Vaccination with the plasminogen activator from Streptococcus uberis induces an inhibitory response and protects against experimental infection in the dairy cow.

Two antigens comprising either concentrated culture filtrate containing the plasminogen activator, PauA (total antigen) or the same preparation from which PauA had been selectively removed by incubation with a PauA-specific monoclonal antibody and immobilisation on Protein-G agarose (depleted antigen) were combined with either Freund's incomplete adjuvant (FIA) or a commercially used adjuvant (SB62) and used to vaccinate dairy cows by a subcutaneous route. Immunisation of four animals with depleted antigen combined with FIA conferred no protection to mastitis following intramammary challenge with S. uberis 0140J. However, immunisation of two groups of four animals with the total antigen combined with either FIA or SB62 induced protection in 3 out of 8 and 5 out of 8 similarly challenged quarters, respectively. Protection corresponded to the production of an inhibitory antibody response to PauA.