Right answer is (a) Streptococcus agaiactiae and Staphylococcus aureaus
Explanation: A total of 137 microbial species, subspecies and serovars have been isolated from the bovine mammary gland. Nucleic acid hybridization studies have restructured the classification of many mastitis pathogens. Streptococcus agaiactiae and Staphylococcus aureaus are two most important etiologic agents of mastitis.