Emergence of transferable ceftazidime-avibactam resistance in KPC-producing Klebsiella pneumoniae due to a novel CMY AmpC β-lactamase in China

Objectives: To evaluate the molecular mechanisms of ceftazidime/avibactam (CAZ/AVI) resistance in six Klebsiella pneumoniae strains that co-produce K. pneumoniae carbapenemase (KPC)-2 and a novel variant of CMY cephalosporinase in a Chinese hospital. Methods: Antimicrobial susceptibility was determined by broth microdilution. Whole-genome sequencing (WGS) was performed to investigate potential resistance determinants. Plasmid conjugation, electroporation, S1 nuclease pulsed-field gel electrophoresis (S1-PFGE) hybridization and cloning experiment were carried out to investigate the resistance plasmids and genes. Results: A high level of CAZ/AVI resistance was observed in six KPC-Kp strains (MIC 128 mg/L). Five strains were isolated in 2015 and one in 2016, before the approval of CAZ/AVI in China. Sequence analysis indicated that all the strains belonged to sequence type (ST) 11 and uniformly carried a novel CMY AmpC beta-lactamase gene, designated bla(CMY-172). When compared with CMY-2, CMY-172 has a deletion of three consecutive amino acids (K290, V291 and A292) in the R2-loop region and a non-synonymous amino acid substitution at position 346 ((NI)-I-346). The bla(CMY-172)-bearing plasmid, pKPCZA02_4, was 93.3 Kb, IncI1-I type, and conjugative; bla(CMY-172) was located in an IS1294-mediated transposon. Plasmid conjugation and DNA fragment cloning proved that bla(CMY-172) was responsible for CAZ/AVI resistance. Conclusions: Our study identified conjugative plasmid-mediated bla(CMY-172) as a new mechanism for CAZ/AVI resistance in clinical KPC-Kp strains. Careful monitoring of CAZ/AVI susceptibility is imperative for preventing the spread of the resistance gene. (C) 2021 European Society of Clinical Microbiology and Infectious Diseases. Published by Elsevier Ltd. All rights reserved.