Conductance and Impedance Methods for Detecting Pathogens

  • F. J. Bolton

Abstract

The impedance of a system is a function of its resistance, capacitance and the applied frequency (Firstenberg-Eden and Eden 1984). It is usually the resistive element which is measured and this is most frequently recorded as changes in conductance. These changes occur in the bulk electrolyte solution (culture medium) due to metabolism of uncharged or weakly charged substrates which are converted to highly charged end products, e.g. proteins to amino acids. Capacitance is related to the behaviour of ions at the surface of the electrode and can be monitored separately from conductance. Several instruments which monitor impedance changes are available and include the Bactometer 123 (Bactomatic Ltd.), Malthus 2000 (Malthus Instruments Ltd.) and the Rapid Automated Bacterial Impedance Technique (RABIT) (Don Whitley Scientific Ltd.). Detection of bacteria can be by direct conductimetry which is achieved by monitoring changes in the growth medium or by indirect conductimetry which monitors changes due to evolution of CO2 produced by the metabolism of substrates in the culture medium. The principle of indirect conductimetry has recently been described by Owens et al. (1989). Direct conductimetry has been used extensively to detect both pathogens and non-pathogens in foods. This presentation concentrates on recent developments for the rapid detection of Salmonella, Campylobacter and Listeria using impedance monitoring.

Keywords

Carbohydrate Lysine Mannitol Staphylococcus Sorbitol 

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References

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Copyright information

© Springer-Verlag Berlin Heidelberg 1991

Authors and Affiliations

  • F. J. Bolton
    • 1
  1. 1.Public Health LaboratoryRoyal Preston HospitalPrestonUK

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