Affinity of E1077, a new cephalosporin, for penicillin-binding proteins of Staphylococcus aureus and its antistaphylococcal activity.

Abstract

Potent antistaphylococcal activity was conferred on E1077 by the introduction of the propenylammonium group at the 3-position in the cephem nucleus and of the fluoromethoxyimino group in the 7 beta-side chain. Antistaphylococcal activity was more markedly increased by the former group than by the latter. This effect seemed likely to be due to the increased high affinity for penicillin-binding protein (PBP) 3, which may be one of the essential PBPs of Staphylococcus aureus, and secondly for PBP 4. E1077 also showed more potent bactericidal activity than did cefpirome at concentrations above the MICs, although the MICs of E1077 for S. aureus were only half those of cefpirome. While cefpirome showed little killing activity within 4 hours at its MIC, the addition of cefoxitin (0.05 micrograms/ml), a specific inhibitor for PBP 4, enhanced the killing activity of cefpirome to match that of E1077. In addition, peptidoglycan (PG) obtained from cells grown with the subinhibitory E1077 concentration was more susceptible to lytic enzymes than that from untreated cells or cefpirome-treated cells. These results indicated that the increased inhibition of PBPs 3 and 4 by E1077, which was brought about by the introduction of two distinctive functional groups, led to the enhanced antistaphylococcal activity and to the production of poorly cross-linked PG, and thereby to rapid bactericidal activity.