Tn1721样转座子携带的blaKPC在耐碳青烯类肺炎克雷伯菌中播散的机制研究

The wide resistant spectrum, fast spread and widespread distribution of carbapenems resistant klebsiella pneumoniae caused by blaKPC have become a great threat to the anti-infective therapy. Currently, we are still unable to control the spread of this drug-resistant bacterium by confirming the source of the infection and cutting off transmission routes based on the theory of cloning spread. Based on the fact that blaKPC was carried mainly by Tn1721and located in different plasmids in China, we build the hypothesis that transposition, plasmid conjugation and clonal propagation co-participate the event of the prevalence of blaKPC. High activity transposon can help resistance genes to find appropriate plasmids and host bacteria, which is the key factor of the spread of Klebsiella pneumoniae carbapenemases (KPCs). Our preliminary experiment showed that there were three forms of Tn1721 that carried blaKPC-2 to move around in different plasmids and strains and the new type cassette of Tn1721-blaKPC-IS26 was the dominant one and transposition experiment confirmed the transposition ability of this cassette, proved the hypothesis above preliminarily. We plan to in-depth study the mechanism of dissemination of KPC by different type transposons; explore the best method to find the source of infection and transmission routes and distinguish local spread and exogenous invasion; meanwhile proceed multicenter study to test this hypothesis, to provide a reliable theory for hospital infection controlling.

blaKPC介导的耐碳青烯类肺炎克雷伯菌耐药谱广，播散快速，分布广泛，危害严重。目前，依据克隆播散理论以菌株的基因型别为线索确认传染源和传播途径建立的院感控制模式，无法有效控制耐药菌的播散。我们基于中国流行的blaKPC由Tn1721样转座子携带，定位于质粒上的事实，提出：Tn1721样转座子携带的blaKPC的播散是由转座、质粒接合和克隆三种方式共同介导，活跃的转座可助耐药基因寻找到合适的质粒和宿主菌，是KPC酶播散的关键。预实验发现blaKPC由三种Tn1721样转座子能通过多种质粒播散到多种肺炎克雷伯菌株，并证实了最多见的新型转座子Tn1721-blaKPC-IS26的转座能力，初步论证了上述假说。现拟深入研究各型转座子传播blaKPC的机制；探索确定KPC酶播散的传染源、传播途径，区分本地传播与外源性入侵的最佳方法；开展多中心研究,论证假说的普遍性，为建立新的院感模式提供理论基础。

耐碳青霉烯类的肺炎克雷伯菌由于致病力强，对大多数抗菌药物耐药，传播广泛，对临床抗感染治疗造成了极大的困扰，2017年，WHO将产酶CRE列为三种“最急需新型抗生素病原体”之一[2]。然而对于CR-KPN为什么能在全世界广泛播散的原因却众说纷纭。由于传播导致CR-KPN最主要的基因blaKPC的细菌主要是CC258群，因此，普遍认为blaKPC的传播主要是克隆传播，但是blaKPC位于质粒上事实却与克隆传播的理论严重相悖，多项研究表明Tn4401和Tn1721样转座子介导的基因水平转移可能是blaKPC-2广泛播散的因素之一。在欧洲、美国、巴西等国家和地区，blaKPC-2主要由Tn4401携带，实验证明Tn4401运动活跃，在blaKPC-2播散中发挥了重要作用；在中国，blaKPC-2则由多种不同结构的Tn1721样转座子携带，但它们的活动能力和转座机制尚不清楚。blaKPC-2在国、内外截然不同的基因环境，提示它在中国可能存在不同的水平转移机制，Tn1721样转座子与blaKPC-2的播散密切相关。本研究通过分子流行病学调查、体内实验和体外实验等手段，分析了携带blaKPC的Tn1721样转座子在肠杆菌科细菌中的分布和动态变化、转座机制、宿主调控因子及各组分的相互作用，了解了Tn1721样转座子促进blaKPC-2在肠杆菌科细菌中水平播散的机制，可为制定有效的干预措施，控制blaKPC-2的播散提供理论基础。