Evaluation of the antimycobacterial activity of crude extracts and solvent fractions of selected Ethiopian medicinal plants

BACKGROUND Tuberculosis (TB) is a global health problem complicated by drug resistance and human immunodeficiency virus that has dramatically increased active TB. Several medicinal plants are used traditionally to treat TB in Ethiopia and investigating these plants is required as plants are an alternative source for development of new anti-TB drugs. The purpose of this study was to investigate antimycobacterial activity of crude extract of Carissa edulis, Otostegia integrifolia, Persea americana, Pterolobium stellatum and Vernonia amygdalina as well as fractions of the most active crude extract. METHODS The effect of various doses of the crude extracts as well as solvent fractions on M. tuberculosis H37Rv and/or MDR-TB clinical isolate was determined using broth microdilution and microtiter resazurin assay methods. Minimum inhibitory concentration was determined by CFU count and resazurin color change observation. RESULTS Chloroform and 80% methanol extracts of P. stellatum and O. integrifolia as well as 80% methanol and acetone extracts of P. americana had significant antimycobacterial activity (p < 0.001) against M. tuberculosis H37Rv. Chloroform extract of V. amygdalina and C. edulis didn't, however, show any significant activity compared to negative controls. P. stellatum chloroform extract was the most active on M. tuberculosis H37Rv (MIC 0.039 mg/ml) and AOZ8W-4 (MDR-TB clinical isolate) (MIC = 0.078 mg/ml). Ethyl acetate fraction of P. stellatum chloroform extract was the most active fraction. CONCLUSION P. stellatum, O. integrifolia and P. americana were found to be endowed with antimycobacterial activity. However, P. stellatum appears to be the most promising plant based on criteria set by different studies. Ethyl acetate fraction of P. stellatum was found to be the most active and future studies should involve this fraction.