title: Function of the outer membrane of Escherichia coli as a permeability barrier to beta-lactam antibiotics.
abstract: On the basis of a simple theoretical model, the ease of penetration of beta-lactam antibiotics through the outer membrane of Escherichia coli was measured. The cell envelope was found to act as a diffusion barrier to both penicillins and cephalosporins. The validity of the model and the cooperative action of cell-bound beta-lactamase and outer membrane were further verified by comparing calculated and experimentally determined velocities of beta-lactam hydrolysis by intact cells and sonically treated cell suspensions. The results showed good correspondence at five different antibiotic concentrations. Similar conclusions could be drawn from a comparison of beta-lactam concentrations on both sides of the outer membrane, calculated from enzyme kinetic measurements and minimal inhibitory concentrations for both a beta-lactamase-producing E. coli and its enzyme-negative variant. in the case of benzylpenicillin and cephalothin, however, no correspondence was found. The joint action of several parameters determining the efficacy of penicillins and cephalosporins against beta-lactamase-producing E. coli is discussed.
mesh_terms: D002473:Cell Wall / Q000378:metabolism; D002510:Cephalosporinase / Q000378:metabolism; D002511:Cephalosporins / Q000378:metabolism*; D004058:Diffusion; D004926:Escherichia coli / Q000201:enzymology / Q000378:metabolism*; D014644:Genetic Variation; D006868:Hydrolysis; D008954:Models, Biological; D010405:Penicillinase / Q000378:metabolism; D010406:Penicillins / Q000378:metabolism*; D010539:Permeability
chemical_list: D002511:Cephalosporins; D010406:Penicillins; D002510:Cephalosporinase; D010405:Penicillinase