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 grow th 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 preser vatives, such as hypertonic NaCl or sucrose. High selectivity of PxB a gainst Gram-negative organisms and the basis for the hyperosmotic stre ss response at sublethal PxB concentrations is attributed to PxB-induc ed mixing of anionic phospholipid between the outer layer of the cytop lasmic membrane with phospholipids in the inner layer of the outer mem brane. This explanation is supported by PxB-mediated rapid and direct exchange of anionic phospholipid between vesicles. This mechanism is c onsistent with the observation that genetically stable resistance agai nst PxB could not be induced by mutagenesis. (C) 1998 Academic Press.