Bacterial mastitis in dairy cattle is caused by various bacteria, including major pathogens like Staphylococcus aureus, Streptococcus agalactiae, and Escherichia coli, and environmental pathogens such as Streptococcus uberis and Klebsiella spp. These bacteria can be categorized as contagious pathogens (spread from cow to cow, e.g., S. aureus) or environmental pathogens (from the environment, e.g., E. coli, Streptococcus uberis, and Klebsiella spp.).