Abstract

Objectives To identify and characterise a novel KPC variant (KPC-271) and evaluate its molecular, phenotypic and fitness impacts in an ST15-KL19 Klebsiella pneumoniae strain. Methods Sequential K. pneumoniae isolates were obtained from a single patient undergoing ceftazidime-avibactam and carbapenem therapy. The following tests were performed: antimicrobial susceptibility testing; plasmid conjugation and transformation assays; bla KPC cloning; whole-genome sequencing; and enzyme kinetic assays. Fitness costs were assessed using plasmid stability, growth curves and competition assays. The genetic environments of the bla KPC were analysed using comparative genomics. Results KPC-271 harboured a D179Y substitution within the omega loop and an insertion (KDDKH) at Ambler position 269 within the 267-275 loop. Antimicrobial susceptibility testing of clinical isolates revealed ceftazidime MICs of >32 mg/L for both KPC-271 and KPC-2, ceftazidime-avibactam MICs of >64 vs. 1 mg/L, meropenem MICs of 2 vs. 64 mg/L, and imipenem MICs of 0.125 vs. 32 mg/L. Analysis of the kinetic parameters of KPC-271 compared to KPC-2 revealed enhanced ceftazidime hydrolysis and reduced avibactam inhibition with an increased IC₅₀ value, but diminished carbapenemase activity. Fitness assays indicated that bla KPC-271 imposed a minimal cost, potentially conferring competitive advantages over bla KPC-2 . Genomic analysis revealed that the bla KPC-271 was located within NTE KPC -Ib-like elements on plasmids that were closely related to those in circulation in Shanghai. Conclusions KPC-271 mediates resistance to ceftazidime-avibactam while restoring carbapenem susceptibility without imposing a significant fitness burden. The localisation of bla KPC-271 within mobile elements highlights its dissemination potential and underlines the need for continuous molecular surveillance and prudent antibiotic use.