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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. [ABSTRACT FROM AUTHOR]

Methicillin-resistant Staphylococcus aureus (MRSA) infection has become a serious clinical problem worldwide, and alternative natural or combination drug therapies are required for its treatment. The aim of the present study was to examined the antimicrobial activity of luteolin (LUT) against MRSA. Luteolin is a polyphenolic flavonoid compound with a wide spectrum of biological activities. The antimicrobial activities of LUT and the antibiotics ampicillin (AM), oxacillin (OX) and gentamicin (GT), used alone or in combination, were evaluated against five clinical MRSA isolates and two reference strains using a minimum inhibitory concentration (MIC) assay, MTT colorimetric assay, checkerboard dilution test and time-kill assay. The MIC of LUT against all strains was found to be 62.5 μg/ml. The combinations of LUT and antibiotics exhibited a synergistic effect against MRSA in the majority of cases, as determined by the checkerboard method. Time-kill curves revealed that a combination of LUT with AM, OX or GT significantly reduced bacterial counts, which dropped below the lowest detectable limit after 24 h. These results indicate that LUT potentiates the effects of β-lactam and aminoglycoside antibiotics against MRSA. [ABSTRACT FROM AUTHOR]

Carvone is one of the naturally occurring monoterpenes, the largest class of secondary metabolites in plants, and exists in two enantiomers, R-carvone (R-car) and S-car. The objective of this study was to investigate the antimicrobial activity of R-car and S-car with gentamicin (GET) against methicillin-resistant Staphylococcus aureus (MRSA). MRSA is a major human pathogen that causes serious problems, including hospital-acquired pneumonia, abscesses and surgical wound infections. Nosocomial MRSA infections often exhibit multidrug resistance. In the present study, antimicrobial susceptibility testing was performed with R-car, S-car and GET using the broth microdilution method. Minimal inhibitory concentration values for R- and S-car against six different strains of S. aureus ranged between 500 and 1,000 µg/ml. Anti-MRSA activity was evaluated using the checkerboard and time-kill assays to investigate the potential synergistic effects of different combinations of the carvone enantiomers and GET. R-car plus S-car, R-car plus GET and S-car plus GET exhibited significant synergistic activity against MRSA. These findings suggest that the single-agent anti-MRSA activities of R-car, S-car and GET are effectively increased through combination therapy. This study showed that carvone may be a potential adjuvant antimicrobial agent. [ABSTRACT FROM AUTHOR]