Bacterial Sample Concentration and Culture Monitoring Using a PEG-Based Osmotic System with Inline Impedance and Voltammetry Measurements

Abstract

Impedance measurements using graphite electrodes were used to detect the increase in culture medium conductivity due to bacteria growth in real time along with simultaneous voltammetric monitoring of pyocyanin concentration. Electrochemical methods were compared to conventional continuous monitoring of bacterial cultures using turbidity measurement at an optical density of 600 nm (OD600). A practical osmotic system was further designed for concentrating bacterial cultures during growth to enable earlier detection using the electrochemical methods. Bacterial cultures, starting from an initial culture density of 1 × 10⁸ cells/mL, were grown inside a sealed cellulose ester dialysis membrane, while polyethylene glycol in LB medium was used as the draw solution outside the membrane to gradually concentrate the growing cultures. 0.7-mm-diameter graphite for mechanical pencils was utilized as working and counter electrodes with a platinum wire reference electrode for electrochemical measurements with and without the osmotic system. In the absence of forward osmosis, impedance measurements detected culture growth ~ 1 h faster than conventional OD600. Integrating osmosis showed a twofold decrease in the time to detect pyocyanin production as an indicator for bacterial growth. For impedance monitoring, removal of water by osmosis was conflated with the impedance decrease due to cell growth; however, the results show a promising ability to detect bacteria growth via an observed shift in osmotic impedance profile when bacteria are present in a sample. By monitoring the deviation in the impedance profile, a threefold improvement in detection time was achieved when compared to conventional OD600 measurements.