Molecular evolution of Salmonella enterica subsp. enterica serovar Gallinarum biovar Gallinarum in the field

•Korean Salmonella biovar Gallinarum (SG) extended polyproline linker (PPL) of SpvB.•Korean SG isolates share specific pseudogenes and constitute an unique cluster.•Early outbreaks of fowl typhoid in Korea was caused by two highly related subgroups.•Korean SG evolved to 10 subgroups by changing PPL length and pseudogene acquisition.