Emergence of Klebsiella variicola harboring blaKPC-2 and blaCTX-M-15 on an IncP-6/IncR hybrid plasmid from a bloodstream infection case in Japan.

OBJECTIVES

Carbapenem-resistant Gram-negative bacteria represent a major global health threat, with Klebsiella pneumoniae carbapenemase (KPC) producers, such as Klebsiella variicola, being particularly concerning due to their association with poor clinical outcomes. Therefore, we aimed to characterize the genome and phenotype of clinical KPC-producing K. variicola isolates in Japan, where such strains are rare.

METHODS

We investigated three K. variicola isolates obtained from blood, urine, and stool samples from a patient with bloodstream infection. The isolates were assessed using antimicrobial susceptibility testing, DNA fingerprinting, whole-genome sequencing analysis, and conjugation assay.

RESULTS

The three K. variicola isolates exhibited resistance or intermediate susceptibility to all β-lactam antibiotics, and DNA fingerprinting revealed identical banding profiles. The isolate from the blood sample harbored blaKPC-2 and blaCTX-M-15 on a hybrid IncP-6/IncR plasmid. Phylogenetic analysis revealed a close relationship between the clinical isolate and a K. variicola strain previously recovered from a sewage tank at the same hospital, despite differences in their antimicrobial resistance gene profiles. The IncP-6/IncR plasmid harbored multiple transposable elements. Additionally, the absence of conjugative transfer suggests that transposon-mediated horizontal gene transfer is the primary mechanism for resistance gene acquisition in the plasmid.

CONCLUSION

This study highlights the emergence of carbapenemase-producing K. variicola in the clinical setting and its potential role as a reservoir for antimicrobial resistance genes. The identification of a novel blaKPC-2/blaCTX-M-15-carrying IncP-6/IncR hybrid plasmid underscores the need for continued surveillance in clinical and environmental contexts to better understand the evolving epidemiology and transmission dynamics of multidrug-resistant bacteria.