Evolution of the ST2250 Clone in Northeastern Thailand Is Linked with the Acquisition of Livestock-Associated Staphylococcal Genes.

is a newly named species previously described as a divergent lineage of that has recently been shown to have a global distribution. Despite growing evidence of the clinical importance of this species, knowledge about its population epidemiology and genomic architecture is limited. We used whole-genome sequencing to evaluate and compare ( = 251) and ( = 68) isolates from adults with staphylococcal sepsis at several hospitals in northeastern Thailand between 2006 and 2013. The majority (82%) of the isolates were of multilocus sequence type 2250 (ST2250). was more diverse, although 43% of the isolates belonged to ST121. Bayesian analysis suggested an ST2250 substitution rate of 4.66 (95% confidence interval [CI], 3.12 to 6.38) mutations per genome per year, which was comparable to the ST121 substitution rate of 4.07 (95% CI, 2.61 to 5.55). ST2250 emerged in Thailand an estimated 15 years ago, which contrasts with the ST1, ST88, and ST121 clades that emerged around 100 to 150 years ago. Comparison of ST2250 genomes from Thailand and a global collection indicated a single introduction into Thailand, followed by transmission to local and more distant countries in Southeast Asia and further afield. and shared around half of their core gene repertoire, indicating a high level of divergence and providing strong support for their classification as separate species. Several gene clusters were present in ST2250 isolates but absent from the other and study isolates. These included multiple exotoxins and antibiotic resistance genes that have been linked previously with livestock-associated , consistent with a livestock reservoir for These genes appeared to be associated with plasmids and mobile genetic elements and may have contributed to the biological success of ST2250. In this study, we used whole-genome sequencing to understand the genome evolution and population structure of a systematic collection of ST2250 isolates. A newly identified ancestral species of , has become increasingly known as a clinically important species that has been reported recently across various countries. Our results indicate that has spread at a relatively rapid pace over the past 2 decades across northeastern Thailand and acquired multiple exotoxin and antibiotic resistance genes that have been linked previously with livestock-associated Our findings highlight the clinical importance and potential pathogenicity of as a recently emerging pathogen.