Comprehensive genomic analysis of carbapenem-resistant Citrobacter freundii and characterization of a co-carrying blaKPC−2 and blaNDM−1 isolate in Zhejiang Province， China

BACKGROUND: co-harboring strain. METHODS: Clinical CRCF isolates were collected from multiple tertiary hospitals in China, and their basic clinical data were obtained. Phenotypic characterization was performed through antimicrobial susceptibility testing and plasmid conjugation transfer assays. Bioinformatic analysis was conducted based on whole-genome sequencing data. RESULTS: co-harboring strain (T1001) confirmed that both genes were located on conjugative plasmids, with IS26 and ISKpn19 facilitating their integration. CONCLUSION: and show high carriage rates of IncX3 and IncFIB plasmids, suggesting a possible association between these replicon types and the dominant clones. Although amikacin, tigecycline, and colistin remain effective in vitro, the complex recombination mechanisms of resistance genes-particularly IS26/ISKpn19-mediated modular dissemination-pose a serious nosocomial threat. Enhanced infection control measures are urgently needed to curb the spread of these multidrug-resistant bacteria and their resistance plasmids.