We detected three major genetic events along the evolutionary history of ST9: the loss of the IEC genes (scn, chp, and sak), which were reported to contribute to virulence in human infections, the acquisition of the SaPIbov4-like element-encoding vwb gene, which is an animal-specific virulence factor responsible for the clotting of animal plasma, and the acquisition of antibiotic resistance genes, including SCCmec, QRDR mutations and the MDRST9 genetic elements. The gene discussed is PLK4; the disease is infection.