Natasha Marvi

Hannah Small

PurellŐs effectiveness is disrupted by water

Is the effectiveness of Purell depleted by the addition of water? Purell, an alcohol based sanitizer, is commonly used as a substitution for soap and water. The sanitizer is a hypertonic solution that kills bacteria by dehydration. In a laboratory experiment, we observed plasmolysis in the cells of an Elodea leaf when placed in salt water, a hypertonic solution. We observed the reversal of the process by the addition of water. We drew a parallel between the experiments and assumed that the addition of water would create the same effect for cells introduced to a hypertonic ethanol solution. We hypothesized that the addition of water would rehydrate the bacteria, decreasing the effectiveness of the sanitizer.

To test this hypothesis we attained 10 agar Petri dishes and divided them into four sections. One of the sections was the control, where the subject placed a thumbprint before using any substance. In the second section the same subject placed an index finger print after the use of Purell. The subject rinsed their hands with water and allowed it to air dry. Then a finger print of their middle finger was placed in one of the remaining sections and their ring finger in the other. Since the first section had no form of antibacterial exposure we expected it to contain the greatest amount of bacteria. The second sample was expected to grow the fewest number of bacteria due to the use of Purell. The last two sections were expected to grow a quantity of bacteria relatively close to the first sample, since the water would reverse the effects of Purell.

There was a significant difference in the average bacterial counts between Purell and Purell with water (p=0.0012). The average number of colonies for Purell was 10.48%, while the Purell with water was 69.63% after correcting for the number of bacterial colonies on the original fingerprint.

We fail to reject out hypothesis because there is a significant increase in the presence of bacteria after the sanitized hand is introduced to water. A potential problem with out experimental procedure could be contamination of the sanitation site by tap water. There were also uneven amounts of Purell used by each sample student, therefore affecting the amount of bacteria that can be dehydrated. To fix these inconsistencies we could have used deionized water. Then to attain a constant use of Purell, the subject could have been assigned a measured amount of Purell to be applied to a designated finger.