Evaluation of a dielectrophoretic bacterial counting technique

Dielectrophoresis, an electrokinetic migration of particles, can occur in n on-uniform alternating electric fields and is dependent upon the dielectric nature of the cells and their suspending medium. An enumeration system uti lising this phenomenon is described, which has the potential to count parti cles selectively, including different bacterial or eukaryotic cell species and even sub-populations of different cell viability states or sizes. Relat ionships were observed between suspension concentrations and the extent of dielectrophoretic (DEP) collection for polystyrene latex beads, pure bacter ial samples and mixtures of bacterial species including Escherichia coli, S erratia marcescens, Pseudomonas aeruginosa and Bacillus subtilis. A similar relationship was utilised for polystyrene latex as a calibration line to e nable the concentration of particles in a suspension to be determined accor ding to the level of DEP collection. The particle concentration of an unkno wn test sample was found to lie within the predicted concentration range de termined on the basis of DEP collection. In addition, the predicted limits were found only to deviate between - 6.2 and + 6.9% from the mean particle concentration. (C) 1999 Elsevier Science S.A. All rights reserved.