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

BACKGROUND

Ceftazidime-avibactam (CZA) is used to treat infections caused by KPC-producing Klebsiella pneumoniae (KPC-Kp). Resistance to CZA is commonly related to point mutations in the bla_KPC gene.

OBJECTIVES

We describe the in vivo emergence of CZA resistance in clinical isolates of KPC-Kp from four patients treated with this combination therapy.

METHODS

Four pre-therapy and five post-therapy isolates were examined. Antibiogram (microdilution; gradient strips) and whole genome sequencing were performed. The role of KPC mutations was validated by cloning bla_KPC genes into competent E. coli.

RESULTS

All 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 in another isolate of two independently described mutations, D179Y and A172T (KPC-95). All KPC-producing K. pneumoniae isolates belonged to ST512. All CZA-resistant isolates with bla_KPC variants had restoration of carbapenem susceptibility.

CONCLUSIONS

Resistance to CZA was related to bla_KPC mutations, including the new KPC-94 and KPC-95 alleles, which did not cause carbapenem resistance.