In vivo selection of KPC-94 and KPC-95 in Klebsiella pneumoniae isolates from patients treated with ceftazidime/avibactam

Ceftazidime/avibactam (CZA) is used to treat infections caused by Klebsiella pneumoniae carbapenemase-producing K. pneumoniae (KPC-Kp). Resistance to CZA is commonly related to point mutations in the bla(KPC) gene. Here we describe the in vivo emergence of CZA resistance in clinical isolates of KPC-Kp from four patients treated with this combination therapy. Four pre-therapy and five post-therapy KPC-Kp isolates were examined. Antibiogram (microdilution and gradient strips) and whole-genome sequencing were performed. The role of KPC mutations was validated by cloning bla(KPC) genes into competent Escherichia coli. All KPC-Kp isolates recovered before treatment with CZA were susceptible to CZA and produced KPC-3. Five KPC-Kp isolates recovered after treatment were resistant to this combination. Three post-therapy isolates from two patients produced KPC-31 (D179Y mutation). Additionally, we identified the novel substitution LN169-170H (KPC-94) in one isolate, and the combination of two independently described mutations, D179Y and A172T (KPC-95), in another isolate. All KPC-Kp isolates belonged to sequence type 512 (ST512). All CZA-resistant isolates with bla KPC variants had restoration of carbapenem susceptibility. In conclusion, resistance to CZA was related to bla(KPC) mutations, including the new KPC-94 and KPC-95 alleles, which do not cause carbapenem resistance. (c) 2022 Elsevier Ltd and International Society of Antimicrobial Chemotherapy. All rights reserved.

Automated summary

This study describes the emergence of CZA resistance in clinical isolates, which is related to mutations in the bla(KPC) gene. The study identifies new alleles, KPC-94 and KPC-95, that do not cause carbapenem resistance.