Nanoemulsion of Mentha piperita essential oil active against Mycobacterium strains

Present investigation aimed to study the antimycobacterial potential of Mentha piperita essential oil fractions, identify its active constituents by GC-MS and preparation of nanoemulsion from biologically active fraction. Four oil fractions (R1, R2, R3, R4) were collected during hydrodistillation of Mentha piperiata leaves and tested in the two of mycobacterial strains by conventional disc diffusion method. Oil fractions R2 and R3 demonstrated maximum zone of inhibition of 39 mm and 36 mm in Mycobacterium smegmatis, 33 mm and 31 mm in Mycobacterium bovis BCG respectively at a dilution of 75% in DMSO compared to standard drug isoniazid (23 mm in 4 mu g/ml). GC-MS analysis of the most active fraction R2 reveals the presence of menthol (70.69%), isomenthone (14.63%) and neomenthol (6.82%) as major constituents. To enhance bioavailability of oil fraction, the nanoemulsions were prepared from R2 by sonication method. Nanoemulsions, N1 and N2 prepared by varying surfactant concentrations were tested in Mycobacterium bovis BCG using quantitative and colorimetric resazurin microtiter assay (REMA). Nanoemulsions, N1 and N2 have shown 97-100 % bacterial growth inhibition at 3.125 % concentration in the culture medium compared with the culture control.