BACTERICIDAL ACTION OF A QUATERNARY AMMON IUM DISINFECTANT, DIDECYLDIMETHYL AMMONIUM-CHLORIDE, AGAINST STAPHYLOCOCCUS-AUREUS

The study was conducted using a quaternary ammonium disinfectant, dide cyldimethyl ammonium chloride (DDAC), whose minimum lethal concentrati on (MLC) against Staphylococcus aureus was 32 mug/ml. No remaining via ble cells were detected even after a short 20 s treatment with DDAC at the MLC. Treatment with DDAC caused to form blebs on the cell surface , and K+, 260 nm absorbing materials and phospholipid leaked out from the cells. The experiment using C-14-labeled DDAC showed that the disi nfectant was taken up in a biphasic curve to the cell regardless of th e treatment temperature or time. The radioactivity was distributed sig nificantly in the membrane fraction and the cytoplasm fraction. Tetram ethyl ammonium chloride showed no biocidal activity and had no effect on the activity or uptake of DDAC. From these results, it was deduced that DDAC, at bactericidal levels, is adsorbed physicochemically, by h ydrophobic interaction, onto the cell membrane, where it can react wit h lipid to cause significant damage to the structure and function of t he membrane, leading to death.