Rose Bengal Agar + Chloramphenicol + Dichloran (DRBC Agar) ISO

Peptone provides the nitrogen, vitamins, minerals and amino acids source. Dextrose is the fermentable carbohydrate as a carbon and energy source. Potassium phosphate is the buffer. Magnesium sulfate provides sulfur and other trace elements. Rose bengal is a selective agent that inhibits the growth of bacteria and limits the size and height of faster-growing molds, allowing for the development and detection of other slower-growing yeasts. Molds appear pink colored. Chloramphenicol serves as a selective agent, inhibiting bacterial growth. It is a recommended antibiotic for neutral media due to its heat stability and wide bacterial spectrum. The addition of dichloran prevents the fast spreading of mucoraceous fungi and also restricts the size of the colonies of other genera, improving the colony count. Bacteriological agar is the solidifying agent.

Typical formula in g/L, adjusted and/or supplemented as required to meet performance criteria.

Preparation

Suspend 31.6 grams of the medium in one liter of distilled water. Mix well and dissolve by heating with frequent agitation. Boil for one minute until complete dissolution. Sterilize in autoclave at 121 °C for 15 minutes. Cool to 44-47 °C, mix well and dispense into plates.

According to ISO 21527

For the enumeration of yeasts and moulds according to ISO 21527:

1. Prepare the test portion, initial suspension (primary dilution) and further dilutions.
2. Transfer 0.1 mL of the test sample to one DRBC agar plate.
3. On a second DRBC agar plate, transfer 0.1 mL of the first decimal dilution (10⁻¹), or 0.1 mL of the 10⁻² dilution.
4. Spread the liquid over the surface of the agar plate until the liquid is completely absorbed into the medium.
5. Incubate the prepared plates aerobically, lids uppermost, at 25 ± 1 °C for 5 days.
6. Count and select the colonies for confirmation.

• King, D.A. and Pitt, J.I. (1979) Dichloran-rose Bengal medium for enumeration and isolation of moulds from foods. Appl. Environm. Microbiol. 37, 959-964.
• ISO 21527 - Microbiology of food and animal feeding stuffs - Horizontal method for the enumeration of yeasts and moulds - Part 1: Colony count technique in products with water activity greater than 0.95.