Prepping for Yogurt Cultures

Thursday May 31, 2018

Today we practiced diluting samples of an example culture so that we will be able to count the

number of bacteria in the same.

Objective: Using a sample of an example culture, we diluted the culture by six different dilution factors so that we can count the number

of bacterial colonies in the sample after they incubate.

Micropipette Used for Extraction

Media Labeled by Dilution Factors

            

Method:

1. Label the test tubes by their dilution factors (10, 102, 103, 104, 105, 106)

2. Using the micropipette, add 1800 μL of LB media to each of the six test tubes .

3. Add 200 μL of the culture to test tube 1 (dilution factor 10). Shake the solution.

4. From test tube 1 (dilution factor of 10), extract 200 μL and carefully add it to the next test tube (test tube 2/ dilution factor of 102). Shake test tube 2.

5. From test tube 2 (dilution factor of 102), extract 200 μL and carefully add it to the next test tube (test tube 3/ dilution factor of 103). Shake test tube 3.

6. From test tube 3 (dilution factor of 103), extract 200 μL and carefully add it to the next test tube (test tube 4/ dilution factor of 104). Shake test tube 4.

7. From test tube 4 (dilution factor of 104), extract 200 μL and carefully add it to the next test tube (test tube 5/ dilution factor of 105). Shake test tube 5.

8. From test tube 5 (dilution factor of 105), extract 200 μL and carefully add it to the next test tube (test tube 6/ dilution factor of 106). Shake test tube 6.

9. Obtain 6 petri dishes. Label them based on the dilution factors and arrange them in descending order.

10. Starting at dilution factor 6, extract 100 μL from the respective test tube (test tube 6/ dilution factor 106). Open the petri dish and place the extraction in the middle of the dish. Put the top back on the dish.

11. Extract 100 μL from test tube 5 (dilution factor 105). Open the petri dish and place the extraction in the middle of it. Put the top back on the dish.

12. Extract 100 μL from test tube 4 (dilution factor 104). Open the petri dish and place the extraction in the middle of it. Put the top back on the dish.

13. Extract 100 μL from test tube 3 (dilution factor 103). Open the petri dish and place the extraction in the middle of it. Put the top back on the dish.

14. Extract 100 μL from test tube 2 (dilution factor 102). Open the petri dish and place the extraction in the middle of it. Put the top back on the dish.

15. Extract 100 μL from test tube 1 (dilution factor 10). Open the petri dish and place the extraction in the middle of it. Put the top back on the dish.

16. Using the sterile L-shaped spreader, spread the extraction evenly in the dish. To evenly distribute it, use one hand to rotate the dish in a circular motion while using the other hand to spread out the solution using the tool. Make sure there is no more liquid left on the surface of the dish.

17. Stack the petri dishes and place them into the 37.0 degree Celsius incubator so that the bacteria can grow.

18. Put the top back on the dish.