IMPEDANCE BACTERIOMETRY: MEDIUM AND INTERFACE CONTRIBUTIONS DURING BACTERIAL GROWTH

CARMELO J. FELICE, MAX E. VALENTINUZZI, MARÍA ISABEL VERCELLONE, ROSSANA E. MADRID

IEEE TRANSACTIONS ON BIO-MEDICAL ENGINEERING

Año: 1992 p. 1310 - 1313

0018-9294

We measured impedance in a cell containing culture broth inoculated with E. coli, before and during bacterial growth. The electrode interface impedance components (Ri, Xi) and the culture medium component Rm were separated by making use of the Warburg`s model frequency dependent properties. Measurements were carried out at different frequences (from 18Hz to 18KHz) with a constant current impedance bridge as growth preceeded. It was found that: Growth curves for Ri and Xi showed a similar temporal pattern within the frequency range of 18-100 Hz. Dispersion was not observed in Rm, meaning that the same growth  response was obtained within the 18-18000 Hz range. At low frequency, the resistive and capacitive reactive components, or Rb and Xb, respectively, were directly measured, where Rb=(2.Ri+Rm) and Xb=2.Xi and, at high frequency (above 5 KHz), Rm was obtained (for Zi is negligible). Thus, Ri was easily discriminated form Rm by simply arithmetic: Ri=[Rb(low f) - Rb(high f)]/2. In four experiments, the maximum spread of Xi, Ri, and Rm was smaller than 5%, indicating good repeatability. There is potential new information in dissecting out the growth curve in three separate component curves.