Dual Action of Avarol Quinone Terpenoid: Disrupting Cell Wall and Membrane Integrity in Staphylococcus aureus

The rising threat of multidrug-resistant bacteria necessitates the discovery of novel antibacterial agents with distinctmechanisms of action. In this study, we investigated the antibacterial activity and mechanism of action of Avarol Quinone Terpenoid (AQT), a polyfunctional compound isolated from the marine sponge Neopetrosia exigua, against Staphylococcus aureusATCC 25923. Minimum inhibitory concentration (MIC) testing revealed that AQT exhibits bacteriostatic activity at 2.6 μg/mL and bactericidal activity at 5.2 μg/mL. To further explore its antibacterial mechanism, a series of in vitro assays were performed to assess its impact on bacterial viability, morphology, membrane integrity, and cellular metabolism. Time-kill analysis demonstrated a concentration-dependent reduction in S. aureusviability. Scanning electron microscopy (SEM) revealed severe morphological alterations in AQT-treated cells, including membrane deformation and collapse. Membrane permeability was significantly increased, as indicated by elevated uptake of crystal violet and propidium iodide dyes. These effects were accompanied by marked leakage of nucleic acids, proteins, potassium, calcium, and ATP, supporting membrane disruption. SDS-PAGE analysis showed reduced total protein content, although lipase activity remained unaffected, suggesting AQT does not inhibit protein synthesis. API Staph tests indicated that AQT inhibited sugar utilization (lactose, maltose, and N-acetylglucosamine) and suppressed arginine dihydrolase activity, potentially impairing ATP generation. Autolysis assays showed increased activity of cell wall-degrading enzymes, consistent with cell wall-targeting antibiotics. Furthermore, membrane depolarization assays using DiSC₃(5) confirmed the dissipation of membrane potential. Collectively, these findings suggest that AQT exerts its antibacterial effects through a multifaceted mechanism targeting both the cell wall and the cytoplasmic membrane, leading to loss of membrane integrity, energy depletion, and bacterial cell death. AQT thus holds promise as a potential anti-S. aureustherapeutic agent.