The Effects of Handwashing

STUDENT HANDOUT:

• The Effects of Handwashing Student Handout

OBJECTIVES:

1. Learn how to culture microorganisms from skin.

2. Learn the effects of hand washing and the proper amount of time individuals should wash their hands.

PRECAUTIONS:

1. Note the general safety precautions in the first chapter of this manual, especially in relation to use of Bunsen burners.  

2. Do not attempt this experiment until you have learned proper aseptic technique.

3. Remember that even non-pathogenic bacteria can cause infections if not properly handled.  

4. Discard all materials in biohazard containers for proper disposal.

5. Autoclave ALL materials as soon as they are no longer needed.

6. Never discard cultures in the trash can. 

MATERIALS (Work In Pairs):

1. 5 Trypticase Soy Agar plates

2. 5 sterile swabs

3. Sink

4. Soap

5. Bunsen burner

6. 37°C incubator

PROCEDURE:

Students will work in pairs.  One student will be the handwasher.  The other student will be the swabber.  

1. Take 5 trypticase soy agar plates and label them 0, 30, 60, 90, 120 seconds.

2. Take a sterile swab and moisten it using sterile water. Roll the swab over a section of the palm of one of your hands.

3. Inoculate the trypticase soy agar plate labeled 0 by rolling the swab over the entire plate.  Remember to use aseptic technique when plating.

4. Wash your hands for 30 seconds under running water.  Do not dry your hands.  

You can watch a video from the Centers for Disease Control (CDC) on how to wash your hands:

5.  Using a new moistened swab, roll the swab over the same section you cultured previously and plate onto the trypticase soy agar plate labeled 30 sec.

6.  Wash your hands for another 30 seconds under running water and repeat the procedure.

7.  Continue swabbing and washing such that you have swab samples for washing your hands for 120 seconds (2 minutes). 

8.  Incubate the plates for 12- 16 hours at 37°C.

OBSERVATIONS/CONCLUSIONS:

1. After incubation, count the number of colonies on each plate.  Record your data in Table 1 of the Laboratory Report Form.  Report your colony counts on the board in your classroom/lab.

2. Calculate the averages for each washing time for your entire class.  Report your average colony counts on the board in your classroom/lab.

3. Over time, what happened to the amount of colonies on the hand as handwashing continued?

4. Is there any time (either your data or the class average) where the number of bacteria increased between samplings?

QUESTIONS:

1. Can you explain the data your class collected?  Why do you see the trend that you do?  (Hint:  think about the fact that our skin contains outer layers (epidermis) and lower layers (dermis)).

2. How does soap work to remove microorganisms from the skin?

3. Can you think of any skin diseases that are due to the presence of microorganisms?

KEY TERMS:

• agar

• aseptic technique

• bacteria (bacterium)

• colony

• dermis

• epidermis

• microbe or microorganism

• soap

• Trypticase Soy Agar

SUGGESTED READINGS:

Ferris Jabr, Ferris.  March 13, 2020  The New York Times:  Why Soap Works.