Nika Joseph R, Latimer Jo L, Ward Christine K, Blick Robert J, Wagner Nikki J, Cope Leslie D, Mahairas Gregory G, Munson Robert S, Hansen Eric J
Department of Microbiology, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA.
Infect Immun. 2002 Jun;70(6):2965-75. doi: 10.1128/IAI.70.6.2965-2975.2002.
Haemophilus ducreyi, the etiologic agent of chancroid, has been shown to form microcolonies when cultured in the presence of human foreskin fibroblasts. We identified a 15-gene cluster in H. ducreyi that encoded predicted protein products with significant homology to those encoded by the tad (for tight adhesion) locus in Actinobacillus actinomycetemcomitans that is involved in the production of fimbriae by this periodontal pathogen. The first three open reading frames in this H. ducreyi gene cluster encoded predicted proteins with a high degree of identity to the Flp (fimbria-like protein) encoded by the first open reading frame of the tad locus; this 15-gene cluster in H. ducreyi was designated flp. RT-PCR analysis indicated that the H. ducreyi flp gene cluster was likely to be a polycistronic operon. Mutations within the flp gene cluster resulted in an inability to form microcolonies in the presence of human foreskin fibroblasts. In addition, the same mutants were defective in the ability to attach to both plastic and human foreskin fibroblasts in vitro. An H. ducreyi mutant with an inactivated tadA gene exhibited a small decrease in virulence in the temperature-dependent rabbit model for experimental chancroid, whereas another H. ducreyi mutant with inactivated flp-1 and flp-2 genes was as virulent as the wild-type parent strain. These results indicate that the flp gene cluster is essential for microcolony formation by H. ducreyi, whereas this phenotypic trait is not linked to the virulence potential of the pathogen, at least in this animal model of infection.
软下疳的病原体杜克雷嗜血杆菌已被证明，在人包皮成纤维细胞存在的情况下培养时会形成微菌落。我们在杜克雷嗜血杆菌中鉴定出一个15个基因的簇，其编码的预测蛋白产物与伴放线放线杆菌中参与该牙周病原体菌毛产生的tad（紧密黏附）位点编码的蛋白产物具有显著同源性。杜克雷嗜血杆菌这个基因簇中的前三个开放阅读框编码的预测蛋白与tad位点第一个开放阅读框编码的Flp（菌毛样蛋白）具有高度同一性；杜克雷嗜血杆菌中的这个15个基因的簇被命名为flp。逆转录聚合酶链反应分析表明，杜克雷嗜血杆菌flp基因簇可能是一个多顺反子操纵子。flp基因簇内的突变导致在人包皮成纤维细胞存在时无法形成微菌落。此外，相同的突变体在体外附着于塑料和人包皮成纤维细胞的能力上存在缺陷。一个tadA基因失活的杜克雷嗜血杆菌突变体在温度依赖性兔实验性软下疳模型中的毒力略有下降，而另一个flp - 1和flp - 2基因失活的杜克雷嗜血杆菌突变体与野生型亲本菌株的毒力相同。这些结果表明，flp基因簇对杜克雷嗜血杆菌形成微菌落至关重要，而这种表型特征与该病原体的毒力潜力无关，至少在这个动物感染模型中是这样。
