Science Buddies: "Ask an Expert"

My experiment compares the solar disinfection to boiling water to kill bacteria. I am required to grow bacteria on agar plates and count the colonies of bacteria to compare the effectiveness of the two disinfection methods, but when I tried to grow bacteria I had so many bacteria that the entire plate was covered and I could not count any colonies. How do I growth countable bacteria colonies? Would a subculture system using the streak method be effective? I appreciate the help!

You are going to want to dilute your bacterial sample. You can do this using LB (luria broth) media or sterile water. Here is a short procedure I found on google to help you out. http://www.waksmanfoundation.org/labs/r ... lution.htm

Originally my bacteria sample was collected from a creek. Do I need to add distilled water to this sample to dilute the sample?

Hi there,

You could dilute your initial sample, or dilute the experimental samples prior to plating. Either way, sterile water would be appropriate.

Let us know if you have further questions!

Heather

Thank you for all the help.