Klebsiella pneumoniae carbapenemase (KPC) producer resistant to ceftazidime-avibactam due to a deletion in the blaKPC3 gene.

OBJECTIVES

Carbapenemase-producing strains of Klebsiella pneumoniae (KPC) are a great health concern, and therapy with ceftazidime-avibactam represents a choice for the treatment of infections involving these strains. We report a strain resistant to ceftazidime-avibactam due to a deletion of six nucleotides in the bla gene sequence.

METHODS

Two strains, namely AMP920 and AMP2009, were isolated from the same patient a month apart. Antimicrobial susceptibility testing was performed both by broth microdilution and by Etest. Immunoenzymatic assay to detect carbapenemase was performed for both strains. The bla gene of both strains was amplified by PCR and sequenced. Enzyme activity towards carbapenems was tested by the CarbaNP test and hydrolysis spectrophotometer assay.

RESULTS

The two isolates differed in antimicrobial susceptibility. AMP920 showed meropenem and imipenem resistance (MIC 32 and 32 mg/mL). A month later the carbapenem MIC decreased to 8 and 1 mg/mL respectively, while the ceftazidime-avibactam MIC increased from 1 to 16 mg/mL. Both isolates showed a positive immunoenzymatic test for the KPC enzyme, but only AMP920 showed a positive CarbaNP test hydrolysing imipenem. The Bla gene was amplified in both strains. After sequencing, the two amplicons showed a KPC3 variant. The gene of the second isolate showed a deletion of six nucleotides at 498-503, resulting in a mutant variant with the deletion of glutamic acid and leucine residues at positions 167 and 168.

CONCLUSIONS

We detected a new deletion in the bla gene of a clinical strain of K. pneumoniae which resulted in resistance to ceftazidime-avibactam. The amino acids deleted are in the Ω loop (amino acids 165-179) of the KPC enzyme, enhancing ceftazidime affinity and preventing avibactam binding.