PurposeTo explore the genetic characteristics of the IMP-4, NDM-1, OXA-1, and KPC-2 co-producing multidrug-resistant (MDR) clinical isolate,Citrobacter freundiiwang9.MethodsMALDI-TOF MS was used for species identification. PCR and Sanger sequencing analysis were used to identify resistance genes. In addition to agar dilution, broth microdilution was used for antimicrobial susceptibility testing (AST). We performed whole genome sequencing (WGS) of the strains and analyzed the resulting data for drug resistance genes and plasmids. Phylogenetic trees were constructed with maximum likelihood, plotted using MAGA X, and decorated by iTOL.ResultsCitrobacter freundiicarryingblaKPC-2,blaIMP-4,blaOXA-1, andblaNDM-1are resistant to most antibiotics, intermediate to tigecycline, and only sensitive to polymyxin B, amikacin, and fosfomycin. TheblaIMP-4coexists with theblaNDM-1and theblaOXA-1on a novel transferable plasmid variant pwang9-1, located on the integron In1337, transposon TnAS3, and integron In2054, respectively. The gene cassette sequence of integron In1337isIntI1-blaIMP-4-qacG2-aacA4′-catB3Δ, while the gene cassette sequence of In2054isIntI1-aacA4cr-blaOXA-1-catB3-arr3-qacEΔ1-sul1.TheblaNDM-1is located on the transposon TnAS3, and its sequence is IS91-sul-ISAba14-aph (3′)-VI-IS30-blaNDM-1-ble-trpF-dsbD-IS91.TheblaKPC-2is located on the transposon Tn2of plasmid pwang9-1, and its sequence isklcA-korC-ISkpn6-blaKPC-2-ISkpn27-tnpR-tnpA.Phylogenetic analysis showed that most of the 34\u00B0C. freundiiisolates from China were divided into three clusters. Among them, wang1 and wang9 belong to the same cluster as two strains ofC. freundiifrom environmental samples from Zhejiang.ConclusionWe foundC. freundiicarryingblaIMP–4,blaNDM–1,blaOXA-1, andblaKPC-2for the first time, and conducted in-depth research on its drug resistance mechanism, molecular transfer mechanism and epidemiology. In particular, we found thatblaIMP-4,blaOXA-1, andblaNDM-1coexisted on a new transferable hybrid plasmid that carried many drug resistance genes and insertion sequences. The plasmid may capture more resistance genes, raising our concern about the emergence of new resistance strains.