| Abstract: | 克雷白氏肺炎桿菌(Klebsiella pneumoniae) 屬於革蘭氏陰性腸內桿菌科(Enterobacteriacea)，為造成社區感染和院內感染常見的病原菌，會導致肺炎，腦膜炎，尿道感染和化膿性肝膿瘍。目前已知K. pneumoniae的致病毒力因子，包括莢膜(capsule)，脂多醣體(lipopolysaccharides,LPS)，黏附因子(adhesion factor)，血清抵抗能力(serum resistance)，以及鐵螯合系統(iron acquisition system)等。最近有一種新型的蛋白質分泌系統被稱為第六型蛋白質分泌系統(Type VI protein secretion system,T6SS)，存在於許多動植物的病原細菌中。目前T6SS的詳細機制仍不清楚，但在許多動物模型中看到細菌藉由第六型蛋白質分泌系統感染宿主。在本研究中，為了探討T6SS在K. pneumoniae毒性中所扮演的角色，我針對T6SS中的重要基因，包括hcp，vgrG，clpV，以及icmF製備單基因與多基因的基因剔除菌株。在肝膿瘍的小鼠模式中，接受T6SS基因剔除的菌株感染的小鼠具有較高的存活率，而且在肝臟和其他器官散布的菌量也是較低的。這個結果顯示T6SS在K. pneumoniae 的毒力上扮演重要的角色。此外，T6SS基因剔除的菌株感染BNL細胞株時，細菌黏附細胞的能力以及細胞毒殺力與野生型菌株相比亦有下降的趨勢。雖然，T6SS是K. pneumoniae毒性表現所必須的因子之一，但更深入的機制仍需要進一步實驗探討。
Klebsiella pneumoniae is an important pathogen belonging to the family Enterobacteriacea. It is a common community- and hospital-acquired pathogen, and mainly causes pneumonia, meningitis, urinary tract infection and pyogenic liver abscess. The major virulence factors of K. pneumoniae include capsular, lipopolysaccharide (LPS), adhesion factors, serum-killing resistance and iron acquisition system. Recently, a novel secretion system, called type VI secretion system (T6SS), has been identified in the genome of K. pneumoniae NTHU-K2044 and numerous animal or plant Gram-negative pathogens. Although the mechanism of T6SS remains unclear, T6SS-dependent phenotypes were demonstrated for various pathogens in animal models. In this study, to determine the role of T6SS in K. pneumoniae virulence, I generated single and multiple gene-specific knockout mutants for hcp, vgrG, clpV, and icmF in K. pneumoniae CG43. In the liver abscess mice model, mice which were infected with T6SS mutants showed higher survival rates and displayed lower bacterial burdens in the liver and spleen as compared to mice that were infected with wild type K. pneumoniae. Furthermore, the adherence and cytotoxicity to BNL cells of T6SS mutants was decreased when compared to the wild type strain. Although T6SS might be functional for the display of K. pneumoniae virulence, the detailed mechanism needs further studies to explore. |
