Many yogurt products contain probiotics (a mixture of benificial bacteria) are advertising they have billions of live bacteria in the bottle. Intrigued by the question that how many live bacteria are still there by the time that I got my yogurt from the grocery store, I start to quantify the number of bacteria in my favoriate yogurt brand Activia Probiotic Dailies. I like it because it is liquid and I can just dump it into my gut without the need of a spoon, which is required for typical greek style yogurt.

CFU assay

From one bottle of vanilla flavored ACTIVIA, I did 1:10000 dilution and spread 80 microliters onto LB and BHI agar plates. After an overnight incubation at 37C, around 2,000 of colonies grow on the plate. So, lets do a simple calculation: each ml of the drink will have 2,000 x 10000 x 1000ul/80ul = 2.5 x 10^8 CFU/ml. So a bottle of ACTIVIA (91.6ml) have 2.29 x 10^10 bacteria that can grow on LB/BHI plates. So, at least in the sample I was selecting have ~23 billions bacteria. Bear in mind that some of bacteria may not grow in the LB/BHI media that I am providing.

Cells under microscope

There are multiple bacteria here. A lot of them are diplobacilli (tow rods) or diplococci (two cocci) or cocci in chains/clusters.