Antibiotic principle of Eupatorium capillifolium.

Ethanolic extracts of Eupatorium capillifolium (Lam) Small showed activity against Bacillus subtilis grown in a chemically defined medium but not in a complex natural medium. The active principle was isolated as a colorless crystalline solid. A study of its properties and mass spectral fragmentation pattern showed that it was costic acid, a sesquiterpenic acid previously isolated from Costus root oil. The observed inactivity of costic acid against B. subtilis in a complex medium was shown to be due to the presence in the medium of glutamic acid, which is capable of reversing 90% of the activity of costic acid.