Antibacterial activity of fractions of Quercus infectoria (nut galls) against enterohaemorrhagic Escherichia coli

Abstract number: p718

Voravuthikunchai  S.P., Suwalak  S., Supawita  T.

Objectives: 

Stimulation of Verocytotoxin (VT) production due to the use of subinhibitory concentrations of quinolones for patients with diarrhoea caused by enterovirulent organisms including enterohaemorrhagic Escherichia coli (EHEC) has been reported. The aim of this study was to analyse the effects of semi-purified fractions of Quercus infectoria nutgalls, which has been previously reported as effective against these organisms, on the production of VT.

Methods: 

Dry powder of crude ethanol extract is further fractionated in quick column chromatography using gradient solution with chloroform of increasing polarity by methanol. Active fractions were screened against different strains of EHEC including two strains of E. coli O157: H7, E. coli O26: H11, E. coli O11: NM, and E. coli O22. Escherichia coli ATCC 25922 was used as a reference strain. Minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) were determined by broth microdilution method using Mueller–Hinton broth and subculturing method onto fresh Mueller–Hinton agar, respectively. The inhibitory effects of the active fractions on the production of VT were tested for their cytotoxicity activity in a Vero cell assay system and reversed passive latex agglutination.

Results: 

Three major fractions (fraction Qi 2, fraction Qi 3, and fraction Qi 4) showed good antibacterial activity against all strains of enterohaemorrhagic Escherichia coli. The fractions Qi 3 and Qi 4 were demonstrated to be highly effective against E. coli O157: H7 with the MIC values of 28 and 56 mg/ml and the MBC values of 56 and 112 mg/ml, respectively. Further study showed that subinhibitory concentration of both fractions significantly depressed the VT production, both VT1 and VT2.

Conclusion: 

Both fractions, Qi 3 and Qi 4, of Quercus infectoria were proved to be very active against EHEC and depressed the VT production. Tannin has been reported to be main the constituent of this plant. It is now being further purified and identified using NMR spectra and mass spectrometry for potentially bioactive components to provide alternative treatment for EHEC infection.

Acknowledgement: 

This work was supported by a fund from Thailand-Tropical Diseases Research Programme. National Center for Genetic Engineering and Biotechnology, Fiscal year 2004.