Isolation and Screening of Antibiotic Producing Actinomycetes from Soil
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Date
2011-10
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Addis Ababa University
Abstract
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
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Keywords
Actinomycetes; Antibiotics; Antimicrobial bioassay; Antimicrobial compound; Disc Diffusion Assay