Antimycobacterial Activity Of Endophytic Actinobacteria From Selected Medicinal Plants

Background: Tuberculosis (TB), caused by Mycobacterium tuberculosis (MTB), poses a serious threat to human life. In addition, certain nontuberculous mycobacterial (NTM) species also cause infections in immune suppressed and even in immunocompetent individuals. With this view, the present study investigated the antimycobacterial properties of endophytic actinobacteria using Mycobacterium smegmatis as a surrogate model. Methods: Endophytic actinobacterial cultures were isolated from seven medicinal plants and their antimicrobial activity against two Gram-positive bacteria, three Gram-negative bacteria, fungi, and M. smegmatis was studied. Crude bioactive metabolites from one potential culture EAM4 were tested against Staphylococcus aureus, Escherichia coli, and M. smegmatis by disc-diffusion method, whereas activity against MTB H37Rv was tested by luciferase reporter phage (LRP) assay. The potential actinobacterial culture EAM4 was identified based on their 16S rRNA analysis. Results: Thirty actinobacterial cultures were isolated and were belonged to the genus Streptomyces. Maximum number of actinobacterial strains was isolated from Selaginella stellata (36.6%) and Pilea microphylla (36.6%). Gram-positive pathogens are inhibited by more number of actinobacterial cultures (>90%) than Gram-negative pathogens (50%). Twenty-eight of thirty actinobacterial cultures showed inhibitory activity against M. smegmatis. Bioactive metabolites from the potential culture EAM4 showed better inhibition against the S. aureus, E. coli, and M. smegmatis. In the LRP assay, 79% inhibition was exhibited against the MTB H37Rv. The potential actinobacterial strain EAM4 was identified as Streptomyces sp. based on their 16S rRNA analysis. Conclusion: Findings of the present study revealed that the endophytic cultures of Streptomyces investigated in this study are the promising source for isolating antimycobacterial metabolites effective against TB and nontuberculous mycobacterial pathogens.