Evaluation of Antimycobacterial and Synergistic Activity of Plants Selected Based on Cheminformatic Parameters

Background: Drug resistance is a major public health problem and a threat to progress made in bovine tuberculosis care and control worldwide. This study aimed at evaluating anti-mycobacterial and synergistic activity of some medicinal plants that were selected by cheminformatics studies against Mycobacterium bovis.

Methods: Considering the strong synergistic antimycobacterial action of oleanolic acid in combination with tuberculosis drugs, NCBI database was explored to find the compounds with over 80% similarity to oleanolic acid, called S1. Plants containing S1-type compounds were traced to and resulted in five plants, including Datura stramonium, Boswellia serrata Lavandula stoechas, Rosmarinus officinalis, and Thymus vulgaris, as experimental samples. Crude extracts were prepared by percolation using 80% ethanol or as the product of a pharmaceutical company. The extracts were screened against Mycobacterium bovis using broth microdilution method and Alamar Blue Assay. Extracts from these plants were used in combination with isoniazid and ethambutol to investigate the possibility of synergy with respect to antimycobacterial activity.

Results: The extracts from D. stramonium, B. serrata a, L. stoechas, R. officinalis, and T. Thymus vulgaris showed antimycobacterial activity of 375, 125, 250, 187.5, 500 µg/ml, respectively. The best synergistic results were for L. stoechas and D. stramonium in combination with ethambutol, the fractional inhibitory concentration index was 0.125 µg/ml for both.

Conclusion: The observed antimycobacterial and synergistic activities are completely novel and obtained from targeted screening designed according to cheminformatics strategy. As for the synergistic action of the extracts, they could be used as supplements in bTB treatment.