Core genome multilocus sequence typing analysis of Finnish Taylorella equigenitalis isolates

In Finland, Taylorella equigenitalis, the causative agent of contagious equine metritis (CEM), was first detected in 1992. The aim of this study was to genotype Finnish T. equigenitalis isolates to investigate the epidemiology of the infection in the Finnish horse population. A total of 34 T. equigenitalis isolates from 24 horses obtained during 1992-2021 were subjected to whole genome sequencing (WGS) and subsequent local ad hoc core genome multi-locus sequence typing (cgMLST) targeting 1259 loci. Classical MLST profiles were extracted from the whole-genome sequence data. Three novel MLST types, ST81, ST82 and ST83, and four previously described sequence types, ST16, ST17, ST50 and ST63 were detected among the isolates. cgMLST minimum spanning tree analysis using 12 allele difference as threshold, resulted in five clusters and three singletons. cgMLST clusters were congruent with the MLST-defined groups, except for the ST83 isolates which were divided into two clusters. However, the high discriminatory power cgMLST allowed differentiation between isolates of the same MLST type as each isolate had a unique core genome ST. Our study suggests that cgMLST has the prospective for being a standardised typing method for T. equigenitalis in the future, and further contributes to worldwide phylogenetic and spatio-temporal analyses needed to better understand the epidemiology of the bacterium.