Abstract Description

The emergence of drug resistance among Mycobacterium tuberculosis (Mtb) strains, coupled with the detrimental side effects linked to tuberculosis (TB) treatment, underscores the persistence of TB as a significant clinical and public health concern in South Africa, thereby necessitating ongoing research in drug discovery. The use of medicinal plants for the treatment of TB has garnered increasing attention, especially in countries where a significant portion of the population relies on traditional medicine as a primary form of healthcare. Crude extracts from nine medicinal plants were investigated for their antimycobacterial activity based on their ethnomedicinal use in respiratory ailments. Extraction was carried out using maceration with hexane, dichloromethane, acetone, methanol, and water. Phytochemical profiling and qualitative antioxidant activity were assessed using thin layer chromatography (TLC), while the 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay quantified antioxidant capacity. Antimycobacterial activity was determined against Mycobacterium smegmatis (ATCC 1441) using the broth microdilution assay, with rifampicin as a positive control. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and LC-MS were employed to evaluate protein expression profiles of M. smegmatis following exposure to inhibitory concentrations of the extracts and rifampicin. Growth kinetics were used to assess bacterial growth responses to inhibitors. Phytochemical profiling revealed that all plants contained various phytoconstituents in differing concentrations. Additionally, the plants exhibited relatively low antioxidant activity, as indicated by their IC50 values. Rosmarinus officinalis and Zanthoxylum capense demonstrated inhibitory effects on the growth of M. smegmatis with a minimum inhibitory concentration of 0.625 mg/ml. The time-kill assays indicate that the plant extracts including those of Gardenia volkensii, Citrus limon, Croton gratissimus and Clerodendrum glabrum exhibited greater growth reduction than rifampicin. Proteomic analysis revealed distinct alterations in protein expression, indicating that the extracts, like rifampicin, disrupt bacterial protein synthesis. Although the investigated plants showed limited antioxidant potential, several exhibited noteworthy antimycobacterial properties, including inhibitory effects on bacterial protein synthesis. These findings provide preliminary evidence supporting the traditional use of these plants and highlight their potential as sources of novel anti-TB drug leads.