1998 年 3 巻 1 号 p. 1-5
The bactericidal activity of a quaternary ammonium salt, didecyldimethylammonium chloride (DDAC), was depressed by the presence of soap, sodium laurate (NaLA): the minimum lethal concentration (MLC) of DDAC against Staphylococcus aureus was 63 and 250 μg/ml in the absence and presence of 0.01% NaLA, respectively. The neutralizing effect was studied in relation with the mode of action of DDAC. The apparent uptake of DDAC by the cell was not repressed by NaLA's presence when compared to that in its absence. The solution of NaLA showed alkaline pH, but the biocidal activity of DDAC was higher at pH 11 than at pH 7. Although the presence of NaLA had no significant effect on DDAC's action on increasing the turbidity of the cell suspension, the mixture of these reagents alone without cells exhibited some turbidity. From these findings it is deduced that NaLA can form a less active complex with DDAC by both ionic and hydrophobic interactions, suggesting that the positive charge as well as the hydrophobicity of the side chains in DDAC moiety plays an important role in its bactericidal activity. Key words: Bacteric
