Standard Method Chromogenic Agar (PCA)

Enzymatic digest of casein provides nitrogen, vitamins, minerals and amino acids essential for growth. Yeast extract is a source of vitamins, particularly the B-group. Dextrose is the fermentable carbohydrate providing carbon and energy. Bacteriological agar is the solidifying agent. Chromogenic substrate allows quicker differentiation of aerobic microorganisms due to the magenta colonies. Yeast colonies grow as white colonies.

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

Preparation

Suspend 23.6 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. AVOID OVERHEATING. DO NOT AUTOCLAVE. Dispense into appropriate containers.

Instructions for use

1. Add 1 mL of the appropriate test dilution to the sterile medium at a temperature of 44-45 °C.
2. Mix gently and pour into sterile Petri dishes.
3. Alternatively, dispense a portion of each test dilution (e.g., 0.1, 0.01 mL) into separate sterile Petri dishes and add 10-12 mL of tempered (45 °C) Standard Method Chromogenic Agar to the Petri dishes containing test dilutions.
4. Swirl the dishes to thoroughly mix the medium and the test dilution.
5. Allow plates to cool and solidify.
6. Incubate the Petri dishes at 32 ± 2 °C for 18-48 hours and count the developed colonies.

• Standard Methods for the Examination of Dairy Products, 13th Ed. APHA, 1972. American Public Health Association.
• Recommended Methods for the Microbiological Examination of Foods, APHA Inc. New York, 1958.
• Standard Methods for the Examination of Water and Wastewater, APHA Inc. New York, 1960.
• APHA: American Public Health Association Inc.