A theoretical approach of disinfectant testing.

The purpose of this study is to compare six methods of disinfectant testing, currently applied in Europe. The testing techniques are analysed into the separate elements, which can influence the activity of the disinfectant. The differences observed in these components allow to explain why in each method other parameters are evaluated and consequently, why the interpretation of the results varies from method to method. The six tests examined are (1) the suspension test of the DGHM, (2) the suspension test of the Committee on Phytopharmacy, (3) the A.O.A.C. use-dilution method, (4) the KELSEY SYKES test, (5) the surface-disinfection test of the DGHM and (6) a modified version of this latter. First of all the final concentrations of the disinfectant in the medication mixture are calculated. On the KELSEY SYKES test differs from the others, in using a much lower final dilution, up to 50% in the 3 rd stage. It is also obvious that the longer the exposure time is, the greater the killing effect on the bacteria in the medication mixture will be. To determine the germicidal activity a method needs to pass the test, the germicidal effect has been assessed starting from the inoculum applied in the medication mixture and, in case of tests that consider the absence of growth in the subcultures as end-point, the minimum extinction required. The lowest number of bacteria is applied in the inoculum of the A.O.A.C. use-dilution method (ca. 10(6)) and the highest in the modified practical surface disinfection test (ca. 10(10)). So the required germicidal effect varies from 5 (in case of the Committee on Phytopharmacy's test and the modified practical test) to more than 8 (in case of the A.O.A.C. use-dilution method). Further on, the protein content of the bacterial suspension which is added to the medication mixture, is experimentically verified. Considerable differences are observed here. In some tests the presence of organic matter is negligible (the A.O.A.C. use-dilution method, the KELSEY SYKES test under clean conditions), whereas in others (the KELSEY SYKES test under dirty conditions and the practical surface disinfection tests) the protein added equals that of serum 10-30%. Finally it is mentioned that the dilutions in the KELSEY SYKES test are made with artificial hard water. From a comparison of the factors described above it clearly appears that in the distinct tests different parameters are used and that the results of one test cannot be applied to another.