You take a water sample, and place 1 ml of this sample into 99 ml of a sterile buffer in a bottle. After mixing this bottle, you then take 0.5 ml from this first blank, and add it to a test tube that contains 4.5 ml of sterile buffer. From this test tube, you take 3 ml and add it to 3 ml of sterile buffer in a second test tube. Now you take 0.5 ml from this second test tube, and spread it on each of 3 agar plates. After overnight growth the plates contain 76, 78 and 80 colonies, respectively. What was the approximate number of colony forming units in the original water sample?

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     3.1 x 106
      7.8 x 105
      7.8 x 104
      3.1 x 104
      3.1 x 105
asked May 16, 2012 in Microbiology by anonymous

1 Answer

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3.1 x 105
answered May 17, 2012 by Bioshare ~Top Expert~ (34,070 points)

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