Various methods, devices, and systems for determining the susceptibility of infectious agents to anti-infectives are disclosed herein. A method comprises introducing an inoculum solution comprising the infectious agent into a sample receiving space of a diagnostic device. The sample receiving space comprises a plurality of growth control wells devoid of the anti-infective and a plurality of active electrode wells comprising the anti-infective at differing concentrations. A water immiscible liquid can be introduced into the sample receiving space to seal the plurality of wells and the diagnostic device can be incubated for a period of time. The minimum inhibitory concentration (MIC) of the anti-infective on the infectious agent can be determined by monitoring and comparing one or more solution characteristics of the inoculum solution within the active electrode wells with the one or more solution characteristics of the inoculum solution with the growth control wells.