Surfactant concentration and type affects the removal of Escherichia coli from pig skin during a simulated hand wash.

The effect of surfactant type and concentration on a bland soap formulation's ability to remove bacteria from hands remains largely unstudied. Several combinations of surfactants and water were combined to test bacterial removal efficacy using a hand-washing device (two pieces of pig skin and a mechanical motor) to simulate a hand wash. A nalidixic acid-resistant, nonpathogenic strain of Escherichia coli (ATCC 11229) was used. Two anionic surfactants, sodium lauryl sulphate and sodium stearoyl lactylate, and two nonionic surfactants, poloxamer 407 and sorbitan monostearate, each in concentrations of 2, 5 and 10% were studied. A slight positive (r(2)=0.17) but significant (P=0.03) correlation was observed between hydrophile-lipophile balance value and mean log reduction. No correlation was observed between pH of the treatment solution and the mean log reduction (r(2)=0.05, P=0.25). A 10% sodium lauryl sulphate mixture showed the highest log reduction (x=1.1 log CFU reduction, SD=0.54), and was the only treatment significantly different from washing with water (P=0.0005). There was a correlation between increasing surfactant concentrations above the critical micelle concentration, and mean microbial reduction (r(2)=0.62, P=0.001). .