Decreased permeation of cephalosporins through the outer membrane of Escherichia coli grown in salicylates

Abstract

Escherichia coli K-12 cells grown in 1 to 5 mM sodium salicylate (SAL) or acetylsalicylate show increased phenotypic resistance to various antibiotics (J. L. Rosner, Proc. Natl. Acad. Sci. USA 82:8771-8774, 1985), including cephalosporins (this study). To determine whether these effects are caused by a decreased uptake of the antibiotics, the permeation of several cephalosporins through the outer membrane was measured. For E. coli K-12 grown in LB broth containing 5 mM SAL or acetylsalicylate, permeation of the outer membrane by the five cephalosporins tested decreased three- to fivefold compared with that in cells not grown in salicylates. Permeation of the outer membrane by cephaloridine decreased within 15 min of the addition of SAL to cells grown in broth and reached a minimum in 1 to 2 h. When cells were transferred from broth with SAL to broth without SAL, their permeability to cephaloridine increased slowly for the first 45 min and more rapidly over the next 1.5 h; the permeability then attained normal levels by 3 h. The permeability changes that occurred after media shifts, either to or from SAL, were prevented by concentrations of chloramphenicol that inhibited protein synthesis. These effects of SAL on outer membrane permeability are fully consistent with their effects on antibiotic resistance and with the report (T. Sawai, S. Hirano, and A. Yamaguchi, FEMS Microbiol. Lett. 40:233-237, 1987) that the outer membranes of SAL-treated cells are deficient in certain porins. Permeation of cephaloridine through the outer membrane also decreased when a virulent strain of E. coli K1 was grown in the presence of as little as 1 to 2 mM SAL. This raises the concern that high levels of salicylates in patients night interfere with cephalosporin or other antibiotic therapies.