Permeability to β-lactams in Bacteroides fragilis

Abstract

Bacteroides fragilis strains TAL2480 and TAL3636 were used to assess outer membrane permeability to various β-lactam compounds. These strains were chosen because they possess β-lactamases capable of hydrolysing all commonly employed β-lactams except monobactams. The β-lactamases are located in the periplasmic space and could be released by sonication and osmotic shock. Permeability was calculated by the method of Zimmerman & Rosselet (1977, Antimicrobial Agents and Chemotherapy12, 368–72). The rank order of permeative ability (from fastest to slowest) was as follows: cephaloridine, imipenem, cefotaxime, cefoxitin, cefoperazone, nitrocefin, cephalothin, and latamoxef. Our results showed that ionic charge, hydrophobicity, and molecular weight influenced β-lactam drug uptake by B. fragilis. These results are similar to findings for Escherichia coli, where increased negative charge and increased molecular weight are associated with decreased drug uptake. However, unlike E. coli, increased drug hydrophobicity, for a given charge and molecular weight of the drug, was associated with increased uptake by B. fragilis.