I used resazurin dye on my assay for testing out the antibacterial properties of prodrugs. The wells turned pink at a higher concentration of the drug and blue at a lower concentration. I have also carried out an agar well diffusion to see if the drug works at a high concentration and it did, but I can’t think of a reason why this happened.
In the presence of bacteria, pink indicates growth of the bacteria and blue indicates a lack of growth. Your result is the opposite of the expectation for a drug that inhibits bacterial growth.
Have you tried this experiment with the drug by itself (no bacteria)? It's possible that the drug is reacting with the dye. The dye turns pink when it is reduced, so if your drug is a reducing agent, it might turn the dye pink.
I like Adam B Shapiro suggestion of using drug only but I wonder if the colour change is caused by a change in pH of the solution on adding the drug .The dye is purple above pH 6.5 and orangy coloured ( I am colour blind) below pH 6.5
In the picture it’s not really a pink colour it’s more red so maybe this could be the reason why.
It is possibly that your drug interact with resasurin. You have to try putting your drug with resazurin with no bacteria and see if it change the colour.
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