Isoflavones as potentiators of antibacterial activity.

Isoflavones isolated from Lupinus argenteus were found to potentiate the antibacterial activity of alpha-linolenic acid, also found in the same plant. The isoflavones also potentiated the activity of the natural plant antibiotic berberine and the synthetic fluoroquinoline antibiotic norfloxacin. The isoflavones increased the uptake of berberine into Staphylococcus aureus cells, indicating that they may be inhibiting a multidrug resistance pump (MDR). Thus, L. argenteus contains a weak antibacterial and also MDR pump inhibitors, which increase its potency.