Aims: In traditional Thai medicine, nutgall of Quercus infectoria G. Olivier is well-documented as an effective agent for wound and skin infections. The present study was aimed to establish modes of action of the ethanol extract of the plant as well as its main constituents to induce anti-methicillin-resistant Staphylococcus aureus (MRSA) activity.
Methods and results: The minimal inhibitory concentration (MIC)/minimal bactericidal concentration (MBC) values of ethyl acetate I, ethyl acetate II, 95% ethanol and 30% ethanol fractions against MRSA were 0.06/0.25, 0.13/0.25, 0.25/0.5 and 0.5/1.00 mg ml(-1), respectively. Ellagic acid, gallic acid, syringic acid and tannic acid as major components of Q. infectoria nutgall extract were included in this study. Among these, gallic acid and tannic acid demonstrated good MIC/MBC values at 0.06/0.06 and 0.13/0.25 mg ml(-1), respectively. A lysis experiment demonstrated that the ethanol extract, ethyl acetate fraction I and all of the main components failed to lyse MRSA cells. In contrast, both MRSA and Staph. aureus ATCC 25923 treated with the ethanol extract, ethyl acetate fraction I, gallic acid and tannic acid displayed significant loss of tolerance to low osmotic pressure and high salt concentration.
Conclusions: The results documented the effect of different fractions of Q. infectoria and purified compounds on MRSA and Staph. aureus. In addition, the study demonstrated that treatment with Q. infectoria extract and the purified compounds results in hypersensitivity to low and high osmotic pressure.
Significance and impact of the study: This study provides scientific information to support the traditional uses of the nutgall extract and suggesting its anti-MRSA mechanisms.
© 2011 The Authors. Letters in Applied Microbiology © 2011 The Society for Applied Microbiology.