Interaction of Quercus infectoria Gall's Extract and Vancomycin Against Staphylococcus aureus with Reduce Susceptibility to Vancomycin

Methicillin-resistant Staphylococcus aureus (MRSA) is a versatile pathogen widespread, and tend to be multi-resistant towards almost all of currently available antibiotics. The gall of Quercus infectoria or locally known as manjakani in Malaysia was known to have antibacterial activity. The aim of this study was to evaluate the interaction effect of Q. infectoria gall extract with vancomycin against five MRSA strains and two Vancomycin Intermediate Staphylococcus aureus (VISA) strains. The extracts were prepared using acetone, methanol and aqueous. The microbroth serial dilution technique was employed using 96-well microtiter plate for determination of MIC values. The effect of interaction between Q. infectoria gall extract and vancomycin was evaluated using the checkerboard method to obtain the Fractional inhibitory concentration (FIC) index value. The extracts combination with vancomycin displayed synergism for acetone extract against MRSA ATCC 43300 (0.3124), Sa7 (0.3750) and VISA U9495 (0.3750), while aqueous extract were synergistic against MRSA Sa7 (0.4167) and VISA U9495 (0.3958) and N316 (0.5000). On the other hand, vancomycin combination with methanol only exhibited synergistic effect towards ATCC 49476 (0.3750) but additive against 6 other strains tested. This interaction effect showed their potential and importance in development or modification of drugs against MRSA.