The antibacterial activities of peppermint oil and green tea polyphenols, alone and in combination, against enterohemorrhagic Escherichia coli

Abstract

The antibacterial activities of peppermint oil and its 53 constituents against Escherichia coli were examined in a preliminary screening test. Peppermint oil and 15 of its constituents had significant bactericidal activity against non-pathogenic E. coli and enterohemorrhagic E. coli O157:H7. Polyphenols from green tea and four catechins from green tea also had antibacterial activity against E. coli O157:H7 in liquid culture medium. Peppermint oil and three of its constituents, namely, menthol, menthone and neomenthol, killed the bacteria within one hour at concentrations above 400 μg/ml in phosphate-buffered saline. Polyphenols from green tea showed bacteriostatic activity in the culture medium, and bactericidal activity in PBS. This latter effect only became evident after several hours. A synergistic effect was observed for peppermint oil and for menthol when combined with green-tea polyphenols. These results suggest that the antibacterial activities of peppermint oil and green-tea polyphenols might involve different mechanisms and combinations of peppermint oil or the active constituents of peppermint oil with green-tea polyphenols might be useful as natural antibacterial agents against E. coli O157:H7.