Introduction

Yogurt is a popular snack that is created by bacteria. Bacteria are very successful, microscopic life forms. They are so small that they cannot be seen with the naked eye, yet they make up more of the total biomass than any lifeforms. There is a great range of types of bacteria, and many can be helpful for humans, and some can be very dangerous. Some examples of benficial bacteria are probiotics, which are found inside the human body and can help digestion and even lower cholesterol. We use many kinds of bacteria to create food and drink because bacteria go through a process called bacterial metabolism or fermentation. During bacterial metabolism, bacteria break down sugars into other chemicals through enzymes. From this process, we make wine, beer, and yogurt. However, harmful bacteria such as typhus, tuberculosis and the bubonic plague have killed millions of people throughout history. All bacteria share some common traits, for example, all bacteria are prokaryotes. The three major shapes that bacteria take are coccus (spherical), bacillus (rod-shaped), and spirillum (spiral).

In this lab, we will make yogurt, practice microbial technique, and test koch's postulates.

Procedure: 1) Label four tubes of milk as
Tube 1 - negative control (only milk)
Tube 2 - positive control (milk and yogurt)
Tube 3 - Yogurt and amp
Tube 4 - E. coli

2)Add 10 ul of ampicillin to tube "Yogurt and amp"

3) Dip fresh inoculation loop into the yogurt and swirl loop into "positive control"

4)Dip same loop into the yogurt again and swirl into "Yogurt and amp". Then put loop into bleach beaker

5) Using a fresh inoculation loop, transfer E. coli to the tube "E. coli"

6)Place tubes in a an incubator for 24-48 hours

Tubes one and two act as control tubes, while tubes three and four are the variables. In this experiment, I believe that tube one will not change, tube two will turn into yogurt, tube three will not change (due to the bacteria killing ampicillin), and tube four will not change

Observation: Tubes "negative control", "yogurt and amp", and "E. coli" all stayed as milk. Tube "positive control" had yogurt qualities (ie: smell and to some extent texture) but it was not fully formed as yogurt.

Discussion: My hypotheses were correct. The only tube that formed yogurt was "positive control", because it had yogurt bacteria and a hospitable place to cultivate. "Yogurt with amp" did not turn into yogurt because the ampicillin killed all the bacteria in the tube. Neither tube "negative control" or "E. coli" had any yogurt bacteria, so they did not turn into yogurt. One possible source of error in this lab is cross contamination. If some ampicillin got into another tube, or if yogurt bacteria got into a tube where it wasn't supposed to be, the results would have been skewed. Another source of error is not putting enough yogurt bacteria. Our "positive control" didn't fully form yogurt possibly because we did not have enough yogurt bacteria to begin with.