Grrrr….once again I am running into the same old problem with way too much growth on my plates. After trying and trying again with different amounts of yogurt or milk being added into the peptone water I still cannot get countable CFUs. The first dilution used to plate was a solution of 99ml peptone water with 1ml of yogurt or milk. Then I used that solution to plate with different amounts (100µl, 75µl, 50µl, 25µl, & 10µl) on five different plates for each yogurt or milk. When the first set of plates came back with too much growth I moved onto trying again with a different amount of product. The second dilution used to plate was a solution of 99ml peptone water with ½ of 1ml of yogurt or milk. Again the solution was used in different amounts on five different plates. Still I kept getting too much growth so I went even smaller with the amount of yogurt or milk being added into the dilution. I gave it two more attempts with the amounts of 1/10 of 1ml and 100µl of yogurt or milk; believe it or not there was still too much growth.
So after realizing that this course of action was not working I went to Cori for help. She suggested that I try to dilute my dilution solution instead of changing the amount of yogurt or milk being added into the peptone water. So my new course of action is to start with 99ml peptone water with 1ml of yogurt or milk then I’ll be taking 1ml of that solution and adding it into a new peptone water then adding 1ml of that solution into another new peptone water. I’ll keep repeating this process until I reach the fifth peptone water. After I have the five dilutions I’ll be taking 100µl from each dilution and plating it. I am keeping my fingers crossed that this course of action gets me the results I need to move forward in my project.
The top picture is of the five dilution of peptone water I prepared inside the lab to see if I can get countable CFUs. The bottom picture is from http://www.personal.psu.edu/ to show a more clear understanding of what I am trying to do to get countable CFUs
