Antibacterial properties of SCE-2787, a new cephem antibiotic.

The in-vitro antibacterial properties of SCE-2787, a new semi-synthetic parenteral cephalosporin, were evaluated by comparing its affinities for penicillin-binding proteins (PBPs), its bactericidal activity and its effects on morphology with those of ceftazidime, cefpirome and E-1040. SCE-2787 and cefpirome had higher affinities for PBPs 1 and 2 of Staphylococcus aureus, and a more potent anti-staphylococcal activity, than ceftazidime and E-1040. All four antibiotics had similar activity against Escherichia coli, and showed similar affinities for PBP 3 of this organism. SCE-2787, ceftazidime and E-1040 were more potent than cefpirome against Pseudomonas aeruginosa, and showed higher affinities for the P. aeruginosa PBP 3. The wide-spectrum antibacterial activity of SCE-2787 can be explained, in general, by its high affinities for PBPs, SCE-2787, at half its MIC level or higher, was bactericidal against all the bacterial strains examined, as were the other antibiotics tested. Exposure of S. aureus to SCE-2787 resulted in the formation of cell walls with irregular septa which subsequently thickened and collapsed. Elongation was the major morphological change of E. coli and P. aeruginosa cells treated with SCE-2787. E. coli cells were converted to 'ghosts', infrequent in P. aeruginosa, after prolonged incubation with higher concentrations of SCE-2787.