Phylogenetic Relationships of the B. mallei Strain that Caused the 2023 Equine Glanders Outbreak in the Trans-Baikal Territory

The aim of the study was to determine the phylogeographic and phenotypic characteristics of the Burkholderia mallei that caused an outbreak of equine glanders in the Trans-Baikal Territory in 2023. Materials and methods. The B. mallei culture was isolated from section material according to Methodological Regulations 4.2.3744-22. Phenotypic characteristics were investigated bacteriologically and using the VITEK®2 GN. Analysis of the B. mallei genomes from public databases was performed using the PubMLST, NGphylogeny, and iTOL v6 resources. Results and discussion . Strains of B. mallei 16050 and 15747, isolated from the horse affected by glanders, identified using PCR, differed in morphological features, but had identical atypical biochemical profiles which lead to misidentification by VITEK®2 GN system as Sphingomonas paucimobillis . Shotgun analysis of the whole genome sequences confirmed the identity of those strains; a subsequent study was performed using a higher quality sequence of B. mallei strain 16050. Phylogenetic analysis based on the results of cgMLST showed the inclusion of the strain B. mallei 16050 in a separate cluster, grouped near the cluster of 5 strains, three of which (B-120, Ц-5, Ц-4) are reliably of Mongolian origin, the other two strains (Z-12 and 10230) have high similarity to Mongolian strains which is demonstrated in the current work. It has been revealed that 87 loci of the strain 16050 have new alleles, which can serve as a marker in genomic surveillance and investigation of imported cases of glanders. The data obtained allow us to assume with a high degree of probability that the outbreak of equine glanders in Chita in 2023 was caused by a strain of Mongolian origin.