A system and method for antibiotic susceptibility testing (AST) efficiently determines whether bacteria are alive or have been killed by antibiotic treatment. The AST device includes at least one bacteria supply reservoir and a microfluidic channel connected to the reservoir, wherein the cross-sectional size of the microfluidic channel is selected to be comparable to the size of the bacterium. The electrical resistance or voltage signal across the microchannel is monitored as bacteria swim into and out of the channel. Alternatively, a small population of bacteria can be immobilized in the microchannel. The resistance or voltage signal fluctuates when the bacteria are alive and moving in and out of the channel or wiggling on the microchannel walls. Dead bacteria have limited motility and the signal fluctuations are significantly smaller. Changes in the signal fluctuations can be monitored to determine whether or not bacteria remain alive after antibiotic treatment.
