SCE-963, a New Potent Cephalosporin with High Affinity for Penicillin-Binding Proteins 1 and 3 of Escherichia coli

A few biochemical activities of SCE-963, a new cephalosporin with potent antibacterial activities against gram-negative bacteria, were compared with those of several currently available cephalosporins against strains of Escherichia coli K-12. The minimum inhibitory concentrations of SCE-963, cefazolin, cephaloridine, cephalothin, and cephalexin were 0.2, 1.56, 3.13, 12.5, and 25 mug/ml, respectively. Affinities of these cephalosporins for the penicillin-binding protein (PBP) 1B of E. coli correlated well with their antibacterial activities; among tested cephalosporins, SCE-963 showed the highest affinity for PBP 1B. SCE-963 inhibited cross-linking of peptidoglycan in a cell-free system the most strongly suggesting that this inhibition results from its high affinity for PBP 1B. SCE-963 also showed the highest affinity for PBP 3; it caused filamentation of cells over a wide range of relatively lower concentrations. Thus its superior antibacterial activity is believed to be manifested through its high affinity for the PBPs.