Staphylococcus aureus (S. aureus) is a gram positive aerobic bacterium which causes several diseases in humans as well as animals (cows, buffaloes and goat). S. aureus represents a major agent of contagious bovine mastitis, a serious disease of livestock resulting in both reduced milk production and quality. Persistent mastitis in livestock caused by S. aureus gives rise to economic losses. In mastitis, the main reservoir for S. aureus is the infected udder, once infection is established, S. aureus colonizes in the mammary gland and destroys cell membranes and damages milk-producing tissue. S. aureus is widely distributed in nature. It can colonize and infect both healthy, immunologically competent people in the community and hospitalized patients with decreased host defenses. S. aureus is the major pathogen of hospital acquired infections.