Emerging clinical threat of NDM-producing Acinetobacter soli in China: a multicentre retrospective genomic epidemiology study

Acinetobacter soli , traditionally regarded as an environmental bacterium, has increasingly emerged as a clinically relevant non- baumannii Acinetobacter species and potential host for dissemination of high-risk antimicrobial resistance genes. However, its role in the dissemination of clinically important antimicrobial resistance genes is not known. We identified 35 bla NDM-1 -positive A. soli isolates among 6422 clinical Acinetobacter isolates from three hospitals in Zhejiang, China, and integrated them with global genomes and a bla NDM-1 -carrying plasmid database. Most isolates were recovered from urine samples (45.71%, 16/35) and showed high-level resistance to meropenem and imipenem (MIC₅₀ > 128 mg/L). Phylogenetic analysis showed marked heterogeneity, with isolates distributed across multiple branches and six global clades, while low-SNP clusters (SNPs <10) indicated local clonal expansion. Long-read sequencing identified five bla NDM-1 -carrying plasmid types, all harboring conserved Tn 125 -like transposons. These plasmid lineages accounted for 78.95% of bla NDM-1 -carrying plasmids in Acinetobacter , with the pR4WN lineage increasing from 2019 to 2025. Only pSU1904NDM and pR4WN were transferred under tested conditions, and pR4WN showed higher transfer frequency, greater stability, and a complex multidrug resistance structure. bla NDM-1 dissemination in A. soli is driven by local clonal expansion and plasmid-mediated horizontal transfer, highlighting environmental Acinetobacter species as potential reservoirs and vectors of carbapenem resistance.