質體可作為基因在細菌間水平轉移的重要工具。許多位於質體上的抗藥基因以及毒力因子可透過接合質體而在細菌間有效的傳播，進而藉由接合生殖的方式進行水平轉移。因此，帶有抗藥基因以及毒力因子的接合質體在臨床上是一嚴重的問題，因為接合質體可將抗藥基因以及毒力因子快速地在細菌間散播。鐵是一種對於致病菌很重要的營養素及生長因子，在細菌的感染中也扮演了重要的角色。細菌為了對抗宿主中缺鐵的環境而演化出多套的攝鐵系統。因此，細菌所攜帶的攝鐵基因亦被認為是毒力基因。
在本篇研究中，我們主要的目的是探討帶有攝鐵系統的抗藥接合質體。首先，我們分別將36株以及27株帶有Ampicillin抗性的大腸桿菌以及克雷白氏桿菌中的接合質體送到攝鐵缺失菌株中,進而將這些帶質體的接合菌株培養在缺鐵的環境並外加不同的鐵離子來檢測這些菌株所攜帶的質體是否具有攝鐵能力。另外，我們也利用CAS assay來檢測接合菌株所攜帶質體是否具有產生siderophore的能力。根據上述的方法，我們發現了三個具有攝鐵能力的質體，包括pEKP8，pEC41以及pEKP70，而其中pEKP70同時具有產生siderophore的能力。我們進一步將pEKP8以及pEC41進行定序後得到以下的結果。pEC41是86 kb大小，IncL/M group的質體，同時帶有blaCTX-M-3 及blaTEM-1抗藥基因，以及攝取檸檬酸鐵的fec 操縱子。我們發現fec 操縱子能夠幫助細菌攝取鐵，同時對於細菌在全身性感染中宿主的血液以及器官中存活扮演了一定的角色。而pEKP8則是136.8 kb，IncFIIK1-FIB型的質體，同時攜帶了blaDHA-1及qnrB4抗藥基因以及損壞的fec 操縱子 fecIR1-259。我們也發現了基因fecIR1 259能幫助細菌攝鐵。總的來說，質體上完整以及損壞的fec操縱子都能夠幫助細菌攝鐵且細菌能利用質體上完整的fec操縱子作為毒力因子，並增強其感染能力。

Plasmids are important vehicles for horizontal gene transfer among bacteria. The antibiotic resistance genes and virulence genes can be carried and horizontally transferred via the plasmid vehicles. Conjugative plasmid can be effectively transferred among bacterial population through conjugation. In clinical setting the conjugative plasmids carrying both antibiotic resistant genes and virulence genes are exceptionally problematic, because the efficient plasmid transmission by conjugation may lead to rapid dissemination of the antibiotic resistance genes and virulence genes among bacterial population. Iron is an important nutrient and growth factor for pathogenic bacteria and plays a vital role in infection. Bacteria have evolved a number of mechanisms for the acquisition of adequate iron from the iron-restricted host environment. Thus, the bacterial genes encoding the iron uptake ability is considered as virulence genes.
In this study, we focused on identifying and characterizing conjugative antibiotic-resistant plasmids that provided the iron acquisition system. We screened 36 Escherichia coli and 27 Klebsiella pneumoniae ampicillin-resistant conjugative plasmids for the ones able to facilitate bacterial iron uptake. These plasmids were transferred into iron-uptake defective E. coli strains through conjugation. Then the trans-conjugants were subjected to the iron source growth promotion test with different iron sources and subjected to chrome azurol S (CAS) assay to screen for the plasmids able to provide the ability to produce siderophore. Three plasmids pEKP8, pEC41, and pEKP70 was identified to be involved in providing iron uptake ability and pEKP70 was shown to be able to produce siderophore. pEKP8 and pEC41 were sequenced and their sizes were determined to be 136.8 kb and 86 kb. EC41 belonged to the IncL/M group, harbored the blaCTX-M-3 and blaTEM-1 genes, and carried the fec operon encoding the ferric citrate transport system. The fec operon was involved in promoting the iron uptake ability of the bacterial hosts. This operon contributed to the bacterial survival in the bloodstream and the host organs during the course of systemic infection. pEKP8 belonged to IncFIIK1-FIB-like, harbored the blaDHA-1 and qnrB4 genes and carried a truncated fec operon fecIR1-259. The fecIR1-259 was shown to be responsible for the iron-uptake ability encoded in pEKP8. In conclusion, the intact and truncated fec operons on the plasmids were able to increase the bacterial ability to acquire iron in hosts. The plasmid-encoded fec operon can serve as virulence genes to facilitate bacterial infections.

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