Development of a Staphylococcus aureus vaccine against mastitis in dairy cows. I. Challenge trials.

A vaccine composed of three field isolates of Staphylococcus aureus (S. aureus) derived from cases of mastitis in cows was developed. The vaccine was administered to nine uninfected cows while 10 other cows were used as controls. All cows were challenged with a highly virulent S. aureus strain administered into two quarters of each cow. Quarters were tested for clinical signs, secretion of S. aureus, and somatic cell count (SCC). No systemic effects were observed in any of the cows, vaccinated or control. Vaccinated cows had 70% protection from infection compared with fewer than 10% in the controls. Moreover, all quarters challenged in the vaccinated cows, regardless of whether they were successfully infected or not with S. aureus, exhibited very mild inflammatory reactions, identified by their low SCCs (<100,000).