Antimicrobial activities of isoalantolactone, a major sesquiterpene lactone ofInula racemosa

Abstract

Isoalantolactone, a major constituent ofInula racemosa (Compositae) was tested for its antimicrobial action against five bacteria, six human and six plant pathogenic fungi. The lactone showed absolute toxicities at 500 μg/mL against 3 soil borne phytopathogenic fungi (Gaeumannomyces graminis var.tritici, Rhizoctonia cerealis andPhytophthora capsici) with the MICs determined to be 100, 100 and 300 μg/mL, respectively. At the MICs, isoalantolactone exhibited its fungistatic nature of toxicity. The lowest fungicidal concentrations of the lactone toG graminis var.tritici, R cerealis andP. capsici were shown to be 150, 150 and 350 μg/mL, respectively. Moreover, isoalantolactone displayed weaker antibacterial activities againstBacillus subtilis, Escherichia coli, Pseudomonas fluorecense, Sarcina lentus andStaphylococcus aureus with MICs of 125, 425, 150, 150 and 100 μg/mL, respectively. The investigation disclosed the strong inhibition of isoalantolactone to the phytopathogenic fungi, raising a possibility that the lactone could be considered as a starting point for the project aiming at the development of new fungicide(s).