Work

Characterization of a multidrug-resistant hypovirulent ST1859-KL35 klebsiella quasipneumoniae subsp. similipneumoniae strain co-harboring tmexCD2-toprJ2 and bla

Year: 2025

Type: article

Abstract: • This is the first report of a novel multidrug-resistant hypovirulent ST1859-KL35 Klebsiella quasipneumoniae subsp. similipneumoniae strain in China. • The ST1859-KL35 strain (KP24) exhibits enhanced virulence compared to the K. quasipneumoniae reference strain ATCC 700,603. • KP24 harbors the rare co-existence of tmexCD2-toprJ2 and bla KPC-2 on a single conjugative plasmid, conferring resistance to last-resort antibiotics. • Phylogenetic analysis suggests that the ST1859 lineage of K. quasipneumoniae subsp. similipneumoniae may be undergoing regional expansion and global dissemination. The rise of multidrug-resistant (MDR) Klebsiella pneumoniae is a significant public health threat. Klebsiella quasipneumoniae is often misidentified as K. pneumoniae, and its genetic and virulence traits remain underexplored. This study characterizes the genomic and phenotypic features of a K. quasipneumoniae subsp. similipneumoniae strain (KP24). Antibiotic susceptibility was tested using microbroth dilution assay. Virulence was evaluated through serum killing assay and Galleria mellonella infection model. Whole genome sequencing (WGS) and bioinformatics analysis determined sequence typing, resistance profiles, and plasmid types. Conjugation assays assessed plasmid transferability, while phylogenetic analysis explored genetic relationships. KP24 exhibited an MDR phenotype, including resistance to carbapenems, ceftazidime/avibactam, and tigecycline. KP24 showed significantly higher serum survival and G. mellonella lethality than ATCC700603, though it was less virulent than the hypervirulent strain NUTH-K2044. WGS identified KP24 as ST1859 and KL35, harboring the aerobactin virulence gene cluster ( iucABCDiutA) and multiple resistance genes, including tmexCD2-toprJ2, bla KPC-2 , bla OXA-10, bla IMP-4 , and qnrS1 . Notably, the tmexCD2-toprJ2 and bla KPC-2 genes were located on the same plasmid (pKP24–1), an uncommon co-existence. Conjugation assays confirmed the independent transferability of pKP24–1 to Escherichia coli J53. Phylogenetic analysis revealed that ST1859 forms a distinct monoclade with low genetic diversity, closely related to ST334, suggesting regional expansion and potential global dissemination. KP24 represents a hypovirulent yet multidrug-resistant strain of K. quasipneumoniae subsp. similipneumoniae, with a concerning combination of virulence and resistance determinants. The co-location of tmexCD2-toprJ2 and bla KPC-2 on a transferable plasmid highlights the potential for horizontal gene transfer of critical resistance mechanisms.

Source: Journal of Global Antimicrobial Resistance

DOI: 10.1016/j.jgar.2025.03.009