Surasak Limsuwan, Silawan Vanmanee, and Supayang Voravuthikunchai

pp. 545 - 554

Abstract

Medicinal plants have been used for treating diarrhoea but the interference mechanisms are not clearly
understood. One possible hypothesis is that of an effect on cell surface hydrophobicity of microbial cells. In
this study, we examined cell aggregation affected by crude extracts of Thai medicinal plants on cell surface
hydrophobicity of Escherichia coli strains by salt aggregation test. Correlation between minimal inhibitory
concentration and cell aggregation was performed. Aqueous and ethanolic extracts of 8 medicinal plants
including Acacia catechu, Holarrhena antidysenterica, Peltophorum pterocarpum, Piper sarmentosum, Psidium
guajava, Punica granatum, Quercus infectoria, and Tamarindus indica were tested with E. coli O157: H7 and
other E. coli strains isolated from human, porcine, and foods. Aqueous extracts of Peltophorum pterocarpum,
Psidium guajava, and Punica granatum were highly effective against E. coli O157: H7 with the MIC values of
0.09 to 0.39, 0.19 to 0.78, and 0.09 to 1.56 mg/ml, respectively. Ethanolic extract of Quercus infectoria and
Punica granatum demonstrated good MIC values of 0.09 to 0.78, and 0.19 to 0.78 mg/ml, respectively. It
was established that aqueous extracts of Punica granatum and Piper sarmentosum at high concentration
(25 mg/ml) enhanced cell aggregation of almost all E. coli strains while aqueous and ethanolic extracts of
Quercus infectoria enhanced cell aggregation of some E. coli strains. Correlation between minimal inhibitory
concentration and cell aggregation was not found in this study.