Recent advances in molecular epidemiology and detection of Taylorella equigenitalis associated with contagious equine metritis (CEM)

Short review: Geographical distribution of equine-associated pVAPA plasmids in Rhodococcus equi in the world

Virulent Rhodococcus equi strains expressing virulence-associated 15-17 kDa protein (VapA) and having a large virulence plasmid (pVAPA) of 85-90 kb containing vapA gene are pathogenic for horses. In the last two decades, following pVAPA, two host-associated virulence plasmid types of R. equi have been discovered: a circular plasmid, pVAPB, associated with porcine isolates in 1995, and a recently detected linear plasmid, pVAPN, related to bovine and caprine isolates. Molecular epidemiological studies of R. equi infection in foals on horse-breeding farms in Japan and many countries around the world have been conducted in the last three decades, and the epidemiological studies using restriction enzyme digestion patterns of plasmid DNAs from virulent isolates have shown 14 distinct pVAPA subtypes and their geographical preference. This short review summarizes previous reports regarding equine-associated pVAPA subtypes in the world and discusses their geographic distribution from the standpoint of horse movements.

Development and Application of a Multiplex Real-Time Polymerase Chain Reaction Assay for the Simultaneous Detection of Bacterial Aetiologic Agents Associated With Equine Venereal Diseases

Venereal diseases caused by bacteria are important to the equine industry due to economic losses caused by decline of conception rate in breeding horses. Therefore, identification of infected animals as well as the implementation of appropriate managerial procedures based on accurate diagnosis is critical. In this study, two types of multiplex real-time polymerase chain reaction with high sensitivity and specificity were developed for the simultaneous detection and differentiation of five commonly associated bacterial pathogens of venereal diseases in horses, consisting of Taylorella equigenitalis, Taylorella asinigenitalis, Pseudomonas aeruginosa, Klebsiella pneumoniae and Streptococcus zooepidemicus. The assay was applied to samples collected as part of the surveillance of T.equigenitalis infection in South Korea. Swab samples collected from horses in 2015 were tested. T. equigenitalis and K. pneumoniae was detected in 21 (21.0%) and two (2.0%) samples, respectively. No samples were positive for T. asinigenitalis, P. aeruginosa, and S. zooepidemicus. Application of this assay to an existing surveillance program has allowed for an enhanced surveillance for a wider range of venereal diseases of equine to be implemented in South Korea.

A new strain of Taylorella asinigenitalis shows differing pathogenicity in mares and Jenny donkeys

BACKGROUND

Three horse mares inadvertently inseminated with semen from a Tayorella asinigenitalis-positive Jack donkey developed severe, purulent endometritis whereas two Jenny donkeys mated naturally to the same Jack donkey did not develop clinical signs of infection.

OBJECTIVES

To isolate and identify the causative agent.

STUDY DESIGN

Case report.

METHODS

Endometrial swabs from the infected mares were cultured on selective and non-selective media under aerobic and microaerophilic conditions. Isolates were subjected to Gram staining, oxidase and catalase tests, the Monotayl Latex Agglutination test and PCR to test for both T. equigenitalis and T. asinigenitalis. In vitro antimicrobial susceptibility testing was performed and the bacterial isolate was genotyped using MLST.

RESULTS

A new sequence type of T. asinigenitalis was confirmed.

MAIN LIMITATIONS

A limited numbers of mares and donkeys are described.

CONCLUSIONS

This strain of T. asinigenitalis causes a severe venereal infection in mares but not in Jenny donkeys.

Comparative Semen Microbiota Composition of a Stallion in a Taylorella equigenitalis Carrier and Non-Carrier State

Simple Summary

Contagious equine metritis carriers have become a new cause of concern in horse stud farms. Their detection can result in significant financial loss and force owners to have their animals undergo antibiotic treatment. Current research has not been able to satisfactorily explain the appearance of carriers in agent-free farms. Studies made on microbial flora have given new insights into the diagnosis and treatment of different issues in animal systems. Next-generation sequencing (NGS) is a powerful tool that can draw an accurate picture of microbial flora. Therefore, the aim of this study was to compare the seminal bacterial composition of one stallion before and after being diagnosed with Taylorella equigenitalis using NGS. Our results show that the microbial seminal flora visibly changed between the samples analyzed. Corynebacteriaceae, an opportunistic bacterial family, was more common in the infected sample. However, Porphyromonadaceae, a natural component in several tissues, was more abundant in the negative sample. Despite the constraints of a single-case study, these findings can open the door to new therapeutic tools, as flora transplants. Similarly, seminal flora analysis may foresee microbial shifts, letting practitioners take preventive actions before a potential outbreak. Furthermore, these actions would have the extra benefit of reducing the administration of antibiotics to treat an infection.

Abstract

Contagious equine metritis is receiving renewed attention due to the continuous detection of carriers in apparent agent-free farms. Interactions of Taylorella with the seminal microflora may be the plausible cause behind these spontaneous changes of the carrier state. Accordingly, the aim of this study was to compare the differences in the seminal microbiome composition of one stallion in the contagious equine metritis carrier state and non-carrier state. Samples were cryopreserved after their extraction. Cell disruption was performed by high-speed homogenization in grinding media. Bacterial families were identified via V3 amplification of the 16S rRNA gene and Ion Torrent sequencing. Only bacterial families with relative abundance above 5% were taken into consideration. The positive sample contained a strong dominance of Corynebacteriaceae (37.75%) and Peptoniphilaceae (28.56%). In the negative sample, the Porphyromonadaceae (20.51%), Bacteroidaceae (19.25%) and Peptoniphilaceae (18.57%) families prevailed. In conclusion, the microbiome seminal composition varies when an individual carries Taylorella from when it is free of it. The wider differences were found in the Corynebacteriaceae, Porphyromonadaceae and Bacteroidaceae families. Due to the limitations of a single-case analysis, further studies are needed for a better understanding of the stallion seminal microflora interactions.

Overview of spatio-temporal distribution inferred by multi-locus sequence typing of Taylorella equigenitalis isolated worldwide from 1977 to 2018 in equidae

The accurate identification of Taylorella equigenitalis strains is essential to improve worldwide prevention and control strategies for contagious equine metritis (CEM). This study compared 367 worldwide equine strains using multilocus sequence typing according to the geographical origin, isolation year and equine breed. The strains were divided into 49 sequence types (STs), including 10 described for the first time. Three major and three minor clonal complexes (CCs), and 11 singletons, were identified. The genetic heterogeneity was low (0.13 STs/strain) despite the wide diversity of geographical origins (n = 16), isolation years (1977-2018) and equine breeds (n = 18). It was highest outside Europe and in the 1977-1997 period; current major STs and CCs already existed before 1998. Previous data associated the major CC1 with the first CEM outbreaks in 1977-1978 in the United Kingdom, Australia and the United States, and revealed its circulation in France. Our study confirms its circulation in France over a longer period of time (1992-2018) and its distribution in Spain and Germany but not throughout Europe. In addition to CC1, relationships between non-European and European countries were observed only through ST4, ST17 and ST30. Within Europe, several STs emerged with cross-border circulation, in particular ST16 and ST46 from the major complexes CC2 and CC8. These results constitute a baseline for monitoring the spread of CEM outbreaks. A retrospective analysis of a higher number of strains isolated worldwide between 1977 and the early 2000s would be helpful to obtain an exhaustive picture of the original CEM situation.

Direct culture-independent sequence typing of Taylorella equigenitalis obtained from genital swabs and frozen semen samples from South African horses

We report herein the use of crude extracts obtained from samples of Taylorella equigenitalis-infected horses for the purpose of multi-locus sequence typing (MLST). Samples (n = 36) were collected from horses in South Africa from 1996 to 2017: 34 from genital swabs (stored at -20°C for 2-3 y) and 2 from cryopreserved raw semen aliquots (stored at -70°C for 18 y) prior to assay. The MLST assay showed a single sequence type (ST), designated ST4, that supported a point introduction and thus a common source for the South African outbreak of contagious equine metritis.

Towards European harmonisation of contagious equine metritis diagnosis through interlaboratory trials

The performance of culture and PCR methods routinely used to diagnose contagious equine metritis (CEM) was evaluated and compared by two interlaboratory trials involving a total of 24 European laboratories, including 22 National Reference Laboratories for CEM. Samples were swab specimens artificially contaminated with bacteria present in the genital tract of Equidae, some with and some without Taylorella equigenitalis, the causative agent of CEM, and T asinigenitalis, responsible for possible misidentification as T equigenitalis Throughout both interlaboratory trials, PCR performed better in terms of specificity and sensitivity than the culture method, supporting the assertion that PCR should be accepted for CEM diagnosis. However, the culture performance during the second interlaboratory trial was better than during the first one, suggesting that the expertise of participants improved. This reveals the advantage of regular interlaboratory trials to constantly improve the expertise of laboratories. It also shows the need to develop new culture media that are more selective and/or better geared to the metabolism of T equigenitalis in order to improve the bacteriological diagnosis of CEM.

Polymerase chain reaction-based national surveillance programme to determine the distribution and prevalence of Taylorella equigenitalis in South African horses

REASONS FOR PERFORMING STUDY

The response to the first outbreak of contagious equine metritis in South Africa included pioneering a web-based platform to coordinate key aspects of a national, real-time polymerase chain reaction (qPCR)-based stallion screening programme to determine the distribution and prevalence of Taylorella equigenitalis in stallions and exposed mares.

OBJECTIVES

To define the hypothesised pre-existing status of T. equigenitalis in the South African equine population and progression of the epidemiological investigation via the implementation of a molecular diagnostic-based surveillance programme.

STUDY DESIGN

Retrospective case series.

METHODS

Screening for T. equigenitalis was via a qPCR assay on genital swabs obtained from predilection sites in stallions and mares with subsequent confirmation using bacterial culture according to prescribed methods.

RESULTS

The initial outbreak investigation identified 4 horses including the index stallion and mare. Traceback of in-contact horses identified 26 horses, including a subpopulation focus at the South African Lipizzaner Centre where 24/33 resident stallions tested positive for T. equigenitalis on qPCR. The national screening programme identified an additional 9 stallions. A total of 39 horses (36 stallions and 3 mares) tested positive for T. equigenitalis by qPCR and T. equigenitalis was isolated from 23 of these stallions and 2 of these mares. In addition to the index property, an artificial breeding centre where the index case was first identified, an additional 12 properties with infected horses were identified in 3/9 provinces. Horses on 11 of these 12 properties were directly linked to the index property. Two incidents of T. equigenitalis transmission associated with artificial insemination were recorded.

CONCLUSIONS

T. equigenitalis was present in a subpopulation focus within the South African horse population prior to the outbreak identification in April 2011. Horizontal fomite-associated spread was the most probable route of transmission between stallions. The targeted surveillance of stallions and exposed mares using a qPCR-based screening programme expedited investigation of the distribution and prevalence of T. equigenitalis infection in South African horses. The application of qPCR provided a sensitive and practical screening test for identification of T. equigenitalis-positive animals as part of an emergency response to the first identified cases of T. equigenitalis infection in South African horses.

Development of a novel molecular detection method for clustered regularly interspaced short palindromic repeats (CRISPRs) in Taylorella organisms

Contagious equine metritis is a bacterial infectious disease of horses caused by Taylorella equigenitalis, a Gram-negative eubacterium. The disease has been described in several continents, including Europe, North America and Asia. A novel molecular method was developed to detect clustered regularly interspaced short palindromic repeats (CRISPRs), which were separated by non-repetitive unique spacer regions (NRUSRs) of similar length, in the Taylorella equigenitalis EQ59 strain using a primer pair, f-/r-TeCRISPR-ladder, by PCR amplification. In total, 31 Taylorella isolates (17 T. equigenitalis and 14 Taylorella asinigenitalis) were examined. The T. equigenitalis isolates came from thoroughbred and cold-blooded horses from nine countries during 1980-1996, whilst the T. asinigenitalis isolates all originated from donkey jacks in France and the USA during 1997-2006. PAGE fractionated all of the 13 CRISPRs separated by 12 NRUSRs in T. equigenitalis EQ59. Permutation examples of CRISPRs, which were separated by NRUSRs for small-sized ladders, consisting of two doublet bands were shown. Putative CRISPRs separated by NRUSRs were amplified with 14/17 (82.4 %) geographically disparate T. equigenitalis isolates using the newly designed primer pair. Approximately 82.4 % of the T. equigenitalis isolates had CRISPRs separated by NRUSRs. The CRISPR locus was also found in the French T. asinigenitalis strain MCE3. Putative CRISPRs separated by NRUSRs were detected similarly in 4/14 (28.6 %) T. asinigenitalis isolates. Overall, a more detailed understanding of the molecular biology of CRISPRs within Taylorella organisms may help elucidate the pathogenic virulence and transmission mechanisms associated with this important equine pathogen.

Draft Genome Sequence of Taylorella equigenitalis Strain MCE529, Isolated from a Belgian Warmblood Horse

Taylorella equigenitalis is the causative agent of contagious equine metritis (CEM), a sexually transmitted infection of horses. We herein report the genome sequence of T. equigenitalis strain MCE529, isolated in 2009 from the urethral fossa of a 15-year-old Belgian Warmblood horse in France.

Survival of taylorellae in the environmental amoeba Acanthamoeba castellanii

Background

Taylorella equigenitalis is the causative agent of contagious equine metritis, a sexually-transmitted infection of Equidae characterised in infected mares by abundant mucopurulent vaginal discharge and a variable degree of vaginitis, cervicitis or endometritis, usually resulting in temporary infertility. The second species of the Taylorella genus, Taylorella asinigenitalis, is considered non-pathogenic, although mares experimentally infected with this bacterium can develop clinical signs of endometritis. To date, little is understood about the basic molecular virulence and persistence mechanisms employed by the Taylorella species. To clarify these points, we investigated whether the host-pathogen interaction model Acanthamoeba castellanii was a suitable model for studying taylorellae.

Results

We herein demonstrate that both species of the Taylorella genus are internalised by a mechanism involving the phagocytic capacity of the amoeba and are able to survive for at least one week inside the amoeba. During this one-week incubation period, taylorellae concentrations remain strikingly constant and no overt toxicity to amoeba cells was observed.

Conclusions

This study provides the first evidence of the capacity of taylorellae to survive in a natural environment other than the mammalian genital tract, and shows that the alternative infection model, A. castellanii, constitutes a relevant alternative system to assess host-pathogen interactions of taylorellae. The survival of taylorellae inside the potential environmental reservoir A. castellanii brings new insight, fostering a broader understanding of taylorellae biology and its potential natural ecological niche.

Genome implosion elicits host-confinement in Alcaligenaceae: evidence from the comparative genomics of Tetrathiobacter kashmirensis, a pathogen in the making

This study elucidates the genomic basis of the evolution of pathogens alongside free-living organisms within the family Alcaligenaceae of Betaproteobacteria. Towards that end, the complete genome sequence of the sulfur-chemolithoautotroph Tetrathiobacter kashmirensis WT001^T was determined and compared with the soil isolate Achromobacter xylosoxidans A8 and the two pathogens Bordetella bronchiseptica RB50 and Taylorella equigenitalis MCE9. All analyses comprehensively indicated that the RB50 and MCE9 genomes were almost the subsets of A8 and WT001^T, respectively. In the immediate evolutionary past Achromobacter and Bordetella shared a common ancestor, which was distinct from the other contemporary stock that gave rise to Tetrathiobacter and Taylorella. The Achromobacter-Bordetella precursor, after diverging from the family ancestor, evolved through extensive genome inflation, subsequent to which the two genera separated via differential gene losses and acquisitions. Tetrathiobacter, meanwhile, retained the core characteristics of the family ancestor, and Taylorella underwent massive genome degeneration to reach an evolutionary dead-end. Interestingly, the WT001^T genome, despite its conserved architecture, had only 85% coding density, besides which 578 out of its 4452 protein-coding sequences were found to be pseudogenized. Translational impairment of several DNA repair-recombination genes in the first place seemed to have ushered the rampant and indiscriminate frame-shift mutations across the WT001^T genome. Presumably, this strain has just come out of a recent evolutionary bottleneck, representing a unique transition state where genome self-degeneration has started comprehensively but selective host-confinement has not yet set in. In the light of this evolutionary link, host-adaptation of Taylorella clearly appears to be the aftereffect of genome implosion in another member of the same bottleneck. Remarkably again, potent virulence factors were found widespread in Alcaligenaceae, corroborating which hemolytic and mammalian cell-adhering abilities were discovered in WT001^T. So, while WT001^T relatives/derivatives in nature could be going the Taylorella way, the lineage as such was well-prepared for imminent host-confinement.

Genomic characterization of the Taylorella genus

The Taylorella genus comprises two species: Taylorella equigenitalis, which causes contagious equine metritis, and Taylorella asinigenitalis, a closely-related species mainly found in donkeys. We herein report on the first genome sequence of T. asinigenitalis, analyzing and comparing it with the recently-sequenced T. equigenitalis genome. The T. asinigenitalis genome contains a single circular chromosome of 1,638,559 bp with a 38.3% GC content and 1,534 coding sequences (CDS). While 212 CDSs were T. asinigenitalis-specific, 1,322 had orthologs in T. equigenitalis. Two hundred and thirty-four T. equigenitalis CDSs had no orthologs in T. asinigenitalis. Analysis of the basic nutrition metabolism of both Taylorella species showed that malate, glutamate and alpha-ketoglutarate may be their main carbon and energy sources. For both species, we identified four different secretion systems and several proteins potentially involved in binding and colonization of host cells, suggesting a strong potential for interaction with their host. T. equigenitalis seems better-equipped than T. asinigenitalis in terms of virulence since we identified numerous proteins potentially involved in pathogenicity, including hemagluttinin-related proteins, a type IV secretion system, TonB-dependent lactoferrin and transferrin receptors, and YadA and Hep_Hag domains containing proteins. This is the first molecular characterization of Taylorella genus members, and the first molecular identification of factors potentially involved in T. asinigenitalis and T. equigenitalis pathogenicity and host colonization. This study facilitates a genetic understanding of growth phenotypes, animal host preference and pathogenic capacity, paving the way for future functional investigations into this largely unknown genus.

Demonstration of the absence of intervening sequences (IVSs) within 16S rRNA genes of Taylorella equigenitalis and Taylorella asinigenitalis isolates

A total of 57 Taylorella equigenitalis (n=22) and Taylorella asinigenitalis (n=35) isolates was shown not to carry any intervening sequences (IVSs) within 16S rRNA gene sequences. By contrast, we have already shown the genus Taylorella group to carry several kinds of IVSs within the 23S rRNA gene sequences.

Development of a new molecular detection method for Taylorella equigenitalis

On PCR amplification of the intervening sequences (IVSs) in the central (helix 45) region within 23S rRNA gene sequences with T. equigenitalis (n = 34), as well as T. asinigenitalis (n = 35) and Bordetella (n = 11) isolates by using the primer pair of f-/r-23STis2, approximately 0.8 kb of the amplicons were generated, sequenced and analyzed. One IVS of approximately 70 bp in length was identified in all the Taylorella organisms but not Bordetella. PCR amplification was further developed for the convenient and rapid molecular detection of T. equigenitalis organisms with the IVS in the helix 45 region within the 23S rRNA genes as target by using the primer pairs (f-IVSde/r-23de). Thus, these results clearly demonstrated that PCR amplification with the primer pair (f-IVSde/r-23de) can be reliable in order to differentiate the T. equigenitalis isolates from both the T. asinigenitalis and Bordetella organisms.

Genome sequence of Taylorella equigenitalis MCE9, the causative agent of contagious equine metritis

Taylorella equigenitalis is the causative agent of contagious equine metritis (CEM), a sexually transmitted infection of horses. We herein report the genome sequence of T. equigenitalis strain MCE9, isolated in 2005 from the urethral fossa of a 4-year-old stallion in France.

Pulsed-field gel electrophoresis genotyping of Taylorella equigenitalis isolates collected in the United States from 1978 to 2010

Taylorella equigenitalis is the etiologic agent of contagious equine metritis (CEM), a venereal disease of horses. A total of 82 strains of T. equigenitalis isolated in the United States were analyzed by pulsed-field gel electrophoresis (PFGE) after digestion of genomic DNA with restriction enzyme ApaI. Twenty-eight of those strains isolated from horses in the 2009 U.S. outbreak (CEM09) were further analyzed with NotI and NaeI enzymes. When ApaI alone was used for analysis, the 82 isolates clustered into 15 different genotypes that clearly defined groups of horses with known epidemiological connections. The PFGE profiles of the CEM09 isolates were indistinguishable after digestion with ApaI, NotI, and NaeI and did not match those of isolates from previous U.S. outbreaks in 1978 and 2006 or of any other isolate from the National Veterinary Services Laboratories (NVSL) culture library. Coupled with the fact that the CEM09 isolates are epidemiologically related, these results suggest a common source for the outbreak not linked to previous occurrences of CEM in the United States.

Molecular identification and characterization of the intervening sequences (IVSs) within 23S ribosomal RNA (rRNA) genes of Taylorella asinigenitalis isolated in France

In the helix 25 region, 32 French Taylorella asinigenitalis isolates carried at least one 23S rRNA gene not containing intervening sequences (IVSs). No IVSs in the region were identified in three isolates and the other remaining 29 isolates carried one or more IVSs (UCD-1(T)IVS1A, UCD-1(T)IVS1B and UK-1IVS1B) described already and two new kinds of IVS (TaIVS1C and TaIVS1D). In the helix 45 region, no T. asinigenitalis isolates not carrying any IVSs were identified. UK-1IVS2B was identified in the region from 26 isolates. Five new kinds of IVSs (TaIVS2D, E, F, G and H) occurred in the region in the 13 isolates. Distinctly different tandem repeat units (RS48 and RS32 and RS-A, -B and -C) were evident in both regions, respectively, from the French (n=32) and American (n=3) T. asinigenitalis isolates. Thus, several different kinds of tandem repeat units and their combinations in IVSs in both regions within the gene were shown in 32 French isolates.

Molecular characterization of the sequences of the 16S-23S rDNA internal spacer region (ISR) from isolates of Taylorella asinigenitalis

Background

Sequence information on the 16S-23S rDNA internal spacer region (ISR) exhibits a large degree of sequence and length variation at both the genus and species levels. A primer pair for the amplification of 16S-23S rDNA ISR generated three amplicons for each of isolates of Taylorella asinigenitalis (UCD-1^T, UK-1 and UK-2).

Findings

Following TA cloning and sequencing, the three isolates of T. asinigenitalis were demonstrated to possess three ISR units of different lengths. Although the three corresponding ISRs (A, B and C) were identified to be identical to each other (UK-1 and UK-2 isolates), the ISRs shared approximately 95.3–98.9% nucleotide sequence similarities between the UCD-1^T and UK-1/-2 isolates. A typical order of two intercistronic tRNA genes (5'-tRNA^Ile-tRNA^Ala-3') with the different nucleotide spacers [44 through 51 base pairs (bp)] in length was identified among the isolates. The consensus sequences of the antiterminators of boxB and boxA were also identified in all ISRs. Thus, three ISRs were identified for each isolate, and therefore, at least three distinctly different ribosomal RNA operons were suggested to occur in the genome of T. asinigenitalis. This was also confirmed by Southern hybridization procedure.

Conclusion

The present study represents a dendrogram constructed based on the nucleotide sequence data of 16S-23S rDNA ISR for T. asinigenitalis, which may aid in the phylogenetic positioning of T. asinigenitalis within the genus Taylorella, and in the molecular discrimination of T. asinigenitalis.

The structure of the polysaccharide of the lipopolysaccharide produced by Taylorella equigenitalis type strain (ATCC 35865)

Taylorella equigenitalis is a Gram-negative bacterium that causes venereally transmitted contagious equine metritis (CEM), and its identification and differentiation from other bacteria and Taylorella species is an important requirement for the control of CEM infection. Based on the results of NMR and MS analysis, the antigenic O-polysaccharide (O-PS) component of the lipopolysaccharide (LPS) produced by the type strain T. equigenitalis (ATCC 35865) was found to be a linear polymer composed of a repeating disaccharide unit, containing partially amidated 2,3-diacetamido-2,3-dideoxy-alpha-L-guluronic and 2,3-diacetamido-2,3-dideoxy-beta-D-mannuronic acids, terminated with a 4-O-methylated non-reducing Gulp-NAc3NAcA residue, and has the structure [structure: see text]. The O-PS of the type strain T. equigenitalis LPS provides a specific antigenic marker for the discrimination of the pathogen from the related type strain of T. asinigenitalis sp. nov, a phenotypically indistinguishable non-pathogenic bacterium having a serologically and structurally unrelated LPS O-antigen. The analysis of a structurally unusual core oligosaccharide of the LPS is also reported.

Structure of the O-polysaccharide of the lipopolysaccharide produced by Taylorella asinigenitalis type strain (ATCC 700933)

Taylorella asinigenitalis sp. nov is a nonpathogenic gram-negative bacterium recently isolated from the genital tract of male donkeys. The bacterium is phenotypically indistinguishable from Taylorella equigenitalis, a pathogen that is the cause of contagious equine metritis, a highly communicable venereal disease of horses. The structural analysis of the lipopolysaccharide produced by T. asinigenitalis sp. nov (ATCC 700933) demonstrated that its O-polysaccharide (O-PS) component is a linear unbranched polymer of repeating disaccharide units composed of 1,3-linked pyranosyl residues of 2,4-diacetamido-2,4-dideoxy-beta-D-quinovose (bacillosamine) and 2-acetamidino-2-deoxy-beta-D-glucuronic acid, and has the structure [-->3)-beta-D-QuipNAc4NAc-(1-->3)-beta-D-GlcpNAmA-(1-->]n. The chemical structure and serological characteristics of the T. asinigenitalis O-PS are distinct from those of the O-PS of the T. equigenitalis type strain, thus providing a cell-surface target macromolecule that can be used to distinguish pathogenic from nonpathogenic Taylorella sp. clinical isolates.

Molecular characterization of the non-coding promoter and leader regions and full-length 16S ribosomal RNA (rRNA) gene ofTaylorella asinigenitalis

The 3,339 base pair (bp) sequences encoding a putative open reading frame (ORF), non-coding promoter and leader regions (approximately 320 bp), full-length 16S ribosomal RNA (rRNA) gene (approximate 1,540 bp) and part of the 16S-23S rDNA internal spacer region (ISR) were determined from genome DNA libraries of the Taylorella asinigenitalis (UK-1) isolate. The non-coding promoter and leader regions included antiterminators (boxB, boxA and boxC) immediately upstream of the 16S rRNA gene sequence. An approximately 680 bp region upstream of the non-coding promoter region appears to contain a putative ORF with high sequence similarity to GTP cyclohydrolase I. In addition, a typical order of intercistronic tRNA genes with the 48 nucleotide spacer of 5'-16S rDNA-tRNA(Ile)-tRNA(Ala)-23S rDNA-3' was demonstrated in a part of the 16S-23S rDNA ISR. The antiterminators of boxB and boxA were also identified in the ISR.A phylogenetic analysis based on the 16S rRNA gene sequence information clearly demonstrated that the five T. asinigenitalis isolates formed a cluster together with the three T. equigenitalis strains, more similar to Pelistega europaea than the other beta-Proteobacteria from the 13 species of 11 genera.

Molecular characterization of the full-length 23S and 5S ribosomal RNA (rRNA) genes of Taylorella asinigenitalis

An approximately 4.2 kbp region encoding 23S and 5S rRNA genes was identified when recombinant plasmid DNAs from two genomic DNA libraries and an inverse PCR product of Taylorella asinigenitalis UK-1 isolate were analyzed. Full-length genes of 23S rRNA (3,225 bp) and 5S rRNA (117 bp) of T. asinigenitalis are described. The present sequence analysis identified a non-coding hypothetically intrinsic transcription terminator region downstream of the 5S rRNA gene. The sequence, however, downstream of the 5S rRNA gene did not show any distal tRNA genes. Surprisingly, an intervening sequence (IVS) of 270 bp in length, including two specific tandem repeat units of 80 bp and one partial unit of 48 bp with unknown functions was identified in the first quarter of the 23S rRNA gene sequence. A second IVS of 70 bp in length was also identified in the central region of the 23S rRNA gene. In addition, by using PCR and sequencing procedures, two T. asinigenitalis isolates, UK-1 and UK-2, carried multiple IVSs in the first quarter and central regions. Moreover, the 23S rRNA fragmentation occurred in the UK-1 isolate. A phylogenetic analysis was first carried out based on the 23S rRNA sequence data from T. asinigenitalis UK-1 and 13 other beta-Proteobacteria. This is the first report of IVSs in the 23S rRNA gene from the beta-Proteobacteria.

Identification of Taylorella equigenitalis responsible for contagious equine metritis in equine genital swabs by direct polymerase chain reaction

A direct-PCR assay was developed for the rapid detection of Taylorella equigenitalis, a Gram-negative bacterium responsible for contagious equine metritis (CEM) in Equidae. The bacteria may be detected in equine genital swabs without need for a preliminary step of DNA extraction or bacterial isolation. Specificity was determined with 125 isolates of T. equigenitalis, 24 isolates of Taylorella asinigenitalis, five commensal bacteria of the genital tract and a facultative intracellular pathogen of foals found in large concentration in soil. Our PCR is specific and amplified a 413-bp 16S ribosomal DNA product only in all T. equigenitalis.

Nucleotide Sequencing and Analysis of 16S rDNA and 16S-23S rDNA Internal Spacer Region (ISR) of Taylorella equigenitalis, as an Important Pathogen for Contagious Equine Metritis (CEM)

The primer set for 16S rDNA amplified an amplicon of about 1500 bp in length for three strains of Taylorella equigenitalis (NCTC11184(T), Kentucky188 and EQ59). Sequence differences of the 16S rDNA among the six sequences, including three reference sequences, occurred at only a few nucleotide positions and thus, an extremely high sequence similarity of the 16S rDNA was first demonstrated among the six sequences. In addition, the primer set for 16S-23S rDNA internal spacer region (ISR) amplified two amplicons about 1300 bp and 1200 bp in length for the three strains. The ISRs were estimated to be about 920 bp in length for large ISR-A and about 830 bp for small ISR-B. Sequence alignment of the ISR-A and ISR-B demonstrated about 10 base differences between NCTC11184(T) and EQ59 and between Kentucky188 and EQ59. However, only minor sequence differences were demonstrated between the ISR-A and ISR-B from NCTC11184(T) and Kentucky188, respectively. A typical order of the intercistronic tRNAs with the 29 nucleotide spacer of 5'-16S rDNA-tRNA(Ile)-tRNA(Ala)-23S rDNA-3' was demonstrated in the all ISRs. The ISRs may be useful for the discrimination amongst isolates of T. equigenitalis if sequencing is employed.

Homogeneity of the 16S rDNA sequence among geographically disparate isolates of Taylorella equigenitalis

Background

At present, six accessible sequences of 16S rDNA from Taylorella equigenitalis (T. equigenitalis) are available, whose sequence differences occur at a few nucleotide positions. Thus it is important to determine these sequences from additional strains in other countries, if possible, in order to clarify any anomalies regarding 16S rDNA sequence heterogeneity. Here, we clone and sequence the approximate full-length 16S rDNA from additional strains of T. equigenitalis isolated in Japan, Australia and France and compare these sequences to the existing published sequences.

Results

Clarification of any anomalies regarding 16S rDNA sequence heterogeneity of T. equigenitalis was carried out. When cloning, sequencing and comparison of the approximate full-length 16S rDNA from 17 strains of T. equigenitalis isolated in Japan, Australia and France, nucleotide sequence differences were demonstrated at the six loci in the 1,469 nucleotide sequence. Moreover, 12 polymorphic sites occurred among 23 sequences of the 16S rDNA, including the six reference sequences.

Conclusion

High sequence similarity (99.5% or more) was observed throughout, except from nucleotide positions 138 to 501 where substitutions and deletions were noted.