Quantification of bacterial load: Serial dilutions

Dr. Spencer: To quantify bacterial load, we need to inoculate our samples on agar plates and count the individual colonies. Bacterial samples typically contain a very high number of cells. If these cells were to be plated directly, the resulting colonies would be too numerous to count accurately. 

You: We can perform serial dilutions so that we can reduce the concentration of bacteria to a level where individual colonies can be grown and easily counted.

Dr. Spencer: That’s right! What dilutions do you think are more appropriate?

Sam: For the more turbid samples (i.e. B and D) 4x100 dilution should suffice and we can use 4x10 dilution for the less turbid samples (A, C and E).

You proceed to make the dilutions, as shown below and in the video.

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