中文摘要：

为进一步致弱胸膜肺炎放线杆菌（APP）毒力，制备基因缺失弱毒疫苗，本研究以本实验室构建的APP血清7型S8菌株双基因缺失株S8ΔclpP/ΔapxⅡC为亲本株，通过同源重组和蔗糖负向筛选的方法，再将铁摄取调节基因fur缺失，构建了无抗生素标记的三基因缺失突变株S8ΔclpP/ΔapxⅡC/Δfur。生物学特性研究表明，该缺失株与野生株S8相比，体外生长速度未发生明显变化，但溶血能力显著下降，与亲本株相比，铁摄取利用轻微降低。致病力试验结果表明，仔猪经气管接种该缺失株毒力显著低于野生型菌株，并且1×10^9 cfu/mL剂量对猪不产生明显的呼吸道症状和肺部病变，表明该缺失株高度安全，可以作为APP基因缺失弱毒活疫苗的候选株。

英文摘要：

Actinobacillus pleuropneumoniae is the etiological agent of porcine pleuropneumonia. To further attenuated the virulence of A.pleuropneumoniae, the S8ΔclpP/ΔapxⅡC/Δfur triple-deletion mutant was constructed by deletion of the iron uptake regulator fur gene based on the S8ΔclpP/ΔapxⅡC double-deletion mutant of A.pleuropneumoniae serotype 7, using homologous recombination and sucrose counter-selection. The identification results showed that the growth rate and ability to take up iron of the triple-deletion mutant did not significantly changed, but the hemolytic had obviously decreased compared to the wild-type strain. The virulence of the triple-deletion mutant was similar to the parental strain which was unable to cause respiratory symptoms and lung lesions by tracheal artificial infection with a dose of 1×10^9 cfu/mL in pigs, indicating that the triple-deletion mutant strain is high safety and might be used as a promising live attenuated vaccine candidate against A.pleuropneumoniae infection.