generation of acid mine drainage. More than 16 isolates of leptospirilla were included in this study, and they were clearly divisible into two major groups. Group I leptospirilla had G+C moles percent ratios within the range 49 to 52% and had three copies of rrn genes, and based on 16S rRNA sequence data, these isolates clustered together with the Leptospirillum ferrooxidans type strain (DSM2705 or L15). Group II leptospirilla had G+C moles percent ratios of 55 to 58% and had two copies of rrn genes, and based on 16S rRNA sequence data, they form a separate cluster. Genome DNA-DNA hybridization experiments indicated that three similarity subgroups were present among the leptospirilla tested, with two DNA-DNA hybridization similarity subgroups found within group I. The two groups could also be distinguished based on the sizes of their 16S-23S rRNA gene spacer regions. We propose that the group II leptospirilla should be recognized as a separate species with the name Leptospirillum ferriphilum sp. nov. Members of the two species can be rapidly distinguished from each other by amplification of their 16S rRNA genes and by carrying out restriction enzyme digests of the products. Several, but not all, isolates of the group II leptospirilla, but none from group I (L. ferrooxidans), were capable of growth at 45 degrees C. All the leptospirilla isolated from commercial biooxidation tanks in South Africa were from group II.

A molecular biological study on identification of common septicemia bacteria using 16s-23s rRNA gene spacer regions

In the search for a rapid and reliable method for identification of bacteria in blood and cerebrospinal fluid , we developed a unified set of primers and used them under polymerase chain reaction(PCR) to amplify the spacer regions between the 16s and 23s genes in the prokaryotic rRNA genetic loci . Spacer regions within these loci showed a significant level of length and sequence polymorphism across most of the species lines. A generic pair of priming sequences was selected from highly conserved sequences in the 16s and 23s genes occurring adjacent to these polymorphic regions. This single set of primers and reaction conditions were used for the amplification of the 16s\|23s spacer regions for 61 strains of standard bacteria and corresponding clinical isolates belonging to 20 genera and 27 species, including \%Listeria, Staphylococcus and Salmonella\% species, et al. When the spacer amplification products were resolved by electrophoresis, the resulting patterns could be used to distinguish most of the bacteria species within the test group, and the amplification products of the clinical isolates clustered at the standard species level. Some species presenting similar pattern were further analyzed by HinfI or AluI digestion or DNA clone and sequences analysis in order to establish the specific 16s\|23s rRNA gene spacer regions map. Analysis of 42 blood specimens from septicemic neonates and 6 CSF specimens from suspected purulent meningitis patients by bacterial culture and PCR\|RFLP(Restriction Fregament Length Polymorphism) showed that 15 specimens of blood culture were positive(35.7%) in the 42 septicemic neonates; 27 specimens were positive(64.2%) by PCR, and that the positive rate by PCR was significantly higher than that by blood culture( P 0.01). Among the 6 CSF specimens, one specimen found positive by blood culture was also positive by PCR, two found negative by blood culture showed positive by PCR; all three were \%S.epidermidis\% according to the DNA map. One \%C.neoformans\% found positive by blood culture showed negative by PCR. The remaining two specimens were both negative by PCR and blood culture. These results indicated that the method of detecting bacterial 16s\|23s rRNA spacer regions using PCR and RFLP techniques was rapid, sensitive and specific in the detection of bacterial infections; and so, has very important application in the clinical diagnosis of sepsis in neonates.

Genotyping of Mycoplasma pneumoniae clinical isolates reveals eight P1 subtypes within two genomic groups.

Three methods for genotyping of Mycoplasma pneumoniae clinical isolates were applied to 2 reference strains and 21 clinical isolates. By a modified restriction fragment length polymorphism (RFLP) analysis of PCR products of the M. pneumoniae cytadhesin P1 gene, 5 subtypes were discriminated among 13 P1 type 1 strains and 3 subtypes were discriminated among 8 P1 type 2 strains. Sequence analysis of the 16S-23S rRNA gene spacer region and part of the 23S rRNA gene revealed one nucleotide difference in the intergenic spacer region in 3 of the 21 isolates. In the 23S rRNA gene sequence of the 8 P1 type 2 strains an extra adenosine was present, but it was absent from the 13 P1 type 1 strains. On the basis of M. pneumoniae genome sequence data, primers were designed to amplify large interrepeat fragments by long PCR, and these fragments were subsequently analyzed by RFLP analysis. Only two types, long PCR types 1 and 2, could be discriminated among the M. pneumoniae isolates. All P1 type 1 strains were assigned to long PCR type 1, and all P1 type 2 strains were assigned to long PCR type 2. These data obtained by three independent typing methods thus confirm the existence of two distinct M. pneumoniae genomic groups but expand the possibility of strain typing on the basis of variations within their P1 genes.

Phylogenetic analysis of Ureaplasma urealyticum--support for the establishment of a new species, Ureaplasma parvum.

In this study, the phylogenetic relationships between the two biovars and 14 serovars of Ureaplasma urealyticum were studied using the sequences of four different genes or genetic regions, namely: 16S rRNA genes; 16S-23S rRNA gene spacer regions; urease gene subunits ureA, ureB, partial ureC and adjoining regions upstream of ureA, ureA-ureB spacer and ureB-ureC spacer; the 5'-ends of the multiple-banded antigen (MBA) genes. U. urealyticum genotypes, based on all four genomic sequences, could be clearly separated into two clusters corresponding with currently recognized biovars 1 and 2. Sequences were generally conserved within each biovar. However, there was heterogeneity within the 5'-end regions of the MBA genes of the four serovars of biovar 1; the sequence of serovar 3 was identical with the previously published sequence and differed by only three bases from that of serovar 14; but there were significant differences between the sequences of serovars 3 and 14 and those of serovars 1 and 6. Based on the phylogenetic analysis, support is given to previous recommendations that the two biovars of U. urealyticum be classified as distinct species, namely U. parvum and U. urealyticum for biovars 1 and 2, respectively. In the future, the relationship between the new species and clinical manifestations of ureaplasma infections should be studied.

Genomic Diversity of Several Corynebacterium Species Identified by Amplification of the 16S–23S rRNA Gene Spacer Regions

In order to investigate whether 16S–23S ribosomal DNA (rDNA) spacer region length polymorphisms are suitable identification of Corynebacterium strains at the species level, the 16S–23S rDNA intergenic spacer region strains belonging to 11 Corynebacterium species were studied by a PCR-based method. The lengths 16S–23S rDNA spacer regions varied from 394 to 585 bp, fragment lengths which are similar to those described for other genera. A single PCR profile was obtained for each of the following species: Corynebacterium renale, Corynebacterium urealyticum, Corynebacterium diphtheriae, Corynebacterium ulcerans, Corynebacterium pseudodiphtheriticum, and Corynebacterium kutscheri. In contrast, two and three PCR patterns were detected for Corynebacterium minutissimum, Corynebacterium striatum, Corynebacterium amycolatum, and Corynebacterium jeikeium, suggesting that genomic heterogeneity occurs in these four species. The 16S–23S rDNA spacer region length polymorphisms allowed us to discriminate among C. minutissimum, C. striatum, and C. amycolatum, three species that are frequently isolated and misidentified in clinical laboratories. Type strain Corynebacterium xerosis ATCC 373, which exhibited a PCR pattern similar to that of C. amycolatum strains classified in PCR group I, could nevertheless be discriminated from PCR group II (C. amycolatum) strains, as Well as minutissimum and C. striatum strains. Type strain C. xerosis ATCC 373 and C. amycolatum strains classified PCR group I could not be distinguished from strains belonging to C. diphtheriae, C. ulcerans, and C. pseudodiphtheriticum. The lipophilic species C. urealyticum and C. jeikeium, which are frequently encountered in clinical specimens, could be clearly distinguished from each other by this method. The use of 16S–23S spacer region length data determined by PCR-mediated amplification is suitable for identification of several Corynebacterium species. This rapid and easy method may be a useful identification tool for clinical microbiologists.

Predominance of two Bartonella henselae variants among cat-scratch disease patients in the Netherlands

Restriction endonuclease analysis of the PCR-amplified 16S-23S rRNA gene spacer region was used to investigate the prevalence of Bartonella henselae variants in samples from cat-scratch disease (CSD) patients. Analysis of spacer PCR fragments from 27 Bartonella DNA-positive samples from Dutch patients with CSD with AluI revealed two restriction fragment length polymorphism (RFLP) patterns, patterns A and B. Twenty samples yielded B. henselae pattern A, and 7 samples yielded B. henselae pattern B. Three samples from North American patients with CSD were shown to contain B. henselae with RFLP pattern B. To be able to detect and differentiate Bartonella DNA in clinical material more sensitively and faster, two B. henselae PCRs which amplify part of the 16S rRNA gene and which can discriminate between two B. henselae variants were developed. Thirty-two of 41 Bartonella DNA-positive samples from Dutch patients with CSD contained type I B. henselae, 7 samples contained type II B. henselae, and two samples were negative in both type-specific PCRs. Two samples from North American patients with CSD both contained type II B. henselae. A 100% correlation was found between the AluI spacer RFLP pattern and the 16S rRNA PCR type. We have shown that Dutch patients with CSD contain a limited number of B. henselae variants, suggesting that, in contrast to systemic bartonellosis, CSD in immunocompetent patients is caused by a limited number of B. henselae variants.

Polyphasic Taxonomy Leading to the Proposal of Moraxella canis sp. nov. for Moraxella catarrhalis-Like Strains

The taxonomic position of a group of 16 Moraxella catarrhalis-like strains, isolated mainly from dogs, was examined by using morphological tests, biochemical tests, serology, ribotyping with oligonucleotide probes, polymerase chain reaction typing of the 16S rRNA gene and the 16S-23S rRNA gene spacer region, polyacrylamide gel electrophoresis of total proteins, fatty acid profiles, moles percent G+C, dot spot and in-solution DNA-DNA hybridizations, and DNA-rRNA hybridizations. It was found that these organisms constitute a distinct cluster within the genus Moraxella. Since they differ genotypically as well as phenotypically from previously described Moraxella species, a new species, Moraxella canis, is proposed to accommodate these isolates. The type strain is LMG 11194 (= N7 = CCUG 8415A).