Conserved mobile genetic contexts associated with bla NDM-1 and bla NDM-5 in Acinetobacter baumannii isolated from two hospitals in Thailand

Background Acinetobacter baumannii has emerged as a major nosocomial pathogen due to its remarkable ability to develop resistance to multiple classes of antimicrobial agents. The emergence and dissemination of the bla NDM gene among multidrug-resistant A. baumannii (MDRAB) are closely associated with mobile genetic elements (MGEs), which facilitate horizontal gene transfer and accelerate the spread of carbapenem resistance. This study investigated the distribution of bla NDM -positive A. baumannii isolates, characterized their antimicrobial resistance phenotypes and genetic determinants, and elucidated the genetic context surrounding bla NDM alleles using whole-genome sequencing (WGS). Methods A total of 286 clinical A. baumannii isolates collected from a tertiary hospital in Thailand were screened for metallo- β -lactamases encoding genes( bla NDM ), OXA carbapenemase-encoding genes, IS Aba1 , and IS Aba125 using polymerase chain reaction (PCR). The bla NDM variants were characterized by gene sequencing, and antibiotic susceptibility profiles were determined. Whole-genome sequencing (WGS) was performed on eight representative bla NDM -positive isolates, comprising four isolates from the present study and four isolates obtained from another hospital in Thailand. Results Among the 286 A. baumannii isolates, 55 (19.23%) carried bla NDM . All bla NDM -positive A. baumannii isolates were identified as carbapenem-resistant A. baumannii (CRAB), and 90.91% were classified as MDRAB strains. The prevalence of bla OXA-23 and bla OXA-58 was 85.45% and 16.36%, respectively. The insertion sequences IS Aba1 and IS Aba125 were detected in 89.09% and 81.82% of the isolates, respectively. Sequence analysis revealed that 49 (89.09%) bla NDM -positive A. baumannii harbored bla NDM-1 , whereas six (10.91%) showed sequence identity with bla NDM-5 . WGS analysis of eight bla NDM -positive A. baumannii demonstrated variability in K-locus and OC-locus types. MLST analysis revealed that the four bla NDM-1 -positive isolates belonged to three distinct sequence types (ST16, ST23, and ST213), while predominance of bla NDM-5 -positive isolates were ST2. Comparative genomic analysis of the genetic environments surrounding the bla NDM genes revealed highly conserved genetic organization, with strong synteny among isolates belonging to the same bla NDM type. Conclusion These findings demonstrate the emergence and persistence of multiple resistance determinants among A. baumannii isolates in Thailand, thereby underscoring the urgent need to strengthen antimicrobial stewardship program and infection prevention control strategies.