Global genetic dissemination and risk stratification of blaNDM-bearing plasmids across clinical and environmental reservoirs

Plasmid-borne bla NDM has become a major driver of carbapenem resistance worldwide. However, its dissemination patterns, co-resistance profiles, and plasmid-level risks remain poorly defined. Here, we assembled a globally curated dataset of 1,654 New Delhi metallo-β-lactamase (NDM)-bearing plasmids and defined putative transmission units by intersecting MOB-suite secondary clusters with 5-kb bla NDM flanking-sequence clusters. For each plasmid, host pathogenicity, resistance cargo, transmission characteristics, and insertion sequence (IS)-mediated mobilisation of bla NDM were integrated into a composite H/R/T/M score. We found that bla NDM-1 and bla NDM-5 were the predominant alleles, whereas IncX3, IncC, and IncFII were the most frequent incompatibility types. Overall, 1,249 plasmid hosts were classified as pathogenic and 405 as non-pathogenic. A total of 588 plasmids were grouped into 52 putative transmission units. The largest unit, which was enriched in IncX3 plasmids, comprised 230 plasmids and showed extensive cross-host dissemination across clinical, animal, and environmental reservoirs. Co-resistance profiling revealed frequent co-occurrence of bla NDM with genes conferring resistance to bleomycin, aminoglycosides, glycopeptides, and sulfonamides. Analysis of bla NDM flanking regions identified 7,595 co-localisation events involving 27 bla NDM genotypes and 60 IS elements. Using the composite H/R/T/M score, plasmids were stratified into four dissemination-risk tiers: critical risk ( n = 164), high risk (n = 575), moderate risk (n = 452), and low risk (n = 463). By linking risk tiers to their constituent putative transmission units, we identified five high-priority units. Rapid assignment of newly recovered plasmids to these putative transmission units could provide a proxy for risk classification in genomic surveillance and infection-control practice.