College of Animal Science and Veterinary Medicine, Henan Agricultural University, Zhengzhou, China.
Jiangsu Co-Innovation Center for Prevention and Control of Important Animal Infectious Diseases and Zoonoses, Yangzhou University College of Veterinary Medicine, Yangzhou, China.
J Antimicrob Chemother. 2019 Nov 1;74(11):3184-3189. doi: 10.1093/jac/dkz327.
To characterize the complete sequences of four plasmids in MCR-1-producing clinical Escherichia coli strain D72, and to depict the formation mechanism and characteristics of the cointegrate plasmid derived from the pD72-mcr1 and pD72-F33 plasmids.
The genetic profiles of plasmids in strain D72 and its transconjugant were determined by conjugation, S1-PFGE, Southern hybridization, WGS analysis and PCR. Plasmid sequences were analysed with bioinformatic tools. The traits of the fusion plasmid were characterized by cointegration, stability and conjugation assays.
Strain D72, belonging to ST1114, contained four plasmids, including mcr-1-carrying pD72-mcr1, blaCTX-M-55-carrying pD72-F33, blaTEM-238-bearing pD72-IncP and pD72-IncX1 carrying aph(3')-Ia, qnrS2 and floR. A single plasmid, pD72C, in the transconjugant was found to be larger than any plasmid in the original strain D72. Sequence analysis showed that pD72C was the fusion product of pD72-mcr1 and pD72-F33, and the recombinant event involved an intermolecular replicative mechanism. Plasmid fusion occurred at a frequency of 1.75 × 10-4 cointegrates per transconjugant. The fusion plasmid presented a high stability and conjugation frequency of 8.00 × 10-3.
To our knowledge, this is the first report of the IS26-mediated fusion of an IncN1-F33:A-:B- plasmid and an mcr-1-carrying phage-like plasmid, providing evidence for the important role of IS26 in the recombination of plasmids. The biological advantages of the fusion plasmid indicated that the fusion event presumably plays a potential role in the dissemination of mcr-1.
对携带 mcr-1 的临床型大肠杆菌 D72 株中 4 种质粒的完整序列进行特征描述，并描绘源自 pD72-mcr1 和 pD72-F33 质粒的融合质粒的形成机制和特点。
通过接合试验、S1-PFGE、Southern 杂交、WGS 分析和 PCR 确定 D72 株及其转导子中质粒的遗传特征。利用生物信息学工具分析质粒序列。通过共整合、稳定性和接合试验对融合质粒的特性进行分析。
属于 ST1114 型的 D72 株含有 4 种质粒，包括携带 mcr-1 的 pD72-mcr1、携带 blaCTX-M-55 的 pD72-F33、携带 blaTEM-238 的 pD72-IncP 和携带 aph(3')-Ia、qnrS2 和 floR 的 pD72-IncX1。转导子中发现的单个质粒 pD72C 比原始菌株 D72 中的任何质粒都大。序列分析表明，pD72C 是 pD72-mcr1 和 pD72-F33 的融合产物，重组事件涉及分子间复制机制。质粒融合的频率为每转导子 1.75 × 10-4 个共整合体。融合质粒具有高稳定性和 8.00 × 10-3 的高接合频率。
据我们所知，这是首次报道 IS26 介导的 IncN1-F33:A-:B- 质粒和携带 mcr-1 的噬菌体样质粒的融合，为 IS26 在质粒重组中的重要作用提供了证据。融合质粒的生物学优势表明，融合事件可能在 mcr-1 的传播中发挥了潜在作用。
