Science Buddies: "Ask an Expert"

I am doing a project on live cultures in yogurt. "Is that bacteria in my yogurt". I am 6 days into my growth on nutrient agar in an anaerobic chamber. I appear to have no growth. I did four different brands of yogurt and two plates each. (chobani, fage, wegmans, and yoplait kids) All brands said they contain live and active cultures. Am I doing something wrong? I thought I should have growth by now. Do I need to just wait. My project is due in 14 days.

THank you.
Hudson

Hi Hudson,

That's quite strange that there's no growth considering that the brands mention that they have live and active cultures. One possibility is that the bacteria from the yogurt brands are slower growing and hence you may need to wait a little longer than six days. I would suggest putting the plates back in the anaerobic chamber and letting them incubate for a couple more days. Another possibility is that the bacteria concentration may be very dilute in the yogurt and the amount you plated may not have been enough for colonies to show up. You can try to plate more yogurt than they suggested to see if that helps. Another possibility is that air is leaking into your anaerobic chamber and hence the bacteria can't grow. If you have time, I would suggest to try the experiment again, this time making sure that air isn't getting into your chamber and perhaps maybe plating a little more yogurt than suggested. However, I would keep incubating your old plates in the anaerobic chamber and check on it everyday because it could be possible that the bacteria are just growing slower than expected.

Let us know if you have anymore questions.

Connie

Thank you for your reply. I let it go a few more days and small colonies were noted. I do believe if I do this again I would not dilute as much with distilled water. Thank you. Hudson