Near-clonal Raoultella planticola isolates co-harboring IncU and IncX3 blaNDM−1 plasmids and blaKPC−2 plasmids

Background Raoultella planticola is an uncommon but increasingly recognized opportunistic pathogen in clinical settings. Its carbapenem-resistance architecture remains insufficiently characterized, particularly at the plasmid level. We investigated the genomic contexts and transfer potential of carbapenemase determinants in two clinical R. planticola isolates. Methods Two clinical R. planticola isolates recovered from separate routine diagnostic specimens at a tertiary-care hospital were analyzed by antimicrobial susceptibility testing, S1 nuclease pulsed-field gel electrophoresis (S1-PFGE), Southern blotting, qualitative conjugation assays, and hybrid whole-genome sequencing using short- and long-read data. Acquired resistance genes, plasmid replicons, and genetic environments surrounding bla NDM−1 and bla KPC−2 were characterized in silico. Results Both isolates were resistant to carbapenems and had low tigecycline and colistin MICs. Each isolate co-harbored two bla NDM−1 -positive plasmids: a large IncU-type plasmid and a smaller IncX3-type plasmid. Each isolate also carried bla KPC−2 on a separate small untypable plasmid. Qualitative conjugation assays confirmed acquisition of bla NDM−1 by Escherichia coli EC600, but did not resolve which bla NDM−1 -positive plasmid backbone had transferred. Comparative genomics identified conserved mobile-element-associated structures around bla NDM−1 , including IS26 -associated arrangements in the IncX3 plasmids. Wry231 and Wry237 differed by one core-genome SNP, supporting near-clonal relatedness and a localized clinical cluster. Conclusions Near-clonal clinical R. planticola isolates can co-harbor IncU- and IncX3-type bla NDM−1 plasmids together with separate small bla KPC−2 plasmids. The qualitative transfer experiments demonstrate acquisition of bla NDM−1 by a heterologous recipient, although the transferred backbone was not determined. These findings broaden the genomic evidence for carbapenem-resistance architecture in this underrecognized pathogen and support continued plasmid-resolved surveillance.