A method to determine the diffusion of cephalosporins through porin pores in vitro was developed, using liposomes reconstituted from phospholipids, lipopolysaccharides, and purified porin trimers. With this method, the roles of several species of porin pores from Escherichia coli and Salmonella typhimurium in the diffusion of cephalexin, cephaloridine, and cephalothin were examined. Results clearly showed that porins from E. coli B and 39,000-molecular-weight porins from S. typhimurium formed the most efficient pores. Thus, these were considered to represent a single functional group. OmpF and OmpE porins of E. coli K-12 and 38,000-molecular-weight porins of S. typhimurium formed moderately efficient pores. OmpC porins of E. coli K-12 and 40,000-molecular-weight porins of S. typhimurium were the least efficient pore formers. The present method can be used to distinguish the role of individual porin pores in the diffusion of cephalosporins.
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