Characterization of a Novel Carbapenem-Resistant Klebsiella michiganensis Strain Coharboring the bla SIM-1 , bla OXA-1 , bla CTX-M-14 , qnrS , and aac(6′)-Ib-cr Genes

Carbapenem-resistant Klebsiella michiganensis (CRKM) and Klebsiella oxytoca (CRKO) strains have occasionally been reported to cause severe infections. However, SIM-producing K. michiganensis strains have never been described. In this study, we phenotypically and genetically characterized 6 CRKM and CRKO strains isolated over the past 10 years at a Chinese tertiary hospital. All six strains were positive for the mCIM test, and five were positive for the MBL test. Carbapenemase-encoding genes ( bla KPC , bla NDM , bla VIM , bla IMP , bla OXA-23 , bla OXA-24 , bla OXA-51 , and bla OXA-58 ) and another 12 resistance genes were screened by PCR, and bla KPC , bla NDM , and bla IMP were identified in five strains. However, the CRKM strain KM41, which was resistant to IPM and MEM with minimum inhibitory concentrations (MICs) of 4 µg/ml and 16 µg/ml, respectively, had positive mCIM and MBL results but lacked the eight carbapenemase-encoding genes. Whole-genome sequencing of the KM41 strain revealed more than 20 drug resistance genes; in particular, bla SIM-1 , bla OXA-1 , bla CTX-M-14 , qnrS , aac(6′)-Ib-cr , aadA17 , and aar-3 were found to be located in a single plasmid. To the best of our knowledge, this is the first description of a K. michiganensis strain coharboring bla SIM-1 , bla OXA-1 , bla CTX-M-14 , qnrS , and aac(6′)-Ib-cr in China.