Using an alternative hand contamination technique to compare the activity of antimicrobial and non-antimicrobial soap under varying test conditions

The Dial Corporation, Microbiology Department, 15101 N. Scottsdale Rd., Scottsdale AZ 85254

^* To whom correspondence should be addressed. Email: Janice.Fuls{at}us.henkel.com.

	Abstract

Antimicrobial hand soaps provide a greater bacterial reduction than non-antimicrobial soap. However, the link between greater bacteria reduction and a reduction of disease has not been definitively demonstrated. Confounding factors such as compliance, soap volume and wash time may all influence the outcome of studies. The aim of this work was to examine the effects of wash time and soap volume on the relative activity and the subsequent transfer of bacteria to inanimate objects between antimicrobial and non-antimicrobial soap. Increasing the wash time from 15 to 30 seconds increased reduction against Shigella flexneri from 2.90 to 3.33 log₁₀ (p= 0.086) for the antimicrobial soap while non-antimicrobial soap achieved reductions of 1.72 and 1.67 log₁₀ (p> 0.6). Increasing soap volume increased bacterial reductions for both the antimicrobial and non-antimicrobial soaps. When normalizing the soap volume based on weight ( 3 g), non-antimicrobial soap reduced Serratia marcescens by 1.08 log₁₀ compared to 3.83 log₁₀ by the antimicrobial soap (P<0.001). The transfer of Escherichia coli to plastic balls following a 15 second hand wash with antimicrobial soap resulted in a bacteria recovery of 2.49 log₁₀ compared to a 4.22 log₁₀ (p < 0.001) bacteria recovery on balls handled by hands washed with non-antimicrobial soap. This indicates that non-antimicrobial soap was comparatively less active and the effectiveness of antimicrobial soaps can be improved with longer wash time and greater soap volume. The transfer of bacteria to objects was significantly reduced due to greater reduction in bacteria following the use of antimicrobial soap.