[A comparison of the results of 4 national methods for the evaluation of disinfectants in 2 laboratories (author's transl)].

At present the testing and assessment of disinfectants is carried out according to different methods in different countries. The result of this is that certain preparations or concentrations are allowed for use in some countries while they are not in neighbouring countries. A study was carried out jointly at two universities with the object of testing the reproducibility of these methods and standardizing them. Furthermore, an attempt was to be made to arrive at common test methods. In 2 labortories (A,B) we tested and compared the disinfectant activity of three disinfectant standards (phenol, aldehyde, iodophor) against Staphylococcus aureus and Pseudomonas aeruginosa (1) in the suspension test according to the "Richtlinien für die Prüfung chemischer Desinfektionsmittel" (Directions governing the testing of chemical disinfectants) of the DGHM, (2) in the suspension test of the "Dutch Commission for Phytopharmacy," (3) according to the "Use-Dilution Method" of the A.O.A.C. and (4) in the capacity test according to KELSEY and SYKES. Every individual test was repeated ten times. In addition we determined the reproducibility of the results by repeating the tests several times with one and the same culture and with different cultures (on different days). The exact method is described elsewhere (7). The statistical evaluation of the mean values (Tables 1,3,5 and 7) and variances (Tables 2,4,6 and 8) leads to the following findings: The results obtained with the various methods depend on the lab. technique and were specific to the germs and preparations tested. The reproducibility was best in the DGHM suspension test and the capacity test according to KELSEY and SYKES; the mean values of the two laboratories were closest for the Dutch test of the Commission of Phytopharmacy. The greatest mean value differences and scatter were observed with the A.O.A.C. "Use-Dilution Method." The conclusion of this investigation is that for the preliminary testing of disinfectants a method should be recommended which enables the determination of the acturl germ count reduction after varying periods of action and with well-defined organic challenge. In order to assess the disinfectant action, however, such a test - which answers most of our questions and has optimum reproducibility - must be supplemented by main tests which simulate practical conditions as near as possible.