Abstract Description

Tuberculosis (TB) is caused by Mycobacterium tuberculosis, which primarily targets the lung parenchyma. Mycobacterium smegmatis is used as a model organism for mycobacteria, as it shares homologous genes. The secondary metabolites of medicinal plants have been reported to contain potent bioactive compounds that can serve as alternative sources of therapeutic agents. The study aimed to determine the antioxidant, antimycobacterial, and antibiofilm activity of medicinal plants against M. smegmatis. Plant leaves were collected, dried, and extracted using solvents of varying polarities. Phytoconstituents and antioxidants were quantified using the colorimetric assays. Quantitative antimycobacterial activity was determined using the broth microdilution and time-kill assays. The antibiofilm activity of sub-MIC values was determined using the crystal violet staining assay. Methanol was the most effective extractant, with Dichrostachys cinerea exhibiting the highest phenolic (237.47 ± 0.49 mg GAE/g of extract) and tannin content (73.99 ± 1.00 mg GAE/g of extract). Buddleja salviifolia had the highest total flavonoid content (94.29 ± 9.08 mg QE/g extract) while Combretum apiculatum had the highest total flavanol content (116.30 ± 1.07 mg QE/g extract). Ascorbic acid had the highest DPPH scavenging activity with an IC50 value of 27.04 µg/mL. C. apiculatum dichloromethane and acetone extracts had the lowest minimum inhibitory concentration (MIC) value of 0.16 mg/mL. Rifampicin and C. apiculatum demonstrated equivalent efficacy in preventing initial microbial cell adhesion, with no statistically significant variation observed. All the extracts were able to prevent biofilm formation at different concentrations, except for B. salviifolia at one-eighth of its MIC. Carissa macrocarpa exhibited a bacteriostatic effect on M. smegmatis for 9 hours, with activity comparable to that of rifampicin in terms of its impact on the culture growth pattern. The selected medicinal plants have potent antioxidant, antimycobacterial, and antibiofilm activity. This shows that they can serve as good sources of anti-TB agents and candidates for isolation and characterisation of bioactive compounds.