show Abstracthide AbstractStreptococcus equi subsp. equi (SEE) is a host-restricted pathogen of horses considered to have evolved from Streptococcus equi subsp. zooepidemicus (SEZ). SEZ is promiscuous in its host range, and is commonly recovered from horses as a commensal. Comparison of a single strain of SEE with a single strain of SEZ using whole genome sequencing, supplemented by quantitative PCR for additional screening of SEE and SEZ strains of select genes these techniques were used to define characteristics that shaped the evolution of SEE. Because of the known genetic variability of SEZ, comparisons of the whole genomes of multiple SEE and SEZ is warranted. To fill this knowledge-gap, we utilized whole genome sequencing to characterize the accessory genome elements and methylomes of 50 SEE and 50 SEZ isolates from Texas.