Osmotic stress in viable Escherichia coli as the basis for the antibiotic response by polymyxin B

Cationic antimicrobial peptides, such as polymyxin B (PxB), below growth inhibitory concentration induce expression of osmY gene in viable E. coli without leakage of solutes and protons. osmY expression is also a locus of hyperosmotic stress response induced by common food preservatives, such as hypertonic NaCl or sucrose. High selectivity of PxB against Gram-negative organisms and the basis for the hyperosmotic stress response at sublethal PxB concentrations is attributed to PxB-induced mixing of anionic phospholipid between the outer layer of the cytoplasmic membrane with phospholipids in the inner layer of the outer membrane. This explanation is supported by PxB-mediated rapid and direct exchange of anionic phospholipid between vesicles. This mechanism is consistent with the observation that genetically stable resistance against PxB could not be induced by mutagenesis. (C) 1998 Academic Press.