Molecular characterisation of two novel KPC variants mediating ceftazidime-avibactam resistance in ST11 Klebsiella pneumoniae.

OBJECTIVE

Mutations in blaKPC that confer resistance to ceftazidime-avibactam pose a new clinical challenge. This study reports the molecular characterisation of two novel KPC variants mediating ceftazidime-avibactam resistance in Klebsiella. pneumoniae.

METHODS

Six K. pneumoniae strains were isolated from the endotracheal aspirate of a single patient. Antimicrobial susceptibility testing, whole genome sequencing, conjugation and cloning assays, enzyme kinetic and growth assays were performed to explore the molecular characterisation and antimicrobial resistance mechanisms.

RESULTS

Two novel KPC variants, KPC-207 (L169Q and 274-275S ins) and KPC-208 (L169Q and D179Y), produced by a patient infected with KPC-producing ST11-KL19 K. pneumoniae which underwent a drug-resistant mutation during treatment. The mutation process encompassed a sequential transition from KPC-2 to KPC-207, then KPC-208, a reversion to KPC-207, and ultimately a return to KPC-208. Both KPC-207-and KPC-208-producing strains were resistant to ceftazidime-avibactam, but showed restored susceptibility to carbapenems. Cloning assays showed a 128- and 64-fold increase in the MIC of ceftazidime-avibactam for clonal strains carrying blaKPC-207 and blaKPC-208 compared to blaKPC-2 carrier. Enzyme kinetic assays revealed diminished hydrolysis of imipenem and meropenem by KPC-207 and KPC-208, along with reduced inhibitory effect of avibactam on both proteins. The core structure of the plasmid harboring the blaKPC-207 and blaKPC-208 genes was Tn1721-ISkpn6-blaKPC-ISkpn27-IS26, which belonged to the A2-type Tn1721. Compared with the blaKPC-2, the blaKPC-207 and blaKPC-208 genes had essentially no effect on the cost of adaptation to K. pneumoniae.

CONCLUSIONS

The antimicrobial susceptibility and the blaKPC should be continuously monitored during clinical treatment of carbapenem-resistant K. pneumoniae with ceftazidime-avibactam.