Baicalin Synergy With β-Lactam Antibiotics Against Methicillin-resistant Staphylococcus Aureus

Objective: To evaluate in-vitro antibacterial activities of 3 kinds of β-lactams antibiotics(Oxacillin, Ampicillin and Cefazolin) alone or in combination with baicalin at various doses against 20 MRSA strains. Methods: MIC50 were determined for each drug combination against 20 clinic isolates of MRSA by tube broth method. Fractional inhibitory concentration (FIC) indices were decided by chekerboard method; Time-kill curves were used to measure the bactericidal activity of each beta-lactam either alone or in combination with baicalin. Results: The MIC50 of Oxacillin, Ampicillin and Cefazolin against MRSA were same(128ug/ml), combined with 32 ug/ml baicalin decreased to 32,32,16 ug/ml, respectively. And these effects were dose-dependent to baicalin. FIC indices showed that the interaction between drugs was additive or synergistic against most MRSA , and indifferent against few MRSA, and not antagonistic. The time-kill curves displayed no bactericidal effect on MRSA at 64ug/ml dose of Oxacillin, Ampicillin and Cefazolin. Combined with baicalin at various doses, respectively, the time-kill curves of 3 kinds of β-lactams antibiotics showed the bactericidal activity risen in different extent, and these effects were dose-dependent to baicalin.Conclusions: The responses of beta-lactams in combination with baicalin against MRSA were synergictic or additive.