Abstract

Background: The MRSA is multi-drug resistant pathogenic bacteria had become a worldwide concern because its susceptibility to vancomycin was decreasing and also administration of high doses of vancomycin has been used to treat. Thus, the combined strategy of bioactive compounds from microorganisms with currently used antibiotics was interested to solve this problem. Objective: This study aimed to evaluate the combination effect between 2, 4-Di-tert-butylphenol and vancomycin against MRSA. Materials and Methods: The anti-MRSA activity of 2,4-Di-tert-butylphenol and vancomycin was initially performed by the broth microdilution method to determine the Minimum Inhibitory Concentration (MIC) value. The combination effect of them was performed by the checkerboard method to determine the Fractional Inhibitory Concentration (FIC) index value. Results: The MIC values of 2, 4-Di-tert-butylphenol and vancomycin were in the range of 15.63-62.50 and 1.56-3.12 μg mL^–1, respectively. Among 10 clinical isolates of MRSA, 5 isolates which showed phenotype as inducible macrolide-lincosamide-streptogramin group B (iMLS<inf>B</inf>) resistance were inhibited by combining the 15.63 μg mL^–1 of 2, 4-Di-tert-butylphenol with 0.39-0.78 μg mL^–1 of vancomycin. The FIC index values were in the range of 0.56-0.75 which could conclude as partial synergism. Contrarily, another 5 isolates that showed phenotype as constitutive MLS<inf>B</inf> (cMLS<inf>B</inf>) resistance were evaluated as indifferent activity which showed the FIC index values were in the range of 1.0-1.5. Conclusion: The 2, 4-Di-tert-butylphenol should not use to combine with vancomycin for treating the infection of MRSA in group of cMLS<inf>B</inf> phenotype, but it might use to combine with vancomycin for treatment in group of iMLS<inf>B</inf> phenotype.