Affinity of penicillin-binding proteins of Escherichia coli K-12 for furbenicillin and other beta-lactam antibiotics

Penicillin-binding proteins (PBP) are vitally important targets in relation to the killing of bacteria by beta-lactams. The affinities of PBP of Escherichia coli K 12 for ampicillin, mecillinam and for ureidopenicillins were studied by sodium dodecylsulphate polyacrylamide slab gel electrophoresis and fluorography. The results showed that furbenicillin, a semisynthetic ureidopenicillin developed in China, bound to all 3 essential target proteins of E coli. The IC50 values of furbenicillin to PBP 1 b, PBP 2 and PBP 3 were 4.55 mg/L, 0.37 mg/L and 0.06 mg/L, respectively. The affinities of the 3 proteins of E coli for furbenicillin were 2.5-, 3.5-, and 2.5-fold, respectively higher than that of azlocillin. Mecillinam bound exclusively to PBP 2 (IC50: 0.16 mg/L). Mezlocillin and piperacillin showed higher affinities for PBP 3 than furbenicillin, but their affinities for PBP 1 b and PBP 2 were much lower than furbenicillin.