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

BACKGROUND: This is the first report testing the antibiotic resistance-modifying activity of Mentha arvensis. METHODS: In this study an ethanol extract of M. arvensis L. and chlorpromazine were tested for their antimicrobial activity alone or in combination with conventional antibiotics against strains of Escherichia coli. RESULTS: The growth of two E. coli strains tested was not inhibited by the extract. The minimum inhibitory concentration and minimal bactericide concentration values were >or=1 mg/ml for both strains of E. coli 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. CONCLUSIONS: It is therefore suggested that extracts from M. arvensis 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.