Liu Feng, Fu Jiyang, Liu Canying, Chen Jing, Sun Minhua, Chen Huanchun, Tan Chen, Wang Xiangru
State Key Laboratory of Agricultural Microbiology, College of Veterinary Medicine, Huazhong Agricultural University, Wuhan, Hubei, China; The Cooperative Innovation Center for Sustainable Pig Production, Huazhong Agricultural University, Wuhan, Hubei, China.
Department of Veterinary Medicine, Foshan University, Foshan, Guangdong, China.
Microbiol Res. 2017 Mar;196:69-79. doi: 10.1016/j.micres.2016.11.013. Epub 2016 Nov 29.
Extraintestinal pathogenic Escherichia coli (ExPEC) can invade and colonize multiple extraintestinal tissues and can cause a wide range of infections; however the mechanisms of its pathogenicity are not well understood. Flagella contribute to the infection of E. coli strains by mediating adhesion and invasion. Our previous bioinformatic analysis revealed two flagella gene clusters in the genome of an ExPEC isolate, PCN033. One encodes the conventional flagellum system (Flag-1) and the other encodes the Flag-2 system, whose function is uncharacterized. Here we aimed to characterize these two flagellum systems and determine their contributions to the flagellum formation and certain pathogenicity-associated phenotypes. Our observations support the involvement of Flag-1 system, but not Flag-2 system, in the synthesis and maturation of the flagellum structure, and in mediating bacterial swimming and swarming. Moreover, flgD, which encodes a flagellar-hook scaffolding protein in the Flag-1 system, is required for flagellum assembly by influencing the production of FliC (flagellin). Deletion of flgD attenuated ExPEC strain PCN033 invasion and colonization in vivo, probably by affecting bacterial adhesion and invasion, and by reducing resistance to phagocytosis by circulating monocytes. In contrast, these phenotypes were not observed in the strain with deletion of lfgD, encoding the FlgD-like protein in the Flag-2 system. Taken together, these findings indicate that Flag-1 flagellum system is the determinative component of bacterial flagella that contributes to the infection.
肠外致病性大肠杆菌（ExPEC）可侵入并定植于多个肠外组织，引发多种感染；然而，其致病机制尚未完全明确。鞭毛通过介导黏附和侵袭，有助于大肠杆菌菌株的感染。我们之前的生物信息学分析揭示，ExPEC分离株PCN033的基因组中有两个鞭毛基因簇。一个编码传统的鞭毛系统（Flag-1），另一个编码功能未知的Flag-2系统。在此，我们旨在对这两个鞭毛系统进行表征，并确定它们对鞭毛形成及某些致病性相关表型的作用。我们的观察结果表明，Flag-1系统参与鞭毛结构的合成与成熟以及介导细菌的游动和群集运动，而Flag-2系统则不然。此外，Flag-1系统中编码鞭毛钩支架蛋白的flgD基因，通过影响鞭毛蛋白FliC的产生，对鞭毛组装至关重要。缺失flgD可能通过影响细菌的黏附和侵袭以及降低循环单核细胞对吞噬作用的抵抗力，减弱ExPEC菌株PCN033在体内的侵袭和定植能力。相比之下，在缺失Flag-2系统中编码类FlgD蛋白的lfgD基因的菌株中，未观察到这些表型。综上所述，这些发现表明Flag-1鞭毛系统是细菌鞭毛中促成感染的决定性组成部分。
