Staphylococcus aureus MDR efflux pump inhibitors from a Berberis and a Mahonia (sensu strictu) species

Bioactivte fractionation. based on multi-drug resistance (MDR) pump inhibition in Staphylococcus aureus resulted in the isolation of the active inhibitors 5 ' -methoxyhydnocarpin-D From leaves of Berberis (formerly Mahonia) trifolioata and pheophorbide a from Beuberis fendleri. The hydnocarpin derivative was not found in the latter species. Pheophytin L (the phytol derivative of pheophorbide if) was identified from both species. but it proved to have no MDR pump inhibitory activity. The somewhat uncommon, and inactive, flavonoid tricin was identified from B. trifoliolata. The occurrence of a flavonolignan in Mahonia-type species and its absence in Berberis sensu strictu may provide a chemical differentiation between the two groups which are now recombined on the basis of DNA studies. The strong bacterial efflux pump inhibition of pheophorbide a could be of importance as a plant defense against natural pathogens. (C) 2001 Elsevier Science Ltd. All rights reserved.