Multi-frequency electrical impedance method for detection of viable micro-organisms, their quantification and their characterization

We present here a novel method for detecting the presence of viable microorganisms in various suspensions along with their quantification and characterization. The underlying principle for our method of detection is based on the fact that in the presence of an AC electric field, the viable bacterial cell membrane becomes polarized leading to buildup of charges across the intact membrane and hence, these viable microbial cells behave like electrical capacitors. An increase in the number of microorganisms due to proliferation thus results in a corresponding increase in the “bulk capacitance” of the suspension containing bacteria. This increase cannot be directly measured since the capacitance of the solid-liquid interface (“double layer” which is usually ~1000X larger than the bulk capacitance) “screens” the former. In the work presented here, we introduce a method that is able to discern such changes with high sensitivity and robustness. We also demonstrate the ability of our method to a) Monitor food quality by detecting bacterial proliferation in milk and apple juice b) Quantify bacteria in a sample by estimating MPN of the viable bacteria c) Detect viable bacteria in blood for diagnosis of Sepsis d) Determine the Minimum Inhibitory Concentrations (MIC) and assay for bactericidal/bacteriostatic activity of various bacteria e) Extend the application to detect presence of other microorganisms such as yeast and mold.