Exploration of Evolutionary Dynamics and Genomic Architecture in Acinetobacter baumannii

Acinetobacter baumannii responsible to cause nosocomial infections in the hospital settings and a leading cause of 80% death across the globe. The genome of Acinetobacter baumannii comprises diverse genetic elements that play a critical role in carrying and disseminating antimicrobial resistance (AMR) genes. Thus, we integrated pan-genome analysis, phylogenomics and compositional analysis to elucidate the genetic landscape. Analyses revealed that A. baumannii has an open, highlighting its remarkable adaptability. Additionally, phylogenomic analysis showed the global population was dominated by the high-risk carbapenem resistant sequence type ST2 lineage, although numerous other sequence types co-existed. Mapping of AMR genes on different genomic segments indicated that resistance genes were primarily acquired through horizontal transfer, with genes from other Gram-negative bacteria including Klebsiella pneumoniae and Shewanella frigidimarina as donor organisms. Further Kullback–Leibler divergence–based analysis of genomic composition showed that genomic islands (GIs) act as semi-stable, compositionally constrained elements that preferentially retain AMR determinants. In other words, these islands are not transient collections of foreign DNA but stable genetic loci containing resistance genes. Clinically, our findings emphasized the need to monitor chromosomes, GIs, prophages and plasmids as reservoirs and vehicles of carbapenem resistance genes. Thus, our analysis revealed the evolutionary dynamics and genome architecture of A. baumannii underscores the importance of genomic surveillance and targeted interventions against this formidable pathogen.