In vitro Anti-mycobacterial activity of selected medicinal plants against Mycobacterium tuberculosis and Mycobacterium bovis Strains

Background: Tuberculosis (TB) is a global burden with one -third of the world's population infected with the pathogen Mycobacterium tuberculosis complex and annually 1.4 million deaths occur due to the disease. This high incidence of infection and the increased rate of multi-drug resistant and extensively-drug resistant strains of the organism further complicated the problem of TB control and have called for an urgent need to develop new anti-TB drugs from plants. In this study, the in vitro activity of root of Calpurnia aurea, seeds of Ocimum basilicum, leaves of Artemisia abyssinica, Croton macrostachyus, and Eucalyptus camaldulensis were evaluated against M. tuberculosis and M. bovis strains. Methods: Five Ethiopian medicinal plants, root of Calpurnia aurea, seeds of Ocimum basilicum, leaves of Artemisia abyssinica, Croton macrostachyus, and Eucalyptus camaldulensis used locally for the management of TB. They were investigated for in vitro antimycobacterial activity against M. tuberculosis and M. bovis strains. 80% methanolic extracts of the plant materials were obtained by maceration. The antimycobacterial activity was determined using 96 wells of microplate with the help of visual Resazurin Microtiter Assay. Results: The crude 80% methanolic extracts of the root of C. aurea, seeds of O. basilicum, and leaves of A. abyssinica, C. macrostachyus, and E. camaldulensis had anti-mycobacterial activity with minimum inhibitory concentration (MIC) ranging from 6.25-100 μg/mL. The MIC of 80% methanol extracts in the order mentioned above ranged 25-100 μg/ml and 12.5-75 μg/mL, 25-100 μg/mL and 25-50 μg/mL, 6.25-50 μg/mL and 12.5-50 μg/mL, 12.5-100 μg/mL and 18.25-50 μg/mL and 6.25-50 μg/mL and 12.5-50 μg/mL, respectively for M. tuberculosis and M. bovis strains.Conclusions: The results support the local use of these plants in the treatment of TB and it is suggested that these plants may have therapeutic value in the treatment of TB. However, further investigations are needed on isolating chemical constituents responsible for eliciting the observed activity in these plants.