Antibacterial activity of calozeyloxanthone isolated from Calophyllum species against vancomycin-resistant Enterococci (VRE) and synergism with antibiotics.

Calozeyloxanthone (1) was re-isolated from the root bark of Calophyllum moonii, an endemic species of Sri Lanka, and found to be active against vancomycin-resistant Enterococci (VRE) and vancomycin-sensitive Enterococci (VSE) with MIC values of 6.25μg/ml and 12.5μg/ml, respectively. Further, a marked synergism between 1 and vancomycin hydrochloride (VCM) against VRE was also observed. These findings suggest that 1 in combination with VCM against VRE may be useful in controlling VRE infections.