Materials
3 brands of hand sanitizer (alcohol-based 70%, alcohol-based 60%, alcohol-free)
Agar plates (5 per condition)
Sterile swabs
Incubator set to 37°C
Marking tape
Gloves
Procedure
1. Have a volunteer touch a shared surface (doorknob) with all five fingers.
2. Swab the volunteer's dominant hand and streak onto an agar plate (control).
3. Apply hand sanitizer per label instructions to the same hand.
4. Wait 30 seconds, then swab and streak onto a fresh agar plate.
5. Repeat for each sanitizer brand.
6. Incubate all plates at 37°C for 48 hours.
7. Count colony-forming units (CFUs) on each plate.
Observations
Control plates averaged 142 CFUs. 70% alcohol sanitizer reduced to an average of 3 CFUs (98% reduction). 60% alcohol sanitizer reduced to an average of 12 CFUs (92% reduction). Alcohol-free sanitizer reduced to an average of 68 CFUs (52% reduction). One alcohol-free plate showed mold growth at 48 hours, excluded from averages.
Notes
Results align with CDC guidance that alcohol-based sanitizers with ≥60% concentration are effective. The dramatic drop-off in the alcohol-free formulation is worth noting. Students should understand this does not replace handwashing with soap and water.