In a semisolid medium containing resazurin, a pink color indicates which condition?

In a semisolid medium containing resazurin, a pink color indicates which condition?

• A. Acid environment
• B. Alkaline environment
• C. Motility
• D. Presence of oxygen

Answer: (D)

Resazurin acts as an oxygen redox indicator in semisolid media. It shifts color based on whether the environment is oxidizing (with oxygen) or reducing (without oxygen). When oxygen is present, resazurin is kept in its oxidized form that appears pink. As redox potential becomes more reducing in anaerobic pockets, the dye changes to colorless or another form, and the pink fades. Therefore, seeing a pink region in the medium indicates that oxygen is available in that area, i.e., aerobic conditions.

Resazurin acts as an oxygen redox indicator in semisolid media. It shifts color based on whether the environment is oxidizing (with oxygen) or reducing (without oxygen). When oxygen is present, resazurin is kept in its oxidized form that appears pink. As redox potential becomes more reducing in anaerobic pockets, the dye changes to colorless or another form, and the pink fades. Therefore, seeing a pink region in the medium indicates that oxygen is available in that area, i.e., aerobic conditions.