Bactericidal Action of Green Tea Extract and Damage to the Membrane of Escherichia coli O157 : H7

The antibacterial activity of green tea extract was investigated on 36 isolates of pathogens. The minimum inhibitory concentration of the extract against some isolates such as Escherichia coli O157: H7 was less than 250 μg/ml. The growth of the organism in culture broth was completely inhibited with 500 μg/ml of the extract. The organism was not detected by culturing on agar plates after 6 h incubation in phosphate buffered saline with 1, 000 μg/ml of the extract. It was observed by fluorescence microscopy and scanning electric microscopy that the cell membranes were damaged with 1, 000 μg/ml of the extract.