Adaptation of Francisella tularensis to the mammalian environment is governed by cues which can be mimicked in vitro
Adaptation of Francisella tularensis to the mammalian environment is governed by cues which can be mimicked in vitro
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DOI：
10.1128/iai.00610-08
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发表时间：
2008-10-01
影响因子：
3.1
通讯作者：
Loegering, Daniel J.
中科院分区：
文献类型：
--
作者：
Hazlett, Karsten R. O.;Caldon, Seth D.;Loegering, Daniel J.
胞内细菌土拉弗朗西斯菌存活于哺乳动物、节肢动物和淡水变形虫中。先前已经确定，用于这种微生物体外繁殖的常规培养基不会产生模拟从受感染的哺乳动物中收获的细菌;这些体外培养的细菌是否类似于节肢动物或阿米巴适应的弗朗西斯菌尚不清楚。作为我们确定F.为了研究哺乳动物感染期间表达的土拉热菌外膜蛋白，我们首先试图鉴定诱导细菌感染衍生表型的体外培养条件。我们比较了在脑心浸液肉汤（BHI;一种很少用于弗朗西斯菌研究的标准微生物培养基）中生长的弗朗西斯菌LVS和在Mueller-Hinton肉汤（MHB;最广泛使用的F.土拉菌培养基，此处用作阴性对照）和巨噬细胞（天然宿主细胞，此处用作阳性对照）。BHI和巨噬细胞生长的F.土拉热菌细胞表现出类似的MglA依赖性和MglA非依赖性蛋白质的表达; MglA依赖性蛋白质的表达受到MHB中存在的游离氨基酸的超生理水平的抑制。我们观察到，在巨噬细胞感染期间，细胞内细菌的蛋白表达与细胞外细菌的蛋白表达不同; BHI生长的细菌反映了后者，而MHB生长的细菌两者都不相似。幼稚巨噬细胞响应BHI和巨噬细胞生长的细菌产生显着较低水平的促炎介质比那些暴露于MHB生长的细菌细胞。与MHB生长的细菌相反，BHI生长的细菌在细胞内复制期间显示出最小的延迟。累积起来，我们的研究结果提供了令人信服的证据，即在BHI中生长产生的细菌重现了从巨噬细胞中出现的弗朗西斯菌属生物体的表型。
The intracellular bacterium Francisella tularensis survives in mammals, arthropods, and freshwater amoeba. It was previously established that the conventional media used for in vitro propagation of this microbe do not yield bacteria that mimic those harvested from infected mammals; whether these in vitro-cultivated bacteria resemble arthropod- or amoeba-adapted Francisella is unknown. As a foundation for our goal of identifying F. tularensis outer membrane proteins which are expressed during mammalian infection, we first sought to identify in vitro cultivation conditions that induce the bacterium's infection-derived phenotype. We compared Francisella LVS grown in brain heart infusion broth (BHI; a standard microbiological medium rarely used in Francisella research) to that grown in Mueller-Hinton broth (MHB; the most widely used F. tularensis medium, used here as a negative control) and macrophages (a natural host cell, used here as a positive control). BHI-and macrophage-grown F. tularensis cells showed similar expression of MglA-dependent and MglA-independent proteins; expression of the MglA-dependent proteins was repressed by the supraphysiological levels of free amino acids present in MHB. We observed that during macrophage infection, protein expression by intracellular bacteria differed from that by extracellular bacteria; BHI-grown bacteria mirrored the latter, while MHB-grown bacteria resembled neither. Naive macrophages responding to BHI- and macrophage-grown bacteria produced markedly lower levels of proinflammatory mediators than those in cells exposed to MHB-grown bacteria. In contrast to MHB-grown bacteria, BHI-grown bacteria showed minimal delay during intracellular replication. Cumulatively, our findings provide compelling evidence that growth in BHI yields bacteria which recapitulate the phenotype of Francisella organisms that have emerged from macrophages.