Synergism of cephalosporins at subinhibitory concentrations and polymorphonuclear leukocytes on phagocytic killing of Escherichia coli and its mode of action.

The interactions between subinhibitory concentrations of cephalosporins and polymorphonuclear leukocytes in the killing of a strain of Escherichia coli are described and an attempt is made to define the responsible mechanism. Ceftizoxime was the most potent agent tested. Pretreatment of the E. coli strain with subinhibitory concentrations of ceftizoxime increased the susceptibility to both; phagocytic killing activity of the polymorphonuclear leukocytes and bactericidal activities of the oxygen metabolites and the granule extracts. A most interesting result was the increased susceptibility of the ceftizoxime-treated E. coli to killing by beta-glucuronidase which normally is not bactericidal. It is suggested that the augmented killing could be due to bacteriolysis by beta-glucuronidase.