Benzoic acid is not typically used as an antifungal agent on MRS agar. MRS agar is a selective and differential agar used to culture lactic acid bacteria, particularly lactobacilli and streptococci. It contains peptones, meat extract, yeast extract, dextrose, and dipotassium phosphate, among other ingredients.

If you are looking for antifungal agents to use on MRS agar, you may want to consider using compounds such as nystatin or cycloheximide, which are commonly used to inhibit the growth of fungi in microbiological media. These compounds can be added to the MRS agar at the appropriate concentration to selectively inhibit fungal growth while allowing the growth of lactic acid bacteria.

It is important to note that the use of antifungal agents on MRS agar is not always necessary or appropriate, depending on the specific research question or clinical application. If you are unsure whether or not to use antifungal agents on your MRS agar, it may be helpful to consult with a microbiologist or other expert in the field.