A multi-chambered module for holding separate samples of nutrient media. A plurality of chambers, with access means into each, is permanently attached to an electrically non-conductive base. Embedded within the base under the chambers is a plurality of electrically conductive leads. Terminal portions at one end of the leads emerge in spaced pairs into each chamber forming electrodes therein. At the other end of the leads terminal portions are exposed for contact with an electrical source. A signal passed through the electrodes in galvanic contact with media permits the impedance thereof to be determined, with changes of impedance directly associated with microorganism growth therein.