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Aim: Isolation of bacteria from soil by serial dilution method Principle: Isolation is often essential for taxonomic and experimental work on micro-organisms. In the microbiological sense, it is the process of separating a single species of microorganism from its natural habitat and growing it by itself, without interference from other organisms, on a sterile substratum, i.e. in medium. The micro-organism can then be distinguished from other species by its individual characters (even if artefacts of laboratory conditions) and propagated to provide experimental material. Methods of isolating micro-organisms from a natural environment, such as soil, litter, air, or water, are numerous. Serial dilution, as the name suggests, is a series of sequential dilutions that are performed to convert a dense solution into a more usable concentration. In simple words, serial dilution is the process of stepwise dilution of a solution with an associated dilution factor. In biology, serial dilution is often associated with reducing the concentration of cells in a culture to simplify the operation. Material Required: Nutrient agar media, petri dish, test tubes, pipette, incubator, autoclave, soil sample. Method: 1. Prepare 100 ml of nutrient agar media and autoclave it along with clean petri dishes. 2. Meanwhile, arrange 7 test tubes in a row and add 9 ml distilled water to each tube. 3. Mark the tubes as 10-1 upto 10-7 4. Add 1 ml of sample in first test tube and mix well by vortexing. 5. Now take 1 ml from first test tube and add it to the second test tube. Repeat the steps till 7th tube is reached. 6. After autoclaving pour 15 - 18 ml of media in each petri dish inside the laminar air flow and allow them to solidify. 7. After the media is solidified, take 1 ml from any of the dilution and add it to the agar plate. 8. Incubate the plates at 37o C from 48 hours 9. Observe the growth. Result: Precautions: Always autoclave media. Never open autoclave media outside laminar air flow. Do not talk while working on laminar cabinet
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