A water sample was analyzed to determine the concentration of bacteria in it. It

Question

A water sample was analyzed to determine the concentration of bacteria in it. It was diluted as follows: 1ml of sample placed in 9ml of sterile water (tube A) from this solution, from that another 1ml was placed in 9ml of sterile water (tube B) and from that 1ml was placed in another 9ml of sterile water (tube C). Spread plates were then made by taking 1.0ml and 0.1ml from the last two tubes. The places were incubated and the results are tube C having 260 CFU from the 0.1 ml volume transfered. Determine the concentration of bacteria.

Explanation / Answer

Tube C is the tube where 2 times serial dilution has takes place. In 0.1 mL, there is 260 CFU of bacteria In 1mL, there will be 260 x 10 = 2600 CFU of bacteria (Tube C) To find the original concentration of bacteria (tube A), we must times hundred times as there is 2 times dilution. Thus, concentration of bacteria = 2600 x 100 = 260,000 CFU/mL Hope this helps!

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