摘要

       替加环素抗性基因tet（X4）广泛存在于各种细菌中。然而，关于携带tet（X4）基因的质粒在不同物种之间传播的信息有限。在这里，我们研究了tet（X4）基因在养猪场细菌之间传播的机制。在同一农场发现了tet（X4）阳性大肠杆菌、肺炎克雷伯菌、阴沟肠杆菌和霍马切肠杆菌。全基因组测序（WGS）分析表明肺炎克雷伯菌属于ST727（n = 11） 和ST3830（n = 1） ，阴沟E.cloacae和荷马E.hormaeche属于ST524（n = 1） 和ST1862（n = 1). 所有tet（X4）基因都位于IncHI1质粒上，该质粒可以在30°C下偶联转移到受体大肠杆菌C600中。此外，在从菌株B12L到C600的接合过程中，鉴定出IncHI1质粒与ISCR2介导的IncN质粒重组的融合质粒（pB12L-EC-1）。在肺炎克雷伯菌（K1L）中也发现了融合质粒，这可能为传播抗微生物耐药性基因提供更多机会。这些细菌中的tet（X4）质粒来源于具有相似结构的同一质粒。此外，GenBank中所有携带tet（X4）基因的IncHI1质粒都属于pST17，即新定义的pMLST。通过肉汤微量稀释法进行抗微生物药敏试验，显示转偶联物从供体菌株中获得了最大的抗微生物耐药性。总之，本报告提供了证据，证明IncHI1/pST17是肠杆菌科细菌中tet（X4）传播的重要载体，这些传播机制可能在环境中发挥作用。The tigecycline resistance gene tet(X4) was widespread in various bacteria. However, limited information about the plasmid harboring the tet(X4) gene spread among the different species is available. Here, we investigated the transmission mechanisms of the tet(X4) gene spread among bacteria in a pig farm. The tet(X4) positive Escherichia coli, Klebsiella pneumoniae, Enterobacter cloacae and Enterobacter hormaeche were identified in the same farm. The whole genome sequencing (WGS) analysis showed that the K. pneumoniae belonged to ST727 (n = 11) and ST3830 (n = 1), E. cloacae and E. hormaeche belonged to ST524 (n = 1) and ST1862 (n = 1). All tet(X4) genes were located on the IncHI1 plasmids that could be conjugatively transferred into the recipient E. coli C600 at 30°C. Moreover, a fusion plasmid was identified that the IncHI1 plasmid recombined with the IncN plasmid mediated by ISCR2 during the conjugation from strains B12L to C600 (pB12L-EC-1). The fusion plasmid also has been discovered in a K. pneumoniae (K1L) that could provide more opportunities to spread antimicrobial resistance genes. The tet(X4) plasmids in these bacteria are derived from the same plasmid with a similar structure. Moreover, all the IncHI1 plasmids harboring the tet(X4) gene in GenBank belonged to the pST17, the newly defined pMLST. The antimicrobial susceptibility testing was performed by broth microdilution method showing the transconjugants acquired the most antimicrobial resistance from the donor strains. Taken together, this report provides evidence that IncHI1/pST17 is an important carrier for the tet(X4) spread in Enterobacteriaceae species, and these transmission mechanisms may perform in the environment.

https://www.frontiersin.org/articles/10.3389/fmicb.2023.1128905/full