水平基因轉移是可以在不同物種間傳遞基因的一種方式，可以傳播抗藥基因、毒力基因以及適應性因子，在細菌的演化上扮演了重要的角色。接合作用被認為是最為重要的一種水平基因轉移的機制。細菌的接合作用可以傳播可接合質體及可傳送質體。如果這些可以透過接合作用傳播的質體又帶有有助於致病細菌感染的適應性因子，則會對於公共衛生造成很大的威脅。
基於上述原因，在本篇研究中透過篩選來自大腸桿菌及克雷白氏桿菌的臨床菌株來探討研究帶有有助於細菌感染適應性因子的可傳播質體。我們透過接合的方式分別將8株及10株帶有Ampicillin抗性的大腸桿菌以及克雷白氏桿菌中的可傳播質體送到共生型大腸桿菌MG1655 strR中。接著，我們將所拿到的接合子和MG1655 strR菌株混和後，同時打到老鼠體內透過皮下感染及泌尿道感染的方式來篩選接合子中所帶有的可傳播質體是否有助於細菌的感染。我們發現其中一個接合子MG1655 strR/EC23在泌尿道感染中所回收的菌數有上升的現象。透過Kado-Liu的方式進行分析發現其接合子透過接合的方式得到4個質體。進一步發現，其中一個質體pEC23-3似乎提供接合的能力而另一個質體pEC23-4則會提供競爭的優勢。將pEC23-4定序後，發現其帶細菌素K及mobilizable基因蔟。在本篇研究中，發現了細菌素K在感染過程中的新作用，其基因蔟在泌尿道感染、全身性感染以及腸道感染的過程中會提供競爭的優勢，而mobilizable的基因蔟則會幫助質體在接合時的移動。此外，我們也發現細菌素K會使質體pEC23-4在腸道內穩定而質體pEC23-4卻會阻礙MG1655 strR在腸道中的生長。

Horizontal gene transfer (HGT) is a way to allow gene transfer between different bacterial species. Through this process the antibiotic resistance genes, virulence factors and other adaptive traits can be spread among bacteria. Thus, HGT plays an important role in bacterial evolution. Conjugation is one of the most important mechanisms of HGT. Bacterial conjugation results in the transfer of conjugative plasmids and mobilizable plasmids. Transmissible plasmids harboring genes that benefit bacteria during infections would be a serious threat to public health.
Accordingly, this study is to identify and characterize novel transmissible plasmids that harboring adaptive traits benefiting bacteria during infections. We screened for plasmids that derived from Klebsiella pneumonia and Escherichia coli clinical isolates. These plasmids were transferred to the commensal E. coli strain MG1655 strR through conjugation. We obtained 8 trans-conjugants that have acquired plasmids from the E. coli clinical isolates, and 10 trans-conjugants that have acquired K. pneumoniae-derived plasmids. Then the trans-conjugants and MG1655 strR were mixed, the mixtures were subjected to the mouse air pouch and urinary tract infection (UTI) models to assess whether the acquired plasmids can benefit invading bacteria during infection. One trans-conjugant MG1655 strR/ EC23 showed significantly increased bacterial counts in the mouse UTI. Based on the Kado and Liu method, we found that the trans-conjugant MG1655 strR/ EC23 obtained more than one plasmid through the conjugation. Among the plasmids, pEC23-3 was identified to be involved in providing conjugation ability, while pEC23-4 was shown to be able to confer competitive advantage. pEC23-4 was sequenced and shown to contain the colicin K gene cluster and the mobilizable gene cluster. This study revealed a novel role of colicin K during infection. The colicin K gene cluster conferred E. coli competitive advantage during the course of UTIs, systemic infections, and intestinal colonization. The mobilizable gene cluster was responsible for mobilizing the plasmid. Furthermore, in the intestine, colicin K facilitated the maintenance of pEC23-4 in E. coli, but the presence of the plasmid hinders the growth of host bacteria.

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