Fast determination of viable bacterial cells in milk samples using impedimetric sensor and a novel calibration method

As a first stage toward the development of an impedimetric biosensor to quantify viable bacterial cells, this work defines the relationships between microbial growth and impedance changes associated with acidification of the culture medium. Escherichia coli bacterium was used as a model of a common pathogenic bacterium found in a foodstuff. Impedance was measured at a fix frequency of 10 kHz using interdigitated microelectrodes. Impedance changes were found to depend on the number of microorganisms in a sample. However, as the kinetics greatly depends on the bacterial concentration, it was not possible to obtain a single calibration curve in a wide concentration range at a fixed incubation time. To resolve this, a novel calibration method was proposed by measuring the sensor response at 270 and 390 min of incubation and taking a mean value. Obtained calibration plots were used to determine E. coli in a spiked milk samples. Performed experiments demonstrated the capacity of the method to detect E.coli concentrations in a range between 102 and 106 cfu mL−1 in milk in only 6 hours with 5-12% error margin.