Department of Microbiology and Immunology, Geisel School of Medicine at Dartmouth College, Hanover, New Hampshire, USA.
University of North Carolina at Chapel Hill School of Medicine, Chapel Hill, North Carolina, USA.
mBio. 2021 Oct 26;12(5):e0209821. doi: 10.1128/mBio.02098-21. Epub 2021 Sep 28.
Burkholderia cenocepacia is a member of the Burkholderia cepacia complex (Bcc), a group of bacteria with members responsible for causing lung infections in cystic fibrosis (CF) patients. The most severe outcome of Bcc infection in CF patients is cepacia syndrome, a disease characterized by necrotizing pneumonia with bacteremia and sepsis. B. cenocepacia is strongly associated with cepacia syndrome, making it one of the most virulent members of the Bcc. Mechanisms underlying the pathogenesis of B. cenocepacia in lung infections and cepacia syndrome remain to be uncovered. B. cenocepacia is primarily an intracellular pathogen and encodes the type VI secretion system (T6SS) effector TecA, which is translocated into host phagocytes. TecA is a deamidase that inactivates multiple Rho GTPases, including RhoA. Inactivation of RhoA by TecA triggers assembly of the pyrin inflammasome, leading to secretion of proinflammatory cytokines, such as interleukin-1β, from macrophages. Previous work with the B. cenocepacia clinical isolate J2315 showed that TecA increases immunopathology during acute lung infection in C57BL/6 mice and suggested that this effector acts as a virulence factor by triggering assembly of the pyrin inflammasome. Here, we extend these results using a second B. cenocepacia clinical isolate, AU1054, to demonstrate that TecA exacerbates weight loss and lethality during lung infection in C57BL/6 mice and mice engineered to have a CF genotype. Unexpectedly, pyrin was dispensable for TecA virulence activity in both mouse infection models. Our findings establish that TecA is a B. cenocepacia virulence factor that exacerbates lung inflammation, weight loss, and lethality in mouse infection models. B. cenocepacia is often considered the most virulent species in the Bcc because of its close association with cepacia syndrome in addition to its capacity to cause chronic lung infections in CF patients (1). Prior to the current study, virulence factors of B. cenocepacia important for causing lethal disease had not been identified in a CF animal model of lung infection. Results of this study describe a CF mouse model and its use in demonstrating that the T6SS effector TecA of B. cenocepacia exacerbates inflammatory cell recruitment and weight loss and is required for lethality and, thus, acts as a key virulence factor during lung infection. This model will be important in further studies to better understand TecA's role as a virulence factor and in investigating ways to prevent or treat B. cenocepacia infections in CF patients. Additionally, TecA may be the founding member of a family of virulence factors in opportunistic pathogens.
洋葱伯克霍尔德菌是洋葱伯克霍尔德菌群（Bcc）的成员之一，该菌群的一些成员可导致囊性纤维化（CF）患者肺部感染。Bcc 感染 CF 患者最严重的后果是洋葱伯克霍尔德菌综合征，该病的特征是坏死性肺炎伴菌血症和败血症。洋葱伯克霍尔德菌与洋葱伯克霍尔德菌综合征密切相关，使其成为 Bcc 中最具毒力的成员之一。洋葱伯克霍尔德菌在肺部感染和洋葱伯克霍尔德菌综合征中的发病机制仍有待揭示。洋葱伯克霍尔德菌主要是一种细胞内病原体，并编码 VI 型分泌系统（T6SS）效应因子 TecA，该因子可转位至宿主吞噬细胞。TecA 是一种脱酰胺酶，可使多种 Rho GTPases 失活，包括 RhoA。TecA 使 RhoA 失活会触发 pyrin 炎症小体的组装，导致巨噬细胞中促炎细胞因子（如白细胞介素-1β）的分泌。先前使用洋葱伯克霍尔德菌临床分离株 J2315 的研究表明，TecA 会增加 C57BL/6 小鼠急性肺部感染中的免疫病理学，并表明该效应因子通过触发 pyrin 炎症小体的组装而充当毒力因子。在这里，我们使用第二个洋葱伯克霍尔德菌临床分离株 AU1054 扩展了这些结果，证明 TecA 会加剧 C57BL/6 小鼠和 CF 基因型小鼠肺部感染中的体重减轻和死亡率。出人意料的是，在这两种小鼠感染模型中，pyrin 对于 TecA 的毒力活性都是可有可无的。我们的研究结果表明，TecA 是洋葱伯克霍尔德菌的一种毒力因子，可加剧小鼠感染模型中的肺部炎症、体重减轻和死亡率。洋葱伯克霍尔德菌通常被认为是 Bcc 中最具毒力的物种，因为它不仅与洋葱伯克霍尔德菌综合征密切相关，而且还能够导致 CF 患者的慢性肺部感染（1）。在 CF 肺部感染的动物模型中，尚未鉴定出与引起致死性疾病相关的洋葱伯克霍尔德菌的毒力因子。本研究的结果描述了一种 CF 小鼠模型及其在证明洋葱伯克霍尔德菌的 T6SS 效应因子 TecA 加剧炎症细胞募集和体重减轻以及需要致死性方面的用途，因此是肺部感染期间的关键毒力因子。该模型将在进一步研究中非常重要，以更好地了解 TecA 作为毒力因子的作用，并研究预防或治疗 CF 患者洋葱伯克霍尔德菌感染的方法。此外，TecA 可能是机会性病原体中一类毒力因子的创始成员。
