Automatic on-line analyser of microbial growth using simultaneous measurements of impedance and turbidity

An apparatus for the measurement of bacterial growth is described. The inst rument applies alternate adequate sequential currents of two different freq uencies through a pair of electrodes immersed in a cultured medium. It moni tors, detects and quantifies the growth of micro-organisms based on the mea surement of the impedance across the two electrodes and, simultaneously, it measures the variation in the medium turbidity. The medium conductivity an d the interface electrode impedance changes can be extracted from the measu red impedance. The variations in turbidity can be calibrated in absorbance or optical density units. Moreover, all these parameters are also proportio nal to bacterial proliferation. The computer-controlled apparatus processes and displays the parameters on a monitor showing bulk resistance, electrod e impedance and turbidity changes as time course events. The equipment can detect aerobic or anaerobic micro-organisms and permits the operator simult aneously to assess impedance and turbidity, or it can produce each paramete r as a separate event. Time growth curves of different micro-organisms are presented in the results.