The checkerboard assay (or sometimes referred to as chequerboard assay) is a well-established in vitro broth microdilution method used to evaluate the interaction between two antimicrobial agents, such as antibiotics, antibiotic potentiator-antibiotic or phage–antibiotic combinations. Each agent is tested across serial dilutions to create a matrix of combinations (“checkerboard”). The minimum inhibitory concentration (MIC) of each agent alone and in combination is assessed to determine their interaction and derive the Fractional Inhibitory Concentration Index (FICI).
The method is a practical, high-throughput alternative to time-kill assays. Although interpretation can vary with readout type and lab protocols, the checkerboard method is a practical, high-throughput alternative to time-kill assays and may inform potential combination therapies and antimicrobial treatments optimization.