Screening of aquatic microorganisms for antimicrobial metabolite production

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The search for novel therapeutic agents for use in the pharmaceutical industry is driven by the need to combat the increase in infections due to antibiotic resistant pathogens. Natural products have been the major source of numerous therapeutic agents producing more than half of the drugs in use today. In this study, microorganisms from Lake Bosomtwe, River Wiwi and the Duakor Sea shore were isolated and screened for antimicrobial metabolite production. Out of 119 isolates subjected to antimicrobial screening, activity against at least one test organism was detected for 27 isolates. Three of the strains, which had the highest inhibitory activity (zones of inhibition > 19mm), were selected for further characterization of their antimicrobial properties and optimization of physical and cultural factors for maximum antibiotic production carried out. The strains, MAI 1, MAI 2 and MAI 3 were identified as Bacillus species (MAI 1) and Pseudomonas species (MAI 2 and MAI 3). The antimicrobial metabolite produced by MAI 1 was heat stable up to 40°C only whereas MAI 2 and MAI 3 metabolites were thermally stable up to 100°C. The metabolites produced by all the three strains deteriorated gradually with time in solution. Results of the optimization procedures for MAI 1 showed that, an incubation period of 9 days, a pH of 8 and a temperature of 25°C were needed for maximum activity of the antimicrobial metabolite. Also glycerol and asparagine produced the best activity as carbon and nitrogen sources respectively for MAI 1. For MAI 2 and MAI 3, an incubation period of 9 days, a pH of 8 and a temperature of 30°C were needed for maximum antibiotic activity. Starch and asparagines were best utilized as carbon and nitrogen source respectively for MAI 2 and MAI 3. Chloroform extract of MAI 2 showed antimicrobial activities with MIC ranging from 250μg/ml to 4000μg/ml. The Thin layer chromatography bio-autography overlay assay showed seven (7) spots with antimicrobial activity, implying that MAI 2 produced more than one antimicrobial agent.
A Thesis submitted to the Department of Pharmaceutics, Kwame Nkrumah University of Science and Technology in partial fulfilment of the requirements for the award of Master of Philosophy (Pharmaceutical Microbiology)