Fill target containers with diluent: Once you have determined the diluent, fill the tubes or wells that you will use to set up the serial dilution with the desired amount of diluent (Figure 3, Step 1).Many compounds can be mixed with distilled water, but for bacteria or cells, for example, a fresh culture medium should be used. ![]() Determine the diluent: First of all, you need to choose the proper diluent for the substance that you want to dilute.While the possible applications of serial dilutions are very varied, the method itself always follows the exact same steps: This means that you will get to a manageable concentration of 100 bacterial cells per milliliter in 7 dilution steps, using only 63 milliliters of diluent. Diluting one milliliter of this dilution in nine milliliters of diluent will allow you to obtain a bacterial concentration of ten million cells per milliliter (Figure 1, Step 2), and so on. After diluting one milliliter of the sample with one billion bacterial cells per milliliter in nine milliliters of diluent, you will get a concentration of one hundred million bacterial cells per milliliter (Figure 1, Step 1). 2 An alternative and more practicable approach is to perform a serial dilution. However, in order to get to such a low concentration from a sample with one billion bacteria per milliliter in one step, you would need to dilute one milliliter of the sample in 10,000 liters of diluent. This is why you have to dilute a small portion of your bacterial culture until you get a more easily countable concentration of 30 to 300 bacterial cells per milliliter. As every milliliter of media could contain a billion bacteria, it is impossible to count them in such high concentrations. Imagine that you have a bacterial culture tube, and want to know how many bacterial cells are growing in it. Serial dilutions are routinely used in microbiology to estimate the number of microorganisms in a sample with an unknown concentration.
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