Purpose: To investigate the occurrence and genetic characteristics of the bla _IMP-26-positive plasmid from a multidrug-resistant clinical isolate, Enterobacter hormaechei  L51.
Methods: Species identification was determined by MALDI-TOF MS and Sanger sequencing. Antimicrobial susceptibility testing was performed by the agar dilution and broth microdilution. Whole-genome sequencing was conducted using Illumina HiSeq 4000-PE150 and PacBio Sequel platforms, and the genome was annotated by the RAST annotation server. The ANI analysis of genomes was performed using OAT. Phylogenetic reconstruction and analyses were performed using the Harvest suite based on the core-genome SNPs of 61 publicly available E. hormaechei  genomes.
Results: The E. hormaechei  L51 genome consists of a 5,018,729 bp circular chromosome and a 343,918 bp conjugative IncHI2/2A plasmid pEHZJ1 encoding bla _IMP-26 which surrounding genetic context was intI1-bla _IMP-26-ltrA-qacE∆1-sul1 . A new sequence type (ST1103) was assigned for the isolate L51 which was resistant to cephalosporins, carbapenems, but sensitive to piperacillin-tazobactam, amikacin, tigecycline, trimethoprim-sulfamethoxazole and colistin. Phylogenetic analysis demonstrated that E. hormaechei  L51 belonged to the same subspecies as the reference strain E. hormaechei  SCEH020042, however 18,248 divergent SNP were identified. Resistance genes in pEHZJ1 including aac(3)-IIc, aac(6ʹ)-IIc, bla _SHV-178, bla _DHA-1, bla _TEM-1, bla _IMP-26, ereA2, catII, fosA5, qnrB4, tet(D), sul1  and dfrA19 .
Conclusion: In our study, we identified a conjugative IncHI2/2A plasmid carrying bla _IMP-26 and bla _SHV-178 in E. hormaechei  ST1103, a novel multidrug-resistant strain isolated from China, and describe the underlying resistance mechanisms of the strain and detailed genetic context of mega plasmid pEHZJ1.
Keywords: Enterobacter hormaechei , multidrug-resistant, bla _IMP-26, IncHI2/2A, genomics