Mutations in<i>bla</i>_KPC-3That Confer Ceftazidime-Avibactam Resistance Encode Novel KPC-3 Variants That Function as Extended-Spectrum β-Lactamases

Abstract

We identified four <i>bla</i>_KPC-3 mutations in ceftazidime-avibactam-resistant clinical <i>Klebsiella pneumoniae</i> isolates, corresponding to D179Y, T243M, D179Y/T243M, and EL165-166 KPC-3 variants. Using site-directed mutagenesis and transforming vectors into <i>Escherichia coli</i>, we conclusively demonstrated that mutant <i>bla</i>_KPC-3 encoded enzymes that functioned as extended-spectrum β-lactamases; mutations directly conferred higher MICs of ceftazidime-avibactam and decreased the MICs of carbapenems and other β-lactams. Impact was strongest for the D179Y mutant, highlighting the importance of the KPC Ω-loop.