Mastitis is considered to be the most costly disease affecting the dairy industry with annual losses in the United States exceeding $2 billion (Philpot, 1984). Losses stem from milk discard, drug costs, veterinary care, increased labor, and premature- culling. Staphylococcus aureus is one of the most important pathogens causing intramammary infections in dairy cattle (Gonzalez et al.,1988) and continues to be one of the major causes of mastitis in dairy herds worldwide (Barkema et al. 1998, Gonzalez et al. 1988, Nickerson et al. 1999, Osteras et al. 1999, Sol et al.