A Method Detecting Bacteria in Culture Medium by Simultaneous Measurement of Electrical Impedance and Turbidity

An identification method is proposed for some bacteria by utilizing the parameters obtained from the simultaneous measurement of electrical impedance and turbidity. The examined bacteria are Escherichia coli, Klebsiella pneumoniae, Enterobacter cloacae, Serratia marcescens, Proteus morganii and Streptococcus faecalis which are clinically isolated and identified by our group. The culture broth is Brain Heart Infusion (BHI). Much effort has been paid on making suitable cell. From the view of sterilization and repeatedly use, the cells are made by glass. The turbidity is measured by pair of CdS-LED (red) elements. The impedance is measured by means of previously proposed four-electrode method. The electrodes are gold and stainless-steel wires (0.7mmφ) which are verified to give no difference in measuring impedance. The recorded impedance decrease is good in its reproducibility comparing it to that of twoelectrode method. The rate of the change of these two quantities are computed from the recorded data yielding reproducible curves against time (denoted as ”rate pattern”). The rate patterns for impedance and turbidity give inherent ones for examined 6 bacteria. Some numerical values, peak value, half width, and so on, of rate patterns are measured from the curves. Some ratios and absolute values of parameters are selected as trial characteristic parameters. Bacteria are classified by each characteristic parameters. 5 characteristic parameters are needed for identifying 6 becteria. The rate patterns seem to be useful in screening or identification of clinical bacteria.