Permeability of the Envelopes of Staphylococcus aureus to some Salts, Amino Acids, and Non-Electrolytes

Abstract

SUMMARY: The passive permeability properties of the plasma-membrane of Staphylococcus aureus (strain Duncan) resemble those of a classical lipid membrane such as that considered by Overton in 1899. In general, solutes carrying more than four water molecules flow across the plasma-membrane only very slowly under an electrochemical gradient. The plasma-membrane is the effective osmotic barrier to small molecular weight solutes and prevents the escape of internal components having a total osmotic concentration corresponding to c. 1 molal sucrose. The protoplast is prevented from swelling by the cell wall which withstands a hydrostatic thrust of some 20 to 30 atmospheres pressure exerted against it by the plasma-membrane in distilled water. The pores in the cell wall, although large enough to permit rapid diffusion of small molecular weight solutes, are too small to allow a dextran of mol. wt. 10,000 to penetrate. The cell wall acts as the osmotic barrier for large molecular weight components, preventing such components in the medium from gaining access to the plasma-membrane surface and preventing such internal components from passing outwards from the surface of the plasma-membrane.