Molecular characterization of O25:H4 ST131 extraintestinal pathogenic Escherichia coli (ExPEC) harboring a blaOXA-48-carrying IncFII plasmid

Backgoround To characterize the antimicrobial resistance and genomic features of an OXA-48–producing Escherichia coli ST131 strain isolated in Japan from a patient without overseas travel history. Methods An O25:H4-ST131 E. coli strain (KIPH_2110030) was isolated from an 88-year-old woman with a urinary tract infection in Osaka. Antimicrobial susceptibility testing was performed using broth microdilution and disk diffusion methods. Carbapenemase activity was assessed via the modified carbapenem inactivation method (mCIM) and inhibitor-based synergy tests. Whole-genome sequencing, PCR, and plasmid analysis were conducted to identify resistance genes, plasmid types, and clade assignment. Results The isolate exhibited resistance to multiple β-lactams and intermediate susceptibility to meropenem and imipenem, despite a positive mCIM result. Genomic analysis revealed the presence of bla OXA-48 on an IncFII-type plasmid and bla CTX-M-27 on an IncFIA-type plasmid. The OXA-48 plasmid (pKIPH-2110030) showed high sequence similarity to a plasmid from a Netherland E. coli strain of a different sequence type, suggesting horizontal gene transfer. Clade analysis assigned the isolate to the C1-M27 lineage, a major ST131 subclade in Japan, but not previously associated with bla OXA-48 . Conclusion This study is the first report of an OXA-48–producing ST131 E. coli C1-M27 strain isolated from a Japanese patient without a history of overseas travel. While the dissemination of bla OXA-48 is primarily associated with IncL-type plasmids, reports involving IncFII-type plasmids are rare. The high sequence similarity to a European-derived plasmid suggests international transmission of carbapenem resistance plasmids and highlights the potential risk of their further spread.