The effects of some tetracyclines on synchronously growing cultures of Escherichia coli B/r

Abstract

Abstract Samples of synchronously growing cultures of Escherichia coli B/r removed at predetermined time intervals after synchronization were added to solutions containing bactericidal concentrations of tetra-cycline. Three active antibacterials, 7-nitro-6-demethyl-6-deoxytetracycline, 9-amino-6-demethyl-6-deoxytetracycline and 6-demethyl-6-deoxytetracycline, and one inactive compound, 7-chloroisotetra-cycline, were studied. Survival curves for the active agents, determined using samples of culture differing in age, were of constant slope for a given tetracycline. It is concluded that interruption of protein synthesis is the primary mode of action at bactericidal concentrations of tetracyclines, the same process as has been established for the action of the tetracyclines at the lower bacteriostatic concentrations.