Impedimetric approach for monitoring bacterial cultures based on the changes in the magnitude of the interface capacitance

Abstract

A previously reported methodology is applied to monitor the concentration of bacterial suspensions from an incubator using impedance spectroscopy and platinum electrodes. The interface capacitance, commonly fitted as a constant phase element, CPE_i, was found sensitive to the suspended bacteria concentration after short exposure times in a wide range of concentrations (from 10² to 10⁷ colony forming units per mL, CFU mL⁻¹) with a limit of detection of 10 CFU mL⁻¹. The effect of the substances released during bacterial growth (enzymes, toxins, exopolysaccharide, etc.) in the CPE_i magnitude was found to be negligible and samples only containing cells washed with saline solutions showed results comparable to those obtained using aliquots directly extracted from the bacterial incubator. This impedimetric approach showed correlation with classical microbiological methods for measuring bacterial concentration such as plating onto agar, optical density and fluorescence microscopy. The impedimetric approach was simplified to a single frequency analysis by selecting the optimal frequency for the measurement.