Science project

What Bacteria Can You Eat?


  • 3 Different brands of plain yogurt that contain live cultures (it should have a “Live and Active Culture” seal on the packaging)
  • Light microscope
  • 3 Slides (labeled 1, 2, 3)
  • 3 Slide covers
  • Water
  • 3 Droppers
  • Pencil 
  • Paper


  1. Clean your slides and covers to make sure there’s no dust or other particles on the surface.
  2. Use the dropper to put a small drop of water on each slide. Why should you add a drop of water to your sample before viewing it under a microscope?
  3. Use the dropper again to drop a bit of one kind of yogurt on a slide.
  4. Clean the inside and outside of the dropper with water.
  5. Repeat steps 3 and 4 with the other two kinds of yogurts.
  6. Place the covers on each slide.
  7. Place the slide on the stage of the microscope.
  8. Turn the microscope on and put it on low power.
  9. See if you can identify bacteria on your slide. The bacteria should look like the image below.
  10. Switch the power to 400x and focus your microscope on the bacteria.
  11. Draw what you see under the microscope.
  12. Repeat for slides 2 and 3.
  13. Analyze your results. Do all of the bacteria from each kind of yogurt look the same? If not, what differences do you notice?


There are three different kinds of bacteria you may find in your yogurts brands. You may also find that the brands you bought all have the same kind. You’ll be able to tell by looking at your drawings and comparing them. Lactobacillus Bulgaricus is rod-shaped. Streptococcus Thermophilus is round and shaped like a ball. And finally, Bifidus Regularis is an irregular shape with some longer rods and some spherical shaped segments.


There are three different forms of bacteria that may be present in live culture yogurt. Unless the packaging you bought has the name listed (most don’t), then you could end up with either Lactobacillus Bulgaricus, Streptococcus Thermophilus, or Bifidus Regularis (only in Dannon).

Yogurt cultures break down the sugars in milk called lactose and turn the milk into yogurt. This process is called bacterial fermentation. These good bacteria can help you maintain a healthy digestive system.

Remember when you mixed a drop of water with the yogurt? This type of preparation is called a “wet mount,” and is an important step in the experiment because the water will help you to see the bacteria in your sample more clearly by thinning out the contents of the yogurt. Adding a water drop will allow light to pass more easily through the slide so that you can have a better view!

Digging Deeper

Take this experiment deeper by testing more brands of yogurts and find out which bacteria is most popular in the food industry. You can also try cooking the yogurt, looking at it under a microscope, and comparing the bacteria to what you found in the cold and uncooked yogurt.

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