Antimicrobial Synergy Study – Checkerboard Testing

Synergy Testing by Checkerboard Assay is used to determine the interaction and potency of two test articles when used concurrently. Using Lorian methodology, this assay determines the effect on potency of the combination of antibiotics in comparison to their individual activities. This comparison is then represented as the Fractional Inhibitory Concentration (FIC) index value.

To quantify the interactions between the antibiotics being tested, the FIC index (the combination of antibiotics that produced the greatest change from the individual antibiotic’s MIC) value is calculated for each strain and antibiotic combination:

A+B=   FICA +   FICB   =   FIC Index
MICA         MICB

where A and B are the MIC of each antibiotic in combination (in a single well), and MICA and MICB are the MIC of each drug individually.

The FIC Index value is then used to categorize the interaction of the two antibiotics tested.

Below is a representation of a checkerboard assay where the synergistic activity of two antibiotics, A and B was determined.

Antimicrobial Synergy Study Checkerboard Testing Chart