Enhancement of the Antibiotic Activity against a Multiresistant Escherichia coli by Mentha arvensis L. and Chlorpromazine

<i>Background:</i> This is the first report testing the antibiotic resistance-modifying activity of <i>Mentha arvensis. </i><i>Methods:</i> In this study an ethanol extract of <i>M. arvensis</i> L. and chlorpromazine were tested for their antimicrobial activity alone or in combination with conventional antibiotics against strains of <i>Escherichia coli</i>. <i>Results:</i> The growth of two <i>E. coli</i> strains tested was not inhibited by the extract. The minimum inhibitory concentration and minimal bactericide concentration values were ≧1 mg/ml for both strains of <i>E. coli</i> used. A potentiating effect of this extract on gentamicin was demonstrated. Similarly, there was a potentiating effect of chlorpromazine on kanamycin, amikacin and tobramycin, indicating the involvement of an efflux system in the resistance to these aminoglycosides. <i>Conclusions:</i> It is therefore suggested that extracts from <i>M. arvensis</i> could be used as a source of plant-derived natural products with resistance-modifying activity, such as in the case of gentamicin, constituting a new weapon against bacterial resistance to antibiotics, as with chlorpromazine.