Co-carriage of bla KPC-33 and tmexCD2-toprJ2 on a Transferable Plasmid in an ST15-KL19 Klebsiella pneumoniae Isolate

Ceftazidime-avibactam and tigecycline remain first-line antibiotics for treating multidrug-resistant Klebsiella pneumoniae , yet their clinical utility is increasingly threatened by evolving resistance, primarily mediated by KPC variants and the TMexCD-TOprJ efflux system, respectively. Of note, their coexistence in K. pneumoniae , particularly on the same mobile genetic platform, represents an emerging antimicrobial resistance concern. In this study, K. pneumoniae strain 1640 was obtained as a clinical isolate and investigated using antimicrobial susceptibility testing, conjugation assays, whole-genome sequencing, and bioinformatic analysis. K. pneumoniae 1640 exhibited resistance to ceftazidime-avibactam but remained susceptible to carbapenems, aztreonam-avibactam, and tigecycline. Whole-genome sequencing revealed that bla KPC−33 and tmexCD2-toprJ2 were co-located on a 146,193-bp transferable multireplicon plasmid, which harbored a conserved backbone and variable resistance regions. Conjugation assays demonstrated successful transfer of this plasmid to Escherichia coli EC600 at a frequency of 1.56 × 10⁻ 5 . Plasmid acquisition resulted in decreased susceptibility to several β-lactams, whereas the tigecycline susceptibility remained unaltered. Phylogenetic analysis placed strain 1640 within the Chinese ST15-KL19 lineage; however, none of the other ST15 isolates examined carried the identical bla KPC−33 / tmexCD2-toprJ2 combination. These findings revealed that the carbapenem and tigecycline resistance determinants carried by strain 1640 were co-located on the same mobile plasmid and might potentially transmit horizontally to additional strains, warranting continued surveillance.