Isolation and Screening of Antibiotic Producing Actinomycetes from Soil

No Thumbnail Available



Journal Title

Journal ISSN

Volume Title


Addis Ababa University


Antibiotics are secondary metabolites produced by microorganisms. Actinomycetes represent the top producer of antibiotics that are widely distributed in the different types of soils. The study was designed to isolate and screen antibiotic producing actinomycetes on samples obtained from soil and rhizosphere of plants. A total of 30 actinomycetes were isolated from Debrezit, Holeta and Arat Kilo campus. Out of the 30 actinomycetes, 18 (60%) showed antimicrobial activities of one of the tested microorganisms of which 9 isolates were selected for their wide spectrum of antibiotic activities. In this study, isolate AAUBA5 and AAUBA30 were found to inhibit all of the test organism, except E.coli ATCC 25922 and the latter was found to be the most resistant that 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 isolate the active compounds of the extract, fermentation was carried out on nine isolates and the former was extracted by using ethyl acetate. The antimicrobial activity of the active compound of the isolates was studied using Disc Diffusion Assay method and found to inhibit the test microorganisms that could not during the preliminary screening. Finally, isolates AAUBA13 was selected for further study based on spectrum activity and inhibition zone diameter in the antimicrobial bioassay. Antimicrobial compound obtained from AAUBA13 isolate was separated and purified with thin layer chromatography (TLC), column chromatography and preparative chromatography. The purified compound found to be active against gram positive bacteria (S.aureus clinical isolate, S.pneumoinae ATCC49619 and S.aureus ATCC25923), gram negative bacteria (E.coli ATCC25922, S.typhi ATCC 6539 Shigella boydii clinical isolates and P.aeruginosa ATCC2585) and effective against Candida albicans ATCC62376. The data, in general, showed that the antimicrobial compounds obtained from AAUBA13 demonstrate broad spectrum and a remarkable antimicrobial activity against bacterial and Candida albicans ATCC62376. It is also suggested that the other isolates should be further processed to fully realize their antibiotic property on different test microorganisms. Key words: Actinomycetes; Antibiotics; Antimicrobial bioassay; Antimicrobial compound; Disc Diffusion Assay



Actinomycetes; Antibiotics; Antimicrobial bioassay; Antimicrobial compound; Disc Diffusion Assay