Genetic diversity of Acinetobacter baumannii from clinical samples via ISSR markers

Background: Acinetobacter baumannii is a major nosocomial pathogen known for its multidrug resistance (MDR) and persistence in hospital settings. Understanding its genetic variability is vital for infection control. This study aimed to assess the genetic diversity of clinical A. baumannii isolates using Inter-Simple Sequence Repeat (ISSR) markers, known for their cost-effectiveness, reproducibility, and suitability in organisms with limited genomic data. Methods: Eighteen A. baumannii isolates were collected from a tertiary care hospital. Antibiotic susceptibility was determined using the Kirby-Bauer disk diffusion method. Genomic DNA was extracted via the boiling method and amplified using 19 ISSR primers. Genetic variation was analyzed through phylogenetic tree construction and Principal Component Analysis (PCA). Results: The majority of isolates (83%) were resistant to Cefoperazone, Meropenem, Levofloxacin, Imipenem, and Aztreonam. Lower resistance was observed for Chloramphenicol (38%) and Colistin (16%), while Tigecycline and Minocycline showed the highest sensitivity. Out of 19 ISSR primers, 17 produced scorable amplicons. ISSR 15 exhibited the highest resolving power and primer index, and ISSRs 1, 3, and 6 generated the most unique bands. Phylogenetic and PCA analyses identified both genetically similar isolates (e.g., S3 and S4) and highly divergent ones (e.g., S171 and S454), reflecting heterogeneous sources and potential transmission events. Conclusions: ISSR marker analysis demonstrated significant genetic diversity among A. baumannii isolates, confirming its value in molecular epidemiology. The findings can inform infection control, support early MDR detection, and help mitigate hospital-acquired infections.