Rafflesia kerrii (RK) has been used as a folk medicine for the treatment of many diseases. Bactericidal activity of its ethanol extract against multidrug-resistant (MDR) bacteria including methicillin resistant Staphylococcus aureus (MRSA), Acinetobacter baumannii, Pseudomonas aeruginosa, and Stenotrophomonas maltophilia was investigated using the microbroth dilution method and time-kill assay. Results showed broad spectrum antibacterial activity against all test bacteria with minimum bactericidal concentrations (MBCs) in the range of 0.78 to 6.25 mg/ml. The extract with a concentration of 2xMBC completely killed the MRSA after 24 h-exposure, whereas it completely killed A. baumannii, P. aeruginosa and S. maltophilia after 3 h-exposure. It contained a high total phenolic content (669.66±38.60 mg TAE/g) and exhibited stronger antioxidant activity than the ascorbic acid standard (EC50 at 1.79±0.02 µg/ml). These results indicate that the RK extract is a potential candidate to be used as an antioxidant and antibacterial agent for MDR bacteria.
