The bacterial outer-membrane permeability of .BETA.-lactam antibiotics.

Abstract

Two penicillins and 5 cephalosporins were evaluated for their ability to pass through the outer membranes of Proteus morganii, Citrobacter freundii and Escherichia coli. Cefazolin, ceftezole and cephaloridine showed high permeability through the outer membranes of these gram-negative bacteria. Benzylpenicillin and cephalothin showed low permeability. The outer membrane permeability of ampicillin and cephalexin varied from species to species. C. freundii had the highest barrier against the penicillins and the cephalosporins and E. coli appeared to have a low barrier against the cephalosporins. The hydrophobic character of the .beta.-lactam antibiotics, which was estimated by a reversed-phase TLC, was closely related to the outer membrane permeability. The more hydrophilic antibiotic showed the higher outer membrane permeability. Cephaloridine, the most lipophilic compound among the antibiotics tested, showed good permeability.