水平基因轉移讓不同的細菌之間可以互相交流獲得新基因，是促進細菌演化的動力來源之一。細菌的基因島與質體一般認為來自於水平轉移，過去發現可能與細菌的致病有關。腸道外致病E. coli CFT073和RS218分別自泌尿道感染患者和新生兒腦膜炎患者中分離，過去文獻指出CFT073擁有一個約16 kb的tkt基因島，RS218則帶有一個約110 kb的質體pRS218，因此在本研究分別探討pRS218和tkt基因島在致病過
程的角色。
　　首先，tkt基因島在膀胱炎相關大腸桿菌的流行率顯著高於糞便分離大腸桿菌，顯示tkt基因島可能跟泌尿道感染有相關。然而在小鼠泌尿道感染實驗中，tkt基因島的存在與否似乎不影響CFT073感染泌尿道的能力。因此，這種流行病學相關的原因有待進一步探討。此外，tkt基因島在由相對年紀較大的宿主分離出的菌株的存在率明顯的比由相對年輕宿主分離株中的比例高。在小鼠腸道試驗中，我們也發現到tkt基因島有助於CFT073在相對年長的老鼠中生存，然而卻不利於在相對年輕的老鼠中的存活。這結果顯示tkt基因島影響致病性大腸桿菌在腸道的存活能力，但是
其影響結果會因宿主年紀而不同。
　　接著在本研究的pRS218部分，小鼠的菌血症實驗中，pRS218的存在與否對於RS218感染血液、脾臟或肝臟組織中的能力沒有明顯的影響。然而在小鼠腸道生存能力上，pRS218有利於其自然的宿主RS218在腸道中生長，但其在共生性大腸桿菌MG1655的背景之下，反而有害在腸道的生存能力。因此，pRS218會影響大腸桿菌
在腸道中的生存能力，但其影響結果會因其細菌宿主的不同而有異。
　　本研究結果顯示tkt基因島與pRS218會影響腸道外致病大腸桿菌在腸道生長的能力，但是這些影響結果會受到細菌背景或動物宿主年紀的影響。因為宿主腸道被認為是腸道外致病性大腸桿菌的傳染窩 (reservoir)，這些致病菌在腸道中的生存能力也會影響其致病力。因此，腸道外致病大腸桿菌經水平轉移獲得的DNA序列對於這
些致病菌株在腸道生存的角色值得注意。

Genomic islands and plasmids, which can be horizontally transferred between bacteria, are often involved in the pathogenesis of extraintestinal pathogenic E. coli (ExPEC). The ExPEC strains CFT073 and RS218, which are associated with urinary tracts infections (UTIs) and neonatal meningitis, contain a tkt genomic island and a plasmid pRS218, respectively.
Our epidemiological analysis showed that the tkt island was association with UTIs. However, our mouse model experiments showed that the island didn't play a significant role in UTIs. In addition, the island facilitated the intestinal survival of CFT073 in relatively elder mice, but hindered the survival of this strain in the relatively younger animals. This suggests that the contribution of the tkt island to the intestinal survival of ExPEC is host age-dependent.
pRS218 didn't affect the ability of ExPEC to survive in the mouse bloodstream, spleen and liver. The pRS218 in RS218 facilitated the bacterial survival in the intestine, while in MG1655 it hindered the intestinal survival, suggesting that the contribution of pRS218 in intestinal survival is strain-dependent.
The presence of tkt island and pRS218 affected the intestinal survival ability of ExPEC. However, the effects are E. coli host age-dependent and strain-dependent. Given that the intestine is considered to be the reservoir of ExPEC, the ability of ExPEC survival in the intestine may contribute their ability to cause infection. Therefore, the roles of the horizontally acquired DNA sequences in the intestinal survival of ExPEC are worth further investigation.

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