Isolation and screening of antibiotic producing actinomycetes from rhizosphere and agricultural soils

摘要

Antibiotics are secondary metabolites produced by microorganisms. Actinomycetes are the top producers of antibiotics. The study was designed to isolate and screen antibiotic producing actinomycetes obtained from rhizosphere of plants and agricultural soils. A total of 30 actinomycetes were isolated. Out of the 30 actinomycetes, 18 (60%) showed antimicrobial activities against one of the tested microorganisms of which 9 isolates were selected for their wide spectrum of antibiotic activities. In this study, isolates AAUBA5 and AAUBA30 were found to inhibit all of the test organisms, except Escherichia coli ATCC 25922. The latter was found to be the most resistant and was only inhibited by 3/18 (17%) of the isolates. The isolates were identified and characterized by cultural, morphological, physiological, and biochemical characteristics and found to be classified under the genus Streptomycetes. In order to extract the active compounds from isolates, fermentation was carried out on 9 isolates and the former was extracted by using ethyl acetate. Finally, isolate AAUBA13 was selected for further study based on spectrum activity from disc diffusion assay. Antimicrobial compound obtained from AAUBA13 isolate was separated and purified with thin layer chromatography (TLC), column chromatography, and preparative chromatography. The finding of this study, in general, showed that, antimicrobial compounds obtained from AAUBA13 demonstrate broad spectrum antimicrobial activity against Staphylococcus aureus ATCC25923, E. coli ATCC 25922, Pseudomonas aeruginosa ATCC25853, S. aureus (clinical isolate), Shigella boydii (clinical isolate), Streptococcus pneumonia ATCC49619, and Candida albicans ATCC62376.