In Vitro Antibacterial Testing

A key step in drug discovery is screening assays to assess antibacterial activity of compounds.  We offer antibacterial testing services for key bacterial families.  We can help you select appropriate assays for your compound and mechanism of action.  We can also develop custom assays tailored to your specific program.  If you don’t see what you need or have any other questions, please contact us.

Minimum Inhibitory Concentration (MIC). MIC assay is used to determine the susceptibility of bacterial strains to antimicrobial candidates. Target organisms are exposed to a dilution range of the test article, to identify the lowest concertation that will inhibit visible growth. This assay is typically performed on planktonic (free floating) bacterial cells. MIC values can be based on optical density using spectrophotometer or by disk diffusion assay. This is a cost and time efficient strategy to screen and identify promising drug candidates. The assay can also be adjusted to determine the minimum concentration of test article required to inhibit growth of 50% or 90% of a panel of test isolates (MIC50 and MIC90). We also provide service for E-test based MIC assays for clinical isolates.

Minimum bactericidal concentration (MBC). MBC assay is used, subsequent to MIC evaluation, to determine the lowest concentration of a test candidate require to kill an organism. The MIC assay dilutions that do not exhibit macroscopic growth are used to make diluted subculture series and aliquoted onto solid medium. A colony count that represents 0.1% (99.9% reduction) of the original inoculum is considered the MBC.

Antimicrobial susceptibility testing. This test measures degree of susceptibility to an antimicrobial compound. The test organism is grown on agar plates with the antimicrobial agent. If bacterial growth is inhibited it results in a clear area of no growth around the antibiotic disc, a zone of inhibition. The diameter of the inhibition zone for a test article is compared to standards to determine degree of susceptibility. We also provide the antimicrobial susceptibility testing for clinical isolates based on standard disc diffusion assays.

Minimum doubling time/growth curve (MDT). MDT testing is used to determine the time required for the bacterial population to double. This assay shows the effect of antibiotics on bacterial growth by comparing growth in broth culture with and without the antimicrobial compound. Optical density values are recorded at multiple timepoints. MDT value is calculated by comparing the optical densities at different timepoints in exponential phase of growth.

Antimicrobial Synergy Testing/Checkerboard Assay. Synergy testing evaluates the interaction of two antimicrobial test articles when used in combination. In this assay the MIC and MBC values of test compounds alone and in combination against each bacterial strain being evaluated is used to calculate the additive, synergistic and antagonistic effects.