Evolution of ceftazidime-avibactam resistance driven by variation in to during treatment of ST11-K64 hypervirulent .

INTRODUCTION

The emergence of pneumoniae carbapenemase (KPC) variants has significantly compromised the efficacy of ceftazidime-avibactam (CZA), a critical antibiotic for treating carbapenem-resistant (CRKP) infections. This study investigates the novel KPC-190 variant, identified in a hypervirulent ST11-K64 strain during CZA therapy, which confers resistance to CZA while partially restoring carbapenem susceptibility.

METHODS

The clinical isolate LX02 harboring was characterized using antimicrobial susceptibility testing, whole-genome sequencing (Illumina and Nanopore), and plasmid analysis. Functional studies included plasmid transformation, cloning assays, and enzyme kinetics (spectrophotometric analysis of purified KPC-190 protein). Genetic context was mapped using bioinformatics tools (RAST, ResFinder, Proksee), and virulence determinants were identified.

RESULTS

KPC-190 exhibited a unique resistance profile: high-level CZA resistance (MIC >64 μg/mL) with reduced carbapenem MICs (imipenem MIC = 2 μg/mL). Enzyme kinetics revealed decreased cat/Km for carbapenems and ceftazidime, alongside a 9-fold higher IC50 for avibactam (0.13 μM vs. KPC-2's 0.014 μM). Genomic analysis identified within an IS26 flanked mobile element (IS26-ISKpn8- -ΔISKpn6-ΔtnpR-IS26) on an IncFII plasmid. The strain also carried hypervirulence markers (, , and type 1/3 fimbriae).

DISCUSSION

The KPC-190 variant underscores the adaptive evolution of under antibiotic pressure, combining CZA resistance via enhanced ceftazidime affinity and avibactam evasion with retained carbapenem hydrolysis. Its association with hypervirulence plasmids and IS26-mediated mobility poses a dual threat for dissemination. These findings highlight the urgent need for genomic surveillance and alternative therapies (e.g., meropenem-vaborbactam) to address KPC-190-mediated resistance.