الفهرس 
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Abstract
The present work deals with the study of Actinobacteria are considered one of the most important bioactive metabolites producers especially genus Streptomyces. The present work involves the comparative study between different isolates belonging to the order Actinomycetales. With the emergence of microorganisms that becoming resistance to available antibiotics that already had been marketed; the need for discovering novel drugs is real A total of 100 diverse actinomycetes species were isolated from different localities in Egypt (Sharm El Sheikh, Burj Al Arab, Marsa Alam, Arish, Baltim and Hurghada). Only 19 isolates exhibited notable activities against multidrug resistant pathogenic bacteria during the primary screening. The results showed that among the antagonistically active isolates, two isolates namely, SH89 and M19 showed pronounced antimicrobial activities against Gram positive and Gram negative bacteria but appeared to be inactive against the tested pathogenic fungi. The detailed comparative study of the cultural properties of the two selected isolates on different media, their morphological characteristics involving spore chain morphology, their physiological properties as well as 16SrRNA enable us to classify the two isolates as follows: M19 (Streptomyces psammoticus) and SH89 (Nocardiopsis chromatogenes). Subsequent experiments were performed to find out the optimum environmental conditions and nutritional requirements for highest antibiotic production by the selected strains. For Streptomyces psammoticus five parameters negatively affect the production. Solvent extraction method was done to isolate the active substances of the supernatant of Streptomyces psammoticus. The culture filtrate was therefore extracted with butanol in the ratio of 1:3 (V/V) at pH 6.5. Separation of antibacterial compounds from the crude extract was done by thin layer chromatography.