Ampicillin susceptibility and ampicillin-induced killing rate of Escherichia coli

Abstract

The killing rate induced by ampicillin was determined in 20 strains of Escherichia coli. The apparent generation rate constant for each E. coli showed a characteristic concentration-dependent course. This course can be mathematically described and is determined by four parameters. Three of these parameters determine the speed of the process, and the fourth parameter determines a minimal concentration. The susceptibility of the strains, measured as the minimal inhibitory concentration by an agar dilution method, correlated with the minimal concentration and with a minimal inhibitory concentration calculated from the curve, but not with the rate-determining parameters.