Characterization of the novel transposon Tn7722 harboring bla NDM-1 : Insights into the evolutionary dynamics of resistance in Klebsiella pneumoniae

TL;DR

This study characterizes a novel transposon Tn7722 carrying bla NDM-1 in Klebsiella pneumoniae, revealing its role in resistance gene spread and highlighting the importance of genomic surveillance for containment.

Contribution

It identifies and analyzes a new transposon Tn7722 mediating resistance gene transfer in K. pneumoniae, providing insights into its evolutionary dynamics and global dissemination.

Findings

Discovery of a novel IS26-mediated transposon Tn7722.

Detection of Tn7722 in diverse bacterial genomes worldwide.

Genetic diversity of NDM-producing K. pneumoniae in French Polynesia.

Abstract

Background: Klebsiella pneumoniae is a major opportunistic pathogen responsible for various invasive infections. The rise of carbapenem-resistant K. pneumoniae, primarily due to acquisition of bla NDM genes, presents a serious global health threat. In French Polynesia, where international travel is frequent, sporadic cases of NDM-producing Enterobacteriales have emerged. This study aims to characterize the genomic features of NDM-producing K. pneumoniae isolates collected in French Polynesia and evaluate the roles of clonal expansion and horizontal gene transfer mediated by mobile genetic elements in bla NDM spread. Materials and Methods: Between July 2006 and September 2021, 17 carbapenemase-producing K. pneumoniae isolates were identified from 715 clinical samples in Tahiti. Whole-genome sequencing using Illumina MiSeq and Oxford Nanopore technologies was performed. Results: Seven NDM-producing K. pneumoniae strains were identified, five bla NDM-1 and two bla NDM-9 variants. All isolates were resistant to ertapenem (MICs 1 to >32 mg/L), with three resistants to imipenem (MICs 8 to >32 mg/L) and six to meropenem (MICs 2 to >8 mg/L). A novel IS26mediated composite transposon, Tn7722 (16,246 bp), was detected in four isolates on IncF and IncR plasmids. This transposon also carried qnrS1 and aph(3')-VI genes, conferring resistance to fluoroquinolones and aminoglycosides. Tn7722-like elements were found in diverse bacterial genomes worldwide, suggesting it facilitates bla NDM transmission across multiple species and regions. Conclusion: NDM-producing K. pneumoniae in French Polynesia remain sporadic but genetically diverse, without evidence of local outbreak. It underscores the role of plasmid and Tn7722-driven evolution and adaptation. Ongoing genomic surveillance is vital to track the evolution of highrisk clones and MGEs guiding effective containment.