Emergence of Ceftazidime-Avibactam Resistance Due to Plasmid-Borne <i>bla</i> _KPC-3 Mutations during Treatment of Carbapenem-Resistant Klebsiella pneumoniae Infections

Abstract

Ceftazidime-avibactam is a novel β-lactam/β-lactamase inhibitor with activity against carbapenem-resistant <i>Enterobacteriaceae</i> (CRE) that produce <i>Klebsiella pneumoniae</i> carbapenemase (KPC). We report the first cases of ceftazidime-avibactam resistance to develop during treatment of CRE infections and identify resistance mechanisms. Ceftazidime-avibactam-resistant <i>K. pneumoniae</i> emerged in three patients after ceftazidime-avibactam treatment for 10 to 19 days. Whole-genome sequencing (WGS) of longitudinal ceftazidime-avibactam-susceptible and -resistant <i>K. pneumoniae</i> isolates was used to identify potential resistance mechanisms. WGS identified mutations in plasmid-borne <i>bla</i>_KPC-3, which were not present in baseline isolates. <i>bla</i>_KPC-3 mutations emerged independently in isolates of a novel sequence type 258 sublineage and resulted in variant KPC-3 enzymes. The mutations were validated as resistance determinants by measuring MICs of ceftazidime-avibactam and other agents following targeted gene disruption in <i>K. pneumoniae</i>, plasmid transfer, and <i>bla</i>_KPC cloning into competent <i>Escherichia coli</i> In rank order, the impact of KPC-3 variants on ceftazidime-avibactam MICs was as follows: D179Y/T243M double substitution > D179Y > V240G. Remarkably, mutations reduced meropenem MICs ≥4-fold from baseline, restoring susceptibility in <i>K. pneumoniae</i> from two patients. Cefepime and ceftriaxone MICs were also reduced ≥4-fold against D179Y/T243M and D179Y variant isolates, but susceptibility was not restored. Reverse transcription-PCR revealed that expression of <i>bla</i>_KPC-3 encoding D179Y/T243M and D179Y variants was diminished compared to <i>bla</i>_KPC-3 expression in baseline isolates. In conclusion, the development of resistance-conferring <i>bla</i>_KPC-3 mutations in <i>K. pneumoniae</i> within 10 to 19 days of ceftazidime-avibactam exposure is troubling, but clinical impact may be ameliorated if carbapenem susceptibility is restored in certain isolates.