The GapC plasmin binding protein genes of Streptococcus dysgalactiae (S. dysgalactiae), Streptococcus agalactiae (S. agalactiae), Streptococcus uberis (S. uberis), Streptococcus parauberis (S. parauberis), and Streptococcus iniae (S. iniae) are described, as well as the recombinant production of the GapC proteins therefrom. Also described is the use of the GapC proteins from those species in vaccine compositions to prevent or treat bacterial infections in general, and mastitis in particular.