First characterization of four repeat regions with the bla (NDM-1) carried on an IncFII plasmid in Enterobacter hormaechei.

Carbapenem-resistant Enterobacteriaceae (CRE) have emerged as a critical threat to global health, and multicopy resistance genes are a potential contributor to increased resistance. This study investigates a novel arrangement of four bla (NDM-1) genes in tandem on an IncFII plasmid from Enterobacter hormaechei. Whole-genome sequencing (WGS) of E. hormaechei isolates L710hy identified a four-tandem repeat of the bla (NDM-1) gene, with each copy's environment nearly identical (ISCR1-aph(3')-VI-ISAba125-bla (NDM-1)-ble-iso-tat-dsbD-cutA-sul1-ISCR1). The study suggests a correlation between the bla (NDM-1) copy number and minimum inhibitory concentration (MIC) values for carbapenems, though further research is needed to confirm this correlation. The stability of these four bla (NDM-1) tandem repeat structures was also investigated. This is the first documented case of bla (NDM-1) tandem repeats in E. hormaechei, and the ISCR1 and other insertion sequence may play a role in this arrangement.