The investigation of the electromagnetic properties of biological cells in the microwave frequencies may enable wireless monitoring of functional activity of microorganisms. Both theoretical and experimental methodologies are applied to obtain the electromagnetic characterization of the E. Coli cells as a simple microorganism. The simulation and experimental results corresponding to the transmission coefficient and sensitivity of a coaxial set-up for different concentration of E. Coli cells are measured up to 3 GHz. Afterwards, the E. Coli is used as the basis to address the electromagnetic changes, in terms of extension and contrast, involved into the creation of a functional activity (action potential) of a neuronal cell.