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Aseptic Technique.

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Aseptic Technique * Wipe the bench you are working on with disinfectant - this kills all the bacteria that may already be on the bench at the start of the experiment. The bench also needs to be wiped down at the end of the experiment. * Wipe tray that you will put all the equipment on with disinfectant - this is done to kill all the bacteria that may already be on the tray so that the sterilised equipment is not contaminated. * Sterilise all equipment - the equipment used is put in an autoclave which sterilises it so that bacteria on the equipment are killed and the equipment is ready to be used. * Light Bunsen Burner near equipment - this is done to create an up draught of air away from the bench to prevent contamination of cultures. * Wash your hands with antibacterial soap - this will get rid of any bacteria that may already be o your hands. ...read more.


7. Remove the tube containing the agar from the water bath and unscrew the lid, taking care not to touch the top of the bottle. 8. Flame the mouth of the tube to make it more sterile when the agar is poured out. 9. Open the Petri dish as little as possible and pour the agar into it. 10. Allow the agar to cool and solidify. 11. Tape down the lid of the Petri dish with clear tape. 12. Invert the Petri dish so that any moisture forming on the lid during incubation cannot drip down onto the agar. Results: Table showing the amount of bacteria colonies in the water. Water : Control Original 10 10 10 10 Tap 1 0 0 0 0 0 0 Tap 2 0 0 0 0 0 0 Tank 1 0 128 23 0 0 0 Tank 2 0 432 10 0 0 0 Tank 3 0 273 64 5 11 16 Estimations of number of bacteria: Tank 1 - 128 = 1280 23 x10 = 230 Tank ...read more.


This removes most of the bacteria. There may be bacteria present in the first few drops of tap water if the tap hasn't been used for a few days and the end of the tap has time to collect bacteria in it, then these bacteria will come out of the tap when it is turned on and water flows out of it. There were 2 main anomalous results, these were obtained from the tank water 3, and were the final 2 dilutions. The 1st three samples gave bacteria counts of similar amounts, but the other two weren't. This could be due 3 main reasons. 1. The test tubes may not have been mixed between each dilution. 2. The lids may have been left off the Petri dishes for too long allowing bacteria to enter and corrupt the results. 3. Many reasons related to the accuracy of the experiment. If the experiment were to be repeated a lot more care would be taken to prevent contamination. The Petri dishes would also be left for longer to give more bacteria the chance to grow. Estimating Bacterial Counts in Water by Dilute Plating Leanne Haines ...read more.

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