Chloramphenicol Agar (YGC Agar) ISO

The antibiotic method for enumerating yeasts and molds in dairy products is the preferred method of choice as it results in a better recovery of injured fungal cells.

Yeast extract is a source of vitamins, particularly of the B-group essential for bacterial growth. Dextrose is the fermentable carbohydrate providing carbon and energy and chloramphenicol is an antibiotic which aids in isolating pathogenic fungi from heavily contaminated material, as it inhibits most contaminating bacteria. It is a recommended antibiotic for use with media due to its heat stability and wide bacterial spectrum. Bacteriological agar is the solidifying agent.

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

Preparation

Suspend 37.1 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 50 °C, mix well and dispense into plates.

According to ISO 6611

For the enumeration of yeasts and molds in milk products according to ISO 6611:

1. Transfer 1 mL of the test sample (liquid product) or of the initial suspension (other products) to two Petri dishes.
2. Transfer 1 mL of the 10⁻¹ dilution (liquid product) or 1 mL of the 10⁻² dilution (other products) to two further Petri dishes.
3. If necessary, repeat using more dilutions.
4. Pour about 15 mL of Chloramphenicol Agar (YGC), previously melted and cooled, into each Petri dish.
5. Gently mix the inoculum with the medium, allowing the mixture to solidify.
6. Incubate the dishes at 25 °C for 5 days.
7. Count the colonies in each dish, differentiating yeasts from molds by colony morphology.

• FIL-IDF (1991) Standard 94B. Enumeration of yeast and moulds. Colony Count Technique at 25 °C.
• ISO 6611: Milk and Milk products: Enumeration of colony-forming units of yeast and/or molds - Colony count technique at 25 °C.
• ISO 7954 - Microbiology - General Guidance for enumeration of yeasts and molds. Colony count technique at 25 °C.
• DIN Standard 10186. Mikrobiologische Milch Untersuchung. Bestimmung der Anzahl von Hefen und Schimmelpilzen.