Antibiotic production and optimization of culture condition of Actinomycetes from some Soda Lakes of Ethiopia.
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Date
2011-07
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Addis Ababa University
Abstract
The demand for new antibiotics increased due to the misuse and over use of antibiotics in
various sectors creating an evolutionary pressure and resulting in multi drug resistant strains
which result in increment of morbidity and mortality in the world. The main objective of this
study was to explore the potential of alkaliphilic actinomycetes isolated from three Ethiopian
soda lakes. About 171 isolates were screened for antibiotic production using cell free culture
supernatant taken from the submerged fermentation and ethyl acetate crude extract of the
culture, of which 93.6% of them showed antibiotic activity with cell free culture supernatant and
76 % of them with crude ethyl acetate extract against the test microorganisms used. Based on
broad spectrum activity, zone of inhibition obtained and their activity with the use of crude ethyl
acetate extract, two isolates LCHACT17and LABACT21 were chosen for further
characterization. Antibiotic production was favored when phosphate concentrations was 0.2 %
for LCHACT 17 and for LABACT 21. Yeast extract and sodium nitrate (for LCHACT 17) and
combination of casein and potassium nitrate (for LABACT 21) were suitable nitrogen sources for
antibiotic production. From the carbon sources used soluble starch was the best carbon source
for antibiotic production by LCHACT17 while sucrose was found to be preferred carbon source
by LABACT 21. Similarly it was observed that 1% sodium chloride concentration was favorable
for antibiotic production by both isolates and the pH parameter indicated that pH10 (for
LABACT 21) and pH11 (for LCHACT17) were the optimum pH for antibiotic production. The
cell free culture supernatant of both isolates was stable at alkaline pH and decreases in activity
at lower pH (pH 6 and below). The cell free culture supernatant of LCHACT17 was stable up to
60oc while LABACT 21 was stable up to 40 oc. The minimum inhibitory concentration (MIC) of
LCHACT17 crude ethyl acetate extract against Streptococcus pneumonia was 12.5 mg/ml.
Key words/ phrases: Alkaliphiles, Antibiotics, Disk diffusion.
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Keywords
Alkaliphiles,, Antibiotics, Disk diffusion.