Diluting Four Brands of Plain Yogurt

June 12th, 2018

Since we found that there were enough bacteria in each yogurt, we decided to dilute all four brands of plain yogurt. 

Procedure:
1. Obtain sterile test tubes, petri dishes with LB media, liquid LB media, a micropipette, and spreader, and label the test tubes and petri dishes. 
2. Add 4.5mL of liquid LB media to each test tube.
3. Extract 500 μL from Dannon plain yogurt to test tube 1 (Labeled as 10x) and shake it.
4. Extract 500 μL from test tube 1 (10x) to test tube 2 (100x) and shake it.
5. Repeat step (3)-(4) for other three brands of plain yogurt.
- Stonyfield: up to 1000x
- Siggi's: up to 10000x
- Chobani: up to 10000x
6. Extract 100 μL of Dannon yogurt with dilution factor of 10x. Place it in the center of the respective plate. Repeat for other two plates.
7. Repeat step (6) for 100x.
- Stonyfield: 100x and 1000x
- Siggi's: 1000x and 10000x
- Chobani: 1000x and 10000x
8. Using the L shape spreader, spread the solution on the plate while rotating it in a circular motion.
9. Incubate the plates at 37.0 degrees Celsius. Observe the bacterial growth after the plates remain in the incubator for 48 hours.

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-After Incubation-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=

June 14th, 2018

Results:
I could only count the Stonyfield plain yogurt with a dilution factor of 100 because other ones had too many bacterial colonies to count. I'll have to increase the dilution factors for other brands and see which factor works the best.

Stonyfield 10²x:
a-18
b-24
c-28
Avg.: 23.3
CFUs = [23.3 x 10²] / 0.1mL = 2.33 x 104