I used a concentration of 0.039–5 mg/mL to determine the MIC for the chitosan solution using the microtitre plate method. The OD value was taken at 630nm. How to calculate MIC90 and MIC50?
You need a calibration curve of you bacteria/fungus test (bacteria concentration vs absorbance or optic density at 630 nm)
Its very important to use the same final volume as in the MIC. And use the same matrix (PBS, medium culture,...)
Calculate percent inhibition from OD values compared to control, then determine MIC for each sample as the lowest concentration with ≥90% inhibition. MIC50 and MIC90 are the concentrations inhibiting 50% and 90% of samples, found by ranking individual MICs accordingly.
Thank you for your answer Abdelhak Maghchiche. How was the inhibition percentage calculated?
Inhibition percentage is calculated as (1− OD sample/ODcontrol)×100%). MIC is the lowest concentration with ≥90% inhibition, while MIC50 and MIC90 represent concentrations inhibiting 50% and 90% of samples, respectively.
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