2.9. Production of crude extracts
The isolates showing potential antibacterial activities from the primary screening was subjected to solid state and submerged state fermentation methods to produce crude extracts.
2.9.1. Solid state fermentation method
In this method, 100 g of the substrate (rice grain) was taken in to 500 mL conical flask and 100 mL of distilled water was added and boiled until the rice grains become softened. The mineral salt solution such as K2HPO4 (2.00 g/L), NaCl (1.00 g/L), MgSO4.7H2O (0.10 g/L) and CaCl2 (0.05 g/L) was added for optimization and autoclaved at 121 °C for 15 minutes. Then it was allowed to cool and inoculated with 2 mL of culture suspension from 7 d old actinomycetes culture grown on starch casein agar. After inoculation, flasks were incubated at 30 °C for two weeks. The completely fermented rice grain was ground with mortar and pestle and allowed to dry for 24 h at room temperature. Later, 100 mL of ethyl acetate and 100 mL of methanol was added to the extract and placed on rotary shaker at 120 r/min for 12 h. Finally, the extract was filtered with Whatman No.1 filter paper and the solvent phase was removed by using rotary vacuum evaporator set at water bath temperature of 60 °C[31].
2.9.2. Submerged state fermentation method
In this method, 1 000 mL of yeast and malt extract broth was prepared in which 100 mL was dispensed into 500 mL Erlenmeyer flask, sterilized and cooled. At room temperature broth was inoculated with 2 mL suspension of isolates and kept for 14 d in a rotary shaker at 200 r/min. Then the culture broth was harvested by centrifugation at 4 000 r/min for 15 min. The supernatant was collected and added equal volumes of ethyl acetate (1:1 v/v) then shaken vigorously for 1 h and repeated twice. The solvent phase was separated from aqueous phase by using a separating funnel and subjected to rotary vacuum evaporator at a water bath temperature of 60 °C at 100 r/min to remove solvent and to get crude extracts[32]
2.9. Production of crude extracts
The isolates showing potential antibacterial activities from the primary screening was subjected to solid state and submerged state fermentation methods to produce crude extracts.
2.9.1. Solid state fermentation method
In this method, 100 g of the substrate (rice grain) was taken in to 500 mL conical flask and 100 mL of distilled water was added and boiled until the rice grains become softened. The mineral salt solution such as K2HPO4 (2.00 g/L), NaCl (1.00 g/L), MgSO4.7H2O (0.10 g/L) and CaCl2 (0.05 g/L) was added for optimization and autoclaved at 121 °C for 15 minutes. Then it was allowed to cool and inoculated with 2 mL of culture suspension from 7 d old actinomycetes culture grown on starch casein agar. After inoculation, flasks were incubated at 30 °C for two weeks. The completely fermented rice grain was ground with mortar and pestle and allowed to dry for 24 h at room temperature. Later, 100 mL of ethyl acetate and 100 mL of methanol was added to the extract and placed on rotary shaker at 120 r/min for 12 h. Finally, the extract was filtered with Whatman No.1 filter paper and the solvent phase was removed by using rotary vacuum evaporator set at water bath temperature of 60 °C[31].
2.9.2. Submerged state fermentation method
In this method, 1 000 mL of yeast and malt extract broth was prepared in which 100 mL was dispensed into 500 mL Erlenmeyer flask, sterilized and cooled. At room temperature broth was inoculated with 2 mL suspension of isolates and kept for 14 d in a rotary shaker at 200 r/min. Then the culture broth was harvested by centrifugation at 4 000 r/min for 15 min. The supernatant was collected and added equal volumes of ethyl acetate (1:1 v/v) then shaken vigorously for 1 h and repeated twice. The solvent phase was separated from aqueous phase by using a separating funnel and subjected to rotary vacuum evaporator at a water bath temperature of 60 °C at 100 r/min to remove solvent and to get crude extracts[32]
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