In-vitro Inhibitory Activity of Extracts of Some Medicinal Plants against Mycobacterium smegmatis

The current drugs used for the treatment of tuberculosis (TB) have become less effective due to the development of resistance by Mycobacterium tuberculosis to the drugs. As such there is a search for new drugs for treatment of TB. Medicinal plants used in traditional medicine for symptoms of TB in endemic countries represent potential sources of new compounds for drug development. This study was designed to investigate the antimycobacterial activities of extracts of some medicinal plants used in Abia State using the Mycobacterium smegmatis (ATCC 19420) model. Crude methanolic extracts and fractions of five medicinal plants (Alchornea cordifolia, Asystacia gangetica, Chromolena odorata, Pterocarpus santalinoides and Garcinia kola) were tested against a strain of M. smegmatis using the agar-well diffusion method to measure the diameter of zone of inhibition (DZI). The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were determined by the broth dilution method. Phytochemical screening of the plant materials was carried out using standard methods. The mean DZI of the methanol extracts ranged from 12.5mm to 18mm at a concentration of 100mg/ml. The extract of G. kola produced the highest mean DZI. The DZI produced by the ethyl acetate (EtAc) and dichloromethane: methanol (DCM:MeOH) fractions ranged from 7.5-14mm. The EtAc fraction of A. cordifolia produced a zone of inhibition of 14mm while all the three fractions (N-Hexane, EtAc and DCM:MeOH) of C. odorata produced inhibition zone of 12.0mm, 13.5mm and 11.5mm, respectively. The MIC values ranged from 25mg/ml to 50mg/ml. Preliminary qualitative phytochemical analysis showed that the plant extracts contained alkaloids, terpenoids, saponins, flavonoids and tannins. The thin layer chromatographic analyses suggested that the antimycobacterial activity was mainly due to the alkaloid constituents. Garcinia kola exhibited the highest activity, followed by A. cordifolia while the activity of P. santalinoides was the lowest. The results of this study demonstrate the in-vitro inhibitory activities of these medicinal plants against M. smegmatis and provide the basis for further studies to isolate and identify the compounds with antimycobacterial activity.