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Biomagnetic separation of Escherichia coli by use of anion-exchange beads: measurement and modeling of the kinetics of cell–bead interactions

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Abstract

Analyses of food-borne pathogens are of great importance in order to minimize the risk of infection for customers. These analyses should be as fast as possible. Any detection method requires enrichment and quantitative analysis of the enriched microbes. Conventional enrichment methods, which take several days, need to be replaced by faster techniques such as biomagnetic separation (BMS). This technique involves the use of paramagnetic microspheres coated with ligands that have special affinity to the microbes that have to be detected. In the studies reported here, enrichment experiments by BMS were carried out using the non-pathogenic E. coli DSM 498 as a model strain and beads coated with a polyethylenimine (PEI) anion-exchange material. The results show that the number of cells separated, as a proportion of the total, was positively correlated with the bead concentration and the length of the period they were mixed together. In addition, a mathematical model, based on the rate of impact between two different sorts of particles, was developed to describe the proportion of separated cells as a function of incubation time and the concentration, size and density of the beads and cells. This is the first mathematical description of cell–bead interactions to be based on well-understood physicochemical principles. The model was confirmed by separation experiments in which the concentration of beads and the incubation period were varied. The developed model enables optimization of the amount of beads added and the reaction period necessary for complete cell separation and thus minimization of costs in BMS.

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Abbreviations

F :

Relative particle flow (m3 s−1)

g :

Acceleration of gravity (m s−2)

n B :

Number of cell-free beads per volume (m−3)

\( n^{0}_{{\text{B}}} \) :

Initial number of cell-free beads per volume (m−3)

n B,B :

Number of cell-bound beads per volume (m−3)

\( n^{0}_{{{\text{B}}{\text{,B}}}} \) :

Initial number of cell-bound beads per volume (m−3)

n C :

Number of unbound cells per volume (m−3)

\( n^{0}_{{\text{C}}} \) :

Initial number of unbound cells per volume (m−3)

n C,B :

Number of bead-bound cells per volume (m−3)

\( n^{0}_{{{\text{C}}{\text{,B}}}} \) :

Initial number of bead-bound cells per volume (m−3)

P C,B :

Proportion of bead-bound cells (−)

r B :

Radius of spherical beads (m)

r C :

Radius of spherical cells (m)

t :

Time (s)

W BC :

Relative velocity between beads and cells (m s−1)

Z CB :

Rate of impact between beads and cells (s−1)

η L :

Dynamic viscosity of the liquid (kg m−1 s−1)

ρ B :

Density of beads (kg m−3)

ρ C :

Density of cells (kg m−3)

ρ L :

Density of the liquid (kg m−3)

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Acknowledgements

The authors gratefully acknowledge the financial support for this work provided by the Bundesministerium für Bildung und Forschung (03I4013A) and would like to thank Mrs A. Lenk for her technical assistance. Special thanks are due to Chemicell GmbH Berlin (Germany) for providing the coated beads.

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Authors and Affiliations

  1. Institute of Food Technology and Bioprocess Engineering, Technische Universität Dresden, 01062, Dresden, Germany

    S. Deponte, J. Steingroewer, C. Löser, E. Boschke & T. Bley

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  1. S. Deponte
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  2. J. Steingroewer
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  3. C. Löser
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  4. E. Boschke
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  5. T. Bley
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Correspondence to J. Steingroewer.

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Deponte, S., Steingroewer, J., Löser, C. et al. Biomagnetic separation of Escherichia coli by use of anion-exchange beads: measurement and modeling of the kinetics of cell–bead interactions. Anal Bioanal Chem 379, 419–426 (2004). https://doi.org/10.1007/s00216-004-2622-1

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  • DOI: https://doi.org/10.1007/s00216-004-2622-1

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