Isolation, Characterization and Antimicrobial Activity of Endophytic Actinobacteria from Medicinal Plants

Abstract

The current study is aimed to isolate endophytic actinobacteria from various medicinal plants for exploring its antimicrobial activity against clinical pathogens. Out of 50 actinobacterial cultures isolated from eleven medicinal plants, 58 % of the cultures showed antimicrobial activity against at least two out of nine pathogens tested. Strain KCA1 isolated from Phyllanthus niruri leaves showed maximum zone of inhibition against all of the nine pathogens tested. Strain KCA1 exhibited maximum level of antimicrobial metabolite production in solid state fermentation during 9 d of incubation. Three well separated spots were observed when the ethyl acetate extract of strain KCA1 was analyzed through thin-layer chromatography. One spot with retardation factor value 0.82 was found to inhibit Staphylococcus aureus in thin-layer chromatography bioautographic assay. The active fraction eluted from thin-layer chromatography was further characterized by gas chromatography-mass spectral analysis. The mass spectral data revealed the presence of three compounds viz., 2,4-di-tert-butylphenol (C14H22O), 1-hexadecanol (C16H34O) and 1-nonadecene (C19H38) present in major proportions which are responsible for the antimicrobial activity of the strain KCA1. In fermentation experiment, variables such as glucose, yeast extract and sodium chloride were found to influence the antimicrobial compound production. The potential strain KCA1 was identified as Streptomyces sp. on the basis of microscopic, cultural, physiological and 16S ribosomal ribonucleic acid analysis.