Identification and characterization of conjugative antibiotic-resistant plasmids that facilitate Escherichia coli to uptake iron

摘要

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

獎項日期	2016 9月 1
原文	English
監督員	Ching-Hao Teng (Supervisor)