[The effectiveness of disinfectants from kinetic viewpoints].

In a pilot project, two instrumental disinfectants were tested quantitatively in germ carrier experiments. The disinfectants chosen belonged to the class of aldehydes. The germ carriers comprised wet and dried cotton pieces as well as mineralized soft rubber tubes. The germs tested were Staphylococcus aureus and Pseudomonas aeruginosa. The germs were exposed to 3 (4) different concentrations of the disinfectants. In each case, 4 exposure times were applied, the germs were counted before and after exposure with a Spiralmeter. In order to rationalize the presentation of the 336 experimental data, a kinetic approach was applied. According to the latter, the efficiency of a (aldehyde) disinfectant can be described by a single quantity alpha = RF/C0t, where RF is the reduction factor and C0t the product of the initial concentration of the disinfectant C0 and the exposure time t. Alpha is shown to be independent of C0 and t, as long as the initial concentration has been chosen high enough so that the consumption of the disinfectant during exposure can be neglected. At low concentrations and with wet cotton pieces, the (local) consumption of the disinfectant leads to a drastic deceleration of the killing rates, an effect that has been ascribed to anomalous resistance of the germ populations. However, this effect is not observed in the case of dry germ carriers which disproves this hypothesis. It would be interesting to check whether the above described kinetic approach also can be applied to experiments like the suspension experiments, and whether it is valid also for other chemical groups of disinfectants like the phenols.