Characterization of a Novel Carbapenem-Resistant Klebsiella michiganensis Strain Coharboring the bla, bla, bla, 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, bla, bla, bla, bla, bla, bla, and bla) and another 12 resistance genes were screened by PCR, and bla, bla, and bla 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, bla, bla, 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, bla, bla, qnrS, and aac(6')-Ib-cr in China.