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

Abstract

OBJECTIVES\nTo evaluate the molecular mechanisms of ceftazidime/avibactam (CAZ/AVI) resistance in six Klebsiella pneumoniae that co-producing K. pneumoniae carbapenemase (KPC)-2 and a novel variant of CMY cephalosporinase in a Chinese hospital.\n\n\nMETHODS\nAntimicrobial susceptibility was determined by broth microdilution. Whole genomic sequencing (WGS) was performed to investigate potential resistant determinants. Plasmid conjugation, electroporation, S1-PFGE hybridization and cloning experiment were carried out to investigate the resistant plasmids and genes.\n\n\nRESULTS\nA 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 all the strains belonged to sequence type (ST) 11 and uniformly carried a novel CMY AmpC β-lactamase gene, designated blaCMY-172. When compared with CMY-2, CMY-172 owns 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 (N346I). The blaCMY-172-bearing plasmid, pKPCZA02_4, was size of 93.3 Kb, IncI1-I type and conjugative. blaCMY-172 located in an IS1294-mediated transposon. Plasmid conjugation and DNA fragment cloning proved blaCMY-172 was responsible for CAZ/AVI resistance.\n\n\nCONCLUSIONS\nOur study identified conjugative plasmid-mediated blaCMY-172 as a new mechanism for CAZ/AVI resistance in clinical KPC-Kp strains. Careful monitoring of CAZ/AVI susceptibility is imperative for preventing spread of the resistant gene.