Question

Suppose you would like to determine the number of bacteria in a culture via an aerobic plate count. Explain (with pictures) how you would set up a dilution series (104, 106, 10) using the fewest number of dilution blanks. Draw and label your tubes and plates with each dilution. Show all volumes including transfers, amounts in tubes, and amounts plated 1. You want to set up a 1:10 dilution series, so that you can plate a 10-1, 102, and a 103 dilution; however, you only have access to two 9 ml dilution blanks. Explain how you could accomplish this task with only two blanks. 2. 3. How much liquid media should you put in your dilution blank if you wanted to serially dilute a 1 ml sample by a factor of 5? 4. You want to dilute a sample by 1/3. For a final volume of 27 ml, how much sample would you add to how much liquid media?

Answer 1

AEROBIC PLATE COUNT is a technique that gives a general estimate of live aerobic bacteria.

1- It consists in plating serial dilutions of a bacterial culture but with the particularity that you have to put on an empty Petri dish the correspondent dilution volumen and the add 20 ml of tempered melted agar (50 Farenheit degrees). Then you wait for solidification of agar and incubated the plates a 37 degrees x 48 hours in an inverted position .

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2-If you have only 2 9ml blank tubes and you have to do 3 serial dilution 10 to 10:

1- put in an empty tube 1 ml cell suspension and 9 ml of dilution blank = 10^-1 dil.

2- plate 1ml in plate1 and 0.1 ml in plate 2 ( in 1ml : 10^-1dil and if you plate 0.1 ml is the same as plating 1 ml of a 10^{-2 dilution)}

3- take 1 ml of 10^-1 and transfer to a new empty tube.add 9 ml of dilution blank Represents the 10^-3 dilution.. Now plate 1 ml of this dilution

See picture

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4- For diluting your sample 3 times in a final volume of 27 ml you have to put 9 ml of cell culture in a fresh tube and add 18 ml of liquid media