Characterization of an NDM-1-Producing Citrobacter koseri Isolate from China.

PURPOSE: The continuous rise in carbapenemase-producing Enterobacteriaceae infections is a major public health concern. However, there is limited information available on New Delhi metallo-β-lactamase-1 (NDM-1) producing Citrobacter koseri . In this study, we isolated a bla NDM-1 -carrying C. koseri from a stool sample of an inpatient. Our aim was to investigate the phenotypic and genomic features of this clinically derived carbapenem-resistant C. koseri isolate and to characterize the transmission pattern of the IncFII/IncN plasmid that carries the bla NDM-1 gene.

METHODS AND RESULTS: S1-PFGE, Southern blot and conjugation assay confirmed the presence of bla NDM-1 gene in a conjugative plasmid. C. koseri L2395 and transconjugant L2395-EC600 strains showed similar resistance spectrum. Whole-genome analysis revealed that pL2395_NDM is an IncFII/IncN plasmid with a length of 67,839 bp. Moreover, bla NDM-1 gene was found encoded in the IS Kpn19-bla NDM-1 - ble-tnpF-dsbD-cutA -IS Kpn19 cassette array. Phylogenetic analysis revealed that strain L2395 was close to an IMP-4-bearing C. koseri from Australia.

CONCLUSION: Ongoing surveillance will be essential to control and prevent the spread of carbapenem-resistant Citrobacter spp. in the future.