Assignment: LAB REPORT-Effect of Disinfectants and Antiseptics on Bacteria
Instructions: Read the Introduction and answer the Pre-Lab Questions. Then read the Experiment Methods and Materials, analyze the Results, and answer the Post-Lab Questions.
Experiment Methods & Materials:
Samples from human skin were obtained with cotton-tipped wooden sticks dipped in either distilled water (1-control), 70% ethyl alcohol (2), or skin soap (3), and applied to sections 1, 2 and 3 of a plate containing general nutrient agar.
Samples from a computer keyboard were obtained with cotton-tipped wooden sticks dipped in either distilled water (4-control), 70% ethyl alcohol (5), or sodium hypochlorite (6-bleach), and applied to sections 4, 5 and 6 of the plate.
The plate (Figure 2) was incubated at 37 degrees Centigrade for 72 hours, and then the number of bacterial colonies, and percent coverage, in each section were noted (see Results table below).
Results
|
Plate Section
|
Number of Colonies
|
Percent Coverage of Section
|
|
1 Skin control
|
70
|
75
|
|
2 Skin alcohol
|
5
|
10
|
|
3 Skin soap
|
10
|
20
|
|
4. Surface control
|
80
|
95
|
|
5. Surface alcohol
|
20
|
30
|
|
6. Surface bleach
|
5
|
10
|
Task
A. Which plate section/s had the highest number of colonies, and percent coverage by bacteria?
B. Which section of the plate had the least bacterial growth?
C. List factors that may be responsible for these results.
D. List sources of error in this experiment that may have affected the results. Describe how you would setup the experiment differently.
E. Which antiseptic used was most effective at limiting bacterial growth? Describe the effect this chemical has on bacterial cell structures.
F. Which disinfectant was most effective at limiting bacterial growth? Describe the effect this chemical has on bacterial cell structures.
G. When you have blood drawn at a doctor's office, the skin is wiped with an alcohol pad before inserting the needle. Why is this practice important?