I have synthesised a cationic peptide which has shown antimicrobial activity in a microdilution. However when I've performed a disk diffusion the results do not align. Only much higher concentrations (compared to the MIC/MBC obtained from the microdilution) of peptide are giving zones of inhibition. I've repeated the disk diffusion 3 times and I have only gotten very small zone's of inhibition when I use nutrient agar (no result when using TSA or MHA). Im thinking its the salt content or charge of the agar interferring with my peptide. Does anyone know of a method modification or agar that I can use instead to yield more accurate results?
Thank you Phil for your input, I appreciate you taking the time to answer. I know they don't have to correlate but given the zones of inhibition did not appear on the TSA and MHA plates for the same concs I'm wondering if I there is an additional factor (e.g. agar salt/sugar content) that's impacting the diffusion of my peptide? Again any thoughts/input would be really appreciated.
The medium itself should not be constraining and as you know MHA is most commonly used for this purpose.
To your thinking - agarose has much of the agaropectin eliminated with their acidic side-groups, such as sulfate and pyruvate giving agarose a neutral charge and less likely to interact with biomolecules.
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