Antibacterial and Biofilm Inhibitory Efficiency of Myrtenol Against Nosocomial Pathogen Acinetobacter baumannii

Acinetobacter baumannii is a clinically significant nosocomial pathogen and has the ability to form biofilms on biotic and abiotic surfaces, contributing to persistent infections. With limited treatment options, plant-derived compounds that attenuate biofilm formation without bactericidal pressure are of interest. Myrtenol, a bicyclic monoterpene, exhibits diverse biological activities, yet its effects on A. baumannii biofilms are poorly understood. Here, we evaluated the antibiofilm and antivirulence potential of myrtenol. The minimum inhibitory concentration (MIC) was 400 μg/mL, and myrtenol inhibited biofilm formation in a concentration-dependent manner, with 200 μg/mL producing approximately 50% inhibition while retaining detectable bacterial metabolic activity. Myrtenol reduced surface motility, enhanced susceptibility to oxidative stress, and decreased ring biofilm formation, total biomass, surface coverage, and biofilm development on multiple abiotic surfaces. Ethidium bromide cartwheel assays indicated altered efflux-associated activity, with increased intracellular ethidium bromide accumulation following myrtenol exposure, while qPCR analysis revealed downregulation of genes coding for biofilm formation, adhesion, and virulence. These findings highlight myrtenol as a potential antivirulence agent against A. baumannii.