Abstract: Twenty field strains of Actinobacillus pleuropneumoniae (APP) were isolated from lung, tonsils and trachea in 85 pigs with sever pleuropneumonia in different districts of Shandong Province. Slide agglutination test and PCR were used to determine their serotype and Apx toxins type, respectively. The results of slideagglutination test indicated that there were 5 serotypes among the 20 field strains, serotype 7(6/20) and serotype 5 (5/20) were the dominant, the other serotypes were serotype 3(4/20), serotype 4(3/20) and serotype 8(2/20). The PCR results indicated that there were four kinds of Apx toxins in the 20 field strains，among them，serotype 3, 4, 8 contain ApxⅡ, ApxⅢ and ApxⅣ，serotype 5 contains ApxⅠ, ApxⅡand ApxⅣ, serotype 7 contains ApxⅡ and ApxⅣ, ApxⅡ and ApxⅣ existed in all the 20 field strains. The results of Apx sequence analysis indicated that the homogeneity of Apx gene was 99.5%－100% in different serotype APP if they had the same type of Apx. The pathogenicity was different when mice inoculated with APP which contain different Apx, serotype 5 APP was very virulent, for it contains ApxI and ApxⅡ. This study has established the foundation for control Porcine infectious pleuropneumonia in immune prevention, subunit vaccine and PCR diagnosis based on ApxⅣ gene.

Key words: Actinobacillus pleuropneumoniae, Porcine infectious Pleuropneumonia, Serotype, Apx toxin type