Emergence of Extensively Drug-Resistant ST170 Citrobacter portucalensis with Plasmids pK218-KPC, pK218-NDM, and pK218-SHV from a Tertiary Hospital, China.

The objective of this study is to characterize the molecular mechanism of a clinical carbapenem-resistant Citrobacter portucalensis strain K218, which coproduces KPC and NDM carbapenemases. K218 was isolated from a patient's blood sample in a Chinese tertiary hospital. Carbapenemases were detected by the immunocolloidal gold technique. The MIC values were determined by VITEK2. Whole-genome sequencing was performed on K218 and sequence data were analyzed using phylogenetics and extensive genomic comparison. This study reveals that K218 contains a single 5.08 Mb chromosome (51.8% GC content) and four plasmids, pK218-KPC (106 Kb), pK218-NDM (111 Kb), pK218-SHV (191 Kb), and pK218-NR (5 Kb). Twenty-nine types of antibiotic resistance genes were carried on K218, including harbored on pK218-KPC and harbored on pK218-NDM. Detailed comparison of related plasmids of pK218-KPC, pK218-NDM, and pK218-SHV showed that they shared similar conserved backbone regions, respectively. Comprehensive annotation revealed large accessory modules were recombined on the genome of K218. Further analysis speculated that mobile genetic elements bearing abundant resistance genes facilitated the formation of these accessory modules. In conclusion, this study provides an in-depth understanding of the genomic characterization of K218, an extensively drug-resistant strain coproducing NDM and KPC carbapenemase. To the best of our knowledge, this is the first report of strain coharboring and from the clinical setting. This is the first report of extensively drug-resistant harboring both and . This study will not only extend the understanding of the structural dissection of plasmids and chromosomes carried in , but also expand knowledge of the genetic environment of the and genes. and genes have been suggested to facilitate the propagation and persistence of their host bacteria under different antimicrobial selection pressures. Large accessory regions carrying and genes have become hot spots for transposition and integration, and their structural variation and evolution should receive attention. The multidrug-resistant plasmids pK218-KPC, pK218-NDM, and pK218-SHV with several multidrug resistance regions and the chromosome cK218 with two novel transposons Tn and Tn contribute to the formation of extensively drug-resistant .