Dielectric analysis of Escherichia coli suspensions in the light of the theory of interfacial polarization.

Dielectric measurements of Escherichia coli suspensions were carried out over a frequency range from 10 kHz to 100 MHz, and marked dielectric dispersions having characteristic frequency of approximately 1 MHz were observed. On the basis of the cell model that a spheroid is covered with two confocal shells, a dielectric theory was developed to determine accurately four electrical parameters for E. coli cells such as the conductivity of the cell wall, the dielectric constant of the cell membrane, and the dielectric constant and the conductivity of the protoplasm. The observed data were analyzed by means of the procedure based on the dielectric theory to yield a set of plausible electrical parameters for the cells. By taking account of the size distribution of the cells and a dielectric relaxation of the protoplasm, the observed dispersion curves were successfully reconstituted by the present theory.