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Published: Kem. Ind. 50 (9) (2001) 501–509
Paper reference number: KUI-26/2001
Paper type: Conference paper
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Optimised Screening of Antibiotic Producing Strains

A. Bago Joksović, E. Gàal, M. Bošnjak+ and D. Hranueli


To recognise microbial strains capable to produce substances with antimicrobial activity the culture conditions enabling, both, the microorganism growth and the expression of antibiotic production, should be applied. Since the optimal culture conditions vary depending on properties of particular strains one can recommend the application of various culture conditions, designed on the basis of different factorial plans, in order to increase the probability of expression of antibiotic production and/or to enhance antibiotic biosynthesis efficiency. In the case of microbial colonies, values of inhibition zone diameters and colony diameters could be considered that they reflect strain properties. In performed experiments different microbial strains were applied. Streptomyces rimosus R6-500 as parental strain and its derivative strains MV9R-1 and MV9R-2, were used as antibiotic (oxytetracycline) producers. Additionally, S. rimosus R6-ZGL1 as producer of new substances with antibiotic activity and S. rimosus MV25W as the strain showing not detectable antibiotic activity, were used also. Bacillus cereus ATCC 11778 was applied as test microorganism sensitive to antibiotic action. Different cultivation media were used, their composition being defined according to different factorial plans. As expected, antimicrobial activity expressed differently in different media. Properties of media reflected differently on particular strains. Results showed that the use of different media can markedly increase the probability of recognising strains with antimicrobial activity. When comparing activities of microbial colonies one can observe that strains S. rimosus R6-500 and S. rimosus MV9R-2 behaved similarly. Antimicrobial activity was not expressed in 50–56 % of cases. The strain S. rimosus MV9R-l expressed its activity even in 81 % of cases and showed to be more efficient than both S. rimosus R6-500 and S. rimosus MV9R-2. In contrast to the colony cultivation on solid media, in submerse cultures the strain MV9R-l showed to be inferior with respect to other two strains mentioned, which showed their similarity also when cultivated as submerse cultures. Correlation between values of potency index and corresponding antimicrobial activities in corresponding submerse cultures was not found to be significant. The main purpose of performed experiments was to test new strains and to detect their possible biological activity. Accordingly, the strain R6-ZGLI was tested, and its antibiotic activity compared with strains R6-500 and MV25W, the later being used as negative control. In 75 % of cases this strain showed biological activity, in some cases even higher than R6-500. It was important to test divergence of different isolates of the same strain to verify whether there is any variation in their properties. Three types of experiments were performed: a) only one isolate was cultivated on 16 different media, b) 4 isolates were put on 16 different agarized media (each of them on 16/4 = 4 different media) and c) 16 isolates were put on 16 different media, i.e. every isolate was cultivated applying only one of 16 different media. Potency indexes were statistically analysed and excellent correlation was established. So it can be concluded that there is no divergence between randomly chosen isolates of strain MV9R-I: i.e. investigated microbial population showed to be of highly homogenous properties.

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screening of strains, antibiotics, method evaluation