Emergence and Global Spread of a Dominant Multidrug-Resistant Variant in Acinetobacter baumannii

The proliferation of multi-drug resistant (MDR) bacteria is driven by the global spread of epidemic lineages that accumulate antimicrobial resistance genes (ARGs). Acinetobacter baumannii , a leading cause of nosocomial infections, displays resistance to most frontline antimicrobials and represents a significant challenge to public health. In this study, we conduct a comprehensive genomic analysis of over 15,000 A. baumannii genomes to identify a predominant epidemic super-lineage (ESL) accounting for approximately 70% of global isolates. Through hierarchical classification of the ESL into distinct lineages, clades, and variants, we identified a stepwise evolutionary trajectory responsible for the worldwide expansion and transmission of A. baumannii over the last eight decades. Particularly, we observed the rise and global spread of a previously unrecognized Variant 2.5.6, which emerged in East Asia in 2006. The epidemic of the variant is linked to the ongoing acquisition of antimicrobial resistance genes (ARGs) and virulence factors facilitated by genetic recombination. Our results highlight the necessity for One Health-oriented research and interventions to address the spread of this MDR pathogen.