流行病学调查表明,碳青霉烯类抗性主要通过位于共轭质粒上的碳青霉烯酶基因在物种之间传播。由于碳青霉烯酶基因的染色体整合很少被发现,只有少数研究调查了它们对碳青霉烯耐药细菌群落的优势。这里,我们证实了在不存在抗生素压力的情况下,与原始质粒相比,大肠杆菌分离物中染色体整合质粒上blaIMP-6的稳定性增加.尽管携带碳青霉烯酶基因的质粒被认为在连续世代中丢失,我们发现,即使偶尔丢失抗生素抗性盒,完整的质粒骨架仍保留在细菌细胞中.已在世界范围内观察到这种主链结构携带各种抗微生物抗性基因。尽管携带blaIMP-6的染色体整合质粒不能通过接合传播,我们发现,美罗培南处理1周允许质粒从染色体中释放,并在对美罗培南敏感的大肠杆菌菌株中传播。质粒上blaIMP-6的拷贝数扩增8倍,导致抵抗力增强。尽管携带染色体碳青霉烯酶基因的碳青霉烯酶生产者由小亚群组成,它们的功能很稳定,碳青霉烯抗性的长期储层,可以通过美罗培南刺激后具有增强抗性的质粒传播。尽管质粒偶尔会失去其抗性盒,作为获得另一个抗性基因的支架,染色体整合可能有助于在人群中有效分享碳青霉烯耐药性,使制定避免抗菌素耐药性传播的战略复杂化。重要事项尽管碳青霉烯类抗生素是对抗多重耐药生物的最后手段,耐碳青霉烯类肠杆菌(CRE)的全球传播威胁公众健康。碳青霉烯酶,负责碳青霉烯抗性的酶,主要由质粒上的基因编码,这些基因可以在细菌物种之间传播。由于染色体编码的碳青霉烯酶基因的稀有性,缺乏在细菌群落中调查它们特性的研究。在我们的研究中,我们揭示了碳青霉烯酶基因在染色体上与质粒上相比的稳定性,尽管质粒主链有很强的保留,但由于抗微生物药物抗性盒的丢失,它可能会丢失。在接触美罗培南之后,整合到染色体中的碳青霉烯酶基因作为质粒释放,通过扩增的碳青霉烯酶基因拷贝数重新开始增强的碳青霉烯抗性的传播。染色体编码的碳青霉烯酶基因可能在细菌群落中充当抗性基因的库,并挑战针对CRE传播的感染控制。
Epidemiological surveys have shown that carbapenem resistance is mainly transmitted across species by carbapenemase genes located on conjugative plasmids. As chromosomal integration of carbapenemase genes has rarely been identified, only a few studies have investigated their advantages to the carbapenem-resistant bacterial community. Here, we confirmed the increased stability of blaIMP-6 on a chromosome-integrated plasmid in an Escherichia coli isolate compared with that on original plasmids in the absence of antibiotic pressure. Although plasmids carrying carbapenemase genes are supposedly lost in successive generations, we found that the complete plasmid backbone was retained in bacterial cells even after the occasional loss of their antibiotic-resistance cassettes. This backbone structure has been observed worldwide to carry various antimicrobial resistance genes. Although the chromosomally integrated plasmid carrying blaIMP-6 could not be transmitted by conjugation, we found that meropenem treatment for 1 wk allowed the plasmid to be released from the chromosome and spread among E. coli strains that were susceptible to meropenem. The copy number of blaIMP-6 on the plasmid was amplified eight times, resulting in enhanced resistance. Although the carbapenemase producers that carry chromosomal carbapenemase genes comprised of small subpopulations, they functioned as stable, long-term reservoirs of carbapenem resistance that could be disseminated via plasmids with amplified resistance upon meropenem stimulation. Although plasmids occasionally lose their resistance cassettes as a scaffold for the acquisition of another resistance gene, chromosomal integration may contribute to the effective sharing of carbapenem resistance within a population, complicating the development of a strategy to avoid the dissemination of antimicrobial resistance. IMPORTANCE Although carbapenem antibiotics are the last resort for combating multidrug-resistant organisms, global dissemination of carbapenem-resistant Enterobacteriaceae (CRE) threatens public health. Carbapenemases, which are enzymes responsible for carbapenem resistance, are mainly encoded by genes on plasmids that can be transmitted across bacterial species. Owing to the rarity of chromosomally encoded carbapenemase genes, studies investigating their properties in bacterial communities are lacking. In our study, we revealed the stability of carbapenemase genes on chromosomes compared with those on plasmids, which can be lost through the loss of antimicrobial resistance cassettes despite robust retention of plasmid backbones. Following exposure to meropenem, the carbapenemase gene integrated into the chromosome was released as a plasmid, restarting the dissemination of enhanced carbapenem resistance through amplified copy numbers of carbapenemase genes. Chromosomally encoded carbapenemase genes may function as a reservoir of resistance genes within the bacterial community and challenge infection control against CRE dissemination.