Antimycobacterial activity against different pathogens and selectivity index of fourteen medicinal plants used in southern Africa to treat tuberculosis and respiratory ailments

• The activities of extracts were determined against four Mycobacterium species.
• The plant species were relatively non-toxic and had antimycobacterial activity.
• M. fortuitum was the best predictor of activity against pathogenic M. tuberculosis.
• Some of these species may be safe and effective against tuberculosis.

Many plants are used in traditional medicine to treat tuberculosis and other respiratory disorders in Africa. The emergence of multiple drug resistance has become a major threat and thus calls for an urgent need to search for new effective and safe anti-TB agents. The aim was to determine the antimycobacterial activity and the safety of the acetone leaf extracts of 14 plant species used in southern Africa to treat tuberculosis and pulmonary ailments.The antimycobacterial activity was evaluated by a tetrazolium violet based broth microdilution method against three fast-growing mycobacteria species (Mycobacterium smegmatis, Mycobacterium aurum and M. fortuitum) and one pathogenic M. tuberculosis field strain. The in vitro cellular toxicity was determined using the MTT assay on Vero monkey kidney cells. The extraction yield, the LC50 and MIC values were used to determine the total activity (TA) and the selectivity index (SI) of the extracts.Extracts had moderate to weak activity with the MIC values ranging from 0.039 to > 2.5 mg/mL. M. fortuitum appeared to be better predictor of activity against pathogenic M. tuberculosis than M. smegmatis and M. aurum. Extracts from Heteropyxis natalensis (3.3) and Hexalobus monopetalus (2.47) had the highest selectivity index.The results substantiate the safety and in some cases the potential efficacy of the traditional use of these species against tuberculosis and pulmonary ailments.