Antibacterial activity of oxyresveratrol against methicillin-resistant Staphylococcus aureus and its mechanism.

Oxyresveratrol (ORV) is a naturally occurring compound found in mulberries that exhibits a wide spectrum of biological activities. However, the underlying mechanism of the action of ORV against the methicillin-resistant S. aureus (MRSA) pathogen has not yet been reported. MRSA is multidrug-resistant, causing skin and other types of infections. The aim of the present study was to examine the antimicrobial activity of ORV and the underlying mechanism of its action on MRSA. The antibacterial activity of ORV was evaluated using a minimum inhibitory concentration (MIC) assay, and the mechanism of its antibacterial action on S. aureus was investigated using a combination of ORV with detergent, ATPase inhibitors and peptidoglycan (PGN). In addition, the survival characteristics and changes in MRSA morphology were monitored using transmission electron microscopy (TEM). The MIC value of ORV against all S. aureus strains was found to be 125 µg/ml. The optical density at 600 nm of each suspension treated using a combination of ORV with Triton X-100, N,N'-dicyclohexylcarbodiimide or sodium azide was reduced by 68.9-89.8% compared with the value upon treatment with ORV alone. In the ORV and PGN combination assay, direct binding of ORV with PGN from S. aureus was evident. Furthermore, TEM examination of MRSA treated with ORV showed alterations in septa formation. In conclusion, these results showed that ORV has a strong antibacterial effect against S. aureus, mainly by increasing membrane permeability and inhibiting ATPase when combined with other drugs.