Characterization of the Role of the Pathogenicity Island and vapG in the Virulence of the Intracellular Actinomycete Pathogen Rhodococcus equi
Characterization of the Role of the Pathogenicity Island and vapG in the Virulence of the Intracellular Actinomycete Pathogen Rhodococcus equi
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DOI：
10.1128/iai.00081-10
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发表时间：
2010-08-01
影响因子：
3.1
通讯作者：
Hondalus, Mary K.
中科院分区：
文献类型：
--
作者：
Coulson, Garry B.;Agarwal, Shruti;Hondalus, Mary K.
马红球菌是巨噬细胞的兼性细胞内病原体，可在幼马驹和患有潜在免疫缺陷的人中引起严重的、危及生命的肺炎。马罗氏菌毒力依赖于一个大毒力质粒的存在，该质粒含有一个致病岛（PAI），编码一个新的表面定位和分泌蛋白家族，其功能很大程度上未知，称为毒力相关蛋白（VapACDEFGHI）。迄今为止，vapA 及其正调节因子 virR 和 orf8 是唯一通过实验确定的位于毒力质粒上的毒力基因。在这项研究中，构建了 PAI 缺失突变体，并且正如预期的那样，由于缺乏 vapA 表达，该突变体在巨噬细胞和小鼠中的生长均减弱。 PAI 突变体中 vapA 从组成型启动子表达，从而消除了对 PAI 编码的 vapA 调节因子的需求，导致体内细菌清除延迟，但未恢复全部毒力，表明额外的毒力基因确实位于删除的致病性岛区域内。根据之前的报道，表明 PAI 携带的基因 vapG 在巨噬细胞和马 R. 马感染马驹的肺部中高度上调，我们假设 vapG 可能是一个重要的毒力因子。然而，对标记的 vapG 缺失突变体的分析确定该基因对于巨噬细胞和小鼠体内的生长是不必要的。
Rhodococcus equi, a facultative intracellular pathogen of macrophages, causes severe, life-threatening pneumonia in young foals and in people with underlying immune deficiencies. R. equi virulence is dependent on the presence of a large virulence plasmid that houses a pathogenicity island (PAI) encoding a novel family of surface-localized and secreted proteins of largely unknown function termed the virulence-associated proteins (VapACDEFGHI). To date, vapA and its positive regulators virR and orf8 are the only experimentally established virulence genes residing on the virulence plasmid. In this study, a PAI deletion mutant was constructed and, as anticipated, was attenuated for growth both in macrophages and in mice due to the absence of vapA expression. Expression of vapA in the PAI mutant from a constitutive promoter, thereby eliminating the requirement for the PAI-encoded vapA regulators, resulted in delayed bacterial clearance in vivo, yet full virulence was not restored, indicating that additional virulence genes are indeed located within the deleted pathogenicity island region. Based on previous reports demonstrating that the PAI-carried gene vapG is highly upregulated in macrophages and in the lungs of R. equi-infected foals, we hypothesized that vapG could be an important virulence factor. However, analysis of a marked vapG deletion mutant determined the gene to be dispensable for growth in macrophages and in vivo in mice.