Dielectric permittivity measurement of hydrophilic and hydrophobic bacterial suspensions:: a comparison with the octane adhesion test

The present article deals with a technique to determine the hydrophobic/hydrophilic features of bacterial suspensions: the high frequency dielectric permittivity measurement. The experimental conditions require the preparation of the sample for the dielectric measurements to be first developed, namely the temperature, ionic strength, pH and biomass concentration. This study showed that the dielectric measurement must be carried out with a temperature-controlled cell, using a sample ionic concentration below 5x10(-2M), without any pH control, provided the pH matches natural values. The dry suspended matter concentration of the sample also had to be controlled. The obtained permittivity values for bacterial suspensions of varying hydrophobicity were then negatively correlated with their hydrophobicity measured through the octane adhesion test. This revealed a linear correlation between the two methods and demonstrated that the dielectric permittivity measurement method is a new way of classifying bacterial strains in relation to one another on their relative hydrophobicity. (C) 1998 Elsevier Science B.V.