Relationship between Lytic and Inhibitory Concentrations of Cephalosporins

Abstract

The β-lactam antibiotics owe their bactericidal activity to their lytic action on the bacterial cell wall. This property sets them apart from other bactericidal antibiotics, such as the amino-glycosides. Shortly after the introduction of benzylpenicillin some 30 years ago much attention was paid to the lysis phenomenon, especially in relation to the “zone effect” (Eagle & Musselman 1948). However, interest in this aspect waned. The recent increase in the number of semisynthetic β-lactam antibiotics has caused a renewed interest in lytic activity, which has been lead by O’Grady and his colleagues (e.g. Greenwood & O’Grady 1973, 1975). An intriguing finding by these workers is that cephalexin is “lytic-deficient”, in that filamentation rather than lysis is the bacterial response over a wide range of antibiotic concentrations (Greenwood & O’Grady 1973). As cephalexin was unique among the 3-lactam compounds which they tested, in that it has a β-methyl sidechain, it seemed possible that there was some simple relationship between chemical structure and lytic ability among cephalosporins. The present study was designed to investigate this possibility.