Evolutionary Dynamics of blaNDM Plasmid Transmission in Clinical Enterobacteriaceae Across Tertiary Hospitals in the South West Geopolitical Zone of Nigeria

The New Delhi metallo-beta-lactamase (NDM) gene, carried on highly mobile conjugative plasmids, represents a paradigmatic example of rapid horizontal gene transfer-mediated resistance dissemination. Understanding the evolutionary dynamics of blaNDM plasmid transmission within and across hospitals in Nigeria is essential for designing effective containment strategies, yet phylogeographic analyses of NDM epidemiology remain absent from Nigerian literature. This study characterized the plasmid-mediated evolutionary dynamics of blaNDM dissemination in Enterobacteriaceae from six tertiary hospitals across the South West geopolitical zone, including facilities in Lagos, Ogun, Oyo, Osun, Ondo, and Ekiti States. blaNDM-positive Enterobacteriaceae were collected over 30 months. Hybrid assembly using Illumina and ONT long-read sequencing resolved complete plasmid architectures. Comparative plasmid genomics, conjugation efficiency experiments, and Bayesian evolutionary phylogenetics using BEAST2 were applied to reconstruct transmission timelines. Results revealed three dominant blaNDM-bearing plasmid replicons (IncF, IncX3, IncC), each associated with distinct transmission dynamics. IncX3-blaNDM-5 plasmids showed the highest inter-hospital transmission rates and widest host range across Enterobacteriaceae genera. Bayesian phylogenetics dated the introduction of NDM into South West Nigerian hospitals to approximately 2015 to 2017, with subsequent accelerated diversification. A significant inter-hospital gene flow event was identified linking a Lagos tertiary hospital to four other zonal hospitals via a shared IncX3 plasmid lineage. This study constitutes an original evolutionary genomics contribution to NDM epidemiology in Nigeria and provides a plasmid surveillance framework. Keywords: blaNDM, plasmid evolution, Enterobacteriaceae, phylogeography, South West Nigeria.