Science Buddies: "Ask an Expert"

In the "Learn to disinfect water" science fair project it says that the bacteria in tryptic soy plates should grow, what does this indicate? For example, does it show that the water is disinfected. I need help ASAP!

Thank You

Hi There!

Tryptic soy agar is what microbiologists use to grow bacteria (I'm actually a microbiologist and use this myself almost everyday!) If bacteria grow on your plates then that indicates there is still bacteria present in your water samples. When you see growth after the 24 hour, 48 hour, 72 hour incubation count the colonies and record them. The higher number of colonies indicate the more bacteria that is in your sample.

A few questions. Are you doing the project as outlined? Do you have various water samples? Some things you can consider if you are still seeing bacteria after the recommended treatments and treatment times is to try varying the time you do your treatment. For example, in the boiling water it says to boil for 5 minutes, you could try additional times. The time it takes to get rid of the bacteria in the sample or lower the number of bacteria in the sample can give a lot of information as to how long it takes to disinfect various water samples.

Also, keep in mind that even though bacteria is everywhere in the environment, be cautious of the bacteria growing on the plates. If you haven't already make sure you check out Microorganisms safety on the Science Buddies website.https://www.sciencebuddies.org/science- ... fety.shtml

Good luck with your project and let us know if you have additional questions.

Nikki