Effect of biocide concentration on electrorotation spectra of yeast cells.

The effect of the biocide Cosmocil (polyhexanide) at different concentrations on the electrorotation spectra of yeast cells is investigated over the frequency range from 1 kHz to 10 MHz. The dielectric properties of the yeast, before and after biocide treatment, were deduced from the electrorotation spectra using two-shell ellipsoid modelling methods that have been well tested for other heterogeneous biological systems. The results show a gradual increase in the cytoplasmic membrane conductivity with increasing biocide concentration, rather than an "all-or-nothing' breakdown of the membrane. The technique gives a quantitative analysis of the toxic damage by chemicals to cells and can be exploited in the development of new pharmacological agents.