| Summary |
A selection of a seed strain for development of Actinobacillus pleuropneumoniae (Ap) vaccine was made from 4 type strains and 21 field strains. Among 25 strains, 21 strains were smooth type, 2 were rough type and 2 were mucus type according colony morphology. The criteria of the selection were based on the secretion of ApxI toxin, since it was one of the major factors of pathogenesis, and on colony morphology. The detection of ApxI toxin was made by immnoblotting test and hemolytic test. The distribution of titer by immnoblotting test and hemolytic test were from negative to 1：256 and from negative to 1：32, respectively. It was coordinated with the hemolytic zone appeared in blood agar cultured. The seed strain selected was a field isolate in 1997 with titer of 1：256 and 1：32 tested by above tests.The cytotoxin contained in culture supernatant of Actinobacillus pleuropneumoniae serotype 1 was concentrated by salting out of ammonium sulfate. The amounts of cytotoxin were lost less than 10% after concentration process when measured by immuno-blotting assay. However, the biological activity of cytotoxin was decreased greatly for more then 90% when detected by hemolytic test. The physical properties, purity, sterility, and safety of prepared inactivated vaccine with addition of a commercialized oil adjuvant were all fit the national corresponding regulation. The evaluation of protective efficacy of prepared bacterin was done by mice protection test. The protective index was 1.41 and the inactivated vaccine was proved to be effective.
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