Abstract: Abstract: Sreptococcus equi subsp zooepidemicus causes swine diseases in China and had made substantial economic losses in recent years. To evaluate the antigenic variability among the 10 local isolated Sreptococcus equi subsp zooepidemicus of pig origin , inbred 12-week-old ICR mice were immunized with formalin-inactivated whole bacterium cell in complete Freund’s adjuvant of the 10 local isolated strains respectively ，which were followed by a similar doses emulsifield in incomplete Freund’s adjuvant four weeks later .10 groups of vaccinated mice and control group mice were challenged two weeks later with 5 LD 50 homogenous strains given intraperitoneally in a dose volume of 0.1 mL, another 10 groups mice were challenged with 1.6×10 5CFU of an 18 h THB culture of Sreptococcus equi subsp zooepidemicus ATCC35246 strain. The results showed that the immunized mice were protected after homogenous strain challenges with 90 pecent protection and shared 80 percent protection against challenge by ATCC35246.

Key words: Sreptococcus equi subsp zooepidemicus, Isolate strain, immunization