Studies on new antimicrobial agents from crude drugs against nosocomial methicillin-resistant Staphylococcus aureus

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To find antimicrobail drugs against methicillin-resistant Staphylococcus aureus (MRSA), crude extracts from plant medicinal resources were screened on the basis of antimicrobial activities against clinical isolates of MRSA and cytotoxic effects against established cell lines of human.From the extracts selected through the screening procecure, 5 effective constituents purified were as follows : gallic acid and ethyl gallate (from Terminalia chebula), xanthatin (from Xanthium sibiricum), apigenia and luteolin (from Scutellaria barbata).Surprisingly, apigenin and luteolin dramatically induced the sensitivity against beta-lactam antibiotics in highly resistant strains of MRSA (MIC,>1000 mug of methicillin/ml). We also found such a synergistic effect by flavone and its related compounds. We named these compounds inducing the sensitivity against beta-lactam antibiotics in MRSA "beta-lactam-sensitizers of MRSA".