Yogurt Lab: Bacteria Tastes Good!

Bacteria are present everywhere in our environment.  They are the most abundant lifeforms on our planet and are present in or on everything in this world.  Bacteria are prokaryotes which means that they are single celled organisms with no separate nucleus to hold their reproductive DNA.  Although, humans associate bacteria with disease, actually only a small number of bacteria cause disease.  We understandably associate them with disease because the ones that do have caused some of the most devastating diseases known to man (cholera, bubonic plague, typhus).  We will base this lab off of Koch's Postulates, which provide the steps for identifying a disease caused by a bacteria.
We will work with the beneficial bacteria that allows found in milk which allows for the production of yogurt (which is more nutritious than milk because it contains enzymes that help break down lactose as well as preventing the growth of dangerous spoilage bacteria).  In this lab we will practice the microbial technique and test Koch's Postulates by isolating the bacteria that allows yogurt to be created when it is fermented with milk.
For the procedure we made our tubes of the yogurt plus milk, milk, yogurt plus ampicilin, and ecoli by mixing the ingredients from the tubes of the substances (ecoli was in an agar plate). then we took them over to the vortex to mix it even more effectively. After that we labeled the tubes and placed them in the incubator overnight. The next day we removed the tubes and tested the pH of the tubes to check to see whether or not they became yogurt or stayed milk, if they became yogurt the pH would be slightly acidic while if they did not then it would remain around neutral. We found that the milk plus yogurt bacteria turned into yogurt in the incubator but the ecoli tube did not turn into yogurt it became spoiled milk. Interestingly, the yogurt plus ampicilin was somewhat of a mixture of the two, the ampicilin did not kill enough of the bacteria that the yogurt making process completely stopped but it did kill enough so it did not become totally yogurt. I found it interesting that the yogurt plus ampicilin became a mixture of the two because I expected the ampicilin to be able to kill all of the yogurt producing bacteria but it could not. We as a group had one main source of error in that we accidentaly mixed a tube with a bleached stick, so we had to observe the bleached tube to test what would happen as well as make a new tube with the right ingredients. (The bleach killed all the yogurt producing bacteria as we expected). But it was cool to be able to see the benefits of some bacteria and be able to test the effectiveness of ampicilin at killing bacteria!