Impedance microbiology

The ability of microbial metabolism to change the electrical conductivity of the growth medium was discovered by Stewart[1] and further studied by other scientists such as Oker-Blom,[2] Parson[3] and Allison[4] in the first half of 20th century.

However, it was only in the late 1970s that, thanks to computer-controlled systems used to monitor impedance, the technique showed its full potential, as discussed in the works of Fistenberg-Eden & Eden,[5] Ur & Brown[6] and Cady.

[citation needed] Until the bacterial concentration is lower than a critical threshold CTH the electrical parameters Rs and Cs remain essentially constant (at their baseline values).

CTH depends on various parameters such as electrode geometry, bacterial strain, chemical composition of the growth medium etc., but it is always in the range 106 to 107 cfu/ml.

The original instrument of 1984 features a multi-incubator system capable of monitoring up to 512 samples simultaneously with the ability to set 8 different incubation temperatures.

[15] A portable embedded system for microbial concentration measurement in liquid and semi-liquid media using impedance microbiology has been recently proposed.

Impedance microbiology has been extensively used in the past decades to measure the concentration of bacteria and yeasts in different type of samples, mainly for quality assurance in the food industry.