Miki Tsuyoshi
Department of Microbiology, School of Pharmacy, Kitasato University.
Nihon Saikingaku Zasshi. 2014;69(4):577-88. doi: 10.3412/jsb.69.577.
Chromobacterium violaceum is a Gram-negative bacterium that infects humans and animals with fatal sepsis. The infection with C. violaceum is rare in case of those who are healthy, but once established, C. violaceum causes sever disease accompanied by abscess formation in the lungs, liver and spleen. Furthermore, C. violaceum is resistant to a broad range of antibiotics, which in some cases renders the antimicrobial therapy for this infection difficult. Thus, the infection with C. violaceum displays high mortality rates unless initial proper antimicrobial therapy. In contrast, the infection mechanism had completely remained unknown. To this end, we have tried to identify virulence factors-associated with C. violaceum infection. Two distinct type III secretion systems (TTSSs) were thought to be one of the most important virulence factors, which are encoded by Chromobacterium pathogenicity island 1/1a and 2 (Cpi-1/-1a and -2) respectively. Our results have shown that Cpi-1/-1a-encoded TTSS, but not Cpi-2, is indispensable for the virulence in a mouse infection model. C. violaceum caused fulminant hepatitis in a Cpi-1/-1a-encoded TTSS-dependent manner. We next have identified 16 novel effectors secreted from Cpi-1/-1a-encoded TTS machinery. From these effectors, we found that CopE (Chromobacterium outer protein E) has similarities to a guanine nucleotide exchange factor (GEF) for Rho GTPases. CopE acts as GEF for Rac1 and Cdc42, leading to induction of actin cytoskeletal rearrangement. Interestingly, C. violaceum invades cultured human epithelial cells in a CopE-dependent manner. Finally, an inactivation of CopE by disruption of copE gene or amino acid point mutation leading to loss of GEF activity attenuates significantly the mouse virulence of C. violaceum. These results suggest that Cpi-1/-1a-encoded TTSS is a major virulence determinant for C. violaceum infection, and that CopE contributes to the virulence in part of this pathogen.
紫色色杆菌是一种革兰氏阴性菌，可导致人类和动物发生致命性败血症。对于健康人群而言，感染紫色色杆菌的情况较为罕见，但一旦感染，紫色色杆菌会引发严重疾病，并伴有肺部、肝脏和脾脏脓肿形成。此外，紫色色杆菌对多种抗生素具有耐药性，这在某些情况下使得针对该感染的抗菌治疗变得困难。因此，除非进行初始适当的抗菌治疗，否则紫色色杆菌感染的死亡率很高。相比之下，其感染机制完全未知。为此，我们试图鉴定与紫色色杆菌感染相关的毒力因子。两种不同的III型分泌系统（TTSSs）被认为是最重要的毒力因子之一，它们分别由紫色色杆菌致病岛1/1a和2（Cpi - 1/-1a和 - 2）编码。我们的结果表明，在小鼠感染模型中，由Cpi - 1/-1a编码的TTSS而非Cpi - 2对于毒力是不可或缺的。紫色色杆菌以依赖Cpi - 1/-1a编码的TTSS的方式引发暴发性肝炎。接下来，我们鉴定了从Cpi - 1/-1a编码的TTS机制分泌的16种新型效应蛋白。从这些效应蛋白中，我们发现CopE（紫色色杆菌外蛋白E）与Rho GTPases的鸟嘌呤核苷酸交换因子（GEF）具有相似性。CopE作为Rac1和Cdc4蛋白的GEF，导致肌动蛋白细胞骨架重排。有趣的是，紫色色杆菌以依赖CopE的方式侵入培养的人上皮细胞。最后，通过破坏copE基因或导致GEF活性丧失的氨基酸点突变使CopE失活，可显著减弱紫色色杆菌的小鼠毒力。这些结果表明，Cpi - 1/-1a编码的TTSS是紫色色杆菌感染的主要毒力决定因素，并且CopE在该病原体的部分毒力中起作用。
