engleski

Optimised screening of antibiotic producing strains

Various methods for screening of antibiotic production by microorganisms were evaluated. Results of test conditions performed according to fractional factorial design were analysed statistically. Streptomyces rimosus derivative strains of known properties were used to test reliability of applied screening methods. Screening of strains under different culture conditions is recommended to increase the chances of antibiotic activity detection. Materials and Methods: S. rimosus R6-500 parental strain, MV9R-1 and MV9R-2 mutants were used as oxytetracycline producers (1), whereas B. cereus was applied to test antibiotic activity. Liquid and solid media of different composition (performed according to different factorial design) were used for culture, applying Petri-dishes of 90 mm diameter and conical flasks of 500 ml (with 50 ml of media) for shaking with a rotary shaker. Oxytetracycline concentration was assayed by spectrophotometry. Overview and discussion of results: Antibiotic production depends on microbial strain properties and culture conditions. To recognise antibiotic activity various culture conditions should be applied to increase the probability of expression of antibiotic production and to enhance synthetic activity (2, 3). The experiments performed with S. rimosus strains showed that antibiotic activity is expressed differently at various culture conditions. Differences were measured by growth of B. cereus as test organism. Its growth was inhibited or in contrast stimulated by products of antibiotic producing strains, depending on conditions applied for their culture. Comparison of results of agar plate cultures with those of corresponding shaken flask cultures showed only a weak correlation between the various methodologies. Each strain showed an individual pattern of optimised antibiotic production under the conditions tested. An array of tests is therefore necessary to enhance chances for antibiotic production by strains with unknown properties. Conclusions: Different culture conditions should be applied to enhance the chances of antibiotic activity detection. To perform different culture conditions the fractional factorial design for 8-16 combinations can be recommended if high numbers of microorganisms have to be screened for antibiotic production. References: (1) Gravius, B. et al., Appl. Environ. Microbiol., 1993, 59, 2220-2228. (2) Normansell, I.D., J Chem. Tech. Biotechnol., 1982, 32, 296-303. (3) Bošnjak M. et al., in: Progress in Biotechnology 6, (Blazej, A., Ottova, A., eds.) pp. 345-358.,Elsevier, Amsterdam, 1990.

Screening of strains; antibiotics; method evaluation

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