Molecular epidemiology of NDM-producing Enterobacterales in Huai'an, China: Genomic diversity and evaluation of aztreonam-avibactam and cefiderocol.

Metallo-β-lactamase-producing carbapenem-resistant Enterobacterales (MBL-CRE) pose a serious threat due to antimicrobial resistance. However, their prevalence in the Huai'an region of Jiangsu Province in eastern China remains unknown. Carbapenem-resistant Enterobacterales (CRE) isolates collected from Xuyi People's Hospital were screened for carbapenemase production using the modified carbapenem inactivation method (mCIM) and EDTA-modified carbapenem inactivation method (eCIM), followed by PCR confirmation. Antimicrobial susceptibility testing, biofilm formation assays, growth kinetics analyses, and whole-genome sequencing with bioinformatics were performed to characterize the isolates. The 12 NDM-producing Enterobacterales identified comprised seven Escherichia coli, three Klebsiella pneumoniae, and two Enterobacter hormaechei. Beyond carbapenem resistance, resistance to aztreonam, tetracycline, fluoroquinolones, and aminoglycosides was common among the isolates. Four isolates (including three E. coli) showed intermediate susceptibility to cefiderocol, and the aztreonam-avibactam combination exhibited synergistic activity against aztreonam-resistant Enterobacteriaceae isolates. Genomic analysis revealed eight isolates carrying blaNDM-5, three carrying blaNDM-1, and one carrying blaNDM-13. All isolates belonged to distinct sequence types, including two novel types. The NDM-13 isolate and one NDM-1-positive E. hormaechei isolate displayed distinct genetic contexts, whereas most isolates harbored a blaNDM-bleMBL-trpF-tat-dct genetic structure. Among the three cefiderocol-intermediate E. coli isolates, mutations were identified in cirA and ftsI. This study reveals the prevalence and diverse genetic backgrounds of MBL-CRE in Xuyi County, demonstrates the potent activity of aztreonam-avibactam, and suggests that cefiderocol resistance may involve multiple factors.