Coexistence of blaNDM–1 and blaIMP–4 in an IncHI5 plasmid harbored by carbapenem- resistant Raoultella ornithinolytica

Background: . Methods: Strain he2023 was identified and subjected to antimicrobial susceptibility testing using the BD Phoenix-M50 fully automated system. The strain was verified using MALDI-TOF. Carbapenemase genes were confirmed by PCR. Whole-genome sequencing (WGS) was performed to identify resistance genes and plasmid types. Conjugation experiments were conducted to assess transferability, and plasmid stability was evaluated through serial subculturing. Results: . Conjugation and transformation assays showed that the plasmid pNDM-IMP was non-transferable but exhibited high structural stability. Conclusion: . Non-transferable plasmids may serve as reservoirs or initial carriers for antibiotic resistance genes. Our findings highlights the importance of mobile genetic elements in the formation of multidrug resistance.