[Emerging and comparative genomic analysis of a novel plasmid carrying bla_KPC-2 in Citrobacter freundii]

Objective: To explore the drug resistance mechanism and gene structure characteristics of a carbapenemase-producing novel incompatibility group plasmid pNY2385-KPC from Citrobacter freundii. Methods: A multi-drug resistant strain was obtained from urine samples of patients with fever in the emergency ward of Li Huili Hospital, Ningbo Medical Center. Bacterial species was preliminary identified and finally confirmed by 16S rRNA gene amplification and the average nucleotide identity alignment, respectively. The minimum inhibitory concentrations of the antimicrobial agents were determined by VITEK 2 Compact System. The complete genome sequence was obtained by "third-generation" sequencing methods, and then detailed annotation of gene function and comparative genomic analysis of plasmid structure were carried out by BLASTP/BLASTN, RefSeq, ConservedDomains, ResFinder, Isfinder, etc. Results: The pNY2385-KPC carried by citrobacter freundii NY2385 belonged a novel incompatibility group, and contained bla_KPC-2 and conjugative transfer (type Ⅳ secretory system, T4SS) genes, which could induce conjugative transfer. A total of 15 plasmids of the same type as pNY2385-KPC were retrieved by NCBI, which were from Citrobacter freundii, and the rest were from Serratia marcescens, Escherichia coli, Enterobacter cloacae, Klebsiella pneumoniae, Raoultella planticola and other bacteria, and were broad-host-range plasmids. The sequence comparative analysis of all 6 of the novel plasmid from Citrobacter freundii showed that the structure of the novel plasmid had certain conserved property, with Tn6296 variant structure carrying bla_KPC-2, and plasmid pCF1807-3 had both repA_pNY2385-KPC and repA_IncX8. Conclusion: The pNY2385-KPC type plasmids in Citrobacter freundii carried bla_KPC-2 resistance gene, which were divided into two subtypes: repA_pNY2385-KPC single replicator and repA_pNY2385-KPC/repA_IncX8 complex replicator, belonging to broad-host-range plasmids. And as a mobile genetic element, the plasmids promote the spread of bla_KPC-2.