Antibacterial and Antibiofilm Activities of 3-Iodoindole against Multidrug-Resistant Acinetobacter baumannii Isolated from Urinary Tract Infections

Background: Acinetobacter baumannii is an important opportunistic pathogen associated with urinary tract infections and notable multidrug resistance. Biofilm formation further complicates treatment and contributes to persistence in clinical settings. Objective: This study aimed to evaluate the antibacterial and antibiofilm activities of 3-iodoindole against multidrug-resistant A. baumannii isolates recovered from patients with urinary tract infections in Baghdad, Iraq. Methodology: A total of 150 urinary isolates were collected from hospitals and laboratories in Medical City, Baghdad. Isolates were identified by conventional culture methods and the VITEK 2 Compact system. Antimicrobial susceptibility was assessed by the Kirby-Bauer method and VITEK 2 AST cards. Biofilm formation was quantified using a microtiter plate assay, and the antibacterial and antibiofilm activities of 3-iodoindole were evaluated at different concentrations. Results: Of the 150 isolates, 100 (66.7%) were confirmed as A. baumannii. High resistance rates were observed against several commonly used antibiotics, whereas colistin and tigecycline remained the most active agents. Biofilm assays showed that 79% of isolates were biofilm producers, including moderate and strong biofilm-forming phenotypes. Strong biofilm formers exhibited significantly higher OD600 values at 24 h than weak biofilm formers. 3-Iodoindole demonstrated marked antibacterial activity, achieving a >3-log reduction in viability at 250 µg/mL within 15 min and significantly reducing biofilm biomass in a dose-dependent manner. Conclusion: 3-Iodoindole exhibited potent antibacterial and antibiofilm effects against multidrug-resistant A. baumannii and may represent a promising candidate for further development as an alternative or adjunctive antimicrobial agent.