Lab 03: Bacteriology
Results: During this experiment we conducted gram stains on four different bacteria, and also tested which antiseptics were most effective on each bacteria. The bacteria that were tested are Bacillus megaterium, Escherichia coli, Micrococcus leutus, and Serratia marcescens.
The gram stain results showed that the Bacillus M. bacterium is gram positive, and has the shape of a rod. When observed under the microscope, it was seen that it was in fact purple meaning it had a thick peptidoglycan cell wall, which is what retained the crystal violet dye giving it the purple color. The same was observed in the Micrococcus L. which took a spherical shape known as cocci.
When E. Coli is a rod shaped bacteria, and as it was observed under the microscope, it was seen that it was gram negative because it had a red color. The red color observed was due to the fact that E. Coli has a thin layer of peptidoglycan in its cell wall, in which it did not retain the crystal violet dye, instead it took the color of the safranin. These same results are seen in the Serratia M. bacterium, which is also rod shaped and gram negative. The results from the inhibiting bacteria growth is shown in the image below. The table below shows the effect each antibiotic and disinfectant had on each bacteria. This is shown by measuring the diameter of the ring formed around the antiseptic, in which indicates how the antiseptic/disinfectant killed the bacteria that remained in that area.
Antiseptics/Disinfectants tested
Bacterium
#5
#2
#4
Disinfectant
Micrococcus l.
D= 3.21 cm
D= 1.39 cm
D= 1.96 cm
D= 1.56 cm
Serratia m.
D= 1.40cm
D= 1.10 cm
D= 0.51 cm
D= 1.30 cm
E. Coli
D= 2.45 cm
D= 1.60 cm
D= 0.26 cm
D= 0.0 cm
Bacillus m.
D= 1.92 cm
D= 2.34 cm
D= 2.71 cm
D= 2.57 cm
Discussion: According to the results from the experiment, the substance that had the most potent effect on the bacteria was the #5 antiseptic (I failed to write down its actual name, only the number it was labeled). The fifth antiseptic had the greatest impact on each bacterium. As it
