Abstract
Acinetobacter baumannii is an opportunistic pathogen frequently implicated in hospital-acquired infections and multidrug resistance (MDR). Its ability to form biofilms on medical devices contributes to antimicrobial resistance and prolonged persistence in clinical settings. Characterizing the molecular basis of biofilm formation is essential for designing efficacious infection prevention and control programs A total of 120 A. baumannii isolates were recovered from multiple clinical sources in an Iraqi hospital setting from June 2025 to April 2026. The isolates were identified based on phenotypic characteristics and confirmed by a PCR assay targeting the intrinsic blaOXA-51-like gene. Microtiter plate assay was performed to assess biofilm formation, whereas antimicrobial susceptibility testing (AST) was conducted using the disk diffusion method according to CLSI guidelines. Conventional and quantitative real-time PCR (RT-qPCR) tests were conducted to determine the presence and expression of biofilm-related genes (bap, ompA, csuE, and blaPER-1) under biofilm-promoting conditions. The prevalence of MDR isolates reached 82.5% with high resistance rates to imipenem (88%) and meropenem (85%) and meropenem (85%), while colistin retained the greatest in vitro activity, with 91% susceptibility. Strong and moderate biofilm formation was observed in 35.0% and 31.7% of isolates, respectively. The most frequently detected genes were ompA (91.7%) and csuE (83.3%), followed by bap (68.3%) and blaPER-1 (56.7%). Gene expression profiling exhibited a marked elevation of bap (5.6 ± 0.4-fold) and ompA (4.9 ± 0.6-fold) in strong biofilm producers. A positive association was recorded between carbapenem resistance and biofilm strength (p < 0.05). The findings indicate that multidrug resistance and biofilm formation are closely associated characteristics in A. baumannii. Higher expression of the investigated genes was associated with stronger biofilm-forming phenotypes, underscoring the potential relevance of molecular surveillance and biofilm-control strategies in Iraqi healthcare settings.