Genetic homogeneity of Taylorella equigenitalis from Norwegian trotting horses revealed by chromosomal DNA fingerprinting

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.

Genomic diversity of Taylorella equigenitalis introduced into the United States from 1978 to 2012

Contagious equine metritis is a disease of worldwide concern in equids. The United States is considered to be free of the disease although sporadic outbreaks have occurred over the last few decades that were thought to be associated with the importation of horses. The objective of this study was to create finished, reference quality genomes that characterize the diversity of Taylorella equigenitalis isolates introduced into the USA, and identify their differences. Five isolates of T. equigenitalis associated with introductions into the USA from unique sources were sequenced using both short and long read chemistries allowing for complete assembly and annotation. These sequences were compared to previously published genomes as well as the short read sequences of the 200 isolates in the National Veterinary Services Laboratories' diagnostic repository to identify unique regions and genes, potential virulence factors, and characterize diversity. The 5 genomes varied in size by up to 100,000 base pairs, but averaged 1.68 megabases. The majority of that diversity in size can be explained by repeat regions and 4 main regions of difference, which ranged in size from 15,000 to 45,000 base pairs. The first region of difference contained mostly hypothetical proteins, the second contained the CRISPR, the third contained primarily hemagglutinin proteins, and the fourth contained primarily segments of a type IV secretion system. As expected and previously reported, little evidence of recombination was found within these genomes. Several additional areas of interest were also observed including a mechanism for streptomycin resistance and other virulence factors. A SNP distance comparison of the T. equigenitalis isolates and Mycobacterium tuberculosis complex (MTBC) showed that relatively, T. equigenitalis was a more diverse species than the entirety of MTBC.

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

In the present review article, recent molecular advances relating to studies with Taylorella equigenitalis, as well as the recently described second species of the genus Taylorella, namely Taylorella asinigenitalis, have been described. Molecular genotyping of T. equigenitalis strains by pulsed-field gel electrophoresis (PFGE) after digestion with the suitable restriction enzyme(s) enabled the effective discrimination of strains, thus allowing the examination of the scientific mechanism(s) for its occurrence and transmission of contagious equine metritis (CEM). Alternatively, polymerase chain reaction (PCR) amplification and nucleotide sequencing of the 16S ribosomal DNA sequence and/or the other species specific sequence(s) as targets were confirmed to be effective for identification of T. equigenitalis. These new analytical methods at the genomic DNA level also enabled the discrimination of the newly discovered donkey-related T. asinigenitalis from T. equigenitalis, and moreover, the performance of phylogenetic analysis of genus Taylorella organisms with other closely related genera. Furthermore, detailed analysis of the genes responsible for CEM within the T. equigenitalis genome would be useful to help elucidate the pathogenic virulence and transmission mechanisms associated with the important equine pathogen associated with CEM.

Clinical, bacteriologic, serologic, and pathologic features of infections with atypical Taylorella equigenitalis in mares

OBJECTIVE

To characterize clinical, serologic, bacteriologic, cytologic, and pathologic endometrial responses of mares to 2 donkey-origin atypical bacterial isolates resembling Taylorella equigenitalis.

DESIGN

Prospective in vivo study.

ANIMALS

10 healthy mares.

PROCEDURE

Mares in estrus (2/group) were inoculated by intrauterine infusion with 2 isolates of classic T equigenitalis or 2 isolates of atypical Taylorella sp or were sham-inoculated. Bacteriologic, serologic, clinical, uterine, cytologic, and pathologic endometrial responses were assessed 4, 11, 21, 35, and 63 days after inoculation and on day 111 in mares with positive culture results on day 63.

RESULTS

One atypical isolate failed to cause infection. The second atypical isolate and both classic T equigenitalis isolates induced similar transient metritis and cervicitis. Both classic isolates and 1 atypical isolate induced anti-T equigenitalis complement-fixing antibodies detectable at day 11. Classic isolates and an atypical isolate provoked intense neutrophilic endometritis followed by a resolving, subacute, neutrophilic-mononuclear endometrial response. The atypical isolate and classic isolates were recovered from the uterus, clitoral fossa, or clitoral sinus of one or both exposed mares for as long as 111 days.

CONCLUSIONS AND CLINICAL RELEVANCE

Atypical Taylorella sp infections should be considered as a differential diagnosis of equine infertility in US-origin mares, even those not exposed to stallions from countries where contagious equine metritis occurs. The origins and prevalence of atypical Taylorella sp infection in US horses and donkeys are undetermined.

Profiles of fragments after pulsed-field gel electrophoresis of cleaved genomic DNA from strains of Taylorella equigenitalis isolated from horses in Norway

The genomic DNA of eight strains of Taylorella equigenitalis, isolated from seven Norwegian Trotters and a Norwegian pony with contagious equine metritis in Norway, was examined by pulsed-field gel electrophoresis after separate digestions with two restriction enzymes, namely, ApaI and NotI. The respective electrophoretic profiles of the fragments were essentially identical but differed from those of T. equigenitalis NCTC11184T and Kentucky 188. They also exhibited slight differences from profiles obtained from Japanese isolates. These results may possibly suggest a common genotype and a common source of infection for all these eight isolates in Norway.