Serial Dilutions/counting viable bacteria in a liquid sample

1. Label sterile test tubes with dilutions. Dilutions are usually 10-fold steps: 1/10, 1/100, 1/1000, 1/10000, etc. Test tubes should already have sterile water (or sterile saline) in them.

Example of Serial Dilution for Lab Report
We tested the number of bacteria in the eighteen hour old S. typhimurium broth culture with a serial dilution. We put nine tenths of a mL of the sterile broth in eight different test tubes with the micropipettor. We then put one tenth of a mL of S. typhimurium broth culture in the first test tube by using the micropipettor and sterile tips. Next we took one tenth from each previous tube and put it into the next tube to finally make a one to the ten to the seventh dilution in the eighth tube. We then plated the last tube by putting the sterile broth and S. typhimuium onto a plate with the hockey stick spreading method.

ALSO acceptable to Serial Dilutions… Ames Strain Serial Dilution Procedure (Basic idea held throughout)

1.) Put 9.9 mL of sterile broth into a test tube
2.) Then add 0.1 mL of Ames Strain Salmonella to that same test tube
3.) Label test tube 1:100
4.) Put 9.9 mL of Sterile broth into a different, new test tube
5.) Then add 0.1 mL of the 1:100 test tube into this second test tube with the 9.9 mL of sterile broth
6.) Label that tube 1:10^4
7.) Put 9.9 mL of sterile broth into a third test tube, add 0.1 mL from the 1:10^4 test tube and label it 1:10^6
8.) Put 4.5 mL of sterile broth into a fourth, small test tube and add 0.5 mL of 1:10^6 test tube and label this new test tube 1:10^7
9.) Get two (2) agar plates, place 0.1 mL from both the 1:10^6 and the 1:10^7 tubes and then spread plate them

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