Toxicity of copper to Escherichia coli in relation to incubation temperature and method of sterilization of media.

The growth of Escherichia coli ATCC 9637 in a basal synthetic medium was very similar in cultures incubated at 35, 37, 40, and 42 °C. The inclusion in the medium of copper at concentrations of 0.1 and 0.2 μg/ml resulted in a decrease in the growth rate at each of these temperatures; the higher the temperature, the greater the decrease. Copper caused a decrease in the growth rate of E. coli in the medium sterilized by filtration as well as in that sterilized by autoclaving. However, in the medium sterilized by heat there were alternate periods in which the optical density (O.D.) of culture increased and periods during which no increase in O.D. occurred. Decreases of 50% or more in the numbers of viable cells occurred in conjunction with the plateaus in the O.D. of the cultures. A greater delay in the initiation of growth occurred in both the copper-free and the copper-containing media sterilized by heat than in the corresponding medium sterilized by filtration; the longer the exposure of the medium to heat...