Heterogeneity of plasmids containing OXA-48-like and NDM-5 carbapenemases and emergence of OXA-181 and NDM-5 co-carrying strains and plasmids in Escherichia coli from veterinary settings.

Plasmids encoding the carbapenemase genes blaOXA-48, blaNDM-5, and blaOXA-181 in carbapenemase-producing Escherichia coli (CP-Ec) from different small animal veterinary settings were characterized to determine their dissemination potential and structural diversity. Twenty-one CP-Ec isolates recovered from canine and feline clinical samples, intestinal carriage, and hospital environments between 2022 and 2025 were subjected to antimicrobial susceptibility testing and whole-genome sequence (WGS)-based phylogenetic and plasmid analyses. The isolates belonged to sequence type (ST) 156 (n = 8), ST410 (n = 8), ST131 (n = 3), ST90 (n = 1), and ST354 (n = 1). Rare conjugative IncFII plasmids containing blaOXA-48 within a Tn6237-like element, previously found in a canine K. pneumoniae isolate, were detected in ST131 and ST410 (subclade B3/H24Rx) strains. Novel conjugative IncA/C plasmids carrying blaOXA-181 and non-conjugative IncFII/FIA/FIB co-carrying blaNDM-5 and blaOXA-181 were identified in ST410 subclades B4/H24RxC and B5/H24RxC, respectively. The blaOXA-181 genetic structure was embedded within an IS26-flanked by composite transposon identical to that found in epidemic IncX3 plasmids among Enterobacterales. Conserved non-conjugative IncFII/FIA/FIB/Q1 NDM-5 plasmids previously described in ST410 were detected in an emerging ST156 lineage, whereas conjugative IncFII/FIA NDM-5 and IncX3 OXA-181 persisted in sporadic ST90 and ST354 strains, respectively. These findings highlight the circulation of heterogenous carbapenemase-encoding mobile genetic elements among high-risk E. coli clones and other Enterobacterales in companion animals and veterinary environments, facilitating plasmid evolution and clonal expansion. WGS-based surveillance should be implemented to monitor CP Enterobacterales and plasmid dissemination in order to support antimicrobial stewardship and infection prevention and control in veterinary medicine.