Groupe de Recherche sur les Maladies Infectieuses du Porc (GREMIP) and Centre de Recherche en Infectiologie Porcine (CRIP), Université de Montréal, Faculté de Médecine Vétérinaire, C.P. 5000, Saint-Hyacinthe, Québec, Canada J2S 7C6.
Infect Immun. 2010 Dec;78(12):5324-31. doi: 10.1128/IAI.00452-10. Epub 2010 Oct 4.
Avian pathogenic Escherichia coli (APEC) strains are associated with respiratory infections, septicemia, cellulitis, peritonitis, and other conditions, since colibacillosis manifests in many ways. The Pho regulon is jointly controlled by the two-component regulatory system PhoBR and by the phosphate-specific transport (Pst) system. To determine the specific roles of the PhoBR regulon and the Pst system in the pathogenesis of the APEC O78 strain χ7122, different phoBR and pst mutant strains were tested in vivo in chickens and in vitro for virulence traits. Mutations resulting in constitutive activation of the Pho regulon rendered strains more sensitive than the wild type to hydrogen peroxide and to the bactericidal effects of rabbit serum. In addition, production of type 1 fimbriae was also impaired in these strains. Using a chicken competitive infection model, all PhoB constitutive mutants were outcompeted by the wild-type parent, including strains containing a functional Pst system. Cumulative inactivation of the Pst system and the PhoB regulator resulted in a restoration of virulence. In addition, loss of the PhoB regulator alone did not affect virulence in the chicken infection model. Interestingly, the level of attenuation of the mutant strains correlated directly with the level of activation of the Pho regulon. Overall, results indicate that activation of the Pho regulon rather than phosphate transport by the Pst system plays a major role in the attenuation of the APEC O78 strain χ7122.
禽致病性大肠杆菌（APEC）菌株与呼吸道感染、败血症、蜂窝织炎、腹膜炎和其他疾病有关，因为大肠杆菌病有多种表现形式。Pho 调控子由双组分调控系统 PhoBR 和磷酸盐特异性转运（Pst）系统共同控制。为了确定 PhoBR 调控子和 Pst 系统在 APEC O78 菌株 χ7122 发病机制中的具体作用，在鸡体内和体外测试了不同的 phoBR 和 pst 突变株的毒力特性。导致 Pho 调控子组成性激活的突变使菌株对过氧化氢和兔血清的杀菌作用比野生型更敏感。此外，这些菌株的 1 型菌毛的产生也受到了损害。使用鸡竞争性感染模型，所有 PhoB 组成型突变体均被野生型亲本竞争淘汰，包括含有功能 Pst 系统的菌株。Pst 系统和 PhoB 调节剂的累积失活导致毒力恢复。此外，单独丧失 PhoB 调节剂在鸡感染模型中并不影响毒力。有趣的是，突变株的衰减程度与 Pho 调控子的激活程度直接相关。总体而言，结果表明 Pho 调控子的激活而不是 Pst 系统的磷酸盐转运在 APEC O78 菌株 χ7122 的衰减中起着主要作用。
