Ceftazidime-avibactam-resistant Klebsiella pneumoniae driven by multiple β-lactamase mutations: a hospital outbreak report.

OBJECTIVES

This study aimed to trace the clonal dissemination of ceftazidime-avibactam-resistant Klebsiella pneumoniae and clarify the complex ceftazidime-avibactam resistance mechanism caused by multiple β-lactamase variants.

METHODS

Six ceftazidime-avibactam-resistant K. pneumoniae clinical strains were isolated from six inpatients in the hepatobiliary surgery department. The antimicrobial resistance phenotypes, genotypes and single nucleotide polymorphisms of the strains were analysed. The resistance mechanism of K. pneumoniae strains to ceftazidime-avibactam was clarified through molecular cloning and enzyme kinetic measurement. The transferability of ceftazidime-avibactam resistance in the strains was verified by conjugation test, S1 pulsed field gel electrophoresis and plasmid sequence analysis. Fitness was determined using bacterial growth curves and plasmid stability tests.

RESULTS

The number of single nucleotide polymorphisms in all six K. pneumoniae strains was less than six, indicating a nosocomial clonal dissemination incident. K. pneumoniae carbapenemase 157 is unable to mediate resistance to ceftazidime-avibactam. The variant CTX-M-249, which mutated from CTX-M-65 (Ser130Gly and Pro167Ser), could mediate resistance to ceftazidime-avibactam, because avibactam alone could not efficiently inhibit enzyme activity. Under the selective pressure of ceftazidime-avibactam, a plasmid carrying blaCTX-M-249 was transferred into a recipient cell. Based on analysis of the genomic evolution and medical history, the selective pressure exerted by ceftazidime-avibactam during transmission may have contributed to the mutation, replication and truncation of the gene region conferring resistance, especially in the complex evolution of blaCTX-M-65. The coexistence of blaCTX-M-65 and blaCTX-M-249 alleles on different plasmids may have evolved into two copies of blaCTX-M-249, enhancing the resistance to ceftazidime-avibactam.

CONCLUSIONS

This study reports the clonal dissemination of K. pneumoniae carbapenemase 157-producing ceftazidime-avibactam-resistant K. pneumoniae strains and reveals the resistance mechanism of a novel bla variant, CTX-M-249 for the first time, to our knowledge. The dissemination of these mutant strains poses an alarm for global infection prevention and control.