Antibacterial activity of flavanone isolated from Sophora exigua against methicillin-resistant Staphylococcus aureus and its combination with antibiotics

5,7,2',4'-Tetrahydroxy-8-lavandulyl-flavanone, isolated from Sophora exigua, completely inhibited the growth of 21 strains of methicillin-resistant Staphylococcus aureus (MRSA) at concentrations of 3.13-6.25 μg/mL. The anti-MRSA effect was based on bactericidal action. In combinations of the flavanone with vancomycin, minocycline and rifampicin, the fractional inhibitory concentration indices were 0.90, 0.88 and 0.85, respectively, indicating partial synergistic effects with anti-MRSA antibiotics. The proposed flavanone would be a potent phytotherapeutic agent against MRSA infections.