Genomic Characterization of the Multidrug Resistome in Extensively Drug-Resistant Acinetobacter baumannii from a Tertiary Hospital in Iraq

Background Carbapenem-resistant Acinetobacter baumannii represents a major global health concern and is classified among the WHO critical priority pathogens due to its multidrug-resistant (MDR) and extensively drug-resistant (XDR) phenotypes. Genomic surveillance is essential for understanding resistance architecture and guiding infection control strategies. Objectives This study aimed to characterize the whole-genome resistome of XDR A. baumannii isolates recovered from a tertiary hospital in Diyala, Iraq. Methods Four blood-derived XDR isolates were subjected to Illumina-based whole-genome sequencing. Antimicrobial resistance determinants were identified using AMRFinderPlus with stringent identity and coverage thresholds. Genotypic findings were compared with phenotypic susceptibility results. Results All isolates harbored a conserved carbapenem resistance backbone comprising blaOXA-23, intrinsic blaOXA-66, and blaADC-73. High-level aminoglycoside resistance was associated with the 16S rRNA methyltransferase armA, detected in selected isolates, alongside multiple aminoglycoside-modifying enzymes with isolate-specific variation. Macrolide resistance determinants, including msr(E) and mph(E), were widely distributed. Chromosomal quinolone resistance-determining region mutations, notably gyrA S81L, were consistently identified. The overall resistome architecture suggests clonal dissemination with limited intra-population variability. Conclusion Whole-genome analysis revealed a stable multidrug resistance framework among XDR A. baumannii isolates in this hospital setting. These findings underscore the importance of genomic surveillance to monitor the persistence and evolution of high-risk resistant clones.