Inhibitory activity and killing activity of extracts from the gall of Quercus infectoria against methicillin-resistant Staphylococcus aureus

Abstract number: r1980

Voravuthikunchai  S., Chusri  S., Kleiner  P.

Objectives: 

Methicillin-resistant S. aureus has been well-documented as a major cause of hospital-acquired infection. Medicinal plants have been increasingly used to reduce the problem of antibiotic-resistant bacteria. Quercus infectoria was previously reported from this laboratory to produce high antibacterial activity. The aims of this study were to closely investigate the antibacterial activities of the extracts from Q. infectoria galls and to determine the effects of these extracts on the growth of clinical MRSA strains.

Methods: 

Fifty-one clinical isolates of MRSA were collected from Hat-Yai hospital. All isolates were multidrug-resistant. Galls of Q. infectoria were extracted with acetone, ethyl acetate, 95% ethanol, and water. Paper disc agar diffusion method was used to determine the antibacterial activity of these extracts. Minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) were evaluated by modified broth microdilution method according to National Committee for Clinical Laboratory Standards. Growth curves demonstrating bacteriostatic and bactericidal activities of Q. infectoria against MRSA strains were documented for 24 h.

Results: 

All extracts of Q. infectoria show antibacterial activities against all strains of MRSA. The inhibition zones ranged from 11–23 mm. The ethanolic extract demonstrated the largest inhibition zone. Most of the MRSA strains treated by the ethanolic extract of Q. infectoria exhibited the MIC and MBC values at 0.4 and at 1.6 mg/ml, respectively. At the MIC concentration, the growth of a representative was inhibited and gradually decreased after 16 h incubation. The survival cells of the MRSA were not detected within 2 h after treated with the extract at its MBC concentration. Staphylococcus aureus ATCC 25923, a reference strain showed similar results.

Conclusion: 

The ethanolic extract of the galls of Q. infectoria have a high potential as antibacterial agent against MRSA. More detailed studies on the extract may provide an alternative way to treat infections caused by MRSA. Use of the active compounds could be developed as antibacterial agent in order to reduce problems with antibiotic-resistant bacteria in the hospitals.

Acknowledgement: 

This work was supported by Thailand Research Fund, Fiscal year 2005–2008.