Antimicrobial Synergy Study – Checkerboard Testing

Synergy testing by checkerboard assay determines 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, 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). MICA and MICB are the MIC of each drug individually.

FIC Index value was 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 Assay