Inhibitory properties of selected South African medicinal plants against Mycobacterium tuberculosis

Ethnopharmacological relevance: Tuberculosis (TB), caused by Mycobacterium tuberculosis (MTB) is the most commonly notified disease and the fifth largest cause of mortality. One in 10 cases is resistant to treatment in some areas. Several plants are used locally to treat TB-related disease.

Aims of the study: The aim was to screen selected South African medicinal plants used to treat TB and related symptoms by traditional healers for antimycobacterial activity.

Materials and methods: Ethnobotanical information on these plants was obtained. Crude acetone, methanol, hexane and ethanol extracts of 21 selected medicinal plants obtained in Venda, South Africa were screened for their ability to inhibit MTB H(37)Ra and a clinical strain resistant to first-line drugs and one second-line drug using tetrazolium microplate assay to determine the minimum inhibitory concentration (MIC). Results were analyzed using Microsoft Excel 2007 and One way ANOVA; p<0.05 was considered for statistical significance.

Results: Few acetone extracts were active against MTB with MIC under 100 microg/mL. Four plants showed lower MIC values; Berchemia discolor Klotzsch Hemsl 12, 5 microg/mL on H(37)Ra and 10.5 microg/mL on the clinical isolate, Bridelia micrantha Hochst. Baill (25 microg/mL), Warbugia salutaris Bertol. F Chiov (25 microg/mL), and Terminalia sericea Burch ex D. F (25 microg/mL) on both H(37)Ra and clinical isolate. However, the roots of Ximenia caffra Sond. Var. caffra, barks of Sclerocarya birrea (A Rich) Hochst, Asclepias fruticosa L, tubers of Allium sativum L, leaves of Carica papaya L, Solanum panduriforme E. Mey C, and roots of Securidaca longepedunculata Fresen gave MIC greater than 100 microg/mL.

Conclusion: The acetone extracts of Berchemiadiscolor, Bridelia micrantha, Terminalia sericea and Warbugia salutaris could be important sources of mycobactericidal compounds against multidrug-resistant MTB.