Optimum Bacterial Suspension for Testing Skin Disinfection.

Abstract

Singer and Arnold 1 and Arnold, Gustafson, Hull, Montgomery and Singer 2 used 1:200 dilutions of broth cultures of bacteria in saline for testing the self-disinfecting power of the skin. We have found that this is not the optimum concentration to be used for this purpose. The 1:200 suspension is too dilute to test this function. We have found that it is necessary to increase the concentration of bacteria in the suspension and to extend the period of the test over 60 minutes instead of 30 minutes. The 1 :200 suspension is so dilute that there can be a considerable variation in the relative self-disinfecting power and still show a 100% destruction of the test bacteria. The accompanying table gives the results of 250 experiments, 50 experiments for each dilution are averaged. The variations for each dilution are on the average of less than 5%. The technic was the same as that used by Arnold, et al. 2

We have found that the 1 :50 dilution is the best for testing the self-disinfecting power of the skin and the time extended over one hour. The reserve self-disinfecting power can be determined if this concentration is used. Palmar and dorsal surfaces of the hand show constant differences, the female's skin varies during certain periods of the menstrual cycle, pathological skin shows considerable variations by this method. These results will be reported in full in the near future.