Specific solute effects with special reference to Staphylococcus aureus

Abstract

Today it is more or less established that the water activity (a w ) of the medium is not the only determining factor regulating the biological response of a microorganism subjected to reduced water activity; the nature of the a w -controlling solute plays a role. Thus, the so-called ‘specific solute effect’ is discussed in detail for Staphylococcus aureus. The influence of changes in the physical properties of the medium (e.g. viscosity, oxygen solubility, oxygen diffusivity, etc.) brought about by solute/s dissolution was considered as a possible cause of specific solute effects. However, it was concluded that, within the ranges studied here, there is not a clear relationship between the S. aureus response and the modification of certain physical properties of the medium. The inhibitory effects of solutes such as sodium chloride and sucrose, which are those most often present in low a w -preserved foods, are primarily related to their ability to lower water activity. However, for other solutes such as ethanol, propylene glycol, butylene glycol and various polyethylene glycols, specific antibacterial effects are important. These antibacterial effects may be attributed mainly to effects of these molecules on membrane enzymes responsible of peptidoglycan synthesis.