克雷伯氏肺炎桿菌致病性莢膜型K1大質體特異致病基因之分析

Abstract

克雷伯氏肺炎桿菌是院內及社區性感染最常見的細菌之一，也是造成社區型肝膿瘍 (community-acquired pyogenic liver abscess)最主要的細菌。一般認為莢膜型K1和K2為重要的致病因子 (virulent factors)，另外也有許多基因被報導和造成肝膿瘍有關。先前研究發現剔除K2菌株CG43上的pLVPK大質體會使細菌的致病力下降，另外也發現在引起肝膿瘍的菌株中，大多有此類大質體存在。同時，本實驗室的研究也發現，在四株莢膜型K1之西方非肝膿瘍菌株中，位於大質體上的iuc基因僅出現在致病力較高的兩菌株 (ATCC8045, ATCC8047)中，而非致病力低的兩菌株 (ATCC35593, A5054)，但將iuc剔除後卻不會影響細菌致病力，因此我們懷疑有其他致病因子存在於大質體上。本研究利用次世代定序 (Next generation sequencing)分析各一株西方致病力高 (ATCC8045)與致病力低 (A5054)的菌株內之大質體DNA序列，並與已有完整序列的 NTUH-K2044作比較，找出致病力高的菌株獨有之基因，目前已完成的定序結果如下：ATCC8045共得到12個長度大於10 kb的大序列片段 (contig)，總長度約有300kb; A5054共得到8個大序列片段，總長度約有270 kb。比較目前已獲得的序列後發現，抗亞碲酸鹽(ter)基因僅出現在致病力高的NTUH-K2044及ATCC8045中。位於大質體上的ter基因含有兩組基因區(terY3-Y2-X-Y1-W和terZ-A-B-C-D-E-F)，僅有 terZ-A-B-C-D-E-F具有抗亞碲酸鹽的功能，而在高致病力的NTUH-K2044中，不論將 terY3-Y2-X-Y1-W或 terZ-A-B-C-D-E-F由大質體上剔除，結果皆會影響此株細菌在小鼠體內的拓殖能力。

Klebsiella pneumoniae is an important pathogen causing nosocomial infections and it is one of the most common bacteria causing community-acquired pyogenic liver abscess (PLA), which has become an emerging infectious disease worldwide. Capsule type K1 and K2 are generally considered as important virulent factors, and there are several gene regions have been reported associated with PLA pathogenesis. Previous studies showed that curing of large plasmid pLVPK would decrease the virulence of K2 strain CG43, and most strains causing PLA exhibit pLVPK-like plasmids. Meanwhile, our previous studies also showed that the two (ATCC8045, ATCC8047) out of four non-PLA western K1 strains harbored the iuc regions and also had high virulence, but the other two strains (ATCC35593, A5054) did not. Since knockout of iuc did not affect its virulence, we speculated that there are other virulent genes in the large plasmid probably play roles in PLA pathogenesis. This study aims to characterize the virulent genes in the large plasmid of virulent K1 strains. In this research, we acquired 10 contigs (total 300 kb) of large plasmid sequences from one virulent strain (ATCC8045) and 8 contigs (total 270 kb) from one avirulent strain (A5054) by Next Generation Sequencing. Comparing the two sequences with that of the fully sequenced large plasmid of NTUH-K2044 virulent K1 strain, the tellurite-resistance (ter) genes were found to be exclusive genes in the two virulent strains. The ter regions include two gene clusters (terY3-Y2-X-Y2-W and terZ-A-B-C-D-E-F). Knockout of either ter regions located on the large plasmid decreased the colonization ability of NTUH-K2044 in liver and spleen, although only terZ-A-B-C-D-E-F were required for tellurite resistance. Our results suggested that deletion of tellurite-resistance (ter) genes in the large plasmid of K. pneumoniae NTUH-K2044 virulent K1 strain reduce the virulence and/or fitness of this pathogen.