LAUSR

Purpose NDM-1-producing Citrobacter portucalensis and Citrobacter freundii simultaneously occurred in a hospital. This study aims to characterize the blaNDM-1-carrying plasmids in these Citrobacter strains. Methods Cf7303, Cf7308, and Cf7313 were recovered from three patients in a teaching hospital from September 24 to October 1, 2021. Bacteria were identified by MALDI-TOF mass spectrometry, and antibiotics susceptibility tests were determined by VITEK® 2 compact system. Whole-genome sequencing (WGS) was performed using the HiSeq Illumina and QNome platform to characterize the genomes. Results Cf7303 was identified as C. portucalensis Sequence Type 328 by WGS, and harbored two plasmids, namely pCf7303 and a novel IncFIB pNDM-Cf7303 on which antibiotic-resistant genes (blaTEM-1, blaCTX-M-14, blaNDM-1, aac (3)-IId, aadA2, fosA3, sul1, sul2, catA2, tetD, dfrA12, qacEdelta1, mph(A), and bleMBL) are located. C. freundii strain Cf7308 and Cf7313 belonged to the same Sequence Type 98. Cf7308 contained two plasmids, pCf7308, and an IncN1 pNDM-Cf7308 with homology to pNDM-BTR in E. coli and pNDM-CWH001 in C. freundii. Conclusion We characterized a putatively novel IncFIB plasmid carrying blaNDM-1 in C. portucalensis. In addition, the closely related blaNDM-1-carrying IncN1 plasmids in E. coli and C. freundii suggest that interspecies or intraspecies horizontal transfer occurs in China.