Genomic Characterization and Qualitative Transfer of blaNDM-5 in Two Porcine Escherichia coli Isolates from Xinjiang China

Genomic information on NDM-5-producing Escherichia coli from livestock in northwestern China remains limited. We characterized two porcine rectal-swab isolates from Changji, Xinjiang, using antimicrobial susceptibility testing, filter-mating assays and whole-genome sequencing of donors and selected transconjugants. Both ST23 donors yielded blaNDM-5-carrying derivatives of E. coli J53. Imipenem MICs were 4 µg/mL for both donors and 4 and 8 µg/mL for the respective transconjugants, compared with 0.25 µg/mL for J53. In the XNCF149 pair, sequence alignments covered the entire 230,309 bp donor IncHI2/IncHI2A-associated contig at approximately 99.96% identity. In the XNCHF151 pair, a blaNDM-5-containing region matched the donor sequence within a 101,751 bp IncFII-associated transconjugant contig. The donors formed a sister pair in a selected 13-genome core-gene phylogeny. Among 7763 deposited assemblies retained after quality screening, species-prediction restriction and BioSample deduplication, 640 carried blaNDM; blaNDM-5 accounted for 474 of these (74.06%). IncX3 showed the greatest proportional enrichment among the displayed replicons in assemblies containing blaNDM. These findings document qualitative blaNDM-5 transfer and distinct recovered sequence configurations in two porcine E. coli pairs. The assemblies leave the timing and mechanism of the second configuration unresolved, and the deposited collection provides comparative genomic context.