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Week5_Section_Nhat_key-2

Week5_Section_Nhat_key-2 - Nhat Pham BIMM120...

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Nhat Pham BIMM120 [email protected] 11/02/09 OH: Mon 5pm-7pm Bonner 3126 Handout #5 DISCUSSION 1. After much research you find that in order for water to be considered sanitary it may contain 150 CFU/ml. In order to determine if water from your sink is sanitary enough to be consumed, you decide to perform a plate count with your sample. In order to cut down on the amount of counting, you dilute your sample. Therefore you place 1 ml of your sample in 9 ml of buffer. You then take that sample and place 1 ml in 49 ml buffer. Finally you take 5 ml of the previous solution and place it in 20 ml of buffer. You plate out 0.1 ml of your sample and find 50 colonies the next day, what is the concentration in the original solution? Step1: Draw the diagram of the dilution (above), and fill in the volume transferred , the volume of buffer in each tube, and the dilution occurs at each step (for example, 1:50). Also include the plating volume , and the colony count . Note: Be careful NOT to divide the volume transferred by the volume of buffer, but by the total volume at the end. Step2: calculate the concentration of the final dilution (the last tube) 1

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Nhat Pham BIMM120 [email protected] 11/02/09 OH: Mon 5pm-7pm Bonner 3126 Handout #5 We count 50 cfu (remember that it’s cfu and NOT cell , because a colony could be started by more than 1 cell ) from plating 0.1ml. Therefore, the concentration of the final dilution is: 50 cfu/ 0.1ml = 500 cfu/ml Step3: calculate the accumulative dilution of the sample used for plating (the last tube) by multiplying all step dilutions
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