In vitro antibiofilm activity of Aquilaria malaccensis leaf extracts and literature-derived docking studies on LasR and RhIR of Pseudomonas aeruginosa

Background: Pseudomonas aeruginosa biofilm-related infections are a major problem owing to their resistance to common antibiotics. Aquilaria malaccensis, with its high phytochemical content, has exhibited some antibacterial activity; nevertheless, its antibiofilm activity has not yet been explored. Methods: The leaves of A. malaccensis were sequentially extracted with hexane, ethyl acetate, and 80% ethanol. The antibiofilm activity of the extracts was assessed using a crystal violet-based microtiter plate assay against clinical isolates of biofilm-producing Pseudomonas aeruginosa. Due to resource limitations, GC-MS analysis was not performed; however, literature-reported sesquiterpenes were chosen for molecular docking experiments based on AutoDock Vina. The target proteins for quorum-sensing inhibition were LasR (PDB: 2UV0) and RhlR (PDB: 8DQ0). Results: The hexane extract possessed the greatest antibiofilm activity (98.32% inhibition at 150 mg/mL), followed by ethyl acetate (75.10%), whereas the ethanol extract did not. Docking analysis indicated that α-bisabolol and jinkoh-eremol had strong affinities for LasR (–8.9 and –8.7 kcal/mol) and RhlR (–9.1 and –8.7 kcal/mol), overcoming the native ligands. These compounds also established multiple hydrogen bonds and hydrophobic interactions, suggesting potential disruption of bacterial quorum sensing. Conclusion: The antibiofilm activity of A. malaccensis leaf extracts, and notably the hexane fraction, can be attributed to sesquiterpenes, such as α-bisabolol and jinkoh-eremol. This study provides the first evidence of the plant's potential antibiofilm activity and indicates its potential as a source of natural quorum-sensing inhibitors.