PERMEABILIZING ACTION OF POLYETHYLENEIMINE ON SALMONELLA-TYPHIMURIUM INVOLVES DISRUPTION OF THE OUTER-MEMBRANE AND INTERACTIONS WITH LIPOPOLYSACCHARIDE

Polyethyleneimine (PEI), a polycationic polymer substance used in vari ous bioprocesses as a flocculating agent and to immobilize enzymes, wa s recently shown to make Gram-negative bacteria permeable to hydrophob ic antibiotics and to detergents. Because this suggests impairment of the protective function of the outer membrane (OM), the effect of PEI on the ultrastructure of Salmonella typhimurium was investigated. Mass ive alterations in the OM of PEI-treated and thin-sectioned bacteria w ere observed by electron microscopy. Vesicular structures were seen on the surface of the OM, but no liberation of the membrane or its fragm ents was evident. Since a potential mechanism for the action of PEI co uld be its binding to anionic LPSs on the OM surface, the interaction of PEI with isolated LPSs was assayed in vitro. The solubility of smoo th-type LPSs of Salmonella, regardless of the sugar composition of the ir O-specific chains, was not affected by PEI, nor was that of Ra-LPS (lacking O-specific chains but having a complete core oligosaccharide) . PEI strongly decreased the solubility of rough-type LPSs of the chem otypes Rb2 and Re, whereas it had only a weak effect on the abnormally cationic Rb2-type pmrA mutant LPS, suggesting that the negative charg e to mass ratio of LPS plays a critical role in the interaction.