Antibody-Mediated Bacteriolysis: Enhanced Killing of Cyclacillin-Treated Bacteria

Abstract

Incubation of Escherichia coli with sublethal concentrations of the semisynthetic penicillins cyclacillin and ampicil-lin substantially increased the susceptibility of the bacteria to subsequent lysis by serum antibody or specifically immunized murine spleen cells in the presence of guinea pig complement. The effect was dependent on the dose of the antibiotic and the length of incubation time and appeared to be due to subtle alterations in the bacterial surface which rendered the organisms more susceptible to immunologic lysis. These results provide a possible mechanism for the greater in vivo efficacy of some antibiotics as compared to their in vitroactivity.