Specific solute effects on Staphylococcus aureus cells subjected to reduced water activity.

The behaviour of Staphylococcus aureus cells subjected to lowered water activity (aw) by the addition of various solutes was examined by transmission electron microscopy. Solutes included sodium chloride, sucrose, propylene glycol, butylene glycol and various polyethylene glycols. Changes in other physical properties of the liquid growth medium brought about by the solutes were estimated theoretically. They did not correlate with the bacterial biological response. The inhibitory effects of sucrose and sodium chloride against S. aureus were primarily ascribed to their water activity-lowering abilities, showing no significant specific solute effects. However, the other solutes examined showed specific antibacterial activity against S. aureus which may be compatible with cell wall attack.