**1. Introduction**

Bovine mastitis is one of the most important bacterial diseases of dairy cattle throughout the world. Mastitis is responsible for major economic losses to the dairy producer and milk processing industry resulting from reduced milk production, alterations in milk composition, discarded milk, increased replacement costs, extra labor, treatment costs, and veterinary services [1]. Annual economic losses due to bovine mastitis are estimated to be \$2 billion in the United States [2], \$400 million in Canada (Canadian Bovine Mastitis and Milk Quality Research Network-CBMQRN), and \$130 million in Australia [3]. Many factors including host, pathogen, and environmental factors influence the development of mastitis; however, inflammation of the mammary gland is usually a consequence of adhesion, invasion, and colonization of the mammary gland by one or more contagious (*Staphylococcus aureus*, *Streptocococcus agalactiae*, *Corynebacterium bovis*, *Mycoplasmsa bovis*, etc.) or environmental (coliform bacteria, environmental *Streptococcus* spp. and some coagulase negative *Staphylococcus* spp., many other minor pathogens) mastitis pathogens.
