POLYETHYLENEIMINE IS AN EFFECTIVE PERMEABILIZER OF GRAM-NEGATIVE BACTERIA

The effect of the polycation polyethyleneimine (PEI) on the permeabili ty properties of the Gram-negative bacterial outer membrane was invest igated using Escherichia coli, Pseudomonas aeruginosa and Salmonella t yphimurium as target organisms. At concentrations of less than 20 mu g ml(-1), PEI increased the bacterial uptake of 1-N-phenyl naphthylamin e, which is a hydrophobic probe whose quantum yield is greatly increas ed in a lipid environment, indicating increased hydrophobic permeation of the outer membrane by PEI. The effect of PEI was comparable to tha t brought about by the well-known permeabilizer EDTA. Permeabilization by PEI was retarded but not completely inhibited by millimolar concen trations of MgCl2. PEI also increased the susceptibility of the test s pecies to the hydrophobic antibiotics clindamycin, erythromycin, fucid in, novobiocin and rifampicin, without being directly bactericidal. PE I sensitized the bacteria to the lytic action of the detergent SDS in assays where the bacteria were pretreated with PEI. In assays where PE I and SDS were simultaneously present, no sensitization was observed, indicating that PEI and SDS were inactivating each other. In addition, a sensitizing effect to the nonionic detergent Triton X-100 was obser ved for P. aeruginosa. In conclusion, PEI was shown to be a potent per meabilizer of the outer membrane of Gram-negative bacteria.