BRAINCAKESerial Dilution
A broth culture may contain millions of bacteria per cm3. Plated directly, the colonies would merge into a lawn and could not be counted. Serial dilution reduces the concentration in known steps until the colonies can be counted.
Method (tenfold dilutions)
1. Put 9.0 cm3 of sterile water (or broth) into each of several sterile test tubes.
2. Using a sterile pipette, add 1.0 cm3 of the culture to the first tube and mix. This is a 10−1 (1 in 10) dilution.
3. With a fresh sterile pipette, transfer 1.0 cm3 from this tube to the next and mix, giving 10−2. Repeat to give 10−3, 10−4 and so on.
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