Metabolites of the "smoke tree", Dalea spinosa, potentiate antibiotic activity against multidrug-resistant Staphylococcus aureus.

Two new 2-arylbenzofuran aldehydes (1 and 2) and three known phenolic compounds (3-5) were isolated from organic extracts of Dalea spinosa. These compounds were evaluated for their intrinsic antimicrobial activity and their ability to perform as multidrug-resistance inhibitors by potentiating the activity of known antimicrobials against a variety of pathogenic microorganisms. Compound 1 and its acetate derivative 6 exhibited no direct antimicrobial activity but enhanced the effect of the weak plant antimicrobial berberine when tested against Staphylococcus aureus. Additional potentiation assays with S. aureus overexpression and knockout isogenic efflux mutants for the NorA pump were done in order to assess whether the potentiating effects were associated with inhibition of this known pump mechanism.