Creative Biolabs has been a long-term expert in the field of antibacterial and antifungal drug discovery. Based on our extensive experience and world-leading technology platforms, Creative Biolabs is always dedicated to assisting our clients with the most satisfactory synergy test of antimicrobial combination.
In the development of antibacterial drugs, when two or more drugs are tested together simultaneously, different phenotypic effects may arise, such as synergism, additivity, antagonism, and indifference. To better evaluate the effect of two combined antimicrobial drugs, there are two different synergy testing methods, E test and the checkerboard.
The fractional inhibitory concentration (FIC) index value represents the effect of antibiotic combinations on potency compared to their respective activities. FIC index can be calculated as follows: FIC index = A/MICA + B/MICB, where A and B are the MIC of each antibiotic in combination, and MICA and MICB are the MIC of each drug individually. In general, the combination is considered synergistic when the FIC index is ≤0.5, additive or indifferent when the FIC index is >0.5 to <2, and antagonistic when the FIC index is ≥2. The synergy time-kill assay can further determine how the combination of antimicrobial drugs affect the bacteria.
Fig.1 Checkerboard method. (Bellio, 2021)
In the checkerboard assay, rows and columns represent 2-fold serial dilutions of compound A and compound B. Two compounds were tested in double serial dilutions, and the concentration of each compound was tested individually and in combination. These controls can be used to determine the MIC value for each group of test compounds and ultimately calculate the FIC value. Additionally, this method can be applied not only in combination with antibacterial compounds, but also in combination with compounds that typically do not have antibacterial properties.
E test, also known as the Epsilometer test, is a well-established for Minimum Inhibitory Concentration (MIC) determination. It is composed of the diffusion of a pre-formed antibiotic gradient from a plastic strip. If the strain of bacterium or fungus is sensitive, it will not grow near a concentration of antimicrobial. E test has been served as an attractive alternative to traditional agar dilution testing due to its versatility, cost-effective, and ease of use. Currently, E test products are available for more than 100 antimicrobial agents, including antibiotics, antifungal agents, and antimycobacterial agents. What’s more, specific Etest products can be used to detect specific resistance mechanisms.
Equipped with world-leading technology platforms and professional scientific staff, we are pleased to offer the most qualified services and products for antibacterial and antifungal drug discovery. If you are interested in our products or services, please do not hesitate to contact us for more detailed information.
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