Determination of the microbicidal effect of laundry detergents

Changes in laundering habits and the efficacy claims made for some recently launched "antibacterial" detergents necessitate a deeper investigation into the testing of the antimicrobial efficacy of laundry detergents and washing processes. We checked the efficacy of some typical detergents under suspension test conditions following EN1276 [4] and compared the results with those obtained in a new test method simulating realistic household washing conditions. In this test method, artificially contaminated microorganism carriers are washed together with sterile ballast fabrics in normal household washing machines under realistic conditions. After the complete washing cycle, the surviving test organisms on the microorganism-carriers are determined and cross-contamination and contamination of the washing liquor are evaluated as well. Since major factors, such as the mechanical action during the washing process and attachment of microorganisms to fabrics, are not covered by the suspension test model, the value of suspension test models should be restricted to screening purposes only. The microbiological efficacy claim for laundry detergents should not be based on the results of the suspension test only. The new test model proposed here is suitable for simulating realistic household washing conditions and uses household-relevant test organisms.