Characterisation of the novel transposon Tn7722 harbouring blaNDM-1: Insights into the evolutionary dynamics of resistance in Klebsiella pneumoniae

Background : Klebsiella pneumoniae is an opportunistic pathogen responsible for invasive infections. The rise of carbapenem-resistant K. pneumoniae , largely driven by acquisition of bla NDM genes, represents a global health threat. In French Polynesia, sporadic cases of NDM-producing Enterobacteriales have been reported. This study characterizes the genomic features of NDM-producing K. pneumoniae isolates from French Polynesia and evaluates the roles of clonal expansion and mobile genetic element (MGE)–mediated horizontal gene transfer in bla NDM dissemination. Materials and Methods : Between July 2006 and September 2021, 17 carbapenemase-producing K. pneumoniae isolates were identified among 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 were resistant to ertapenem (MICs 1 to >32 mg/L), with three resistant to imipenem (MICs 8 to >32 mg/L) and six to meropenem (MICs 2 to >8 mg/L). A novel IS 26 -mediated composite transposon, Tn 7722 (16,246 bp), carrying bla NDM-1 , qnrS1 and aph(3’)-VI genes, was detected in four isolates on IncF and IncR plasmids. Tn 7722 -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. This suggests a contribution of plasmid and Tn 7722 -associated elements to the diversity and evolution of carbapenem resistance. Ongoing genomic surveillance is vital to track the evolution of high-risk clones and MGEs guiding effective containment.