Medium and interface components in impedance microbiology

FELICE, CARMELO JOSÉ; VALENTINUZZI, MÁXIMO EUGENIO

IEEE Transactions on Biomedical Engineering

Año: 1999 vol. 46 p. 1483 - 1487

Classic impedance microbiology (CIM) is based on themeasurement of the impedance components that appear between a pairof electrodes submerged in a cell containing inoculated broth. Eithera bipolar or a tetrapolar technique can be applied, requiring about1.10E3 to 3.10E7 cells/ml to produce detectable changes in the impedancecurves. Theoretical analysis of the electrode-electrolyte interface duringbacterial growth is lacking, with no generally accepted measuring standards.Besides, there is considerable disagreement. We separated outthe interface and medium components using the frequency variationtechnique (FVT) and also analyzed the interface reactance-resistancediagram, both before and after bacterial growth. Medium resistanceRm, interface reactance Xi, and interface resistance Ri, were quantifiedas time functions growth curves, from the complex bipolar impedanceseen between two electrodes. We took into account the electrical currentdensity, the temperature and the associated circuitry, also explaining thetheoretical and experimental bases that justify the proposed dissectingprocedure. It was found that, within the working frequency range, Rm,Ri, and Xi percental growth curves are frequency-independent, i.e.,neither Rm(f), nor Xi(f) nor Ri(f) changed their slopes before, duringand after bacterial growth. Besides, no alfa-dispersion effect in Rm curveswas detected. It is concluded that impedance microbiology could becomea fertile area for interdisciplinary knowledge; its development might offernew avenues for basic and applied research.