Endophytes are organisms that are intimately associated with various parts of plants. Endophytic actinomycetes represent actinomycetes of various genera that are associated with various parts of the plants. The beneficial interactions of endophytic actinomycetes with plants are being considered as an important area of research. These endophytic actinomycetes are an attractive source of novel bioactive compounds having pharmaceutical and agricultural importance. Endophytic actinomycetes are associated with different parts such as roots, stem and leaves. Their isolation requires the selection of plant parts and their surface sterilization so as to remove adhering dirt and organisms. A range of surface sterilants such as ethanol, sodium hypochlorite, sodium thiosulfate and sodium carbonate are used for this purpose. Media such as potato dextrose agar, yeast extract-malt extract agar, actinomycetes isolation agar and starch casein agar are used for isolation of actinomycetes. Identification of isolated endophytic actinomycetes is usually based on cultural, microscopic, staining, biochemical and genetic studies. The antimicrobial potential of endophytic actinomycetes is tested by primary as well as secondary screening procedures. Methods such as cross streak and dual inoculation method are used in primary screening. Disk diffusion and well diffusion techniques are commonly employed for secondary screening. Crude extracts and purified compounds from endophytic actinomycetes are shown to exhibit a range of bioactivities such as antimicrobial, antiviral, antioxidant and anticancer activity. Among these, antimicrobial potential of endophytic actinomycetes appears to be an important one. Several researchers have worked on isolation and antimicrobial activity of endophytic actinomycetes isolated from different parts of various plants. It is found that endophytic actinomycetes exhibit inhibitory activity against Gram positive bacteria, Gram negative bacteria, yeasts and filamentous fungi. The isolates and their metabolites are shown to exert detrimental effect against drug resistant pathogens such as methicillin resistant Staphylococcus aureus (MRSA) and penicillin resistant S. aureus. Many isolates are effective against phytopathogenic fungi. These endophytic actinomycetes appear promising resources of bioactive agents and hence, they can be exploited for protection of crops and production of therapeutic agents active against disease causing agents.

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