Abu Kwaik Y
Department of Microbiology and Immunology, University of Kentucky Chandler Medical Center, Lexington 40536-0084, USA.
Appl Environ Microbiol. 1996 Jun;62(6):2022-8. doi: 10.1128/aem.62.6.2022-2028.1996.
Legionella pneumophila is an intracellular parasite of protozoa and human phagocytes. To examine adaptation of this bacterium to parasitize protozoa, the sequence of events of the intracellular infection of the amoeba Hartmannella vermiformis was examined. The previously described uptake phenomenon of coiling phagocytosis by human monocytes was not detected. A 1 h postinfection with wild-type strain AA100, mitochondria were observed within the vicinity of the phagosome. At 2.5 h postinfection, numerous vesicles surrounded the phagosomes and mitochondria were in close proximity to the phagosome. At 5 h postinfection, the bacterium was surrounded by a ribosome-studded multilayer membrane. Bacterial multiplication was evident by 8 h postinfection, and the phagosome was surrounded by a ribosome-studded multilayer membrane until 15 h postinfection. The recruitment of organelles and formation of the ribosome-studded phagosome was defective in an isogenic attenuated mutant of L. pneumophila (strain AA101A) that failed to replicate within amoebae. At 20 h postinfection with wild-type strain AA100, numerous bacteria were present in the phagosome and ribosome were not detected around the phagosome. These data showed that, at the ultrastructural level, the intracellular infection of protozoa by L. pneumophila is highly similar to that of infection of macrophages. Immunocytochemical studies provided evidence that at 5 h postinfection the phagosome containing L. pneumophila acquired an abundant amount of the endoplasmic reticulum-specific protein (BiP). Similar to phagosomes containing heat-killed wild-type L. pneumophila, the BiP protein was not detectable in phagosomes containing the mutant strain AA101A. In addition to the absence of ribosomes and mitochondria, the BiP protein was not detected in the phagosomes at 20 h postinfection with wild-type L. pneumophila. The data indicated that the ability of L. pneumophila to establish the intracellular infection of amoebae is dependent on its capacity to reside and multiply within a phagosome surrounded by the rough endoplasmic reticulum. This compartment may constitute a rich source of nutrients for the bacteria and is probably recognized as cellular compartment. The remarkable similarity of the intracellular infections of macrophages and protozoa by L. pneumophila strongly supports the hypothesis that adaptation of the bacterium to the intracellular environment of protozoa may be the mechanism for its ability to adapt to the intracellular environment of human alveolar macrophages and causes pneumonia.
嗜肺军团菌是原生动物和人类吞噬细胞的细胞内寄生虫。为了研究这种细菌对寄生原生动物的适应性，我们检测了其在阿米巴虫（哈特曼内阿米巴）细胞内感染的一系列事件。未检测到先前描述的人类单核细胞的卷曲吞噬摄取现象。用野生型菌株AA100感染1小时后，在吞噬体附近观察到线粒体。感染后2.5小时，大量囊泡围绕着吞噬体，线粒体与吞噬体紧密相邻。感染后5小时，细菌被布满核糖体的多层膜包围。感染后8小时细菌增殖明显，直到感染后15小时，吞噬体一直被布满核糖体的多层膜包围。在嗜肺军团菌的同基因减毒突变体（菌株AA101A）中，细胞器的募集和布满核糖体的吞噬体的形成存在缺陷，该突变体无法在阿米巴虫内复制。用野生型菌株AA100感染20小时后，吞噬体内存在大量细菌，吞噬体周围未检测到核糖体。这些数据表明，在超微结构水平上，嗜肺军团菌对原生动物的细胞内感染与对巨噬细胞的感染高度相似。免疫细胞化学研究提供的证据表明，感染后5小时，含有嗜肺军团菌的吞噬体获得了大量内质网特异性蛋白（结合免疫球蛋白蛋白）。与含有热灭活野生型嗜肺军团菌的吞噬体类似，在含有突变菌株AA101A的吞噬体中未检测到结合免疫球蛋白蛋白。除了没有核糖体和线粒体外，用野生型嗜肺军团菌感染20小时后，吞噬体中也未检测到结合免疫球蛋白蛋白。数据表明，嗜肺军团菌建立对阿米巴虫细胞内感染的能力取决于其在被糙面内质网包围的吞噬体内生存和增殖的能力。这个区室可能是细菌丰富的营养来源，并且可能被识别为细胞区室。嗜肺军团菌对巨噬细胞和原生动物的细胞内感染具有显著相似性，这有力地支持了以下假设：细菌对原生动物细胞内环境的适应性可能是其适应人类肺泡巨噬细胞细胞内环境并导致肺炎的机制。
