Identification of Thymol as an Antitubercular Agent from Ocimum gratissimum Leaf Essential Oil

Ocimum gratissimum consumed as a vegetable is used to treat cough, tuberculosis and dysentery in Nigeria. Hydro-distillation of the fresh leaves of O. gratissimum yielded a golden yellow essential oil 0.5% v/w which exhibited minimum inhibitory concentration (MIC) of 48 µg/ml against Mycobacterium bovis BCG strain. Activity-guided fractionation of the oil into neutral and acidic portions followed by column chromatography led to the isolation of a crystalline compound with MIC of 9.8 µg/ml while the control drug isoniazid had MIC of 0.07 µg/ml. GC-MS and 1H NMR analyses revealed the bioactive crystalline compound to be thymol.