In vitro synergistic effects of baicalin with oxytetracycline and tetracycline against Staphylococcus aureus.

OBJECTIVES In this study we examined the in vitro synergistic effect of baicalin, the flavone constituent of Scutellaria spp., in combinations with oxytetracycline and tetracycline on the growth of Staphylococcus aureus. METHODS The MICs were determined by the broth microdilution method and the effect of combinations was evaluated according to the sum of fractional inhibitory concentration indices (FICIs). RESULTS Synergistic activity (FICI  ≤  0.5) was observed for combinations of baicalin with oxytetracycline or tetracycline against 4 of 10 strains tested, whereas the baicalin/oxytetracycline combination possessed the strongest synergistic effect (FICI = 0.418). CONCLUSIONS Baicalin acts synergistically with oxytetracycline and tetracycline, enhancing its antimicrobial activity against S. aureus, including methicillin- and tetracycline-resistant strains.