Multi-frequency electrical impedance method for detection of viable micro-organisms, their quantification and their characterization
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Despite advances in DNA based technologies and molecular methods, there are still several drawbacks to these methods and hence, there is a need for development of a new technology for microbial detection and quantification. We present here a novel method for detecting the presence of viable microorganisms in various suspensions ranging from bacterial growth media, to food substrates such as milk and apple juice, water and complex suspensions like blood along with their quantification and characterization. The underlying principle for our method of detection of microorganisms is based on the fact that in the presence of an AC electric field, the intact/viable bacterial cell membrane becomes polarized. This polarization leads to the 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, due to an increase in the total amount of charge stored in the interior of a suspension. However, 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) in effect "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/safety by detecting bacterial proliferation in "real world" liquid food samples like milk and apple juice b) Quantify the bacteria in a sample by estimating the MPN of the viable bacteria c) Detect presence of 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.