Evaluation of OxoPlate for real-time assessment of antibacterial activities.

We have evaluated the OxoPlate OP96F for its usefulness in the characterization of antibacterial compounds. Each well of the plate carries two different fluorescent dyes, an oxygen-sensitive indicator dye and a reference dye. Fluorescence intensity is proportional to the amount of dissolved oxygen in the medium. Growth of bacterial cells is measured indirectly via the gradual depletion of oxygen. In this study, Bacillus subtilis was treated with 14 different antibacterials of various modes of action. The OxoPlate was not only useful to deduce MIC values directly from the oxygen-depletion curves, but was also able to discriminate bactericidal from bacteriostatic compounds. Oxygen levels of cultures treated with bactericidal compounds dropped initially and then increased after the cells had died. In contrast, oxygen levels remained low when cultures were treated with bacteriostatic compounds. The system described herein gives valuable insight into the kinetics of growth inhibition and killing, and we conclude that the OxoPlate is highly useful for the initial characterization of antibacterials.