If greater detail is desired, a light microscope is required. More information about our experiments can be found as follows.
Methods:.
Effective aseptic techniques are very important to this experiment. We must try to avoid the growth of any bacteria in our cultures not directly being collected in our test sample. Our workbenches were thoroughly wiped down with 70% alcohol, and a Bunsen burner was used to sterilize all equipment used. .
Milk Experiment:.
In 8 petri dishes, we poured agar to act as a medium to culture the bacteria. We then used 2 dishes each for control groups, fresh milk, 24 hour old milk, 4 day old milk, and 8 day old milk. The milk was applied to the agar using a streaking pattern to allow the milk to be less concentrated. The dishes were then sealed shut and put in the incubator. Upon allowing the colonies of bacteria to grow, we made slides to examine the bacteria. The smeared slides were created as follows: add small drop of water on slide, let evaporate, add a small amount of bacteria on slide with toothpick, spread and let evaporate, wave over fire 2 times at 45 degrees, stain as desired, and finally cover slide with a cover slip. We used two methods of staining for the bacteria: crystal violet and gram staining. The crystal violet consisted of staining with the crystal violet solution. We let dry for less than 60 seconds and washed with distilled water then allowed it to dry again. Gram staining included the above with a few additional steps. Prior to covering, alcohol is added and the new stain is added, and then recover the slide. Crystal violet staining detects the presents of bacteria. Gram staining identifies volatile verses nonvolatile bacteria. .
E. coli Experiment:.
In 8 petri dishes, we again poured agar to act as a medium for the bacterial growth. We then smeared all 8 with the bacteria E. Coli. We kept 2 for control groups, then added the antibiotic agent ampicillin to each dish, in different concentrations.