Bioactivity of traditional medicinal plants used in the treatment of tuberculosis in the Free State, South Africa

Abstract

Many medicinal plant species were once used as a primary source of all medicines in the world and they continue to provide humankind with new remedies. Tuberculosis (TB) is one of the dreaded diseases that have been managed using medicinal plants. TB continues to be one of the airborne diseases that cause more deaths in the world than any other infectious diseases. The TB bacteria (Mycobacterium tuberculosis) has become resistant to the orthodox drugs used to treat TB diseases. Most strains of TB which have become resistant to all major anti-TB drugs have emerged. In the present study, eight medicinal plant species (Dicoma anomala, Xysmolobium undulatum, Hermania depressa, Lotinonius lanceolata, Senecio harveianus, Lentsweni, Eucomis automnalis and Drimia depressa) that are traditionally used in the Free State province for the treatment of respiratory infections were collected for investigation. An ethnobotanical survey was conducted from January to June 2014 in consultation with the traditional healers and herbalists of the Free State Province. Plants were collected, extratced and tested for phytochemicals, antibacterial, antifungal and antimycobacterial activity. The phytochemical carried out revealed some of the secondary metabolites being absent in some of the plants and present in others. X. undulatum and E. automnalis revealed the presence of saponins only. Lentsweni and H. depressa revealed the presence of tannins, saponins and terpenoids, whereas L. lanceolata and S. harveianus revealed the presence of tannins, saponins, flavonoids and cardiac glycoside.Antibacterial activity was tested using four bacterial strains; two Gram-positive strains (Bacillus pumilus and Staphylococcus aureus) and two Gram-negative strains (Klebsiella pneumoniaeand Escherichia coli), while the antifungal activity was tested against two fungal species namely Candida albicans and Trichophyton mucoides. The test for antimycobacterial activity was done against the causative agent of tuberculosis (M. tuberculosis). Extracts exhibiting low or no antibacterial activity were D. anomala (methanol and aqueous extracts), X. undulatum (acetone and aqueous extracts), Lentsweni (methanol extract), E. automnalis (ethanol and methanol extracts). Good antibacterial activity was observed with the acetone and ethanolic extracts of D. anomala having the highest activity against K. pneumonia (0.130 mg/ml) and E. coli (0.781 mg/ml), with B. pumilis and S. aureus having the best antibacterial activity (MIC value of 0.098 mg/ml). Promising results were detected with the ethanolic extracts prepared from X. undulatum, L. eriantha and D. depressa against all the bacterial strains with MIC values of 1.563 mg/ml. The antifungal activity of the acetone, ethanol, methanol and aqueous extracts prepared from the eight selected medicinal plant species displayed the best activities against C. albicans and T. mucoides, with sMIC values ranging between 0.098 to 0.781 mg/ml. The best antimycobacterial activity was detected with all lipophilic extracts prepared from S. harveianus with MIC values of 0.195 mg/ml. H. depressa organic solvents extracts exhibited good activity against M. tuberculosis with MIC values of 0.78 mg/ml. The selected medicinal plants used for the treatment of respiratory ailments in the Free State Province have demonstrated significant activities, which may better explain and justify their frequent use by the traditional healers. These results might give some leads for further analysis in order to develop new pharmaceutical drugs derived from plants.