The effect of practical conditions on the efficacy of disinfectants

Abstract

The concentration of disinfectants needed to achieve and maintain good hygiene depends to a great extent on the conditions found in practice. These conditions can be simulated in the laboratory using efficacy tests which can be defined by the use of water of known hardness, the inclusion of clean and/or dirty conditions as well as the effect of the contact time. The spectrum of activity of disinfectants is significantly affected by these practical conditions. In the case of quaternary ammonium compounds this efficacy can vary greatly against different bacterial species depending on the degree of water hardness and the specific chemical structure of the compound under evaluation. Comparative studies examining the influence of a low resp. high protein load on the killing effect of quaternary ammoniums and hypochlorite clearly demonstrate that a high protein load has little effect on the rate of kill of both disinfectants against gram negative bacteria. However studies have shown that a high protein load does significantly reduce the efficacy of both disinfectants against gram positive bacteria. A high protein load has also been found to greatly reduce the killing performance of hypochlorite against yeasts. This effect has not been found with quaternary ammonium compounds which maintain their activity under these conditions. Its significance is not fully understood. The surprising effect on the efficacy of clean and dirty conditions on this chlorine release compound on the killing effect to bacteria and yeasts will be discussed. Studies into the effect of time/temperature relationships on the efficacy of disinfectants indicate that normally the major influence is that associated with the test species. The studies presented in this paper illustrate, that the efficacy of disinfectants is regulated by a complex system of interactions between the test microrganisms, the practical conditions and the specific disinfectant under evaluation.