Science Buddies: "Ask an Expert"

Hi,
I am doing a Science Fair project on probiotics. I am testing 6 different foods that have been known to be high in probiotics and seeing which one has the highest probiotic count. I plan to do serial dilutions to figure out the number of probiotics. I know probiotic foods have lactobaccillus and that lactobacillus like to grow on MRS nutrients. But I cannot get MRS, so I have nutrient agar. Will lactobacillus grow on the nutrient agar? And should I just count all of the bacteria as probiotics?
Thanks, Willow

Hi Willow,

Yes, Lactobacillus bacteria can grow on nutrient agar.

In my opinion, you can count all of the bacteria in yogurt as probiotics (be careful in your dilutions as you may introduce another source of bacteria in your samples). Also, it is important to keep in mind that there are also Streptococcus thermophilus bacteria in yogurt, besides Lactobacillus bacteria (you will see the difference between them in the agar plates).

Good luck with your project!

Best,
Elise

Thank you so much, that was really helpful.
I am testing GT Daves kombucha, homemade kombucha, Saugeen Country yogurt, Island Farms yogurt, kimchi, pickles and probiotic pills. Should I test how much are in a serving or in mL? Also, how long should I let the bacteria sit for?
Willow

Hi Willow,

I'm glad you came back with more questions.

To make sure the consistency of the experiment, I think it would be better to test in mL (because the serving sizes are different in different products).

For the second question, the bacteria may grow after 2-3 days of incubation, depending on the incubating temperature. My advice is to research (google) the optimal temperature and incubation time of the bacteria. Also, remember to observe the plates at least once a day to make sure bacteria are not overgrown in the plates.

Best wishes,

Elise

Thanks Elise, you saved me again!
My project is pretty much taken care of, but I'll come back if I have any more questions.
Thanks again,
Willow

Glad to hear that. You are welcome!

Elise