Development of ceftazidime-avibactam resistance driven by conversion of blaKPC-2 to blaKPC-78 during treatment of ST463 carbapenem-resistant Pseudomonas aeruginosa infection.

OBJECTIVE

The emergence of ceftazidime-avibactam (CZA)-resistant carbapenem-resistant Pseudomonas aeruginosa (CRPA) poses a major clinical challenge in contemporary clinical practice. In this study, we report the first identification of blaKPC-78, which is driven by a mutation from blaKPC-2 in a clinical CRPA strain.

METHODS

Six blaKPC-78 CRPA isolates, along with two blaKPC-2 strains from one patient, were subjected to antimicrobial susceptibility testing (AST), whole-genome sequencing (WGS), conjugation, and growth assays. Mechanistic investigations included structural modelling and docking, cloning experiments, efflux inhibition, and reverse transcription quantitative polymerase chain reaction (RT-qPCR).

RESULTS

The emergence of CZA resistance in CRPA isolates was driven by a mutation from blaKPC-2 to blaKPC-78 during CZA therapy. The AST results showed that all KPC-78-producing CRPA exhibited a multidrug-resistant phenotype. WGS revealed that these strains belong to ST463, and blaKPC-78 gene was located in a type I plasmid and carried by the Tn6296 transposon. Additionally, the co-occurrence of efflux pump overexpression and KPC-78 enzyme's stronger binding affinities for both ceftazidime and avibactam contributed to high-level resistance to CZA in CRPA. Moreover, despite the slower logarithmic growth of KPC-78-producing P. aeruginosa in monoculture, in vitro competitive co-culture experiments revealed that it conferred a competitive advantage over the KPC-2-producing strains.

CONCLUSIONS

We report the first identification of blaKPC-78 in CRPA, delineate its evolutionary trajectory, and describe its genetic characteristics. The elevated hydrolytic activity of the KPC-78 producing strain, along with the overexpression of efflux pumps, contributes to its high-level resistance to CZA. Considering the widespread occurrence of ST463 CRPA in China, it is imperative to enhance the surveillance of KPC-producing CRPA.