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 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 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 variants had restoration of carbapenem susceptibility. In conclusion, resistance to CZA was related to bla mutations, including the new KPC-94 and KPC-95 alleles, which do not cause carbapenem resistance.