To evaluate the immunoprotection of Streptococcus agalactiae pilus island fusion protein AP1-AP2, AP1-BP,BP-AP2 and AP1-BP-AP2 in BALB/c mice, the groups of mice were immunized with the 4 kinds of fusion antigens emulsified with Freund's adjuvant, respectively, at dose of 50μg/mouse for 4 times. Then, the antibody titers were detected after the 4 th immunization and the antibody titer in mice immunized with AP1-BP-AP2 fusion antigen was the highest, up to 1 ∶25,600. The mice were challenged with clinical is...