Evaluation of in vitro antimycobacterial activity of Nigerian plants used for treatment of respiratory diseases

The global threat of tuberculosis (TB) demands for search for alternative antimycobacterial drugs. Some Nigerian medicinal plants used in the treatment of TB and other respiratory diseases were evaluated for activity against a clinical isolate of Mycobacterium tuberculosis and a strain of Mycobacterium bovis (BCG). The crude methanolic extracts of eight plant species were screened for activity against a clinical isolate of M. tuberculosis using broth microdilution method. Four out of the eight plant extracts exhibited inhibitory activities against M. tuberculosis at 78 and 1250 µg/mL. The crude extracts of Entada africana, Hymenocardia acida, Sterculia setigera and Stereospermum kunthianum did not inhibit significantly even at high concentration of 1250 ig/mL. The hexane fractions obtained after fractionation were the most active fractions for all the plants tested against BCG, having Anogeissus leiocarpus and Terminalia avicennioides exhibiting the highest activity at 312 and 200 µg/mL, respectively. Fractions Ta5 and Al4 obtained on further purification exhibited most significant activity (MIC of 4.7 and 7.8 g/mL, respectively). From the results of phytochemical analysis, terpenes and triterpenoid saponins are the most prominent compounds in these fractions and several reports earlier indicated that these metabolites are potential antimycobacterial agents. This class of metabolites presents interesting area for further investigation with special attention on the Combretaceae family from Nigeria flora.