Screening of Bacteria using Impedance Flow Cytometry

Christian Vinther Bertelsen*

*Corresponding author for this work

Research output: Book/ReportPh.D. thesisResearch

7 Downloads (Pure)


In this industrial PhD project, an impedance flow cytometer developed by the Danish company SBT Instruments A/S is used to study the enumeration and characterization of bacterial cells. The device can measure the total concentration of bacteria in a liquid sample in 5 minutes. This is opposed to the growth-based methods used today, which usually take 1-3 days to provide a result. The slow response time is a problem in multiple industries that rely on fast measurements of the microbial burden for quality and hygiene control, such as in food production, health care environments and at drinking water plants.

The technology employed for bacteria characterization is called Impedance Flow Cytometry (IFC). In IFC a liquid containing bacterial cells is continuously injected across a set of detection electrodes placed on the top and bottom of a microfluidic channel. The changes in current during the passing of a bacterium are measured simultaneously at two frequencies probing different parts of the bacteria structure. The technology has been implemented in a tabletop device developed by SBT Instruments called BactoBox and is used to experimentally investigate the impedance response of bacterial cells and other particles.

BactoBox has been used to investigate the impedance response of six different bacteria species to determine if specific cell characteristics can be extrapolated directly from the impedance measurements. Differences between the species were observed, but it was not possible to correlate the differences to the bacteria shape or the gram-type, which emphasize the complexity and variation of bacterial morphology.

BactoBox has also been used to probe the viability state of E. coli bacteria after inactivation with three common disinfection and sterilization methods, ethanol, heat and autoclaving. The results show that the viability of E. coli bacteria can be determined using IFC, but that the sensitivity and selectivity of the classification depends considerably on the inactivation method. For example, prolonged exposure during heat inactivation improved the viability classification with IFC significantly.

Finally, BactoBox was used to evaluate the antibiotic susceptibility of two known colistinsensitive strains of E. coli and Pseudomonas aeruginosa as well as a known colistinresistant Pseudomonas aeruginosa strain. The impedance response of the cells changed as they were exposed to increasing concentrations of colistin and the change in impedance happened at higher antibiotic concentrations for the resistant Pseudomonas aeruginosa strain.

The thesis presents this experimental work together with the theoretical models needed for dielectric modelling of bacterial cells in an impedance flow cytometer system. In the thesis a walk-through of the functional parts of the flow cytometer (microfluidic chip, electronics, sample handling and data analysis) is also presented and their function and interrelation are discussed.

The work presented in this thesis will appeal to anyone interested in novel methods for bacteria detection and enumeration focused on electrical characterization of the cells, and to anyone excited by the technology development happening on the border between academia and industry.
Original languageEnglish
Place of PublicationKgs. Lyngby, Denmark
PublisherDTU Bioengineering
Number of pages212
Publication statusPublished - 2021


Dive into the research topics of 'Screening of Bacteria using Impedance Flow Cytometry'. Together they form a unique fingerprint.

Cite this