Bactericidal Action of A Quaternary Ammonium Disinfectant, Didecyldimethyl Ammonium Chloride, against Staphylococcus aureus

The study was conducted using a quaternary ammonium disinfectant, didecyldimethyl ammonium chloride (DDAC), whose minimum lethal concentration (MLC) against Staphylococcus aureus was 32 μg/ml. No remaining viable 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 ^<14>C-labeled DDAC showed that the disinfectant was taken up in a biphasic curve to the cell regardless of the treatment temperature or time. The radioactivity was distributed significantly in the membrane fraction and the cytoplasm fraction. Tetramethyl 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 hydrophobic interaction, onto the cell membrane, where it can react with lipid to cause significant damage to the structure and function of the membrane, leading to death.