Ward C K, Inzana T J
Center for Molecular Medicine and Infectious Diseases, Virginia-Maryland Regional College of Veterinary Medicine, Virginia Polytechnic Institute and State University, Blacksburg 24061-0342, USA.
Infect Immun. 1997 Jun;65(6):2491-6. doi: 10.1128/iai.65.6.2491-2496.1997.
Actinobacillus pleuropneumoniae synthesizes a serotype-specific capsular polysaccharide that acts as a protective barrier to phagocytosis and complement-mediated killing. To begin understanding the role of A. pleuropneumoniae capsule in virulence, we sought to identify the genes involved in capsular polysaccharide export and biosynthesis. A 5.3-kb XbaI fragment of A. pleuropneumoniae serotype 5a J45 genomic DNA that hybridized with DNA probes specific for the Haemophilus influenzae type b cap export region was cloned and sequenced. This A. pleuropneumoniae DNA fragment encoded four open reading frames, designated cpxDCBA. The nucleotide and predicted amino acid sequences of cpxDCBA contained a high degree of homology to the capsule export genes of H. influenzae type b bexDCBA, Neisseria meningitidis group B ctrABCD, and, to a lesser extent, Escherichia coli K1 and K5 kpsE and kpsMT. When present in trans, the cpxDCBA gene cluster complemented kpsM::TnphoA or kpsT::TnphoA mutations, determined by enzyme immunoassay and by restored sensitivity to a K5-specific bacteriophage. A cpxCB probe hybridized to genomic DNA from all A. pleuropneumoniae serotypes tested, indicating that this DNA was conserved among serotypes. These data suggest that A. pleuropneumoniae produces a group II family capsule similar to those of related mucosal pathogens.
胸膜肺炎放线杆菌合成一种血清型特异性荚膜多糖，它作为吞噬作用和补体介导杀伤的保护屏障。为了开始了解胸膜肺炎放线杆菌荚膜在毒力中的作用，我们试图鉴定参与荚膜多糖输出和生物合成的基因。与b型流感嗜血杆菌帽输出区域特异性DNA探针杂交的胸膜肺炎放线杆菌血清型5a J45基因组DNA的一个5.3kb XbaI片段被克隆并测序。这个胸膜肺炎放线杆菌DNA片段编码四个开放阅读框，命名为cpxDCBA。cpxDCBA的核苷酸和预测氨基酸序列与b型流感嗜血杆菌bexDCBA、B群脑膜炎奈瑟菌ctrABCD的荚膜输出基因高度同源，在较小程度上与大肠杆菌K1和K5的kpsE和kpsMT同源。当以反式存在时，cpxDCBA基因簇通过酶免疫测定和对K5特异性噬菌体恢复的敏感性来互补kpsM::TnphoA或kpsT::TnphoA突变。一个cpxCB探针与所有测试的胸膜肺炎放线杆菌血清型的基因组DNA杂交，表明该DNA在血清型之间是保守的。这些数据表明胸膜肺炎放线杆菌产生一种与相关黏膜病原体相似的II族家族荚膜。
