Genomic analysis of IMP-8-producing Enterobacter hormaechei with a novel plasmid pK432-IMP

Carbapenem-resistant Enterobacter cloacae (CR-ECC) complex has posed significant challenges to the clinical treatment of infections, and Enterobacter hormaechei (E. hormaechei) is the most commonly identified nosocomial pathogen of CR-ECC.

Carbapenemases were detected by the immunocolloidal gold technique. The minimum inhibitory concentration (MIC) values were determined by VITEK2. The genome sequence of strain K432 was obtained and analysed.

We isolated the IMP-8-producing E. hormaechei strain K432 from a patient's urine specimen in a Chinese hospital, which exhibited resistance to multiple antibiotics, including ceftazidime, piperacillin/tazobactam, aztreonam, imipenem, meropenem, ciprofloxacin, levofloxacin, minocycline, and trimethoprim/sulfamethoxazole. The genome of strain K432 was composed of the chromosome cK432 (4863 kb) and 3 plasmids: pK432-IMP (45.8 kb), pK432-TEM (75.6 kb), and pK432-NR (4.8 kb). In K432, six drug-resistant genes were detected, including bla_ACT-7 and fosA on cK432, bla_IMP-8, and qnrS1 on pK432-IMP, bla_SFO-1, and bla_TEM-1 on pK432-TEM. The pK432-IMP belonged to a novel incompatibility group, and pK432-TEM was an incompatibility (Inc) R plasmid. Both of these two plasmids shared similar conserved backbone regions with their reference plasmids, respectively. However, the single accessory regions in these two plasmids were different from their reference plasmids, indicating that new recombination and integration events had occurred in K432.

This study provides a comprehensive understanding of the genomic characterization of K432 and identified a novel plasmid for IMP transmission. Further investigation and surveillance are warranted for pK432-IMP-type plasmid. While routine monitoring of MDR E. hormaechei strains is necessary in China.