Antimicrobial Action of Sucrose Monolaurate on Staphylococcus aureus

Abstract

The action of sucrose monolaurate (SL) against S. aureus was studied. The influence of SL on the leakage of nucleic acid from the cells and its pH dependence were investigated. The pH dependence of the adsorption of SL on the cell wall and the effects of SL upon the activity of some enzymes of the cell envelope were also determined. The results may be summarized as follows.The leakage of nucleic acid was found to increase on treatment of the cells with SL and the increase was greater at pH 7.0 than at pH 5.0. On the other hand, SL was adsorbed more strongly at pH 5.0 than at pH 7.0. As for the enzymes, the activity of alkaline phosphatase (Alpase) of the intact cells was enhanced by the treatment with SL at either pH. The Alpase of the intact cells was also activated by the addition of SL to the incubation mixture, but that of the cell membrane was not. In contrast, acid phosphatase (Acpase) of both the intact cells and the cell membrane was inhibited by the addition of a high concentration of SL. Inactivation of lactate dehydrogenase (LDH), namely prevention of the oxidation of lactate, in the intact cells and cell membrane by SL was much stronger at pH 5.0 than at pH 7.0.From these findings, it was deduced that the antimicrobial action of SL against S. aureus is probably initiated by the adsorption of SL on the cell envelope, leading to disruption of physiological processes.