Characterization of ceftazidime-avibactam resistant blaKPC-35-harbouring Klebsiella pneumoniae ST15 from bloodstream infection.

The emergence of carbapenem-resistant Klebsiella pneumoniae (CRKP) poses a significant challenge globally. This study reports on a ceftazidime-avibactam resistant KPC-35 producing K. pneumoniae strain from a patient with cerebral hemorrhage undergoing ceftazidime-avibactam (CZA) treatment. In this study, three K. pneumoniae strains were isolated from blood samples of a patient after intracerebral hemorrhage. Broth microdilution, checkerboard assays, and time-kill assays were employed to evaluate antimicrobial susceptibility and combination regimens. Whole-genome sequencing (WGS) was used to investigate the genetic characteristics of the three K. pneumoniae strains. The results showed that, K. pneumoniae KP29870 strain belonged to ST15, it was KPC-35 positive and exhibited a 16-fold higher minimum inhibitory concentration (MIC) of CZA (32 vs 1-2 mg L-1) but significantly lower MICs of imipenem (2 vs ≥ 16 mg L-1) and meropenem (1 vs ≥ 16 mg L-1), compared to the other two K. pneumoniae strains, that harboured KPC-2. CZA resistant K. pneumoniae remained highly susceptible to aztreonam-avibactam (MIC 0.03/4 mg L-1). The single base mutation (T503C) resulted in the substitution of leucine with proline at Ambler amino acid position 169 (L169P), corresponding to an evolution from blaKPC-2 to blaKPC-35. Checkerboard and time-kill assays demonstrated synergistic antibacterial effects for CZA combined with imipenem, meropenem, or with aztreonam against KPC-35 positive K. pneumoniae. This is the first report in China of a K. pneumoniae ST15 strain harboring blaKPC-35 emerging from a blaKPC-2-positive ancestor during CZA treatment. The new β-lactamase inhibitor combination such as aztreonam-avibactam monotherapy or CZA combined with carbapenems or with aztreonam represents promising treatment strategies against such KPC mutants. We recommend prompt susceptibility testing and KPC genotyping if resistance emergence is suspected during CZA therapy.