This paper reports on a novel impedance-based cytometer, which can detect and characterize sub-micrometer particles and cells passing through a microfluidic channel. The cytometer incorporates a resonator, which is constructed by means of a discrete inductor in series with the measurement electrodes in the microfluidic channel. The use of a resonator increases the sensitivity of the system in comparison to state-of-the-art devices. We demonstrate the functionality and sensitivity of the cytometer by discriminating E. coli and B. subtilis from beads of similar sizes by means of the resonance-enhanced phase shift of the current through the microfluidic channel. The phase shift can be correlated to size and dielectric properties of the measured objects.