Hamburger Experiment
...meat would already have a small enough number of bacteria to count. Methods A. We first had to obtain all of our supplies. We collected eight empty Petri plates, a couple 1mL sterile pipets, and a marketing pencil. B. While Tiffany weighed out 4.0g of hamburger meat using disposable gloves and Michael measured 156ml of sterile water into a sterile graduated cylinder, I labeled the eight Petri plates. On the backs of the Petri plates I labeled them: 1.0ml A1, 0.1ml A1, 1.0ml A2, 0.1ml A2, 1.0ml B1, 0.1ml B1, 1.0ml B2, 0.1ml B2. Since we were to prepare duplicates of the samples we agreed to label them A1, A2, B1, B2. The reason I labeled the backs of the Petri dishes instead of the lids is because there was a good chance we could have mixed up the lids and contaminated our samples with a more abundant amount of bacteria. C. We then blended the 4.og of hamburger meat with 156ml of sterilized water together for exactly two minutes. D. By using a sterile 1ml pipet, we carefully removed 0.2ml of hamburger dilution by adding 0.1ml to tube B. We mixed the tubes by shaking them vigerously. We then repeated this step again. E. Michael then measured out 0.1ml from tube A and placed it in the correct perti plate (0.1ml A1), while Tiffany sterilized the top of the flask to eliminate any bacteria while pouring the melted agar onto the petri dish with the 0.1ml. I then used the figure eight method in order to mix the agar and the bacteria together. Being careful not to splash the lid, I mixed it ten times in the method explained above. We repeated this procedure for 1.0ml from tube A and also for petri dishes 0.1ml A2 and 1.0ml A2. F. We then repeated step E again, using a new sterile pipette for tube B. We placed the bacteria and the agar into petri dishes: 0.1ml B1, 1.0ml B1, 0.1ml B2, 1.0ml B2, and used the mixing method explained in the step above. G. After mixing the Petri dishes we let them set with no disturbance to allow solidification of the bacteria and agar. H. We then stacked all eight of our petri dishes on top of each other to store so they could solidify. Once they have solidified, they could be put in incubator until Wednesday. I. When we came to lab on Wednesday (two days later) the bacteria would have already formed into colonies in and on top of the agar. By using the colony counter and the “clickly thingie,” we counted all the colonies that we could see on the plate. If we counted colonies over 300 then we stopped and pronounced them TNTC (too numerous to count). J. Each step of this procedure was performed in this way to account for accuracy for measuring everything and using sterile supplies so it would disturb the results. This process is a complex medium because it is a mixture of things and we didn’t know how many bacteria colonies we would encounter. We used this general purpose method because it’s to easy and nutrient rich. Results The results are shown on the next page in the form of a graph. In order to calculate the time elapsed I counted the time it was taken out of the refrigerator to the time of the morning and afternoon labs. Sample time: Sun. 3:30pm Sun. 9:30pm Mon. 6:30am Mon. 9:30am Mon. 3:30pm Morning: 18 hours 12 hours 3 hours 0 hours ...