A method and apparatus for performing microbial antibiotic susceptibility testing include disposable, multi-chambered susceptibility plates and an automated plate handler and image acquisition and processing instrument. The susceptibility plates are inoculated with a microorganism (any suitable organism such as bacteria, fungi, protozoa, algae or viruses) and anti-microbial agent(s) are applied such that the microorganism is exposed to a variety of concentrations, or a gradient of each anti-microbial agent. The plates are then placed in the instrument, which monitors and measures the growth (or lack thereof) of the microorganisms. This data is used to determine the susceptibility of the microorganism to the antibiotics. Such a system automates antimicrobial susceptibility testing using solid media and Kirby-Bauer standardized result reporting. The system provides a level of automation previously associated only with broth microdilution testing, while retaining the advantages of the manual disk diffusion test.