Purpose/Objectives:
Many antibacterial hand sanitizers advertise to kill 99.99% of the most common germs that may cause illness. You will evaluate this claim by comparing the effectiveness of both hand sanitizer and regular soap and water at reducing bacterial growth on hands.
Methods/Procedure:
DAY 1:
1. Within your group, choose 2 students for the control treatment, 2 students for the soap treatment, and 2 students for the sanitizer treatment.
2. Label the bottom of your Petri dish with your group number and treatment (“control”, “soap”, or “sanitizer”). Do NOT open the Petri dish!
3. Label one half of the Petri dish as “before” and one half as “after.”
4. Work with your treatment partner (control, soap, or sanitizer).
5. Remove a sterile swab from the package, touching only the handle.
6. Moisten the swab by dipping it into a vial of sterile water.
7. Collect a sample from your partner by rubbing the moistened swab in the shape of a “Z” over the palm of his or her dominant hand (See Figure 1).
Figure 1
8. Open the Petri dish by holding the lid around the outside rim with your fingertips and lifting it slightly to the side (See Figure 2).
Figure 2
9. Gently drag the swab in a zigzag pattern over the “before” half of his or her Petri dish to spread the sample for growth (See Figure 3).
Figure 3
10. Repeat steps 5-9 for the other partner.
11. Apply the appropriate treatment:
a. Control: Rub your hands together for 30 secondswithout soap or sanitizer.
b. Soap: Wash your hands with a quarter-sized amount of soap, rubbing for 30 seconds.
c. Sanitizer: Apply a quarter-sized amount of sanitizer to your hands and rub for 30 seconds.
12. Repeat steps 5-10 using the SAME hand, but apply the sample to the “after” half of the Petri dish.
13. Incubate the plates for 48-72 hours at 37C.
DAY 2:
Always wear gloves when handling bacterial cultures!
1. Collect your Petri dish and record qualitative observations under “Data/Observations” on your lab write-up.
2. Under “Results,” make a drawing of the bacterial growth on your Petri dish.
3. For each half of your Petri dish (“before” & “after”), count the number of individual bacterial colonies. If there are too many colonies to count, record the growth as “lawn.”
4. Record these numbers in TABLE 1.
5. Collect data from your group members to complete TABLE 1.
6. Dispose of your Petri dish and gloves in the biohazardous waste provided.
Analysis:
To determine the % reduction in bacterial growth:
1. Subtract the colony count “after” from the colony count “before.”
2. Divide this “Difference” by the “before” number.
3. Multiply by 100 to get a % value.
1 / Minority Science Programs – School of Biological Sciences – University of California, Irvine