Division-inhibition capacity of penicillin in Escherichia coli is growth-rate dependent.

Growing bacteria are sensitive to various beta-lactam derivatives due to their interference with peptidoglycan biosynthesis. At low concentrations, penicillin G (benzylpenicillin) blocks cell division without affecting mass growth rate. The MIC for division of Escherichia coli B/r (H266) was found to depend on the growth rate, which was modified by the nutritional conditions. Our hypothesis, that division sensitivity is proportional to the rate of peptidoglycan synthesis for septum formation, as well as to cell circumference, was thus confirmed.