New activity for old drug: In vitro activities of vitamin K3 and menadione sodium bisulfite against methicillin-resistant Staphylococcus aureus

To discover new lead compounds against methicillin-resistant Staphylococcus aureus (MRSA), trimethylhydroquinone, vitamins K1, K2, K3 and menadione sodium bisulfite were targeted for anti-MRSA assay. Their anti-MRSA activities were evaluated by agar diffusion method, and their minimum inhibitory concentrations (MICs) were determined by broth microdilution method. The results showed that trimethylhydroquinone, vitamin K3 and menadione sodium bisulfite presented obvious anti-MRSA activity, and their MICs against MRSA ATCC 33592 and three clinical MRSA isolates were successively 16 to 32, 8 to 16 and 16 µg/ml. Vitamins K1 and K2 showed no anti-MRSA activity when the test discs respectively carried 1024 µg of them. These indicated that the anti-MRSA activity would disappear when the methyl of vitamin K3 was substituted by alkyl that contained four isopentenyl units, and vitamin K3 probably has an ancillary effect on the treatment of MRSA infection. Key words: Vitamin K3, menadione sodium bisulfate, trimethylhydroquinone, methicillin-resistant Staphylococcus aureus (MRSA).