Lysis enhancement: a novel form of interaction between beta-lactam antibiotics.

A novel form of synergy has been observed to occur between cephalexin and certain other beta-lactam antibiotics. In the presence of cephalexin a reduction was found in the concentration of other beta-lactam agents needed to induce lysis of Escherichia coli; the effect was particularly marded when cephalexin was allowed to act for a short time before the addition of the second agent. The basis of this type of synergy--which is not likely to be of therapeutic value--is discussed in terms of a theroy perviously put forward, whcih suggests that penicillins and cephalosporins have two distinct sites of action in Gram-negative bacilli.