Medium and interface components in impedance microbiology

Classic impedance microbiology (CM) is based on the measurement of the impe dance components that appear between a pair of electrodes submerged in a ce ll containing inoculated broth. Either a bipolar or a tetrapolar technique can be applied, requiring about 1 x 10(3) to 3 x 10(7) cells/ml to produce detectable changes in the impedance curves. Theoretical analysis of the ele ctrode-electrolyte interface during bacterial growth is lacking, with no ge nerally accepted measuring standards. Besides, there is considerable disagr eement. We separated out the interface and medium components using the freq uency variation technique (FVT) and also analyzed the interface reactance-r esistance diagram, both before and after bacterial growth. Medium resistanc e R-m, interface reactance X-i, and interface resistance R-i, were quantifi ed as time functions growth curves, from the complex bipolar impedance seen between two electrodes. We took into account the electrical current densit y, the temperature and the associated circuitry, also explaining the theore tical and experimental bases that justify the proposed dissecting procedure . It was found that, within the working frequency range, R-m,R- R-i, and X- i percental growth curves are frequency-independent, i.e., neither R-m(f), nor X-i(f) nor R-i(f) changed their slopes before, during and after bacteri al growth. Besides, no alpha-dispersion effect in R-m curves was detected. It is concluded that impedance microbiology could become a fertile area for interdisciplinary knowledge; its development might offer new avenues for b asic and applied research.