Bactericidal activity of herbal extracts

The antimicrobial activity of total herbal extracts has been investigated. The MIC of extracts of Evodia rutaecarpa and grape kernel ranged between 0.25 and 1 mg/ml against gram-positive cocci and P. aeruginosa. Cocci were killed after 30-90 min of incubation in grape kernel extract (0.5 - 1.5 mg/ml), and after 8 h in evodia extract (0.5 - 1 mg/ml), respectively. C. albicans was only susceptible to evodia (MIC 0.5 mg/ml). The organic solvents of the preparations contributed to the antibacterial effect of herbal extracts with MICs of ethanol between 4 and 10 vol% and those of methanol between 6 and 10 vol%. Taking this into consideration, mastic and thyme extracts exerted hardly any microbicidal activity, while grape kernel extract and evodia were still effective at 2- to 6-fold dilutions below the MIC of the solvent. Because of the weak antimicrobial activity of total herbal extracts we recommend to give preference to preparations of single or more purified compounds.