Parasite viability by electrorotation

The safety of water supplies is threatened by waterborne protozoan pathogens of man. Many of these pathogens are highly resistant to standard disinfection methods, have low infectivity doses and cause protracted disease. Single organisms subjected to a uniform rotating electric field acquire an induced electric dipole moment. The dipole and field interact and can produce a torque that makes the organism spin. The rate and direction of spin is a sensitive function of the dielectric properties of the organism and the suspending medium, namely the conductivity and permittivity. During a pathogen's lifecycle, numerous physico-chemical changes occur, which alter its dielectric properties. Electrorotation can detect these changes, enabling the viability of the pathogen to be determined. Using a microfabricated planar gold electrode array optimised for electrorotation and energised with quadrature sinusoidal voltages, we investigated the electrorotational properties of two protozoan parasites; Giardia muris and Cyclospora cayetanensis. We present differences in their electrorotational response due to viability, which was confirmed by vital dye assay for G. muris. Based on this work, we propose that electrorotation can be used to determine the viability of C. cayetanensis, for which no vital dye assays are available. The potential of this technique as a rapid and precise assay for the determination of parasite viability is particularly applicable to the food, water and healthcare industries. Furthermore, electrorotation is a non-invasive technique, allowing organisms to be further analysed using, for example, DNA sequencing, to establish likely pathogen sources. (C) 2001 Elsevier Science B.V. All rights reserved.