For more than 30 years, vancomycin has been a reliable treatment for Gram-positive bacterial infection. Injectable forms of vancomycin were introduced, and have been used exclusively for methicillin-resistant Staphylococcus aureus (MRSA) infection. Recently, the MRSA strain, which contains the vanA gene, with high resistance to vancomycin (MIC Ͼ128 mg/ml) has been reported in clinical isolates.
1,2)The emergence of vancomycin resistant bacterial strains is a very serious public health problem. Therefore, a new anti-MRSA antibiotic is clinically of interest. Dipropofol ( Fig. 1) was recognized as an oxidative dimerization metabolite of propofol (2,6-diisopropylphenol), a novel sedative and anesthetic agent having antioxidant activity, but not antibacterial activity.3,4) Dipropofol was investigated to have a higher antioxidant activity than that of propofol, and to show potent antibacterial activity against Grampositive strains including MRSA and vancomycin resistant Enterococci (VRE). 4,5) However, the insolubility of dipropofol in water could be plausible for its efficacy and application fields. Consequently, the solubilization of dipropofol in water was a next target. To obtain the water-solubility of the compounds, many researchers have used synthetic approaches and selected suitable derivatives.6,7) However, we selected another method of adding other types of compounds, expecting complex formations and synergistic activity with the additions.
MATERIALS AND METHODSChemicals Dextrose anhydrous, saccharose, ascorbic acid and lecithin (from egg) were purchased from the Wako Pure Chemical Co. (Osaka, Japan). D(Ϫ)-Fructose, D(ϩ)-mannose, D(ϩ)-xylose, maltose monohydrate, and D-sorbitol were purchased from Sigma-Aldrich Japan K.K. (Tokyo, Japan). Dipropofol was synthesized by the method reported previously.
4)Antimicrobial Susceptibility The disk-diffusion test, using S. aureus 209P and E. coli JCM5491 (ATCC25922) was applied to determine the antimicrobial activity of the test compounds. The test organisms were grown overnight at 37°C by shaking in a TSB medium and the aliquots (100 ml) were streaked onto trypticase soy agar plates. A dipropofol solution (1 mg/ml in methanol) was suspended with saccharide (1 g) or ascorbic acid (1 g). The perfect removal of methanol produced a dipropofol complex with saccharide or ascorbic acid, which dissolved in distilled water (5 ml). For plate diffusion tests, 50 ml of the test compound was dropped on paper disks (diameter 8 mm), which were dried under sterile conditions and put on and an agar plate inoculated with the test organism. The plates were cultivated at 37°C for 24 h.
Combination Study and Synergism DeterminationThe in vitro combinational effect of the dipropofol with ascorbic acid was examined by the checkerboard titration method. Overnight a culture of S. aureus, grown in 10 ml of Mueller-Hinton broth at 37°C, was diluted 10 3 -fold with fresh Mueller-Hinton broth, followed by the addition of S. aureus (about 5ϫ10 4 CFU) onto 20 ml Mueller-Hinton agar layers which co...
