How Effective Is Your Favorite Sanitizer?

There are certainly more hand sanitizer options available today than ever before! Different brands, different scents, sprays, gels, and cloths, Oh my! Are all sanitizers created equal? Here is a simple activity that you can do at home to investigate and compare the effectiveness of hand sanitizers. You can compare different brands, alcohol vs nonalcoholic versions, different alcohol % or different delivery methods. You’ll also practice some basic microbiology techniques, like preparing or "pouring" Agar plates and a simple swabbing technique. And I’ve saved the best for last – this is a great activity to do with family and friends since at least 4 pairs of hands are going to be needed!

Materials Needed:

Pack of sterile petri dishes CH0374APK25

Prepared Nutrient Agar IS5350

Cotton swabs/Q-tips

Various types of hand sanitizer

You will need 1 set of unwashed hands for each type of sanitizer plus 1 set of unwashed hands for a positive “no sanitizer” control

Preparation:

1. Melt Nutrient Agar – loosen cap slightly and place prepared nutrient agar bottle in microwave or boiling water. Heat until the Agar is thoroughly melted, swirling contents often.

2. Fill each petri dish (about 1/3 full) with the melted Nutrient Agar. Place covers on each dish after pouring.

3. Allow Agar to cool and completely solidify (2-4 hours, overnight if possible)

4. Label prepared petri dishes with name of each sanitizer as well as (1) negative control, (1) “No Sanitizer” positive control

Inoculating Prepared Petri Dishes:

1. Inoculate (1) negative control plate – Take a clean Q-tip, touch it near the top of the solidified Agar plate, and drag down the plate making a zig-zag (Note: this Q-tip is not touching any sanitizer or hands). Replace the cover.

2. Inoculate (1) positive control “No Sanitizer” plate - Take a clean Q-tip, swab the palms of 2 hands that have not been washed or sanitized (rub the Q-tip against the skin), touch the Q-tip near the top of the solidified Agar plate, and drag it down the plate in a zig-zag pattern. Replace the cover.

3. Sanitize each pair of hands with a different sanitizer. Allow sanitizer to dry.

4. Inoculate each sanitizer labeled plate - Take a clean Q-tip, swab the palms of 2 hand(s) that has not been sanitized with one of the sanitizer brands (rub the Q-tip against the skin), touch the Q-tip near the top of the solidified Agar plate, and drag down the plate in a zig-zag pattern. Replace the cover.

Incubate and Observe:

1. Allow the covered, inoculated petri dishes to incubate for 48-72 hours.

2. Count and record the number of bacterial colonies on all dishes. Compare the number of colonies in the positive control “no sanitizer” dish and various experimental dishes to determine the effectiveness of each hand sanitizer.

• Is there significantly less growth in the petri dishes swabbed with sanitized hands compared to the positive control?

• Did any of the sanitizer plates show more or less growth than others?

What do you think?

• Is there any growth in the negative control petri dish? What may have caused this?

• What factors aside from the sanitizer brand may have caused different amounts of growth on the Agar?

Want to explore more?

• Repeat this activity comparing the effectiveness of hand sanitizers to that of soap

• Compare different hand washing techniques or lengths of time

• Compare using different amounts of hand sanitizer