S100A4 and Bovine mastitis: In this study, protein expression of GPX4 was decreased in K. pneumoniae infected bMECs; meanwhile, expression of S100A4, a ferroptosis-related protein that paralleled GPX4, and ACSL4 was decreased in K. pneumoniae-infected bMECs, suggesting that K. pneumoniae induced ferroptosis in bMECs. The ferroptosis induced by K. pneumoniae may aggravate bovine mastitis, as ferroptosis can regulate the inflammatory microenvironment through metabolic changes or secretion of related substances between microorganisms and host cells [33, 34].