Pig skin as test substrate for evaluating topical antimicrobial activity.

The feasibility of using pathogen-contaminated pig skin as a model substrate for evaluating skin disinfectants was demonstrated. A test methodology is described that is safe, convenient to use, and adaptable to a variety of hand-washing conditions. The treatment protocol, pathogen contamination conditions, and application technique variables can all be carefully controlled to simulate clinical use conditions. The number of organisms transferred by contact was compared with the total organism count on the pig skin. The quantity of organisms transferred ranged from 10 to 60% of the total organisms, depending on the nature of the contamination conditions. The cumulative results of multiple imprint and stripping measurements were consistent with the concentration of inoculated organisms. Tests with alcohol solutions validated the methodology and clearly showed the dependence of topical antimicrobial activity on both the concentration and structure of the alcohol. Activity increased with increasing alcohol concentration and in the following order: ethanol, isopropanol, and n-propanol. All of the alcohols became less active as the severity of the test conditions was increased, i.e., higher inoculum levels for a longer incubation time before treatment. The contact imprint and stripping methods used to evaluate bacterial growth on the skin clearly showed that the alcohol treatments reduced but did not eliminate the inoculated pathogens. It was found that long lifetimes (several hours) for pathogens on the skin are possible under some environmental conditions. This observation strongly suggests that frequent hand washing is a necessary infection control practice even when opportunities for repeated pathogen contamination have not occurred.