利奈唑胺耐药基因optrA KLDP变异体跨种属传播的机制研究

利奈唑胺是临床上治疗革兰阳性菌尤其是多重耐药菌株所引起感染的重要抗菌药物，其耐药性的出现和传播给抗感染治疗带来严重威胁。2015年我们在肠球菌中发现一种新型的利奈唑胺耐药基因optrA，随后该基因在全球范围陆续检出，但尚未出现在临床分离的金黄色葡萄球菌中。我们的前期研究发现健康人群肠道中optrA基因阳性肠球菌的携带率达到惊人的43.8%，在26种optrA变异体中，仅KLDP可接合转移至金黄色葡萄球菌，提示optrAKLDP基因可借助具有广泛宿主范围的质粒实现跨种属转移，然而其转移机制和播散能力并不明确。本项目拟通过研究optrAKLDP基因侧翼结构及其编码质粒的遗传特征，揭示该变异体的传播机制；通过研究optrAKLDP质粒在宿主细菌中的稳定性及宿主细菌的适应性代价，明确该变异体跨种属传播的能力和风险，为控制optrA基因的播散和延缓利奈唑胺耐药性的发展提供科学依据。

Linezolid is an important antimicrobial agent for the clinical treatment of infections caused by Gram-positive bacteria, especially multidrug-resistant strains. The emergence and spread of linezolid resistance is a serious threat to anti-infective therapy. We identified a novel linezolid resistance gene optrA in enterococci in 2015. This gene has been subsequently discovered in worldwide enterococci but has not been detected in clinical isolate of Staphylococcus aureus. We detected a particular high carriage rate (43.8%) of optrA-positive enterococci in intestinal tract of healthy humans in our previous study. Among 26 optrA variants, KLDP is the only variant that can be transferred to S. aureus RN4220 by conjugation. These data suggest that optrAKLDP gene can be transferred across different species and genera through plasmids with a broad host range. However, the transfer mechanism and dissemination ability of such plasmids are unclear. This project aims to disclose the transmission mechanism of optrAKLDP by analyzing the flanking structure of this gene and the genetic characteristics of the optrAKLDP-carrying plasmid, and to evaluate the ability and risk of interspecific and intergeneric transmission of optrAKLDP-carrying plasmid by determining the stability of plasmid in host bacteria and the fitness cost of host bacteria, and finally to provide the scientific basis for preventing the spread of optrA genes and delaying the development of linezolid resistance.