Effect of growth rate on streptomycin accumulation by Escherichia coli and Bacillus megaterium.

Abstract

The rate of accumulation of streptomycin by streptomycin-sensitive strains of Escherichia coli and Bacillus megaterium, grown in chemostats, was related to the growth rate prior to addition of the antibiotic. For E. coli the length of the lag period that preceded accumulation was also growth rate-dependent. Thus faster growing cultures accumulated streptomycin more rapidly and with a shorter lag than slower growing cultures. The rate of efflux of streptomycin from bacteria that had accumulated streptomycin was not greatly influenced by growth rates of the cultures. At a particular growth rate, accumulation of streptomycin was found to be faster at higher concentrations of the antibiotic. Rapid accumulation of streptomycin was not observed with continuous cultures of a streptomycin-resistant strain of E. coli. Accumulation of streptomycin was abolished when growth was inhibited by either terminating the flow of fresh medium to a chemostat or by adding inhibitors that block protein synthesis. These results suggest that the rate of accumulation of streptomycin is related to the concentration of streptomycin-sensitive ribosomes that are actively engaged in protein synthesis within the bacterial cells.